Evolution of GSMA RCS standards

When the GSMA has specified the RCSe standards with the brand name of "Joyn" for the first time in April 2011, many global telecom companies expected that the Joyn could become a counterpart against the existing and prominent OTT services such as Whatsapp, Viber, KakaoTalk, etc. From operator's view, it was believed that such OTT services had been growing dramatically by piggybacking on the teco's qualified infrastructure and they were even taking telco's revenue sources by providing free mVoIP and messaging service features.

In Korea, big three telcos have started Joyn service at the end of 2012 along with some European telecommunication companies such as Vodafone, Orange in Spain, Germany and Italy. Since then, it has been more than two year passed now. The Joyn service in each country didn't grow that much, whereas OTT services are steadily growing in the market. Given this circumstances, most of other telcos which didn't provide Joyn service yet are hesitating to launch their own ones. Even such telcos which are already providing Joyn service are also hesitating with further investment on their service.

Even in this dire situation of the Joyn service, RCS technologies and the related specifications in GSMA have been evolving to keep up with the market trends. This article will skim over the roadmap of evolving communication technologies in terms of global standards, which would be a help to understand better about how telecommunication industry is making an effort to keep up with the market trends.

1. The advent of IP Messaging Service and evolution towards Converged IP Messaging

The OMA(Open Mobile Alliance) has specified the SIMPLE IM technology as the first IP based messaging technology around mid-2000. The SIMPLE IM provides typical SIP based messaging features such as 1-1 and group session-based messaging(i.e., chat). This SIMPLE IM became the basis of the following technical standards of communication technologies. Since 2005, the OMA MWG WG(i.e., COM WG as of now) started developing CPM(Converged IP Messaging) technologies(1), which adopted many service features and technologies from SIMPLE IM. The CPM provides a converged communication service feature by integrating legacy messaging services(e.g., SMS, MMS, Email) on top of IP chat features, voice streaming, video streaming, etc. The CPM also considers multiple devices in a way to provide users with converged  communication environment and consistent user experiences across multiple devices.

Strictly speaking, the converged communication environment and the consistent user experiences had already widely been accepted by users via PC based messenger services such as ICQ, AOL, MSN messenger, etc even before OMA came up with OMA CPM. Such 3rd-party services were providing Chat, Presence Information sharing, SMS/MMS integration, File Transfer, conversation history backup features on top of IP network. Therefore such standards activities by OMA can be interpreted as an effort of many global operators to apply similar user experiences to mobile environment expecting they can add up another revenue sources by providing a proven service features in their network.

2. OTT vs Operators

Since the iPhone has tapped into the market in late 2000s, all the device manufacturer started to come up with their own smartphones. The wave of smartphone since then has changed many things in the eco-system of telecom industry. With Apple's AppStore and Googles Android Market(i.e., Google Play as of now), 3rd-party application developers could become service providers by themselves. The operator-centered vertical value chain was collapsed and lots of 3rd-party services started to come out for free. Many tech leaders started to claim that operators will become a dumb-pipe in the end. The operators lost negotiation power in the market as consumers eager to stick to free OTT services. There were some attempt to regulate the traffic from the OTT services however, it was banned by the market and by the law under the name of the network neutrality. Some OTT services such as KakaoTalk, Line, Whatsapp became heros in the messaging market as they flourishes. Many 3rd-party services who have successfully grabbed the early market of smartphone era started to overpass traditional operators.

With the advent of prominent OTT services, operators started to lose their traditional key territories such as messaging and voice call. OTT service providers who gained the early market kept growing as a result of lock-in effect. Revenues from messaging service of operators plummeted along with traffic.

This radical changes in the market drived global operators to gather in GSMA in order to find the way to stand against threats from OTT services and they kicked off RCS(Rich Communication Suite) project within the GSMA to provide enriched IP based communication services. The RCS service requirements were specified and many technical details to meet the requirements were adopted from the OMA SIMPLE IM and CPM. The RCS specification has been developed and published up to RCS release-4(2,4).

3. Joyn

The RCS r4.0 included most of advanced features of OMA SIMPLE IM and CPM. However there was no operator coming up with RCS service as they were skeptical about the benefits and feasibilities of the service. It might look too complicated to implement RCS r4.0 due to its technical difficulties and various service features. While operators were developing technical standards and hesitating to build RCS service out of whatever reasons, the number of OTT subscribers were soaring up in the market and operators revenue kept declining. Given this circumstances, operators might have felt that they need a time-to-market service that is simple enough to build within a short period of time. As a result of such discussion, operators came up with a simplest RCS service with a brand-name of "Joyn" of which standards is a RCSe and currently updated to RCSe 1.2.2(3). The following is the list of main features of RCS-e r1.2.2:

