Lucent Technologies DEFINITY Enterprise Communications Server Release 5, CallVisor, ASAI Protocol Reference Instructions Manual

							Ending an ASAI Association
Issue 6  June 1997
2-55
Rejects an Invalid/Protocol Violation FIE — Terminates Association’’ on page 
5-68 of Chapter 5, “Byte Level Messages.” For domain control coding, see 
‘‘Domain Control: Endpoint Rejects an Invalid/Protocol Violation FIE — 
Terminates Association’’ on page 5-96 of Chapter 5, “Byte Level Messages.”
The ECS does not attempt to retry during any association where an adjunct 
rejects an FIE that the ECS has sent. If the ECS receives a Reject component in a 
FACility message, the ECS immediately replies with a RELease COMplete that 
terminates that association.
ASAI and BRI Parser Interactions
Since ASAI is provided on a BRI interface, the ASAI adheres to certain protocol 
procedures for BRI. The BRI Parsing subsystem implements the following Q.931 
procedures (shown in order of precedence):
nThe ECS ignores any incoming message less than three bytes or greater 
than 260 bytes.
nThe ECS checks for a valid protocol discriminator.
— The REGister, FACility, RELease COMplete, RESTart, RESTart 
ACKnowledge, and STATUS messages must carry the BRI protocol 
discriminator (0x08).
The ECS ignores any message with an improper protocol discriminator.
nThe ECS sends a RELease COMplete message with a Cause IE having 
value 97 (Message Type Invalid or Not Implemented) if a message other 
than REGister, FACility, RELease COMplete, STATUS, RESTart, or 
RESTart ACKnowledge is received.
19 For more information regarding BRI, 
see the 
ISDN Basic Rate Interface (BRI) Specification, 801-802-100.
nThe ECS ignores STATUS messages.
nThe ECS then checks to insure that the CRV is a permitted length. The 
CRV must be either the Global CRV, or its length must be the length 
permitted on the ASAI over which the message arrived. For each ASAI link, 
the customer administers the length of the ASAI CRV values to be either 1 
or 2 bytes. The parameter settings may be different for different ASAI 
interfaces. When the CRV length is administered as 2 bytes:
— An adjunct is permitted to send messages containing a CRV with 
length 1 or 2.
— The ECS always sends 2-byte CRVs (even though the CRV value 
may fit into a single byte).
The ECS ignores any message containing a CRV with a value that is 
either: 1) not permitted with the administered length, or 2) zero length (for 
example, the Global Call Reference Value).
19. BRI allows the network the option of sending STATUS or RELease COMplete in this 
situation. The ECS ASAI sends RELease COMplete. 
						

							Messaging Sequences and ASAI
2-56Issue 6  June 1997 
nThe ECS checks to make sure that in-use and available CRVs are used 
appropriately in ASAI messages. If the ECS receives:
1. A REGister message containing a CRV that is already in use on the 
ASAI for another association, then the ECS responds with a 
RELease COMplete message containing Cause CS0/81, “Invalid 
CRV.” This message does not contain an FIE.
2. A FACility message containing an idle CRV, then the ECS responds 
with a RELease COMplete message containing Cause CS0/81, 
“Invalid CRV.” This message does not contain an FIE.
nThe ECS sends a RELease COMplete message with a Cause IE having 
value 96 (Mandatory IE missing) if a mandatory IE is omitted. For more 
information, see 
ISDN Basic Rate Interface (BRI) Specification, 
801-802-100. This message may not contain an FIE. Specifically, this ECS 
takes this action if it receives a REGister or FACility message without the 
mandatory Facility Information Element. 
20
nIf an incoming REGister message contains an FIE, but the FIE does not 
contain an Invoke component, the ECS responds with a RELease 
COMplete message with a Cause IE having value 100, “Invalid IE 
contents.” This message does not contain an FIE.
nIf the ECS receives a REGister message (for example, a request to begin a 
new association) when it is in an overload state, the ECS denies the 
request as described in “Endpoint Denies A Request” earlier in this section.
nAny unrecognized or unexpected information element in a message is 
ignored; processing continues with recognized information elements. For 
more information, see the 
ISDN Basic Rate Interface (BRI) Specification, 
801-802-100.
nAny unexpected or unrecognized information elements contained (as ASAI 
parameters) within an FIE are also ignored; processing continues with 
recognized information elements.
nWhen a mandatory parameter is not present within an FIE, the ECS sends 
a FACility or RELease COMplete message containing a Return Error 
component with a Cause IE having value 96 (Mandatory IE Missing). The 
ECS sends a FACility message in exactly the same situations as it would 
send a FACility message for denial; otherwise the ECS sends a RELease 
COMplete message.
nThe ECS does not send any response to a RELease COMplete with an 
unrecognized (inactive) CRV.
nIf the request contains a FACility IE with an operation value that is outside 
of the ASAI subset that the ECS supports, the ECS responds with 
CS0/111, “Protocol error.”
20. Note: BRI allows the network the option of sending STATUS or terminating the ASAI 
association in this situation. The ECS implementation of ASAI terminates the association. 
						

