What are T1 and E1?

T1 is a digital carrier signal that transmits the DS – 1 signal. It has a data rate of about 1.544 megabits / second. It contains twenty four digital channels and hence requires a device that has digital connection. This digital connection is called as the CSU / DSU – Customer Switching Unit or Digital Switching Unit. The scalability of the T1 is up to 200 and above users. It also provides some services similar to the internet provider. Most of the computer uses a T1 connection. This technology makes your modem to have higher speeds and it is an affordable technology.

E1 is similar to the T1. T1 is the North American term whereas the E1 is the European term for the transmission (digital). The data rate of E1 is about 2 mega bits per second. It has 32 channels at the speed of 64 Kbps. It is important to know that 2 channels among the 32 are already reserved. One channel is used for signaling while the other channel is used for controlling. The difference between T1 and E1 lies in the number of channels here. The speed remains the same. There may be inter – connection between the E1 and T1 lines. This is interconnected because it is used for international purpose.

Differences in the physical delivery:

Here are we are going to discuss the differences in the physical delivery.

Data Rate: The main difference is the data rate. T1 has a data rate of 1.544 mbps and E1 has a data rate of 2.048 mbps.

Copper Delivery: In the T1 signal there is a copper delivery among 4 wires. It is grouped into two pairs. One pair is the RX (1+2) and another is TX (4+5). The RX is the data that is from the network and the TX is to the network. In the E1, there are two types of physical delivery; balanced physical delivery and unbalance physical delivery. The unbalance physical delivery has 4 copper wires. It is similar to that of T1. Whereas in the balance physical delivery there is a coax connector which has one cable for RX and one cable for TX.

Services: T1 has a specific type of service. It has repeaters for every six thousand feet, a pulse or waveform shape and a jitter. The E1 has 32 timeslots. This can be said as DS. Each DS is about 8 bits wide.

Differences in the Framing Format:

Let us discuss the differences in the framing format.

Framing: In T1, there are two types of framing formats. One is D4 (twelve bits group) – used in aligning the equipment which is used for framing and another is ESF (twenty four bits group) – used in aligning the frames as well as in the maintenance of the channel which is facilitated by the data link. In E1, there are two framing formats. One is a called the double frame – it uses the DS0 and another is the multi frame which is the independent form.

More about T1 and E1

An E1 link operates over two separate sets of wires, usually twisted pair cable. A nominal 3 volt peak signal is encoded with pulses using a method that avoids long periods without polarity changes. The line data rate is 2.048 Mbit/s (full duplex, i.e. 2.048 Mbit/s downstream and 2.048 Mbit/s upstream) which is split into 32 timeslots, each being allocated 8 bits in turn. Thus each timeslot sends and receives an 8-bit PCM sample, usually encoded according to A-law algorithm, 8000 times per second (8 x 8000 x 32 = 2,048,000). This is ideal for voice telephone calls where the voice is sampled into an 8 bit number at that data rate and reconstructed at the other end. The timeslots are numbered from 0 to 31.

One timeslot (TS0) is reserved for framing purposes, and alternately transmits a fixed pattern. This allows the receiver to lock onto the start of each frame and match up each channel in turn. The standards allow for a full Cyclic Redundancy Check to be performed across all bits transmitted in each frame, to detect if the circuit is losing bits (information), but this is not always used.One timeslot (TS16) is often reserved for signaling purposes, to control call setup and teardown according to one of several standard telecommunications protocols. This includes Channel Associated Signaling (CAS) where a set of bits is used to replicate opening and closing the circuit (as if picking up the telephone receiver and pulsing digits on a rotary phone), or using tone signaling which is passed through on the voice circuits themselves. More recent systems used Common Channel Signaling (CCS) such as ISDN or Signaling System 7 (SS7) which send short encoded messages with more information about the call including caller ID, type of transmission required etc. ISDN is often used between the local telephone exchange and business premises, whilst SS7 is almost exclusively used between exchanges and operators. In theory, a single SS7 signaling timeslot can control up to 4096 circuits per signaling channel using a 12-bit Channel Identification Code (CIC),[3] thus allowing slightly more efficient use of the overall transmission bandwidth because additional E1 links would use all 31 voice channels. ANSI uses a larger 14-bit CIC and so can accommodate up to 16,384 circuits. In most environments, multiple signaling channels would be used to provide redundancy in case of faults or outages.Unlike the earlier T-carrier systems developed in North America, all 8 bits of each

sample are available for each call. This allows the E1 systems to be used equally well for circuit switches data calls, without risking the loss of any information.While the original CEPT standard G.703 specifies several options for the physical transmission, almost exclusively HDB3 format is used.

DefinitionLink a unidirectional channel residing in one timeslot of a E1 or T1 Line, carrying 64 kbit/s (64'000bit/s) raw digital data.

Line a unidirectional E1 or T1 physical connection.

Trunk A bidirectional E1 or T1 physical connection