Telecommunications - Configuration of X.25 RPOA Selection


Subscription Option- RPOA Selection

RPOA (Recognised Private Operating Agency) related facilities provides for the calling DTEs designation of a sequence of one or more RPOA transit network(s) within the originating country through which the call is to be routed when more than one RPOA transit network exists at a sequence of one or more gateways.

Is an optional user facility which may be agreed for a period of time by. This user facility, if subscribed to, applies (unless overridden for a single virtual call by the RPOA selection facility) to all virtual calls where more than one RPOA transit network exist at a sequence of one or more gateways.

RPOA is supported by the network equipment although the facility could only be used if international agreements are made with other administrations.

See X.75

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
RPOA selection 1.31 A .

| RPOA selection......................| 1.31 A | . |




| |UK(b) Extended RPOA facility format will be supported from release 5.

UKa claim to support this option at release 4.

table build questions:

TNDTED Q122( new ) subscription: send RPOA facility

|TNDTED Q122| new | subscription: send RPOA facility.....#(ALLOWED/REQUIRED/FORBIDDEN)

default ALLOWED

This question determines whether the subscription to send the RPOA facility is permitted for the DTE. The RPOA facility allows a DTE, initiating an international call, to specify which international gateway is to be used.

TNDTED Q124( new ) subscribe: default RPOA (YES/NO)

|TNDTED Q124| new | subscribe: default RPOA..............#default NO

if Q122=ALLOWED or FORBIDDEN the DTE must subscribe to a default RPOA for inter-network calls.

TNDTED Q125( new ) enter default interchange carrier (RPOA)

|TNDTED Q125| new | enter default interchange carrier #(0001-7999)

TNDTED Q126( new ) DTE receive RPOA (YES/NO) default NO

|TNDTED Q126| new | DTE receive RPOA....................#does the DTE subscribe to receive the RPOA from the network.

UKa Answers

Questions: How is RPOA defined in tables? how does the TP know which DNICs are associated with which RPOAs? How does it override existing routing info?

Answer : A default RPOA can be defined per line in TNDTED71 (Q129) if the line subscribes to default RPOA.

The TP does not know which DNICs are associated with which RPOAs.

The TP will route a call with a single RPOA (Basic or Extended format) on the DNIC portion of the called address unless the DNIC equals the system DNIC whereby the RPOA request will be disregarded and the packet routed on the destination address.

Call Requests with multiple RPOA selection request (Extended Format) will route on the first non-system DNIC available from the RPOA list.

The Routing tables will be modified to support RPOA routing as follows :-

If no CQDT is required, the routing entry will identify a direct path to the RPOA.

If CQDT is required, the CQDT will be stored first. Any direct path data will follow immediately afterwards.

The routing algorithm will be modified to bypass CQDT entries when performing routing on RPOA addresses to force a search for a direct path. If no direct path exists then the call is cleared in accordance with currently established procedures.

&UKb& = yUKb support

Release 4 - yes



To RPOA Macro

Syntax: TORPOA ({rpoa,ln[,...,ln9]})

Default: none; all of the available links to the host can be

used to place the call

Range: rpoa is 2000 to 7999;

1n is 0 to 31

This macro assiUK a subset of the links assigned to the host in the preceding Host Links (HOSTLI) macro to a Recognised Private Operating Agency (RPOA). This allows the interface to select a valid link over which to route an incoming call containing an RPOA Selection facility. If this macro is not specified, all of the available links assigned to the host in the HOSTI macro are considered valid links over which to route the call, by default. However, if this macro is specified to limit RPOA calls to a subset of the available links and none of these links are available at the time an incoming call arrives at the interface, the interface does not route the call over the alternative links to the host; the interface clears the call.

The parameter rpoa specifies the four-digit decimal DNIC of the RPOA to which the links are assigned. Although only one RPOA and DNIC can be specified for each TORPOA macro, multiple TORPOA macros-to-multiple DNICs can be specified per host; the total number of TORPOA macros specified for the interface, however, must not exceed the value specified in the Maximum Number of TORPOA Assignments (MAXTOR) macro. If the MAXTOR macro is not defined in the interface Tymfile, the default is the number of TORPOA macros explicitly defined for the interface.

The 1n parameters specify the link number or range of link numbers to be assigned to the specified RPOA DNIC. Only links assigned to the host in the preceding HOSTLI macro should be specified for each link parameter. Links can be specified individually separated by commas (in the form 1n0, 1n1,...ln9) or in a range separated by a hyphen (in the form 1n0-1n9). Although only 10 link parameters can be specified in a single TORPOA macro, the same rpoa value can be repeated in more than one TORPOA macro per host to indicate a continuation of a previous TORPOA macro.

When more than one available link can be assigned to an RPOA call, the interface selects one of the links according to the criteria specified in the Rotate Links (ROTATE) and Link Bias (LINKBI) macros.


The RPOA Selection facility and the TORPOA macro generally apply only in a gateway configuration.

Because any RPOA Selection information entered by the CONSAT user is not currently used by the interface, this macro currently applies only to calls that orginate at a packet-mode DTE.



The XCOM interface can route each call (destined for the host defined in the preceding HOSTLI macro) containing an RPOA Selection facility/utility that requests the call to be routed through DNIC 2345, only to link 2, 3, 4, or 5.

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)

FS9b - RPOA Selection - basic..... P = Prohibited

FS9e - RPOA Selection - extended.. P = Prohibited

Therefore release 4 is compatible with ONA for this option.

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