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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dispatch R. Jesske 3 Internet-Draft L. Liess 4 Intended status: Informational Deutsche Telekom 5 Expires: July 14, 2011 January 10, 2011 7 Requirements for the use of the Reason header filed in Session 8 Initiation Protocol (SIP) responses 9 draft-jesske-dispatch-req-reason-in-responses-02 11 Abstract 13 Although the use of the Reason header field in responses is 14 considered in RFC3326, doing so is not specified for any existing 15 response code. Nonetheless, the Reason header field has been widely 16 used in responses to carry Q.850 reason codes for failure responses 17 to INVITEs that have been gatewayed to PSTN systems. This document 18 specifies and formally permits the use of the Reason header field in 19 SIP responses to carry Q.850 reason codes for this and other 20 purposes. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on July 14, 2011. 39 Copyright Notice 41 Copyright (c) 2011 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 This document may contain material from IETF Documents or IETF 55 Contributions published or made publicly available before November 56 10, 2008. The person(s) controlling the copyright in some of this 57 material may not have granted the IETF Trust the right to allow 58 modifications of such material outside the IETF Standards Process. 59 Without obtaining an adequate license from the person(s) controlling 60 the copyright in such materials, this document may not be modified 61 outside the IETF Standards Process, and derivative works of it may 62 not be created outside the IETF Standards Process, except to format 63 it for publication as an RFC or to translate it into languages other 64 than English. 66 Table of Contents 68 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 4. Overall Applicability . . . . . . . . . . . . . . . . . . . . 6 72 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 75 8. Normative References . . . . . . . . . . . . . . . . . . . . . 9 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 78 1. Terminology 80 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 81 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 82 document are to be interpreted as described in [RFC2119]. 84 This document uses terms from [RFC3261]. 86 2. Overview 88 With introducing the Session Initiation Protocol [RFC3261]into the IP 89 Multimedia Subsystem (IMS) which is defined by the 3rd Generation 90 Partnership Project the it was required to interoperate with the 91 PSTN/ISDN. The European Telecommunication Standards Institute (ETSI) 92 has defined a Next Generation Network (NGN) where a substantial part 93 of it is based on the IMS. 95 ETSI has developed a number of requirements to support the usage of 96 SIP in Next Generation Networks that interoperate, at the service 97 level, with the Public Switched Telephone Network (PSTN), the 98 Integrated Services Digital Network (ISDN), the 3GPP IP Multimedia 99 Subsystem (IMS), and SIP networks and terminals that implement the 100 service logic. 102 Also ITU-T has specified an interworking between SIP and PSTN/ISDN 103 networks [ITU.Q1912.5.2004] and [TS29.163] where reason within 104 responses are already supported. 106 In order to provide full support in SIP of existing services, 107 extensions to SIP are needed. 109 This document proposes the use of the Reason header field in 110 responses. This is needed for creating services that must be 111 interoperable with the PSTN/ISDN network and the interoperability of 112 traversing communications through SIP not using SIP-I. 114 The main used case for reason header within responses are 115 interworking situations with PSTN/ISDN networks where the ISUP cause 116 In many cases the mapping of specific cause values will result in a 117 generic SIP Response like it is shown below. 119 [RFC3398] and other Interworking specifications like [RFC3326] are 120 describing the mapping of ISUP Cause Values to SIP and vice versa. 121 Looking on the specific mapping shows that information will be lost 122 when the call traverses ISUP without using SIP-T. 124 Example: 126 [RFC3398] describes the mapping of following ISUP Causes to 503 and 127 408 like follows. 129 ISUP Cause value SIP response 130 ---------------- ------------ 131 34 no circuit available 503 Service unavailable 132 38 network out of order 503 Service unavailable 133 41 temporary failure 503 Service unavailable 134 42 switching equipment congestion 503 Service unavailable 135 47 resource unavailable 503 Service unavailable 136 58 bearer capability not presently 503 Service unavailable 137 Available 138 88 incompatible destination 503 Service unavailable 140 18 no user responding 408 Request Timeout 142 The mapping back is shown as follows: 144 Response received Cause value in the REL 145 ----------------- ---------------------- 146 503 Service unavailable 41 Temporary failure 148 408 Request timeout 102 Recovery on timer 149 expiry 151 The Example with 503 shows that a couple of different ISUP Cause 152 values are interworked to only one SIP response. With 408 the 153 meaning of the release cause is changed when interworked back to 154 ISUP. Also Services built on Cause 18 (e.G. a 2nd call attempt on an 155 other number, this service is like a sequential forking) will not 156 work. 158 3. Requirements 160 A UA may have the ability to display ISUP specific release causes or 161 show a equivalent text. 163 In SIP-to-PSTN gateway scenarios, it is desirable to provide the UAC 164 with the specific call release reason provided by the PSTN. To 165 support this: 167 REQ-1: Provide in SIP responses a way to carry PSTN call release 168 codes, along with indication of any context or variant identification 169 needed to interpret the code unambiguously. 171 REQ-2: Provide an extensibility mechanism so that further information 172 about the call release can be specified. 