RFC Number : 3057
Title : ISDN Q.
Network Working Group K. Morneault
Request for Comments: 3057 Cisco Systems
Category: Standards Track S. Rengasami
M. Kalla
Telcordia Technologies
G. Sidebottom
Nortel Networks
February 2001
ISDN Q.921-User Adaptation Layer
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the 'Internet
Official Protocol Standards' (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document defines a protocol for backhauling of ISDN Q.921 User
messages over IP using the Stream Control Transmission Protocol
(SCTP). This protocol would be used between a Signaling Gateway (SG)
and Media Gateway Controller (MGC). It is assumed that the SG
receives ISDN signaling over a standard ISDN interface.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
Table of Contents
1. Introduction................................................. 2
1.1 Scope..................................................... 2
1.2 Terminology............................................... 3
1.3 IUA Overview.............................................. 4
1.4 Services Provided by the IUA Layer........................ 9
1.5 Functions Implemented by the IUA Layer.................... 12
1.6 Definition of IUA Boundaries.............................. 14
2. Conventions.................................................. 16
3. Protocol Elements............................................ 17
3.1 Common Message Header..................................... 17
3.2 IUA Message Header........................................ 20
3.3 Description of Messages................................... 22
4. Procedures................................................... 45
4.1 Procedures to Support Service in Section 1.4.1............ 45
4.2 Procedures to Support Service in Section 1.4.2............ 46
4.3 Procedures to Support Service in Section 1.4.3............ 47
5. Examples...................................................... 56
5.1 Establishment of associations between SG and MGC examples.. 56
5.2 ASP Traffic Fail-over Examples............................. 58
5.3 Q.921/Q.931 primitives backhaul Examples................... 59
5.4 Layer Management Communication Examples.................... 61
6. Security..................................................... 61
6.1 Threats.................................................... 61
6.2 Protecting Confidentiality ................................ 62
7. IANA Considerations.......................................... 62
7.1 SCTP Payload Protocol Identifier........................... 62
7.2 IUA Protocol Extensions.................................... 62
8. Acknowledgements............................................. 64
9. References................................................... 64
10. Authors' Addresses........................................... 65
11. Full Copyright Statement..................................... 66
1. Introduction
In this document, the term Q.921-User refers to an upper layer which
uses the services of Q.921, not the user side of ISDN interface [1].
Examples of the upper layer would be Q.931 and QSIG.
This section describes the need for ISDN Q.921-User Adaptation (IUA)
layer protocol as well as how this protocol shall be implemented.
1.1 Scope
There is a need for Switched Circuit Network (SCN) signaling protocol
delivery from an ISDN Signaling Gateway (SG) to a Media Gateway
Controller (MGC) as described in the Framework Architecture for
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
Signaling Transport [4]. The delivery mechanism SHOULD meet the
following criteria:
* Support for transport of the Q.921 / Q.931 boundary primitives
* Support for communication between Layer Management modules on SG
and MGC
* Support for management of active associations between SG and MGC
This document supports both ISDN Primary Rate Access (PRA) as well as
Basic Rate Access (BRA) including the support for both point-to-point
and point-to-multipoint modes of communication. This support
includes Facility Associated Signaling (FAS), Non-Facility Associated
Signaling (NFAS) and NFAS with backup D channel. QSIG adaptation
layer requirements do not differ from Q.931 adaptation layer, hence;
the procedures described in this document are also applicable for a
QSIG adaptation layer. For simplicity, only Q.931 will be mentioned
in the rest of this document.
1.2 Terminology
Interface - For the purposes of this document an interface supports
the relevant ISDN signaling channel. This signaling channel MAY be a
16 kbps D channel for an ISDN BRA as well as 64 kbps primary or
backup D channel for an ISDN PRA. For QSIG, the signaling channel is
a Qc channel.
Q.921-User - Any protocol normally using the services of the ISDN
Q.921 (e.g., Q.931, QSIG, etc.).
Backhaul - A SG terminates the lower layers of an SCN protocol and
backhauls the upper layer(s) to MGC for call processing. For the
purposes of this document the SG terminates Q.921 and backhauls Q.931
to MGC.
Association - An association refers to a SCTP association. The
association will provide the transport for the delivery of Q.921-User
protocol data units and IUA adaptation layer peer messages.
Stream - A stream refers to an SCTP stream; a uni-directional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the un-ordered delivery service.
Interface Identifier - The Interface Identifier identifies the
physical interface at the SG for which the signaling messages are
sent/received. The format of the Interface Identifier parameter can
be text or integer, the values of which are assigned according to
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network operator policy. The values used are of local significance
only, coordinated between the SG and ASP. Significance is not
implied across SGs served by an AS.
Application Server (AS) - A logical entity serving a specific
application instance. An example of an Application Server is a MGC
handling the Q.931 and call processing for D channels terminated by
the Signaling Gateways. Practically speaking, an AS is modeled at
the SG as an ordered list of one or more related Application Server
Processes (e.g., primary, secondary, tertiary).
Application Server Process (ASP) - A process instance of an
Application Server. Examples of Application Server Processes are
primary or backup MGC instances.
Fail-over - The capability to re-route signaling traffic as required
between related ASPs in the event of failure or unavailability of the
currently used ASP (e.g., from primary MGC to back-up MGC). Fail-
over also applies upon the return to service of a previously
unavailable process.
Layer Management - Layer Management is a nodal function that handles
the inputs and outputs between the IUA layer and a local management
entity.
Network Byte Order - Most significant byte first, a.k.a Big Endian.
Host - The computing platform that the ASP process is running on.
1.3 IUA Overview
The architecture that has been defined [4] for SCN signaling
transport over IP uses multiple components, including an IP transport
protocol, a signaling common transport protocol and an adaptation
module to support the services expected by a particular SCN signaling
protocol from its underlying protocol layer.
This document defines an adaptation module that is suitable for the
transport of ISDN Q.921-User (e.g., Q.931) messages.
1.3.1 Example - SG to MGC
In a Signaling Gateway, it is expected that the ISDN signaling is
received over a standard ISDN network termination. The SG then
provides interworking of transport functions with IP Signaling
Transport, in order to transport the Q.931 signaling messages to the
MGC where the peer Q.931 protocol layer exists, as shown below:
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
****** ISDN ****** IP *******
* EP *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|Q.931| (NIF) |Q.931|
+-----+ +----------+ +-----+
| | | | IUA| | IUA |
| | | +----+ +-----+
|Q.921| |Q.921|SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP | | IP |
+-----+ +-----+----+ +-----+
NIF - Nodal Interworking Function
EP - ISDN End Point
SCTP - Stream Control Transmission Protocol (Refer to [3])
IUA - ISDN User Adaptation Layer Protocol
It is recommended that the IUA use the services of the Stream Control
Transmission Protocol (SCTP) as the underlying reliable common
signaling transport protocol. The use of SCTP provides the following
features:
- explicit packet-oriented delivery (not stream-oriented)
- sequenced delivery of user messages within multiple streams,
with an option for order-of-arrival delivery of individual user
messages,
- optional multiplexing of user messages into SCTP datagrams,
- network-level fault tolerance through support of multi-homing
at either or both ends of an association,
- resistance to flooding and masquerade attacks, and
- data segmentation to conform to discovered path MTU size
There are scenarios without redundancy requirements and scenarios in
which redundancy is supported below the transport layer. In these
cases, the SCTP functions above MAY NOT be a requirement and TCP can
be used as the underlying common transport protocol.
1.3.2 Support for the management of SCTP associations between the SG
and ASPs
The IUA layer at the SG maintains the availability state of all
dynamically registered remote ASPs, in order to manage the SCTP
Associations and the traffic between the SG and ASPs. As well, the
active/inactive state of remote ASP(s) are also maintained. Active
ASPs are those currently receiving traffic from the SG.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
The IUA layer MAY be instructed by local management to establish an
SCTP association to a peer IUA node. This can be achieved using the
M-SCTP ESTABLISH primitive to request, indicate and confirm the
establishment of an SCTP association with a peer IUA node.