							Link Management and Maintenance Procedures
Issue 6  June 1997
2-57
nIf a field within an IE contains an invalid, reserved, or unrecognized code 
point, the ECS returns CS0/100, “Invalid IE Contents.”
Link Management and Maintenance 
Procedures
Maintenance procedures use additional messages beyond the REGister, FACility, 
and RELease COMplete messages that carry capability invocations discussed 
previously. These ISDN messages (RESTart, RESTart ACKnowledge) provide 
additional procedures to keep the ECS and adjunct synchronized.
NOTE:
Adjunct support for heartbeat and restart procedures is mandatory for 
operation with DEFINITY ECS.
Maintenance Heartbeat Procedure
One ASAI endpoint queries the other to see if the ECS is processing layer 3 ASAI 
messages.
1. The initiating endpoint sends a REGister message containing an invoke 
FIE with:
Operation Value = Heartbeat
For coding, see ‘‘Heartbeat’’ on page 5-188 of Chapter 5, “Byte Level 
Messages.”
2. The receiving endpoint replies with a RELease COMplete message 
containing a return result FIE. The invoke-id in the return result has the 
same value as the invoke-id in the heartbeat.
For coding, see ‘‘Response to Heartbeat’’ on page 5-189 of Chapter 5, 
“Byte Level Messages.”
Platform developers should be aware of another important use for Heartbeat 
messages. The layer 2 transport protocol underlying ASAI (ISDN LAPD) uses 
several timers to detect that a packet has not been received and to attempt 
retransmittal. The result is that the time it takes layer 2 to report a link failure to 
layer 3 may be too long for certain applications. In an environment where, for 
example, link failure needs to be detected in three seconds, the adjunct platform 
should send a Heartbeat message every three seconds to ensure that it can 
detect a link failure within the desired time. 
						

							Messaging Sequences and ASAI
2-58Issue 6  June 1997 
ASAI Restart Procedure
Both the ECS and adjunct must adhere to the Restart Procedure on an ASAI 
link.21 The Restart Procedure insures that if one ASAI endpoint detects a layer 2 
drop (and therefore clears all its CRVs for the interface), ASAI messaging cannot 
continue on that interface without the other endpoint clearing its CRVs, also.
22 
Both ECS and adjunct begin the Restart Procedure when:
nAn ASAI has been established at layer 2.
nAn ASAI layer 2 link has been re-established after a link failure. 23
nAn ECS or adjunct maintenance subsystem determines a need to restart 
(and resynchronize) the ASAI.
Platform developers must be aware that it is possible for an ASAI link to drop 
without the ECS going down (for example, the cable is unplugged). When the ECS 
detects a link drop, it clears all its ASAI data structures. Then, if the link has 
returned to service, the ECS begins the Restart Procedure. It is possible to unplug 
a link and return it to service before the ECS has cleared the ASAI data 
structures. This can occur, for example, if there are thousands of domain (station) 
associations on the link. The ECS divides the cleanup of the ASAI data structure 
into a number of subtasks so that critical call processing can continue as it cleans 
up the ASAI data structures. Thus, adjunct platforms are advised to wait for the 
initiating RESTart message from the ECS. The ECS ignores any RESTart 
messages that it receives from the adjunct during a cleanup period.
The Restart Procedure also incorporates a method for adjuncts to select a 
particular version of the ASAI protocol they wish to run on the link. Presently, there 
are three versions, V1, V2 and V3. If the adjunct does not include any version 
specification options, V1 is the default version that the ECS supplies.
NOTE:
Version selection is per link. Version selection facilitates the use of older 
ASAI applications when switches are upgraded with newer ASAI features.
Sending RESTart
An endpoint sends the RESTart message to return all Q.931/Q.932 resources (for 
example, Call Reference Values on an ASAI) to an idle state. The ECS encodes 
the RESTart message to restart the entire ASAI.
nThe RESTART message must contain the Global CRV.
21. In ISDN Basic Rate Interface (BRI) Specification, the procedure is optional in the 
user-to-network direction.
22. It is possible, on a BRI interface, for one endpoint to detect an LAPD drop and 
re-establishment while the other endpoint does not detect the drop.
23. Note: T309 procedures are not provided for ASAI CRVs. 
						

