Hi Neels, On Thu, Mar 24, 2022 at 11:29:20PM +0100, Neels Hofmeyr wrote:
> Looking at gtp_echo_responder.c, I see that the code uses none of the Osmocom > structures (osmo_fd, logging, osmo_select, osmocom/core/endian.h), and it > implements GTPv1-C and GTPv2-C, but I need GTPv1-U. yes, look at the license. It was specifically created to be used under permissive license (MIT) and hence cannot use the existing libosmo* infrastructure. This is also outlined in the commit message: https://gerrit.osmocom.org/c/osmo-ggsn/+/25652 > osmo-hnodeb/gtp.c does use Osmocom structures. It has its own struct > gtp1u_hdr. > But apparently osmo-hnodeb doesn't do any GTP ECHO handling at all. The latter part is likely a bug, and should be addressed. Though, to be honest, I'm not 100% sure if the use of GTP-U on any other interface than that between GSNs (SGSN/SGW and GGSN/PGW) mandates GTP ECHO support... > I am now only concerned with GTPv1-U, so TS 29.281 should be all I need. Still > interesting to know, do the echos differ between the protocol versions and > planes? Can I use the GTPv1-C code from gtp_echo_responder.c for GTPv1-U? GTPv0 is not really relevant anymore in 99.9% of all situations. GTPv1C and GTPv2C are completely differnt protocols. GTP-U v1 is used by GTPv1C and GTPv2C as well as on many other interfaces that don't use GTP-C for the control plane. > The fact that the GTPv1-U header contains a TEID confused me at first, then I > found in 29.281 that the TEID shall be all zeros in the ECHO req + resp > messages. So, yes, ECHO is done between GSNs as a whole, not on each tunnel. ACK. > Will we spawn all-new GTP implementations in every osmocom repository that > touches GTP, or should I rather implement a re-usable GTP echo response now? to be fair, responding to a GTP-U echo request is hardly a very complex task. > One proper (TM) way seems to be to rearrange libgtp in such a way that a > caller > can just use the msg coding part for specific messages, and can use UDP > sockets > without having to set up a complete struct gsn_t. That's some work. I think libgtp is fundamentlaly un-osmocom-like due to its history and it doesn't make sense to spend time on it. > Another way that comes to mind is opening a libosmo-gtp section in > libosmocore, > absorb protocol definitions across the various GTP versions there, and use > them > in the places where we do GTP coding now. Seems a lot of work. I would say for the struct definitions it would make sense to put it in include/osmocom/gsm/protocol/ or even better include/osmocom/gprs/protocol/ osmo-hnodeb and osmo-upf could then use that code. But that's about it. > ...or I go the apparently quickest, easiest way, do a copy/paste/reimplement > from scratch of GTP echo coding, so that we have yet another partial GTP > implementation in osmo-upf.git. That's what I'm doing now, but it feels wrong. In general, I hear you, but in this case "partial" means 0.01% of what GTP is... -- - Harald Welte <[email protected]> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)