The IUA layer MAY also need to inform local management of the status
of the underlying SCTP associations using the M-SCTP STATUS request
and indication primitive. For example, the IUA MAY inform local
management of the reason for the release of an SCTP association,
determined either locally within the IUA layer or by a primitive from
the SCTP.
1.3.3 Signaling Network Architecture
A Signaling Gateway is used to support the transport of Q.921-User
signaling traffic to one or more distributed ASPs (e.g., MGCs).
Clearly, the IUA protocol is not designed to meet the performance and
reliability requirements for such transport by itself. However, the
conjunction of distributed architecture and redundant networks does
allow for a sufficiently reliable transport of signaling traffic over
IP. The IUA protocol is flexible enough to allow its operation and
management in a variety of physical configurations, enabling Network
Operators to meet their performance and reliability requirements.
To meet the ISDN signaling reliability and performance requirements
for carrier grade networks, Network Operators SHOULD ensure that
there is no single point of failure provisioned in the end-to-end
network architecture between an ISDN node and an IP ASP.
Depending of course on the reliability of the SG and ASP functional
elements, this can typically be met by the provision of redundant
QOS-bounded IP network paths for SCTP Associations between SCTP End
Points, and redundant Hosts, and redundant SGs. The distribution of
ASPs within the available Hosts is also important. For a particular
Application Server, the related ASPs SHOULD be distributed over at
least two Hosts.
An example logical network architecture relevant to carrier-grade
operation in the IP network domain is shown in Figure 1 below:
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
Host1
******** **************
* *_________________________________________* ******** *
* * _________* * ASP1 * *
* SG1 * SCTP Associations | * ******** *
* *_______________________ | * *
******** | | **************
| |
******** | |
* *_______________________________|
* * |
* SG2 * SCTP Associations |
* *____________ |
* * | | Host2
******** | | **************
| |_________________* ******** *
|____________________________* * ASP1 * *
* ******** *
* *
**************
.
.
.
Figure 2 - Logical Model Example
For carrier grade networks, the failure or isolation of a particular
ASP SHOULD NOT cause stable calls to be dropped. This implies that
ASPs need, in some cases, to share the call state or be able to pass
the call state between each other. However, this sharing or
communication of call state information is outside the scope of this
document.
1.3.4 ASP Fail-over Model and Terminology
The IUA layer supports ASP fail-over functions in order to support a
high availability of call processing capability. All Q.921-User
messages incoming to an SG are assigned to a unique Application
Server, based on the Interface Identifier of the message.
The Application Server is, in practical terms, a list of all ASPs
configured to process Q.921-User messages from certain Interface
Identifiers. One or more ASPs in the list are normally active (i.e.,
handling traffic) while any others MAY be unavailable or inactive, to
be possibly used in the event of failure or unavailability of the
active ASP(s).
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
The fail-over model supports an n+k redundancy model, where n ASP(s)
are the minimum number of redundant ASPs required to handle traffic
and k ASPs are available to take over for a failed or unavailable
ASP. Note that 1+1 active/standby redundancy is a subset of this
model. A simplex 1+0 model is also supported as a subset, with no
ASP redundancy.
To avoid a single point of failure, it is recommended that a minimum
of two ASPs be in the list, resident in separate hosts and therefore
available over different SCTP Associations. For example, in the
network shown in Figure 2, all messages from a particular D Channel
(Interface Identifier) could be sent to ASP1 in Host1 or ASP1 in
Host2. The AS list at SG1 might look like the following:
Interface Identifier(s) - Application Server #1
ASP1/Host1 - State=Up, Active
ASP1/Host2 - State=Up, Inactive
In this 1+1 redundancy case, ASP1 in Host1 would be sent any incoming
message for the Interface Identifiers registered. ASP1 in Host2
would normally be brought to the active state upon failure of, or
loss of connectivity to, ASP1/Host1. In this example, both ASPs are
Up, meaning that the related SCTP association and far-end IUA peer is
ready.
The AS List at SG1 might also be set up in load-share mode as shown
below:
Interface Identifier(s) - Application Server #1
ASP1/Host1 - State=Up, Active
ASP1/Host2 - State=Up, Active
In this case, both the ASPs would be sent a portion of the traffic.
In the process of fail-over, it is recommended that in the case of
ASPs supporting call processing, stable calls do not get released.
It is possible that calls in transition MAY fail, although measures
of communication between the ASPs involved can be used to mitigate
this problem. For example, the two ASPs MAY share call state via
shared memory, or MAY use an ASP to ASP protocol to pass call state
information. The ASP to ASP protocol is outside the scope of this
document.
1.3.5 Client/Server Model
It is recommended that the SG and ASP be able to support both client
and server operation. The peer endpoints using IUA SHOULD be
configured so that one always takes on the role of client and the
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other the role of server for initiating SCTP associations. The
default orientation would be for the SG to take on the role of server
while the ASP is the client. In this case, ASPs SHOULD initiate the
SCTP association to the SG.
The SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA
is 9900.
1.4 Services Provided by the IUA Layer
1.4.1 Support for transport of Q.921/Q.931 boundary primitives
In the backhaul scenario, the Q.921/Q.931 boundary primitives are
exposed. IUA layer needs to support all of the primitives of this
boundary to successfully backhaul Q.931.
This includes the following primitives [1]:
DL-ESTABLISH
The DL-ESTABLISH primitives are used to request, indicate and confirm
the outcome of the procedures for establishing multiple frame
operation.
DL-RELEASE
DL-RELEASE primitives are used to request, indicate, and confirm the
outcome of the procedures for terminating a previously established
multiple frame operation, or for reporting an unsuccessful
establishment attempt.
DL-DATA
The DL-DATA primitives are used to request and indicate layer 3
(Q.931) messages which are to be transmitted, or have been received,
by the Q.921 layer using the acknowledged information transfer
service.
DL-UNIT DATA
The DL-UNIT DATA primitives are used to request and indicate layer 3
(Q.931) messages which are to be transmitted, by the Q.921 layer
using the unacknowledged information transfer service.
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1.4.2 Support for communication between Layer Management modules on SG
and MGC
It is envisioned that the IUA layer needs to provide some services
that will facilitate communication between Layer Management modules
on the SG and MGC. These primitives are pointed out in [2], which
are shown below:
M-TEI STATUS
The M-TEI STATUS primitives are used to request, confirm and indicate
the status (assigned/unassigned) of a TEI.
M-ERROR
The M-ERROR primitive is used to indicate an error with a received
IUA message (e.g., interface identifier value is not known to the
SG).
1.4.3 Support for management of active associations between SG and MGC
A set of primitives between the IUA layer and the Layer Management
are defined below to help the Layer Management manage the SCTP
association(s) between the SG and MGC. The IUA layer can be
instructed by the Layer Management to establish an SCTP association
to a peer IUA node. This procedure can be achieved using the M-SCTP
ESTABLISH primitive.
M-SCTP ESTABLISH
The M-SCTP ESTABLISH primitives are used to request, indicate, and
confirm the establishment of an SCTP association to a peer IUA node.
M-SCTP RELEASE
The M-SCTP RELEASE primitives are used to request, indicate, and
confirm the release of an SCTP association to a peer IUA node.
The IUA layer MAY also need to inform the status of the SCTP
associations to the Layer Management. This can be achieved using the
M-SCTP STATUS primitive.
M-SCTP STATUS
The M-SCTP STATUS primitives are used to request and indicate the
status of the underlying SCTP association(s).
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
The Layer Management MAY need to inform the IUA layer of an AS/ASP
status (i.e., failure, active, etc.), so that messages can be
exchanged between IUA layer peers to stop traffic to the local IUA
user. This can be achieved using the M-ASP STATUS primitive.
M-ASP STATUS
The ASP status is stored inside IUA layer on both the SG and MGC
sides. The M-ASP STATUS primitive can be used by Layer Management to
request the status of the Application Server Process from the IUA
layer. This primitive can also be used to indicate the status of the
Application Server Process.
