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How to Test Your T1?

Posted by Cliff on from the ensuring-your-bandwidth-pipe-works-as-advertised dept.

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!"

3 of 453 comments (clear)

  1. Not sure I understand your question...do you? by dillon_rinker · · Score: 5, Interesting

    Cytlid has a good point - you get a T-1 from the phone company (or a reseller/CLEC) and it either IS a T-1 or it IS NOT.

    I suspect that you're asking how you can tell whether or not your ISP is selling 50 million T-1 lines when he himself only has a T-3 connection with the rest of the world.

    I think the simplest way is to ask. Talk to the sales engineers who work for the larger guys - tell them "Ok, you're trying to scare me away from a smaller vendor...how can I prove for myself how he's configured?" Ask the small guy "This looks like a really good deal...can you demonstrate to me I'll get X level of performance?"

  2. 3 letters by Khan · · Score: 5, Interesting

    S.L.A. (Service Level Agreement)
    If said small provider is telling the truth, then he won't have a problem signing one. I've found in my area that the big guys are the bullshiters when it comes to SLA's.

    --

    "Klaatu, verada, necktie!" -Ash

  3. Re:A Full T1 is ... by Harik · · Score: 5, Interesting
    T1's are sub-1k these days. And if you think any ISP isn't over subscribing their uplink(s), you are a certified idiot. Every ISP over subscribes their bandwidth -- by very large margins in far too many cases. That's the only way to make any money... sell people something they don't need and will never use.

    BZZT. Remind me to never buy any bandwidth from you.
    Kids, this is what happens when you save a few bucks. You go with tier-19523 providers who are selling T1's off a SDSL circuit from a guy who splits colo space with a cleaning buisness.

    From REAL ISPs (AT&T, Sprint, UUnet, etc) the story is quite a bit different. They DO oversubscribe to an extent, but to where? You and 500 other T1 customers go into a POP (Either on a frame cloud or through a bigass MUX) Coming out of that is at-minimum 3-4 OS3 links (155meg each) High-traffic nodes frequently run OC-12 or OC-48.

    Now, if you all try to get to a single site, not only would the remote site not be able to handle the bandwidth but quite possibly you'd flood out the backbone links between you and them.

    By the same token, however, all the OTHER backbone links would be unused.

    So yes, you can say "I'm oversold", but you'd be wrong. Let's go into a true oversubscription example now:

    Billy the Janitor decides he wants to be an ISP. So, after gunning down some of the druglords in his neighborhood, he gets a DS-3 (45 meg) into his hovel.

    Finding that he can wire every other crackhouse in the neighborhood cheap since he knows people in the local telco monopoly, he starts selling "full T1s" for $400 a month. Wow, what a deal!

    And they are "Full T1s", too... for the first 30 or so customers. After that, billy starts to oversubscribe. And, at $400/month, he sells HUNDREDS of T1s. Say, 200.

    Now we have 300meg coming out of a router with 45 meg going in. Mmm, bottleneck. See how this is different from a multihomed POP in the case above?

    Some real numbers:
    Today sprint Peaked at 1523/1503 kb/s (in/out)
    UUnet peaked at 1510/1508 (Delivered over frame, slightly lower peak bandwidth)
    A frac T3 frame to bell only got 3313/3412 today, but it's pretty lightly loaded. I've done 5.5meg on it (and it's sold as a 4.5 meg CIR carried on a 6meg pipe)

    The REAL answer is: Are you going to use the bandwidth, and if so, is it worth the premium it costs to get a tier-1 provider.

    If you're just using corperate websurfing/email, HELL NO: buy the cheap one in a heartbeat. If you're reselling yourself, don't even THINK about doing anything BUT tier-1.

    And don't forget latency. As the famous paper was titled: "It's the latency, stupid." You'd be amazed what a 10ms pingtime does for your effective bandwidth.

    (Before I get flamed, I know bellsouth is technically tier-2. Especially since the twits don't know the difference between peer and transit BGP setups. YAY unreachability. They're working on it)