• HTTP-based Configuration Provisioning for primary device(i.e., PS-access device): Provisioning of service related configurations to RCS enabled device.
• Service Capability Discovery: Procedures to find a contact who has RCS capabilities.
• IP Messaging (i.e., 1-1 Chat, Group chat)
• Store and Forward in a 1-1 Chat: Temporary message store while the recipient RCS user is not available and forwarded later when it becomes available.
• 1-1 File Transfer
• Image Sharing based on IR.79 : Real time image sharing with a peer engaged in a voice call.
• Video Sharing based on IR.74 : Real time video sharing with a peer engaged in a voice call.
• Social Presence Information sharing(i.e., anonymous fetch, optional) : Viewing of contact's social presence information such as portrait icon, free text, favorite link, availability, etc.

4. Adoption of CPM architecture in RCS

The GSMA RCS has adopted OMA SIMPLE IM architecture in the beginning of RCS work. As the RCS is updated to r4.0, it has updated the architecture by adopting OMA CPM, which introduces several more components on top of SIMPLE IM architecture, that is, Network based Message Storage and Interworking Function. 

<source: GSMA RCS5.0>

The Network based Message Storage is used to store RCS user's conversation history and synchronize conversation history across RCS user's multiple devices. The Interworking Function is used to integrate legacy messaging services such as SMS and MMS in the network side. The Email interworking function in OMA CPM was not included in RCS. 

5. RCS r4 and RCS-e merged into RCS r5.x

The GSMA RCS r5 has come out based on RCS r4 and RCS-e r1.2.2(5). All the technologies and service features have been merged into RCS r5. As of now, RCS r5 has been evolved up to RCS r5.4. The RCS r5.x intends to integrate all the communication features on the basis of IP network. Legacy messaging services such as SMS & MMS are integrated into IP Chat features. IP Voice/Video call features are integrated with VoLTE service and they support various supplementary services. All of these communication services is presented to the user with an Integrated UX/UI. The following provides brief descriptions on main features of RCS r5.1

• The Configuration Provisioning has been extended in RCS r5.1 in a way to accommodate non-PS access device and RCS user's secondary device. A number of configuration parameters also have been added.
• The Standalone Messaging gives the same user experiences as SMS/MMS in a sense that both are session-less communications. There are two types of modes defined in Standalone Messaging based on the size of message to be sent:
• The Pager Mode message delivery( <=1,300 bytes)
• The Large Message Mode message delivery(>1,300 bytes)
• The Multimedia within the IP chat session has been allowed in RCS r5.1. The RCS users can send multimedia within the IP chat session. In case the size of multimedia is over the pre-defined size that is allowed within the chat session, the multimedia content is sent using File Transfer mechanism. The file transfer session will be separated from the existing chat session in order to be processed in parallel. Even when it is sent as a File Transfer and in a separate session, the RCS user will be able to view the transferred multimedia content within the same conversation context of the existing chat session. 
• The Store and Forward in a Group Chat improves the reliability of message delivery in a group chat session. The participant who has been disconnected involuntarily from the group session due to connectivity loss, battery drain, etc can rejoin the group session after the device regains its connectivity. The rejoining participant can receive all the RCS messages that were missed while he/she was disconnected(Basic Store and Forward). Even the late participant in the group session can also receive a full conversation history(Full Store and Forward).
• The Group session restart(Long Lived Group) catches up the current user experiences provided in OTT services where users can start chat session by sending any message in a conversation thread stored in a local device. In RCS r5.1, the group chat session will be released if the inactivity timer is expired. After the group session is closed, the conversation history will remain in a participant's local device as long as users do not delete it. Thereafter user can re-start the same group session by sending a new chat message or file within the conversion history thread. In order for the group session to be re-started, the group session identity should be kept in the RCS system. If the group session can not be re-started as the corresponding group session identifier was removed from the RCS system, the RCS client may automatically attempt to start a new group session.
• The HTTP and MSRP based File Transfer is to use HTTP or MSRP for File Transfer. In case of using HTTP, the file to be sent is uploaded to a certain contents storage in the network by an originator and the location url of the stored object is obtained in return. The location url is sent via chat session or as a standalone message to the recipient. The recipient can retrieve the file from the received location url.  
• The File Transfer Thumbnail preview is to send a thumbnail to the recipient along with other file information such as file name, file type, file size, etc within the file transfer request. The recipient RCS user may determine whether to accept the file transfer request based on these received information.  
• The File Transfer pause and resume is to pause file transfer while the file transfer is in progress and resume whenever the user wants. The file transfer can also be paused unexpectedly due to, e.g., connectivity loss. If the file transfer is resumed by either end user later on, the file can be transferred from the location where it was paused. In multiple devices environment, the RCS user needs to use the same device to resume the file transfer. Otherwise the file transfer will start from the beginning as there is no file fragment in that device. 
• The File Transfer Store and Forward is to store the file temporarily when the recipient is not available and transferred later when the recipient becomes available. 
• The File Transfer in Group Session
• The Social Presence Information has been enriched in RCS r5.1 by accommodating the location information of the RCS user. The Social Presence Information is supposed be shared between RCS users who have established Social Presence Relationship with each other.
• The VIP contact is the type of contact whose change in Social Presence Information is notified in real time to the RCS user. If the contact with whom RCS user is in Social Presence Relationship is not a VIP contact, the RCS user needs to perform one-time subscription to that contact to view his/her Social Presence Information.
• The Network based Personal Black list can be created/deleted/modified by RCS users. Any RCS messages or communication attempt from a contact who is in the blacklist will be blocked. 
• The Geolocation Sharing Push/Pull is to share geolocation between RCS users. The RCS users can push his/her location information to an RCS contact(Push) or request contact's location information(Pull).
• The Contents Sharing is to share image or video clip in real time between RCS users. In RCSe, the Contents Sharing feature has  dependency on the existing voice call session, which means Contents Sharing feature is available only when there is an existing voice call session. Whereas, the Contents Sharing feature in RCS r5.1 is independent from the voice call session. RCS users can use Contents Sharing service as a standalone service feature.
• The Network based Message Storage is used to store conversation history of an RCS user. The conversation history stored in the Network based Message Storage can be synchronized with one or more devices of an RCS user. The network based message storage feature provides the user with the consistent user experience across multiple devices.
• The Legacy Messaging Interworking is support in RCS r5.1, which includes SMS and MMS. Given this feature, all the conversation history is integrated in the same conversation thread regardless of messaging type.
• The IP Voice/Video Call and VoLTE is integrated in RCS r5.1 along with IP chat features. 

