Internet DRAFT - draft-straw-sip-traceroute

draft-straw-sip-traceroute




STRAW Working Group                                           H. Kaplan 
Internet Draft                                                   Oracle 
Intended status: Standards Track                          July 14, 2013 
Expires: January 30, 2013                                               
                                                                        
                                                                        
                                                                        
    
    
                   A Media-based Traceroute Function for  
                   the Session Initiation Protocol (SIP) 
                       draft-straw-sip-traceroute-00 
    
    
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   This Internet-Draft will expire on January 14, 2014.  
    
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   Section 4.e of the Trust Legal Provisions and are provided without 
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Abstract
    
   SIP already provides the ability to perform hop-by-hop traceroute 
   for SIP messages using the Max-Forwards header field, in order to 
   determine the reachability path of requests to a target.  A 
   mechanism for media-loopback calls has also been defined separately, 
   which enables test calls to be generated which result in media being 
   looped back to the originator.  This document describes a means of 
   performing hop-by-hop traceroute-style test calls using the media-
   loopback mechanism, in order to test the media path when SIP 
   sessions go through media-relaying B2BUAs. 
    
    
Table of Contents
    
   1. Terminology...................................................2 
   2. Introduction..................................................3 
   3. The SIP Traceroute Mechanism..................................4 
      3.1. Processing a Received Max-Forwards Header Field..........4 
      3.2. Answering the INVITE.....................................5 
   4. Security Considerations.......................................5 
   5. IANA Considerations...........................................5 
   6. Acknowledgments...............................................6 
   7. References....................................................6 
      7.1. Normative References.....................................6 
   Author's Address..................................................6 
    
    
1. Terminology
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC 2119.  The 
   terminology in this document conforms to RFC 2828, "Internet 
   Security Glossary". 
    
   B2BUA: a SIP Back-to-Back User Agent, which is the logical 
   combination of a User Agent Server (UAS) and User Agent Client 
   (UAC). 
    
   UAS: a SIP User Agent Server. 
    
   UAC: a SIP User Agent Client. 
    
   Traceroute: a mechanism to trace a path of hops from an originator 
   to a destination.  For IP, this is typically done using the TTL 
 
 
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   field of the IP header, starting at the value 1 and incrementing by 
   1 as each IP hop responds with an ICMP error.  For SIP this can be 
   done using Max-Forwards header field starting with the value 0, in a 
   similar fashion to the TTL field. 
    
   It is assumed the reader is already familiar with media-loopback 
   [RFC6849]. 
    
2. Introduction 
    
   In many deployments, the media for SIP-created sessions does not 
   flow directly from the originating user's UAC to the answering 
   user's UAS.  Often, SIP B2BUAs in the SIP signaling path participate 
   in the media plane, either for injecting media such as rich-
   ringtones or music-on-hold, or for relaying media in order to 
   provide functions such as transcoding, IPv4-IPv6 conversion, NAT 
   traversal, SRTP termination, media steering, etc. 
    
   As more and more SIP domains get deployed and interconnect, the odds 
   of a SIP session crossing such media-plane B2BUAs increases, as well 
   as the number of such B2BUAs any given SIP session may go through.  
   In other words, any given SIP session may cross any number of 
   B2BUA's both in the SIP signaling plane as well as media plane. 
    
   If failures or degradation occurs in the media plane, it is 
   difficult to determine where in the media path they occur.  In order 
   to aid managing and troubleshooting SIP-based sessions and media 
   crossing such B2BUAs, it would be useful to be able to test the 
   media path to each B2BUA separately from the source.  A mechanism to 
   perform media-loopback test sessions has been defined in [RFC6849], 
   but it would be difficult to use the mechanism directly to test 
   B2BUAs because typically the B2BUAs do not have an Address of Record 
   (AoR) to be targeted, nor is it known a priori which B2BUAs will be 
   crossed for any given session. 
    
   For example, suppose calls from Alice to Bob have media problems.  
   Alice would like to test the media path to each B2BUA in the path to 
   Bob separately, to determine which segment has the issues.  Alice 
   cannot target the B2BUAs directly for each test call, because she 
   doesn't know what URIs to use to target them; nor would using such 
   URIs guarantee the same media path be used as a call to Bob.  A 
   better solution would be to make a test call targeted to Bob, but 
   with a SIP traceroute-type mechanism that makes the call terminate 
   at the B2BUAs, such that she can perform test sessions to test the 
   media path to each downstream B2BUA. 
    
   This document defines how such a mechanism can be employed, using 
   the [RFC6849] mechanism along with the Max-Forwards SIP header field 
   such that a SIP User Agent can make multiple test calls, each 
 
 
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   reaching a B2BUA further downstream.  Each B2BUA in the path that 
   supports this mechanism would answer the media-loopback call, and 
   thus the originating SIP UA can test the media path up to that 
   B2BUA. 
    
3. The SIP Traceroute Mechanism 
    
   The Max-Forwards header field can already be used to perform a 
   simple SIP-request traceroute mechanism by generating a SIP request 
   initially using a Max-Forwards value of 0, receiving a 483 Too Many 
   Hops response from the next-hop, and then incrementing the value for 
   subsequent SIP requests, thereby reaching SIP devices further and 
   further downstream and receiving 483 from each of them. 
    
