T1 Problems...Very bad ping times from Router

Answered Question
Nov 12th, 2007

Hi Guys,

Just wanted to ask for advice regarding the the following problem. I have a T1 line for data to AT&T. The interface is up and and line is up. However, I am getting intermitten ridiculous ping times to my 1st hop AT&T gateway. It's causing my VPN users to get extremely bad voice quality (Cisco IP communicator). I originally had service policy QoS applied for voice on the outgoing serial interface. However, with the slow ping times, I removed it just in case it was affecting performance. Even with no policy outgoing or incoming on the serial interface, I am still getting bad ping times. Here's the sh interface for the serial interface:

Serial0/0/1:0 is up, line protocol is up

Hardware is GT96K Serial

Internet address is 12.X.X.X/X

MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,

reliability 255/255, txload 20/255, rxload 139/255

Encapsulation PPP, LCP Open

Listen: CDPCP

Open: IPCP, loopback not set

Keepalive set (10 sec)

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 6d15h

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 0/9/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 1152 kilobits/sec

5 minute input rate 839000 bits/sec, 103 packets/sec

5 minute output rate 122000 bits/sec, 74 packets/sec

17747759 packets input, 694178341 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

40 input errors, 40 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

12549691 packets output, 2116392419 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 output buffer failures, 0 output buffers swapped out

1 carrier transitions

Timeslot(s) Used:1-24, SCC: 1, Transmitter delay is 0 flags

Thanks guys,

ANy help is appreciated.

I have this problem too.
0 votes
Correct Answer by Kevin Dorrell about 7 years 5 months ago

I would think with the difference in speed between the T1 and Ethernet, and the fact that you have 70% for voice, it is highly unlikely that the Ethernet QoS has anything to do with it. I assume the voice gets a priority queue anyway on that side.

There is not much you can do with ingress QoS. The QoS needs to be applied at the other end of the link. You could ask AT&T if they would be willing to do that for you, but I bet they would prefer to sell you a second line. You aould also ask them for drop statistics from their end.

I suppose you could install some WRED so you slow down any TCP sessions when the loading gets high. As I said, ping is not a very good metric for judging this, but voice quality is.

But all in all, it looks like you are trying to squeeze a quart into a pint pot.

Kevin Dorrell

Luxembourg

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Kevin Dorrell Mon, 11/12/2007 - 07:50

If your link bandwidth is 1536 kbps, and over the last 5 minutes you have been averaging 839 kbps on input, then I would say you need a faster line. Furthermore, it is your input rate that is nearing the limit, so there is very little you can do with QoS on this side. It is the other end that will have to police the traffic. Do you have control at the other end as well? How is your output drop counter at the other end.

Occasionally you are dropping packets on egress, but very few indeed: 21 drops in 17 MegaPackets is negligable. How is your voice traffic when you have the QoS in place?

As for ping, you should remember that ping is the lowest priority task in the box, so you are likely to get the same results what ever you do with QoS. And if the ping times do improve by removing the QoS, then it is at the expense of your production traffic.

Just one final thought, is this fractional T1, with different timeslots going to different destinations?

Kevin Dorrell

Luxembourg

tomtom001 Mon, 11/12/2007 - 14:21

Thanks Kevin.

It is a full T1 with 1.5 Mbps connection from AT&T. They control the gateway, so I do not have access te their end.

I have removed the Qos service policy on the serial interface and the high ping times are still there.

I still have the Qos policy for outbound on my FastEthernet connection to the internal Lan (set up for 70% voice 5% Voice Control 25% everything else). Could that be affecting my IP Communicator call quality also?

If it needs be, I can approach the admin about adding another PRI data connection. But I want to make sure that it will resolve the issues.

Thanks again for the help!

Correct Answer
Kevin Dorrell Mon, 11/12/2007 - 23:49

I would think with the difference in speed between the T1 and Ethernet, and the fact that you have 70% for voice, it is highly unlikely that the Ethernet QoS has anything to do with it. I assume the voice gets a priority queue anyway on that side.

There is not much you can do with ingress QoS. The QoS needs to be applied at the other end of the link. You could ask AT&T if they would be willing to do that for you, but I bet they would prefer to sell you a second line. You aould also ask them for drop statistics from their end.

I suppose you could install some WRED so you slow down any TCP sessions when the loading gets high. As I said, ping is not a very good metric for judging this, but voice quality is.

But all in all, it looks like you are trying to squeeze a quart into a pint pot.

Kevin Dorrell

Luxembourg

tomtom001 Wed, 11/14/2007 - 06:35

Thank you again Kevin. I appreciate your advice.

Have a great day!

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Posted November 12, 2007 at 7:39 AM
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