Oracle Communications EAGLE (Hardware)
 

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In this Document

Symptoms

Cause

Solution

Created from <SR 3-10148156291>

Applies to:

Symptoms

Link congestion and discard Information. What measurement or threshold is used to determine the different levels of congestion and message discard?

Cause

Congestion may be caused by different issues.
 

Solution

Excerpts from GR-246 below:

GR-246 Telcordia Technologies Specification of Signaling System Number 7

9.3 Procedure in the Congestion Situation

The receiving end of a signaling link that detected a congestion situation periodically returns a link status signal unit containing a status indication "B" to the remote transmitting end of the link at interval T5. The receiving level 2 also withholds acknowledgment of the message signal unit, which triggered off the congestion detection, and of message signal units received during the congestion situation; that is, fill-in signal units or message signal units are sent as usual, but with the backward sequence number and backward indicator bit assigned the values that are contained in the last transmitted signal unit before the congestion is recognized.

 At the remote end of the signaling link, every reception of a link status signal unit containing indication “B” causes the excessive delay of acknowledgement timer T7 to be restarted if the timer is already running. In addition, the first reception of the link status signal unit containing a status indication “B” starts a long supervision T6, only if there are message signal units in the retransmission buffer and the timer T6 is not running.

As an option, transmission of new message signal units may be stopped (this option is not reflected in the SDLs). Should the timer T6 expire, "link failure indication" is generated and Network Management is notified.

9.4 Congestion Abatement Procedure

When congestion abates at the receiving end of the signaling link, transmission of link status signal units containing status indication "B" is stopped and normal operation is resumed. At the remote end, the supervision timer T6 is stopped when a negative or positive acknowledgment, whose backward sequence number acknowledges a message signal unit in the retransmission buffer, is received in the case of the basic error correction method, or a positive acknowledgment is received in case of the preventive cyclic retransmission method. If transmission of new message signal units had stopped, it is resumed when timer T6 is stopped.

NOTE: Congestion onset and abatement detection is an implementation dependent function. Sufficient hysteresis should be provided in the implementation to prevent excessive oscillation between congested and noncongested states.

Excerpts from the customer documentation:

Database Administration Manual - SS7 Configuration - 910-6279-001 Revision A, January 2012

 It is possible that a problem on a signaling link can cause one signaling link in a linkset to go into congestion, even though the traffic on the linkset is not high enough to cause congestion. For example, if a link has a large number of retransmissions, the throughput of the signaling link could drop enough to cause congestion on that signaling link. To help prevent this from happening, the EAGLE 5 ISS starts the level 3 T31 timer whenever a signaling link goes into congestion. If the signaling link remains in the same congestion state until the level 3 T31 timer expires, the signaling link is removed from service. The signaling link becomes unaligned, and then the alignment procedure is started. The congestion level that starts the level 3 T31 timer can be set to either congestion level 1 or congestion level 2 using the chg-stpopts command with the mtpt31ctl parameter. This congestion level can be verified with the rtrv-stpopts command and is shown in the MTPT31CTL field. The level 3 T31 timer is started when the signaling link reaches this congestion level or a higher level. An increase in congestion level or abatement to a lower congestion level restarts the timer. When the congestion level goes below the congestion level configured in the chg-stpopts command, the level 3 T31 timer is stopped. If the level 3 T31 timer expires and the signaling link’s congestion level has not changed, the signaling link is restarted.

For example, if the level 3 T31 timer is set at 60 seconds and a signaling link goes into congestion level 1, the level 3 T31 timer is started. If, after 45 seconds, the signaling link’s congestion increases to level 2, the timer is restarted to 60 seconds. If the signaling link remains at congestion level 2 for 60 seconds, the signaling link is taken out of service and it becomes unaligned. Then the alignment procedure is started, and the EAGLE 5 ISS attempts to realign the signaling link. The level 3 T31 timer can only be assigned to ANSI SS7 linksets and signaling links. The level 3 T32 timer helps to prevent a signaling link from oscillating in and out of service. When the EAGLE 5 ISS begins restoring an out of service signaling link, the EAGLE 5 ISS starts the level 3 T32 timer. If the signaling link fails to get back into service before the level 3 T32 expires, the EAGLE 5 ISS does not attempt to continue to bring the signaling link into service until the level 3 T32 timer expires. Once the level 3 T32 timer expires, the EAGLE 5 ISS attempts to restore the signaling link into service. The level 3 T32 timer is only started after a signaling link fails, not when a signaling link is manually deactivated. When a signaling link is manually taken out of service using the dact-slk command, the level 3 T32 timer is stopped, if it is running. When the signaling link is brought back into service using the act-slk command, the level 3 T32 timer is not started. The level 3 T32 timer is not started when a new signaling link is first aligned. The level 3 T32 timer can only be assigned to ANSI SS7 linksets and signaling links.

rtrv-stpopts

MTPT31CTL—MTP T31 congestion trigger level. The signaling link congestion level at which the system starts the level 3 t31 timer. When the level 3 t31 timer expires, the associated signaling link is removed from service for realignment.

