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3G/UMTS |
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SS (Supplementary Service)
Supplementary Service is a set of services that modifies or compensate (supplement) the basic telecommunication services. It is a little bit difficult to define it clearly in a few words since the spectrum of the services are so wide. If you look into each of those services, you would gradually absorb the meaning of those services. (Don't try to memorize them.. just try to dig into each services one by one as you come across). For the details, refer to following 3GPP specification as framework
In terms of RRC/NAS protocol, it is very similar to SMS. Like SMS, it is using control channel to carry the data. In WCDMA, it use DCCH to carry the data and in GSM it use SDCCH to carry the data.
< Channel Requirement >
As I mentioned above, SS messages is carried by an RRC message which is mapped onto DL/UL DCCH (in case of WCDMA) and SDCCH(in case of GSM). So to perform a Supplementary Service, UE should be in a states where necessary channels are established. For example, in case of WCDMA, we can perform a Supplementary Service anywhere in between RRC Connection Setup Complete and RRC Connection Release. Exactly when to initiate this service is completely up UE and network implementation.
< Major SS Messages >
In terms of messages, Supplimentary Services are made up of following three component messages.
< Operation Code >
How to implement such a wide variaties of services using only a couple of messages ? Secret lies in Operation code in 'Register' message. Register message contains 'Facility' IE in it and within the IE lies 'operationCode'. Depending on the value of operationCode, different type of Supplementary Service will be performed.
operationCode has very long list of elements in it as shown below. It would take pretty long time and a lot of reading to understand the details of each of these parameters. I will explain on each of these parameters as I come accross.. I don't know how long it would take to cover all of these -:)
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