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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Engineering Task Force Adam Roach 2 Internet Draft Ericsson Inc. 3 Category: Informational March 2000 4 Expires September 2000 5 7 Automatic Call Back Service in SIP 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance 12 with all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as 17 Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other 21 documents at any time. It is inappropriate to use Internet-Drafts 22 as reference material or cite them other than as "work in 23 progress". 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/lid-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html 31 This document is an individual submission to the IETF. Comments 32 should be directed to the authors. 34 Abstract 36 This document describes a proposed implementation of an Automatic 37 Call Back (ACB) service using SIP. This service is somtimes 38 refered to as "camp on extension," "call again," "automatic 39 redial," and "automatic recall." 41 1. Introduction 43 Most services that exist in the public switched telephony network 44 (PSTN) can be implemented trivially using SIP [1] , either by 45 itself or with currently proposed extensions. 47 An effiicient implementation of the ACB service, however, cannot 48 be accomplished without a mechanism for notification when a 49 called party has become free. This document proposes a method of 50 implementing this functionality using the SUBSCRIBE and NOTIFY 51 methods defined in "Call Event Notification in SIP" [2] . 53 2. Service Description 54 Typically, the caller initiates a call in the normal fashion for 55 their access device (e.g. dialing a number, selecting an entry 56 from an address book application). When the user receives 57 indication of "ringing" or "busy," they may choose to activate 58 the ACB service. The method of activation will vary depending on 59 the access device. For a hardware phone, there will typically be 60 a dedicated "callback" button; PC-based clients may have a menu 61 option and/or a hot key; and PSTN bridges may play a series of 62 prompts to guide the user in activating the service. The user 63 receives confirmation of service activation. 65 Once the callee's device becomes available, the caller's phone 66 will indicate that the ACB service has been triggered. For 67 hardware phones and PSTN bridges, this will typically be a 68 distinctive ring; for PC-based clients, it may be an audio alert 69 accompanied by a dialogue box. 71 The user responds to this alerting as if he were answering an 72 incoming call. Upon doing so, he receives indication of the far 73 end alerting, and the call proceeds as normal. 75 At any time before the ACB service is triggered by the callee's 76 device becoming available, the caller may cancel outstanding ACM 77 requests. 79 3. "Event" header value 81 This service uses an event type of "terminal-free" in its 82 SUBSCRIBE and NOTIFY messages. This event is defined to occur 83 whenever a logical terminal transitions to an idle state (i.e. 84 has no ongoing calls). 86 4. Example Messages 88 The following sections give example messages for various 89 ACB-related scenarios. Some details, such as SDP bodies and 90 "Via:" headers, have been omitted for the sake of clarity. 92 4.1. Requesting notification with SUBSCRIBE (callee busy) 94 INVITE sip:exuadam@ws592.ericsson.com SIP/2.0 95 To: Adam Roach 96 From: Joe Public ;tag=38bec5a6-0000000a 97 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 98 CSeq: 5231 INVITE 99 Contact: sip:jpublic@terminal17.isp.net 100 Content-Type: application/sdp 101 SIP/2.0 486 Busy 102 To: Adam Roach ;tag=638bec5a6758941 103 From: Joe Public ;tag=38bec5a6-0000000a 104 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 105 CSeq: 5231 INVITE 106 Content-Length: 0 108 ACK sip:exuadam@ws592.ericsson.com SIP/2.0 109 To: Adam Roach ;tag=638bec5a67589416288 110 From: Joe Public ;tag=38bec5a6-0000000a 111 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 112 CSeq: 5231 ACK 113 Content-Length: 0 115 Notice that, since this is a non-call-related subscription, the 116 Call-ID is unique and does not match the previous INVITE request. 118 SUBSCRIBE sip:exuadam@ws592.ericsson.com SIP/2.0 119 To: Adam Roach 120 From: Joe Public ;tag=8a553c7c-38bebcb1 121 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 122 CSeq: 16939 SUBSCRIBE 123 Contact: sip:jpublic@terminal17.isp.net 124 Expires: 14400 125 Event: terminal-free 126 Content-Length: 0 128 SIP/2.0 200 OK 129 To: Adam Roach ;tag=346538bebcb150e 130 From: Joe Public ;tag=8a553c7c-38bebcb1 131 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 132 CSeq: 16939 SUBSCRIBE 133 Expires: 3600 134 Content-Length: 0 136 4.2. Requesting notification with SUBSCRIBE (no answer) 138 This call flow demonstrates the flow of messages if a user 139 decides to activate the ACB service after the callee's terminal 140 has started alerting, but before the callee answers. 