Subject: Re: [PATCH 1/1] gtp: support SGSN-side tunnels

From: Pablo Neira Ayuso <[email-masked]>
Date: Mon, 6 Feb 2017 12:08:58 +0100

Hi Jonas,

On Fri, Feb 03, 2017 at 10:12:31AM +0100, Jonas Bonn wrote:
> The GTP-tunnel driver is explicitly GGSN-side as it searches for PDP
> contexts based on the incoming packets _destination_ address.  If we
> want to write an SGSN, then we want to be idenityfing PDP contexts
> based on _source_ address.
> 
> This patch adds a "flags" argument at GTP-link creation time to specify
> whether we are on the GGSN or SGSN side of the tunnel; this flag is then
> used to determine which part of the IP packet to use in determining
> the PDP context.

So far the implementation that I saw in osmocom relies on userspace code
to tunnel data from ME to the SSGN/SGW running on the base station.

The data we get from GGSN -> SGSN needs to be places into a SN-PDU (via
SNDCP) when sending it to the BTS, right? So I wonder how this can be
useful given that we would need to see real IP packets coming to the
SSGN that we tunnel into GTP.

Thanks!