Telecommunications - Configuration of X.25 Networks


 

CCITT defined DTE facilities


In order to support the OSI Network Service over a packet switching network CCITT has specified a number of end-to-end DTE facilities. These facility fields are validated by the network for correct facility code, facility code not duplicated etc. but the contents of the facility are not acted on by the network but are passed through the network unchanged.

In order to support these facilities the following have been added -

a) facility field maximum length increased to 109 bytes

b) CCITT specified DTE facility marker added

Beginning of marker OSI DTE facility Marker
00 0F

| | | | 00 | 00000000 | Marker 000F = DTE facility marker........#

X.2 LEVEL 3 PER CALL FACILITY X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
DTE facilities .
DTE facility marker .
calling address extension .
called address extension .
minimum throughput class .
end to end transit delay .
expedited data negotiation .

&UKa& = yUKa support

CCITT defined DTE facilities are supported at release 4

It is not a subscription option, it will be allowed in calls provided both ends of the call are DX2s

*** check --- what if call is transiting through DX1s ***

The network will clear the call if:

* The CCITT facility marker must come after the normal facilities not before. If there are any normal facilities after the CCITT marker the call will be cleared 034D.

* called and calling address extension limited to 16 bytes (32 BCD digits)


9.1 CCITT defined DTE facilities - Calling Address

extension facility

Description of Facility

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

| CB calling address | length | use | BCD address |

| extension | in bytes| | |

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

^

|

bits 8 7

--------

0 0 = to carry a calling address

assigned according to

recommendation X.213

ISO 8348

0 1 = reserved

1 0 = other (to carry a calling

address not assigned

according to X.213

1 1 = reserved

bits 1-6

--------

length (in BCD digits) upto 40

of address
3

| | | | CB | 11001011 | Calling Address extension facility.......#&UKa& = yUKa support

Yes, supported in release 4.

Only the facility code and length are validated by Public Network. This facility is passed through the network transparently


This facility will facilitate interworking with private networks.


9.2 CCITT defined DTE facilities - Called Address

extension facility

Description of Facility

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

| C9 called address | length | use | BCD address |

| extension | in bytes| | |

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

_

+--------+

|bits 8 7|

+--------|

|0|0|= to carry a called address

| | | assigned according to

| | | recommendation X.213

| | | ISO 8348

|0|1|= reserved

|1|0|= other (to carry a called

| | | address not assigned

| | | according to X.213

|1|1|= reserved

+---+

bits 1-6

--------

length (in BCD digits) upto 40

of address
3

| C9 | 11001001 | Called Address extension facility........#&UKa& = yUKa support

Yes, supported in release 4.

Only the facility code and length are validated by Public Network. This facility is passed through the network transparently

FR22 - Called address extension .................. M = Mandatory

Therefore release 4 is compatible with ONA for this option.

Implementation issues

This facility will facilitate interworking with private networks.


9.3 CCITT defined DTE facilities - Minimum Throughput Class

Description of Facility

Minimum Throughput Class Negotiation

0A Minimum Throughput Class|
^
|
bits 1-4 = from called DTE
bits 5-8 = from calling DTE
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

| 0A | 00001010 | Minimum Throughput Class.................#&UKa& = yUKa support

Yes, supported in release 4.

Only the facility code are validated by Public Network. This facility is passed through the network transparently

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

FS23 - Minimum Throughput class negotiation........ M = Mandatory

FR23 - Minimum Throughput class negotiation........ M = Mandatory

Therefore release 4 is compatible with ONA for this option.

Implementation issues

Public Network cannot guarantee a given throughput class. This value is end-to-end so it does not affect us directly.


9.4 CCITT defined DTE facilities - end-to-end transit delay

Description of Facility

end-to-end transit delay

CA length cumulative requested end- maximum acceptable
2,4 or 6 transit delay to-end transit end-to-end transit
2 bytes delay 2 bytes delay 2 bytes

| CA | 11001010 | End-to-end transit delay.................#Transit delay is expressed in milliseconds. The value of all ones indicates that the cumulative transit delay is unknown or exceeds 65534 milliseconds.

&UKa& = yUKa support

Yes, supported in release 4.

Only the facility code and length are validated by Public Network. This facility is passed through the network transparently


FS24 - end-to-end transit delay ................... M = Mandatory

FR24 - end-to-end transit delay ................... M = Mandatory

Therefore release 4 is compatible with ONA for this option.

Implementation issues

Public Network cannot guarantee a given transit delay. This value is end-to-end so it does not affect us directly.


9.5 CCITT defined DTE facilities - priority facility

Description of Facility

D2 length target values for lowest acceptable values
1 to 6 priority of data for priority of data on
on connection 3 bytes connection 3 bytes

| D2 | 11010010 | Priority facility........................#


9.6 CCITT defined DTE facilities - Protection facility

Description of Facility

protection facility

D3 length length of protection value protection value

00xxxxxx reserved

01xxxxxx source address specific

10xxxxxx destination address specific

11xxxxxx globally unique

_

|

| D3 | 11010011 | Protection facility......................#

9.7 CCITT defined DTE facilities - Expedited data negotiation

facility

Description of Facility

Expedited data negotiation facility

0B Value
xxxxxxx0 = no use of expedited data
xxxxxxx1 = use of expedited data

| 0B | 00001011 | Expidited data negotiation facility......#

&UKa& = yUKa support

Yes, supported in release 4.

Only the facility code is validated by Public Network. This facility is passed through the network transparently


 


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