SIP for Telephony. Third-Party Call Control (3PCC) 6 5 ACK SDP(B) 1 INVITE no SDP. Supplementary Services. Call Hold and Retrieve

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1 Third-Party Call Control (3PCC) for Telephony yet another set of services!! Examples: Click-to-dial, conference bridge control,!! Several approaches with different advantages / drawbacks!! Simplest call flow: U U U 7 U media 1 no SDP OK SDP() 2 OK SDP() 4 3 SDP() 6 5 SDP() Controller Step 1 Step 2 Controller 2010 Jörg Ott Jörg Ott 3 Supplementary Services!! The easy ones first!! Call Diversion!! Intrinsic support (301/302 redirection)!! Call Forwarding (unconditional, busy, no answer)!! Performed by proxy and indicated by means of 181 Call Is eing Forwarded response!! Call screening (for incoming and outgoing calls) at proxy!! Respond with 403 Screening Failure when needed!! Call Waiting!! Implemented in endpoints!! More sophisticated signaling required for!! 3 rd party call control!! Call transfer!! Call park and pickup!! Message waiting!! PSTN (ISUP) and PX (QSIG) interworking!! Conferencing Call Hold and Retrieve!! Call Hold and Retrieve!! Media-level operation only (does not affect call state!)!! User agent sends re- to mute other party (a=inactive)!! Repeated offer/answer exchange!! Hold condition may apply into one direction only!! a=sendonly indicates that the initiator will not pay attention to incoming media!! nother round of re-s to re-establish media (a=sendrecv)!! Call Hold with Music on Hold!! Create a separate dialog with music server!! Connect the peer to the music server by forwarding SDP!! Direct music stream to the peer on hold!! ctually: U putting peer on hold acts as third-party call controller!! When taking user off hold, close the dialog to music server!! Redirect peer to talk to local U again 2010 Jörg Ott Jörg Ott 4

2 Call Hold (with Consultation) ctive dialog m=audio a=sendonly m=audio a=sendonly No (but RTCP) m=audio a=sendrecv m=audio a=sendrecv 2010 Jörg Ott 5 C!! Part of Call Control Framework Call Transfer!! Uses basic protocol features and extensions!! REFER method to invoke another () transaction!! NOTIFY (with implicit subscription) to indicate success or failure!! New Replaces: header to indicate substitution of an existing call!! Refer-To: header to indicate to peer which target to contact!! Referred-y: header to inform refer target about origin of call!! Supports numerous variants!! ttended!! Unattended!! Intermediate three-way calling!! Optional protection of transfer target 2010 Jörg Ott 7 Call Hold with Music on Hold ctive dialog (SDP_MS) (SDP_) (music) (SDP_) (SDP_) 2010 Jörg Ott 6 (Ø) (SDP_MS) (SDP_) Music Server Simple Unattended Transfer ctive dialog REFER Refer-To: sip:c@tzi.org 202 ccepted 2010 Jörg Ott 8 On-hold (INV//) NOTIFY Content-Type: message/sipfrag Content-Length: 6 Referred-y: a@tzi.org C

3 Consultation Call C Call C ends ttended Transfer ctive dialog On-hold (INV//) REFER Refer-To: sip:c@tzi.org 202 ccepted NOTIFY Content-Type: message/sipfrag Content-Length: Jörg Ott 9 Referred-y: a@tzi.org Replaces: C C Call Park & Pickup!! Park a call from one endpoint, pick up from another!! Requires remote URI and session identification!! Park on the endpoint itself!! Park elsewhere (refer to some parking area, e.g. a server)!! For pickup, endpoint contacts remote URI and provides session identification!! Use Replace: header to substitute (early) dialog!! Pickup U needs to learn about dialog-specific information!! Use SUSCRIE/NOTIFY with dialog event package!! Other alternatives for shared state conceivable, too!! Pick up a call destined for another phone!! Common PX feature, e.g., in working groups 2010 Jörg Ott 11 Consultation Call C Call C ends ttended Transfer C (hold) Call Pickup (-id) (Replaces: - id) CNCEL (-id) 487 Req. Term. SUSCRIE NOTIFY (-id) NOTIFY (-id) 481 Does not exist C 2010 Jörg Ott Jörg Ott 12