   The mechanism described in this document uses such a Max-Forwards 
   style traceroute to perform media-loopback testing.  To perform a 
   SIP media-plane traceroute, the originating UAC generates a SIP 
   INVITE to a target AoR, with SDP based on [RFC6849].  When the 
   request reaches the first B2BUA that supports this mechanism, if the 
   B2BUA allows such testing from the requesting UAC, then the B2BUA 
   will answer the INVITE to establish the dialog and create a media-
   loopback session. 
    
   The originating UAC can then generate another INVITE to the same 
   target AoR with a B2bua-Hops header value of 1, which will reach the 
   second B2BUA that supports this mechanism, and so on.  A defined 
   [SDP] origin-line sess-id value will be in the SDP answer from each 
   B2BUA answering the INVITE, until the INVITE reaches the final UAS, 
   which does not use the defined sess-id value. (see Section 3.2 for 
   details) 
    
   Using this mechanism a SIP UAC can test the path from itself to each 
   successive B2BUA on the path to a target.  Such a mechanism could 
   also be useful for establishing a permanent test call between an 
   Enterprise and a Service Provider across a SIP Trunk, for example, 
   or for automated measurement systems to test the media path between 
   domains, etc. 
 
3.1. Processing a Received Max-Forwards Header Field 
 
   As currently defined in [RFC3261], the UAS half of a B2BUA does not 
   technically need to inspect the Max-Forwards header field value for 
   received requests - only Proxies do.  This behavior was updated by 
   [draft-loop-detection], such that a compliant B2BUA needs to both 
   inspect the value in order to prevent loops, as well as copy and 
   decrement the value as if it were a Proxy.  This document also 
   requires such behavior in order to succeed, therefore a B2BUA 
   supporting the traceroute mechanism defined in this document MUST 
   also comply with [draft-loop-detection]. 
 
 
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3.2. Answering the INVITE  
    
   If a SIP B2BUA or UAS receives a dialog-creating INVITE request with 
   a Max-Forwards header value of 0, with SDP for media-loopback based 
   on [RFC6849], and the policies of the B2BUA/UAS allow it to answer 
   such a request, then it is answered as if the original target of the 
   request were the local SIP B2BUA/UAS.  The normal procedures of SIP 
   apply, as well as [RFC6849], as if the request had been targeted at 
   the local B2BUA device all along.   
    
   The SDP answer in the SIP response is also generated following 
   [RFC6849], with one exception: the B2BUA MUST also generate an [SDP] 
   origin ('o=') line <sess-id> value of "314159265".  This not-quite-
   randomly-chosen number is an indication that the media/SDP responder 
   is not the final target, but rather a B2BUA responding based on this 
   document's mechanism.  This allows the call generator to detect that 
   it can try the INVITE again with a higher Max-Forwards value to go 
   beyond the B2BUA, and continue doing so until it reaches the final 
   target UAS, which MUST NOT respond with this <sess-id> value. 
    
    
4. Security Considerations 
    
   There are security implications for the mechanism defined in this 
   document.  Answering media-loopback calls in a B2BUA consumes 
   resources on the B2BUA, and network bandwidth in between; therefore, 
   B2BUAs should have some means of controlling who can make such test 
   calls, how many concurrent calls can be established and maintained, 
   and for how long.  Such policies are typically vendor-specific based 
   on local policies, and do not need to be defined in this document. 
    
5.   IANA Considerations 
    
   This document makes no request of IANA yet - if a new parameter or 
   field needs to be inserted when answering the INVITE, then it will 
   be registered in IANA. 
    











 
 
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6.   Acknowledgments 
    
   The general concept of performing media-loopback on a hop-by-hop 
   basis using a decrementing header traceroute style approach came out 
   of discussions several years ago, between the author, Kaynam 
   Hedayat, Nagarjuna Venna, Patrick MeLampy, and others.  Other people 
   that have contributed to the topic over the years since then: Zaid 
   Ally, Dianna Stiller, Jon Boone, and several others whom I have lost 
   the names of since. 
    
   Funding for the RFC Editor function is provided by the IETF 
   Administrative Support Activity (IASA). 
 
7.   References 
    
7.1. Normative References 
 
    [RFC6849]  Kaplan, H., et al, "An Extension to the Session 
         Description Protocol (SDP) for Media Loopback", RFC 6849, 
         February 2013. 
     
    [SDP] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session 
         Description Protocol", RFC 4566, July 2006. 
     
    [draft-loop-detection] Kaplan, H., and Pascual, V., "Loop Detection 
         Mechanisms for Session Initiation Protocol (SIP) Back-to-Back 
         User Agents (B2BUAs)", draft-ietf-straw-b2bua-loop-detection-
         00, April 2013. 
 
 
Author's Address
    
   Hadriel Kaplan
   Oracle
   Email: hadriel.kaplan@oracle.com
 
    












 
 
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