Telecommunications - Configuration of X.25 Default Packet & Window sizes

 

Subscription Option - Nonstandard Default Packet sizes

Subscription Option - Nonstandard Default Window sizes

Subscription Option - Default Throughput Classes Assignment


Description of Option

If no packet size is specified in the call request packet the default packet size of 128 is normally used.

This facility allows a default other than 128 to be used.

Non standard Packet Sizes supported:

UK(a) - 16,32,64,256,512,1024

UK(b) - 16,32,64,256,512,1024,2048,4096

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

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

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

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

| Non-standard default packet sizes...| 1.3 A | T |

|

|

|

| |

+--------------------------------------------------------------------------------------------+
3

| Non-standard default packet sizes...| 1.3 A | T |

|

|

|


10.10 - Subscription Option - Nonstandard Default Window sizes

Description of Option

If no window size is specified in the call request packet the default window size of 2 is normally used.

This facility allows a default other than 2 to be used.

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
Non-standard default window sizes... 1.2 A T

| Non-standard default window sizes...| 1.2 A | T |


10.11 - Subscription Option - Default Throughput Classes Assignment

Description of Option

The usual default throughput class corresponds to the user class of service of the DTE (ie the speed of their line).

This facility allows a default throughput class to be defined which is lower than the speed of the users line.

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

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
Default throughput class assignment. 1.4 A p

| Default throughput class assignment.| 1.4 A | | |

|

|

|

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 our users.

UKa support

DX1: yes, except 2048 and 4096 are cleared

DX2: yes, except 2048 and 4096 are negotiated to 1024

TP4/III: ?

This is already supported by UKa (16-1024 only). It is not currently offered on Public Network as part of our standard product due to the administration and maintenance problems that it would involve.

UKa will allow values from 16-1024 to be defined independently for each direction.

Values 2048 and 4096 are not supported by UKa.

table build questions:

TNDTED Q134(was Q14 ) default max packet size to DTE

|TNDTED Q134| Q14 | default max packet size to DTE......#(16,32,64,128,256,512,1024) default 128

standard Public Network settings = 128

TNDTED Q135(was Q15 ) default max packet size from DTE

|TNDTED Q135| Q15 | default max packet size from DTE....#(16,32,64,128,256,512,1024) default 128

standard Public Network settings = 128

see10.14 for flow control parameter negotiation


packet sizes supported: 16,32,64,128,256,512,1024,2048,4096

CCITT compatibility

X.2 1984 ... A - additional service

X.2 1988 ... A - additional service

ISO 8878 compatibility

ONA compatibility

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

V9s - Packet sizes supported sending...

16,32,64,128,256,512,1024,2048,4096

V9r - Packet sizes supported receiving ...

16,32,64,128,256,512,1024,2048,4096

V1s - Default packet sizes supported, sending:

16,32,64,128,256,512,1024

V1r - Default packet sizes supported, receiving:

16,32,64,128,256,512,1024

Therefore release 4 is compatible with ONA for the default values but not for the negotiated values.

ONA appears to require support of non-standard packet size, which seems unnecessary

Test plan and implementation issues

Values 2048 and 4096 are not supported by current Public Network network.

see per-call facilities section for details of changes regarding 2048 and 4096.

We should consider if we want to accept the extra maintenance overhead in supporting this feature.

If we wish to start supporting this facility then it will need to be added to our test scripts.

This is already supported by UKa. It is not currently offered on Public Network as part of our standard product due to the administration and maintenance problems that it would involve.

UKa will values from 1-7 to be defined independently for each directection.

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

table build questions:

TNDTED Q173(was q58 ) default window size to dte (1-7)

|TNDTED Q173| q58 | default window size to dte..........#default 2

standard Public Network settings = 2

TNDTED Q174(was q59 ) window size from dte (1-7)

|TNDTED Q174| q59 | window size from dte................#default 2

standard Public Network settings = 2

see10.14 for flow control parameter negotiation

&UKb& = yUKb support

SVC: yes

PVC: yes

X.32: no

UKb supports window sizes from 1 to 127 in each direction

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.

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

V10s - window sizes supported sending... 1-7

(1-127 if modulo 128 support)

V10r - window sizes supported receiving .1-7

(1-127 if modulo 128 support)

V2s - Default window sizes supported, sending: 1-7

(1-127 if modulo 128 support)

V2r - Default window sizes supported, receiving: 1-7

(1-127 if modulo 128 support)

Therefore release 4 is compatible with ONA for this option.

ONA appears to require support of non-standard window size, which seems unnecessary

Test plan and implementation issues


Currently International Public Network links are built with a default value of 4.

This option is not generally used on X.25 lines and will need to be added to the test plans if required.

&notes& = y

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 our 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 questions:

TNDTED Q184(was q72 ) i/c throughput class value (3-12)

|TNDTED Q184| q72 | i/c throughput class value..........#default none

standard Public Network settings = 3 (for all line speeds)

TNDTED Q185(was q73 ) o/g throughput class value (3-12)

|TNDTED Q185| q73 | o/g throughput class value..........#default none

standard Public Network settings = 3 (for all line speeds)

see10.15 for throughput class negotiation

UKa Answers

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 ... A - additional service

X.2 1988 ... A - additional service

ISO 8878 compatibility

ONA compatibility

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

V11s - throughput classes supported sending...

75,150,300,600,1200,2400,4800,9600,19200,48000

V11r - throughput classes supported receiving

75,150,300,600,1200,2400,4800,9600,19200,48000

V3s - Default throughput classes supported, sending:

75,150,300,600,1200,2400,4800,9600,19200,48000

V3r - Default throughput classes supported, receiving:

75,150,300,600,1200,2400,4800,9600,19200,48000

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

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 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.


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