| 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
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)
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* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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)
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* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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)
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* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
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)
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
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.
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)
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* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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)
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.
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.
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.
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:
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:
* 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.
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.
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.
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.
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
could, for example be round-robin or based on information in the Data
message, such as Interface Identifier, depending on the requirements
of the application and the call state handling assumptions of the
collection of ASPs in the AS. The SG responds to the ASPAC with a
ASP-Active Ack message to the ASP.
4.3.3.5 ASP Inactive
When an ASP wishes to withdraw from receiving traffic within an AS,
the ASP sends an ASP Inactive (ASPIA) to the SG. In the case where
an ASP is configured/registered to process the traffic for more than
one Application Server across an SCTP association, the ASPIA contains
one or more Interface Identifiers to indicate for which Application
Servers the ASPIA applies.
There are two modes of Application Server traffic handling in the SG
IUA when withdrawing an ASP from service - Over-ride and Load-
sharing. The Type parameter in the ASPIA 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, where normally another ASP has
already taken over the traffic within the AS with an Over-ride ASPAC,
the ASP which sends the ASPIA is already considered by the SG to be
"Inactive". An ASPIA Ack message is sent to the ASP, after ensuring
that all traffic is stopped to the ASP.
In the case of a Load-share mode AS, the SG moves the ASP to the
"Inactive" state and the AS traffic is re-allocated across the
remaining "active" ASPs per the load-sharing algorithm currently used
within the AS. An ASPIA Ack message is sent to the ASP after all
traffic is halted to the ASP. A NTFY (Insufficient ASPs) MAY be sent
to all inactive ASPs, if required.
If no other ASPs are Active in the Application Server, the SG sends a
NTFY (AS-Pending) to all inactive ASPs of the AS and either discards
all incoming messages for the AS or starts buffering the incoming
messages for T(r)seconds, after which messages will be discarded.
T(r) is configurable by the network operator. If the SG receives an
ASPAC from an ASP in the AS before expiry of T(r), the buffered
traffic is directed to the ASP and the timer is cancelled. If T(r)
expires, the AS is moved to the "Inactive" state.
4.3.3.6 Notify
A Notify message reflecting a change in the AS state is sent to all
ASPs in the AS, except those in the "Down" state, with appropriate
Status Identification.
In the case where a Notify (AS-Pending) message is sent by an SG that
now has no ASPs active to service the traffic, or a NTFY
(Insufficient ASPs) is sent in the Load-share mode, the Notify does
not explicitly force the ASP(s) receiving the message to become
active. The ASPs remain in control of what (and when) action is
taken.
4.3.3.7 Heartbeat
The optional Heartbeat procedures MAY be used when operating over
transport layers that do not have their own heartbeat mechanism for
detecting loss of the transport association (i.e., other than the
SCTP).
After receiving an ASP Up Ack message from the SG in response to an
ASP Up message, the ASP MAY optionally send Beat messages
periodically, subject to a provisionable timer T(beat). The SG IUA,
upon receiving a BEAT message from the ASP, responds with a BEAT ACK
message. If no BEAT message (or any other IUA message) is received
from the SG within the timer 2*T(beat), the SG will consider the
remote IUA as "Down". The SG will also send an ASP Down Ack message
to the ASP.
At the ASP, if no BEAT ACK message (or any other IUA message) is
received from the SG within 2*T(beat), the SG is considered
unavailable. Transmission of BEAT messages is stopped and ASP Up
procedures are used to re-establish communication with the SG IUA
peer.
The BEAT message MAY optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Beat Ack
message. The ASP upon examining the contents of the returned BEAT
Ack message MAY choose to consider the remote ASP as unavailable.
The contents/format of the Heartbeat Data parameter is
implementation-dependent and only of local interest to the original
sender. The contents MAY be used, for example, to support a
Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
timestamp mechanism (to evaluate delays).
Note: Heartbeat related events are not shown in Figure 4 "ASP state
transition diagram".
5.0 Examples
5.1 Establishment of Association and Traffic between SGs and ASPs
5.1.1 Single ASP in an Application Server (1+0 sparing)
This scenario shows the example IUA message flows for the
establishment of traffic between an SG and an ASP, where only one ASP
is configured within an AS (no backup). It is assumed that the SCTP
association is already set-up.
SG ASP1
|
|<---------ASP Up----------|
|--------ASP Up Ack------->|
| |
|<-------ASP Active--------|
|------ASP Active Ack----->|
| |
5.1.2 Two ASPs in Application Server (1+1 sparing)
This scenario shows the example IUA message flows for the
establishment of traffic between an SG and two ASPs in the same
Application Server, where ASP1 is configured to be Active and ASP2 a
standby in the event of communication failure or the withdrawal from
service of ASP1. ASP2 MAY act as a hot, warm, or cold standby
depending on the extent to which ASP1 and ASP2 share call state or
can communicate call state under failure/withdrawal events. The
example message flow is the same whether the ASP-Active messages are
Over-ride or Load-share mode although typically this example would
use an Over-ride mode.
SG ASP1 ASP2
| | |
|<--------ASP Up----------| |
|-------ASP Up Ack------->| |
| | |
|<-----------------------------ASP Up----------------|
|----------------------------ASP Up Ack------------->|
| | |
| | |
|<-------ASP Active-------| |
|-----ASP Active Ack----->| |
| | |
5.1.3 Two ASPs in an Application Server (1+1 sparing, load-sharing case)
This scenario shows a similar case to Section 5.1.2 but where the two
ASPs are brought to active and load-share the traffic load. In this
case, one ASP is sufficient to handle the total traffic load.
SG ASP1 ASP2
| | |
|<---------ASP Up---------| |
|--------ASP Up Ack------>| |
| | |
|<------------------------------ASP Up---------------|
|-----------------------------ASP Up Ack------------>|
| | |
| | |
|<--ASP Active (Ldshr)----| |
|----ASP Active Ack------>| |