Telecommunications - Configuration of X.25 Extended Packet Sequence Numbering

 

Subscription Option - Extended Packet Sequence Numbering

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Description of Option

This facility allows packets to contain sequence numbers operating modulo 128 (as opposed to modulo 8).

This facility allows the possibility of a greater throughput on a logical channel with extended packet sequence numbering, because more packets can be transmitted without waiting for an acknowledgement.

This facility is indicated by bits 5 and 6 in the GFI and it requires an extra byte in the packet header of DATA,RR,RNR and REJ packets to hold the sequence numbers.

UK(a) - this facility is not supported.

UK(b) - this facility is technically possible, although it does not provide any benefit since packet level acknowledgements are local in UK(b). UK(b) supports standard (modulo 8) and extended (modulo 128) packet sequence numbering, the numbering scheme is dependent on link configuration. Only one sequence scheme may be used during the subscription period.

+--------------------------------------------------------------------------------------------+

| X.2 LEVEL 3 PER USER SUBSCRIPTION | X.2 (1984) | UK(a) | UK(b) |interworking|

| OPTIONS | REF CLASS | now | now |R5a|R5b| R6 | |

+-------------------------------------+-------------+--------+-----+---+---+----+------------|

| Extended packet sequence numbering..| 1.1 A | . |


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