Cisco MGX 8800 Series Switches

Field Notice: AXSM MultiMode Fiber Back Cards Do not Support Y-Cable Redundancy

November 21, 2002

Products Affected

  • MMF-8-155-MT

  • MMF-8-155-MT/B

Problem Description

Data errors prevent successful implementation of Y-Cable redundancy.


MultiMode Fiber (MMF) interfaces on the AXSM and AXSM/B back cards cannot support Y-cable redundancy because the standby MMF transmitter does not shut off. In the Y-cable configuration, both MMF transmitters are on and transmitting, which results in interference at the MMF receiver at the far end of the fiber.

Problem Symptoms

The symptoms include loss of frame, data errors, or intermittent operation at the receiving ends of each fiber.


Use APS redundnacy instead of Y-Cable redundancy.Use Single Mode Fiber back cards with AXSM or AXSM/B if Y-redundancy is required. If MMF back cards are required, use the AXSM-8-155-E and its associated back card, the MMF-4-155/C.

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: