Telecommunications - Configuration of X.25 Transit Delay Selection and indication

 

Per-call facility options - Transit Delay Selection and indication


Description of Facility

A DTE wishing to specify a desired transit delay in the call request packet uses the Transit delay Selection facility to indicate the desired value.

The network, when able to do so, should allocate resources and route the virtual call in a manner such that the transit delay applicable to that call does not exceed the desired transit delay.

The incoming call packet transmitted to the called DTE and the call connected packet transmitted to the calling DTE, will both contain the indication of the transit delay applicable to the virtual call. This transit delay may be smaller than, equal to, or greater than the desired transit delay requested in the call request packet.

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

| Facility/utility code | Delay in milliseconds |

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

| 49 hex | MSB | LSB |

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

65535 (all ones)

if network does not

support

| 49 | 01001001 | Transit Delay Selection and indication...#

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

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

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

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

| Transit delay selection and indicati| 2.10 E | . | | | | | | |

| |

P P P

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

UK(a) - not supported

UK(b) - Will be supported from release 6

&UKa& = yUKa support

This facility is supported by release 4.

The value requested will not effect the routing selected through the network.

UKa answers

Question: What value will be returned by the TP4 in the Transit delay indication facility? will this give customers information about the number of hops the call will take across the network ? can this be prevented ?

Answer : The value returned by the TP4 for X25 DTE's is the remote TPs "Transit Delay Factor" multiplied by the hopcount incremented by one. For X75 STE's the TDS requested is added to this figure.

TSYSP83 template Q151 :-

- Enter TP Transit Delay Factor in Milliseconds.

This will not explicitly give information on the hop count

to customers.

If you do not wish to allow your customers to use this then

you can prevent them by setting TNDTED71 Q13(X75),Q125(X25)

to No.

Q13 : Does STE subscribe to receipt of Transit Delay (TDSI)

Q125: Does DTE subscribe to receipt of Transit Delay (TDSI)

&UKb& = yUKb support

X.25: Supported

UKb does not currently route a virtual call based on requested transit delay values.

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)

FS12 - Transit Delay selection and indication...... M = Mandatory

FR12 - Transit Delay selection and indication...... M = Mandatory

we need to check this out.

Test plan and implementation issues

need to test the effect of this option.

Does it generate a fixed value for transit delay based on the hop count - We need to test this out.


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