Cisco IGX 8400 Series Switches

February 18, 1999

• More Field Notices

Products Affected

Problem Description

After a modem call is placed, permanent virtual circuits (PVCs) terminating on CVMs fail to return to the downgraded state. Trunk bandwidth is used unecessarily and may prevent the affected connection and other connections from proper operation.

Problem Symptoms

User symptoms may include slow responses while accessing remote servers or applications. Trunks may indicate packet or cell discards. Use the dspconst command to observe the CVM displaying this symptom. See the display below:

nodename           VT    StrataCom       IGX 8430  9.1.04    Dec. 1 1998  00:23 GMT


Connection status display

+ offhook, - onhook, m slow modem, M fast modem, F Fax

                1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
Line  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

23    M M M + + + + + + + + + + + + + + + + + + + + M M M + 
24    + M M + + + + + + + + + + + + + M + M M + M M + + + + + + M M
25    M + + + + + + + + + + M M + + + + + + + +

This Command: dspconst

Note that during a Fast Modem call, an "M" should appear in the channel. After terminating the call, the "M" should revert to a minus sign or a plus sign, depending on the signaling type and channel configuration. This bug is manifested if the "M" remains on the screen after terminating the call.

Background

When a CVM channel detects a 2100 Hz tone, the channel converts to the Fast Modem mode of operation by disabling echo cancellation and upgrading the channel bandwidth to 64 kBps or to a Cisco-proprietary 32 kBps throughput. After the 2100 Hz tone is removed, the CVM channel should downgrade to the speed that was originally configured.

This bug allows the modem call to upgrade the PVC bandwidth, but does not allow the bandwidth to revert to the configured bandwidth. If several CVM channels are "stuck" in the upgraded mode, trunk utilization stays high which may result in cell or packet discards on any PVCs traversing the trunk.

Workaround/Solution

Workaround:

1. Configure the voice channel utilization to 40% (which is default). Any channel utilization value between 32% and 63% or between 96% and 100% may be used and will inhibit this bug from occurring. Channel utilization less than or equal to 31% or between 64% and 95% (inclusive) will exhibit this bug. Use the cnfchutl slot.chan command to configure channel utilization.

2. Add the connections as "P" type if there is sufficient trunk bandwidth to permit this.

Solution:

Short term: The PVC stuck in the "M" state must be deleted (using the delcon slot.chan command). Then, add the PVC back in (using the addcon slot.chan command).

Long term: Upgrade to switch software 9.1.07 or later release. Switch software may be downloaded from CCO with your CCO user account. Once logged in, go to the WAN Switches page and click on the "Cisco WAN Switching Upgrade Planner" link to find the latest software and firmware.

DDTS

This defect has Cisco bug ID CSCdk69942. To follow the bug ID link below and see detailed bug information, you must be a registered user and you must be logged in.

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:

• Open a service request on Cisco.com
• By email
• By telephone