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Cisco VISM Installation and Configuration Guide
Release 3.0, Part Number OL-2521-01 Rev. D0, June 2004
Chapter1 Overvi ew of the VISM and VISM-PR Cards
VISM and VISM-PR Card Features
•Line loopback (DS1) toward the TDM lines.
•Channel loopback (DS0) toward both the TDM lines and the ATM network.
•Transmission and reception of bit error rate tester (BERT) signals over loopbacked lines.
•Redundant alarm indication signal (RAI) and alarm indication signa l ( AIS ) al arm s.
•Extracting a DS0 CCS channel and directing it to the TDM signaling function.
•1:N cold redundancy using subrate multiplexing (SRM)-3T3 (bulk mode support for T1 lines only)
and SRM-E (for OC3) capabilities. Calls do not persist during switchover.
•Graceful shutdown of ongoing voice calls when the VISM is taken out of service for maintenance
or other reasons. Forced shutdown is also supported.
Caution A forced shutdown of the VISM or VISM-PR card may result in droppe d cal ls.
Redundancy and Bulk Distribution
Redundancy for VISM cards with or without bulk distribution can be provided throu gh the Servi ce
Redundancy Module (SRM) and SRM-E. Redundancy for VISM is also provided by Media Gateway
Controller (MGC) redundancy groups. VISM redundancy is cold redundancy in which ong oing calls do
not persist during switchover.
Note SRM-E is supported with PXM1 and PXM1E cards only.
Redundancy with bulk distribution requires a spare VISM card to be installed. The system uses the three
T3 ports of the SRM back card instead of the normal T1 lines on the VISM back cards. VISM cards in
bulk distribution mode do not require back cards.
The TDM voice data transmitted or received over the T3 ports are distrib uted to the VISM card as if th ey
had been received over VISM T1 back card ports in the normal manner. This feature reduces the number
of physical lines required to support VISM, but requires external equipment to multiplex and
demultiplex the T1 data onto the T3 lines.
With or without bulk distribution, redundancy allows for th e spare VISM c ard to automat ically tak e ov er
the functions of a failed VISM card. When the failed card is repaired, switching back to the repaired card
is not automatic. You must manually change the repaired c ard ba ck to the active state with the command
line interface. See Chapter4, “Configuring VISM Fea ture s. ”
Note 1:1 redundancy using Y-cables is not supported by VISM.
Redundancy can also be configured at the ATM permanent virtual circuits (PVCs) level. Two separate
PVCs can be set up, each using a different PXM physical port and each routed to a separate router.
Configure one PVC as active and the other as standby. Both PVCs are monit o red by heartbeat OAM F5
loopback cells every 200 ms. If three consecutive OAM cells are lost, the PVC fails, and only the
remaining PVC is active. A PVC will recover automatically when five consecutive OAM cells are
received while the PVC remains in standby mode (no automatic fallback to active state is provided).
Control and bearer PVCs can be set up with a redundant PVC.