Subject: RE: [manet] bandwidth calculation at a node

From: Harpreet Arora <[email-masked]>
Date: Wed, 23 Jul 2003 20:22:38 -0400

Thanks Philippe. This is certainly useful. However, the paper assumes that a
channel is divided into time slots and reservations are made by reserving
time slots. I am trying to figure out if it is possible to make QoS
assurances in an 802.11-DCF   based network.  In such a network, each node
has to keep track of the amount of bandwidth which is being used by the
neighboring nodes (nodes which are transmitting within the interference
range of  this node) before it can make any reservations or admission
control decisions. Is there any work done which discusses how bandwidth can
be calculated in this scenario?

thanks,
Harpreet

>===== Original Message From Philippe Jacquet <[email-masked]> 
=====
>Hello, Harpreet,
>
>We have extended the available bandwidth calculation per node (or per link)
>up to an arbitrary number H_I of hops from the node. Interferences can
>extend much further than one hop. With IEEE 802.11 the interference range
>extend between two and three hops. However we prove in
>http://www.inria.fr/rrrt/rr-4876.html that the problem of finding a route
>that fits the bandwidth requirement of a new connection is NP hard in
>general as soon as H_I>0. We show example with slotted ad hoc TDMA networks.
>This result is in sharp contrast with wired network (H_I=0) where the
>finding of an optimal route is polynomial.
>
>Philippe
>
>----- Original Message -----
>From: Harpreet Arora <[email-masked]>
>To: <[email-masked]>
>Sent: Monday, July 21, 2003 10:18 PM
>Subject: [manet] bandwidth calculation at a node
>
>
>> Hi,
>>
>> I have read a number of papers offering QoS solutions in MANETs. Most of
>them
>> assume that nodes somehow have an idea of the available bandwidth in their
>> neighborhood and either pass this information around or make admission
>control
>> decisions based on this information. The SWAN model computes bandwidth at
>a
>> node by tapping all packet transmissions within the neighborhood of the
>node
>> within a certain period of time and updating the estimate of the bandwidth
>> being used based on that information. However, this does not capture the
>> scenario where two nodes are within interfering range of each other but
>not in
>> reception range. Are there any papers in this regard?
>>
>> thanks,
>> Harpreet S. Arora
>>
>> Research Assistant, ITCSL
>> Drexel University
>> Philadelphia, PA-19104
>> Ph: 215-895-6198
>>
>> --------------------------------------------------------------------
>> Harpreet S. Arora
>> Research Assistant, ITCSL
>> Drexel University,
>> Philadelphia, PA-19104
>> Ph. # 215-895-6198
>> http://www.pages.drexel.edu/~ha33
>> ----------------------------------------------------------------------
>>
>>
>> _______________________________________________
>> manet mailing list
>> [email-masked]
>> https://www1.ietf.org/mailman/listinfo/manet
>
>
>_______________________________________________
>manet mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/manet

--------------------------------------------------------------------
Harpreet S. Arora
Research Assistant, ITCSL
Drexel University,
Philadelphia, PA-19104
Ph. # 215-895-6198
http://www.pages.drexel.edu/~ha33
----------------------------------------------------------------------

_______________________________________________
manet mailing list
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https://www1.ietf.org/mailman/listinfo/manet

---

From: Christian de Waal <[email-masked]>
Date: Thu, 24 Jul 2003 10:02:24 +0200

Hi Harpreet,

QoS assurances are not possible in 802.11 DCF networks. Period. To make 
assurances, you need something like a slotted MAC layer, because 
"simply" knowing the available bandwidth at the sending and at the 
receiving station is not enough: The stations also have to negotiate at 
what times the medium is free at _both_ stations. If half of the link 
bandwidth is available at both stations, but one station is blocked when 
the other is not and vice versa, then these stations cannot communicate 
unless some re-scheduling is performed.

I can once again point you to our ASWN'03 paper which describes these 
difficulties in detail.

http://web.informatik.uni-bonn.de/IV/Mitarbeiter/dewaal/aswn03.html

Best regards,
Christian

-- 
____________________________________________________________________
Christian de Waal

University of Bonn                            Phone: +49 228 73-4548
Institute of Computer Science IV                Fax: +49 228 73-4571
Roemerstr. 164                         E-mail: [email-masked]
53117 Bonn, Germany                    http://www.cs.uni-bonn.de/IV/

---

From: Isabelle Guérin Lassous <[email-masked]>
Date: Thu, 24 Jul 2003 16:21:59 +0200

Hi Harpreet,

We have designed a bandwidth reservation protocol (called BRuIT for 
Bandwidth Reservation under InTerferences) for MANET that tries to 
address the interference notion. You can find the first paper on the 
subject at http://www.inria.fr/rrrt/rr-4308.html. The protocol is not 
perfect, but it was a first step towards the integration of 
interferences notion into QoS protocols for MANET. We have gone on 
working on the subject since this paper, and we have now a more detailed 
protocol. I hope a more complete paper will appear soon.

Do not hesitate if you have some questions. Regards,

Isabelle Guérin Lassous

---

From: "Dr Manthos Kazantzidis" <[email-masked]>
Date: Thu, 24 Jul 2003 11:26:02 -0700

Hi Harpreet and Christian,

 While I agree with the email, I wanted to add that there
is an issue of available bandwidth definition and measurement
method. For example if there is a local measurement
that takes into account the MAC mechanisms then one
can say that the available bandwidth can be predicted at some
value - of course this does not imply when you sent a packet
it will be received but just that under some scheduling (similar to such of
the past
if you will) if no additional flows enter the link etc the available
bandwidth will be that.

