Re: [manet-dlep-rg] DLEP session establishment

["Dowdell, John" <[e-mail]>]

Just to add my two pennyworth.

We need to agree that the operating scenario is one router and N modems. If we do need to move to more than one router and N modems, the situation is more complex in terms of who does the TCP serving. Can we agree that please?

Also, given the resistance we seem to be experiencing from modem manufacturers to get involved, I would want to give them the least complex half of the implementation. This means they will not have to upgrade hardware, TCP stacks and/or operating systems beyond that which is necessary. I would suggest that we want the modem manufacturers to add value in extracting relevant metrics from the modem and pass through DLEP to the router or other interested process, rather than insisting they upgrade their TCP stacks.

John

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Henning Rogge
Sent: 13 November 2013 10:19
To: Taylor, Rick
Cc: DLEP Research Group ([e-mail]); Teco Boot; Stan Ratliff
Subject: Re: [manet-dlep-rg] DLEP session establishment

I think we can even leave out the TCP address (and maybe even the
port) by just demanding that the UDP Peer_Discovery has to come from
the relevant address (and port) of the TCP socket.

I cannot see an use case for using a different source port/address for
the UDP Peer_Discovery at the moment.

Henning Rogge

On Wed, Nov 13, 2013 at 11:12 AM, Taylor, Rick
<[e-mail]> wrote:
> My thoughts:
>
> The principle of keeping the modem code as small and light as possible is good.  In general modems are not only getting bigger and smarter, they are also getting physically smaller and lower power.  Routers however are not getting so small so quickly, so even though there are full TCP stacks in many radios, we should not force a full server implementation on them.
>
> So, Lets keep the 3-way handshake we have discussed, but make the router the advertiser/server:
>
>
>    Router                                        Modem
>    ===================================================
>
> 1) TCP Listen()
>
> 2) UDP Peer_Discovery ------------------------------->
>      + Version TLV
>      + TCP address:port
>
> 3)                                       TCP Connect()
>
> 4) <-------------------------------- Peer_Initialize()
>                                       + Version TLV
>                                       + Ident TLV
>                                       + Mandatory TLVs
>
> 5) Peer_Initialize_Ack ------------------------------>
>      + Status TLV
>      + Ident TLV
>
> I withdraw my suggestion about cookies.  As Teco has pointed out, just do security properly (TLS or IPSec or whatever).  Putting in a lightweight/half-baked authentication process in the protocol may lead some implementers to assume this provides security.
>
> I have also suggested just Version TLV and TCP endpoint address in the UDP discovery packet to save space.  This should allow a listening modem to decide whether to start a session with a router before TCP connect.
>
> At step 5, the router has the opportunity to send a negative ACK, by including an error Status TLV in the Peer_Inialize_Ack and then shutdown the connection.  This captures Teco's SHOULD condition "The router SHOULD NOT start a session with a modem that does not advertise mandatory metric TLVs"
>
> Would it help to have a state machine in the draft?
>
> Comments?
>
> Rick Taylor
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