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[manet-dlep-rg] DLEP session establishment

Teco Boot <teco@inf-net.nl> Mon, 11 November 2013 18:01 UTC

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From: Teco Boot <teco@inf-net.nl>
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Date: Mon, 11 Nov 2013 19:01:42 +0100
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To: Henning Rogge <hrogge@googlemail.com>
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Subject: [manet-dlep-rg] DLEP session establishment
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Op 11 nov. 2013, om 16:58 heeft Henning Rogge <hrogge@googlemail.com> het volgende geschreven:

> I like this sequence except for a tiny little bit in the middle:
> 
> On Sun, Nov 10, 2013 at 11:00 AM, Teco Boot <teco@inf-net.nl> wrote:
>>   <---------Peer Offer-----------   Modem starts DLEP session with Offer
>>   ----------Peer Offer---------->   Router starts DLEP session with Offer
>>   --------Peer Offer ACK-------->   Router finishes DLEP session set up
>>   <-------Peer Offer ACK—--------   Modem finishes DLEP session set up
> 
> This opens the code for some strange timing conditions... why not just
> make it a normal 3-way (or 4 way) handshake?
> 
> Modem sends Peer Offer to Router.
> Router answers with Peer Offer ACK...
> only after this the router sends a Peer Offer to the Modem...
> Modem answers with a Peer Offer ACK.
> 
> This way the timing of the messages can only happen in a single way,
> no need to guess who answers first.

Agreed. 

Stan suggested a two-way handshake, enough for TLV exchange.
Third message eliminates reception of unexpected messages.

  Router                    Modem
  ===============================

  ... after TCP connection established, router sets up the DLEP session:
  ----------Peer Offer---------->   Router starts DLEP session with Offer
  <--------Peer Offer ACK--------   Modem joins in DLEP session with Offer ACK
  ---------Peer Offer ACK------->   Router completes DLEP session with Offer ACK

After Router has send Peer Offer ACK, it may send other messages.
After Modem has received Peer Offer ACK, it may send other messages.
If something unexpected or unacceptable occurs, TCP connection is closed and as a result the DLEP session is closed.

Maybe rename the message to Peer Initialize and Peer Initialize Ack (following Stan here).

Teco

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