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Cisco MGX 8230 Edge Concentrator Installation and Configuration
Release 1.1.31, Part Number 78-11215-03 Rev. B0, May 2001
Chapter2 Module and Service Descriptions
Service Resource Module
Service Resource Module
A service resource module (SRM) provides three main functions for the service modules:
•Bit Error Rate Testing
•1:N Service Module Redundancy
•Bulk Distribution Mode
See Figure 2-9 for an illustration of the MGX-SRM-3T3/C front card and the MGX-BNC-3T3-M back
card.

Bit Error Rate Testing

After a service module line or port is put into loopback mode, the SRM can generate a test pattern over
the looped line or port, read the received looped data, and report on the error rate. This operation can be
performed on a complete T1 or E1 line, on a fractional T1 or E1 line, on a SD0 bundle (N x DS0), or on
a single DS0 channel. The SRM can support BERT only one line or channel at a time. BERT is capable
of generating a variety of test patterns, including all ones, all zeros, alternate one zero, double alternate
one zero, 223-1, 220-1, 215-1, 211-1, 29-1, 1 in 8, 1 in 24, DDS1, DDS2, DDS3, DDS4, and DDS5.

1:N Service Module Redundancy

Service module redundancy provides 1:N redundancy for multiple groups of service modules (a
group consists of N active and one standby service module). The redundant se rvice module in a
group must be a superset (wit h respect to functionality) of the cards. Upon the detection of a failure
in any of the service modules, the packets destined for the failed se rvice module are carried over the
CellBus to the SRM in its ch assi s. The SRM receives the packets and s wi tc he s th em to the backup
service module via the Cel lB us.

Bulk Distribution Mode

Each of the T3 ports can be used to support up to 28 multiplexed T1 lines, which are distributed to T1
service module ports in th e s w it ch. Called bulk distribut io n, this feature is perform e d wh e n th e S R M is
in “bulk mode.” The purpose of this feature is to allow large numbers of T1 lines to be supported over
T3 lines rather than over ind ividual T1 lines.
Any T1 channel in a T 3 l ine can be distribut ed to any eight port ser v ice module in any slo t . E a ch
MGX 8230 shelf can support up to 64 T1 lines.
The SRM-3T3 can also be operated in “nonbulk mode” on a port -by-port basis. For a po rt configured in
nonbulk mode, bulk distribu tion is disabled and the SRM provides BERT and 1:N redundan cy functions
only.
Linking the MGX-SRM-3T3/C to a destination card causes the switch to take CPE traffic through the
MGX-SRM-3T3/C rather than the T1 car d ’s line module. Linkage is a card-level condition. If you link
just one T1 channel on a servi ce module to the MGX-SRM-3 T3/C, the back card on the se rvice module
becomes inoperative, so you must l ink al l other T 1 ports on that servi ce modu le to th e MGX-SRM -3T3/C
if you want them to operate.