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Sixty times faster than a T1!

Discussion in 'Fred's House of Pancakes' started by daniel, Sep 15, 2009.

  1. daniel

    daniel Cat Lovers Against the Bomb

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    Comcast launches 100 Mbps service

    But it's only for businesses in one area, and costs $370 per month. :eek:

    What surprises me about the above quote is the statement that a T1 line is only 1.5 Mbps. I'm getting around 28 Mbps with the cheapest internet Comcast offers.
     
  2. Dan-Wolfe

    Dan-Wolfe Member

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    T-1, also known as DS-1, I believe has a speed of 1.544 Mbps. It was originally designed to carry 24 voice calls. This standard has been around for ages.

    I suspect that T1 appears faster because unlike cable and DSL, it's not shared.
     
  3. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    ...but not sixty times as available/reliable, and not sixty times less oversold, and I'd wager doesn't come with an SLA.
     
  4. jayman

    jayman Senior Member

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    T1 has been around for decades, and is consistently fast as, noted above, you are not sharing. T1 was originally conceived in the late 1950's for voice only.

    The T1 has 23 voiceband channels with an out-of-band used for signaling, now 24 channels with "robbed bit" signaling. It originally used PCM and TDMA. Every individual DS0 in a T1 is coded at 64 kbps, with 8 kbps allocated for signaling or framing out of band.

    Or, put another way, each T1 frame is 193 bits: 24 channels, 8 bits per channel, 1 frame bit = 193

    To prevent a string of zeros from latching up the frame being sent, coding with AMI or B8ZS. There are also T2, T3, etc, which are all but obsolete with the advent of fiber optic communications

    With fiber optics, an OC-1 is around 51 Mbps, contrasted to T1 1.544 Mbps. An OC-3 is around 155 Mbps. OC-192 is fairly common now (Around 10,000 Mbps) and OC-768 is up and running (Around 40,000 Mbps)

    If anybody would like me to go into the more obscure parts of T1 framing, error detection and correction, or SONET stuff like BLSR and VTBM with VT mappers, please let me know
     
  5. jayman

    jayman Senior Member

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    If you're referring to the old T1 service, yes, it DID come with a SLA, uptime was kept very strict, usually three 9's or better

    The T1's couldn't be oversold because they couldn't be shared. But historically, only the largest businesses and/or government could afford them, as T1's could cost as much as $3,000 a month

    Modern fiber optic communications are definitely shared. But the equipment is so reliable, and the speeds so fast, to us it appears reliable. You can also get SLA's with business and corporate/government fiber optics, but probably not for consumer use
     
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  6. daniel

    daniel Cat Lovers Against the Bomb

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    I understand none of the above replies to my post.

    I used to think, when someone said they had a T1, that it was many times faster than we common folks had. But if it's only 1.5 Mbps and my bottom-of-the-list Comcast service is 28 Mbps, well, I feel sorry for those poor unfortunate folks with a T1. :D
     
  7. SageBrush

    SageBrush Senior Member

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    Shared fibre-optic in my 'hood though Qwest has marketing tiers from 6 - 20 Mbps downstream, and 1.2 Mbps up upstream. I tend to jump back and forth between Qwest and Comcast cable to take advantage of promotions. Surprising at least to me, Qwest has been the (much) more reliable ISP.
     
  8. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    Until you have a service outage that costs you money like a business with a T-1/3/whatever. And before you say "well I haven't ever had an outage" - just because you haven't had one does not mean it will not happen. A turkey fed everyday by it's keepers has no expectation of Thanksgiving day either, never having experienced it (credit to Nicholas Nassim Taleb for that example).
     
  9. jayman

    jayman Senior Member

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    Again, a T1 had an SLA so you absolutely got that speed. Figure 10-15 years ago, it was much faster than anything else. But you sure paid for it

    With consumer offerings promising "up to" 28 Mbps, or even 100 Mbps, you have to read the Agreement. The magic phrase is "up to"

    Whether a nation-wide ISP (Eg, Shaw Cable here in Canada, or Bell Canada) or a mom-n-pop, service problems can and all too frequently DO occur. I sure wouldn't trust a life-critical item to an ISP

    I find Internet technology fascinating. Historically, it evolved from a purely military communications requirement to have a robust backbone that would not only reliably communicate incoming radar tracks to regional SAGE command centers, and on to NORAD, but to also keep working in a thermonuclear environment

    Billions of taxpayer dollars were shoveled into developing the system, and at first the hardware was exotically expensive. For example, the first Interface Message Processor was built by BBN (Bolt, Beranek, and Newman) and used a military version of the Honeywell DDP-516. The original cost was millions per unit

    Similar hardware now costs around $350

    I doubt the original ARPANet would have functioned in a thermonuclear weapons environment as originally envisioned. The effects of high altitude EMP were poorly understood back then. Most likely, the entire network would have latched up

    But, it sure is amazing how we went from a critical military network, to Internet porn on demand.
     
  10. daniel

    daniel Cat Lovers Against the Bomb

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    Comcast tells me I have 12 Mbps download speed. I don't remember what they say my upload speed is supposed to be. Speedtest.net tells me I actually have 28 down and 8 up. Better than double what Comcast promises me.

    There are service outages. But not very often. In Fargo, the office I worked in had DSL from Qwest, and the office had outages more often than I do with Comcast.
     
  11. SageBrush

    SageBrush Senior Member

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    I'm skeptical. Try another speed test, and be sure of the measurement units.
     
