How to Test Your T1? 488
lawpoop asks: "We have a T1 line for our building with a local ISP. Right now, we're looking for competitive bids from different companies. The local guy is offering a good price, but the larger guys are saying he may be overselling the T1 service through a DS-3. He swears he's not. So, how do I tell? The sales guys say 'There's bandwidth meters on the web,' but they fail to mention exactly how I can tell if I have a true T1. I've tried a half-dozen bandwith meters on various websites, and the results are highly variable. We've gotten 300-900 Kbps. Each site has disclaimers as to internet traffic, time of day, etc. Furthermore, we split the T1 out over a hub with two other tenants in the building. I'm coming through from behind that hub. How can I tell for certain that I'm getting a full T1? A service tech with a line tester? Any dead-on bandwith meters? What would an oversold T1 read out to be as compared to a true T1? If the larger guys are trying to scare me to their service with stories of oversold T1s, I need to know that they aren't doing it also!"
4 letters (Score:4, Informative)
Re:Packet Sniffer? (Score:2, Informative)
If their upstream is overselling the DS-3, that will not dump extraneous traffic over the T-1 connection they have bought. It will simply lower the effective bandwidth.
And as to why he should care... because he's *paying* for T-1, not some fraction thereof.
Re:dslreports.com (Score:3, Informative)
author said, he wants to know if it's a true T1
vs, oversold DS3, which is not nessicarily
detectable by a bandwidth meter
MRTG (Score:3, Informative)
Then there's always MRTG
http://people.ee.ethz.ch/~oetiker/webtools/
Welp. (Score:5, Informative)
Now, as for your bandwidth, that's a different story. It is accepted practice to have oversubscription on your network; ISPs simply don't have the money to provide a full, balls-to-the-wall, 1.544mbps connection to the net for every single one of their customers. Local loop charges for simply a T1 from their office to yours starts at around $200 (in Alabama), and that's only if you use a CLEC. The bandwidth is what you're wondering about, and quite frankly, without having someone in the know inside your ISP, you will *never* find out how oversubscribed they are. What you pay above and beyond local loop charges are bandwidth access charges; you're actually paying for internet access at that point. Roughly analogous to paying for a phone line (local loop), then paying for dialup internet service (the T1, in this analogy).
Basically, unless you're buying a DS3 (44.762mbps) or above, you will never ever get committed, 100% full bandwidth on demand all the time.
Re:4 letters (Score:3, Informative)
Rule #1. EVRYTHING IS OVERSOLD (Score:5, Informative)
If your ISP is overselling (Score:5, Informative)
The real test, frankly, is to get bandwidth from someone with heavy-duty backbone connection (e.g. AT&T) and just plain hammer it with mondo file transfers scattered across the day. If your transfer times are varying with Net traffic periods, your ISP is the bottleneck.
You might be able to get similar information cheaper by doing repeated traceroutes and logging the delay between the ISP and the next router up, which would indicate the queueing delay at the ISP's routers.
No. (Score:1, Informative)
http://www.netiq.com/qcheck/howqcheckworks.asp
It's a myth (Score:4, Informative)
Today, few ISP's actually have upstream bandwidth equal to what they've sold downstream. And it gets even more complicated when you consider that there are usually multiple routes out of an ISP, some of which can be easily overloaded, others less so, depending on where the traffic is destined.
The only worthwhile measure is a subjective one. Can you get 1.5Mb throughput on ANY site? On some sites but not others? Do you think you're going to get better service from somebody else? There's no exact answer as to whether you're getting your money's worth; experienced net admins have used a several connections over time, and usually know within a day or two whether they're on a good one or not.
Check the CSU/DSU (Score:5, Informative)
First of all, if you have *the whole T1* then you should have control of the CSU/DSU and the router at your end. Accept no substitutes. If the guy is, in fact, splitting a T1's worth of bandwidth off a DS-3 (say) then you should (at the least) have monitoring privileges on the router and DSU, either via web, SNMP, or telnet.
As mentioned earlier, the DSU should show that your connection to the line is using 24 x 64Kbps channels, for a total of 1.544Mb/sec (minus a few k for channel overhead gives you 1536). ALL of those channels should be coming out your end of the CSU/DSU.
If you have control of the router, then you might try (again, as mentioned earlier) ping-flooding the router at the other end of the T1 and checking how many packets/sec get through, then multiplying by your packetsize. That should give you a reasonably close answer.
If the guy isn't bullshitting you, then he should have no problem giving you read access to the SNMP MIB on the router and letting you watch traffic - if you can access this, you can run bandwidth monitors like MRTG.
Good luck.
Re:well, one way (Score:2, Informative)
Use "bing" (Score:4, Informative)
Bing [www.cnam.fr] works well for symmetric links. It's not much use for DSL lines, but for true symmetric lines it's pretty accurate.
It will check the bandwidth between two IPs, as long as the one IP is in the path to the other from your machine.
Re:dslreports.com (Score:3, Informative)
And while that page is great, the only real accurate test would be throughput on his router.
Re:FTP (Score:4, Informative)
Ahh, but what about stat mux? (Score:2, Informative)
The only real way to know is to ask your ISP exactly how many customers are using that DS3, and hope they're telling the truth.
But wait, what if your ISP's ISP is oversubscribing *their* DS3....
Does it really matter? (Score:3, Informative)
So if the ISP is selling you 24 channels of the DS3 and calling it T1, then you're getting a T1. Quitcherbitchin.
Nathan
Lies, damned lies, and statistics. (Score:5, Informative)
This even applies to phone lines.. That's why It's sometimes hard to get a call through on Mothers' day. The phone companies provision to handle 99%+ of the volume spikes, and mothers' day can consistently make it into that last percentile. Even so... handling 99% of the traffic spikes still comes to far less than one circuit for every two subscribers.
To test if your T1 is really a T1, you can try setting up for an FTP (or whatever) session with your buddies... Change things to make sure that you've each got the route to the other going through the first hop on your T1. As long as that router doesn't icmp-redirect the traffic, (in which case your measured bandwidth will be more in line with local ethernet traffic) you should be able to get a good estimate as to the raw bandwidth of your 'last mile'. (it'll actually be the lesser of your uplink speed and your downlink speed minus a little bit)
The next hop would be to set up a transfer with something inside of your ISP's primary network. (did they give you a web site on one of their systems, etc??). That'll allow you to test for local bandwidh bottlenecks and give you a theoretical maximum to the outside world.
The last link check would be to find a machine on a fast network that's not on your local ISP's but is (topologically) close. Try doing traceroutes to nearby universities.. See if you can find one that doesn't put you through 3 different ISPs. Then try and transfer data from/to them and see how fast it goes.
You'd be best to try connections to a few semi-local sites. Otherwise it'll be hard to tell if a low bandwidth reading is the fault of your ISP, or the server's ISP.
It's pretty much useless to check bandwidth to random (distant) sites. Once you get a site that's a reasonable ways away (topologically or geographically), then you run into the vagraties of internet traffic (see the article earlier this week about 'net quakes)..
BTW: When I speak of being topologically close, this is different from geographically close. I remember one case where getting a packet to a machine not more than 100 feet away (but on another ISP) sent traffic from Vancouver, down the coast to Silicon Valley and back. Needless to say, ping times stank. In that case we were geographically close, but topographically distant.
THere would be two times to test these transfer speeds: Low time (e.g. 4am) and prime time (Last time I peeled apart ISP traffic stats, traffic peaks were around 8-9pm for home traffic and about 4PM and 9AM for commercial traffic)
Re:Don't Hub, Use a Switch (Score:4, Informative)
As was mentioned in an earlier post, a T1 uses something called a DSU/CSU to manage the 24 BLines on your T1. This is sometimes built into a router, on a card in a router, or an external device running to some sort of high speed serial line (not always HSSI though) that can be linked to your router.
You can check the settings on this DSU/CSU to make sure you have a full T1 and not a fractional (all 24 channels is a full T1, less than 24 is fractional), but that won't help with finding oversubscription at the other end. There's really no easy way to check that, but if you never notice, who cares? Just make sure you get an SLA for the bandwidth you expect (usually the full 1.544Mb/sec on a T1) and if you at any time are unable to get that due to oversubscription by your ISP (all of them do it, some more than others though), you are entitled to compensation (often a partial refund or even being paid).
Basic constants of the "Internet Universe"... (Score:2, Informative)
First off, excluding some very odd and sparse cases, from a telco "loop" perspective (the wire and associated hardware involved in providing a T1 from you to the telco's office or remote), a T1 is a T1, regardless of it being frame relay, fractional, point to point, or otherwise. Basically, 1.544Mbps raw data rate. The only thing the telco can tell you is that it is working within acceptable limits, with an acceptably low BER (Bit Error Rate). Nothing more. If it's a non frame relay dedicated T1 (aka point-to-point or "nailed up"), you should see something like 160kBps on a single transfer over an otherwise idle circuit. Frame relay is a totally different ballgame - you run into the circuit's "CIR" - Committed Information Rate (or also referred to as Certified Information Rate on occasion). Basically, it works like this - even though your local loop (wire from you to the telco) supports T1 rates, they're only provisioning your chunk of the frame relay "cloud" to support the bandwidth you purchase. Depending on the provider, it could be a "hard" limit (ie - you'll never get more than that), or a "soft" limit, meaning that you may get more speed if there is sufficient packet bandwidth left, but when it's busy, you'll get choked down to your CIR.
Second immutable fact of the Internet - providers (particularly tier 2 non-backbone providers) will always oversell their bandwidth. Think about it - how do they make any money at it otherwise? It's their bandwidth "sold" to bandwidth "available" ratio that tells you anything about the quality of service you may expect to see from them. It can be virtually anything really. It's similar to the subscriber to modem ratio dialup ISP's keep, or subscriber to bandwidth broadband ISP's keep.I'm not sure what the averages are anymore with the changing scene of broadband right now.
As for testing your speed with one of the online "speed test" sites, take the results with a grain of salt - a very BIG grain. It's only benchmarking the ability for you to transfer data between your location on the Internet to their location on the Internet. Nothing more, nothing less. More oft than not, their results are less than what your circuit (or broadband connection) are configured for, and sometimes, dramatically less. I've seen 256k DSL connections that "felt" as they should speed wise, bench in at dialup speeds using those sites because of bottlenecks beyond their or their provider's control.
A better test of bandwidth, and possibly more importantly connectivity, is to do some basic homework. Ask your provider to provide some traceroute and ping data to some common sites potentially used in your day to day activity - taken at different times of the day, preferrably at the times you're most interested in. Or better yet, ask them if they would let you do the tests yourself from their facility. Choose some sites you frequently visit, business or pleasure, and trace their progress theough the Net. Fewer hops = better speed and reliability overall.
I may catch a little hell for this, but I've found it to be a good general benchmark - download something that is known to be cached at at Akamai cache farm. NAI virus updates used to be a good test. Akamai is generally connected very well, in strategic points through the Internet, and provides at least a benchmark to go from. Downloading from Microsoft is sometimes a decent test, sometimes not, depending on what's downloaded and when. And, no, that wasn't meant to be a troll or flamebait, just a basic fact really.
In all, if it generally looks right, feels right, and provides stable, repeatable performance during the times you need it, it's probably fine. There is no good, clear, black and white method of determining if your "T1" is a "T1".
They may just be shooting you a good deal because they have plenty of bandwidth, and sales prospects are limited because of the economy. Who knows. Just do your homework, limit your exposure to marketdroids and the resultant weasel-words, and go from there.
Remember, for all intents and purposes, the Internet is basically the data version of the public road and highway system. You'll find construction, detours, and bottlenecks regardless of how many 12 lane super-highways exist. You just need to live with it and work within those limits as best you can...
Brad
Nearly all bandwidth is oversold (Score:2, Informative)
Here's how I've done it... (Score:3, Informative)
Yes, that's about 15 T-1 lines worth of bandwidth - my 1.5 Mb DSL line is always saturated when loading stuff down from it.
