Subject: Re: [16NG] Comments on Transmission of IPv4 packets over IEEE 802.16's IP CS draft

From: Bruno Sousa <[email-masked]>
Date: Fri, 07 Mar 2008 18:31:53 +0000

Hi Samita

I also agree with Wes, regarding the MTU specification value.
In my opinion the text does not clearly justifies the choice of 
1400bytes. It refers to the overhead of GRE tunnels and the size of the 
802.16 MAC header, but these 'arguments' allow others values such as 
1500bytes, as Wes pointed out.

Moreover, I have some comments regarding other sections of the document:

Section 1. Introduction
"This document also mentions about ARP (Address Resolution Protocol)
   and Multicast Address Mapping whose operation is similar to any other
   point-to-point link model."

I think there a reference to a point-to-point link model would help to 
understand the point-to-point link model specified in this document.

Section 6. Subnet Model and IPv4 Address Assignment.
"   The point-to-point link between MS and AR
   is achieved using a set of IEEE 802.16 MAC connections (identified by
   CIDs) and at least an L2 tunnel (usually GRE tunnel) per MS between
   BS and AR."

It is recommend the setup of a GRE tunnel between the BS and the AR, 
nevertheless the 'moment' and how this tunnel is established per MS is 
not clear. For instance should BS set-up a tunnel after the network 
entry (as defined in IEEE 802.16) performed by the MS?

Section 7. Address Resolution Protocol
"   The IP CS does not allow for transmission of ARP [3] packets,
   accordingly, other mechanisms for address resolution must be used.
   In a point-to-point link model, address resolution may not be needed."

If Address resolution is needed what other mechanisms can be used?
Shouldn't we have also a reference here for other documents, for 
instance the 'IP-over-ethernet-over-802.16' specification?

Bruno Sousa

Samita Chakrabarti wrote:
> Hi Wes,
>
> Your points are noted on default MTU being 1500 for IPv4CS and recommending
> the following for new-clients while old clients suffer fragmentation.
>
> We have debated on the IPCS MTU size for a while, but we can request and
> work with Wimax folks at IETF to see what the best way to lay out the MTU
> message in the IPCS document. 
>
> Thanks for your input.
> -Samita
>
>   
>>  >
>>     
>>> In order to make use of higher bandwidth network (such as 100 GE),
>>>       
>> perhaps
>>     
>>> we can ensure that the new clients would be intelligent enough to ask for
>>> link MTU  through the DHCP service or some other means. This will avoid
>>> backward in-compatibility problems with old-implementations/devices.
>>>       
>> Why couldn't that be covered as a recommendation in this draft? I think we
>> all know that the longer we wait, the more deployments start happening,
>> and they all contribute to the inevitable inertia that resists change, no
>> matter how much sense it makes.
>>
>> Regards,
>> Wes
>>     
>
>
>
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>
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>   

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---

From: "Samita Chakrabarti" <[email-masked]>
Date: Sun, 9 Mar 2008 21:09:33 -0700

Hi Bruno,

Please see in-line.

I also agree with Wes, regarding the MTU specification value. 
In my opinion the text does not clearly justifies the choice of 1400bytes.
It refers to the overhead of GRE tunnels and the size of the 802.16 MAC
header, but these 'arguments' allow others values such as 1500bytes, as Wes
pointed out.

[SC>]  Let's discuss on MTU at the 16ng meeting. We would like some comments
from the Wimax-forum liasons/participants as well to help us reach a
conclusion.

Section 1. Introduction

[SC>] We assume that from IP perspective, the link between the MS and the AR
is a point-to-point link. We can use some text from Wimax docs in the
appendix section of the document to make it clear.

It is recommend the setup of a GRE tunnel between the BS and the AR,
nevertheless the 'moment' and how this tunnel is established per MS is not
clear. For instance should BS set-up a tunnel after the network entry (as
defined in IEEE 802.16) performed by the MS?

[SC>] How the tunnel is setup or how the point-to-point link is formed
between MS and AR is not in the scope of this document, however, I think
some explanation from Wimax doc in the appendix would help. 

If Address resolution is needed what other mechanisms can be used?
Shouldn't we have also a reference here for other documents, for instance
the 'IP-over-ethernet-over-802.16' specification?

[SC>]  I think it is a good idea to point to the IP over EthCS doc.

Thanks,

-Samita

Bruno Sousa

Hi Wes,

 
Thanks for your input.
-Samita

perhaps

 
Regards,
Wes