Specifications

Common Equipment Description 2-3
System Overview
The Service Resource Module (SRM) communicates with all service modules over a Bit Error Rate
Test (BERT) bus and provides the capability for testing T1 and E1 and subrate service module lines.
The SRM can issue various loopup and loopdown commands towards the CPE and generate test bit
patterns for any user specified Nx64 kbps port. The SRM can also provide 1:N redundancy for
FRSM, AUSM, and CESM cards. The SRM is an optional card.
NoteThe ASC and the BNM together are referred to as the core modules and at least one set must
be installed in the shelf. If redundancy is required, BOTH the ASC and the BNM must be configured
with redundant cards. If configured, the SRM is also part of the core modules. Failure of an ASC or
BNM will cause switchover to the redundant ASC, BNM and SRM cards. Failure of the active SRM
card will only cause switchover if the SRM is included in the redundant set as well.
The Service Modules provide the customer interfaces. Up to ten service modules may be configured
in a shelf. Service modules may be intermixed in the same shelf.
The overall operation of the shelf is to:
• Accept customer traffic received over the service interface lines, adapt them to ATM, and
multiplex them onto the BNM trunk for transmission to the BPX network.
• Accept ATM cells received over the BNM trunk, map them into the specified service protocols,
and transmit them over the appropriate service interface.
The Inverse Multiplexing for ATM Trunk Module (IMATM) is housed in the MGX 8220 shelf in a
service module slot. It is an extension to the BPX 8620 BNI card that supports BPX 8620 ATM
trunks over multiple (up to 8) T1 and E1 lines instead of single T3 or E3 line. The IMATM does not
use the MGX 8220 cell bus as other service modules do, but provides its own trunk to the BPX 8620.
In performing these functions the MGX 8220 shelf collects a wide variety of statistics about frames
and cells, error conditions, congestion, and so on.
A simplified block diagram of the MGX 8220 hardware is shown in Figure2-2. As shown by the
dashed lines, the ASC, SRM, and cell bus are all 1 for 1 redundant. This means that one ASC, BNM,
SRM slot set is attached to one cell bus, and the remaining ASC, BNM and SRM slot set is tied to
the other cell bus.