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student25

join:2011-01-14
Charlotte, NC

Clarifications about T1 connection...

Hello Forum,

a T1 broadband connection is a digital, TDM type connection with high Qos.
T1 can be supported over different types of physical layer: we can have a T1 over copper wires, coaxial cable, correct?

Is the T1 techonology specifically electrical or can it also be optical? Can we have T1 over fiber optics or wireless?

The TDM is based on 125 um frames. When 4 T1 are combined (aggregated) via a multiplexer they become a single T2 with a speed of 6312 kbps. The T2 frames must be much shorter in time duration, correct?

Thanks
Student25


tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
Reviews:
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The term T-1 has been much abused. Officially it refers to digital transmission over a copper circuit. Over time it has morphed to mean any 1.544 Mbps full duplex circuit.

Originally T-1 required two copper pairs, one in each direction. Modern T-1 uses similar technology as DSL delivering T-1 service over a single pair.

You are correct, as you move up the digital hierarchy the time it takes to transmit a bit goes down.

Here is chart showing the telecom digital signaling hierarchy compared to Ethernet.
»www.tschmidt.com/writings/Broadb···24054247

/tom

student25

join:2011-01-14
Charlotte, NC
Thanks Tom.
Your replies are very clear. Just to continues on this telecom topic: cable companies started by offering TV over coxaxial cable and now they offer internet connection too.

I guess TV was offered over satellite and copper at the very beginning, correct?

In the DSL case the user (CPE) with its copper wires is connected to the closest local central office. The traffic is then moved to other trunks.
In the case of cable service, how is the cable company organized for its internet traffic? Do the coaxial cables connect to a local central office too? What about the TV service and traffic? Does it travel over the internet too?

Coaxial is surely better than copper wire for broadband....

With all these new bandwidth hungry applications, like HD TV, etc... , do you think cable service (trasmission of TV and data traffic over coaxial cable) will become obsolete and cable companies will go out of business? Or will they switch to fiber and still be called "cable companies"?

Thanks
student25

student25

join:2011-01-14
Charlotte, NC
reply to student25
Tom,

great website! I guess it contains some of the answers to my questions already...

student25


tschmidt
Premium,MVM
join:2000-11-12
Milford, NH
kudos:9
Reviews:
·G4 Communications
·Fairpoint Commun..
·Hollis Hosting
reply to student25
said by student25:

I guess TV was offered over satellite and copper at the very beginning, correct?

TV began as over the air (OTA) transmission. Cable TV originally called Community Access TV (CATV) began in the late 1940's early 1950s in mountainous areas where TV reception was poor.

The first satellite TV transmission was Bell Labs Telstar in the 1960's in low earth orbit. Today TV satellites are in geosynchronous orbit, called the Clarke orbit after Arthur C. Clarke the science fiction author that first proposed the notion.

said by student25:

Coaxial is surely better than copper wire for broadband.

Coaxial cable is copper. The real difference is between fiber optics and copper. The telephone and cable industry layered Internet access on networks designed for other purposes. There are pros and cons with each approach. The ideal solution is a network designed from the start for digital data.

In general cable offers higher speed. But all customers on a node share that bandwidth. Reducing node size is relativity expensive. Upload capacity is at a premium in Cable.

DSL is distance limited. The longer the distance the slower the speed. Maximum DSL distance is about 18,000 feet. Reducing circuit length requires building remote terminals to move the DSLAM closer to the customer.

said by student25:

With all these new bandwidth hungry applications, like HD TV, etc... , do you think cable service (trasmission of TV and data traffic over coaxial cable) will become obsolete and cable companies will go out of business? Or will they switch to fiber and still be called "cable companies"?

This is both a technical and business issue. With enough bandwidth there is no longer a need to have traditional Cable company. By that I mean a company that performs two roles: content aggregator and first-mile access. Broadcast transmission is very bandwidth efficient. But it means one program is sent to all customers at the same time. Demand based viewing is much more demanding as each customer will be viewing the content of their choice at whatever time they chose.

It is very difficult for companies to adapt to massive technology change. They are very good at what they do, know how to do it better, and have tremendous resources invested in the status quo. At the same time first-mile Internet access is a natural monopoly. It is extremely capital intensive so the barriers to entry are high and profitability is low discouraging multiple players from entering the market.

My personal preference is that first mile Internet access be treated similarly to electric power distribution, as regulated monopoly. Physical infrastructure will be a wholesale network so a myriad of ISPs can compete to offer value add services.

Glad you found the web article useful.

/tom
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