6. SIMPLE IM 2.0

Since the OMA SIMPLE IM 1,0 was adopted by the RCS in the beginning, the RCS has been evolved with additional features. The OMA SIMPLE IM 2.0 has an intention to fill the gap between RCS and SIMPLE IM(6).

- Delivery of notifications for IM sent within 1-1 IM session

- Delivery of out-of-session notifications 

- Store and Forward for messages and notifications sent within the 1-1 IM session

7. CPM 2.0

The CPM 1.0 architecture was adopted by RCS r4.0 and the RCS r4.0 has evolved into RCS r5.x accommodating RCSe features. In the same way as SIMPLE IM 2.0, The OMA CPM 2.0 has an intention to fill the gap between RCS and CPM 1.0(7). The CPM 2.0 has also included some clarifications for the previous version. 

• Store and Forward in a Group Session
• Support of Closed Group, Long Lived Group
• Support of live recording of chat messages
• Interworking over NNI with SIMPLE IM 2.0
• File Transfer while having ongoing CPM session
• Store and Forward in File Transfer
• File Transfer pause and resume
• Support of Maximum File size policy
• Support of thumbnail preview in File Transfer

8. RCS Blackbird
Chronologically, the RCS blackbird has been specified only after the RCS r5.1 came out for time-to-market(8). However, from service feature point of view, the RCS blackbird is an intermediary version between RCSe and RCS r5.x. The RCS blackbird includes most of features of RCSe except the Presence related functions. The RCS blackbird also includes many features from RCS r5.x in a way to provide the similar user experiences. For example, the RCS Blackbird integrates legacy messaging features on UX/UI level by internal interworking between RCS client and the SMS/MMS client within the UE. Currently, the RCS Blackbird has been updated up to release 4.0.

***

The RCS service features have been evolving from RCSe to RCS blackbird and to RCS r5.x. The RCSe includes the basic IP chat features and the RCS blackbird focuses on messaging and integrated communications from UX/UI perspective. The RCS r5.x has integrated all the features in a box, where IP chat, legacy messaging, IP Voice/Video Call, VoLTE service are converged and provides users with unified user experiences. Feature-wise,  the RCS technologies branded as "Joyn" seems surpassing the existing OTT features. The users will be given the same user experiences as previous communication services when they make a call or send messages and at the same time, their user experiences will be enriched based on the benefits the RCS brings on top of IP network. While the GSMA is coming up with time-to-market service requirements, the OMA is providing technical details to support those requirements by upgrading SIMPLE IM and CPM. The 3GPP is cooperating with GSMA and OMA from core network perspectives by considering the technical details to be implemented. In this way, many SDOs(Standards Developing Organization)s are working in harmony with each other to come up with competitive communication service features and technologies.

Last updated: Jun 2015 

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