Cellular Network Infrastructure » Distributed GSM

h1. SMS

h2. SMS between two autonomous networks

{{mscgen_link()

msc {

  hscale = 2;

  ms [label="MS (village A)"], vlr [label="MSC/VLR/SMSC (village A)"], vlrb [label="MSC/VLR/SMSC (village B)"], msb [label="MS (village B)"];

  ms => vlr [label="SMS SUBMIT"];

  vlr => vlr [label="Store SMS in local queue"];

  ms <= vlr [label="SMS SUBMIT ACK"];

  vlr => vlrb [label="mDNS Query (dest MSISDN"];

  vlr <= vlr [label="mDNS Response (MSC[B] IP addr"];

  vlr => vlrb [label="MO-Forward-SM REQ"];

  vlrb => msb [label="Paging / Channel Setup"];

  vlrb <=> msb [label="MM Common Procedures (AUTH, ...)"];

  vlrb => msb [label="SMS DELIVER"];

  vlrb <= msb [label="SMS DELIVER ACK"];

  vlr <= vlrb [label="MO-Forward-SM RESP"];

  ...;

  ...;

  ...;

}

}}

* we store the SMS in a queue/database in the local village to ensure SMS are ACKed as soon as possible to

** minimize use of radio resource (air time)

** smooth user experience (SMS can be sent without problems, like in normal network) - even in case of backhaul outage

* the village-local SMSC then stores the message in its queue and regularly (re-)tries to reach village B

* there is no queueing in village B in the current proposal, meaning SMS delivery is only successful if both MS B is registered and village A has connectivity to village B at the same time

** this is now it works in regular GSM networks

** we could probably also have a queue on the B side, this is TBD

h2. SMS from external network

same as above, with MS-A and MSC-A replaced with some external entity.  It starts with the mDNS query to find out where MS-B currently is registered