Sixty times faster than a T1!

[daniel]

Comcast launches 100 Mbps service

The high-speed service uses Comcast's DOCSIS 3.0 technology, also called wideband. The company estimates that the 100 Mbps download speeds (15 Mbps upload speeds) would let businesses download a large 2 GB file in about 2 ½ minutes compared to the more than 3 hours it would take on a typical business class 1.5 Mbps T1 line.

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

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.

[Dan-Wolfe]

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.

[a_gray_prius]

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

[jayman]

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

[jayman]

Originally Posted by a_gray_prius

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

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

[daniel]

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.

[SageBrush]

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.

[a_gray_prius]

Originally Posted by daniel

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.

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).

[jayman]

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.

[daniel]

Originally Posted by jayman

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

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.