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 |
¬es& = 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.
