From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guy Harris Subject: Re: gsmtap design/extensions? Date: Sat, 13 Apr 2019 00:49:59 -0700 Message-ID: <7C48A51C-852F-480B-9F6D-C5BFEBB1A389@alum.mit.edu> References: <46474c61d7748042cc0a1f23773186786020638e.camel@sipsolutions.net> <20190410234555.GO25552@nataraja> <20190413071227.GC24451@nataraja> Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20190413071227.GC24451@nataraja> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Unsubscribe: To: Harald Welte Cc: Johannes Berg , Vadim Yanitskiy , OpenBSC Mailing List , Sean Tranchetti , radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org, Dan Williams , netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Aleksander Morgado , Subash Abhinov Kasiviswanathan , =?utf-8?Q?Bj=C3=B8rn_Mork?= List-Id: radiotap@radiotap.org On Apr 13, 2019, at 12:12 AM, Harald Welte wrote: > On Fri, Apr 12, 2019 at 07:15:56PM +0200, Johannes Berg wrote: >=20 >> 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. >=20 > Sure, like with most protocols you can wrap them in anything you want. >=20 > 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. 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.