Additional octets in FTN (Forward To Number) in Register-SS OTA message

Question:

Why additional octets appear in FTN (Forward To Number) in Register-SS OTA message?

Answer:

Higher layers of AMSS sends a FTN to NAS during register-SS operation. But the OTA
message has two additional octets in FTN number.



This is due to Long-FTA feature. Some networks support this feature. The additional two octets are optional octets as below. Networks which do not support this feature will ignore the additional octets. But there will not be any side affects of this octets.

See 29.002 Section 17.7.4

RegisterSS-Arg ::= SEQUENCE {
ss-Code SS-Code,
basicService BasicServiceCode OPTIONAL,
forwardedToNumber [4] AddressString OPTIONAL,
forwardedToSubaddress [6] ISDN-SubaddressString OPTIONAL,
noReplyConditionTime [5] NoReplyConditionTime OPTIONAL,
...,
defaultPriority [7] EMLPP-Priority OPTIONAL,
nbrUser [8] MC-Bearers OPTIONAL,
longFTN-Supported [9] NULL OPTIONAL }


The addition of LFTN in registerSS message was mainly for catering to GCF requiremens. Some of the latest GCF test cases need the support of LFTN in the registerSS operation.

From NAS point of view, 28 digits of Forward to Number are supported..