So, I wrote a quick PHP script to take a 100k file off the disk, and hurl it at you repeatedly 1000 times, with a mime-type of application/octet-stream. That's a 100 MB file being downloaded by HTTP.
Then, I hit the script with lynx -dump >
In my case, we did get effectively 1.48 Mbit on the T-1 line being tested, which is close enough to satisfy my curiousity.
I'd be happy to perform this test for you... BTW - if you are in North California, I recommend o1.com as an excellent provider!
Re:A Full T1 is ... (Score:2, Informative)
Re:Don't Hub, Use a Switch (Score:2, Informative)
You can't just run the T1 into every device on a network, you either have to hub it (Cheap but SLOW) or switch it (More $, but better performance). Take my old High School for example: The district has a seriours cash problem (namely, no money) because we have no city government, they get no city taxes, and they get $0 corporate donations. So they chose to get a T1, but hub the hell out of it. In the English "Computer Lab" alone there were 2, 36 (I believe) port 3 Com hubs. This was the case all over the school, aside from our 1 router, every thing else was hubed, and this was also true for the whole district. As a result, the network worked fine at 6 AM when no one was there and everything was off, but by 10 AM, it dragged bad. It was so horrible that I was actually able to get faster bandwidth using a dial-up.
Re:dslreports.com (Score:2, Informative)
He would have to wait until the DS3 was full (maybe during peak hours), but the problem with this is that the rest of the internet is congested too, and therefore the speed from dslreports to the end user would not be accurate.
The other problem is, tests such as ftp test (which use 1500 byte packets), give results that have a huge variation. To get any good results you will have to use ftp a huge file (many many MB) so that the transfer can come to steady state.
The only true way to test this is really in a lab scenerio!
Ask the ISP how he gaurantees that the ds3 is not oversubscribed. Is it set up for Qos/Cos, and if so, how is it set up?
Good Luck!
Why Hubs? (Score:2, Informative)
Hubs? You actually use hubs? No wonder it seems slow.
Here [google.ca] is a Google cache of the difference between hubs and switchs (basic).
If you're in charge of the network, you need to take some courses. No offence.
Re:Packet Sniffer? (Score:2, Informative)
Re:Getting a T1 or getting a "T1"? (Score:2, Informative)
Sure, the subject seems kind of amusing at first glance, but the post is actually informative.
Fucking moderators *waits for the negative mod'ing to begin*
How to test speed, and tons more info! (Score:5, Informative)
Now, on to determine if you have a 'real' T1. Many providers tend to sell frame relay service as a 'T1'. While its true that the circuit itself from the telco to your place of business is a T1 (unless you have say 56k DDS service, etc), after your traffic hits the telco's switch, it transverses their frame relay network, and eventually gets sent to the frame host on your provider's network. This can suck for many reasons, however the biggest one is that the provider can get away with purchasing a CIR that is less than 1.5 mbps (like 768kbps), and just have it be able to burst up to 1.5. This can suck a whole lot if the telco's frame network is congested, and you can never burst, and/or you constantly want to use more than the CIR etc..
You can tell what kind of circuit it is by quite a few ways, if its installed and you have access to the router you can simply check the encapsulation on the T1 (if its set to frame relay, its a frame circuit, if its set to PPP or HDLC its a point to point circuit), you can also tell by the format of the circuit id (the first part of
If you have a frame circuit they should be charging you quite a bit less than a point to point T1, especially if the CIR is low (the lower the CIR the less expensive generally). Point to point T1s are preferible in almost all cases unless your worried about cost.
