T1 Internet - What is T1?

First how do you know if you need a T1 Internet Connection? If you answer yes to any of the following questions, then you need to seriously consider one.

  • Do you rely on business Internet Services?
  • Does your business rely on multiple phone lines?
  • Do you have four or more people trying to use the internet and make calls?

A T1 line gives you the most reliable high speed internet connection you can get. If your business can not afford to be off line for any length of time then you should seriously consider a T1 line. A T1 Line guarantees bandwidth in both your uplink and downlink directions allowing significant bandwidth for multiple people and multiple applications.

So what is a T1 Internet Connection?

If you have ever searched for business Internet, business VoIP or have been serious about using any business telecom service then you will have come across the term T1.


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So what is T1? Well T1 really defines 4 things:

  1. The bandwidth or clock rate.
  2. The physical medium used.
  3. The type of signaling and encoding used.
  4. The format or frame the data is transferred in.

The T1 bandwidth is 1.544Mbits/sec for one direction, one of the advantages of a T1 carrier is that you get this dedicated bandwidth in both the uplink and downlink directions, it is symmetrical.

With a T1 internet connection there are two physical mediums that are used. One is based on 100 Ohm twisted shielded differential pair and the other is based on 75 Ohm coaxial cable. Typically inside patch panels the 100 Ohm twisted pair is used as it is cheap and flexible but for transmission to the outside world a balun is used to match to the 75 Ohm coaxial cable which is typically used to connect to the Internet Service Provider (ISP) or Private Branch Exchange (PBX).

The T1 carrier uses a signal encoding called B8ZS which stands for Binary 8-zero Substitution - quite a mouthful. Without going into too much detail, this type of encoding allows data and a clock to be sent across the same T1 cable - vital for synchronous data transfer.

Finally the format. Each T1 line is split into 24 channels referred to as DS0's. Each channel is 8 bits wide and the frame is sent on a 8KHz boundary. The data capacity is therefore 24x8x8000 = 1.536Mbits/sec. There is also something referred a framing bit, this is 1 bit every frame that a receiver on the other end can lock onto to ensure that whatever equipment is there can extract the correct DS0's in the correct order. This framing bit adds an extra 8000 bits/sec giving a grand total of 1.544Mbits/sec.

Below is a pictorial view of a T1 frame:

T1 frame structure

There are basically three different types of T1 lines:

  1. A Data T1 Line.
  2. A Voice T1 Line.
  3. A Primary Rate Interface T1 Line - usually referred to as PRI T1.

A Data T1 line is a T1 line dedicated to carrying data, i.e. high speed internet access or high speed data connections for point to point transfers between offices. For high speed internet, multiple DSO's can be grouped together to give you the high bandwidth you need. Since a T1 line has the same high bandwidth in both directions this gives you an advantage over cable and DSL as they tend have a large downlink bandwidth but a small uplink bandwidth.

A Voice T1 line has the ability to carry 24 simultaneous phone calls. Each DSO can carry one phone call. The only major difference between a Voice T1 and a Data T1 is how the T1 is terminated at the Central Office or switch. If you require a voice T1 then the provider will physically connect your T1 line to a voice only T1 Line card in a switch such as the Lucent 5ESS. If you need only data then you are likely to be connected to a physically different piece of hardware such as a Cisco 7500.

Primary Rate Interface or PRI T1 as it is more commonly know as, is probably the most flexible T1 line available. A T1 is made up of 24 individual channels called DS0's. With a PRI T1 interface 23 of these channels, often referred to as Bearer (B) channels, are available for data or voice and the 24th channel, the Data (D) channel is used for signaling. This Data channel can dynamically set up any of the other 23 Bearer channels to carry any sort of data. So one PRI T1 may carry voice, high speed data and then if say you require a video conference call then 6 channels can be grouped together to carry the video and voice. This flexibility makes the PRI T1 line a great solution for small businesses that do not want to purchase multiple T1 lines for different solutions.