  12. RobH

    RobH Senior Member

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    I worked with a programming group that used host # 8 of the Arpanet. Network addresses were 8 bits, with no name lookup service. Actually, 8 bits overstates it, as it was actually 6 bits of IMP address, and the remaining 2 bits the host number on that IMP. The network backbone ran at the incredible speed of 64Kb.

    TIPs (an IMP that connected to computer terminals) supported about 10 users, typically at 0.110Kb. The first upgrade was to 0.300 Kb, and I think they even went to 1.2 Kb (not sure about that one - maybe it was just the IBM computer that was upgraded to 1.2 Kb per terminal). One of the arguments against squandering bandwidth of 1.2 KB on a terminal was that no one could read that fast.

    We had both the ruggedized IMP and an ordinary DDP-516. As I recall, the ruggedized version had its core memory set in epoxy to help survive a bomb blast. The initial testing of the core memory set in epoxy didn't work, as the epoxy held the core memories so tight that the bits couldn't change. The solution was to cycle the memory as the epoxy was setting. That left enough wiggle room for the cores to flip state.

    Then there were the 3" diameter eyehooks on the top (and bottom?) of the IMP. They were there so that the IMP could be mounted on springs to help survive that bomb. Ours just sat on the floor like the rest of the equipment, but it still had the eyehooks.

    Our IMP was connected to an IBM computer that was used part time in secure computing. When secret data was being used on the computer, anyone not on the approved list was prohibited from crossing the white line marking the perimeter of the computer. It got to be such a hassle that the IMP was finally moved to a non-secure lab on the next floor. It made the security types so much happier that the geeks were finally excluded from access to the secure computer. Apparently nobody ever explained to them that that computer was connected to the IMP, and thus to the rest of the Arpanet.
     
  13. apriusfan

    apriusfan New Member

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    How is DSL 'shared'?
     
  14. daniel

    daniel Cat Lovers Against the Bomb

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    Interesting!

    Speedtest.net connected to Liberty Lake (a stone's throw from here: I can drive my little Xebra there and back several times without recharging if I want to) gives 29.69 Mbps and 8.48 Mbps; connected to Seattle it gives 31 and 3.61. A friend of mine nearby gets similar results.

    Speakeasy.net gives 3125 Kbps and 6766 Kbps respectively the first time I tried, but 15 minutes later it gave 30515 Kbps and 2331 Kbps.

    Auditmypc claims to have the "most accurate" test, and offers two different kinds, and I got two very different results: 14.75 and 10.19 Mbps for one test, and 3672 and 4375 Kbps on the other test, which is pretty extreme difference for two versions of "the most accurate" speed test.

    I recently switched from a very old modem to a new one, and I can tell that my speeds are much faster than they were.
     
  15. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    There are a *lot* of DSL lines hooked up to the CO (central office) DSLAM (DSL access multiplier). So there might be 500 1Mb/sec lines connected to a 10Mbps pipe.
     
  16. apriusfan

    apriusfan New Member

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    You may be seeing the impact of sharing of the cable connection with the different speed results. An objective network bandwidth availability analysis would cost $ that could be better spent elsewhere.
     
  17. apriusfan

    apriusfan New Member

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    According to that definition, a T-1 connection is 'shared' as well. The typical definition of shared vs. dedicated is from the Central Office to the end user termination point. Cable bandwidth is truly shared between all of the users on the sublink. Get a group that are down or uploading files (like Youtube videos) at the same time and the response time goes into the toilet. With DSL and T-n, the only way your response time drops off (barring line failure between the CO and the termination point) is if the connection between the Central Office and the rest of the web tanks.
     
  18. jayman

    jayman Senior Member

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    I've had cable service in other areas, with rapid growth, and initially the speed was quite good. But they couldn't keep up with rapid growth and subscriber signups, and then the speed and connection quality really tanked

    Correct, the military version of the DDP516 was designed to handle extreme shock loading, eg a nearby bomb blast. I now highly doubt it would have resisted the EMP and the entire network would have latched up

    If I recall, the eyebolts were for lifting the thing, and the skid at the base had slots for a forklift truck or a handtruck. I've seen a couple mounted on springs, but the usual approach by the late 1970's was to have a "floating" room for the equipment

    It was easier and more reliable to design the floating room, as it offered consistent performance

    I had an old Terayon cable modem. When Shaw upgraded me to a newer Motorola SB5102, my download speeds easily tripled. Motorola claims this cable modem supports 30 Mbps download speeds, and is DOCSIS 2 compliant

    Correct. Typically the line drawers BIC/DBIC's have to be properly engineered to account for customer DSL use. You can use add-on DSL, the so-called "pizza box" upgrade, but the quality is far more iffy

    True that DSL is more consistent but spikes in Internet use can still cause problems, especially if poor attention is paid to how DSL subscribers are assigned in line drawers
     
  19. hobbit

    hobbit Senior Member

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    Back when I was doing a little telecom/pbx maint, we had a couple
    of T1s hung off the main pbx -- one with a microwave shot to
    another office, and one upstream to the telco. It was fun to
    hang a scope off it, get the timing stable, and actually see
    the 24 little slots in the whole frame. I could tell which
    channels were active or not, and in many cases could "see" people
    talking as the little block of bits changed. And even seize a
    particular trunk for an outgoing call and watch my own "test! test!"
    bursts show up.
    .
    _H*
     
  20. jayman

    jayman Senior Member

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    Of course, you never ever purposely busied out any particular channels to annoy people

    I am a bad man