4 Dialog Event Package!! Event package for -initiated dialogs ( dialog ) at endpoints!! Entities authenticated with same or as the endpoint!! XML-based extensible format!! Parameters!! call-id:, from-tag:, to-tag: Uniquely identifies a dialog!! with-sessd:!! Contained elements!! State ( early, trying, proceeding, terminated, confirmed )!! possibly with event and reason parameter!! Duration (since creation of the dialog state machine)!! Referred-y and Replaces!! Peers of the dialog ( local and remote )!! Identity, target ( URI), SDP session description!! NOTIFY message body MIME type: application/dialog-info+xml 2010 Jörg Ott 13 Further Supplementary Services!! utomatic redial ( call completion on busy subscriber )!! gain: use dialog event package!! Calling U subscribes to dialog state of called party!! Caller is notified when the call state at the called party changes!! Calling U can automatically re-invoke call setup (i.e., send )!! Click-to-dial!! Server-side implementation!! Client needs to provide its own URI and is then called back!! E.g., by means of third party call control on server side!! Client-side implementation!! Plug-in for web browser (linked to sip: and sips: as URI schemes)!! Configured with local IP phone (or 3PCC server)!! Sends REFER message to IP phone with target URI in Refer-To: header!! May require explicit user confirmation (risk of malicious dialer pages otherwise) 2010 Jörg Ott 15 Dialog Event Package <?xml version="1.0" encoding="utf-8"?>!! Event package <dialog-info for -initiated xmlns="urn:ietf:params:xml:ns:dialog-info" dialogs ( dialog ) at endpoints!! Entities authenticated xmlns:xsi=" with same or as the endpoint xsi:schemalocation="urn:ietf:params:xml:ns:dialog-info"!! XML-based extensible version="1" format state="full"> <dialog id="123456">!! Parameters <state>confirmed</state>!! call-id:, from-tag:, to-tag: <duration>274</duration> Uniquely identify a dialog!! with-sessd:!! Contained elements <target uri="sip:alice@pc33.example.com"> <param pname="isfocus" pval="true"/>!! State ( early, trying, proceeding, terminated, confirmed ) <local> <identity display="lice">sip:alice@example.com</identity> <param pname="class" pval="personal"/>!! possibly with event and </target> reason parameter!! Duration (since creation </local> of the dialog state machine) <remote>!! Referred-y and Replaces <identity display="ob">sip:bob@example.org</identity>!! Peers of the dialog ( local <target and uri="sip:bobster@phone21.example.org"/> remote )!! Identity, target ( </remote> URI), SDP session description </dialog> </dialog-info>!! NOTIFY message body MIME type: application/dialog-info+xml 2010 Jörg Ott 14 fork() & execve() exit (0) exit (0) sip applet REFER (Refer-To: ) 401 uth. Req. REFER (Refer-To: ) WWW-uth: 202 ccepted NOTIFY () NOTIFY (180) NOTIFY (200) Click to Dial (sip: ) 2010 Jörg Ott 16

5 Message Waiting Indication!! synchronously notify endpoint(s) about messages!! Voice, fax, pager, multimedia, text (per RFC 3458)!! Defines a new event package!! Subscribe to one or more mailboxes!! Results from many sources may be merged!! Content-Type: application/simple-message-summary!! General indicator for new messages!! Message type followed by new/old and (new-urgent/old-urgent)!! Encoding as plain text!! May include selected RFC 2822 message headers!! Example Messages-Waiting: yes Message-ccount: jo@tzi.org Voice-Message: 4/8 (1/2) Text-Message: 238/42116 (0/1) 2010 Jörg Ott 17 Interfacing to the PSTN!! Preserve feature transparency! transport information (ISUP MIME type)!! Conversion between different ISUP versions to be done on s!! Provide enough routing information to find callee! (partially) translate ISUP to!! Support for tel:-urls to indicate Called Party Number!! ddress resolution using ENUM or TRIP!! Enable early media (e.g., in-band alerting and announcements)!! Convey additional information during call!! PSTN PSTN case! INFO method (RFC 2976)!! to PSTN mapping!! Call flows for basic interoperation (RFC 3372, 3398, 3666)!! RFC 3578: Support for Overlap Sending 2010 Jörg Ott 19 Interfacing to the PSTN asic -ISUP Mapping 1.! PSTN PSTN 2.! PSTN IP based network Proxy order element maps to and vice versa PSTN IM CM CPG NM REL RLC PSTN 18x 18x 2010 Jörg Ott Jörg Ott 20

