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Cross Connections | 136
E1 Framed Modes
Framed Mode Description
E1 – PCM 30 Provides 30 timeslots to transport traffic. Timeslot 16 carries channel
associated signalling data (CAS).
E1 – PCM 31 Provides 31 timeslots to transport traffic. Timeslot 16 can be used for common
channel signalling or to transport traffic.
E1 – PCM 30C Same as E1 – PCM 30 mode but supports CRC-4.
E1 – PCM 31C Same as E1 – PCM 31 mode but supports CRC-4.
E1 CRC-4 (cyclic redundancy check) is used to ensure correct frame alignment and also used to
gather E1 performance statistics e.g. Errored Seconds (ES), Severely Errored Seconds (SES).
The first three bits of timeslot 0 NFAS (bits 0,1 & 2) and all of timeslot 0 FAS are not transported
across the link, but rather terminated and regenerated at each terminal.
The last five bits of timeslot 0 NFAS (bits 3 – 7) are the National Use Bits (NUBs) which can be cross
connected locally or over the link.
E1 - PCM 30 mode
E1 - PCM 30 modes are used when access to the signalling bits (ABCD) is required, for example:
Splitting a PCM 30 E1 into two separate PCM 30 E1s
Cross connecting signalling from DFXS, DFXO or Q4EM interfaces into an PCM 30 E1
Drop and Insert connections between PCM 30 E1s
In PCM 30 / PCM 30C mode, the timeslot table left column is used to map timeslot bits and the
timeslot table right column is used to map CAS bits (ABCD) for signalling. Timeslot 16 is reserved to
transport the CAS multi frame.
One use of this mode is to connect the 4 wire E&M interfaces to third-party multiplexer equipment over
the E1 interface using CAS in TS16 to transport the E&M signalling.
To configure this mode correctly, you must have a detailed knowledge of the CAS signalling modes for
the third-party equipment to ensure the signalling bits are compatible and configured to interoperate.
E1 - PCM 31 mode
E1 - PCM 31 modes are used to cross connect timeslots bits without the signalling bits (ABCD).
TS16 can be cross connected between E1 ports (to transport the entire CAS multi frame) or used for
common channel signalling or to transport traffic.
The timeslot table left column is used to map timeslot bits but the timeslot table right column for CAS
bits (ABCD) is not used.