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

Thu Mar 23 18:58:07 EST 2006

I got this from Our Cisco SE:

Regarding the ability of a VWIC-2MFT to support two T1s:

A 2 port VWIC-2MFT-T1 cannot be clocked off 2 different service
providers.  When both T1's are configured for clock source line, the
port 0 is the default primary clock source and port 1 is by default
secondary clock source and is loop-timed.  Only one port per VWIC can be
clocked externally. On the other hand, if they are sync'd clocking from
the same provider, you could use a 2-port VWIC.

Else you will get clock slips causing errored data or even echo on voice
trunks.  If the two T1s both need to be clocked externally and
independently, then you should use 2 separate 1-port VWICs.  

Examples:

1. BellSouth T1 Data + BellSouth PRI - Valid for VWIC-2MFT

2. Two BellSouth PRI - Valid for VWIC-2MFT

3. AT&T T1 Data + BellSouth PRI - NOT valid for VWIC-2MFT - use TWO
single VWICs, or a WIC-T1 + VWIC-1MFT

4. AT&T LD PRI + BellSouth Local PRI - NOT valid for VWIC-2MFT - use TWO
single VWIC-1MFT

Does this help?

Jim

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Clayton Zekelman
Sent: Thursday, March 23, 2006 5:58 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] VWIC-2MFT-T1 & VWIC-1MFT-T1 Timing Issues

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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