M-ASP-UP
The M-ASP-UP primitive can be used by Layer Management to send a ASP
Up message for the Application Server Process. It can also be used
to generate an ASP Up Acknowledgement.
M-ASP-DOWN
The M-ASP-DOWN primitive can be used by Layer Management to send a
ASP Down message for the Application Server Process. It can also be
used to generate an ASP Down Acknowledgement.
M-ASP-ACTIVE
The M-ASP-UP primitive can be used by Layer Management to send a ASP
Active message for the Application Server Process. It can also be
used to generate an ASP Active Acknowledgement.
M-ASP-INACTIVE
The M-ASP-UP primitive can be used by Layer Management to send a ASP
Inactive message for the Application Server Process. It can also be
used to generate an ASP Inactive Acknowledgement.
M-AS STATUS
The M-AS STATUS primitive can be used by Layer Management to request
the status of the Application Server. This primitive can also be
used to indicate the status of the Application Server.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
1.5 Functions Implemented by the IUA Layer
1.5.1 Mapping
The IUA layer MUST maintain a map of the Interface Identifier to a
physical interface on the Signaling Gateway. A physical interface
would be a T1 line, E1 line, etc., and could include the TDM
timeslot. In addition, for a given interface the SG MUST be able to
identify the associated signaling channel. IUA layers on both SG and
MGC MAY maintain the status of TEIs and SAPIs.
The SG maps an Interface Identifier to an SCTP association/stream
only when an ASP sends an ASP Active message for a particular
Interface Identifier. It MUST be noted, however, that this mapping
is dynamic and could change at any time due to a change of ASP state.
This mapping could even temporarily be invalid, for example during
failover of one ASP to another. Therefore, the SG MUST maintain the
states of AS/ASP and reference them during the routing of an messages
to an AS/ASP.
One example of the logical view of relationship between D channel,
Interface Identifier, AS and ASP in the SG is shown below:
/---------------------------------------------------+
/ /------------------------------------------------|--+
/ / v |
/ / +----+ act+-----+ +-------+ -+--+-|+--+-
D chan1-------->|IID |-+ +-->| ASP |--->| Assoc | v
/ +----+ | +----+ | +-----+ +-------+ -+--+--+--+-
/ +->| AS |--+ Streams
/ +----+ | +----+ stb+-----+
D chan2-------->|IID |-+ | ASP |
+----+ +-----+
where IID = Interface Identifier
Note that an ASP can be in more than one AS.
1.5.2 Status of ASPs
The IUA layer on the SG MUST maintain the state of the ASPs it is
supporting. The state of an ASP changes because of reception of
peer-to-peer messages (ASPM messages as described in Section 3.3.2)
or reception of indications from the local SCTP association. ASP
state transition procedures are described in Section 4.3.1.
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At a SG, an Application Server list MAY contain active and inactive
ASPs to support ASP load-sharing and fail-over procedures. When, for
example, both a primary and a back-up ASP are available, IUA peer
protocol is required to control which ASP is currently active. The
ordered list of ASPs within a logical Application Server is kept
updated in the SG to reflect the active Application Server
Process(es).
Also the IUA layer MAY need to inform the local management of the
change in status of an ASP or AS. This can be achieved using the M-
ASP STATUS or M-AS STATUS primitives.
1.5.3 SCTP Stream Management
SCTP allows a user specified number of streams to be opened during
the initialization. It is the responsibility of the IUA layer to
ensure proper management of these streams. Because of the
unidirectional nature of streams, an IUA layer is not aware of the
stream number to Interface Identifier mapping of its peer IUA layer.
Instead, the Interface Identifier is in the IUA message header.
The use of SCTP streams within IUA is recommended in order to
minimize transmission and buffering delay, therefore improving the
overall performance and reliability of the signaling elements. It is
recommended that a separate SCTP stream is used for each D channel.
1.5.4 Seamless Network Management Interworking
The IUA layer on the SG SHOULD pass an indication of unavailability
of the IUA-User (Q.931) to the local Layer Management, if the
currently active ASP moves from the ACTIVE state. The Layer
Management could instruct Q.921 to take some action, if it deems
appropriate.
Likewise, if an SCTP association fails, the IUA layer on both the SG
and ASP sides MAY generate Release primitives to take the data links
out-of-service.
1.5.5 Congestion Management
If the IUA layer becomes congested (implementation dependent), it MAY
stop reading from the SCTP association to flow control from the peer
IUA.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
1.6 Definition of IUA Boundaries
1.6.1 Definition of IUA/Q.921 boundary
DL-ESTABLISH
DL-RELEASE
DL-DATA
DL-UNIT DATA
1.6.2 Definition of IUA/Q.931 boundary
DL-ESTABLISH
DL-RELEASE
DL-DATA
DL-UNIT DATA
1.6.3 Definition of SCTP/IUA Boundary
An example of the upper layer primitives provided by SCTP are
available in Reference [3] section 10.
1.6.4 Definition of IUA/Layer-Management Boundary
M-SCTP ESTABLISH request
Direction: LM -> IUA
Purpose: LM requests ASP to establish an SCTP association with an SG.
M-STCP ESTABLISH confirm
Direction: IUA -> LM
Purpose: ASP confirms to LM that it has established an SCTP
association with an SG.
M-SCTP ESTABLISH indication
Direction: IUA -> LM
Purpose: SG informs LM that an ASP has established an SCTP
association.
M-SCTP RELEASE request
Direction: LM -> IUA
Purpose: LM requests ASP to release an SCTP association with SG.
M-SCTP RELEASE confirm
Direction: IUA -> LM
Purpose: ASP confirms to LM that it has released SCTP association
with SG.
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M-SCTP RELEASE indication
Direction: IUA -> LM
Purpose: SG informs LM that ASP has released an SCTP association.
M-SCTP STATUS request
Direction: LM -> IUA
Purpose: LM requests IUA to report status of SCTP association.
M-SCTP STATUS indication
Direction: IUA -> LM
Purpose: IUA reports status of SCTP association.
M-ASP STATUS request
Direction: LM -> IUA
Purpose: LM requests SG to report status of remote ASP.
M-ASP STATUS indication
Direction: IUA -> LM
Purpose: SG reports status of remote ASP.
M-AS-STATUS request
Direction: LM -> IUA
Purpose: LM requests SG to report status of AS.
M-AS-STATUS indication
Direction: IUA -> LM
Purpose: SG reports status of AS.
M-NOTIFY indication
Direction: IUA -> LM
Purpose: ASP reports that it has received a NOTIFY message
from its peer.
M-ERROR indication
Direction: IUA -> LM
Purpose: ASP or SG reports that it has received an ERROR
message from its peer.
M-ASP-UP request
Direction: LM -> IUA
Purpose: LM requests ASP to start its operation and send an ASP UP
message to the SG.
M-ASP-UP confirm
Direction: IUA -> LM
Purpose: ASP reports that is has received an ASP UP Acknowledgement
message from the SG.
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M-ASP-DOWN request
Direction: LM -> IUA
Purpose: LM requests ASP to stop its operation and send an ASP DOWN
message to the SG.
M-ASP-DOWN confirm
Direction: IUA -> LM
Purpose: ASP reports that is has received an ASP DOWN
Acknowledgement message from the SG.
M-ASP-ACTIVE request
Direction: LM -> IUA
Purpose: LM requests ASP to send an ASP ACTIVE message to the SG.
M-ASP-ACTIVE confirm
Direction: IUA -> LM
Purpose: ASP reports that is has received an ASP ACTIVE
Acknowledgement message from the SG.
M-ASP-INACTIVE request
Direction: LM -> IUA
Purpose: LM requests ASP to send an ASP INACTIVE message to the SG.
M-ASP-INACTIVE confirm
Direction: IUA -> LM
Purpose: ASP reports that is has received an ASP INACTIVE
Acknowledgement message from the SG.
M-TEI STATUS request
Direction: LM -> IUA
Purpose: LM requests ASP to send a TEI status request to the SG.
