On Jan 26, 2012, at 4:59 PM, John R Pierce wrote: > On 01/26/12 3:43 PM, Gordon Messmer wrote: >> Yes, the cost for a T1 will seem very high. It is antiquated telco >> tech. T1s are generally very reliable, but very very slow. >> >> 1.5Mbps is not faster than 40Mbps. There's nothing hidden in the way >> they advertise speeds. >> >> DSL and DOCSIS technologies have advanced and matured over the last >> couple of decades. T1 has not. A T1 connection is the same now as it >> has always been. > > a modern T1 (aka DS0) is likely delivered to the end premises over HDSL > using 2 pairs. while its slower than those consumer oriented > technologies you mention, its far more reliable and has a guaranteed SLA > (service level agreement) you won't get from DOCsis (cable) or end user > ADSL, and tends to have very deterministic latencies...
Wow, that's just ... wrong. There's nothing to "mature" in a T1. It's a telco transport standard that is well-known, and utilized everywhere as part of the Bell System standards for multiplexing and demultiplexing from smaller circuits to larger and back down. Ratified by the ITU for decades. "T1" is a channelized synchronous telecommunications circuit type first designed in the late 60s, updated in the 70s. After removing framing bits, 1.544 Mb/s. "DS0" is a sub-channel of a T1 when broken up into frames. Extended SuperFrame being the typical method these days. 24 of them at 64K per channel. "HDSL" is a completely different technology than T1. "DOCSIS" is the name of the standard utilized to deliver data services over a Cable Modem. "ADSL" is a single-pair high speed connection that's very distance limited from the origination point. "SLA" is a Service Level AGREEMENT. The key word being AGREEMENT. Your businesspeople are free to negotiate with any provider of ANY of the above technologies for anything they're willing to pay for. TYPICAL SLA's might be as stated above, but it's a contract... negotiate whatever you like. What you might want SLA's on when ordering IP bandwidth: - Maximum CONTINUOUS data rate upstream AND downstream simultaneously, and what thresholds are considered an OUTAGE on the SLA even if traffic is still flowing. - Latency from your end of the circuit to a known point will never EXCEED "X" amount or it will be considered an outage under your SLA. - Whether or not an UPSTREAM routing outage will be considered an SLA OUTAGE by your local carrier/ISP in terms of your bill. (In other words, how many backbone connections do they have and can they route around a problem, or are you stuck waiting for their one piddly edge router to be fixed in the case of fly-by-night providers.) - In the case of a cable cut, are trucks rolled 24/7, or only during business hours? Etc etc etc... there's more. Read up. SLA's are themselves a playground for lawyers and businesspeople to dicker over. Now the real world: - Any company relying on a single IP connection via a single route... is so far down the food chain they're not going to get service during a larger scale outage anyway. And... remember... - An SLA just gives you a refund of your money for the outage. It doesn't keep you in business if the service provider doesn't keep their side of the bargain. - If you have something that must be connected to the Internet 24/7 or you're out of business... buy more than one connection. An SLA won't matter at all when the backhoe cuts the only path out of your building. - Or... host it in a data center that has far more than one backbone connection via more than one physical route. Let's not mix all the technical details up with the business ones. That posting was the most misleading post I've read in quite a while, and shows a lot of the misconceptions out there. *** ANY of the above technologies can deliver a certain number of bits, at a certain latency, a certain direction, across a certain type of physical media, to some network at the other end. *** Whether that upstream provider has oversubscribed upstream connectivity, has latency issues, doesn't respond to fix their circuits in the middle of the night, pays you back for outages, scratches your back at the beach after signing that multi-million dollar bandwidth contract with giant SLA attached large enough to fund their entire fleet of trucks for a year... That's all up to the contract... _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
