Cisco WAN Switching Modules

Field Notice: Trunk Failure Observed on IMA UXM Clock Switch

Revised January 31, 2002

October 16, 2000

Products Affected




Observed only on UXM with E1 or T1 IMA enabled


Observed only on UXME with E1 or T1 IMA enabled

Problem Description

A trunk failure may result when an Inverse Multiplexing over ATM (IMA) Universal Switching Module (UXM) or Universal Switching Module Enhanced (UXME) clock source or a clock path switches across, or on, an IMA UXM trunk


Each IGX-8400 and BPX-8600 in a WAN Switch network uses a single clock source. This clock source may be derived from a trunk or a line that is connected locally, or one that is connected to a remote node. Also, the clock may be derived from an internal oscillator, or an external clock source, connected to the WAN Switch External Clock input connector

Problem Symptoms

The most common symptom is observed in the event log. Use the display log command and look for IMA or Physical Line failures:

Info   Clock switch to oscillator of SCC                       03/22/99 10:38:00
Major  TRK 14.1 Loss of Cell                                   03/22/99 10:37:59
Major  PHYSLN 14.1 Loss of Cell                                03/22/99 10:37:59

In extreme cases, depending on network topology, nodes may be unreachable for up to several minutes. This can be observed using the dsplog or dspalms commands. Below is example output from the dsplog command indicating a communication break:

Minor   Comm Break with igx1 03/22/99 10:38:10



Inhibit clocking over UXM or UXME IMA trunks by configuring the trunks' Pass Sync parameter to No using the cnftrk slot.port command. Do not configure any IMA trunks as a clock source. This is the recommended resolution if trunks other than IMA trunks are available for passing clock synchronization.


The solution requires the UXM/UXME firmware version A.A.E or later, and an upgraded System Clock Module of hardware version D or later. The assembly number version of the IGX-SCM cabling is 73-3341-02. Revision X or later of the 73- level is needed, as seen below in the dsppwr command output:

node1          TN    StrataCom       IGX 8420  9.2.20    May  5 1999  07:31 GMT

Power Supply Status                                        Cabinet Temperature

Monitor Rev AS, Ser # 435857  -  Status: Active               27        80

   AC Supply    Status                                     C  60  |  |  140  F
A  1  Present   OK                                         e      |  |       a
B  1  Present   OK                                         n  50  |--|  122  h
C  1  Empty                                                t      |  |       r
D  2  Empty                                                i  40  |  |  104  e
E  2  Empty                                                g      |  |       n
F  2  Empty                                                r  30  |  |  86   h
                                                           a      |  |       e
                                                           d  20  |  |  68   i
                                                           e      `--''      t

Last Command: dsppwr

Note: In the underlined, bolded "AS" above, the second letter indicates that the IGX-SCM 73- level hardware revision is "S". The appropriate revision is "X" or later. In this example, the IGX-SCM cabling should be replaced if the symptoms and conditions discussed in this Field Notice appear. Also note that this SCM hardware revision is required only for networks with UXMs or UXMEs using IMA functionality. Additionally, the IGX-8400 must be powered down to replace the IGX-SCM; therefore, do not recommend replacing this component without first knowing if the firmware is revision A.A.E or later, and whether there are other clocking problems in the network


To follow the bug ID link below and see detailed bug information, you must be a registered user and you must be logged in.




UXM IMA with T1 backcard logs trunk failures upon clock switch of node


UXM, IMA Inverse Mux Failure, cannot pass sync

Physical Replacement of Parts

Submit a return material authorization (RMA) to order any quantities of IGX-SCM= cabling.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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