Re: [MMUSIC] I-D Action: draft-ietf-mmusic-media-path-middleboxes-06.txt

Gonzalo Salgueiro <> Thu, 10 January 2013 22:46 UTC

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From: Gonzalo Salgueiro <>
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Date: Thu, 10 Jan 2013 17:46:31 -0500
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Subject: Re: [MMUSIC] I-D Action: draft-ietf-mmusic-media-path-middleboxes-06.txt
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I have simply updated the version of this draft to prevent expiration because recent discussions with the chairs have confirmed that we are ready now to progress this milestone. As part of that effort the chairs requested we clearly define the purpose, scope, and intended audience for the document. 

I came a bit late to the party but from my perspective this draft's purpose is to provide guidance and best practices on mitigating the issues middleboxes (particularly NATs and firewalls) can cause to end-to-end SIP/SDP-signaled media streams in different architectures.  The target audience is anyone (i.e. NAT/FW vendors, protocol designers, etc.) wanting such information ond that might benefit from the design tips to make their network/protocol/device more middlebox friendly.

I believe Flemming's recent comments (as an individual) masterfully summarized the scope, purpose and target audience for this document. Thus, I don't want to repeat (less eloquently) what I consider to be the right approach to this document.  For your convenience, here are those comments:


A lot of the SIP and SDP work started out with a somewhat "purist" Internet view of the world, where things such as middleboxes were not considered. As other standards and industry organizations became interested in using SIP and SDP, different architectures were defined and some of those arcitectures did include the notion of middleboxes (e.g. 3GPP IMS and CableLabs PacketCable). From an IETF point of view, there was, at least initially, not a great deal of knowledge about these architectures and what the middleboxes defined by them were doing. Conversely, there was (is) also a concern that such middleboxes may break end-to-end transparency and hence there was a desire to try and alleviate that. 

To that effect, it was seen as useful to have a document that could
a) Explain what/how middleboxes might be operating in these architectures
b) Provide guidelines as to how such middleboxes could minimize (ideally avoid) impacting end-to-end transparency and/or how protocols could be used to try and alleviate any impact such middleboxes might have. 

The middleboxes draft is trying to address the above as it relates to the media path. The target audience is thus IETF participants that would like an overview of how these middleboxes may affect SIP/SDP-signaled media streams as well as what can be done to try and overcome that. Similarly, the document is targeted at people involved in these "other" architecture efforts, with a goal of making it clear how middleboxes may affect the operation of SIP/SDP-signaled media streams and hence provide some "design principles". This is not unlike some of the NAT work that was done in BEHAVE. 

It could be argued that these architectures have now been around for so long that producing the above document will not make any difference at this point. While I have some sympathy for this, I also think we have to recognize the importance of documenting what we know and to make that readily available for new people that will be working in this space. 

In other words, I still believe there is value in pursuing this document. As to whether it should be a BCP or Informational, I don't have any strong opinions. 


As a group can we agree on this scope and that is worthwhile to finally complete this milestone?  Feedback welcome.



On Jan 10, 2013, at 5:45 PM, wrote:

> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> This draft is a work item of the Multiparty Multimedia Session Control Working Group of the IETF.
> 	Title           : Analysis of Middlebox Interactions for Signaling Protocol Communication along the Media Path
> 	Author(s)       : Brian Stucker
>                          Hannes Tschofenig
>                          Gonzalo Salgueiro
> 	Filename        : draft-ietf-mmusic-media-path-middleboxes-06.txt
> 	Pages           : 22
> 	Date            : 2013-01-10
> Abstract:
>   Middleboxes are defined as any intermediary box performing functions
>   apart from normal, standard functions of an IP router on the data
>   path between a source host and destination host.  Two such functions
>   are network address translation and firewalling.
>   When Application Layer Gateways, such as SIP entities, interact with
>   NATs and firewalls, as described in the MIDCOM architecture, then
>   problems may occur in the transport of media traffic when signaling
>   protocol interaction takes place along the media path, as it is the
>   case for recent key exchange proposals (such as DTLS-SRTP).  This
>   document highlights problems that may arise.  Unfortunately, it is
>   difficult for the end points to detect or predict problematic
>   behavior and to determine whether the media path is reliably
>   available for packet exchange.
>   This document aims to summarize the various sources and effects of
>   NAT and firewall control, the reasons that they exist, and possible
>   means of improving their behavior to allow protocols that rely upon
>   signaling along the media path to operate effectively.
> The IETF datatracker status page for this draft is:
> There's also a htmlized version available at:
> A diff from the previous version is available at:
> Internet-Drafts are also available by anonymous FTP at:
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