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RE: [rohc] FW: ESP and header compression (ROHC)
Yaron,
That clarified the scenario, just note that "ROHC over tunnels"
has not yet been addressed in the ROHC WG. I do not say that
that there must be problems with that, but it should be noted
that the link assumptions made for ROHC might not match a
tunneling case.
Anyway, I am not sure you need anything special in the ESP
header, but can do per-link compression of the whole chain. You
would have an outer and an inner IP header, and the ESP header
would be part of a compressed chain (RFC 3095 section 5.8, 5.8.4.3).
However, if the inner headers are encrypted, you can of course
not compress all headers on a per-link basis. Is that the case
you are considering?
Cheers,
/L-E
> -----Original Message-----
> From: Yaron Sheffer [mailto:yaronf@gmx.net]
> Sent: den 14 april 2003 15:26
> To: Lars-Erik Jonsson (EAB); IPSec List; rohc@ietf.org
> Subject: Re: [rohc] FW: ESP and header compression (ROHC)
>
>
> Hi Lars-Erik,
>
> I may have been misunderstood. To clarify, I am discussing
> the following
> stack:
>
> PPP | IP(1) | ESP | IP(2) | UDP | RTP | Payload
>
> In some cases, depending on the nature of the flows that use
> the ESP tunnel,
> ESP plays the role of a link. In those cases, it makes sense
> to compress the
> "internal" headers, i.e. IP(2)+UDP+RTP. In a simple end-to-end SIP
> conversation there will be a single RTP flow within the
> tunnel, and ROHC is
> beneficial for the internal headers.
>
> In fact, you can use ROHC *twice*, once for IP(1)+ESP and once for
> IP(2)+UDP+RTP.
>
> Regards,
> Yaron
>
> ----- Original Message -----
> From: "Lars-Erik Jonsson (EAB)" <Lars-Erik.Jonsson@epl.ericsson.se>
> To: "'Yaron Sheffer'" <yaronf@gmx.net>; "IPSec List"
> <ipsec@lists.tislabs.com>; <rohc@ietf.org>
> Sent: Monday, April 14, 2003 10:04
> Subject: RE: [rohc] FW: ESP and header compression (ROHC)
>
>
> > Hi all,
> >
> > A few notes:
> > 1) ROHC is applied on a per-link basis, e.g. over PPP
> > 2) Based on the above point, there are ROHC compression profiles
> > defined for IP/UDP, IP/UDP/RTP, IP/ESP (and soon IP-only)
> >
> > Compressing the network layer header is most important to gain
> > anything, but that can only be done on a per-link basis. Header
> > compression is thus applied per-link to compress network and
> > transport layer headers (and by heuristics also the application
> > layer RTP header). It is also simpler to do compression per-link,
> > as one can optimize for certain assumed characteristics (such as
> > in-order delivery). Further, it makes most sense as header
> > compression is an optimization for "narrow links".
> >
> > Therefore, I can not see why/how one could do "ROHC over ESP".
> >
> > BR
> > /Lars-Erik
> >
> >
> >
> >
> > > -----Original Message-----
> > > From: Yaron Sheffer [mailto:yaronf@gmx.net]
> > > Sent: den 13 april 2003 21:26
> > > To: IPSec List; rohc@ietf.org
> > > Subject: [rohc] FW: ESP and header compression (ROHC)
> > >
> > >
> > > (please reply to both lists)
> > >
> > > Below is my question to Steve Kent (author of the new rev
> of ESP, and
> > > co-author of the original RFC) and his reply. I understand
> > > that IPCOMP is
> > > inferior to ROHC for RTP streams, and I'd like to hear
> other opinions
> > > regarding the usefulness of an "ROHC" indicator in ESP.
> > >
> > > This might certaily add complexity to IPSec, but if you make it
> > > non-negotiable and non-mandatory, it cannot be too terrible.
> > >
> > > Thanks,
> > > Yaron
> > >
> > > -----Original Message-----
> > > From: Stephen Kent [mailto:kent@bbn.com]
> > > Sent: Thursday, April 10, 2003 12:06 AM
> > > To: Yaron Sheffer
> > > Cc: Sara Bitan; kent@bbn.com
> > > Subject: Re: ESP and header compression (ROHC)
> > >
> > >
> > > At 11:25 PM +0200 4/9/03, Yaron Sheffer wrote:
> > > >Hi Steve,
> > > >
> > > >I have lately looked at issues with IPSec encryption of RTP
> > > streams (I am
> > > >aware of SRTP but I think we will want RTP over IPSec for
> > > some time to
> > > >come). A major issue is packet overhead. You can use
> Robust Header
> > > >Compression (ROHC) on the external IP+ESP headers - this is
> > > defined by the
> > > >ROHC RFC. But if you want to header-compress the RTP packets
> > > before it is
> > > >tunneled in ESP (IP+UDP+RTP headers), you cannot do it
> > > because there's no
> > > >way to detect ROHC packets in the ESP header. I'd expect ESP
> > > to contain a
> > > >marker for ROHC packets, similarly to PPP. Has this option
> > > been considered
> > > >for the new version of ESP?
> > > >
> > > >Thanks,
> > > > Yaron
> > >
> > > No, the WG has not considered that option. The WG has
> been striving
> > > to make IPsec simpler and thus adding support for ROHC is
> contrary to
> > > that theme. For example, ROHC would have be be implemented within
> > > IPsec, after the SA lookup was performed, and ROHC decompression
> > > would have to be implemented in IPsec at the receiver, since the
> > > receiver has to check the headers against the SAD. IPsec already
> > > supports IPCOMP as a compression method for whole
> packets, not just
> > > headers, and thus it might be hard to persuade the WG to add ROHC
> > > support too.
> > >
> > > But, that's just my impression. You can always raise the
> > > question on the
> > > list.
> > >
> > > Steve
> > >
> > > _______________________________________________
> > > Rohc mailing list
> > > Rohc@ietf.org
> > > https://www1.ietf.org/mailman/listinfo/rohc
> > >
> >
>