下午看了a document，which describes the Lawful Intercept Procedure using Session Initiation Protocol (SIP) used by the Open Mobile Alliance (OMA) for Push to talk over Cellular (PoC) along with their applicability, which is limited to the OMA PoC application.
PoC （Push to talk over Cellular）「隨按即說」是一種建立在蜂巢式行動電話架構下的新興服務。使用者在設定完群組名單之後，只需要在支援PoC服務的手機上按下PoC按鈕，即可快速地與其他PoC使用者進行一對一或者一對多的語音通話，省去一一通知群組內每位成員的麻煩。
Talk Burst: A Talk Burst is the flow of media from a PoC User while that has the permission to send media.
FBI Agent:Not that Federal Bureau of Investigation:),is a PoC Client/User who has special access to tap any other PoC user supported by the PoC server.
Mode-of-Tapping: The tapping shall be done in split or combined mode.
Lawful Interception Operation in PoC
The Lawful Interception request information contains a series of information lines. Each line contains some part of the operation information and follows text based encoding rules and procedures that could be carried in the SIP signaling message.
Procedure at the PoC User to perform Legal Interception:
The FBI Agent, who has the special privileges to listen to any PoC User, is himself a PoC User. The FBI Agent (PoC User)
1. SHALL Set the Request-URI of the SIP INVITE request to the Conference-factory-URI for the PoC service in the Home PoC Network.
2. SHALL add the Lawful Intercept Message body which carries the information regarding
a. PoC User to be tapped.
b. The mode in which the tapping should be done.(Split or Combined mode)
c. The direction in which the tapping should be done.(Only in case of split mode.(send or receive))
i. If "direction=send", the FBI agent (PoC User) requests for tapping only the media streams sent out by the PoC User who is to be tapped.
ii.If "direction=receive", the FBI agent (PoC User) requests for tapping only the media streams that is received the PoC User who is to be tapped.
3. SHALL generate an initial SIP INVITE request according to the rules and procedures of [RFC3261] and the general procedure as in section 126.96.36.199 with the media stream direction as "sendonly" in the session description parameter
Procedures at the PoC Server performing the Lawful Intercept function：
PoC Control Plane Procedure：
PoC User Plane Procedure
Procedure at the PoC User to stop Legal Interception:
Procedure at the PoC Server to stop Legal Interception:
Lawful Intercept Request Protocol Syntax
The media type follows the conventions of the SIP (RFC 3261 ) for Lawful intercept request header information formatting. The Lawful intercept request header information contains a series of information headers with each of the information header lines terminated by a CRLF.
Lawful-intercept request-info = *info-header
info-header = "header-name" HCOLON header-value *(COMMA header value)
It is required that the Mode-of-Tapping header field be present as the first header field.
Mode-of-Tapping = " Mode-of-Tapping" HCOLON Modes-of-Tapping
Modes-of-Tapping = "split" | "combined"
Example: Mode-of-Tapping: split
The Direction header field defines the direction in which the split mode of tapping is done.
Direction = "Direction" HCOLON Directions
Directions = "send" | "receive"
Example: Direction: send
PoC-User-to-be-Tapped = "PoC-User-to-be-Tapped" HCOLON SIP-URI or TEL-URI
SIP-URI = "sip:" [ userinfo ] hostport uri-parameters [ headers ]
Example: PoC-User-to-be-Tapped: sip:firstname.lastname@example.org
The Lawful Intercept request information is sent in the INVITE method by the FBI Agent who wants to tap a PoC User listed in his request information.
INVITE sip:FBI_Agent@conference-factoryURI.net SIP/2.0
P-Preferred-Identity: "FBI_Agent" <sip: FBI_Agent @networkA.net>
User-Agent: PoC-User/OMA1.0 Acme-Talk5000/v1.01
Authorization: Digest username=" FBI_Agent-private@networkA.net",
Contact: <sip: FBI_Agent @conference-factoryURInet >
Allow: INVITE,ACK,CANCEL,BYE,REFER,MESSAGE,SUBSCRIBE, NOTIFY,PUBLISH
Content-Type: multipart/mixed; boundary=unique-boundary-1
o=ezimmerer 2890844526 2890842807 IN IP4 188.8.131.52
c=IN IP4 motds.mot.com
m=audio 3456 RTP/AVP 97
m=application 2000 udp TBCP
a=fmtp:TBCP queuing=1; tb_priority=2; timestamp=1
The "application/lir" mime type
This draft registers the "application/lir" MIME media type.
The Lawful intercept request (lir) information is text-based. It follows the recommendations of RFC 2045 for the usage of text-based data for MIME.
This media type is defined by the following information:
Media type name: application
Media subtype name: lir
Required Parameters: None
Encoding scheme: ASCII
Security considerations: See section 10
9 Formal Syntax
The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 .
The grammar for this mime-type is mostly derived out of the SIP specification (RFC 3261). The following definitions are derived from the SIP specification (RFC 3261) token DIGIT HCOLON quoted-string
Lawful-Intercept-Request-Info = *(Information-Header)
Information-Header = (Advice-State / Mode-of-Tapping /
Direction / PoC-User-to-be-Tapped)
Mode-of-Tapping = " Mode-of-Tapping" HCOLON Modes-of-Tapping Modes-
of- Tapping = "split" | "combined"
Direction = "Direction" HCOLON Directions Directions = "send" |
PoC-User-to-be-Tapped = "PoC-User-to-be-Tapped" HCOLON SIP-URI or TEL-
URI SIP-URI = "sip:" [ userinfo ] hostport
uri-parameters [ headers ]
10 Security Considerations
The Lawful Intercept request message body contains sensitive information that requires the use of encryption. Lawful Intercept request information should not be trusted until it is ensured that it is received through reliable sources.