Video Share is an IP Multimedia System (IMS) enabled service for mobile networks that allows users engaged in a circuit switch voice call to add a unidirectional video streaming session over the packet network during the voice call. Any of the parties on the voice call can initiate a video streaming session. There can be multiple video streaming sessions during a voice call, and each of these streaming sessions can be initiated by any of the parties on the voice call. The video source can either be the camera on the phone or a pre-recorded video clip. Video share is initiated from within a voice call. After a voice call is established, either party (calling or called) can start a Video Share (VS) session. The sending User is then able to stream one-way live or recorded video. The default behavior is that the receiving handset will automatically go to speakerphone mode when video is received, unless the headset is in place. The sender will be able to see what is being streamed on their handset, along with the receiving User. In this scenario, the sender can “narrate” over the CS audio connection while both parties view the video. Both users will have the ability initiate a video share session, and either the sender or recipient in a video share session can terminate the session at any time. As part of the VS invitation, the recipient can choose to reject the streamed video. It is intended that both sender and receiver will receive feedback when the other party terminates a session or the link drops due to lack of coverage. The Video Share service is defined by the GSM Association (GSMA). It is often referred to as a Combinational Service, meaning that the service combines a circuit switch voice call with a packet switch multimedia session. This concept is described in the 3rd Generation Partnership Project (3GPP) specification documents 3GPP TS 22.279, 3GPP TS 23.279 and 3GPP TS 24.279. The Video Share service requires a 3GPP compliant IMS core system. GSM Association has split the Video Share service definition into 2 distinct phases. The first phase (also called Phase 1) involves sharing a simple peer-to-peer, one-way video stream in conjunction with, but not synchronized to a circuit switch voice call. The second phase (also called Phase 2) introduces the Video Share Application Server in the solution and supports more complex features and capabilities, such as point-to-multipoint video share calls, video streaming to a web portal, and integration of video share with instant messaging. In the industry, Video Share is also referred to by other names such as See What I See and Rich Voice Call. Video Share is supported only in UMTS and EDGE (with DTM) networks. It is not supported in a GPRS or a CDMA network. The Video Share Client will drop a VS session when the handset transitions from UMTS to GSM during the session. The CS voice call will remain connected. AT&T (formerly Cingular) is one of mobile operators who have deployed the Video Share service nationwide.
Peer-to-peer video sharing was introduced by Nokia phones first in 2004. This was a proprietary solution on top of a SIP or IMS infrastructure. Some European operators offered commercial services based on these phones already in 2005. Similar services popped under the names of See What I See, Rich Voice Call, Push-to-Video (P2video or PTV), etc.
The GSMA Video Share service  was originally defined, implemented and tested during the Session Initiation Protocol (SIP) trials conducted by the GSM Association in 2005/2006. During the SIP trials, the Video Share service used to demonstrate IMS interworking over SIP. Video Share was also tested on the IPX  to prove that the service might become universally available in the future.
Subsequently, GSMA decided to create a separate project for Video Share. Phase 1 of the Video Share project built on and leveraged the results from the SIP trials. Service definition for the first phase of the Video Share project was completed in September/October 2006. Mobile operators worldwide, such as AT&T, have deployed the Video Share service  based on the Phase 1 service definition. An interoperability technical reference specification for Video Share  is also available from GSMA.
Phase 2 of the GSMA Video Share project was kicked off in May/June 2007 and is currently in progress.
Video Share is sometimes confused with traditional two-way Video Call service. Video Call involves simultaneous two-way Video and Audio transmission between the 2 parties (from start to finish), whereas Video Share involves adding and removing one or more one-way Video sessions to an existing voice call between the 2 parties. There are other subtle differences between the two services as far as the user experience is concerned:
Extensions to Video Share include Video Clip Sharing, where a video clip recorded on the phone (or resident in the network) can be shared between two parties – something not delivered in a typical Video Call implementation.
The Phase 2 Video Share solution consists of a Client Application running on mobile handsets and an Application Server deployed in the mobile network. The Phase 1 Video Share architecture does not include an Application Server, i.e. media is transferred directly between the terminals. The Video Share service uses the standard IMS Core infrastructure to transmit signaling and media traffic. IP Packet Exchange (IPX) proxies may be part of this infrastructure to allow interconnection between operators and to provide a collection point for session accounting records used for inter-operator traffic charging. https://handwiki.org/wiki/index.php?curid=1175453
The Video Share (VS) Client is a software application running on the mobile handset. Typically, the Video Share Client is implemented as a native application running on mobile operating systems such as Windows Mobile, Symbian, Linux, and proprietary RTOS. VS-compliant handsets contain an ISIM/USIM properly provisioned with IMS public/private identities and access credentials. A user’s subscription is usually bound to their smart card (ISIM/USIM) such that the Video Share service is portable in the sense that the user may be able to send and receive video share on any capable handset.
The Video Share Client supports SIP and RTP/RTCP transmission. SIP is used for call control and signaling, and RTP/RTCP is used for video transmission. Functionality supported by a GSMA Video Share Client includes:
The Video Share Application Server is an IMS Application Server that interfaces with the S-CSCF network element in the IMS network through the 3GPP-defined ISC interface. The Application Server supports the SIP Back-to-Back User Agent (B2BUA) call control architecture that enables service policy control and enforcement capabilities of the video share session. The Video Share Application Server typically runs on a carrier grade fault tolerant hardware platform.
Functionality supported by the Video Share Application Server includes:
The basic steps involved in setting up and tearing down a Video Share session are as follows:
The Video Share session begins with Circuit Switch call between User A and User B. The next step is the Capability Exchange in which the other handset is queried to determine if the recipient is capable of supporting a Video Share session. This is performed with the SIP OPTIONS method. Both handsets can perform this capability exchange. The Video Share session is initiated by sending a SIP INVITE message to the called party. https://handwiki.org/wiki/index.php?curid=1672930
After the Video Share session has been set up, transmission of the actual video can begin. Video is sent between Video Share clients using RTP (Real-Time Transport Protocol), which is widely used in internet and mobile communities for video streaming. The video transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery using RTCP RR (Receiver Report) and RTCP SR (Sender Report) packets. When either party decides to stop the Video Share session, the session will be torn down (using RTCP BYE) and the SIP session stopped (using SIP BYE). After these steps the Circuit Switch voice call session still exists.
In the case of a Web Portal-based Video Share session, the video is streamed to the Portal instead of User B, and accessed using a PC with a web browser.
There are multiple options for deploying the Video Share service.