Much Ado about Registration

Registration is something what was missing in the times of wires. Ok, not completely but it was done more or less once when an MSISDN was assigned to some line.

IMS Registration
IMS Registration

In contrast to the previous types of the networks the 4G network is ‘user-centric’. It means the user can use multiple devices and identities and we have to deal with it. The main purpose of the registration is to create a binding between user (her public identity) and IP address of the device, so we know where we can send the data to. That’s why there is a Contact header in the SIP REGISTER message. The Contact header contains an address which identifies the current location of the user (Point-of-Presence – e.g. IP/FQDN of a particular client). During the registration is the Contact Address is linked to a Public Identity (IMPU, AOR in SIP terminology). The IMPU is an equivalent to MSISDN in GSM and has to be present in the To header of the SIP REGISTER. One identity can by used by more terminals and as each terminal can have different capabilities this has to be also taken into account. This information is part of the Contact header.

Contact: <sip:119560022547@152.67.235.234:49635;transport=tcp>;
   expires=3200;
   +g.oma.sip-im;
   language="en,fr";
   +u.asmc.apn="6a6044869e2aba3d23d4cfc0ef1384d00da28854c2408ddbbf";
   +sip.instance="<urn:uuid:D4196919-ED8A-4E00-9436-B9CDD1E76813>"

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Messaging in RCS

Instant (multimedia) messaging is a key feature for RCS as it should replace SMS service. There are more types of messages which can be sent through the IMS network.

When we will take a look on the SIP indication of capabilities by Accept header there are quite a few of supported formats:

  • Text/plain
  • Message/CPIM
  • Application/reginfo+xml
  • Application/vnd.3gpp.sms
  • Message/imdn+xml
  • Application/3gpp-ims+xml

For common Instant Messages we typically use Common Profile for Instant Messaging (CPIM). This format allows compatibility among various messaging technologies. Notifications are then sent as in Instant Message Disposition Notification (IMDN) format.

Messages can be exchanged over SIP or MSRP protocol. Sometimes  also http/ws is being used for transfer of rich content.

Update: For the information about RCS Universal profile read the post GSMA Advanced Messaging – RCS Universal Profile.

RCS 5.2 defines two basic types of messaging. They are the Session Mode Messaging which is based on SIP INVITE and MSRP session and the Pager Mode Messaging which is based on SIP Message. The RCS refers to OMA CPM which is considered to be an evolution of the SMS/MMS messaging services.

Note that SIP MESSAGE can be used also for other than messaging purposes in IMS network (e. g. during eSRVCC registration)

 

Session Mode Messaging

Session mode does use SIP INVITE and SDP protocol to establish the session. Within the session MSRP protocol is used. This allows to split ones conversation into dialogs and use “..is typing” notifications. On the other hand more resources is needed.

IMS and MSRP
IMS and MSRP

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RCS – Rich Communication Services

 

So what is the RCS?

Update: For the information about RCS Universal profile read the post GSMA Advanced Messaging – RCS Universal Profile.

RCS is an attempt of mobile operators and their vendors to be more than just connectivity providers. With the 3rd generation of mobile networks many people started to believe that they’ll not need the operators soon – as long as they can connect to the Internet they have VoIP, Instant messaging, Emails, Facebook, etc (Over-the-top  applications OTT). Why should anyone pay for roaming or use SMS anymore? But for the operators Voice services and SMS were/are the main sources of income. VoLTE and RCS should give their customers the user experience they know from Skype, Whatsapp, Viber or Line and enable them to stay relevant.

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