How many ds0s are used in a t1

DS0 is the bandwidth you need to transmit one digitized telephone call using the legacy telephone standard for PCM or Pulse Code Modulation. It's an 8 bit channel transmitted at 8 Kbps or a total of 64 Kbps. That's the gold standard for "toll quality" voice. That same channel can also be used to carry 64 Kbps of data rather than a telephone call. The data bits might represent a dial-up modem connection, a portion of a broadband Internet service, a portion of an Ethernet signal, a small portion of a video transmission, or signaling and Caller ID information to support a call center.

But a T1 line runs at 1. What's missing? The extra 8 Kbps represents the framing bit that T1 adds to each group of 24 DS0 channels so that the CSU or channel service unit at the other end of the line knows where to demultiplex the frame of 24 DS0s.

With synchronous lines such as T1, framing bits are needed to keep the sending and receiving ends tightly synchronized. Remember that most people will associate DS1 with T1 and that's normally how you would get DS1 service. If you needed a lot more bandwidth, you might order DS3 service that would be delivered on a T3 line. A normal phone line like this is delivered on a pair of copper wires that transmit your voice as an analog signal.

When you use a normal modem on a line like this, it can transmit data at perhaps 30 kilobits per second 30, bits per second. The phone company moves nearly all voice traffic as digital rather than analog signals.

Your analog line gets converted to a digital signal by sampling it 8, times per second at 8-bit resolution 64, bits per second. Nearly all digital data now flows over fiber optic lines, and the phone company uses different designations to talk about the capacity of a fiber optic line. If your office has a T1 line, it means that the phone company has brought a fiber optic line into your office a T1 line might also come in on copper. A T1 line can carry 24 digitized voice channels, or it can carry data at a rate of 1.

If the T1 line is being used for telephone conversations, it plugs into the office's phone system. If it is carrying data it plugs into the network's router. It is also extremely reliable -- much more reliable than an analog modem. I obviously did not have any influence over the terms, though, so we are stuck with frame and superframe; I use the industry standard terms because the usages are entrenched.

When you first plug in a T1 cable, an alarm indicator will still complain about the lack of framing. After synchronization is complete, bits can be transmitted to the remote end, which locks on to the transmitted frames and clears any remote alarm conditions. For financial reasons, fractional T1 service is popular in many areas. It allows you to purchase multiple DS0s with an easy upgrade path to higher speeds. Fractional T1 equipment is the same equipment used to provide full T1 service, so there is no additional equipment cost to upgrade from fractional to full T1 services.

Fractional T1 is provided using the same facilities as full T1. The telco providing fractional T1 will transmit data only on some of the 24 time slots in the T1 frame. For example, a kbps FT1 is a T1 with only 4 of the 24 time slots active. Because clock synchronization is maintained by monitoring pulse times, the T1 specifications mandate a certain pulse density so that both ends stay synchronized.

Two minimums are imposed by the standards:. A maximum of 15 consecutive time slots without a pulse. Modern digital repeaters can handle much longer strings of zeros, but this requirement was instituted well before such equipment was available.

There is no easy way of knowing the capability of repeaters on any stretch of cable, so all commercial equipment is still built to the older specification. When a T1 is installed, the telco technician may hook a handheld device with lots of buttons and blinking lights on it up to the new T1 jack. The testing device can perform stress tests on the new line to measure its quality and clarity. After looping back the T1, the testing device injects a specific bit stream.

Returning bits are compared against the original sequence to determine the bit error rate BER. Several common tests are used:. The QRS bit sequence is not guaranteed to meet pulse-density requirements. AMI-encoded links should not alter the signal to meet minimum pulse-density requirements, but misconfigured equipment on the line may be configured to do so.

Errors observed in the QRS test indicate one of two things: a line that is bad, or a line that has misconfigured equipment. When used on AMI-encoded links, the 3-in test sends the framed pattern , which meets both the minimum pulse density and maximum zero length, and stresses the link by sending the lowest density signal allowed by the specification.