E1 and T1

North America's 24-channel modulation PCM (T1), with a rate of 1.544 Mbit/s

European 30-Channel Pulse Code Modulation PCM (E1), with a speed of 2.048 Mbit/s

China adopts the European E1 standard.

A time-division multiplexing frame of E1 (its length t = 125us) is divided into 32 equal time slots, and the time slot number is ch0 ~ Ch31. The time slot ch0 is used for frame synchronization, and the time slot ch16 is used for transmitting signaling ~ Ch15 and ch17 ~ A total of 30 time slots in ch31 are used as 30 channels. Each time slot transmits 8 bits, so the 256bit is shared. 8000 frames are transmitted per second. Therefore, the data rate of group E1 in one PCM Group is 2.048 Mbit/s.

The T1 system used in North America has a total of 24 channels. Each channel sample pulse is coded in 7 bits, followed by a 1-bit signaling code element. Therefore, a channel occupies 8 bits. The frame synchronization code is 1 bit after the 24-way encoding, so that each frame has a total of 1.544 bits. Therefore, the data rate of the T1 group is Mbit/s.

When a higher data rate is required, the multiplexing method can be used. Four groups can form a secondary group.

The following table lists the route number and data rate of each higher-order group:

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System type | one group | secondary group | three groups | four groups | five Groups

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European system | symbol | E1 | E2 | E3 | E4 | E5

| Number of calls | 30 | 120 | 480 | 1920 | 7680

| Data rate | 2.048 | 8.448 | 34.368 | 139.264 | 565.148

| (Mbit/s) |

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North American system | symbol | T1 | T2 | T3 | T4 |

| Number of calls | 24 | 96 | 672 | 4032 |

| Data rate | 1.544 | 6.312 | 44.736 | 274.176 |

| (Mbit/s) |

 

Appendix:

E1European Standard 2048 kbit/s

E2European Standard 8 Mbit/s (4 x E1, exotic)

E3European Standard 34 Mbit/s (4 x E2)

E4European Standard 140 Mbit/s (4 x E3)

T1American Standard 1544 kbit/s

T2American Standard 6 Mbit/s (4 x T1, exotic)

T3American Standard 45 Mbit/s (7 x t2, used a lot)

OC-1American Standard 51 Mbit/s (SONET, verpakt 1 T3)

OC-3American Standard 155 Mbit/s (SONET, 3 x OC-1)

STM-1European Standard 155 Mbit/s (SDH snelheid = OC-3)

STM-4European Standard 622 Mbit/s (4 x STM-1)

STM-16European Standard 2488 Mbit/s (16 x STM-1; Gbit/s)

STM-64European Standard 9952 Mbit/s (16 x STM-1; 10 Gbit/s)