atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's T1 slow in one direction and fast in the other

I’m trying to identify a problem between 2 locations that are connected by three T1 lines. The problem that we are experiencing is a drastic slowdown in one direction and a fast speed in the other direction. Pings in either direction appear to be normal and it averages around 35ms & 45ms. We tested copying an 11MB file in one direction which averages about a minute in one direction and about 8 minutes in the other direction. We tried to copy a 100MB file over night and it will stall and will not finish.

Now, having said all of this, I’m a Server Administrator and all of the network devices are supported by another group out of state. We tried to explain the problem to them and I don’t think they have a clue where to start. I wanted to throw this issue out to the experts on this forum and see if anyone has experienced this problem and can give me some suggestions on where I can have the network group start to troubleshoot this issue. I’m basically new at this location and from what I understand, this problem has been like this since it was installed about 2 or 3 years ago.

Any help would be appreciated!!

REP61

If you're sayint the identical problem happens on all 3 t-1's than I'm sure it's not a t-1 problem. Now I'm no computer expert, but if you're pinging ok to the routers than the trouble is beyond your router.

I was told that we are on three T1 lines, so I’m basically taking their word for it. Is there a way I can somehow verify this? Also, when three T1 lines are installed between 2 sites are these configured independently for fault tolerance purposes? If so, is this basically the same speed as a T3 except it has fault tolerance?

Sure, go to where the lines come in and look. 3 T-1's don't equal a T3. The T-1's would all be the same as far as specs go. Sounds like you might want to get someone in to help you determine what you have.

Do you have CSU's and routers at each end?

We have two T-1's running between our two plants. One is voice and data and one is data only. It's usually an error in a router after trouble shooting. I am not as informed as others though it may be one option to look at.

A "T-1" is 1.536 (or 1.54) MB/S of voice or data. The term is thrown around loosely these days. A T-1 sometime is used to describe an ISDN PRI, which is 23 B or bearer channels and one D channel. It is also used to describe a CAS circuit which uses robbed bit signaling and has 24 usable channels. It can also be used for a frame-relay circuit that has a burstable speed of 1.54 and a CIR (Committed Information Rate) of say 768k. Typically all "flavors" of T1 have symmetrical speeds, that is the transmit and receive speeds are identical. Asymmetrical technologies include ADSL and Cable which have different speeds for upload and download.

A T3 or DS3 is 44.736 MBPS or roughly 28 T1 or DS1 circuits. Remember each DS1 is 24 DS0s.

In testing your speed make sure the interface has no load and do a file xfer with a client with a speed monitor. Test both ways.

The following is a show interface on a Cisco router with no load. Notice the Tx and Rx as 255 fraction. Each direction is represented, this is a lab router with only 1/255 in both directions.

R1#sh int s0/1
Serial0/1 is up, line protocol is up
Hardware is PowerQUICC Serial
Internet address is 10.1.1.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:03, output 00:00:05, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 21
Queueing strategy: weighted fair
Output queue: 0/1000/64/21 (size/max/total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 1158 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
565107 packets input, 37602682 bytes, 0 no buffer
Received 301876 broadcasts, 0 runts, 0 giants, 0 throttles
1 input errors, 0 CRC, 1 frame, 0 overrun, 0 ignored, 0 abort
565252 packets output, 42688654 bytes, 0 underruns
0 output errors, 0 collisions, 5 interface resets
0 output buffer failures, 0 output buffers swapped out
69 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

I agree with Rhonda that your problem is most likely isolated to either a CSU or a router. Possibly a bad port (or you have a port that is enabling communication only in one direction, resulting in your high loss of bandwidth in the oppisite direction). The T1s are probably fine... I'd focus on the terminating equipment at either end of the T1s (CSUs or routers).

What model of routers, channelbanks, CSU's are you using on both ends.

Most routers have the option to have priorty for data in a single direction. There are other options that can cause this problem as well. For instance. If one router is set to use the full t1 to send data accross and the other is set to use the fractional t1 to send data. I have seen a router setup this way and the customer complained aabout the same problem.

I have also seen a firewall setup to do diverse routing that has not switched back to using both circuits after an outage.

Knowing exactly what routers and a config file would certainly help in isolating the problem.

I appreciate everyone’s response, but unfortunately, I have to rely on other people to answer your questions and I’m not sure how long this will take.

Thanks again for your responses!

Another point to consider is if these T's are dedicated "point-to-point" circuits. For all you know, they're simply internet T1's from a ISP, and the ISP or your IT guys manage a VPN through the internet, but carried over these T1's. The difference being, that if they're dedicated point-to-point, then you have some weird problem. If they're simply local loop T1's to the internet, then you have the latency of the internet to consider between the to locations, where it's more logically possible that one end is a little faster than the other.