From saujain at neo.tamu.edu  Thu Jan  5 07:26:05 2006
From: saujain at neo.tamu.edu (Jain, Saurabh)
Date: Thu, 5 Jan 2006 15:26:05 -0000
Subject: [xcp] Error handling in XCP code (nodiv version)
Message-ID: <200601051526.k05FQ5iT065065@xyzzy-3.tamu.edu>

Hi All,

How is error recovery done by the end hosts in the XCP code (nodiv version) 
whenever a packet is lost? Is the congestion window reduced to half and fast 
recovery and fast retransmission invoked while keeping the congestion window 
frozen as long as the host recovers from the error? Does the code uses SACK 
or can it be enabled?

Thanks in advance,
Saurabh



From falk at ISI.EDU  Mon Jan  9 10:45:23 2006
From: falk at ISI.EDU (Aaron Falk)
Date: Mon, 9 Jan 2006 10:45:23 -0800
Subject: [xcp] Error handling in XCP code (nodiv version)
In-Reply-To: <200601051526.k05FQ5iT065065@xyzzy-3.tamu.edu>
References: <200601051526.k05FQ5iT065065@xyzzy-3.tamu.edu>
Message-ID: <4CB8335E-B8F0-4A08-BE6A-94D148606571@isi.edu>


On Jan 5, 2006, at 7:26 AM, Jain, Saurabh wrote:

> Hi All,
>
> How is error recovery done by the end hosts in the XCP code (nodiv  
> version)
> whenever a packet is lost? Is the congestion window reduced to half  
> and fast
> recovery and fast retransmission invoked while keeping the  
> congestion window
> frozen as long as the host recovers from the error? Does the code  
> uses SACK
> or can it be enabled?
>

Saurabh-

The error recovery code in the nodiv version is unchanged from the  
normal BSD TCP code.  SACK is enabled.   When TCP notices a loss  
(after sufficient DUPACKs have been received or an ECN mark, etc) it  
cuts cwnd in half.  However, the cwnd growth is determined by the XCP  
algorithm, not slow-start and congestion avoidance.  So, the next XCP  
packet arriving modifies cwnd by the network allocation.  Unless the  
packet loss is from  a congested XCP router (very unlikely), cwnd  
will rapidly grow -- in the same way as a new flow entering the  
network.  This is not a intentional behavior.  It is just a side  
effect of how we put the code in.  If you run XCP in a network with  
all XCP routers and mostly lossless links, it is rarely executed.

However, it is likely that any realistic deployment of XCP will be in  
a network with queues that are not XCP-enabled.  We are currently  
developing new behavior for the scenario where the congestion  
bottleneck is a non-XCP router and packets are lost.  More about this  
as it matures...

Hope this helps,

--aaron



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From haldar at ISI.EDU  Mon Jan  9 10:50:57 2006
From: haldar at ISI.EDU (Padmaparna Haldar)
Date: Mon, 9 Jan 2006 10:50:57 -0800 (PST)
Subject: [xcp] error with xcp-1.1 and ns2.28
In-Reply-To: <C48880D4-A516-400E-A19B-C69D4D979385@isi.edu>
References: <20051115160939.M60276@ee.ucl.ac.uk>
	<C48880D4-A516-400E-A19B-C69D4D979385@isi.edu>
Message-ID: <Pine.LNX.4.62.0601091048450.31968@rim.isi.edu>


Hi Moses,

What kind of problem do you see when you run xcp_test.tcl?
Are you trying to use nam?
Thanks,
--Padma

>> From: "Moses Woldeselassie" <mwoldese at ee.ucl.ac.uk>
>> Date: November 15, 2005 8:13:36 AM PST
>> To: xcp at ISI.EDU
>> Subject: [xcp] error with xcp-1.1 and ns2.28
>> 
>> Hi all
>> 
>> I did try to use the XCP-1.1 and xcp_test.tcl with the ns2.28:
>> 
>> I did replace these files queue.c and queue.h in nam-1.11.
>> 
>> but my problem is with the xcp: xcp.cc, xcp-end-sys.cc and xcp-end-sys.h
>> 
>> how do I modifie this Makefile/Makefile.in for the xcp.cc and xcp- 
>> end-sys.cc?
>> what do I need beside that to run the xcp_test.tcl?
>> 
>> I am looking forward to hearing from you.
>> 
>> Cheers
>> Moses
>> 
>> ***************************************************************
>> Electronic & Electrical Engineering @ UCL
>>             www.ee.ucl.ac.uk
>> ***************************************************************
>> 
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