At

End-to-end versus Explicit Feedback Measurement in 802.11 Networks -ISCC02

downloadable from http://www.cs.ucla.edu/~kazantz/

I am attempting a per-neighbour measurement of available bandwidth
using the ACK times.

I am considering the neighbour and neighbour's neighborhood by combining
a source, destination specific throughput measurement
(which indirectly depends on 802.11 timers) with the node utilization.
If the paper is not very clear I can post additional slides and some
results that show that -in simulation- works very well for multimedia
adaptation, if interested.

Regards,
Manthos

PS: I have not read that paper but will do.

---

From: Frank Li <[email-masked]>
Date: Mon, 28 Jul 2003 09:38:02 +0200

Hello Manthos,

We recently built an ns2 model  similar to your ISCC'02 paper,  trying 
to measure the available bandwidth (throughput) using probe packets. 
There are three nodes within the transmission range, one receiver plus 
two senders. The first sender is transmitting ordinary CBR traffic to 
the receiver while the other one sends regularly probe packets to the 
same receiver. The probe packets were sent at quite low bitrate to avoid 
'stealing' much bandwidth  from  CBR traffic when the load is heavy. We 
measure the packet throughput by packet_length/(T_ack - T_send) and the 
measured throughput is the average value from, say, 30 probe packets.

The preliminary results show that the measured throughput is almost the 
same as the maximum throughput when there is no CBR traffic. But as the 
load from ordinary source inceases, the results become more and more 
unrealiable, especially when the channel is saturated.  For instance, 
when the offered CBR load > maximum throughput,  the probing node can 
still obtain quite high 'available' bandwidth. However, the measured 
throughput roughly reflects the channel congestion status.

So I basically feel that this probing-based method may not act as an 
accurate measurement for available bandwidth, but only as an indicator 
for channel condition. You claimed in sec. 3.1 of your paper that 'our 
measurement is very accurate under low load conditions'. How about the 
case when the load is heavy? Could you please post more results?

BR,
Frank

Dr Manthos Kazantzidis wrote:

>>>Thanks Philippe. This is certainly useful. However, the paper assumes
>>>      
>>>
>that a
>  
>
>>>channel is divided into time slots and reservations are made by
>>>      
>>>
>reserving
>  
>
>>>assurances in an 802.11-DCF   based network.  In such a network, each
>>>      
>>>
>node
>  
>
>>>control decisions. Is there any work done which discusses how bandwidth
>>>      
>>>
>can
>  
>

---

From: "Dr Manthos Kazantzidis" <[email-masked]>
Date: Mon, 28 Jul 2003 01:56:47 -0700

Dear Frank,

My suggestions are:

1- Check that your CBR source does not create
any synchronization effect in the simulation. If so,
you cannot measure accurately (that would not happen
in a real scenario). Use a source (can be CBR viewed 
at a larger interval) that has a random 
packet interarrival time for example.

2-  As the congestion increases your sample variance
increases and you would need more samples to 
find the available bandwidth. Some samples will be at
maximum throughput since they will only be affected
by a small carrier sense interval if they do not coincide
with a CBR traffic packet. 

3- Take into account lost packets as well in case you do not.

I believe that measurement proposed is very accurate bc
it indirectly takes into account MAC collision avoidance 
timers that 'sense' the neighborhood contention .

I hope this helps

Manthos

  ----- Original Message ----- 
  From: Frank Li 
  To: Dr Manthos Kazantzidis 
  Cc: [email-masked] 
  Sent: Monday, July 28, 2003 12:38 AM
  Subject: Re: [manet] bandwidth calculation at a node

  Hello Manthos,

  We recently built an ns2 model  similar to your ISCC'02 paper,  trying to measure the available bandwidth (throughput) using probe packets. There are three nodes within the transmission range, one receiver plus two senders. The first sender is transmitting ordinary CBR traffic to the receiver while the other one sends regularly probe packets to the same receiver. The probe packets were sent at quite low bitrate to avoid 'stealing' much bandwidth  from  CBR traffic when the load is heavy. We measure the packet throughput by packet_length/(T_ack - T_send) and the measured throughput is the average value from, say, 30 probe packets. 

  The preliminary results show that the measured throughput is almost the same as the maximum throughput when there is no CBR traffic. But as the load from ordinary source inceases, the results become more and more unrealiable, especially when the channel is saturated.  For instance, when the offered CBR load > maximum throughput,  the probing node can still obtain quite high 'available' bandwidth. However, the measured throughput roughly reflects the channel congestion status. 

  So I basically feel that this probing-based method may not act as an accurate measurement for available bandwidth, but only as an indicator for channel condition. You claimed in sec. 3.1 of your paper that 'our measurement is very accurate under low load conditions'. How about the case when the load is heavy? Could you please post more results? 

  BR,
  Frank

At

Regards,
Manthos

----- Original Message ----- 
From: "Christian de Waal" <[email-masked]>
To: "Harpreet Arora" <[email-masked]>; <[email-masked]>
Sent: Thursday, July 24, 2003 1:02 AM
Subject: Re: [manet] bandwidth calculation at a node

  Hi Harpreet,

Best regards,
Christian

Harpreet Arora wrote:

thanks,
Harpreet