[c-nsp] VWIC-2MFT-T1 & VWIC-1MFT-T1 Timing Issues

[Clayton Zekelman]

We have a customer who has 2 T1's between 2 sites.

At site "A" they have a router with 2 VWIC-1MFT-T1's

At site "B" they have a router with a VWIC-2MFT-T1

One of the T1's was installed a few years ago, and was provisioned 
with HDSL on both ends.

The second T1 was installed recently, and was provisioned on a fiber 
mux at site A, and on HDSL at site B.

The T1's are configured in a Multilink group.

Site A (VWIC-1MFT-T1) has both T1's set to clock internally, and site 
B (VWIC-2MFT-T1) is set to derive clock from the incoming line.

For some strange reason, they're getting errors on the HDSL to HDSL 
T1, despite the fact that testing from the middle in either on 30 
minute multi-pattern tests to a CSU loopback shows 100% error free 
operation.  The H2TU-C's facing site B are also showing 100% clean.

I even set up CSU loops at each end and tested multi-pattern from the 
middle - again 100% clean.

I'm suspecting a timing issue.  I'm wondering if the VWIC-2MFT-T1 
card is having an issue because the circuit latency is different on 
the 2 lines.  Can both T1 ports on this card operate independently 
with loop derived timing?

These are the types of errors:


Serial0/1:0 is up, line protocol is up
   Hardware is GT96K Serial
   MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,
      reliability 255/255, txload 8/255, rxload 9/255
   Encapsulation PPP, LCP Open, multilink Open
   Link is a member of Multilink bundle Multilink1, loopback not set
   Keepalive set (10 sec)
   Last input 00:00:00, output 00:00:07, output hang never
   Last clearing of "show interface" counters 4d05h
   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
   Queueing strategy: weighted fair  [suspended, using FIFO]
   FIFO output queue 0/40, 0 drops
   5 minute input rate 57000 bits/sec, 60 packets/sec
   5 minute output rate 50000 bits/sec, 48 packets/sec
      16433815 packets input, 978755407 bytes, 0 no buffer
      Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
      3039 input errors, 3038 CRC, 1663 frame, 454 overrun, 0 
ignored, 1020 abort   <-----------------------------------------------
      13591876 packets output, 3206919358 bytes, 0 underruns
      0 output errors, 0 collisions, 0 interface resets
      0 output buffer failures, 0 output buffers swapped out
      0 carrier transitions
   Timeslot(s) Used:1-24, SCC: 1, Transmitter delay is 0 flags

The things we haven't tried yet are:

1) Frogging the 2 T1's in the middle to see if the errors move
2) Changing the timing to be internal on the VWIC-2MFT-T1, and line 
on the VWIC-1MFT-T1's.

Its perplexing, because the circuit shows as 100% good with the test set.


---
Clayton Zekelman
Managed Network Systems Inc. (MNSi)
344-300 Tecumseh Rd. E.
Windsor, Ontario
N8X 5E8

tel. 519-985-8410
fax. 519-258-3009 


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