So now that you've determined the type of circuit you have, you can check what speeds your getting. Its usually best to do as other people have mentioned and download (and UPLOAD too.. you should check both speeds) from an FTP server on the provider's network. This will give you the most accurate picture of how fast your connection
You should also do a separate test to a major site.. You could download the 1.4.0 Java SDK from Sun for instance (that should give you a decent speed). Don't worry if this is somewhat lower than 192KB/s, as that can be caused by congestion in a network inbetween you and sun that has nothing to do with your provider, etc.. If its consideribly lower than that speed consistantly (and other sites with bandwidth to spare yield the same results), then I would contact your provider about it. It could be that your provider doesnt have enough upstream capacity, or about a billion other things, but they might be able to tell you any known issues, or that the problem isn't them and/or tell you the current utilization levels of their upstream circuits.. heh
Re:A Full T1 is ... (Score:5, Informative)
Furthermore, the 'local guy' should be more than happy to show you his DS3 MRTG graphs. There is absolutely nothing wrong with a DS3. 99% of the networks in the world have less than a T1s worth of bandwidth. The amount of bandwidth a company has is irrelevant, really. As long as the amount of available bandwidth is greater than the bandwidth you need, and you experience no increased latency or packet loss, they have sufficient connectiviy.
You can always ask to see the local guys MRTG graphs...
Andy
Re:Welp. (Score:2, Informative)
Point to Point: Kinda a generic term, but what you refer to (a pair of copper from you to your friend, usually with appropriate amplification for voice along the way) a Leased Line. These often have POTS modems run over them, or sometimes T carrier.
Frame Relay: Passing frames along until it either gets dropped or gets to it's destination. Most of the time the actual physical links in these networks are T carrier or ATM. Your description seems fairly accurate on this one, but I have little experience with Frame Relay, so I may be wrong.
The Word You're Looking for is CIR (Score:2, Informative)
He cannot, by law, lie about the CIR. If he does, the company he works for gets major fragmentation from the shit that hits the fan. I can sell T-1 service all day long, but if all 24 channels only amount to a CIR of 1 MBPS, I'm hardly competitive with companies who are selling my T-1 lines with 1.4 Mbps CIR.
BTW, why are you getting a T-1 line? Are you splitting it for both voice and data, or is it pure data. A number of clients I've consulted for in the past really only needed a cable or dsl connection for their uses (basically, web collaboration and surfing).
Re:Lies, damned lies, and statistics. (Score:3, Informative)
having worked at the phone company, the numbers are approximately 9 phones per carrier line capacity in residential installs and 4 to 1 in businesses. incidentally, on some systems, when capacity is full, you get a busy signal after dialing (so a busy signal is not necessarily a sign that the receiver is busy).
Re:FTP - NOT (Score:3, Informative)
You need to test OUT to the internet.. and even then it's shakey as net traffic, router configurations, hell even cache servers can screw it up.. (yes sonny, I can put a transparent squid cache on your T1 to make things look incredibly fast for most of the time to you...)
Simple solution... Ask to tour his connectivity closet with a trained T1,T3,DS3,OC3 person with you (Only $250.00 an hour) and that person can tell you at a glance how many T1's are coming in and going out... giving you a good idea about the infrastructure.. if they will not let you see the connectivity room then they have something to hide.
FTP speed testers, beware of TCP/IP limitations (Score:5, Informative)
Those who test by FTPing large files and watching the transfer rate, should understand these limitations [vad1.com] (kindly explained to me by J.Spencer Love).
I had a similar problem trying to host a large-bandwidth video clip. It turned out the bandwidth of my 10Mbps line did not saturate at all (in fact, it was utilized at mere 5%), so neither did the trans-Atlantic connection. The bottleneck was the internal buffer in client and server software.
This also means you may not need that much bandwidth to push the speed of your FTP/TCP-based tasks to its limit.
Re:Welp. (Score:3, Informative)
PRI is similar to channelized T1, it's just more strictly defined.
it's ALL time division multiplexing.
You got Frame Relay right.. it used to be used, say, when a company wants to join a lot of offices together over long distances (not using the internet). They don't want dedicated links between each office.. that would get really expensive.. so they all get a single link into the same frame relay cloud... and then they just set up whatever data rates they wnat to guarantee thorugh the cloud
Telcos set up frame clouds and then sell customers on the idea because it means the telco has to throw less bandwidth at the problem... you want to connect point a to b, someone else wants to connect c & d... so rather than 2 dedicated lines across town, it's just 2 shorter lines into the frame cloud.. and guaranteed rates, cheaper for everyone.
burstable I always thought was more about QOS at the internet router, and not really on the T1 at all.. ie: You can use all you want, but when push comes to shove, you only get 512Kbps at our gateway.