SOME CONGESTION RULES

Link Congestion occurs when too many messages are queuing in the Transmit and ReTransmit buffers. It has nothing to do with the link utilization.

The below values are only valid for TDM LSL links.

· Congestion state “Abatement level 1” : - 60 messages waiting in the buffer -> DOC_ONSET (Danger Of Congestion onset 59 MSU's). - Eagle will clear the congestion. - Eagle does not  generate TFCs (Transfer Controlled) yet.

· Congestion State “Onset Level 1” : - 80 messages - Eagle starts generating TFCs

· Congestion State “Discard Level 1” : - ANSI : 100 messages; ITU : 127 messages - Eagle discards priority 0 & 1 messages

· Congestion state “Abatement level 2” : 81 messages

· Congestion State “Onset Level 2” : - 100 messages - Eagle starts generating TFCs

· Congestion State “Discard Level 2” : - ANSI : 110 messages; ITU : 127 messages

· Congestion state “Abatement level 3” : 101 messages

· Congestion State “Onset Level 3” : - 110 messages - Eagle starts generating TFCs

· Congestion State “Discard Level 3" : - ANSI : 120 messages; ITU : 127 messages

On ANSI the Eagle will filter the messages according to their priority and measurement counters will be pegged according to the MSU’s priority.

-If discard level 1 is reached then MSU with priority 0 and 1 are discarded and MSU with priority 2 and 3 are processed.

-if discard level 2 is reached then MSU with priority < 2 are discarded and MSU with priority > 2 are processed.

-if discard level 3 is reached then all MSUs are discarded.

ANSI MSU priorities are based on the Service Indicator Values (SIO)

Decimal                   Binary Value Type of Payload

Decimal 0 - 0000 Signaling Network Management Messages

Decimal 1 - 0001 Signaling Network Testing and Maintenance Messages

Decimal 2 - 0010 Signaling Network Testing and Maintenance Special Messages (ANSI) or Spare (ITU-T)

Decimal 3 - 0011 SCCP

Decimal 4 - 0100 Telephone User Part

Decimal 5 - 0101 ISDN User Part

Decimal 6 - 0110 Data User Part (call and circuit-related messages)

Decimal 7 - 0111 Data User Part (facility registration and cancellation messages)

Decimal 8 - 1000 Reserved for MTP Testing User Part

Decimal 9 - 1001 Broadband ISDN User Part

Decimal 10 - 1010 Satellite ISDN User Part

Decimal 11 to 15 - 1011 – 1111 Spare [*]

For ITU there is no message priority. However the level of congestion would be output by the eagle indicating the buffer occupancy. The Eagle will discard messages only if discard level 3 is reached. The MSUDISC0 measurement counter is the only counter that is pegged since there is no priority on ITU MSU's and will increment each time an MSU is discarded. The MSUDISC1 MSUDISC2 and MSUDISC3 measurement counters will never be pegged, these counters and their explanations are found in the measurements documentation - Component Link Measurements and are used in both ANSI/ITU networks report measurements.

How does Eagle recover the congestion?

1. Hoping the far end acknowledges enough messages to alleviate the congestion.

2. Generating TFCs to get the OPCs to stop sending low priority traffic.

     Note: Priority is just valid for ANSI.

3. Discarding low priority traffic

     Note: Discarding is dependent of the network domain as explained above

4. Waiting for T31 to expire and take the link OOS due to "stuck-in-congestion" timer expiry

     Note: There is no T31 implemented for ITU. T31 is applicable and used for ANSI only.

Additional Remarks:

- When TFCs are generated, Eagle does not care about the status of any other link in the linkset. 1 link of 16 is enough to begin generating TFCs.

- Congestion is never cleared in the Eagle by moving to an alternate route.

- Diverting traffic to an alternate route to ease congestion will lead to sequencing problem. Traffic is delivered to a specific link based on SLS value.

- The TFCs generation indicates that a node is congested, but is generated when a link (that may be to another STP) is congested, and the node may be fine.

Congestion measurement commands are listed below:

LINK COMP Report

Command Examples

• OAM

rept-meas:type=comp:enttype=link:loc=xxxx:link=x

rept-meas:type=comp:enttype=link:lsn=ls3

• Measurements Reports

rept-ftp-meas:type=comp:enttype=link

LINK NM Report

Command Examples

• OAM

rept-meas:type=nm:enttype=link:loc=xxxx:link=x

rept-meas:type=nm:enttype=link:lsn=ls3

• Measurements Reports

rept-ftp-meas:type=nm:enttype=link

LINK MTCD ReportLINK MTCD Report

Command Examples

• OAM

rept-meas:type=mtcd:enttype=link:loc=xxxx:link=x

rept-meas:type=mtcd:enttype=link:lsn=lsn123

• Measurements Reports

rept-ftp-meas:type=mtcd:enttype=link

LINK MTCDTH Report

Command Examples

• OAM

rept-meas:type=mtcdth:enttype=link:loc=xxxx:link=x

rept-meas:type=mtcdth:enttype=link:lsn=lsn123

• Measurements Reports

rept-ftp-meas:type=mtcdth:enttype=link

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