How Fast is a T1? really.

Hi all:

I just successfully turned up a T1 from NYC, US to Manila, Philippine. Both routers are Cisco 2600.

The ping time is about 268ms, every time.

My questions:

How fast is a T1 really? we're going to do VOIP and we're going to use g723 codecs and we want to know how many "agents" can be on the T1. I heard someone once said that a T1 is about 200k per second.

What is the usual ping time from here to a country like Philippine or India, anyone knows?

Thank you all!.

Reply to
john
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No kidding, the air distance is about 8500 miles. 1/4 second sounds about right for a geosync satellite hop. It's hard to imagine why you'd get a satellite link with the glut of fiber, but it should be easy enough to ask.

Reply to
John R. Levine

Got a correction from

I was wrong, and this is correct, so the "network distance" is really

16500 - 17000 miles. Or about twice the actual distance, so it still sounds a bit slow. Do you have engineering documents from your carrier? They might have some hints.
Reply to
Erik Freitag

Hi all:

Thanks for the fascinating information. I could ask the carrier to see what they have. Is there something specific that I can ask from them or just a broad question?

Maybe I should set up an ftp server on the US or Manila side and do around 10-20 ftp sessions and average out the result to find the "real" speed.

How about that?

TIA.

John.

Reply to
john

Philippine.

My first assumption was that this must be an internet T1 with VPN. However, reading again it seems like you have installed a private T1??? I would think that would be a very expensive proposition. If so, first check the throughput on the circuit. If it is being heavily utilized, then you would see higher ping times - QOS would probably fix this. If there is low traffic, check with your telco to see what they have for an SLA. I'd assume that they would be surprised to hear these results and you should troubleshoot together with them to figure out where the problem is - it could be your equipment.

One consideration is - what else are your routers doing? While 2600's (even the older models) are plenty of router to handle a full T1, if it has too many other things it is doing, it could degrade your system performance.

BTW - FTP tests will not show usability for IP Telephony, although they might signal other bigger problems. Since TCP is just happy to have the packets arrive in any order with high latencies, what you are experiencing may not affect the transfer much - some, but not a lot. On the other hand, such high latency with IP Telephony would cause serious jitter. Even with QOS, the calls are likely to be very poor quality given your current situation. Throughput and latency are very different issues.

An interesting/funny article for the Shark Tank fans out there:

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Reply to
Scooby

Ping latency has nothing to do with the speed of the line. Latency has to do with the speed of routers and switches on the route.

Sincve I seriously doubt you actually have a pt to pt T1 between the US and phillipines, you must be going over frame relay, atm, vpn, or something. Need to know extacly how the T1 connects you to the phillipines to be able to say why the latency is so high.

Reply to
T. Sean Weintz

1.544 Mbps --- about as fast as a 1x cdrom reader.

Reply to
H Brett Bolen

Hi John

Firstly a true T1 is a point to point link and can not slow down or speed up so without congestion causing delays inside the router due to queing or CPU exhaustion all traffic should reach the destination in the same time.

The speed of a T1 link is 1.544M unchannelised or 1.536M if channelised into

24 slots.

As for RTD if this was a true T1 link and we can ascertain that the local/remote routers are not under any processing strain due to any other connections etc.and we were not trying to overutilise the link from time to time (no queing) then this would not vary. The bulk of the RTD would be propogation delay. i.e. distance related and can only be improved by shortening the distance. I hear people whince here as we can't move the US closer to the Philapines. The truth is though that the cable routing might not be as straight as you think (but this is probably not your problem). All assumtions in this news group have been based on your testing (quite rightly) but can you confirm you are only testing the link by pinging the ip address each end of the link. If this is a proper T1 link then there is no real need to try to load the link for this as you cant slow down a T1 link, the RTD should be pretty constant, again assuming no CPU/Queing problems.

Some good fellow on this thread has done a lot of maths and concluded that this must be a really long routing to get the RTD you are getting. which is good evidence that you havent got a dedicated link at all to the phillapines but a T1 link to a service provider to be onwardly forwarded via frame relay/ATM etc. This will mean that your traffic will get switching delays as well as queuing delays and possibly discards depending on your service contract. One sure fire way of finding out if you have a point to point cct is to change the encapsulation type at both ends from what ever you are using to a different type and see if it still works (sensibly with a planned outage of course). If you are running frame relay encapsulation though you can have a good guess by looking at the config of the 2 routers. On a point to point cct then one router must be running Frame-Relay Switching and also this routers interface will also be running Frame-Relay Intf-type DCE. If they are not you are using a frame relay network in-between each site with switches etc. There are probably checks for other types of encapsulation also but I can't advise here.

If you ascertain that you are in fact running through other networks then you will need to contact your service provider to be able to give priority to your voip traffic over the link. This can be done in frame-relay via 2 pvc's being used one for voip and the other for data. but this can only be discussed/cured by your service provider and no one here on this group. If your service provider can not give you what you need at the price you need the I'm afraid it's back to shopping around.

Toby

Reply to
Toby

This is what the carrier emailed me back:

It was technically provisioned via our Freeway Service which is our direct connection to LA.

Freeway runs on ATM over C2C-JUNC cable routes.

-John

Reply to
john

Philippine.

If this is a "real" T1, then it may be protected by SDH - the numbers look more like the circuit could be going "the wrong way" around the world - which is quite possible with sdh and a telco not forcing the shorter path....

ask for the circuit routing, and expected latency - then check if it looks close to what you expect.

if you have internet access at both sites - try a ping via the internet to compare the results.

i have seen a european cross border circuit routed via the US after a fault which gave similar differences between expected and actual latency.

this houldnt affect the latency, but the ping results may vary if you start having Qing in the routers.

Reply to
stephen

300ms to parts of Asia from US is not unreasonable. But if you're doing bulk file transfer over high latency pipes, you need to consider RFC 1323.
Reply to
Hansang Bae

Which doesn't tell very much, other than it is not a true point to point T1. For starters what the heck are "c2c-junc" cable routes? Google search on that term turns up nothing.

The latency is obviously occuring in the ATM cloud. Since I am not familial with the topology of their "freeway service", I can't tell you where or why.

Reply to
T. Sean Weintz

I would suggest the iperf utility instead of ftp for testing throughput.

Reply to
James Lewis

Have you asked the service provider what latency your service contract should expect from the US to the Philapines. With Layer 2 switching such as ATM they usually can provide maximum figures.

You can expect that a pure T1 whould be the fastest as there are no queues to manage and virtually negligable multiplexing delays. ATM uses a shared network and as such will induce switching/queing delays and these can be expected although ATM switching is very fast and queing is only due to congestion either on your access link or within the SP cloud. It is provided as a cheaper alternative to dedicated point-point links as it is shared but still the service provider should provission there bandwidth to accomodate the traffic levels expected and only penalise the abusers.

If the SP is not providing what they have prommised get them to re-route the ATM PVC. If they are remember we can't change the laws of physics and also shouldn't expect perfection on a budget. Of course you would still have a claim if the service has been mis-sold to you on these accounts.

Toby

Reply to
Toby

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