Burstable can also be simply not a technical measure, but only about how your bandwidth fees are calculated ie: average rate over 24 hour periouds, or over a week.
This pricing model can be better than simply charging for bytes sent because it encourages a certain type of network usage... so you don't get someone who only pays for bytes transferred then absolutely jams his ocnnection up for 1 random day a week and doesn't use it at all... he's actually a harder customer to manage network wise than the guy who simply uses 256Kbps more or less constantly.
You got ISDN right.
I think D means Data though (telco data, ie, which call is coming in on what channel, calling number, etc)
They all use TDMA
Burstable T1 is usually something like (though I may be wrong) the T1 and everything is normal...
Re:A Full T1 is ... (Score:2, Informative)
Anyway, the point is this: the connection speed should approach 1.54Mb/s. Will it ever get there? Prolly not. Also, in most metro's, T1s go for around $900/month fullrate-nonbursted.
Re:Welp. (Score:5, Informative)
PRI's are delivered on T1 circuits and almost always cost more than a T1 because they MUST be terminated into a PRI capable switch on one end. This is usually done in the square red brick building with the funny looking bell symbol on the front.
T1's are made up of 24 64K timeslots. Things get can get confusing because different line codings can reduce those to 56K timeslots (DS0's).
Bandwidth can be delivered with T1 signalling as either full or fractional T1, which is more or less still a T1 in which the telco allows you to send data in Nx64K timeslots(channels) where N24, and pads the remaining channels with a pattern to maintain framing.
Frame-Relay service can be delivered via 56KDDS circuit, ISDN BRI in some places, Frac T1/T1, and Frac DS3/DS3 circuits. In all cases, you buy a circuit to the closest Frame-relay switch your provider has available. This is the access portion of the charge. Then you will also purchase a port on that Frame-relay switch.
Your access circuit must match your frame port so it is important to properly size this to allow for the maximum speed you want to be able to use. Most providers will allow you to "burst to port" speed, at least for a limited time, as long as the switch has bandwidth on the backplane.
You will also buy CIR, or Committed Information Rate, on your PVCs. This is the minimum guaranteed speed of your circuit. You can send traffic up to this speed as much and as long as you want and should see no ill effects; once you exceed CIR, your data will become eligible for discard by the frame network if it experiences congestion and you will need to rely on higher layer protocols to ensure data delivery.
DLCIs are more or less pointers that have meaning only between either a switch an a router, or two switches. DLCIs are used by the network devices to tag which traffic goes to what PVC, and may be different at each point in the network, even within the same PVC.
Hope this helps some-
Joe
Re:T vs. DS vs. OC vs. TDM (Score:3, Informative)
Let me see if I can expound a bit. There are actually two different digital hierarchies in this discussion.
The basic unit in North American TDM is the DS0, 8 bits of data at a constant 8 kHz rate for 64 kbps unless the carrier is using robbed bit signalling where 1 bit is used for in band signalling information and the remaining 7 are used for data at a 56 kbps rate. An entire DS1 can be used to carry non-voice data. In this case some control & signalling overhead is not needed and can be given to the user. Also there is fractional T1, where you rent 2 to 24 DS0s within a DS1 for data. Thus you buy nx64 bps of bandwidth (or nx56 if your provider is using robbed bit signalling).
Take 24 DS0s along with some additional bits for signalling, synchronization and maintenance and you get a DS1. The DS1 describes a particular arrangement of bits, it really comes in many variations. if this DS1 data is transmitted over 2 twisted pairs of wire with proscribed impedance, drive, and levels then this electrical representation of the DS1 data is called T1.
This was still too little bandwidth, so 28 DS0s were aggregated into a DS3, which is T3 when it's pumped over a pair of wires. There were also other attempts at aggregating data: DS2 is 4 DS1s and had some limited use as a means of transmitting digital video and DS4 contains 6 DS3s. Each of these conglomerations of data were independently conceived, so are quit different. Only the DS3 achieved widespread use and it is being superceded by the STS1.
