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What is a T1 Line?

By R. Kayne
Updated May 16, 2024
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A T1 line refers to a specific type of copper or fiber optic telephone line that can carry more data than traditional telephone lines. The T-carrier line, as it is sometimes called, was developed by AT&T Bell Labs for North America and Japan.

Twisted copper telephone lines have been the standard for decades, transmitting voice and data via analog signals. Today that standard is slowly being upgraded to fiber optic lines, (lines made of bundled glass fibers), but most T1 lines are still made of twisted copper. The T1 line creates a "pipe" capable of blowing through larger datastreams.

While standard telephone lines can transfer data and voice at a rate of about 30,000 bits per second (30 kbps) using a dial-up modem, a T1 line can transmit 1.544 megabits per second, or can be used to transmit 24 digitized voice channels. Hence it can be used for phone service in a commercial building, for instance, or for data transfer on a network, providing service up to 60 times faster than a traditional modem. Businesses with more than 8 phone lines may save money by getting a dedicated T1 line to loop to the place of business from the local phone company office. This can reduce telecom charges and provide high-speed Internet access at the same time. The business is charged for one T1 line, rather than eight (or more) separate telephone lines. Pricing for the T1 line will depend on the distance of the loop, or the mileage between the telcom and the place of business.

The cost of a T1 line can be expensive, but prices are dropping as demand grows. Internet service providers (ISPs) will lease T1 lines to provide service to their network of clients. Other multiplexed fiber optic lines include T2 and T3 lines, which can transfer up to 44.736 megabits per second. A T3 line is equal to having 28 T1 lines, and is used by larger businesses with higher data and voice demands. More advanced T-standards also exist, though are not in high use.

The European Union uses a different, incompatible type of carrier line, called the E1 and E3. The E2 line is also available but less common.

Generally speaking, a T1 line is not cost-effective for individual or residential use. In this case DSL or cable service is a better choice. Small businesses and government agencies — particularly those using a PBX — will benefit most from a dedicated T1 line.

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Discussion Comments
By anon958961 — On Jun 30, 2014

The problem with internet is your government, not your phone company. But don't worry the government is coming to help. You wonder why a T1 is so expensive. Ask a congressman. The FCC and the PUC of each state sets the price.

All of the old Ma Bell companies are regulated and can not change there prices on any traditional phone lines. Pots, ISDN, T1, T3. This all Tech from the 50's stagnate do to the taxes and fees placed on them by the fed, state and local gov. Everyone of them get there share. Ma Bell invented the computer, linx, uinx, the transistor, the deep space network that put men on the moon, The satellite, co-axial cable, Twisted pair. cat 1-6, 8 Nobel prizes and you think They can't write a phone bill you can understand? They can't because your government won't let them! What do you think they are going to do with the web? Net Neutrality is going to be Net TAX-yum.

By anon350569 — On Oct 06, 2013

@anon9403 a cat has a theoretical maximum speed of 100 Mbps so in theory, 1 cat5 cable (not the cat5e or cat6) can carry 98.5 T1 lines.

By anon333057 — On May 02, 2013

Why are copper phones being phased out if they are more reliable in storms than fiber optic?

By anon272864 — On Jun 04, 2012

A T1 is reliable, however it is not cheap. 1.544 Mbps both ways vs. a 12Mbps or ever 112Mbps you can get from cable, even if it is async. Normally when I download a file from the internet I can get a 4 MB mp3 on a 8Mbps cable in four seconds. That would take 24 secs on a T1, assuming I can use the entire data stream. On a 768kbps standard dial up which a lot of T1s are segmented into that would be 576 seconds for a 4MB download. Waiting 10 minutes for an MP3? No way!

For comparison, one Cat5 cable can carry over 650 T1 lines worth of data, even only over about 100 yards.

A T1 is great for low bandwidth mission critical data for business, but for surfing the web, or videos or anything else, it's not really an option.

By bill2810mt — On Jul 06, 2011

I am in a location that does not have DSL or cable. The option my family has been using has been satellite internet. It is slow and has limited capacity.

Recently, I've toyed with getting a T1 line which would allow me to get rid of my Qwest phone line and my Internet satellite internet. Overall, the cost will be a bit more. I'm even wondering about getting rid of satellite TV. What am I missing in my logic and my approach. Are there any other ideas or solutions I'm missing? Thanks.