M-TEI STATUS indication
Direction: IUA -> LM
Purpose: ASP reports that is has received a TEI status indication
from the SG.
M-TEI STATUS confirm
Direction: IUA -> LM
Purpose: ASP reports that is has received a TEI status confirm from the
SG.
2.0 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
[RFC2119].
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
3.0 Protocol Elements
This section describes the format of various messages used in this
protocol.
3.1 Common Message Header
The protocol messages for Q.921-User Adaptation require a message
header which contains the adaptation layer version, the message type,
and message length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 Common Header Format
All fields in an IUA message MUST be transmitted in the network byte
order, unless otherwise stated.
3.1.1 Version
The version field contains the version of the IUA adaptation layer.
The supported versions are the following:
Value Version
----- -------
1 Release 1.0
3.1.2 Message Classes and Types
The following List contains the valid Message Classes:
Message Class: 8 bits (unsigned integer)
0 Management (MGMT) Message [IUA/M2UA/M3UA/SUA]
1 Transfer Messages [M3UA]
2 SS7 Signalling Network Management (SSNM) Messages [M3UA/SUA]
3 ASP State Maintenance (ASPSM) Messages [IUA/M2UA/M3UA/SUA]
4 ASP Traffic Maintenance (ASPTM) Messages [IUA/M2UA/M3UA/SUA]
5 Q.921/Q.931 Boundary Primitives Transport (QPTM)
Messages [IUA]
6 MTP2 User Adaptation (MAUP) Messages [M2UA]
7 Connectionless Messages [SUA]
Morneault, et al. Standards Track [Page 17]
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8 Connection-Oriented Messages [SUA]
9 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined Message Class extensions
The following list contains the message names for the defined
messages.
Q.921/Q.931 Boundary Primitives Transport (QPTM) Messages
0 Reserved
1 Data Request Message
2 Data Indication Message
3 Unit Data Request Message
4 Unit Data Indication Message
5 Establish Request
6 Establish Confirm
7 Establish Indication
8 Release Request
9 Release Confirm
10 Release Indication
11 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined QPTM extensions
Application Server Process State Maintenance (ASPSM) messages
0 Reserved
1 ASP Up (UP)
2 ASP Down (DOWN)
3 Heartbeat (BEAT)
4 ASP Up Ack (UP ACK)
5 ASP Down Ack (DOWN ACK)
6 Heatbeat Ack (BEAT ACK)
7 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPSM extensions
Application Server Process Traffic Maintenance (ASPTM) messages
0 Reserved
1 ASP Active (ACTIVE)
2 ASP Inactive (INACTIVE)
3 ASP Active Ack (ACTIVE ACK)
4 ASP Inactive Ack (INACTIVE ACK)
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined ASPTM extensions
Morneault, et al. Standards Track [Page 18]
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Management (MGMT) Messages
0 Error (ERR)
1 Notify (NTFY)
2 TEI Status Request
3 TEI Status Confirm
4 TEI Status Indication
5 to 127 Reserved by the IETF
128 to 255 Reserved for IETF-Defined MGMT extensions
3.1.3 Reserved
The Reserved field is 8-bits. It SHOULD be set to all '0's and
ignored by the receiver.
3.1.4 Message Length
The Message length defines the length of the message in octets,
including the Common header.
3.1.5 Variable-Length Parameter Format
IUA messages consist of a Common Header followed by zero or more
variable-length parameters, as defined by the message type. The
variable-length parameters contained in a message are defined in a
Tag-Length-Value format as shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Tag | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Parameter Value /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Mandatory parameters MUST be placed before optional parameters in a
message.
Parameter Tag: 16 bits (unsigned integer)
The Tag field is a 16 bit identifier of the type of parameter. It
takes a value of 0 to 65534.
The value of 65535 is reserved for IETF-defined extensions. Values
other than those defined in specific parameter description are
reserved for use by the IETF.
Morneault, et al. Standards Track [Page 19]
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Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Tag, Parameter Length, and Parameter
Value fields. The Parameter Length does not include any padding
bytes.
Parameter Value: variable-length
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Tag, Parameter Length and
Value fields) MUST be a multiple of 4 bytes. If the length of the
parameter is not a multiple of 4 bytes, the sender pads the Parameter
at the end (i.e., after the Parameter Value field) with all zero
bytes. The length of the padding is NOT included in the parameter
length field. A sender SHOULD NEVER pad with more than 3 bytes. The
receiver MUST ignore the padding bytes.
3.2 IUA Message Header
In addition to the common message header, there will be a specific
message header for QPTM and the TEI Status MGMT messages. The IUA
message header will immediately follow the Common header in these
messages.
This message header will contain the Interface Identifier and Data
Link Connection Identifier (DLCI). The Interface Identifier
identifies the physical interface terminating the signaling channel
at the SG for which the signaling messages are sent/received. The
format of the Interface Identifier parameter can be text or integer.
The Interface Identifiers are assigned according to network operator
policy. The integer values used are of local significance only,
coordinated between the SG and ASP.
The integer formatted Interface Identifier MUST be supported. The
text formatted Interface Identifier MAY optionally be supported.
Morneault, et al. Standards Track [Page 20]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier (integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x5) | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DLCI | Spare |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 IUA Message Header (Integer-based Interface Identifier)
The Tag value for the Integer-based Interface Identifier is 0x1. The
length is always set to a value of 8.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier (text) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x5) | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DLCI | Spare |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 IUA Message Header (Text-based Interface Identifier)
The Tag value for the Text-based Interface Identifier is 0x3. The
length is variable.
The DLCI format is shown below in Figure 6.
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | SPR | SAPI |
+-----------------------------------------------+
| 1 | TEI |
+-----------------------------------------------+
Figure 6 DLCI Format
SPR: Spare 2nd bit in octet 1, (1 bit)
Morneault, et al. Standards Track [Page 21]
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SAPI: Service Access Point Identifier, 3rd through 8th bits in octet
1 (6 bits)
TEI: Terminal Endpoint Identifier, 2nd through 8th bits in octet 2
(7 bits)
The DLCI field (including the SAPI and TEI) is coded in accordance
with Q.921.
3.3 IUA Messages
The following section defines the messages and parameter contents.
The IUA messages will use the common message header (Figure 3) and
the IUA message header (Figure 4 and Figure 5).
3.3.1 Q.921/Q.931 Boundary Primitives Transport (QPTM) Messages
3.3.1.1 Establish Messages (Request, Confirm, Indication)
The Establish Messages are used to establish a data link on the
signaling channel or to confirm that a data link on the signaling
channel has been established. The MGC controls the state of the D
channel. When the MGC desires the D channel to be in-service, it
will send the Establish Request message.
When the MGC sends an IUA Establish Request message, the MGC MAY
start a timer. This timer would be stopped upon receipt of an IUA
Establish Confirm or Establish Indication. If the timer expires, the
MGC would re-send the IUA Establish Request message and restart the
timer. In other words, the MGC MAY continue to request the
establishment of the data link on periodic basis until the desired
state is achieved or take some other action (notify the Management
Layer).
When the SG receives an IUA Establish Request from the MGC, the SG
shall send the Q.921 Establish Request primitive to the its Q.921
entity. In addition, the SG shall map any response received from the
Q.921 entity to the appropriate message to the MGC. For example, if
the Q.921 entity responds with a Q.921 Establish Confirm primitive,
the IUA layer shall map this to an IUA Establish Confirm message. As
another example, if the IUA Layer receives a Q.921 Release Confirm or
Release Indication as an apparent response to the Q.921 Establish
Request primitive, the IUA Layer shall map these to the corresponding
IUA Release Confirm or Release Indication messages.
The Establish messages contain the common message header followed by
IUA message header. It does not contain any additional parameters.
Morneault, et al. Standards Track [Page 22]
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3.3.1.2 Release Messages (Request, Indication, Confirmation)
The Release Request message is used to release the data link on the
signaling channel. The Release Confirm and Indication messages are
used to indicate that the data link on the signaling channel has been
released.
