In 3GPP/GSMA specifications Image sharing is define as a service for sharing images between users during a mobile phone call. These specifications were defined by the GSM Association for cellular network. Because Mercuro IMS Client is an IMS Client for PC desktop all these specifications do not apply. This mean that no CS voice call set up is required prior to sharing the images.
In case of Mercuro IMS Client context, Image Sharing session (based on SIP protocol for signalling) could be started before or after the voice call is set up. Image Sharing session is based on packet switched connection (PS). Before setting up Image Sharing session, capabilities negotiation is performed to present (GUI side) the possibility of sharing one or several images. In this beta version only one image can be shared for each session.
When the endpoint accepts the images, then image transfer start using packet switched connection with MSRP (RFC 4975) protocol to transport media (chunks). This transfer is done as peer2peer service, i.e. no server required in the network for sharing the images.
The end-user can send multiple pictures during the PS session by establishing a new SIP session for transferring the next picture after the previous session has been torn down.
The Message Session Relay Protocol (MSRP), IETF RFC 4975, is mandatory for the Image Share Service. Image data information settings in SIP/SDP follow IETF File transfer draft “draft-ietf-mmusic-file-transfer-mech-07.txt” (Mercuro IMS Client use version 8).
Mercuro IMS Client uses multi-body (both SDP+icon) messages as defined in “draft-ietf-mmusic-file-transfer-mech-08.txt” but only base64 format is used to embed icons.
Only pre-stored images can be shared using Mercuro IMS Client (no way to share live images).
In Mercuro IMS Client Image Sharing session consists of the following steps:
1. Capability query
2. Invitation procedure (SIP)
3. Image transmission (MSRP)
4. Termination procedure (SIP)
Capability query
Mercuro IMS Client uses service identifier (3GPP TS 24.229 – subclause 7.2A.9 and 7.2A.8) to query for terminal capabilities (endpoint is capable to support certain media features?). For this, service identifier tag is used to identify the media aspects of service/application for variety of purposes both by terminal and network side.
Mercuro IMS Client uses ‘urn:urn-xxx:3gpp-application.ims.iari.gsma-is’ as IARI to indicate support of Image Sharing IMS service.
OPTIONS sip:bob@192.168.16.33 SIP/2.0
Via: SIP/2.0/UDP 192.168.16.108:1223;rport;branch=z9hG4bK19912
From: <sip:mamadou@v4.ims.test>;tag=16015
To: <sip:bob@v4.ims.test>;tag=49a4177c-1235491482375000-037
Call-ID: 1235491356210@192.168.16.108
CSeq: 402 OPTIONS
Max-Forwards: 70
Allow: INVITE, ACK, CANCEL, BYE, MESSAGE, OPTIONS, NOTIFY, PRACK, REFER
Contact: <sip:mamadou@192.168.16.108:1223;transport=udp>;expires=1000;+g.oma.sip-im
User-Agent: IM-client/OMA1.0 Mercuro-Gold/v4.0.1196.0
P-Preferred-Service: urn:urn-xxx:3gpp-service.ims.icsi.mmtel
Accept-Contact: *;+g.3gpp.icsi%5fref="urn%3Aurn-xxx%3A3gpp-service.ims.icsi.mmtel"
Route: <sip:mo@pcscf.v4.ims.test:4060;lr>,<sip:mo@scscf.v4.ims.test:6060;lr>,<sip:mt@scscf.v4.ims.test:6060;lr>,<sip:mt@pcscf.v4.ims.test:4060;lr>
P-Access-Network-Info: ADSL;utran-cell-id-3gpp=00000000
Privacy: none
P-Preferred-Identity: <sip:mamadou@v4.ims.test>
Content-Length: 0
When Mercuro IMS Client receive an OPTIONS request then it creates a 200 OK response including Image Share IARI in the Contact header and send it back.
Invitation procedure
After capabilities of both ends are known and the user has located the target image to share, the next step is the actual Image Share session setup. SIP/SDP offer/answer model is used to perform negotiation.
INVITE sip:bob@v4.ims.test SIP/2.0
Via: SIP/2.0/UDP 192.168.16.108:1223;rport;branch=z9hG4bK3548
From: <sip:mamadou@v4.ims.test>;tag=2520
To: <sip:bob@v4.ims.test>
Call-ID: 1235491356211@192.168.16.108
CSeq: 501 INVITE
Max-Forwards: 70
Allow: INVITE, ACK, CANCEL, BYE, MESSAGE, OPTIONS, NOTIFY, PRACK, REFER
Contact: <sip:mamadou@192.168.16.108:1223;transport=udp>;+g.3gpp.app%5fref="urn%3Aurnxxx%3A3gpp-application.ims.iari.gsmais";explicit;+g.oma.sip-im
User-Agent: IM-client/OMA1.0 Mercuro-Gold/v4.0.1196.0
Supported: sdp-anat
Route: <sip:192.168.16.225:4060;lr=true;transport=udp>,<sip:orig@scscf.v4.ims.test:6060;lr>
P-Preferred-Service: urn:urn-xxx:3gpp-service.ims.icsi.mmtel
Accept-Contact: *;+g.3gpp.app%5fref="urn%3Aurnxxx%3A3gpp-application.ims.iari.gsmais";explicit
Accept-Contact: *;+g.oma.sip-im
Content-Type: application/sdp
P-Access-Network-Info: ADSL;utran-cell-id-3gpp=00000000
Privacy: none
P-Preferred-Identity: <sip:mamadou@v4.ims.test>
Allow-Events: presence, presence.winfo
Content-Length: 555
v=0
o=- 3344 3344 IN IP4 192.168.16.108
s=Mercuro IMS Client Session
t=0 0
m=message 1248 TCP/MSRP *
c=IN IP4 192.168.16.108
a=sendonly
a=accept-types:text/plain message/cpim
a=accept-wrapped-types:*
a=file-selector:name:"Image 18.png" type:image/png size:78169 hash:sha-1:4A:FB:E2:01:A9:0B:C0:6F:EB:C7:23:BD:2E:26:21:A6:5D:2B:6C:DB
a=file-disposition:render
a=file-date:creation:2008-10-15T10:40:46.405Z
a=file-icon:cid:test@mercuro.net
a=path:msrp://192.168.16.108:1248/fnfozvsrtkj;tcp
a=file-transfer-id:prepggxrpnrvystmwcysyycqpevikeff
Image transmission
If the invitation procedure succeeds, then the image will be transmitted via uni-directional MSRP connection (TCP). Large images will be sent in several chunks (2048 bytes per chunk).
Transmission is done following the RFC 4975.
Termination procedure
When Transfer is done Mercuro IMS Client will tear down SIP session (UDP) and media transfer side (Close TCP connection). See RFC 4975 for more information.
RCS Release 2 update
This subclause has been added to provided which changes have been made to be compliant with GSMA RCS 2.
- GSMA IR79 document version changed from v1.0 (IR79_11) to v1.2 (IR7912)
- "draft-ietf-mmusic-file-transfer-mech-07.txt" becomes RFC 5547
- Use "urn:urn-7:3gpp-application.ims.iari.gsma-is" instead of "urn:urnxxx:3gpp-application.ims.iari.gsmais" as IARI
References:
http://en.wikipedia.org/wiki/Image_share
http://www.gsmworld.com/documents/ireg/ir79_11.pdf
http://www.gsmworld.com/documents/IR7912.pdf
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