Reliance E1 Links with Loop Convertor needs to invert clock at times to work properly with Cisco routers V.35 cards.

We had an E1 from Reliance in North India- Delhi.
This was provided on their MUX located at both the ends. So effectively there was no copper on the path.

Both the end terminals (DTE) were Cisco routers with V.35 interfaces.
At end A the modem used was: Loop 1510-S-11-120-AC
At end B the modem used was: Loop 1510-S-11-120-AC

We were seeing heavy CRC errors on the Link once they were connected to the cisco routers. whereas the BERT run from a loop given at one end and tested on a BERT meter for over 24 hours was error free.

So Reliance, arrogantly at that , insisted that there was no problem at their end and that we need to call the cisco vendor to get the DTE (routers, cables, cards) tested.

however we did all that we could do at the Cisco End, we swapped cables, cards at both ends & still had the same CRC errors problem.

After which we contacted Reliance Mumbai engineer. He suggested we try toggling the CRC & the Clock DIP switches located on the rear of the LOOP modems.

It has been noticed that some cisco gear invert the clock and hence modems need to counter the same.

Thus we toggled the following DIP switch(es) on the LOOP modem(s)
Clock Switch: 7th DIP Switch at End B
CRC Switch: 3rd DIp Switch to set CRC OFF: at End A and End B.

And Voila, the Link is stable now.
Pls find below the o/p of various cisco commands which might help you troubleshoot a similar problem



*******At End A*****
#sh int s0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is GT96K Serial

Cisco IOS Software, 3800 Software (C3845-ENTBASEK9-M), Version 12.4(5a), RELEASE SOFTWARE (fc3)

*******At End B********
#sh int s0/1/1
Serial0/1/1 is up, line protocol is up
Hardware is GT96K Serial

Cisco IOS Software, 2800 Software (C2800NM-ENTBASEK9-M), Version 12.4(5a), RELEASE SOFTWARE (fc3)

c3845 with NM-1A-OC3-POM needs a 10db attenuator to work with Nortel Passport Card 2pOC3SmAtm2

We had a cisco 3845 router for which we ordered NM-1A-OC3-POM for our connectivity with Nortel Passport.

Our Nortel Passport interfaces with service providers MUX to provide L2 connectivity over ATM/FR.

Now we realised that the Nortel Passport card was a LR (Long Reach one) whereas the SFP for c3845 (POM) that we ordered was a IR (Intermediate Reach).

Thus either we had to replace the card on the passport or the SFP on the C3845.
Both were difficult to do. Considering not readily available in India and the high price.

Luckily when we approached Cisco TAC and provided them details with Nortel passport's Power Details, the TAC confirmed that the Passport was transmitting too high a power for c3845 IR SFP to handle and hence was loading it.

Thus Cisco TAC recommended we use a 10db attenuator to circumvent the power problem.
Once we did that, our Links came UP.

Thus next time you try doing inter vendor operability, pls ensure that:-
1) You consult the vendors before placing the orders.
2) Review the Technical Specifications

unfortunately we didn't do the above and had to suffer at least 1 month of delay to get the circuits up.

I paste below the Snippet of the various outputs from the c3845

Cisco IOS Software, 3800 Software (C3845-ENTSERVICESK9-M), Version 12.4(5a), RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2006 by Cisco Systems, Inc.
Compiled Sat 14-Jan-06 02:38 by alnguyen


ATM OC3-POM (SMIR) Port adapter, 1 port
Product (FRU) Number : NM-1A-OC3-POM

interface ATM2/0
description : Connect to Nortel Passport
no ip address
no ip redirects
no ip proxy-arp
atm sonet stm-1
no atm ilmi-keepalive
end

Nortel Passport Chassis:-
nortel passport 7480

Nortel Passport Card Used:-
Card type:- 2pOC3SmAtm2 and productCode NTNQ66AA-21