Dear list members, I posted the following message to the IETF DISPATCH mailing list earlier today. It's got a bit of a lengthy intro, as that community is not familiar with OpenBTS (and probably not OpenBSC either), and in preliminary discussions with them it was clear that it needed a good explanation.
I invite you all to join the IETF DISPATCH list, and participate in the discussion. Tim Panton has already raised some good points. See http://trac.tools.ietf.org/wg/dispatch/trac/wiki for info about the DISPATCH group and https://www.ietf.org/mailman/listinfo/dispatch to join the list. -- Jim Range Networks Begin forwarded message: > From: Jim Forster <[email protected]> > Subject: [dispatch] SIP and GSM/UMTS with OpenBTS > Date: February 5, 2014 at 12:09:45 PM GMT+5:30 > To: "[email protected]" <[email protected]> > > Dear DISPATCH group, > > OpenBTS and OpenBSC are projects are combining GSM phones and SIP in new and > interesting ways. I think there is some value to the community in discussing > these in the DISPATCH mailing list and having an related meeting at the > London IETF. There is both some short-term, relatively straightforward work > to be done to agree on the usage of SIP in these existing implementations. > There may also be some very interesting work to be done on more advanced > approaches. > > First, some background: OpenBTS is an open source project started by the > founders of Range Networks to make a 'GSM system in a box', by implementing a > system which supports the air interface for GSM phones (Um) using a Software > Defined Radio (SDR) for the RF. While the GSM & 3GPP defined air interface > to the phones is supported, OpenBTS diverges from these standards by > immediately gatewaying the call to SIP. Each GSM or UMTS phone can then > appear on the Internet as a SIP endpoint. A local SIP switching decision is > made to route the call; Asterix, Freeswitch, Yate have been. The call is > then sent to another local connected phone or to some other SIP service point > on the Internet. > > With this in place, because the air interface to the phones is supported with > no changes, standard GSM/UMTS phones can make calls to other phones on the > same OpenBTS system or to any SIP endpoint on the Internet, and thence to the > PSTN via any of the many SIP-PSTN gateways in operation. > > A fair question would be "Why do all this? What's wrong with GSM & 3GPP > systems?". One reason is that the OpenBTS approach allows very small, stand > alone systems, which efficiently connect GSM and UMTS phones to the Internet > based SIP systems with a minimum of other systems. Certainly GSM/3GPP based > micro cells exist, but are tied to the 3GPP 'Core' which is usually beyond > the means of smaller users. OpenBTS aspires to be the simplest way for a > GSM/UMTS phone to make phone calls to the SIP & PSTN world. > > At least several hundred, and likely several thousand of these systems are > deployed already. Many are in labs, but others are production usage on all > continents. Universities find these systems very attractive for teaching and > researching: all the code from RF to Signaling is visible and may be changed > as desired. > > Furthermore, additional SDRs are popping up all the time. There are 3-4 > separate SDR based systems that run OpenBTS and more are coming. Right now > they range from $2000 up, but it's easy to see them dropping to $500 or so > this year; even Kickstarter campaigns are funding some of them. There's no > natural floor below that; adding GSM/UMTS to a home router and making it a > micro-cell running SIP to the Internet could conceivably be a $10 HW delta > and some more SW. Secondly, there are several countries that have unlicensed > GSM band (Sweden, Netherlands, UK?) so some efforts are underway to do > exactly that. > > When facing the Internet, OpenBTS is simply a SIP client. However, to assure > interoperability, there may be value in standardized behavior, including > these issues: > > * Which elements of SIP are needed for this operation? > * Should these be documented in a profile of SIP usage to be OpenBTS Ready? > * Should ICE be recommended or possibly be required for operation behind NATs? > * What about BTS-BTS neighbor discovery > * Use of SIP Re-invite for hand-over when a mobile phone moves from one BTS > to a neighbor > * For somewhat different use cases: one could separate signaling from media > transport and thus might support WebRTC or other such systems. E.164 > addresses are used in phones, but temporary numbers can be assigned as needed > (as done in Roaming) and not surfaced to the WebRTC level. > * What Changes required for IPv6? > * Required and recommended security provisions > * Is IETF an appropriate forum for this, or should it be in 3GPP, or > Sipforum.org, or a separate industry group formed? > > I look forward to discussion on the mailing list, and hopefully meeting and > discussing in London. > > Yours, > > Jim Forster > Range Networks > _______________________________________________ > dispatch mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/dispatch
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