E1 carrier Bit Rate

E1 carrier comes with European digital transmission format devised by the ITU-TS (International Telecommunication Union Telecommunication Standardization Sector). This name is given by the Conference of European Postal and Telecommunication Administration (CEPT). Normally E1 carrier operates on European and some Asian countries. But E1 is equivalent standard of the T1 carrier system in North American. 

E2 through E5 are carriers in increasing multiples of the E1 format. But in the Industry only E1 and E3 versions are used. Actually E1 is transmitted as 32 time slots and E3 is capable of carrying 5120timeslots.There are two time slots for framing (For synchronization) and another one for signaling (For allocating call setup). E-carrier systems permanently assign capacity for a voice call for its whole period. Therefore this makes sure high call quality because the transmission arrives with the same short delay and capacity at all times.

Here are the data rates of multiple E carriers.

E0 - 64 kbit/s

E1 - 2.048 Mbit/s

E2 - 8.448 Mbit/s

E3 - 34.368 Mbit/s

E4 - 139.264 Mbit/s

E5 - 564.992 Mbit/s

In E1 carrier there are 32 channels in the frame. The bit rate can be calculated as follows;

Time taken for the whole frame              = 125μs

Number of bits in a time slot                   = 8 bits
Number of time slot in a frame               = 32
Therefore number of bits in a frame       = 32 x 8 bits

                                                                         265 bits

We know bit rate can be achieved as follows;

                        Bit rate of E1 carrier           = number of bits /time taken

                                                                          256 bits/125μs

                                                                          2.048 Mbit/s

PCM and TDM operation

Time division multiplexer is a digital processes that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving device.

·        After the Encoding each byte comes to the multiplexer, then multiplexer gather 30 bytes together (in every125 µs).

·        Then these 30 bytes (channels) are gathered as Frames. It is called E1 carrier.

·        Before multiplexing synchronizing bit and signaling bit is added to the frame.  Synchronizing bit is in the 1^st time slot and signaling bit is in the 16^th time slot.

·        Now this frame has 32 bytes and one by one goes to the destination end time division de-multiplexer.

·         De-multiplexer decomposes each frame by discarding the framing bits and extracting each character in turn.

Why we use Low Pass FIlter in PCM

If a low pass filter is not implemented prior to the sampling modulator, we have to face more problems, when the voice is passing through a copper cable.

 In sampling modulator we use a low pass filter to pass only low frequency of the voice signal. It compressed human voice bandwidth (20 kHz-20000 kHz) into small bandwidth of 0.3 kHz-3.4 kHz.

                      We know if want to transmit more distance, need a low bandwidth. Human voice bandwidth is a wider one, using that bandwidth can’t transmit that much of distance through the copper cable. It needs small bandwidth. That’s why we use low pass filter.

                      If it is not implemented prior to sampling modulator can’t transmit signal much distance through the copper cable.

                      And ccItt experimented on the range which most suitable for voice transmission and found out that 0-4kHz would be sufficient enough to transmit any message clearly.