Subject: [rohc] Feedback channels in ROHC-TCP

From: "Tan Wee Lum" <[email-masked]>
Date: Thu, 21 Oct 2004 14:03:49 +0800

Hi,

In the ROHC-TCP draft version 7, it is mentioned in Section 3.1 that 
the disadvantage of the full header request mechanism in IPHC 
is that it requires a feedback channel that may be unavailable in 
some circumstances.

I am wondering what are the circumstances in which a feedback channel
is not available? I thought that a TCP connection would require a
full-duplex
channel to work?

Thanks for any clarification.

Wee Lum

_______________________________________________
Rohc mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/rohc

---

From: Carsten Bormann <[email-masked]>
Date: Thu, 21 Oct 2004 16:33:21 +0200

> I thought that a TCP connection would require a
> full-duplex
> channel to work?

TCP does require bidirectional packet (L3) connectivity between the end 
hosts.

Here we are talking about (L2) ROHC channels (see RFC3759).
These are between two nodes on the path from one end host of the TCP 
connection to the other end host of the TCP connection.
Any one (L2) link on this path need not be bidirectional -- the (L3) 
path back may traverse different (L2) links.

Think satellite downlink from Sat-ISP A with a modem return path to an 
ISP B.
The fact that packets ultimately do have to arrive back at the source 
of the packets that are being sent via A does not help with creating a 
bidirectional ROHC channel on the satellite.

Gruesse, Carsten

---

From: gorry fairhurst <[email-masked]>
Date: Mon, 25 Oct 2004 11:56:18 +0100

I agree that an Asymmetric Network Path is an important case.
Thats is: a link may see only forward packets, or only return direction 
(ACK/Control/etc) packets, or both.

Although you could optimise for a (fairly common) case where you see all 
packets in both directions via the same link. This is not required 
(unless, of course, this is the first or final link along the end to end 
internet path :-)). Note that tunnel encapsulations, and security need 
not be the same in both directions either:-)

Gorry

Carsten Bormann wrote:

> The fact that packets ultimately do have to arrive back at the source of 
> the packets that are being sent via A does not help with creating a