Telecommunications - Configuration of X.25 Throughput class negotiation


Per-call facility options - Throughput class negotiation

Description of Facility

This facility allows the effective throughput rate of the virtual circuit to be signalled.

Facility code Parameter field
02 hex 3=75 bps 4=150 bps 5=300 bps
6=600 bps 7=1200 bps 8=2400 bps
9=4800 bps 10=9600 bps 11=19200 bps
12=48000 bps

| 02 | 00000010 | throughput class negotiation.............#


| X.2 LEVEL 3 PER CALL FACILITY | X.2 (1984) | UK(a) | UK(b) |interworking|

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


| Throughput class negotiation........| 2.7 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 bps per logical channel, we need to check this with UKb. If it is true it could cause a problem for users.

Question: If throughput class (TNDTED71 Q170) is set to yes will throughput class facility always be sent to the DTE or only when it is received from the call originator.

Answer : Yes, the default values in TNDTED71 Q188,Q189 will be included in the Call Request packet.

CCITT compatibility

X.2 1984 ... E - essential facility

X.2 1988 ... E - essential facility

ISO 8878 compatibility

ONA compatibility

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

V11s - throughput classes supported sending...


V11r - throughput classes supported receiving


Therefore release 4 is compatible with ONA for default values. Although Release 4 does not fully implement throughput class.

ONA appears to require support of non-standard throughput class, which seems unnecessary

Implementation issues

metadata block
see also:


Correspondence about this page

Book Shop - Further reading.

Where I can, I have put links to Amazon for books that are relevant to the subject, click on the appropriate country flag to get more details of the book or to buy it from them.

cover The Essential Guide to Telecommunications (Essential Guide).

Commercial Software Shop

Where I can, I have put links to Amazon for commercial software, not directly related to the software project, but related to the subject being discussed, click on the appropriate country flag to get more details of the software or to buy it from them.


This site may have errors. Don't use for critical systems.

Copyright (c) 1998-2022 Martin John Baker - All rights reserved - privacy policy.