13 Apr
2019
13 Apr
'19
9:49 a.m.
On Apr 13, 2019, at 12:12 AM, Harald Welte <laforge(a)gnumonks.org> wrote:
On Fri, Apr 12, 2019 at 07:15:56PM +0200, Johannes
Berg wrote:
Or you can just have LINKTYPE_RTP/DLT_RTP and supply them inside nothing.
However, unlike RTP, there is no reason *not* to do that for GSMTAP - it's not as if
the IP or UDP headers in a packet from a host supplying GSMTAP-encapsulated packets
provide any information necessary or even useful for dissecting the encapsulated packets.
Whether it's useful, or possible, to have any interfaces on a *host* with cellular
modem connectivity supply the cellular-network traffic as packets with GSMTAP headers -
which appears to be what Johannes is thinking of - is another matter (but even if the
answer is no, there is, as per my other message, a use for a LINKTYPE_GSMTAP/DLT_GSMTAP
header type). That might not be possible, as cellular modems, as you note, tend to hide a
lot of lower-layer details from the host.
Agree. Sorry about that. No disrespect was
intended, but I'm still not
sure I understand the need for UDP encapsulation *as part of the
protocol*. I guess saying "GSMTAP can optionally be encapsulated in UDP
with the well-known port xyz" would be something else, and it'd make
more sense to me than saying it has to be.
Sure, like with most protocols you can wrap them in anything you want.
Let me put it like this:
You don't have to run RTP inside UDP, you could equally put the RTP
frames in to SCTP or DCTP. It's just not what the original users of
the protocol/spec had envisioned, but it can for sure be done, and has
no side-effect other than not being interoperable with existing
implementations.