6 Example for and Overlap Sending (1)!! pproach 1: Collect digits in!! Use timeout!! Collect minimal number of digits PSTN IM SM SM SM PSTN service 2010 Jörg Ott 21 INFO Method!! Transmit application-layer information during call (RFC 2976)!! Use signaling path of current session!! Information is carried in message headers or body!! Specific MIME types defined for, e.g., ISUP (application/isup)!! No change of (-related) call state PSTN INFO application/isup proxy INFO application/isup PSTN Some event ISDN phone 2010 Jörg Ott 23 Example for and Overlap Sending (2)!! pproach 2: Send multiple s!! Use timeout, possibly collect minimal number of digits!! Wait for feedback from the network!! CNCEL obsolete s PSTN IM SM SM SM PSTN CNCEL 2 3 service sip:314@ sip:31415@ sip: @ 183 Session Progress Message!! INFO not applicable before call is established!! ISUP mapping requires inband data prior to final response! provisional response 183!! dditional information in message body!! SDP description of early media stream (e.g., for announcements)!! Message headers also conceivable!! May be made reliable (100rel)!! So that sender can count on synchronized state!! PR message to confirm receipt of Jörg Ott Jörg Ott 24

7 Early Media Support!! Early media during call setup ( )!! One-way transmission to report progress!! nnouncements, specific dial tones,!! No charge!! Inhibit local alerting at calling user agent!! Problem: Media negotiation!! Send SDP message in provisional response " fast setup!! Create SDP from initial s capability set " What if not suitable for early media session?!! Calling U will establish early media session " Cannot decline session or change codecs!! UPDTE may be used for modifying media session 2010 Jörg Ott 25 Interworking with QSIG (ISDN PXes)!! Interconnecting a -based signaling environment with a traditional (ISDN) PX!! Relevant for stepwise migration from traditional to IP telephony!! First, create islands connected to the PX!! Old PX runs as master!! Then, switch trunk from old PX to (IPbased) server!! nd run old PXes as slaves!! Finally, throw away PX and old phones!! Gateway function needed for semantic mapping between and QSIG!! Call signaling (stateful operation)!! Numbering plans!! Support for overlap sending!! Naturally limits available functionality server Gateway PX Interworking Function 2010 Jörg Ott 27 TCP, IP Link QSIG PISN Lower layers PX U Use of Early Media: PSTN Call With In-band lerting 183 Progress proxy 183 Progress PSTN IM CM NM PSTN -QSIG: Call Setup (en-bloc dialing) PISN Gateway SETUP ( ) sip: @... CLL PROCEEDING LERTING CONNECT CONNECT DISCONNECT RELESE RELESE COMP. PR 2010 Jörg Ott Jörg Ott 28

8 -QSIG: Call Setup (overlap sending 1) PISN Gateway SETUP (+358) SETUP INFORMTION ( ) INFORMTION (2460) CLL PROCEEDING LERTING CONNECT CONNECT sip: @... PR 2010 Jörg Ott 29 -QSIG: Call Setup (overlap sending 2) PISN Gateway SETUP (+358) SETUP INFORMTION ( ) INFORMTION (2460) CLL PROCEEDING LERTING CONNECT CONNECT 484 sip: @... PR 2010 Jörg Ott 30