My client has implemented a system in which 2951 routers with E&M cards have been used to extend what was essentially a 4 wire leased line circuit.
The system at either end of the IP cloud are connected using 4 wire modems. One site is primarily a transmit site and the other is primarily a receive site. The E&M cards are configured as 4-wire Type 2 cards and the interface cables between the E&M ports and the modems are special-made Ethernet cables - standard RJ-45 jack on the Cisco end and going to bare wires to connect to the modems. The strands used or 3,4,5,and 6 (blues and greens). These correspond to the 4 audio wires of a card configured as a 4 wire Type 2 card. Leads 1, 2, 7, and 8 (corresponding to E, M SG, and SB) are all unterminated. The voice ports are also configured with connection trunk - pointing to each other - in effect creating a continuously open 4 wire audio circuit. When all equipment is turned on, everything is fine. However, when the receiving computer system (and its modem) are powered off - with the intervening Cisco routers and E&M cards remaining powered on - the transmitting side of circuit appears to receive messages looped back to itself (the system has a transmit and receive message counter - the receive message counter increases when there is no system on the other end doing any transmitting). Another tech that I am working with has had commercial (non Cisco ) telco experience and he swears that the E&M card has a failover loopback mode. He has essentially convinced the client that when the E&M card does not "sense" that it is connected to anything, that it places itself into a maintenance loopback condition - thus producing the symptoms that are being seen. I have spent days searching and am unable to find any references to such a mode. I know of the "test voice port network/local loopback" command - I am referring to a process that happens automatically. Anyone? -------------------------------------------------------------------------------------- Dr. Jeffrey T. Girard (Jeff), PhD Colonel, United States Army (Retired) Owner, Network Engineer, VoIP Engineer - Wire Me Happy, LLC www.wiremehappy.com (607) 835-0406 (home office) (845) 764-1661 (mobile) (607) 835-0458 (fax)
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