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Question about T3 error rates.

Thu Mar 18, 2010 9:05 pm

I'm curious to hear from anyone out there who has more experience than I do working with T3's for data WAN connectivity (which should be most of you).

I'm testing out an MPLS WAN link for a customer. It's a pair of T3's on either end throttled for 15mbps of throughput. I'm using Wankiller to stress it. I'm finding I get some errors, though not a lot (see below). Not having a lot of experience with T3's I don't have a good sense of whether this is within spec or something I should bark at ATT about before going live with this thing.

The counters below show what I've seen over about 25 minutes of testing, pushing a little over 13mbps of traffic across it.

Thanks,

Ben


MPLS#sho int s1/0
Serial1/0 is up, line protocol is up
Hardware is DSXPNM Serial
Internet address is 12.112.7.174/30
MTU 4470 bytes, BW 15338 Kbit/sec, DLY 200 usec,
reliability 255/255, txload 1/255, rxload 220/255
Encapsulation PPP, LCP Open
Open: IPCP, crc 16, loopback not set
Keepalive set (10 sec)
Last input 00:00:12, output 00:00:07, output hang never
Last clearing of "show interface" counters 00:24:56
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 13288000 bits/sec, 1115 packets/sec
30 second output rate 0 bits/sec, 0 packets/sec
1667013 packets input, 2483307665 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
105 input errors, 105 CRC, 6 frame, 5 overrun, 0 ignored, 6 abort
370 packets output, 9595 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DSU mode 0, bandwidth 15300, real bandwidth 15338, scramble 0
MPLS#
MPLS#
MPLS#
MPLS#sho controllers t3
T3 1/0 is up.
Applique type is Subrate T3
No alarms detected.
MDL transmission is disabled

FEAC code received: No code is being received
Framing is C-BIT Parity, Line Code is B3ZS, Clock Source is Line
Data in current interval (590 seconds elapsed):
0 Line Code Violations, 0 P-bit Coding Violation
0 C-bit Coding Violation, 0 P-bit Err Secs
0 P-bit Severely Err Secs, 0 Severely Err Framing Secs
0 Unavailable Secs, 0 Line Errored Secs
0 C-bit Errored Secs, 0 C-bit Severely Errored Secs
Total Data (last 1 15 minute intervals):
0 Line Code Violations, 17 P-bit Coding Violation,
17 C-bit Coding Violation, 5 P-bit Err Secs,
0 P-bit Severely Err Secs, 0 Severely Err Framing Secs,
0 Unavailable Secs, 0 Line Errored Secs,
5 C-bit Errored Secs, 0 C-bit Severely Errored Secs

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Re: Question about T3 error rates.

Fri Mar 19, 2010 7:53 am

It used to be fairly common for parts of a T1 or T3 to be mis-configured within the telco cloud, as voice circuits used to use a different line encoding than data circuits. This would cause errors on certain strings of data; ie, if a packet contained eight 0s in a row, etc. You can try to ping from one end to the other with certain patterns and try to see if one will have issues (such as all zeros, all ones). Its easy to do this from an enable prompt ("ping 12.112.7.173 data ffff size 1000" or "ping 12.112.7.173 data aaaa size 1000" and/or "ping 12.112.7.173 data 0000 size 1000").

With that being said, your error rate isn't horrible (average of one out of 15876 packets), but certainly it can't hurt to have the telco test it, since its a new circuit. Most likely the telco will loop the circuit and not find any issues; sometimes the problems mysteriously disappear after the telco tests it ;-)

Perhaps http://www.cisco.com/en/US/tech/tk713/t ... 418d.shtml can be of further help?
"A problem well stated is a problem half solved". (Charles Kettering)

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Re: Question about T3 error rates.

Fri Mar 19, 2010 9:49 pm

A loopback test would be ideal. Run some extended pings of different patterns like Dinger suggested to get a better sense of if there's a problem with the circuit. You may also want to try a physical loopback at both ends to try to eliminate your equipment and cabling (you can get an adapter at radio shack that makes it very easy).

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Re: Question about T3 error rates.

Fri Mar 19, 2010 11:02 pm

Thanks guys. I'll try the pings. I don't know that I can do a loopback test being MPLS. It's not like a clear T where I control both sides. One side is my CPE back to ATT, then the same at the other side. So it's ATT who would have to loop it. Trying to explain what I wanted them to do there would just be too painful.

I did manage to get ftp servers up and running on either side of the link. I'll do something like zip the entire Solarwinds toolset together ten times to create on big honking file and then pull it back and forth, maybe while also running Wankiller. That ought to fill that baby up with traffic. Pull that file back and forth twenty times and I should sniff out any trouble with the line.

The problem up here in the northeast is that facilities stink. I've spent more time over the years arguing with Verizon (now Fairpoint) about whether it's my equipment or their lines causing the problem. I don't know that I'll ever get this thing down to zero.

Ben

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Re: Question about T3 error rates.

Mon Mar 22, 2010 7:32 pm

Thought I would post a quick follow up.

I did try the pings with the all 1's and all 0's patterns. Those didn't produce any problems. But I have this big, honkin' 679MB file I created by zipping a bunch of crap together. I've found that I can't pull or push that thing across the link without generating somewhere between 100 and 300 input errors consistently. And that's the only set of machines using the link. If I'm getting that many errors consistently with just two workstations (the ftp client and server) I'm worried about what the errors will be like when I have a couple hundred workstations and phones using it.

So I'm opening a ticket. Troubleshooting with ATT. Aren't I lucky.

Thanks for the suggestions.

Ben

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Re: Question about T3 error rates.

Wed Mar 24, 2010 9:06 am

So, I got with a helpful ATT engineer in the transport group this morning. We ended up enabling scramble on both sides of both links. Since then I haven't taken any errors.

Do you guys have any thoughts on that? Is scramble something one should just enable by default on these circuits? I've heard that it can also cause some problems, but it sure made these errors go away.

Haven't taken a single one since we enabled it.

Ben

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