Attention is currently required from: osmith, pespin.
laforge has posted comments on this change. ( 
https://gerrit.osmocom.org/c/osmo-bsc-nat/+/27767 )

Change subject: bssap: forward paging to relevant BSCs only
......................................................................


Patch Set 1:

(1 comment)

Patchset:

PS1:
we also have to think of the case when a BTS is added during runtime of the 
BSC.  At this point the bsc-nat doesn't know yet about the related cell 
identifier.

A new BTS cannot yet have any subscribers registered to it, so one could still 
use CIL sniffing of the COMPLETE L3 INFO in addition to the BSSMAP RESET based 
mechanism.

So we'll need the RESTET based mechanism, and either
* CIL sniffing duriung COMPLETE L3 INFO, or
* some new non-standard BSSMAP message to let the bsc-nat know of cell-ids that 
have been added

I would think  the CIL sniffing is the more elegant approach.  So The RESET 
based list helps us with the initial state after e.g. a bsc-nat reset, and the 
CIL sniffing helps us to keep up with changes afterwards.

Last, but not least we *may* have to keep in mind that BSSMAP message have a 
maximum length (typically imposted by the underlying SCCP/M3UA capability) and 
a very long list of BTSs in the BSC might overflow the BSSMAP RESET message 
that we're generating.  For a pure SIGTRAN network this should not be a 
problem.  However, for anything that actually still uses traditional SS7 
circuits, there is a 272 byte limit on the MTP level.  I guess we can ignore 
that for now but make sure to document this in the (bsc?) user manual, i.e. 
that with a large numer of BTSs this BSSMAP RESET message size could exceed the 
272 byte limit of circuit-switched SS7/MTP, and that it is intended to be used 
over pure M3UA/SIGTRAN where such constraints don't exist (see RFC 4666 Section 
1.3.2.1).



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Gerrit-Project: osmo-bsc-nat
Gerrit-Branch: master
Gerrit-Change-Id: Iad3d1de8339206fa80f9fd10ac9213a7728a3c73
Gerrit-Change-Number: 27767
Gerrit-PatchSet: 1
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