If a response to the Release Request message is not received, the MGC
MAY resend the Release Request message. If no response is received,
the MGC can consider the data link as being released. In this case,
signaling traffic on that D channel is not expected from the SG and
signaling traffic will not be sent to the SG for that D channel.
The Release messages contain the common message header followed by
IUA message header. The Release confirm message is in response to a
Release Request message and it does not contain any additional
parameters. The Release Request and Indication messages contain the
following parameter:
REASON
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xf) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for Reason are shown in the following table.
Define Value Description
RELEASE_MGMT 0x0 Management layer generated release.
RELEASE_PHYS 0x1 Physical layer alarm generated release.
RELEASE_DM 0x2 Specific to a request. Indicates Layer 2
SHOULD release and deny all requests from
far end to establish a data link on the
signaling channel (i.e., if SABME is
received send a DM)
RELEASE_OTHER 0x3 Other reasons
Note: Only RELEASE_MGMT, RELEASE_DM and RELEASE_OTHER are valid
reason codes for a Release Request message.
3.3.1.3 Data Messages (Request, Indication)
The Data message contains an ISDN Q.921-User Protocol Data Unit (PDU)
corresponding to acknowledged information transfer service.
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The Data messages contain the common message header followed by IUA
message header. The Data message contains the following parameters:
PROTOCOL DATA
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xe) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The protocol data contains upper layer signaling message e.g. Q.931,
QSIG.
3.3.1.4 Unit Data Messages (Request, Indication)
The Unit Data message contains an ISDN Q.921-User Protocol Data Unit
(PDU) corresponding to unacknowledged information transfer service.
The Unit Data messages contain the common message header followed by
IUA message header. The Unit Data message contains the following
parameters
PROTOCOL DATA
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xe) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.2 Application Server Process Maintenance (ASPM) Messages
The ASPM messages will only use the common message header.
3.3.2.1 ASP Up (ASPUP)
The ASP Up (ASPUP) message is sent by an ASP to indicate to an SG
that it is ready to receive traffic or maintenance messages.
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The ASPUP message contains the following parameters:
Info String (optional)
The format for ASPUP Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The optional INFO String parameter can carry any meaningful 8-bit
ASCII character string along with the message. Length of the INFO
String parameter is from 0 to 255 characters. No procedures are
presently identified for its use but the INFO String MAY be used for
debugging purposes.
3.3.2.2 ASP Up Ack
The ASP Up Ack message is used to acknowledge an ASP Up message
received from a remote IUA peer.
The ASPUP Ack message contains the following parameters:
INFO String (optional)
The format for ASPUP Ack Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.3.1).
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3.3.2.3 ASP Down (ASPDN)
The ASP Down (ASPDN) message is sent by an ASP to indicate to an SG
that it is NOT ready to receive traffic or maintenance messages.
The ASPDN message contains the following parameters:
Reason
INFO String (Optional)
The format for the ASPDN message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xa) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.3.1.).
The Reason parameter indicates the reason that the remote IUA
adaptation layer is unavailable. The valid values for Reason are
shown in the following table.
Value Description
0x1 Management Inhibit
If a ASP is removed from Management Inhibit, the ASP will send an ASP
Up message.
3.3.2.4 ASP Down Ack
The ASP Down Ack message is used to acknowledge an ASP Down message
received from a remote IUA peer.
The ASP Down Ack message contains the following parameters:
Reason
INFO String (Optional)
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The format for the ASP Down Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xa) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.2.1.).
The format of the Reason parameter is the same as for the ASP Down
message (See Section 3.3.2.3).
3.3.2.5 ASP Active (ASPAC)
The ASPAC message is sent by an ASP to indicate to an SG that it is
Active and ready to be used.
The ASPAC message contains the following parameters
Traffic Mode Type (Mandatory)
Interface Identifier (Optional)
- Combination of integer and integer ranges, OR
- string (text formatted)
INFO String (Optional)
Morneault, et al. Standards Track [Page 27]
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The format for the ASPAC message using integer formatted Interface
Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1=integer) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x8=integer range) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StartN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StopN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x1 or 0x8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format for the ASPAC message using text formatted (string)
Interface Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3=string) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Traffic Mode Type parameter identifies the traffic mode of
operation of the ASP within an AS. The valid values for Type are
shown in the following table:
Value Description
0x1 Over-ride
0x2 Load-share
Within a particular Interface Identifier, only one Traffic Mode Type
can be used. The Over-ride value indicates that the ASP is operating
in Over-ride mode, where the ASP takes over all traffic in an
Application Server (i.e., primary/back-up operation), over-riding any
currently active ASPs in the AS. In Load-share mode, the ASP will
share in the traffic distribution with any other currently active
ASPs.
The optional Interface Identifiers parameter contains a list of
Interface Identifier integers (Type 0x1 or Type 0x8) or text strings
(Type 0x3) indexing the Application Server traffic that the sending
ASP is configured/registered to receive. If integer formatted
Morneault, et al. Standards Track [Page 29]
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Interface Identifiers are being used, the ASP can also send ranges of
Interface Identifiers (Type 0x8). Interface Identifier types Integer
(0x1) and Integer Range (0x8) are allowed in the same message. Text
formatted Interface Identifiers (0x3) cannot be used with either
Integer (0x1) or Integer Range (0x8) types.
If no Interface Identifiers are included, the message is for all
provisioned Interface Identifiers within the AS(s) in which the ASP
is provisioned. If only a subset of Interface Identifiers are
included, the ASP is noted as Active for all the Interface
Identifiers provisioned for that AS.
Note: If the optional Interface Identifier parameter is present, the
integer formatted Interface Identifier MUST be supported, while the
text formatted Interface Identifier MAY be supported.
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.2.1.).
An SG that receives an ASPAC with an incorrect Traffic Mode Type for
a particular Interface Identifier will respond with an Error Message
(Cause: Unsupported Traffic Handling Mode).
3.3.2.6 ASP Active Ack
The ASPAC Ack message is used to acknowledge an ASP-Active message
received from a remote IUA peer.
The ASPAC Ack message contains the following parameters:
Traffic Mode Type (Mandatory)
Interface Identifier (Optional)
- Combination of integer and integer ranges, OR
- string (text formatted)
INFO String (Optional)
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The format for the ASPAC Ack message with Integer-formatted Interface
Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1=integer) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x8=integer range) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StartN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StopN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x1 or 0x8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format for the ASP Active Ack message using text formatted
(string) Interface Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3=string) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Traffic Mode Type and Interface Identifier
parameters is the same as for the ASP Active message (See Section
3.3.2.5).
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.2.1.).
3.3.2.7 ASP Inactive (ASPIA)
The ASPIA message is sent by an ASP to indicate to an SG that it is
no longer an active ASP to be used from within a list of ASPs. The
SG will respond with an ASPIA Ack message and either discard incoming
messages or buffer for a timed period and then discard.
The ASPIA message contains the following parameters
Traffic Mode Type (Mandatory)
Interface Identifiers (Optional)
- Combination of integer and integer ranges, OR
- string (text formatted)
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INFO String (Optional)
The format for the ASP Inactive message parameters using Integer
formatted Interface Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1=integer) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x8=integer range) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StartN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StopN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x1 or 0x8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format for the ASP Inactive message using text formatted (string)
Interface Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3=string) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Traffic Mode Type parameter identifies the traffic mode of
operation of the ASP within an AS. The valid values for Traffic Mode
Type are shown in the following table:
Value Description
0x1 Over-ride
0x2 Load-share
The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP Active message (See
Section 3.3.2.3.).
The optional Interface Identifiers parameter contains a list of
Interface Identifier integers or text strings indexing the
Application Server traffic that the sending ASP is
configured/registered to receive, but does not want to receive at
this time.
Morneault, et al. Standards Track [Page 34]
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3.3.2.8 ASP Inactive Ack
The ASP Inactive (ASPIA) Ack message is used to acknowledge an ASP
Inactive message received from a remote IUA peer.
