RCS/RCS-e : What is it ?


As of now, my single line description of RCS is 'Mobile version of Microsoft Lync'. Of course, RCS is not Microsoft implemenation, but in terms of user level (service level) functionality, the goal/function of RCS is very similar to what you currently see/using with Microsoft Lync.

If you want to get more formal description about RCS function, see Common Core Services of RCS section.


Whenevery you get confused by anything when you try to catching up the new technology/words, one of the best way would be to refer to any person/document from which/who the word/technology is orignated.


It seems that the origination of RCS/RCS-e comes from GSMA. So I decided to dig things from GSMA.


A simple/clear definition of RCS/RCS-e from  


  • RCS (Generic Term) = the generic term used to describe Rich Communication Services?
  • RCS (Special Term) = Project name for the GSMA's promotion of rich communications among MNOs (Rich Communications Services).
  • RCS-e = Technical spec name for the preferred methods of providing first stage interoperability among MNOs (Rich Communication Services ? enhanced). RCS-e is the latest version of Rich Communication Suite (RCS) which will enable mobile phone end users to use instant messaging (IM), live video sharing and file transfer across any device on any network operator


Another good definition of RCS can be found at Wikipedia ( as follows.

  • RCS initiative is an industry effort focused on the use of IMS for providing mobile phone communication services. "Rich Communication" in itself is meaningless jargon, which refers to the use of more than just voice for communication, but has long been touted as a benefit of IMS. It is to be noted that much of the capability of RCS is already available from Internet service providers.


If you want some intuitive 'feeling' about this, go to


As is described above, RCS initiative is a "joint efffort in the industry". It implies that many stakeholders in the industry (both Network Operators and UE manufacturer) should join in the effort and come out with some 'agreed rule (specification)' and implement them according to the specification. I don't know exactly how many Network Operators and UE makers are participating in this joint effort, but seems that there would be over 80 companies (Network Operators + UE Maker).


There are very wide spectrum of technicalogies specified in the RCS, but a couple of Core technology that almost everybody talks about RCS are as follows.


    i) Enhanced Phonebook : This phone book give you not only simple phone numbers but also presence information and service capability. With these information, you can initiate the communication by selecting one of the available communication types. You can use the Presence information  to communicate any personalized contact features including photo, availability and free text

    ii) Enhanced Messaging : This enables a large variety of messaging options like SMS, MMS, Instant Messaging and buddy related communication history.

    iii) Enriched Call : This enables multimedia contents sharing during the voice call. (e.g, video share, image share and file transfer)


You can find the detailed Technical Specification of RCS-e from

If you are interested specifically on how to test these features, please refer to the test specification at GSMA site.

RCE IOT001 RCS-e Test Cases.



Progress in the Industry


I put a couple of different versions of my comments to show how the things has been changing.


< Comments in mid 2013 >


As more and more people gets interested in IMS more than the simple SMS, I am hearing more and more about RCS.

RCS stands for 'Rich Communication Service'. You will find quite a lot of material by googling it, but it would be hard to get a 'short/tangible' understanding of what it really is. Is RCS a kind of specification ? Is it a kind of software package ? Is it a kind of name for a technology ?


Confused !!!...


< Comments in Jan 2015 >


Now much clear at least in terms of feature. Things seems to be clearer on what do we want to have with RCS and we start seeing some commercialized and engineering mobile phone supporting (or claimed to support) RCS. So at least we can try things in real implementation. But I see a lot of unclear issues in terms of detailed implementation, like SIP message sequence and detailed parameter settings within those SIP message. At least, we will see/experience a lot of testing going on and will have excellent chance to learn.


< Comments in Feb 2015 >


I had chance to try with some engineering devices being tested in carrier labs and verified that several important RCS feature is working with test equipment. 1-to-1 chat, file transfer seemed to be pretty stable. Group Chat worked OK as well. VoLTE over RCS was not that stable yet.


< Comments in late 2015 >


A couple of more device for another carrier were tested mostly for VoLTE over RCS. It seems that different carrier implemented RCS in a little different manner in terms of triggering RCS, so we had more problems with meeting the precondition (e.g, Special Authentication, RCS Capability exchange etc) for UE to trigger RCS even before testing main RCS features (e.g, 1-to-1 chat, file transfer, VoLTE over RCS)



Common Core Services of RCS


There can be various ways of designing RCS Services and it's implementation, but it is highly likely to follow the guide lines specified by GSMA. Following is the Common RCS Core services listed in GSMA RCC-61-Service-Desc-Doc-v1-0.pdf.


< High Level Service >

  • 1-to-1 Chat
  • Group Chat
  • File Transfer Incl. Geolocation Push
  • Audio Messaging
  • IP Voice Call
  • IP Video Call
  • In Call Services


< Component Features to implement High Level Service >

  • Capability Discovery and Service Availability
  • Operator Message
  • Messaging for Multi-Device
  • API Extensions
  • Security against Malware
  • RCS Settings



Basic Procedures in RCS


Since we are in relatively early stage of RCS, you might have not seen many examples of RCS message sequence. It is same case for me.

I will put down some simple examples for various RCS procedures. I will extend this list as I get more experiences.