[cisco-voip] E&M cards -

[Jeffrey Girard]

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?

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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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