The ASPIA Ack message contains the following parameters:
Traffic Mode Type (Mandatory)
Interface Identifiers (Optional)
- Combination of integer and integer ranges, OR
- string (text formatted)
INFO String (Optional)
Morneault, et al. Standards Track [Page 35]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1=integer) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x8=integer range) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StartN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StopN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x1 or 0x8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Morneault, et al. Standards Track [Page 36]
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The format for the ASP Inactive Ack message using text formatted
(string) Interface Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xb) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Mode Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3=string) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Traffic Mode Type and Interface Identifier
parameters is the same as for the ASP Inactive message (See Section
3.3.2.7).
The format and description of the optional Info String parameter is
the same as for the ASP Up message (See Section 3.3.2.1).
3.3.2.9 Heartbeat (BEAT)
The Heartbeat message is optionally used to ensure that the IUA peers
are still available to each other. It is recommended for use when
the IUA runs over a transport layer other than the SCTP, which has
its own heartbeat.
The BEAT message contains the following parameters:
Heartbeat Data Optional
Morneault, et al. Standards Track [Page 37]
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The format for the BEAT message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 9 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Heartbeat Data * |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Heartbeat Data parameter contents are defined by the sending
node. The Heartbeat Data could include, for example, a Heartbeat
Sequence Number and, or Timestamp. The receiver of a Heartbeat
message does not process this field as it is only of significance to
the sender. The receiver MUST respond with a Heartbeat Ack message.
3.3.2.10 Heartbeat Ack (BEAT-Ack)
The Heartbeat Ack message is sent in response to a received Heartbeat
message. It includes all the parameters of the received Heartbeat
message, without any change.
3.3.3 Layer Management (MGMT) Messages
3.3.3.1 Error (ERR)
The Error message is used to notify a peer of an error event
associated with an incoming message. For example, the message type
might be unexpected given the current state, or a parameter value
might be invalid.
The Error message will only have the common message header. The
Error message contains the following parameters:
Error Code
Diagnostic Information (optional)
Morneault, et al. Standards Track [Page 38]
RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xc) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x7) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diagnostic Information* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Error Code parameter indicates the reason for the Error Message.
The Error parameter value can be one of the following values:
Invalid Version 0x01
Invalid Interface Identifier 0x02
Unsupported Message Class 0x03
Unsupported Message Type 0x04
Unsupported Traffic Handling Mode 0x05
Unexpected Message 0x06
Protocol Error 0x07
Unsupported Interface Identifier Type 0x08
Invalid Stream Identifier 0x09
Unassigned TEI 0x0a
Unrecognized SAPI 0x0b
Invalid TEI, SAPI combination 0x0c
The 'Invalid Version' error would be sent if a message was received
with an invalid or unsupported version. The Error message would
contain the supported version in the Common header. The Error
message could optionally provide the supported version in the
Diagnostic Information area.
The 'Invalid Interface Identifier' error would be sent by a SG if an
ASP sends a message with an invalid (unconfigured) Interface
Identifier value.
The 'Unsupported Traffic Handling Mode' error would be sent by a SG
if an ASP sends an ASP Active with an unsupported Traffic Handling
Mode. An example would be a case in which the SG did not support
load-sharing.
The 'Unexpected Message' error would be sent by an ASP if it received
a QPTM message from an SG while it was in the Inactive state (the ASP
could optionally drop the message and not send an Error). It would
Morneault, et al. Standards Track [Page 39]
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also be sent by an ASP if it received a defined and recognized
message that the SG is not expected to send (e.g., if the MGC
receives an IUA Establish Request message).
The 'Protocol Error' error would be sent for any protocol anomaly
(i.e., a bogus message).
The 'Invalid Stream Identifier' error would be sent if a message was
received on an unexpected SCTP stream (i.e., a MGMT message was
received on a stream other than '0').
The 'Unsupported Interface Identifier Type' error would be sent by a
SG if an ASP sends a Text formatted Interface Identifier and the SG
only supports Integer formatted Interface Identifiers. When the ASP
receives this error, it will need to resend its message with an
Integer formatted Interface Identifier.
The 'Unsupported Message Type' error would be sent if a message with
an unexpected or unsupported Message Type is received.
The 'Unsupported Message Class' error would be sent if a message with
an unexpected or unsupported Message Class is received.
The 'Unassigned TEI' error may be used when the SG receives an IUA
message that includes a TEI which has not been assigned or recognized
for use on the indicated ISDN D-channel.
The 'Unrecognized SAPI' error would handle the case of using a SAPI
that is not recognized by the SG. The 'Invalid TEI, SAPI
combination' error identify errors where the TEI is assigned and the
the SAPI is recognized, but the combination is not valid for the
interface (e.g., on a BRI the MGC tries to send Q.921 Management
messages via IUA when Layer Management at the SG SHOULD be performing
this function).
The optional Diagnostic information can be any information germane to
the error condition, to assist in identification of the error
condition. To enhance debugging, the Diagnostic information could
contain the first 40 bytes of the offending message.
3.3.3.2 Notify (NTFY)
The Notify message used to provide an autonomous indication of IUA
events to an IUA peer.
Morneault, et al. Standards Track [Page 40]
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The Notify message will only use the common message header. The
Notify message contains the following parameters:
Status Type
Status Identification
Interface Identifiers (Optional)
INFO String (Optional)
Morneault, et al. Standards Track [Page 41]
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The format for the Notify message with Integer-formatted Interface
Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xd) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Type | Status Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1=integer) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifiers* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x8=integer range) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop1* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Start2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier Stop2* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StartN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier StopN* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x1 or 0x8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format for the Notify message with Text-formatted Interface
Identifiers is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0xd) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Type | Status Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x3=string) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Interface Identifiers |
| of Tag Type 0x3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO String* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status Type parameter identifies the type of the Notify message.
The following are the valid Status Type values:
Value Description
0x1 Application Server state change (AS_State_Change)
0x2 Other
The Status Identification parameter contains more detailed
information for the notification, based on the value of the Status
Type. If the Status Type is AS_State_Change the following Status
Identification values are used:
Value Description
1 Application Server Down (AS_Down)
2 Application Server Inactive (AS_Inactive)
3 Application Server Active (AS_Active)
4 Application Server Pending (AS_Pending)
Morneault, et al. Standards Track [Page 43]
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These notifications are sent from an SG to an ASP upon a change in
status of a particular Application Server. The value reflects the
new state of the Application Server.
If the Status Type is Other, then the following Status Information
values are defined:
Value Description
1 Insufficient ASP resources active in AS
2 Alternate ASP Active
These notifications are not based on the SG reporting the state
change of an ASP or AS. In the Insufficient ASP Resources case, the
SG is indicating to an 'Inactive' ASP(s) in the AS that another ASP
is required in order to handle the load of the AS (Load-sharing
mode). For the Alternate ASP Active case, an ASP is informed when an
alternate ASP transitions to the ASP-Active state in Over-ride mode.
The format and description of the optional Interface Identifiers and
Info String parameters is the same as for the ASP Active message (See
Section 3.3.2.3.).
3.3.3.3 TEI Status Messages (Request, Confirm and Indication)
The TEI Status messages are exchanged between IUA layer peers to
request, confirm and indicate the status of a particular TEI.
The TEI Status messages contain the common message header followed by
IUA message header. The TEI Status Request message does not contain
any additional parameters.
In the integrated ISDN Layer 2/3 model (e.g., in traditional ISDN
switches), it is assumed that the Layer Management for the Q.921
Layer and the Q.931 layer are co-located. When backhauling ISDN,
this assumption is not necessarily valid. The TEI status messages
allow the two Layer Management entities to communicate the status of
the TEI. In addition, knowing that a TEI is in service allows the
ASP to request the SG to establish the datalink to the terminal (via
the IUA Establish message) for signaling if the ASP wants to be in
control of data link establishment. Another use of the TEI status
procedure is where the Layer Management at the ASP can prepare for
send/receive signaling to/from a given TEI and confirm/verify the
establishment of a datalink to that TEI. For example, if a datalink
is established for a TEI that the ASP did not know was assigned, the
ASP can check to see whether it was assigned or whether there was an
error in the signaling message. Also, knowing that a TEI is out of
service, the ASP need not request the SG to establish a datalink to
that TEI.
