RCS – Rich Communication Services

As this is a blog, I’m not going to recap all the stuff you can find in wikipedia about RCS. Wikipedia is a great source of information but sometimes you can’t see the forest for the trees. The RCS is really a big theme so I guess it would be better to write several posts than to try put all the relevant information in one. I’ll probably use some simplifications, the details and exceptions will be described later.


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.

What is RCS from the technical point-of-view?

RCS does use the same network as VoLTE. That means EPC from LTE and IMS framework. RCS services are:

  • Voice & Video chat and group chat
  • Instant Messaging
  • Enhanced Addressbook
  • Social sharing, Geolocation ..

These services are implemented as application servers in IMS network. Usually there will be several servers required for the RCS:

  • CPM – Common platform messaging server
  • IPSMGW – Gateway towards 3G networks
  • PS – Presence server (social presence)
  • Content server – data transfer
  • Media Server – voice, video transfer, media streaming and conversion
  • Addressbook service
  • Configuration server
  • Additional services (Gaming, Alert Severs, News, OTT gateways, Legal intercept, History ..)
  • LDAP databases, Prepaid systems, Charging systems, Monitoring servers, Provisioning, ..

Various protocols are used to interconnect these services. SIP/SDP for signaling is given by IMS. But XMPP can be used for the addressbook and/or presence. Some kind of HTTP (REST, SOAP, XHR).. is used for the configuration, provisioning and OTT services. With HTML5 websocket – WS is beeing used more and more. Voice and video is usually transferred via RTP protocol. For databases LDAP is kind of industry standard, Diameter for prepaid and service triggering.

The basic flows will be described in next posts.


What are the problems?

  • Complexity
    • Comparing to services in 2G or 3G networks the ecosystem is much more complex. That was also the reason why the RCSe specification was created. The ‘e’ stands for ‘enhanced’ but in fact it was simplified RCS. And as always complex means expensive.
  •  Standards
    • The standards are not settled down yet. Although SIP and IMS specifications exist for more than a decade, the implementation differs vendor to vendor. The standards will be discussed in some other post.
  • Complexity & Standards
    • As withing one deployment (e.g. one operator) there are typically more vendors involved, each delivering one of the systems (including those for IMS), it is usually quite difficult to find the common ground. Especially if more clients are allowed.
  • Presence
    • Presence and reliability is a big issue for all the real time communication

 presencetaken from http://www.slideshare.net/saghul/sip-beyond-voip



The biggest issue so far with all the OTT was the interoperability. Mobile operators were able to find a common ground and IMS is a well recognized standard. Hence operators are able support calls among themselves. (However in practice they are mostly not interconnected yet when it comes to VoLTE, that’s the task for RCS UP.)

One of the added values should be 3G gateways. Instant message can fall back to SMS, picture can be delivered as MMS, voice is voice. All this should be done seamlessly.

On the other hand the gateways towards OTT providers are questionable. There is a very limited will to provide interfaces by companies as Google or Facebook. There had been such an interface (XMPP) for Google talk in past.  But as the service is more successful the more users it has providers are trying to avoid this.


Why not to stay with OTT applications?

Well, there are some reasons as network neutrality issue or consolidation of digital identities. Operators are also trying to offer a better quality and (guaranteed) reliability of services and emergency services. Plus the 3G fallback, of course.  Last but not least operators – in contrast to OTT providers – have to respect the local laws.

How would it look without RCS and VoLTE? There would be several OTT applications (Skype, Viber, Whatsapp, Line, Facebook, Google hangout, ..) and based on what technology your contact is present you’d use the appropriate client. In case you’d need to contact the counterpart in GSM/CDMA you’d pay to your OTT provider. Emergency calling? Nope. Access Transfer? Nothing. What about company accounts? Instead of one provider there would have to be several in order to support all customers/partners/vendors. This doesn’t sound nice, however some mix of OTT and RCS is possible. The question is traffic distribution.

Now the RCS is doing its first baby steps and no one can’t predict if this technology will be a success (SMS) or not (WAP). Anyway RCS is a part of 4G evolution so we can expect that in some form it will be relevant in the coming years. Learning from the past Skype was very successful when we speak about roaming. In case of local calls GSM still rulez. In messaging SMS is used by banks all over the world to inform people about balance on their accounts. But for example in Taiwan the legacy messaging has been nearly replaced by Line.


Can I use it or not?

It depends on what country you are living in and what operator you have. Generally speaking most operators are in an early phase of 4G network adaptation. Mostly they use to start with the VoLTE and the next step will be the RCS. See the map.


Where to go next:




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