By anon191896 — On Jun 29, 2011

'T1 obsolete.' That's interesting, since most DSL service runs over bundled T1s or T3s prior to hitting the neighborhood loops. Anyway, T1s are becoming less attractive in areas that offer direct ethernet solutions. However, ethernet is more limited by distance than T1 and thus not as widely available. (DSL is also more limited by distance than a T1 - but my argument is that DSL/cable is not for the same application and for the med to ent level organization, should never be considered for more than maybe a failover scenario). T1 and DSL or cable don't really compete. A home user wouldn't have much use for a T1 line, even though they have gotten much cheaper they don't typically have enough value for a home user, but they do for businesses, especially medium size companies and up.

First, if a company has multiple voice lines (more than five) and hasn't made the move to VOIP, then a T1 is much more affordable than SBLs and will make a lot more sense for hooking up a PBX. Also with dynamic T1 or PRI, you can have the line be used for both voice and data, so you have 1.5 mbs/1.5 mbs of data and if someone in the organization makes a phone call, you lose a small portion of that for handling the voice traffic. (Or like in my case where our organization has an ethernet connection, we have a dynamic T1 for our PBX that is also connected to the firewall for failover if the ethernet went down.) Note: we have up to 10 lines of voice on a digital PBX system, and T1 is the cheapest way to go unless we switch to VOIP and that has a lot of hardware cost, so having the T1 as a data failover is virtually free. Is DSL free?

Also, even if looking strictly at data use, the speed down/up is not the only measurement or consideration, which is just as important for networks supporting many users is ping response speed and jitter, packet loss, up time, consistency of speed and what I refer to a 'stickiness'. The telecom companies are federally mandated to repair T1 service prior to repairing phone or dsl, and their up time, response time and guarantees are much better on a T1 service (compared to DSL, and cable service is even worse). In organizations, you often have multiple users (hundreds for some) sharing your WAN connections, the initial connection (the response speed you see on a ping test) is independent from the overall line speed, and is slower on DSL and cable lines than a T1.

Jitter is how much the initial response speed varies, which also causes slow down in the communication between locations, routers, switches, NICs, etc., all of which like consistency when 'talking'. Failure rate which can be as high as 2-3 percent on a DSL line (sometimes do to jitter) and even higher on cable is also a problem -- when a packet fails the whole packet has to be resent.

T1's have less than 1 percent failure rates on each packet. And then there is 'stickiness.' This is the term I use to describe how a DSL or cable line tends to allocate and hold on to more bandwidth than it needs - so if user X starts to download a file he may grade all 5 mbs of your DSL bandwidth for the download even though the file isn't even coming down that fast, meanwhile user Y requests something from the internet and that DSL connection seems like it is practically down or crawling for him.

Also, after user X gets his file the DSL/cable line may hold that bandwidth for a second or two before deciding to allow it to be allocated elsewhere. T1s are much better at channelizing the data stream and sharing it among multiple sessions even mid-stream. Now that might not sound like much if you (or even two or three people) are the only ones using the connection, but in an organization with 10, 20, 50, 100, etc. users, these things start to have a lot more impact than the speed of the connection, especially in the typical business use of the internet, where instead of having one user trying to download a video, you have a lot of users just following links or working on a hosted database or sending email etc., this works both ways too. If you are hosting a website or email server, or have remote users accessing your network, etc., having the consistent upload spread and channelization of a T1 will often out perform a much 'faster' DSL line. (It is similar to a copier's print speed versus its first print speed. If your copier can run 100 copies per minute once it gets going but takes 15 seconds for the first print - that might be great for the person/organization who runs nothing but large jobs, but for the organization that has lot of users just needing one or two copies all through out the day - that copier sucks). Just my $.02, but don't knock the T1 unless you actually know the application it is getting implemented for. Otherwise you might sound a bit ignorant.

By anon186987 — On Jun 16, 2011

In the US, most cable companies can provide 50 Mbps down and 5 Mbps up. I get this in my house for around $45 per month. So, it may be asynchronous speed, but its still faster. Only DSL lite has slower upload speeds than a T1.

If you get a PepLink router you can bond a DSL and a Cable connection together for extra speed and reliability and still be cheaper than a T1.

By anon149596 — On Feb 04, 2011

T1 is obsolete in areas served by broadband fiber and cable.

By anon145023 — On Jan 21, 2011

A T1 is generally 'guaranteed' 1.5 megabits in both directions. DSL is much slower in the direction toward the internet. If you are running a web server or email server your users may suffer on DSL, although some new DSL lines near the phone company office are faster than T1 on the upload.

Phone companies detect and fix a broken T1 connection quickly, often within 30 minutes, DSL is fixed after all the T1s, in maybe one or two days. My experience is DSLs cut off for an hour or so on Sunday nights and other times for service and reconfiguration.