Morneault, et al. Standards Track [Page 44]
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The TEI Status Indication, and Confirm messages contain the following
parameter:
STATUS
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x10) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The valid values for Status are shown in the following table.
Define Value Description
ASSIGNED 0x0 TEI is considered assigned by Q.921
UNASSIGNED 0x1 TEI is considered unassigned by Q.921
4.0 Procedures
The IUA layer needs to respond to various primitives it receives from
other layers as well as messages it receives from the peer IUA layer.
This section describes various procedures involved in response to
these events.
4.1 Procedures to support service in section 1.4.1
These procedures achieve the IUA layer's 'Transport of Q.921/Q.931
boundary' service.
4.1.1 Q.921 or Q.931 primitives procedures
On receiving these primitives from the local layer, the IUA layer
will send the corresponding QPTM message (Data, Unit Data, Establish,
Release) to its peer. While doing so, the IUA layer needs to fill
various fields of the common and specific headers correctly. In
addition the message needs to be sent on the SCTP stream that
corresponds to the D channel (Interface Identifier).
4.1.2 QPTM message procedures
On receiving QPTM messages from a peer IUA layer, the IUA layer on an
SG or MGC needs to invoke the corresponding layer primitives (DL-
ESTABLISH, DL-DATA, DL-UNIT DATA, DL-RELEASE) to the local Q.921 or
Q.931 layer.
Morneault, et al. Standards Track [Page 45]
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4.2 Procedures to support service in section 1.4.2
These procedures achieve the IUA layer's 'Support for Communication
between Layer Managements' service.
4.2.1 Layer Management primitives procedures
On receiving these primitives from the local Layer Management, the
IUA layer will provide the appropriate response primitive across the
internal local Layer Management interface.
An M-SCTP ESTABLISH request from Layer Management will initiate the
establishment of an SCTP association. An M-SCTP ESTABLISH confirm
will be sent to Layer Management when the initiated association set-
up is complete. An M-SCTP ESTABLISH indication is sent to Layer
Management upon successful completion of an incoming SCTP association
set-up from a peer IUA node
An M-SCTP RELEASE request from Layer Management will initiate the
tear-down of an SCTP association. An M-SCTP RELEASE confirm will be
sent by Layer Management when the association teardown is complete.
An M-SCTP RELEASE indication is sent to Layer Management upon
successful tear-down of an SCTP association initiated by a peer IUA.
M-SCTP STATUS request and indication support a Layer Management query
of the local status of a particular SCTP association.
M-NOTIFY indication and M-ERROR indication indicate to Layer
Management the notification or error information contained in a
received IUA Notify or Error message respectively. These indications
can also be generated based on local IUA events.
M-ASP STATUS request/indication and M-AS-STATUS request/indication
support a Layer Management query of the local status of a particular
ASP or AS. No IUA peer protocol is invoked.
M-ASP-UP request, M-ASP-DOWN request, M-ASP-INACTIVE request and M-
ASP-ACTIVE request allow Layer Management at an ASP to initiate state
changes. These requests result in outgoing IUA ASP UP, ASP DOWN, ASP
INACTIVE and ASP ACTIVE messages.
M-ASP-UP confirmation, M-ASP-DOWN confirmation, M-ASP-INACTIVE
confirmation and M-ASP-ACTIVE confirmation indicate to Layer
Management that the previous request has been confirmed.
Morneault, et al. Standards Track [Page 46]
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Upon receipt of a M-TEI Status primitive from Layer Management, the
IUA will send the corresponding MGMT message (TEI Status) to its
peer. While doing so, the IUA layer needs to fill various fields of
the common and specific headers correctly.
All MGMT messages are sent on a sequenced stream to ensure ordering.
SCTP stream '0' SHOULD be used.
4.2.2 Receipt of IUA Peer Management messages
Upon receipt of IUA Management messages, the IUA layer MUST invoke
the corresponding Layer Management primitive indications (e.g., M-AS
Status ind., M-ASP Status ind., M-ERROR ind., M-TEI STATUS...) to the
local layer management.
M-NOTIFY indication and M-ERROR indication indicate to Layer
Management the notification or error information contained in a
received IUA Notify or Error message. These indications can also be
generated based on local IUA events.
All MGMT messages are sent on a sequenced stream to ensure ordering.
SCTP stream '0' SHOULD be used.
4.3 Procedures to support service in section 1.4.3
These procedures achieve the IUA layer's 'Support for management of
active associations between SG and MGC' service.
4.3.1 AS and ASP State Maintenance
The IUA layer on the SG needs to maintain the states of each ASP as
well as the state of the AS.
4.3.1.1 ASP States
The state of the each ASP, in each AS that it is configured, is
maintained in the IUA layer on the SG. The state of an ASP changes
due to the following type of events:
* Reception of messages from peer IUA layer at that ASP
* Reception of some messages from the peer IUA layer at other
ASPs in the AS
* Reception of indications from SCTP layer
The ASP state transition diagram is shown in Figure 7. The possible
states of an ASP are the following:
Morneault, et al. Standards Track [Page 47]
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ASP-DOWN: Application Server Process is unavailable and/or the
related SCTP association is down. Initially, all ASPs will be in
this state. An ASP in this state SHOULD NOT be sent any IUA messages.
ASP-INACTIVE: The remote IUA peer at the ASP is available (and the
related SCTP association is up) but application traffic is stopped.
In this state the ASP can be sent any non-QPTM IUA messages (except
for TEI Status messages).
ASP-ACTIVE: The remote IUA peer at the ASP is available and
application traffic is active.
Figure 7 ASP State Transition Diagram
+-------------+
+----------------------| |
| Alternate +-------| ASP-ACTIVE |
| ASP | +-------------+
| Takeover | ^ |
| | ASP | | ASP
| | Active | | Inactive
| | | v
| | +-------------+
| | | |
| +------>| ASP-INACT |
| +-------------+
| ^ |
ASP Down/ | ASP | | ASP Down /
SCTP CDI | Up | | SCTP CDI
| | v
| +-------------+
+--------------------->| |
| ASP-DOWN |
+-------------+
SCTP CDI: The local SCTP layer's Communication Down Indication to
the Upper Layer Protocol (IUA) on an SG. The local SCTP will send
this indication when it detects the loss of connectivity to the ASP's
peer SCTP layer. SCTP CDI is understood as either a SHUTDOWN
COMPLETE notification and COMMUNICATION LOST notification from the
SCTP.
4.3.1.2 AS States
The state of the AS is maintained in the IUA layer on the SG.
The state of an AS changes due to events. These events include the
following:
Morneault, et al. Standards Track [Page 48]
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* ASP state transitions
* Recovery timer triggers
The possible states of an AS are the following:
AS-DOWN: The Application Server is unavailable. This state implies
that all related ASPs are in the ASP-DOWN state for this AS.
Initially the AS will be in this state.
AS-INACTIVE: The Application Server is available but no application
traffic is active (i.e., one or more related ASPs are in the ASP-
INACTIVE state, but none in the ASP-ACTIVE state). The recovery
timer T(r) is not running or has expired.
AS-ACTIVE: The Application Server is available and application
traffic is active. This state implies that at least one ASP is in
the ASP-ACTIVE state.
AS-PENDING: An active ASP has transitioned from active to inactive or
down and it was the last remaining active ASP in the AS. A recovery
timer T(r) will be started and all incoming SCN messages will be
queued by the SG. If an ASP becomes active before T(r) expires, the
AS will move to AS-ACTIVE state and all the queued messages will be
sent to the active ASP.
If T(r) expires before an ASP becomes active, the SG stops queuing
messages and discards all previously queued messages. The AS will
move to AS-INACTIVE if at least one ASP is in ASP-INACTIVE state,
otherwise it will move to AS-DOWN state.