Clumping more and more DS0s into a single glob meant that at each node you had to track each and every DS1. So the DS3's get torn apart into DS1s that then get grouped together in different compinations depending on their destination. New DS3s are formed to be sent out on T3s to various destinations. Of course, DS1s for subscribers local to this node get torn apart into DS0s and sent out (converted to analog as needed). Incoming DS0s get aggregated into DS1s, that get clumped into DS3s, that get sent out as T3s. Oh yea, smaller towns might just get T1s. So you have a mix of everything, and everything is different -- very confusing.
In an effort to make something better, the STSs & OCs, the SONET hierarchy, came about. The STS1 is a facility (an electrical method of transporting data, as a T1 or a T3 are). The STS is designed to contain tributaries of various size. there are Virtual Tributaries (VT) within the STS1 that are sized to contain various sizes of tributary within them. VTs have header information that helps the STS maintain time synchronization of the data contained within the VT. Furthermore you can aggregate VTs within VTGroups. A common way of carrying 28 DS1s within an STS1 is to put 7 VTGroups into the STS1, 4 VT1.5s into each VTGroup, and each VT1.5 can contain a DS1. If you transmit the bits of an STS1 optically then this is called an OC1. Confusing? The advantage is that as you grow the STS/OC larger you have a common interface to lower levels, the VTs act as wrappers around other conglomerations of data, and smaller STSs can be contained in larger STSs in a well defined manner. As the STS/OC hierarchy grows there's no need to invent new ways of packing the resultent bits. At the lower end, phone companies could just pipe their DS1s & DS3s into the STS1s. This allowed them to gradually add a mix of TDM & SONET, slowly growing into SONET with minimal disruption to service and gradual training of their workforce as they made the transition.
Now an STS3 is three times the size of an STS1. Three STS1s are contained within the STS3. Alternatively, if you're using the DS3 to just move a large amount of generic digital data, you can use an STS3c, c stands for concatenated. This eliminates some header information, and the huge field of data is left open for whatever you wish. A veru common use is ATM, which is a packet based data transfer system. unlike ip, it has a numer of different services available (e.g. CBR - constant bit rate, VBR - Variable Bit Rate) as well as Quality of Servis feature.
This is extended upwards, although for STSx & OCx there is no equipment available for most x. As you say, there is oc1 & oc3, but no oc2, then it skips to oc12. One reason is the desire to use common transmission equipment to carry both North American TDM, as well as European TDM which is based on 64 kbps E0s, of which 31 are grouped into an E1 (though 1 is usually used for signalling leaving 30 for voice) ... The European equivalent of SONET is SDH. Oh yes, Japan is slightly different. The have a slightly modified version of North Amaerican TDM, and their T1 is often called a J1 to differentiate it.
It does make sense in a historical perspective. Different carriers had different needs (rural carriers with few customers space wide apart vs. urban carriers with many customers close together). Various solutions came about, and then there was an attempt to fit all of these together into one method of transmission, since phone companies often use their equipment for decades. Nothing gets thrown away so new standards must be able to work with decades old standards.
How accurate do you want to test? (Score:2, Informative)
Telnet to your CPE router (Score:2, Informative)
This will show you info like your line quality, errors and the rate of the bits going accrss it. 9 out of 10 times your T1 will operate full capacity, the big question is what kind of network and peering does your provider has. Are they over subscribed?
IE. My cable modem can do 27 mbps, but RoadRunner doesn't have the capacity to handle that.
The peice of cooper that terminates at your site will almost always be the same wire that all the T-1 providers will provide. It's just depends which cage on the other side of the wire you hooked into.
zin
Re:Does it really matter? (Score:3, Informative)
Re:A Full T1 is ... (Score:5, Informative)
Ignore what you've seen in the news about GX, that's upper management bullshit. They still have a quality IP network with quality engineers. Overselling is a way to cut costs, but when you consider how much they paid for that network, it's still there, and it still has, for lack of a better term, a metric assload of capacity.
