CONTENTS

1 Scope
2 Basic frame structures
2.1 Basic frame structure at 1544 kbit/s
2.1.1 Frame length
2.1.2 F-bit
2.1.3 Allocation of F-bit
2.2 Basic frame structure at 6312 kbit/s
2.2.1 Frame length
2.2.2 F-bits
2.2.3 Allocation of F-bits
2.3 Basic frame structure at 2048 kbit/s
2.3.1 Frame length
2.3.2 Allocation of bits number 1 to 8 of the frame
2.3.3 Description of the CRC-4 procedure in bit 1 of the frame
2.3.4 Synchronization Status: San
2.4 Basic frame structure at 8448 kbit/s
2.4.1 Frame length
2.4.2 Frame alignment signal
2.4.3 Service digits
2.5 Basic frame structure at 44 736 kbit/s
2.5.1 Multiframe length
2.5.2 Multiframe overhead bits
2.5.3 Allocation of the multiframe overhead bits
3 Characteristics of frame structure carrying channels at various bit rates in 1544 kbit/s
3.1 Interface at 1544 kbit/s carrying 64 kbit/s channels
3.1.1 Frame structure
3.1.2 Use of 64 kbit/s channel time slots
3.1.3 Signalling
3.2 Interface at 1544 kbit/s carrying 32 kbit/s channel time slots (see Note)
3.2.1 Frame structure
3.2.2 Use of 32 kbit/s channel time slot
3.2.3 384 kbit/s 12-channel time slot grouping
3.2.4 32 kbit/s signalling grouping channel multiframe structure
3.2.5 Signal grouping channel unused bits
3.2.6 Loss and recovery of signalling channel multiframe alignment
3.3 Interface at 1544 kbit/s carrying n 64 kbit/s
4 Characteristics of frame structures carrying channels at various bit rates in 6312 kbit/s interfaces
4.1 Interface at 6312 kbit/s carrying 64 kbit/s channels
4.1.1 Frame structure
4.1.2 Use of 64 kbit/s channel time slots
4.1.3 Signalling
4.2 Interfaces at 6312 kbit/s carrying other channels than 64 kbit/s
5 Characteristics of frame structures carrying channels at various bit rates in 2048 kbit/s interfaces
5.1 Interface at 2048 kbit/s carrying 64 kbit/s channels
5.1.1 Frame structure
5.1.2 Use of other 64 kbit/s channel time slots
5.1.3 Signalling
5.2 Interface at 2048 kbit/s carrying n 64 kbit/s
5.2.1 One n 64 kbit/s signal on the tributary side of a multiplex equipment
5.2.2 One or more n 64 kbit/s signal on the multiplexed signal side of a multiplexing equipment
6 Characteristics of frame structures carrying channels at various bit rates in 8448 kbit/s interface
6.1 Interface at 8448 kbit/s carrying 64 kbit/s channels
6.1.1 Frame structure
6.1.2 Use of 64 kbit/s channel time slots
6.1.3 Description of the CRC procedure in 64 kbit/s channel time slot 99
6.1.4 Signalling
6.2 Interface at 8448 kbit/s carrying other channels than 64 kbit/s
Annex A Examples of CRC implementations using shift registers
A.1 CRC-6 procedure for interface at 1544 kbit/s (see 2.1.3.1.2)
A.2 CRC-5 procedure for interface at 6312 kbit/s (see 2.2.3.2)
A.3 CRC-4 procedure for interface at 2048 kbit/s (see 2.3.3.5)
Annex B Alphabetical list of abbreviations used in this Recommendation