174 4. Overall Applicability 176 The SIP procedures specified in this document are foreseen for 177 networks providing simulation services and/or interworking to the 178 PSTN/ISDN. 180 The document is describing the use of the Reason header in SIP 181 responses. These procedures are only valuable if the reason 182 contained in the element "protocol" is "Q.850". A inclusion of a SIP 183 reason (protocol="SIP") is not helpful due to the fact that the 184 response already provides the SIP reason. The Release Causes are 185 described within [Q.850]. (Note: The ETSI specifications can be 186 downloaded under http://pda.etsi.org/pda/queryform.asp free of 187 charge.) 189 The appearance of the Reason header is applicable to final responses 190 3xx, 4xx, 5xx and 6xx and 18x and 199 provisional responses 191 [I-D.ietf-sipcore-199], the procedures for that are described within 192 [draft-jesske-dispatch-reason-in-responses-02] . 194 5. Example 196 Figure 1 shows the example of SIP interworking with the PSTN/ISDN. 197 Cause #87 is sent when the connecting user is not member of a Closed 198 User Group. 200 A Gateway Proxy AS 201 | IAM | | | 202 |------------------>| INVITE | | 203 | |----------------->| INVITE | 204 | | 100 Trying |----------------->| 205 | |<-----------------| 100 Trying | 206 | | |<-----------------| 207 | ACK SDP held | | | 208 |<------------------| | 603 Decline | 209 | | 603 Decline | Reason Q850 #87 | 210 | | Reason Q850 #87 | | 211 | REL Cause #87 | |<-----------------| 212 | |<-----------------| | 213 |<----------------- | | | 214 | | | | 215 | | | | 216 | | | | 218 Figure 1: ISUP-SIP Call 220 Figure 2 shows the example where the SIP network is used as transit 221 between PSTN/ISDN networks. This avoids that the Mapping back to the 222 Q.850 cause within ISUP change the meaning of the reason for release 223 of the call. 225 A Gateway Gateway B 226 | IAM | | | 227 |------------------>| INVITE | | 228 | |----------------->| IAM | 229 | | 100 Trying |----------------->| 230 | |<-----------------| 100 Trying | 231 | | 603 Decline | | 232 | | Reason Q850 #87 | REL Cause #87 | 233 | REL Cause #87 | |<-----------------| 234 | |<-----------------| | 235 |<----------------- | | | 236 | | | | 237 | | | | 238 | | | | 240 Figure 2: Transit case 242 Figure 3 shows the example where the SIP network puts an announcement 243 towards the UAB. The AS sends an announcement with a specific text 244 back. After some Time the Response will be sent back to the UA A and 245 closes all open transactions. With this possibility the SIP user can 246 informed with more specific information than only the Response code. 248 A AS Gateway B 249 | INVITE | | | 250 |------------------>| INVITE | | 251 | |----------------->| IAM | 252 | | 100 Trying |----------------->| 253 | |<-----------------| | 254 | | 503 Decline | | 255 | | Reason Q850 #41 | REL Cause #41 | 256 | | |<-----------------| 257 | Announcement |<-----------------| | 258 |< ================ | | | 259 | | | | 260 | 503 after Timeout| | | 261 |<----------------- | | | 263 Figure 3: Transit case 265 Figure 3: Call Release within the PSTN with an announce played within 266 the SIP network. 268 6. Security Considerations 270 The presence of the Reason header in a response does not affect the 271 treatment of the response. 273 Including such a header by an untrusted entity could adulterate the 274 reactions of the originating entities. E.G. sending back a cause 275 value "87" can cause an announcement within the PSTN/ISDN saying that 276 the call was rejected due to the Closed User Group service. 278 Therefore it is RECOMMENDED to include the Reason header information 279 in Responses only by trusted entities as it is described within 280 [RFC3325]. 282 7. IANA Considerations 284 This document does not have any implications for IANA. 286 8. Normative References 288 [I-D.ietf-sipcore-199] 289 Holmberg, C., "Response Code for Indication of Terminated 290 Dialog", draft-ietf-sipcore-199-00 (work in progress), 291 April 2009. 293 [ITU.Q1912.5.2004] 294 International Telecommunications Union, "Interworking 295 between Session Initiation Protocol (SIP) and Bearer 296 Independent Call Control protocol or ISDN User Part [ITU-T 297 Recommendation Q.1912.5 (2004)]", ITU Recommendation 298 Q.1912.5, April 2004. 300 [Q.850] "Usage of cause and location in the Digital Subscriber 301 Signalling System No. 1 and the Signalling System No. 7 302 ISDN User Part [ITU-T Recommendation Q.850]", 303 ITU Recommendation Q.850, April 1998. 305 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 306 Requirement Levels", BCP 14, RFC 2119, March 1997. 308 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 309 A., Peterson, J., Sparks, R., Handley, M., and E. 310 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 311 June 2002. 313 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 314 Extensions to the Session Initiation Protocol (SIP) for 315 Asserted Identity within Trusted Networks", RFC 3325, 316 November 2002. 318 [RFC3326] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason 319 Header Field for the Session Initiation Protocol (SIP)", 320 RFC 3326, December 2002. 322 [RFC3398] Camarillo, G., Roach, A., Peterson, J., and L. Ong, 323 "Integrated Services Digital Network (ISDN) User Part 324 (ISUP) to Session Initiation Protocol (SIP) Mapping", 325 RFC 3398, December 2002. 327 [TS29.163] 328 "3rd Generation Partnership Project; Technical 329 Specification Group Core Network and Terminals; 330 Interworking between the IP Multimedia (IM) Core Network 331 (CN) subsystem and Circuit Switched (CS) networks (Release 332 8)". 334 [draft-jesske-dispatch-reason-in-responses-02] 335 Jesske, R. and L. Liess, "Use of the Reason header filed 336 in Session Initiation Protocol (SIP) responses", 337 March 2010. 339 Authors' Addresses 341 Roland Jesske 342 Deutsche Telekom 343 Heinrich-Hertz-Strasse 3-7 344 Darmstadt, 64307 345 Germany 347 Phone: +4961516282766 348 Email: r.jesske@telekom.de 350 Laura Liess 351 Deutsche Telekom 352 Heinrich-Hertz-Strasse 3-7 353 Darmstadt, 64307 354 Germany 356 Phone: +4961516282761 357 Email: Laura.Liess@telekom.de