Isdn Pri and Channelized E1 and T1

CiitOteom

In the figure, the ISDN PRI specifies:

■ 23 B (U.S. T1) or 30 B (European E1) channels at 64 kbps each

■ Framing and synchronization at 8 kbps (T1), or 64 kbps (E1)

■ Total speed 1.544 Mbps (T1), or 2.048 Mbps (E1)

Because an ISDN BRI comprises two B channels and one D channel, it is often referred to as "2B+D." Likewise, a U.S. T1 PRI is commonly referred to as "23B+D," and a European E1 PRI as "30B+D."

In Europe the D channel is carried in timeslot 16. In the United States it is in timeslot 24. Note In an E1 PRI there are actually 32 channels: 30 B, 1 D, and 1 synchronization channel.

The table below displays the relationships between the DS level, speed, "T" designations, and number of channels.

North American Digital Hierarchy

Digital Signal Level

Speed

"T" Designation

Channels or DS-0s

DS-0

64 kbps

-

1

DS-1

1.544 Mbps

T1

24

DS-3

44.736 Mbps

T3

672

In some cases, a DS-0 can carry only 56 kbps, usually because of legacy telco equipment or a signaling method called robbed-bit signaling (RBS).

In Europe, the equivalent of a T1 facility is an E1 facility.

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