							Link Management and Maintenance Procedures
Issue 6  June 1997
2-59
nThe RESTART message MUST NOT contain the optional Channel 
Identifier IE. The absence of this IE indicates that the interface is to be 
restarted. Since a Channel Identification IE is present in a BRI RESTart 
message only to restart a specific B-channel [see the 
ISDN Basic Rate 
Interface (BRI) Specification
], this information element is not applicable to 
the ASAI. The ECS ignores the Channel Identification IE if it is present.
nThe RESTART message MUST contain the Restart Indicator IE with the 
class set to 
all interfaces [see the ISDN Basic Rate Interface (BRI) 
Specification
].
nStarting with G3V3, switches include Version IEs for each supported ASAI 
Version in RESTART messages.
Upon transmitting RESTart, the sender initiates layer 3 Timer T316 (120 seconds) 
and waits for a RESTart ACKnowledge message. Receipt of REST ACK cancels 
timer T316. If a REST ACK is not received before the expiry of timer T316, the 
sending endpoint may retransmit the REST message 
once. If there is no response 
to a second transmission, the sending endpoint must take appropriate 
maintenance and recovery actions. The sending endpoint may not make or accept 
ASAI requests on the interface until recovery action is taken.
The originator of a REST message MAY NOT establish any ASAI associations 
over the interface while receipt of REST ACK is pending.
Receiving RESTart
An ASAI endpoint that receives a RESTart message for an ASAI frees all CRVs 
for that interface, terminates the corresponding ASAI associations, and then 
returns RESTart ACKnowledge.
nIf the ECS receives a RESTART message containing a non-global CRV, the 
ECS responds with a RELease COMplete message containing the 
received CRV and a Cause IE with cause value 81, “Invalid CRV.”
nIf the REST message does not contain a Restart Indicator IE, then the ECS 
ignores the RESTART message.
nIf the Restart Indicator IE does not specify all interfaces for class, the ECS 
ignores the message.
nIf the contents of the REST message are correct, the ECS terminates all 
ASAI associations on the interface and then sends a REST ACK containing 
the CRV (always the Global CRV) and Restart Indicator IE (always single 
interface class) that it received.
Starting with G3V3, the adjunct may select the ASAI version that is to be run on 
the link. The ECS RESTART message contains a Version IE for all versions that 
the ECS supports. The adjunct may include one of these IEs in the RESTart 
ACKnowledgement message to select a version. If no Version IE is included in the 
REST ACK, the ECS defaults to V1. If the adjunct responds with an invalid or 
unsupported version, the ECS again ignores the REST ACK and sends a 
RESTART upon expiry of Timer T316 with a list of available versions. The  
						

