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5350 T1 back to back loop connection

Unanswered Question
Dec 19th, 2002
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Hello guyz !

I have a 5350 and i want to connect 2 T1 back to back ( loop ). Is it possible to connect like this or not . I am expecting VoIP calls from ethernet and will go into 1 T1 and will come out from other and then will send it where i want. It will be a great help if i get the working config or the link which explains this, i did an extensive search but couldnot get anything like this on cisco site. Help will be appriciated. Thanks

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pacameron Mon, 12/23/2002 - 21:05
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It is possible ... any particular reason why you want to do this ? If you are doing VOIP to POTS and then POTS to VOIP this will be a double compression cycle and the voice quality will drop noticebly, as well as the latency (delay) of the call doubling.


We really would not recomend this ...


If you must do it , you would use a T1 loopback cable to cross over the TX and RX pairs :


1 ---- 4

2 ---- 5

4 ---- 1

5 ---- 2


and set up one port as internal clocking to drive the second port.


PRI would be the best signalling, so one D channel would be need to be configured as ISDN layer 3 network side as well.


You would use POTS dial peers to direct the call out, and if necessary manipulate the digits so a VOIP dial peer can redirect the call to a new destination.



net-sol Tue, 12/31/2002 - 22:06
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Thanks a lot for your reply. I did the same config but i was making sure is it the right way. For ISDN layer 3 Network we have the only option of configuring the Switch type primary-net3, it supports Network side setup as well.


The reason for doing such thing is i am expecting many calls from different providers to my network. I want to make a POP for them to send the calls to just one gateway and from there i will send it to its ultimate destinations. Any other openion about this will be appricaited. Thanks

pacameron Thu, 01/02/2003 - 22:51
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Remember what I said about double compression - the delay and distortion will be magnified.



net-sol Sun, 01/05/2003 - 23:18
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There are some other issues also. When i try to simulate a call my PRI goes down and up. i guess my call goes loop again and again. here the output of debug isdn q931 any suggestion?

4w2d: ISDN Se3/2:23: overriding plan/type for , isdn/unknown to isdn/subscriber

4w2d: ISDN Se3/2:23: overriding plan/type for 2145621, unknown/unknown to isdn/subscriber

4w2d: ISDN Se3/2:23: overriding plan/type for 2145621, unknown/unknown to isdn/subscriber

4w2d: ISDN Se3/2:23: TX -> SETUP pd = 8 callref = 0x0018

4w2d: Bearer Capability i = 0x8090A2

4w2d: Channel ID i = 0xA98381

4w2d: Calling Party Number i = 0xC1, Plan:ISDN, Type:Subscriber(local)

4w2d: Called Party Number i = 0xC1, '2145621', Plan:ISDN, Type:Subscriber(local)

4w2d: ISDN Se3/3:23: RX <- SETUP pd = 8 callref = 0x0018

4w2d: Bearer Capability i = 0x8090A2

4w2d: Channel ID i = 0xA98381

4w2d: Calling Party Number i = 0xC1, Plan:ISDN, Type:Subscriber(local)

4w2d: Called Party Number i = 0xC1, '2145621', Plan:ISDN, Type:Subscriber(local)

4w2d: ISDN Se3/3:23: TX -> SETUP_ACK pd = 8 callref = 0x8018

4w2d: Channel ID i = 0xA98381

4w2d: ISDN Se3/2:23: RX <- SETUP_ACK pd = 8 callref = 0x8018

4w2d: Channel ID i = 0xA98381

4w2d: %LINK-3-UPDOWN: Interface Serial3/3:23, changed state to down

4w2d: ISDN Se3/3:23: Could not bring up interface

4w2d: ISDN Se3/1:23: Event: Syncing Discards: L2 Discards 1, L2D_Task Counter 0

4w2d: ISDN Se3/3:23: Event: received MNL_RESET_REQ

4w2d: %CONTROLLER-5-UPDOWN: Controller T1 3/3, changed state to up

4w2d: %CSM-5-PRI: add PRI at slot 3, unit 3, channel 23 with index 2

4w2d: %CONTROLLER-5-UPDOWN: Controller T1 3/2, changed state to up

4w2d: %CSM-5-PRI: add PRI at slot 3, unit 2, channel 23 with index 3

4w2d: %LINK-3-UPDOWN: Interface Serial3/3:23, changed state to up

4w2d: ISDN Se3/2:23: Event: Syncing Discards: L2 Discards 3, L2D_Task Counter 1

4w2d: ISDN Se3/2:23: Event: Syncing Discards: L2 Discards 3, L2D_Task Counter 2

4w2d: %LINK-3-UPDOWN: Interface Serial3/2:23, changed state to up



pacameron Mon, 01/06/2003 - 20:39
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Would need to see complete router configs to see how things are set up. Either paste them here, or better still open a TAC case on this issue. Also, set the debug timestamps to the msec - in config mode add:


service timestamps debug datetime localtime msec






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