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Neels Hofmeyr nhofmeyr at sysmocom.deOn Tue, Dec 03, 2019 at 05:20:33PM +0100, Harald Welte wrote: > == DNS zone / .msisdn suffix === > > .{msisdn,imsi}.dgsm.osmocom.org ? Sure, the packets will get larger by sure, we can do that. An idea is to do that merely on the DNS encoding, and strip it off to have only *.imsi in the mslookup client? (If we add other methods, we might not use the domain kind of representation at all there) > == MSISDN format == > > Another thought is whether or not there are any concerns regarding the > MSISDN format. Historically, this is one of the weaknesses of OsmoMSC, > inherited from the OpenBSC days where we just thought in terms of PBX > extension numbers. In reality, a MSISDN consist of a TON (type of > number), NPI (numbering plan indicator) and the related digits. IIRC, > in the TON one can also specify if it's supposed to be national or > international, i.e. if it's prefixed with the country code or not. > > It would be great to make sure that the format used in the mDNS queries > is somewhat standardized, if not at least only by the documentation > requiring that all queries should be done in fully qualfiied form with > country code present. NPI is sort-of bogus as IMOH E.164 is the only > one applicable for MSISDN. > > Any thoughts? So far it just works (TM) ... we reflect the MSISDNs saved in the HLR DB 1:1, not sure what a TON representation might change about that. It always passes through the MSC and SIP first. If it's any consolation, the PBX gets the TON in the SIP INVITE (if it does), and it could choose to treat numbers in any fashion. For mslookup to work though, the MSISDN must reflect whatever we find in the HLR database. If that is unable to reflect a TON (like it currently is unable to) then handling non-naive MSISDNs would have to happen in the SIP dialplan anyway. As soon as a given string is becomes parseable by an mslookup server, i.e. say we implement some +123 notation in osmo-hlr, then it would suddenly start to work out. mslookup itself doesn't care much about the msisdn, but I think we do call osmo_msisdn_str_valid() on it. That could change easily, point being it really is an arbitrary string (without dots) that gets sent as MSISDN. > == The use of 'age' vs. absolute timestamp == > > Given that the delays we're talking about are probably all sub-second or > maybe possible about 1s, it's probably not a problem. I went through the same thoughts. When I do a first attach to a site, I find it expected that a caller might not reach me for five more seconds. If it is even that much, ever. So I favored the elegance of 'age' vs absolute timestamp, because an entire timezone/clockdrift/faulty GPS receiver family of problems simply vanishes completely. > == GSUP keepalives / connection loss detection == > > In the presence of unreliable back-haul mesh between villages, the GSUP > connection can also not be seen as reliable. We would expect to see TCP > stalls due to packet loss, etc. > > Have you considered this in your implementation and/or done any testing > based on simulated lossy networks to ensure we properly use either TCP > keepalives or IPA application-level PING/PONG to detect lost connections > and recover from such situations (by closing the old and > re-establishing)? > > Unreliable networks can be easily simulated by Linux built-in 'tc netem' > for providing configurable packet loss / latency / jitter. > > I also saw some comments / code related to "if a second connection using > the same IPA ID arrives, we're screwed" (paraphrasing here). I would > expect this not to be uncommon even if every MSC/HLR out there is > configred correctly exactly because e.g .the remote MSC/HLR has already > decided that the TCP/GSUP is dead and starts to reconnect by performing > a local-end release, while the "local" MSC/HLR still thinks the old > connection is alive. If the old connection "wins" (i.e. is preferred) > I see potential trouble here. > > Situations like that probably warrant some carefully designed tests to > create exactly those situations. We haven't tested this at all. Should become an issue on redmine. ~N -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 833 bytes Desc: not available URL: <http://lists.osmocom.org/pipermail/openbsc/attachments/20191204/0b866d7d/attachment.bin>