It is worth mentioning at this point a technology known as Voice over IP (VoIP), also referred to as Broadband Phone and Internet Phone service. VoIP technology is growing at an incredible rate, particularly for Small to Medium sized Businesses (SMB). This technology should not be confused with the Voice T1 line discussed above, which is a circuit based technology where each channel is dedicated to one telephone call. VoIP is a packet based technology so the voice is actually treated like the Data T1 discussed above. Each telephone call is sent as a packet on the Data T1 line and then travels over the Internet to reach its destination. The Internet is not taxed like the Plain Old Telephone System (POTS) and the packets are sent on a need basis so the cost for such calls is dramatically reduced. VoIP also gives a tremendous flexibility in terms of the services and features it has to offer, it is also particularly well suited to Small to Medium Sized Business that have geographically separate offices by using a service called Hosted VoIP.

What is the cost of a T1 Internet Connection?

The cost of a T1 internet connection is really dependant on two factors:

Distance from the Central office - The physical distance from your business to the central office is a big factor. A T1 line one can only be used for distances of about 2 miles before a repeater is required. After 2 miles the signal becomes degraded enough that information could be lost. This repeater adds to the overall cost in addition to the extra cable required.

Type of T1 - You typically pay about a 20% premium for a PRI T1 over a voice T1 or data T1. The PRI T1 is an excellent solution for Small to Medium sized Businesses (SMB) where both voice and data will be shared on the same T1 line.

It is vital that if you do want a T1 for your business you get quotes from several providers as the Central office will be in different locations. Let WhichT1.com do this work for you - Fill in the form above and we will send your information to 3 - 5 providers in your geographical area and you can compare their prices. If you are unsure of what you need, do not worry our experts who contact you will provide guidance.

We have talked a lot about what a T1 is and that the benefits it provides such as the increased available bandwidth and reliability it gives your business over say, a business class DSL service. But where does it fit in on the bandwidth scale for different bandwidth offerings and how much does a T1 circuit typically cost. Well first of all, here is a brief summary of various bandwidth options available:

33.6 K (Modem) 33,600 bps
56 K (Modem) 56,000 bps
64 K (DS-0) 64,000 bps
128 K (ISDN) 128,000 bps
256 K (DSL) 256,000 bps
640 K (DSL/Cable) 640,000 bps
768 K (DSL/Cable) 768,000 bps
T1, DS-1 1.544 Mbps
T3, DS-3 44.736 Mbps
OC-1 51.840 Mbps
OC-3 155.520 Mbps
OC-12 622.080 Mbps
OC-48 2.488 Gbps
OC-192 10 Gbps

As you can see, the T1 is the next step up from DSL/Cable but not only do you get twice the bandwidth you get a significant increase in reliability. The T1 provider guarantees a Quality of Service(QoS) through a Service Level Agreement(SLA). This ensures your business will always have the full bandwidth as per the SLA.

Once you submit your quote request and are happy with the services you will be getting it will take around 25 to 50 days to actually get your T1 install completed. So plan ahead. This time is mainly gated by the local exchange carrier who needs to coordinate the installation.

How much should you pay for a T1 Connection?

Typical costs for a T1 circuit range from around $350 to as high as $650 per month. As we stated above this discrepancy is that the last mile from the Central Office to your premise has a high weighting in this calculation. So if you are close to the Central Office, you will be closer to the $350 price. However, the best way to make sure you are getting the best deal, is the good old method of getting more than one quote. This is where we can help by getting multiple quotes for you based on your needs.

In summary, Small to Medium sized Businesses should never need anything more than a T1 line or multiple T1 lines. Some businesses prefer to get two T1 lines for load-balancing and redundancy, especially if it is running VoIP on its network.

What if you still have questions? Hopefully the information above has given you an insight to what is available but you may still not know what you really need. When you fill out the quote request above, our experts will contact you to advise on what is best for your particular business needs.