The VISM is front and back card set. Each VISM supports up to eight E1 lines (using RJ48 or SMB connectors) through ports located on the back card of the two-card set. Each line is configured either for binary 8-zero substitution (B8ZS) or alternate mask inversion (AMI) coding, with voice compression to G.711, G.726 (32K), and G.729ab coder-decoder (codec) standards. Line failures that are detected cause the VISM to generate E1 facility alarms, and lines can be tested using continuity tests and line loopbacks. The VISM can connect directly to the time-division multiplexing (TDM) E1 lines through ports located on the back card, or optionally via the bulk distribution capability of the SRM/E card.The VISM communicates with the packet network for transmitting and receiving the voice payload by using the STM-1 port on the PXM-1 card. Permanent virtual circuits (PVCs) are setup between the MGX and the edge router, and all packets are sent across these PVCs regardless of their destination. The router is responsible for extracting the IP address and correctly routing the cells. For reliability, VISM supports two independent STM-1 interfaces each connected to a separate router, and each with its own PVC - one is designated the primary and one the secondary.