T1 occasional high-latency

I have a T1 Internet connection that occasionally gets 200+ ms delays. (See below.) This is a recurring problem that I anticipate will be detrimental to VoIP.

What would cause these instances of high-latency? I have worked with the ISP and have not found anything unusual. This occurs both during peak hours and off-peak hours. Bandwidth utilization on this link is minimal. Short BERTs show a clean line. CPU utilization on both routers are also minimal (0% and 5%). My router is a Cisco 7206VXR using T1 modules, and I believe the ISP gateway is a 3600 series router with an external CSU/DSU.

! Extended ping to the T1 gateway Sending 10000, 100-byte ICMP Echos to ---.---.---.201, timeout is 2 seconds: Reply to request 0 (1 ms) Reply to request 1 (4 ms) Reply to request 2 (1 ms) Reply to request 3 (4 ms) Reply to request 4 (1 ms) Reply to request 5 (4 ms) Reply to request 6 (4 ms) Reply to request 7 (1 ms) Reply to request 8 (4 ms) Reply to request 9 (1 ms) Reply to request 10 (4 ms) ...................................... Reply to request 74 (4 ms) Reply to request 75 (104 ms) Reply to request 76 (1 ms) ...................................... Reply to request 170 (4 ms) Reply to request 171 (24 ms) Reply to request 172 (1 ms) Reply to request 173 (4 ms) Reply to request 174 (4 ms) Reply to request 175 (1 ms) Reply to request 176 (220 ms) Reply to request 177 (220 ms) Reply to request 178 (204 ms) Reply to request 179 (204 ms) Reply to request 180 (204 ms) Reply to request 181 (204 ms) Reply to request 182 (200 ms) Reply to request 183 (200 ms) Reply to request 184 (200 ms) Reply to request 185 (200 ms) Reply to request 186 (200 ms) Reply to request 187 (84 ms) Reply to request 188 (4 ms) Reply to request 189 (1 ms) Reply to request 190 (4 ms) ...................................... Reply to request 6924 (1 ms) Reply to request 6925 (224 ms) Reply to request 6926 (220 ms) Reply to request 6927 (220 ms) Reply to request 6928 (220 ms) Reply to request 6929 (220 ms) Reply to request 6930 (208 ms) Reply to request 6931 (200 ms) Reply to request 6932 (208 ms) Reply to request 6933 (200 ms) Reply to request 6934 (204 ms) Reply to request 6935 (200 ms) Reply to request 6936 (200 ms) Reply to request 6937 (76 ms) Reply to request 6938 (1 ms) Reply to request 6939 (4 ms) Reply to request 6940 (4 ms) ...................................... Reply to request 9999 (1 ms) Success rate is 100 percent (10000/10000), round-trip min/avg/max =

1/3/224 ms
Reply to
hack.bac
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"hack.bac" ha scritto nel messaggio news: snipped-for-privacy@x40g2000prg.googlegroups.com...

Hi,

It seems (since only "two samples" are given there is no statistical significance) that the high latency pings occur in "bursts".... if the line is "clear" and these "high latency burst" occur periodically (also while line is IDLE) maybe the cause is a recurring process which monopolize the CPU (possibly at the ISP router) (i.e. BGP scan, etc.).

This is only my opinion from the few info provided of course.

Regards, Gabriele

Reply to
Gabriele Beltrame

messaggionews: snipped-for-privacy@x40g2000prg.googlegroups.com...

You can usually eliminate (or include) the far end router's cpu by pinging a different internet host at the same time as the far end router - several more if you like.

My guess is that it is likely to be the line that is saturated for these periods. If you ping a few targets on the far side of the link and the latency to all goes up at the same time then it is pretty certainly just traffic.

IIRC 200ms is typical of a T1 when it is full. This time depends of the transmit buffer size of the router.

Reply to
Bod43

messaggionews: snipped-for-privacy@x40g2000prg.googlegroups.com...

another problem sometimes is using two-wire T1 circuits instead of four-wire, the two wire is HDSL, similar to you home DSL that is an ATM modulated signal that does not require repeaters for great distances, but is prone to degradation due to noise and other issues.

May want to check which you have going to the smart jack.

Reply to
MC

Ping is not a reliable measure of delay on a circuit, in fact it is very, very UNRELIABLE. Both the near end and far end routers must CPU process the sending and replying of the packet, and this is a very low priority process. If the near or far end routers have a busy CPU, the ping round trip includes the time it took to create, queue and send, the actual time on the wire, the time it takes the far end to queue, process, create a reply, queue, send, time over the wire, then the sending router to receive, then process the reply. In short, the ping time does not take into affect the amount of time the ping packet is spent waiting to get processed on the near and far end routers. Packets being sent THROUGH a router, are CEF switched meaning that it doesn't usually matter if the CPU is busy or not (depending on the routing platform).

Scott

Reply to
Thrill5

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