142 INVITE sip:exuadam@ws592.ericsson.com SIP/2.0 143 To: Adam Roach 144 From: Joe Public ;tag=38bec5a6-0000000a 145 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 146 CSeq: 5231 INVITE 147 Contact: sip:jpublic@terminal17.isp.net 148 Content-Type: application/sdp 150 SIP/2.0 180 Ringing 151 To: Adam Roach ;tag=638bec5a6758941 152 From: Joe Public ;tag=38bec5a6-0000000a 153 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 154 CSeq: 5231 INVITE 155 Content-Length: 0 157 Notice that, since this is a non-call-related subscription, the 158 Call-ID is unique and does not match the previous INVITE request. 160 SUBSCRIBE sip:exuadam@ws592.ericsson.com SIP/2.0 161 To: Adam Roach 162 From: Joe Public ;tag=8a553c7c-38bebcb 163 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 164 CSeq: 16939 SUBSCRIBE 165 Contact: sip:jpublic@terminal17.isp.net 166 Expires: 14400 167 Event: terminal-free 168 Content-Length: 0 170 SIP/2.0 200 OK 171 To: Adam Roach ;tag=346538bebcb150e 172 From: Joe Public ;tag=8a553c7c-38bebcb 173 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 174 CSeq: 16939 SUBSCRIBE 175 Expires: 3600 176 Content-Length: 0 178 Now that the service is activated, the client can cancel the 179 INVITE transaction. 181 CANCEL sip:exuadam@ws592.ericsson.com SIP/2.0 182 To: Adam Roach 183 From: Joe Public ;tag=38bec5a6-0000000a 184 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 185 CSeq: 5231 CANCEL 186 Content-Length: 0 187 SIP/2.0 200 OK 188 To: Adam Roach 189 From: Joe Public ;tag=38bec5a6-0000000a 190 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 191 CSeq: 5231 CANCEL 192 Content-Length: 0 194 SIP/2.0 487 Call Canceled 195 To: Adam Roach ;tag=638bec5a6758941 196 From: Joe Public ;tag=38bec5a6-0000000a 197 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 198 CSeq: 5231 INVITE 199 Content-Length: 0 201 ACK sip:exuadam@ws592.ericsson.com SIP/2.0 202 To: Adam Roach ;tag=638bec5a6758941 203 From: Joe Public ;tag=38bec5a6-0000000a 204 Call-Id: 34a6-38bec5a6-61103dd1-3@terminal17.isp.net 205 CSeq: 5231 ACK 206 Content-Length: 0 208 4.3. Conveying terminal-free status using NOTIFY 210 The NOTIFY request contains the same Call-ID as the SUBSCRIBE 211 that asked for it. 213 NOTIFY sip:jpublic@terminal17.isp.net SIP/2.0 214 To: Joe Public 215 From: Adam Roach ;tag=38bebe1c-4953 216 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 217 CSeq: 15739 NOTIFY 218 Contact: sip:exuadam@ws592.ericsson.com 219 Event: terminal-free 220 Content-Length: 0 222 SIP/2.0 200 OK 223 To: Joe Public ;tag=346e38bebe434931fb51f33 224 From: Adam Roach ;tag=38bebe1c-4953 225 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 226 CSeq: 15739 NOTIFY 227 Content-Length: 0 229 Now, a brand new INVITE is issued to begin a call to the 230 newly-freed terminal. 232 INVITE sip:exuadam@ws592.ericsson.com SIP/2.0 233 To: Adam Roach 234 From: Joe Public ;tag=38bec5a6-7265482 235 Call-Id: 355e-38bed457-269136c2-6@terminal17.isp.net 236 CSeq: 17960 INVITE 237 Contact: sip:jpublic@terminal17.isp.net 238 Content-Type: application/sdp 240 SIP/2.0 180 Ringing 241 To: Adam Roach ;tag=55e38bed45700ca 242 From: Joe Public ;tag=38bec5a6-7265482 243 Call-Id: 355e-38bed457-269136c2-63@terminal17.isp.net 244 CSeq: 17960 INVITE 245 Content-Length: 0 247 The call now continues as normal 249 4.4. Cancelling a previous ACB request 251 SUBSCRIBE sip:exuadam@ws592.ericsson.com SIP/2.0 252 To: Adam Roach 253 From: Joe Public ;tag=8f21337c-38a8191 254 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 255 CSeq: 7837 SUBSCRIBE 256 Contact: sip:jpublic@terminal17.isp.net 257 Expires: 0 258 Event: terminal-free 259 Content-Length: 0 261 SIP/2.0 200 OK 262 To: Adam Roach ;tag=213985987f9872a 263 From: Joe Public ;tag=8f21337c-38a8191 264 Call-Id: 3465-38bebcb1-5e86e396-6@terminal17.isp.net 265 CSeq: 7837 SUBSCRIBE 266 Expires: 0 267 Content-Length: 0 269 5. References 271 [1] M. Handley/H. Schulzrinne/E. Schooler/J. Rosenberg, "SIP: 272 Session Initiation Protocol", RFC 2543, IETF; March 1999. 274 [2] Adam Roach, "Event Notification in SIP", Internet Draft 275 , IETF; March 2000. 276 Work in progress. 278 6. Security Considerations 280 This draft intoduces no security considerations beyond those 281 discussed in the referenced documents. 283 7. Author's Address 285 Adam Roach 286 Ericsson Inc. 287 Mailstop L-04 288 851 International Pkwy. 289 Richardson, TX 75081 290 USA 291 Phone: 972-583-7594 292 Fax: 972-669-0154 293 E-Mail: adam.roach@ericsson.com