Telecommunications - Configuration of X.25 Call redirection


Subscription Option - Call redirection

An optional user facility agreed for a period of time. This user facility, if subscribed to, redirects incoming calls destined to this DTE when:

a) the DTE is out of order, or

b) the DTE is busy (all logical channels in use)

Some networks may offer in addition:

c) systematic call redirection due to prior request by the subscriber

When the call is redirected the call accepted packet (or the clear indication packet) transferred to the calling DTE will contain the called address of the alternate DTE and the Called Line Address Modified Notification (CLAMN) facility, indication the reason why the called address is different from the one originally requested.

When the virtual call was redirected, some networks may indicate to the alternate DTE that the call was redirected, the reason for redirection and the address of the originally called DTE, using the Call Redirection Notification (CRN) facility in the incoming call packet.

CCITT permits multiple addresses in redirect list.

UK Redirect support:

X.2 LEVEL 3 PER USER SUBSCRIPTION X.2 (1984) UK(a) UK(b) interworking
OPTIONS REF CLASS now now R5a R5b R6
Call redirection on out of order. 1.28 A p
on busy......... p
systematic...... . . . p

| Call redirection on out of order.| 1.28 A |





| | | # | on busy.........| |

| . | . |


| | | # | systematic......| | . | . | . |


| | | #

UK(a) UK(b)
Redirect on out-of- order
Redirect on busy
Redirect systematic from rel 5
CLAMN from rel 5b
CRN from rel 5b
chaining (ie redirect max 2 hops
to line which itself
has redirect
Source Rotary x
ie redirection which only applies to calls from a specific address
Destination Rotary ¹
ie redirection which applies to calls from all addresses
sub-address options *unchanged on redirect
*set to zero on redir
*new subaddress
limitations the caller must have extended format capability for redirect to occur (so that the caller can be informed that redirect has taken place)
redirect on hunt not recommended
group hunt group takes priority over redirect but only if hunt groups are all on one node

UK(b) - redirection is done by putting the hosts in a HOSTLIST which has an alphanumeric name which is known globally on the network. The main destination will be the 'home' destination.

If redirection on all LCNs busy is required then the HOSTPO macro must be enabled. This causes a message to be sent to the supervisor when the number of LCNs in use rises above a specific value. This should be less than the total number of incoming channels because it is possible for the LCNs busy message to collide with an incoming call request.

I don't know how (or if) a HOSTLIST can be specified in an X.25 NUA. We need to check this with UKb.

UKa already supports redirection.

If both HUNT group (multiline) and redirection are subscribed to the priority of these two facilities will depend on whether the multiline is spread over several switches.

At release 4, CLAMN and CRN have been added as subscription options to meet the CCITT spec.

UKa allows only one redirection address per line. Only two redirections can be 'chained' before the call is cleared.

Normally on Public Network a 12 digit redirect address is used (upto 14 digits can be specified), this causes the subaddress in the call request packet to be passed on to the redirected DTE.

Table build questions:

TNDTED Q198(was q86 ) redirection address length (0,5-14)

|TNDTED Q198| q86 | redirection address length..........#default 0

(if alternate addressing chosen)

we do not use alternate addressing so you should never need to answer this question.

TNDTED Q199(was q87 ) redirection address length (0,5-14)

|TNDTED Q199| q87 | redirection address length..........#default 0

(if UKa addressing chosen)

values other than 0 enable redirection when the originally called DTE is .

TNDTED Q202(was q8 ) redirect on no VCs (YES/NO)

|TNDTED Q202| q8 | redirect on no VCs..................#default NO

allows redirect on busy in addition to out-of-order

TNDTED Q203( new ) subscribe: systematic call redirection

|TNDTED Q203| new | subscribe: systematic call redir.....#(YES/NO)

if yes always redirects.

TNDTED Q204(was q90 ) redirection address

|TNDTED Q204| q90 | redirection address.................#

TNDTED Q118(was Q10 ) CRN facility (YES/NO) default NO

|TNDTED Q118| Q10 | CRN facility........................#a DTE subscribing to this facility will be informed each time it is chosen as an alternate destination for a call. The address of the original destination DTE and the reason why the call has been redirected, will be provided to the alternate DTE in the incoming call packet .

TNDTED Q120(was Q13 ) receipt of CLAMN facility (YES/NO)

|TNDTED Q120| Q13 | receipt of CLAMN facility...........#default NO

A DTE that subscribes to this facility is notified whenever one of its calls has been routed to an alternate DTE. The notification includes the address of the alternate called DTE in the address field, and the reason why the called address was changed. This facility is included in the call connected or clear indication packet.

Possible reasons why the called address is changed are:

A CLAMN facility can be originated by:

note: redirection will only occur if calling DTE is built as enhanced

TNDTED Q165(was q49 ) enhanced DTE (YES/NO)

|TNDTED Q165| q49 | enhanced DTE........................#

redirect diagram

&UKb& = yUKb support

v 4.03

SVC: partial support

does not support Call Redirection Notification CRN

facility or CLAMN facility (generated by the DCE).

How many addresses

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)

FS10 - Called Line Address Modified Notification ... O = Optional

FR11 - Call redirection Notification ............... O = Optional

Therefore release 4 is compatible with ONA for this option.

Test plan and implementation issues

Customers may now be given additional option of CLAMN and CRN subscription.

Another tricky one to test - we need to try all combinations of -

call redirection group



enhanced DTE

call originator 1980

call receiver 1980

+ all facility options that could be generated by either end

+ mixing with other options such as hunt group

*** check can multiple redirect addresses be supported?

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