Unless it's broken, a T1 provides 1.544 megabits end-to-end, but what happens when the bits fall off the other end is up to the company who terminates it. That'll be in the service agreement you signed, what does it say?
Yes... Effectively, a T1 is a pipe that is capable of carrying EXACTLY
1.544Kbps of data, no more and no less (assuming it is working "normally"). If you are being told "that a T1 has a loss of signal and that it does not provide exactly the advertised speed of 1.544kbps", then someone is either "dumbing down" an explanation of the reason for what you are seeing, or they are talking porkies (lies) and you do not really have a full T1 link. I suspect its probably the former...
HOWEVER, its my guess that YOUR PARTICULAR TESTING is not really capable of providing exact measurements for a variety of reasons, and some of what you are seeing probably relates to your method of testing.
What follows is a fairly detailed explanation, please use or discard as appropriate...
Things that need considering when performing "bandwidth tests" using real world traffic include - 1. You are passing traffic between 2 devices that are NOT directly connected to the ends of that pipe. IE you may be testing other components of the link that could also affect the results. A traceroute between your TCP/IP end points should reveal the extra components of your testing, a pure T1 has NO TCP/IP component itself, so it will be BETWEEN 2 of those hops of the traceroute. 2. The TCP/IP protocol itself consumes some bandwidth (its wraps your data inside its own management data) and this adds approx. 5-15% to the actual data moved. 3. The devices that process TCP/IP are not 100% efficient at USING the available bandwidth (although they can get quite close to 100%).
Therefore you need to take into account limitations on the available bandwidth affecting your "testing" of the T1.
The ONLY way to to get an truly accurate test of WAN bandwidth is using what is known as a BERT (Bit Error Rate Tester) which is special testing H/W that is connected DIRECTLY to each end of the WAN link, and this devices "tests" the link capacity and quality by 100% saturation of the available bandwidth. If you do NOT have a true open Pipe like a T1 provides, then you will not be able to even start a BERT.
So the 1.544Kbps is probably guaranteed, but your testing may be taking other factors into account.
Incidentally, if you have access to the devices (Routers) connected to the end points of a WAN link, then they should be able to provide a pretty good indication of the true WAN Bandwidth.
BTW, a T1 is not usually provided using any form of xdsl technology, however in some situations SDSL is being used for exactly this work these days. The ones I have seen like this seem to work reasonably well, but I do wonder about some additional factors that SDSL can introduce (such as end-to-end latency). Oddly enough these can have an affect on overall TCP/IP performance, but its usually much smaller than what you are seeing.
From that computer to *WHAT*? If to some generic site on the Internet, then those speeds are consistent with a T1 connecting to the Internet.
That means a T1 from one end to the other, not to any random computer anywhere in the world.
Look, I have a computer right in front of me that has a 256Kbps connection to the Internet. No matter how fast your T1 is and how well it's working, you're not going to get 1100k to it, up or down.
It should be perfectly guaranteed from one end of the T1 to the other end of the T1.
Read your contract. If you control at least one end of the T1, you should be able to access the error counters. For example, here's the stats from one end of a T1: Module type is T1/fractional Receiver has no alarms. Framing is ESF, Line Code is B8ZS, Current clock source is line, Fraction has 24 timeslots (64 Kbits/sec each), Net bandwidth is 1536 Kbits/sec. Last module self-test (done at startup): Passed Last clearing of alarm counters 13:10:20 loss of signal : 0, loss of frame : 0, AIS alarm : 0, Remote alarm : 0, Module access errors : 0, Total Data (last 52 15 minute intervals): 0 Line Code Violations, 0 Path Code Violations 0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins 0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs Data in current interval (621 seconds elapsed): 0 Line Code Violations, 0 Path Code Violations 0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins 0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
You'll notice that it shows 24 timeslots of 64Kbps each, for exactly
1,536Kbps and there are no errors at all. You should be able to get similar information if you control the device at at least one end of the T1.
Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.