Subject: [Tsvwg] RE: draft-riegel-tuexen-mobile-sctp-00.txt

From: Tuexen Michael <[email-masked]>
Date: Thu, 14 Mar 2002 15:33:43 +0100

Hi,
see my comments below.
Best regards
Michael

Michael Tuexen    Tel.:   +49 89 722 47210
Siemens AG        Fax:    +49 89 722 48212
ICN WN CS SE 5    E-mail: [email-masked]

> -----Original Message-----
> From:	Armando L. Caro Jr. [SMTP:[email-masked]]
> Sent:	Thursday, March 14, 2002 3:20 PM
> To:	Tuexen Michael
> Cc:	[email-masked]; Riegel Maximilian
> Subject:	RE: draft-riegel-tuexen-mobile-sctp-00.txt
> 
> On Thu, 14 Mar 2002, Tuexen Michael wrote:
> 
> > > In section 4.1: "During the time where the mobile client is reachable via
> > > two different access networks it has to make sure that it uses both
> > > links."  Why is this requirement necessary?
> > >
> > 	[Tuexen Michael]  We want the client to use two paths
> > 	whenever it is possible. Then the client can also use SCTP
> > 	parameters to compare the two paths (round trip time,
> > 	retransmission counter, ...). However, if you do not want
> > 	to do this you can use SCTP also in a single-homed setup.
> 
> Well the example given in the document is that one link is used for
> sending and the other for receiving. Using both links this way doesn't
> give the client parameters to compare. Instead, both links would have to
> be used for sending and receiving is some sort of load-balancing fashion.
> Is this what you mean? Also, since the client is multihomed only during
> the transient phase when handing off, is it likely that the client will
> have enough time to determine these network parameters for comparison?
	[Tuexen Michael]  Where is it stated that the links
	are only used in one direction? Transmission in both
	directions can use the same physical link or seperate
	one. The primary paths in both directions are independent.
	We do not talk (at the moment) about load sharing. But even
	if a path is idle you use the SCTP HEARTBEAT mechanism to
	get path parameters like round trip time and so on. So you
	do not need to do DATA transfer to get these parameters.
	The client is multihomed if it has connections to two base
	stations. This is true during the hand off period. But it can
	also be true if the mobile client has one connection via
	a cellular network and the other connection via WaveLAN,
	because the client is in an appropiate area. Then this 
	mulihoming period is much longer and not only a transient 
	phase.
>  
> 
> > > In section 4.2: "The server must use multiple IP-addresses and a SCTP
> > > implementation supporting the extension [ADDIP]."  Why must the server be
> > > multihomed?
> > 	[Tuexen Michael]  The server must be multihomed because
> > 	we want the client to have two paths towards the server
> > 	(see above) to be able to make use of both network connections
> > 	of the client. But if you only want to use single homed setup...
> 
> Ok, I see that, but I don't see the advantage. Again, the client is
> multihomed only during the transient phase when it is handing off... So
> how useful is it that the client has 2 distinct paths?
> 
	[Tuexen Michael]  See above. The 'transient phase', which
	means the dualhomed phase can be quite long and also more like
	a stable phase. 
	This could be made clearer in the ID.
> ~armando
> 
> 0--                                                --0
> | Armando L. Caro Jr.     |       [email-masked] |
> | University of Delaware  |  www.cis.udel.edu/~acaro |
> 0--                                                --0

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