Incidentally, a good way to spot an oversold pop is to measure throughput and jitter from at least three to four hops out. This clears your pop and gets into backbone links. Another thing to keep an eye on is what those same 3-4 hop measurements do on days when the network is really sucking. Wild variations on your uplink or just beyond it are good indications of routers having a hard time handling network flaps, or are carrying saturated links.
Pay attention to your nearest backbone links. When you traceroute out, you'll see a handful of common pipes, all the time. Any given POP should have at least two egress paths, if not more for major metro areas.
Keep on eye on big media events, like the release of a Star Wars or LOTR trailer. Those days usually set records for network utilization, and are good days to eyeball performance.
Find a handful of hosts that sit just outside or on various peering points, and test to those. Get too far beyond the peers, and you start running into capacity issues on other networks. Test edge to edge, for what edges you know exist. Your ISP is only responsible for performance on their backbone.
Yes, I'm *that* billn.
Testing your T1 (Score:5, Informative)
What the competitors are telling you is that this particular provider has a DS3 circuit that has basically 45 Mb/s of throughput. In other words it can support 29.22 T1 users running at full throttle. In reality if you are using your full bandwidth then you are not!!! VERY IMPORTANT HERE!!! If your T1 is loaded then the routers on each end are dropping packets since they don't have very big buffers. This causes packets to be retransmitted, messages to be sent requesting TCP connections throttle down, timeouts, etc. Remeber that the real goal is how many WWW pages, email messages, FTP files, etc. that you can move. It is NOT how many bits per second you can send! If you are running at about 90% capacity then you can consider the line MAXED out. The same thing goes for your provider on his DS3 line.
If you throw in the burstyness of TCP/IP traffic your traffic really maxes out bouncing around somewhere between 65% and 90% of its max rated load. When you add in the fact that people like to have headroom and the size steps between T1 and T3 or partial T3 nobody uses their max bandwidth all of the time. This is something that your provider uses to his advantage by selling more than 29.22 T1's. In reality that provider may have 1000 dial up customers, many more DSL customers, people with dedicated 56K connections, and maybe even some old ISDN connections on top of the other T1's that he has sold. It is fairly safe for a provider to oversell a connection somewhere between 5x and 20x. Especially if you consider that people that have DSL's usually leave them on but don't use them for that many hours in the day. Headroom is defined as being prepared for the slashdot effect!
You need to figure out if your provider speciallizes in retail (home) customers or business customers. If it is home customers then his load will spike in the evening when poeple get home from work and on the weekend. If it is business customers then his load will spike during business hours. Also consider if your provider is hosting very much traffic beyond home users personal WWW pages. If he is then that is bandwidth that is not available to resell.
The only real way to tell is to look at your provider's router logs. Don't just look at averages for a day! Look at averages generated at least every hour over the course of at least a week so you can see when his network (which you will be a part of) loads up. If he consistantly stays below 80% of his upstream bandwidth and will upgrade his upstream connection if it passes that then you are fairly safe. On the other hand if he routinely pushes his max then that is exactly what his competitors are warning you about! If he loads up then everyone downstream from him will slow down as that will become the bottleneck.
Another thing to consider is that it sounds like he has a single DS3 upstream connection. Ask him if that is true and if he has any plans to become multi-homed. This has two major advantages over a single fat pipe: redundancy and load balancing. If he connects to two or more of the backbone providers then the traffic can most likely pick the shortest route to its destination while still having the other one available if one of the DS3 lines goes down. I'm sure the people @ /. have more than one connection if they are served from their business. It is more likely that they are hosted by a large hosting company that is already multi-homed though. A final thing to ask is if this provider does any traffic shaping. This can throttle users that are consuming more than their fair share. But if you are paying for a T1 you should get all of it. Sometimes though a customer will have a partial T1 (this requires a full T1 connection from their site to the provider though) and get to use any excess if it is available.
This is what I used to do for a living so I know a little bit about what I'm talking about! Once again his logs can tell you if he has oversold his service as his competitors suggest. But put some value on a provider that has more than one connection to the upstream Internet regardless of how large their single pipe is. If you want to have some fun ask him how much an OC196 would cost. 8-)
Regards, Tres