Subject: traffic characteristics and generators

From: Henrik Lundgren <[email-masked]>
Date: Thu, 22 Nov 2001 14:57:39 +0100 (MET)

Hi, 

To those of you out there who perform simulations or 
run real-world tests on ad hoc routing protocols, 

- What kind of traffic characteristics do you load 
the network with? CBR, Self-similar or other distributions?
Is there any realistic traffic patterns considering applications
or scenarios of an ad hoc network?

- Do you usually consider only UDP? Or TCP as well?

- What traffic generators do you use for this? 
(For real-world tests I often only see Ping being used.)

Best regards,
Henrik Lundgren

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From: [email-masked]
Date: Thu, 29 Nov 2001 18:25:54 +0100 (CET)

On Thu, 22 Nov 2001, Henrik Lundgren wrote:

<SNIP>

> or scenarios of an ad hoc network?

It's hard to specify what traffic patterns are "realistic". Everybody can
play the game of "show me 'your' protocol, and I shall make up a
'realistic' scenario where 'my' protocol outperforms 'yours'" ;)

On a more serious note, it seems that manets are thought to be deployed
in very varying situations - varying degrees of mobility and traffic. It
can be argued that a network with mostly little mobility and mostly
static traffic patterns is "realistic" as can it be argued that a high
degree of mobility and random traffic is a "realistic" scenario.

It would be interresting, though, if someone with "real" (and
non-military) scenarious would step forward and provide details as to how
they would like to use the protocols.

> - Do you usually consider only UDP? Or TCP as well?

Usually, CBR-traffic (UDP) is being used. However, as we've shown at the
last IETF in London, two instances of two protocol (in our case, an
instance of OLSR and an instance of AODV) can show similar performance for
CBR-traffic. The same protocol instances, but this time using TCP,
one would outperform the other by a large margin.

This does not necessarilly show that either protocol has a problem. It
just goes to show that otherwise identically performing protocols can perform
very differently, depending on the transport layer. It also goes to show,
that it's probably worth investigating the interaction between the
transport protocol used, and the routing protocols.

> (For real-world tests I often only see Ping being used.)

In simulations, we've just used basic traffic generators as provided by
ns2.

Best regards

-- 

-------------------------------------------
  Thomas Heide Clausen
  Civilingeniør i Datateknik (cand.polyt)
  M.Sc in Computer Engineering

  E-Mail: [email-masked]
  WWW:    http://www.cs.auc.dk/~voop
-------------------------------------------

---

From: [email-masked]
Date: Thu, 29 Nov 2001 12:03:53 -0800

It is well known that TCP has problems in mobile networks, since
it was designed to perform well in fixed networks in which congestion
is the main cause of packet loss.  Therefore, although it is
interesting to show that one protocol performs better than
another protocol using TCP, it would probably be better to use 
a modification of TCP that is better suited for wireless networks.

I am curious to know *why* OLSR performs better than AODV when TCP 
is used.  My *guess* is that the delays caused by route discovery 
(either initially or when the path fails) in on-demand protocols 
result in the window size being decreased exponentially, and after 
a path is discovered, the window size is increased more slowly.  
Thus, proactive routing protocols would have an advantage since
they do not incur any delay for route discovery.  

Richard