
XRT84L38
173
REV. 1.0.1
OCTAL T1/E1/J1 FRAMER
CAS Multi-Frames are only relevant if the user is using CAS or Channel Associated Signaling. If the user is
implementing Common Channel Signaling then the CAS Multi-Frame is not available. The exact role of CAS
Multi-Frames is discussed in some detail in the next section.
2.2.2.1
Channel Associated Signaling
If the user operates an E1 channel in Channel Associated Signaling (CAS) mode, then the timeslot 16 octets
within each E1 frame will be reserved for signaling. Such signaling would convey information such as On-
Hook, Off-Hook conditions, call set-up, control, etc. In CAS, this type of signaling data that is associated with a
particular voice channel will be carried within timeslot 16 of a particular E1 frame within a CAS Multi-Frame.
The CAS is carried in a Multi-Frame structure which consists of 16 consecutive E1 frames. The framing/byte
format of a CAS Multi-Frame is presented in
Figure 18
.
Figure 18
indicates that timeslot 16 within Frame 1 of the CAS Multi-Frame, contains 4 bits of signaling data
for voice channel 1 and 4 bits of signaling data for voice channel 17. Likewise, timeslot 16 within Frame 2
contains 4 bits of signaling data for voice channel 2 and 4 bits of signaling data for voice channel 18; and so on.
Timeslot 16 within frame 0 is a special octet that is used for two purposes.
1.
To convey CAS Multi-Frame alignment information, and
2.
To convey Multi-Frame alarm information to the Remote Terminal.
The bit-format of timeslot 16 within frame 0 of a CAS Multi-Frame is 0000 xyxx.
The upper nibble of this octet contains all zeros and is used to identify itself as the CAS Multi-Frame alignment
signal. If CAS is used, then the user is advised to insure that none of the other timeslot 16 octets contain the
value "0000". The lower nibble of this octet contains the expression "xyxx". In this case, the x-bits are the spare
bits and should be set to "0" if not used. The y-bit is used to indicate a Multi-Frame alarm condition to the
Remote terminal. During normal operation, this bit-field is cleared to "0". However, if the Local Receive E1
Framer detects a problem with the incoming Multi-Frames, then the Local Transmit E1 Framer will set this bit-
field within the next outbound CAS Multi-Frame to "1".
F
IGURE
18. F
RAME
/B
YTE
F
ORMAT
OF
THE
CAS M
ULTI
-F
RAME
S
TRUCTURE
Frame 0
Frame 1
Frame 2
Frame 15
0000
xyxx
Timeslot 16
Timeslot 16
Timeslot 16
Timeslot 16
ABCD
ABCD
Signaling Data
Associated with
Timeslot 1
Signaling Data
Associated with
Timeslot 17
ABCD
ABCD
ABCD
ABCD
CAS Multiframe
Alignment Pattern
x = “dummy bits”
y = Carries the Multiframe “Yellow Alarm” bit
Signaling Data
Associated with
Timeslot 2
Signaling Data
Associated with
Timeslot 18
Signaling Data
Associated with
Timeslot 15
Signaling Data
Associated with
Timeslot 31
A Single CAS Multiframe