							Messaging Sequences and ASAI
2-60Issue 6  June 1997 
expected response is a REST ACK either with no version IEs or with a version IE 
indicating one of the available versions. Any other response causes the ECS to 
log a maintenance error.
Suspend/Resume ECS Alarming on ASAI Link
These procedures let an adjunct:
nSuspend any ECS alarming in effect for an ASAI link when the adjunct 
takes the link out of service for scheduled maintenance or for graceful 
termination of the link for some other reason.
nResume ECS alarms when the adjunct brings the link back into service.
Unnecessary alarms in these conditions may increase servicing and maintenance 
costs to the customer.
To suspend or resume alarms, the following message sequence is used:
1. The adjunct sends a Management Information Message (MIM) message 
containing a Management Information Element (MIE) with Link Alarm 
Status Change Request to Suspend or Resume Alarms. Upon 
transmission, the adjunct starts timer TM100 with a value of four seconds.
2. The ECS responds with a MIM containing a return result MIE.
3. If the timer TM100 expires without a response, the adjunct may retransmit 
the request and again set the TM100 timer. If there is no response to the 
transmission, the adjunct may continue to retry, but should use the timer 
TM200 with a value of at least 120 seconds.
If the adjunct sent an incorrectly encoded MIM, the ECS responds with a 
REJECT MIM.
For coding, see ‘‘Suspend/Resume Alarming for ASAI Interface’’ on page 5-190 of 
Chapter 5, “Byte Level Messages.” 
						

							Application Timers
Issue 6  June 1997
2-61
Application Timers
Timing of ASAI Responses (ACKs/NAKs)
The ASAI specification does not contain timers for situations where message loss 
results in an application waiting infinitely for the message from the other endpoint. 
Rather, ASAI applications are required to set timers when they make requests. If 
the timer expires and the application has not received a response, the application 
must abort the association, and it may retry if it desires.
Certain adjunct programming environments may take responsibility for such 
timers. The application programmers must ascertain whether they must explicitly 
include such timers in their application programs.
Any adjunct application level timers used in this fashion have a recommended 
minimum value of 10 seconds.
Initial Messages on an ASAI Link
Adjunct application developers must be aware that ASAI links have various flow 
control and hyperactivity thresholds. When an ASAI link drops and is 
re-established, the adjunct association may send several layer 3 queries (ASAI 
messages) to re-synchronize its internal data with current ECS data. When 
several queries are required to do this, the adjunct should pace the sending of the 
queries. To avoid an inadvertent triggering of any administered link alarms, the 
recommended maximum rate is five queries per second. 
						

							Messaging Sequences and ASAI
2-62Issue 6  June 1997  
						

							Issue 6 June 19973-1
3
Message Descriptions
This chapter details the ASAI messages introduced in Chapter 1.
Message Overview
ASAI is based on standard protocols, including CCITT Recommendations Q.931 
and Q.932, and the 
ISDN Basic Rate (BRI) Interface Specification, 803-802-100. 
These protocols contain such information as allowable message types and 
required format, which ASAI follows.
Table 3-1 lists the ASAI message types described in this chapter.
Table 3-1. Messages for ASAI
ASAI Message
FACility
Management Information Message (MIM)
REGister
RELease COMplete
RESTart
RESTart ACKnowledge 
STATUS 
						

							Message Descriptions
3-2Issue 6 June 1997 
Each explanation includes:
nA brief description of the message direction and use
nA table listing the information elements contained in the message. For each 
information element, the table indicates:
— The direction in which the information element may be sent; for 
example, adjunct-to-ECS, ECS-to-adjunct, or both. (All information 
elements for these messages are “both.”)
— Whether the information element is mandatory (M) or optional (O).
— The allowed length, in bytes. A question mark (?) identifies when a 
length is restricted only by the maximum length of an ASAI 
message.
The information elements are listed in their order of appearance in the message. 
The relative order of information elements is the same for all message types.   
See Chapter 4 for a full description of the information elements.
FACility Message
The FACility message is sent during an ASAI association to invoke an operation or 
convey information from one endpoint to another as part of the message 
exchange for that association.
Message type: FACility
Direction: both
Table 3-2. FACility Message Content
Information Element Direction Type Length
Protocol discriminator both M 1
Call reference both M 2-3
Message type both M 1
Locking Shift to Code Set 6 both M 1
Facility both M 8-?