Telecommunications - Configuration of X.25 Throughput Class Negotiation

 

Subscription Option - Throughput Class Negotiation

Description of Option

When the calling DTE has subscribed to the throughput class negotiation facility, it may request the throughput classes of the virtual call in the facility field of the call request packet for both directions of data transmission. If throughput classes are not explicitly requested the network will assume the default values for both directions of data transmission.

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
Throughput class negotiation........ 1.6 E p

| Throughput class negotiation........| 1.6 E | | |

|

|

|

| | # UK(a) - not supported

UK(b) - allows 4 'levels'

value requested resources allocated for
bits per second characters per second
1-6 256 32
7 1280 160
8-9 4096 512
10-11 16384 2048

&notes& = y

Temporary note for reviewers

UK(a) - the throughput is limited only by the availability of bandwidth on the links, and resources within the network. If throughput gets too low due to high traffic levels, then extra trunk lines or switching equipment has to be provided, if this is not done then network nodes may go into congestion.

UK(b) - Each logical channel is throttled back to the throughput shown above, backpressure is applied across the network by adjacent nodes sending an array every 0.5 second for each channel (trickle and gush array). This appears to put a hard limit of 2048 cps = 16.4 Kbps per logical channel, we need to check this with UKb. If it is true it could cause a major problem for our users.

\info\computer\UK\x25-sub\tc-t.t1

UK(a) - the throughput is limited only by the availability of bandwidth on the links, and resources within the network. If throughput gets too low due to high traffic levels, then extra trunk lines or switching equipment has to be provided, if this is not done then network nodes may go into congestion.

UK(b) - Each logical channel is throttled back to the throughput shown above, backpressure is applied across the network by adjacent nodes sending an array every 0.5 second for each channel (trickle and gush array). This appears to put a hard limit of 2048 cps = 16.4 bps per logical channel, we need to check this with UKb. If it is true it could cause a major problem for users.

UKa allow the parameter to be set. However this is passed transparently through the network and it has no effect on the throughput of data through the network.

This 'implementation' is currently on the network, there is no change at release 4.

table build question:

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

|TNDTED Q165| q49 | enhanced DTE........................#TNDTED Q166(was q50 ) throughput class negotiation facility

|TNDTED Q166| q50 | throughput class negotiation fac....#standard Public Network settings = NO

only applies if Q165=YES

*** check if throughput class always sent to DTE if Q166=YES ***

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

FR2 - Flow control parameter negotiation ... M = Mandatory

FS2 - Flow control parameter negotiation ... M = Mandatory

May be compatible with ONA for this option. Upto now we have not allowed customers to use flow control parameter negotiation, we need to test carefully before we can claim compatibiliy.

Test plan and implementation issues


The efficiency of packet switching networks depends on the sharing of resources (trunks and switches) and it would be expensive to guarantee a given throughput (even for the duration of a call).

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

We need to test all combinations of Default throughput classes, and per call throughput class facility requests at both ends of the call to find out exactly under what circumstances new software will insert a throughput class and when it will clear a call because of a lack of, or invalid, throughput facility. When we have done this we will be in a better position to say what degree of support we can claim.




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