My T1 never stops. It goes 24/7. Also, 99.9 percent of T1s are two copper pairs of wires. T1s can affect DSL lines on the same cable, never the other way around.

A T1 copper pair is tested for digital use before installation by the phone company. They typically pick the best pairs in the cable and disconnect bridged circuits (split-offs to multiple houses) at the customer end. DSL just gets hooked up, often by the customer, and you get what you get. You mostly have to sign up for two years without any guarantee of what the final speed will be.

By anon134822 — On Dec 16, 2010

RE: "T1 is typically fiber optic." Since when? (I install T1's).

By anon118196 — On Oct 13, 2010

T1 is still being used at the business level. Those rates you get with u-verse are not as stable and the upstreams and are usually a lot slower. Good luck.

By anon75161 — On Apr 05, 2010

t1 service can run over both copper and fiber optic cable. they can come in a 2 wire or 4 wire feed to the premises, if on copper they to have a signal repeater every 6k to 10k feet to keep signal strength up. they are monitored by your provider 24/7 to make sure loop is up at all times. ask your local cable comp. if their service is that good.

By anon72924 — On Mar 24, 2010

While it is certainly has been around for a while, T-1 is still very common in the existing installations. While it was originally designed to serve as a link between different telephone switches in central offices it has remained as a reliable means of sending signals over 4-wire circuits. Mainly copper. And it does not require cat5 cable. Or fiber. Voice grade lines (cat3) is all that is necessary.

By anon64817 — On Feb 09, 2010

Can a T1 line be transmitted by radio signal?

By anon62921 — On Jan 29, 2010

I believe that T1 is kind of extinct. When you have AT&T dropping U-verse, for Version FIOS offering 15MB symmetrical connections. t1 is kind of a joke.

By anon62769 — On Jan 28, 2010

T1 is not the broadband communication of the future. EOC will surpass it

By anon62492 — On Jan 26, 2010

Many, many carriers offer voice and/or data T1 service these days, so it definitely pays to shop around for the best rate.

By anon55309 — On Dec 06, 2009

The USA standard 1.544 mbps, allows for (usually) up to 24 voice grade channels of 64 kbps each. Depending upon your configuration, if data is "Shared", it will use 768 kbps, or 12 of the possible 24 channels, using a "sub-rate data card"

Usually they will share in groups of 4, IE: 256, 512, etc.

T-1 can be delivered to denmark via copper UTP or fiber. Fiber is becoming more common, and only requires a small "transceiver:, data in, light wave out.

By anon54720 — On Dec 02, 2009

T1 use 4 wire (2 pairs): one for transmit and the other one for receiver.

By dekelley1 — On Oct 08, 2009

Is this just a regular T1 or a PRI circuit?

By anon47954 — On Oct 08, 2009

A Cat 5 will carry 2 T1's as a T1 only needs 2 pairs. Because the voltage is the same there should be no issues. I.e., many times when a EU has DSL and installs a T1, they will complain about poor signal on the DSL. That's because the T1 circuit was installed too close to the DSL circuit.

By anon35066 — On Jul 02, 2009

For distance, there's no limit, but you will need a repeater for every 6K feet.

By anon33832 — On Jun 12, 2009

What's the standard distance for T1 cable?

By vincejr — On May 26, 2009

What is a T1 cable made of? Is it 4#18 or what? Please explain?!

By senton — On Apr 07, 2009

I work in a facility that has a T1 carrier for voice and data. What are the pros and cons for trading in a T1 for cable? Is a cable (broadband) faster for both data and voice?

By anon17443 — On Aug 29, 2008

We are going to put a T1 in our office building. There seems to be some debate as to how much data vs voice can be used at the same time. We have 13 phone lines. One of our phone guys says these are used as voice only, as faxes and data going to an iDisk which is shared, is transferred through the internet and not considered data. He said data is credit card machines etc. The other guy says just the reverse. We are also told that only 9 or 10 lines should be used as voice if others used as data. Who is right. Please help.

By anon16526 — On Aug 08, 2008

Agreed, T1's are typically brought into a customers premise over standard copper cabling (such as Cat5 etc). A T1 costs around $450/month

By anon12953 — On May 16, 2008

anon9403, A T1 does not have any pairs of wires. Pairs of wires are copper, whereas T1 is typically fiber optic.

By anon12746 — On May 13, 2008

T1's are usually copper lines, not fiber optic.

By anon9403 — On Mar 05, 2008

A CAT 5 contains 4 pair of wires, how many T-1s will one cable carry?

By anon8077 — On Feb 07, 2008

This is an excellent article because T1 internet service is the broadband communications of the future.

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