Morneault, et al. Standards Track [Page 49]
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Figure 8 AS State Transition Diagram
+----------+ one ASP trans ACTIVE +-------------+
| |------------------------>| |
| AS-INACT | | AS-ACTIVE |
| | | |
| |< | |
+----------+ +-------------+
^ | Tr Trigger ^ |
| | at least one | |
| | ASP in UP | |
| | | |
| | | |
| | | |
one ASP | | one ASP | | Last ACTIVE ASP
trans | | all ASP ------ trans to | | trans to INACT
to | | trans to ACTIVE | | or DOWN
INACT | | DOWN | | (start Tr timer)
| | | |
| | | |
| | | |
| v | v
+----------+ +-------------+
| | -| |
| AS-DOWN | | AS-PENDING |
| | | (queueing) |
| |<------------------------| |
+----------+ Tr Expiry and no +-------------+
ASP in INACTIVE state
Tr = Recovery Timer
4.3.2 ASPM procedures for primitives
Before the establishment of an SCTP association the ASP state at both
the SG and ASP is assumed to be 'Down'.
As the ASP is responsible for initiating the setup of an SCTP
association to an SG, the IUA layer at an ASP receives an M-SCTP
ESTABLISH request primitive from the Layer Management, the IUA layer
will try to establish an SCTP association with the remote IUA peer at
an SG. Upon reception of an eventual SCTP-Communication Up confirm
primitive from the SCTP, the IUA layer will invoke the primitive M-
SCTP ESTABLISH confirm to the Layer Management.
At the SG, the IUA layer will receive an SCTP Communication Up
indication primitive from the SCTP. The IUA layer will then invoke
the primitive M-SCTP ESTABLISH indication to the Layer Management.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
Once the SCTP association is established and assuming that the local
IUA-User is ready, the local ASP IUA Application Server Process
Maintenance (ASPM) function will initiate the ASPM procedures, using
the ASP Up/-Down/-Active/-Inactive messages to convey the ASP state
to the SG - see Section 4.3.3.
The Layer Management and the IUA layer on SG can communicate the
status of the application server using the M-AS STATUS primitives.
The Layer Management and the IUA layer on both the SG and ASP can
communicate the status of an SCTP association using the M-SCTP STATUS
primitives.
If the Layer Management on SG or ASP wants to bring down an SCTP
association for management reasons, they would send M-SCTP RELEASE
request primitive to the local IUA layer. The IUA layer would
release the SCTP association and upon receiving the SCTP
Communication Down indication from the underlying SCTP layer, it
would inform the local Layer Management using M-SCTP RELEASE confirm
primitive.
If the IUA layer receives an SCTP-Communication Down indication from
the underlying SCTP layer, it will inform the Layer Management by
invoking the M-SCTP RELEASE indication primitive. The state of the
ASP will be moved to 'Down' at both the SG and ASP.
At an ASP, the Layer Management MAY try to reestablish the SCTP
association using M-SCTP ESTABLISH request primitive.
4.3.3 ASPM procedures for peer-to-peer messages
All ASPM messages are sent on a sequenced stream to ensure ordering.
SCTP stream '0' SHOULD be used.
4.3.3.1 ASP Up
After an ASP has successfully established an SCTP association to an
SG, the SG waits for the ASP to send an ASP Up message, indicating
that the ASP IUA peer is available. The ASP is always the initiator
of the ASP Up exchange.
When an ASP Up message is received at an SG and internally the remote
ASP is not considered locked-out for local management reasons, the SG
marks the remote ASP as 'Inactive'. The SG responds with an ASP Up
Ack message in acknowledgement. The SG sends an ASP-Up Ack message
in response to a received ASP Up message even if the ASP is already
marked as 'Inactive' at the SG.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
If for any local reason the SG cannot respond with an ASP Up, the SG
responds to a ASP Up with a with an ASP-Down Ack message with Reason
'Management Blocking'.
At the ASP, the ASP Up Ack message received from the SG is not
acknowledged by the ASP. If the ASP does not receive a response from
the SG, or an ASP Down Ack is received, the ASP MAY resend ASP Up
messages every 2 seconds until it receives a ASP Up Ack message from
the SG. The ASP MAY decide to reduce the frequency (say to every 5
seconds) if an ASP Up Ack is not received after a few tries.
The ASP MUST wait for the ASP Up Ack message from the SG before
sending any ASP traffic control messages (ASPAC or ASPIA) or Data
messages or it will risk message loss. If the SG receives QPTM, ASP
Active or ASP Inactive messages before an ASP Up is received, the SG
SHOULD discard these messages.
4.3.3.2 ASP Down
The ASP will send an ASP Down to an SG when the ASP is to be removed
from the list of ASPs in all Application Servers that it is a member
and no longer receive any IUA traffic or management messages.
Whether the ASP is permanently removed from an AS is a function of
configuration management.
The SG marks the ASP as 'Down' and returns an ASP Down Ack message to
the ASP if one of the following events occur:
- to acknowledge an ASP Down message from an ASP,
- to reply to ASPM messages from an ASP which is locked out for
management reasons.
The SG sends an ASP Down Ack message in response to a received ASP
Down message from the ASP even if the ASP is already marked as 'Down'
at the SG.
If the ASP does not receive a response from the SG, the ASP MAY send
ASP Down messages every 2 seconds until it receives an ASP Down Ack
message from the SG or the SCTP association goes down. The ASP MAY
decide to reduce the frequency (say to every 5 seconds) if an ASP
Down Ack is not received after a few tries.
4.3.3.3 IUA Version Control
If a ASP Up message with an unsupported version is received, the
receiving end responds with an Error message, indicating the version
the receiving node supports and notifies Layer Management.
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
This is useful when protocol version upgrades are being performed in
a network. A node upgraded to a newer version SHOULD support the
older versions used on other nodes it is communicating with. Because
ASPs initiate the ASP Up procedure it is assumed that the Error
message would normally come from the SG.
4.3.3.4 ASP Active
Any time after the ASP has received a ASP Up Ack from the SG, the ASP
sends an ASP-Active (ASPAC) to the SG indicating that the ASP is
ready to start processing traffic. In the case where an ASP is
configured/registered to process the traffic for more than one
Application Server across an SCTP association, the ASPAC contains one
or more Interface Identifiers to indicate for which Application
Servers the ASPAC applies.
When an ASP Active (ASPAC) message is received, the SG responds to
the ASP with a ASPAC Ack message acknowledging that the ASPAC was
received and starts sending traffic for the associated Application
Server(s) to that ASP.
The ASP MUST wait for the ASP-Active Ack message from the SG before
sending any Data messages or it will risk message loss. If the SG
receives QPTM messages before an ASP Active is received, the SG
SHOULD discard these messages.
There are two modes of Application Server traffic handling in the SG
IUA - Over-ride and Load-sharing. The Type parameter in the ASPAC
message indicates the mode used in a particular Application Server.
If the SG determines that the mode indicates in an ASPAC is
incompatible with the traffic handling mode currently used in the AS,
the SG responds with an Error message indicating Unsupported Traffic
Handling Mode.
In the case of an Over-ride mode AS, reception of an ASPAC message at
an SG causes the redirection of all traffic for the AS to the ASP
that sent the ASPAC. The SG responds to the ASPAC with an ASP-Active
Ack message to the ASP. Any previously active ASP in the AS is now
considered Inactive and will no longer receive traffic from the SG
within the AS. The SG sends a Notify (Alternate ASP-Active) to the
previously active ASP in the AS, after stopping all traffic to that
ASP.
In the case of a load-share mode AS, reception of an ASPAC message at
an SG causes the direction of traffic to the ASP sending the ASPAC,
in addition to all the other ASPs that are currently active in the
AS. The algorithm at the SG for load-sharing traffic within an AS to
all the active ASPs is implementation dependent. The algorithm
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RFC 3057 ISDN Q.921-User Adaptation Layer February 2001
could, for example be round-robin or based on information in the Data
message, su |
