Hi
First of all i would like to thanks for your response.
Vyatta router is implemented for test based linux distribution, cannot find any
thing on internet.But the important thing is ROHC behavior for a channel loss
between compressor & de-compressor.
a/ Compressor & d-ecompressors are directly connected through wire. Netem queue
add losses for compressed traffic which send out fromthe ethernet interface at
compressor end.Furthermore, UDP/IPv4 traffic (periodic pattern) is generated
from compressor towards de-compressor through MGEN.
b/ The mode which i have noticed through packet traces is O-mode. Because there
is no periodic updates.
e/ The de-compressor fails for a consecutive number of packet drop e.g. 30 or
more than 30 packets which is understood thing. But the surprising thing is
that some time compressor goes back to a lower compression state (IR or FO) to
send more information to the decompressor without error recovery request. It is
like periodic refresh or time out period at compressor for a queue packet
loss/delay.
I cannot say it as periodic update because it is not unidirectional mode.
Note: For only loss percentage (more than 60%) observe only feedback request by
de-compressor. But for packet loss (46 % or more) plus correlation
percentage(90%) compressor sends IR header after consecutive packet drops (30
or more) without feedback request from de-compressor.
Kind Regards
Faraz
________________________________
From: Didier Barvaux <[email protected]>
To: ROHC Library <[email protected]>
Sent: Sunday, March 24, 2013 11:38 AM
Subject: [Rohc] ROHC robustness (Was: Re: Fw: Linux kernel support)
Hi,
> I am Msc (ICT) student in final year at University of Agder ,
> Norway. I am doing thesis work on ROHC based Linux router (vyatta).
> My task is to analyze the ROHC performance for one hop/multihops
> Adhoc nodes. I have linux based routers with ROHC implemented.
I didn't know that vyatta put the ROHC library in their software. I
found nothing about ROHC on http://vyatta.org/. Am I looking at the
right place?
> For a real scenario testbed i have added Netem queue at the
> compressor outgoing interface and add loss, delay etc parameters. In
> this case i observed the behavior at de-compressor end.
>
> Observation:
> 1. Beyond 46% loss (netem root queue), de-compressor send error
> recovery compressed message to compressor and then compressor send
> full header.
> 2. When
de-compressor missed 30 or more then 30 packets
> then it send error recovery request to compressor.
>
> Questions
> 1. How much loss (percentage) for which ROHC is robust.?
There is no absolute answer. That depends on several things:
a/ the kind of traffic you're compressing: ROHC on a very regular
stream (= packets with headers that don't change much) will be more
robust to network loss than a stream with big changes.
b/ the ROHC mode in which you run: U-, O-, or R-mode.
c/ your network latency when feedbacks are used to report
decompression failures.
d/ the parameters used for ROHC: the widths of the W-LSB windows, the
context refreshes timeouts...
e/ the kind of network loss you emulate: losing N packets in a row
will probably cause more more damage than losing 1 packet N times.
For example, if
your traffic is a single IPv4/UDP stream with constant
IP-ID, the robustness should be quite important: if N packets are lost
in a row between the compressor and the decompressor, the decompressor
should not fail to decompress the next packets. If not, tell me, there
is perhaps a problem with your test and/or with the ROHC library.
> 2. Sometime compressor sends full header at packet loss instant
> without error recovery request from de-compressor.
Difficult to say without more information. One possible hypothesis is
that the compressor decided it was time for periodic refresh of the
context. In such a case the compressor goes back to a lower compression
state (IR or FO) to send more information to the decompressor.
Regards,
Didier
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