Subject: RE: Qos and L2TP (was: Do we want a new L2TP Header?)

From: "Chen, David" <[email-masked]>
Date: Fri, 15 Jun 2001 10:42:34 -0400

Evan,

LCP's PPP negotiation is sender sends out one LCP packet and wait for
receiver respond back one LCP packet.
It seems no out-of-sequence LCP packet issue since only one packet at 
a time.
So is in authentication phase and IPCP.

I am wonder why the l2tp has to provide in-order-packet delivery for 
PPP's control packets?

On the PPP's data packet, since it encapsulate the IP, 
it seems no need for l2tp provide packet in-order delivery.

However, it is possible that PPP peers negotiated successive
(state-sensitive) compression 
that it requires compressed packet deliver in order. 
Even it can recover form compressed packet drop,
it will improve the data bandwidth usage 
if l2tp provide in-order-packet delivery service.

Regards,

--- David

-----Original Message-----
From: Evan Caves [mailto:[email-masked]]
Sent: Thursday, June 14, 2001 12:57 PM
To: [email-masked]
Subject: Re: Qos and L2TP (was: Do we want a new L2TP Header?)

With the proposed new sequencing paradigm I think the questions that
need to be asked is "What types of traffic need to be sequenced 
and have separate QOS attributes?" and "Can multiple streams of this 
traffic type exist within one PPP session?". If we can come up with 
some real world examples then there MAY be a need to split a single
PPP session into multiple L2TP sessions.

Certainly the typical environements are just IP over PPP over L2TP. 
In these cases the PPP control traffic SHOULD be sequenced and have a 
single DS mark. The IPCP packets need not be sequenced and the outer 
IP header can be DS marked accordingly.

evan
-

---

From: James Carlson <[email-masked]>
Date: Fri, 15 Jun 2001 11:05:28 -0400 (EDT)

> receiver respond back one LCP packet.

Not true.  Think retransmit.

> I am wonder why the l2tp has to provide in-order-packet delivery for 

It's a basic assumption of PPP itself.

> it seems no need for l2tp provide packet in-order delivery.

Assuming only plain IP over PPP, sure, that's true.  For bridging, VJ,
CCP, MP, and many other things PPP carries, that's not true.

> it will improve the data bandwidth usage 

The data compression protocols have been designed with *drops* in
mind.  Not reordering.

-- 
James Carlson, Internet Engineering       <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677