Telecommunications - Configuration of X.25 Flow control Parameter Negotiation


Subscription Option - Flow control Parameter Negotiation

related documents:

This facility allows the packet and window size to be negotiated in the facility field of the call request and call connected packets.

If this facility is not subscribed to then the default values must be used.

This facility is only provided, by UK, when extended format is subscribed to. This is because 'extended format' call accept packets are required to carry the facility field which holds the negotiation values.

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
Flow control parameter negotiation.. 1.5 E

| Flow control parameter negotiation..| 1.5 E |





| | #UK(a) - supported. In order to use this facility both ends of the call must subscribe to parameter negotiation, otherwise the values will be negotiated down to their default values.

UK(b) - supported. Packet and Window size is set independently at both ends of the call. The network will perform the appropriate concatenation and splitting of packets as required. If a packet has been split the M-bit will be set, except for the final packet.

Since UK(b) uses local significance and 128 byte packets internally within the network, an increase in Packet or window size may NOT increase the throughput, in fact this assembling and disassembling of packets may actually slow down throughput.

&notes& = yTemporary note for reviewers

UK(a) - If very high packet and window sizes are used and data is sent at a high rate, ie with only 1 or 2 flags between frames. This may cause the network node to crash. (Kevin Joseph has the figures).

UK(b) - High packet and window sizes should be discouraged since they do not improve throughput and they require a large amount of memory for the slot, this could reduce the number of ports that can be built on an engine, or cause the engine to go into congestion or crash.

This facility is already available in UKa software.

UKa does not support Packet sizes of 2048 and 4096, if these values are requested in the call request packet the call is cleared. At release 4 Public Network will not clear the call but will set the facility value to 1024.

table build questions:

TNDTED Q165(was q49 ) enhanced DTE (YES/NO)

|TNDTED Q165| q49 | enhanced DTE .......................#TNDTED Q167(was q51 ) packet size negotiation (YES/NO)

|TNDTED Q167| q51 | packet size negotiation.............# this question only applies if Q165=YES

TNDTED Q168(was q52 ) window size negotiation (YES/NO)

|TNDTED Q168| q52 | window size negotiation.............#this question only applies if Q165=YES

standard Public Network settings = these questions are set to YES if the customer subscribes to extended format otherwise they are set to NO.

UKa Answers

Question: Are fast select and enhanced DTE subscription options independent?

Answer : Yes.

UKa Answers

Question: Is fast select supported with reverse charge? if the call is cleared who pays for the call?

Answer : Yes it is, the remote end will pay for the call.

&UKb& = yUKb support

V 4.03

UKb 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.

Packet sizes supported 16,32,64,128,256,1024,2048,4096


RD 0004 part 8:1.C (PICS proforma Public Network1984)

FR1 - Flow control parameter negotiation ... M = Mandatory

FS1 - Flow control parameter negotiation ... M = Mandatory

Release 4 is compatible with ONA for this option.

Test plan and implementation issues

Currently on Public Network this facility is 'bundled' together with another facility (extended call accept packets) and is known as 'extended format'.

In CCITT terminology 'extended format' refers only to the extended form of the call connected, clear request and clear indication packets.

We need to do some tests to find out if extended format, fast select and flow control are independent of each other.

We need to test - if flow control parameter negotiation is enabled - will all incoming calls have this facility inserted if not sent by the originator of the call.

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