E1 R2 CAS
An E1 circuit is similar to a T1 circuit. It is a TDM circuit that carries several DS-0s in
one connection. E1 circuits are widely used in Europe, Asia, and Central and South
America.
One big difference between an E1 and a T1 is that an E1 bundles 32 time slots instead of
24. This results in a bandwidth of 2.048 Mbps. With an E1, one time slot is used for
framing and one is used for signaling. This leaves 30 time slots available for user data.
E1 digital circuits can be deployed using R2 signaling. These trunks are called E1 R2
trunks. To understand how E1 R2 signaling works, you need to understand the E1 multiframe
format, which is used with E1 R2.
A multiframe consists of 16 consecutive 256-bit frames. Each frame carries 32 time slots.
The first time slot is used exclusively for frame synchronization. Time slots 2 to 16 and
18 to 32 carry the actual voice traffic, and time slot 17 is used for R2 signaling.
The first frame in an E1 multiframe includes the multiframe format information in time
slot 17. Frames 2 to 16 include the signaling information, each frame containing the signaling
for two voice time slots.
Using this signaling method, E1R2 supports inbound and outbound DNIS and ANI.
Figure 4-4 shows the signaling concept used by E1 R2.
190 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
Carry Signaling (ABCD Bits)
for Two Voice Channels
Frames 2–16
Frame 1 Indicates Start of Multiframe
Time Slot 17
Frame
Synchronization
Time Slot 1
16 Frames
=
Multiframe
2.048 Mbps
1. Frame: Start of Multiframe
2. Frame: Signaling for Voice Slots 2 and 18
3. Frame: Signaling for Voice Slots 3 and 19
4. Frame: Signaling for Voice Slots 4 and 20
5. Frame: Signaling for Voice Slots 5 and 21
6. Frame: Signaling for Voice Slots 6 and 22
7. Frame: Signaling for Voice Slots 7 and 23
8. Frame: Signaling for Voice Slots 8 and 24
9. Frame: Signaling for Voice Slots 9 and 25
10. Frame: Signaling for Voice Slots 10 and 26
11. Frame: Signaling for Voice Slots 11 and 27
12. Frame: Signaling for Voice Slots 12 and 28
13. Frame: Signaling for Voice Slots 13 and 29
14. Frame: Signaling for Voice Slots 14 and 30
15. Frame: Signaling for Voice Slots 15 and 31
16. Frame: Signaling for Voice Slots 16 and 32
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Figure 4-4 E1 R2 CAS
Time slot 17 is used for signaling, and each of its frames carries information for two
voice time slots. This results in the following frame allocation for signaling:
■ 1. Frame, Time slot 17: Declares the multiframe
■ 2. Frame, Time slot 17: Signaling for time slots 2 and 18
■ 3. Frame, Time slot 17: Signaling for time slots 3 and 19
■ 4. Frame, Time slot 17: Signaling for time slots 4 and 20
■ 5. Frame, Time slot 17: Signaling for time slots 5 and 21
■ 6. Frame, Time slot 17: Signaling for time slots 6 and 22
■ 7. Frame, Time slot 17: Signaling for time slots 7 and 23
■ 8. Frame, Time slot 17: Signaling for time slots 8 and 24
■ 9. Frame, Time slot 17: Signaling for time slots 9 and 25
■ 10. Frame, Time slot 17: Signaling for time slots 10 and 26
■ 11. Frame, Time slot 17: Signaling for time slots 11 and 27
■ 12. Frame, Time slot 17: Signaling for time slots 12 and 28
■ 13. Frame, Time slot 17: Signaling for time slots 13 and 29
■ 14. Frame, Time slot 17: Signaling for time slots 14 and 30
■ 15. Frame, Time slot 17: Signaling for time slots 15 and 31
■ 16. Frame, Time slot 17: Signaling for time slots 16 and 32