tree 013780b4daf07e725223c5d27ced524b4099513e
parent f33e8358cc2350e6fecb8653dc726770afa9fede
author Neels Hofmeyr <nhofmeyr@sysmocom.de> 1461589532 +0200
committer Harald Welte <laforge@gnumonks.org> 1474955755 +0000

hnbap: accept UE Register Requests with TMSI and pTMSI

Add the option to allow UE Register Requests with a TMSI identity.
Add VTY command to enable this option, 'hnbap-allow-tmsi'.
Add hnbgw_tx_ue_register_acc_tmsi().

HNBGW so far keeps track of UEs that have registered, with their IMSI. When a
UE registers with only a TMSI, we obviously can't store an IMSI. However, since
we're so far never *using* the list of UEs in osmo-hnbgw, we might as well just
accept the TMSI registration and carry on as usual. All that is needed for
proper operation is a valid UE context.

This is aimed at the ip.access nano3G femto cell, as it apparently feeds
whichever identification the UE sends through to HNBAP (TMSI+LAI, pTMSI+RAI),
instead of an IMSI as expected. So far this caused failures and the need to
make the UE clear its TMSI (wait several minutes or attempt to subscribe to a
different network), so that UE registration switched back to IMSI. When simply
accepting the TMSI in osmo-hngw, no problems are apparent in our current code
state.

For example, a Samsung Galaxy S4 seems to send a UE_Identity_PR_tMSILAI (CS
identity), and a GT-I9100 seems to send a UE_Identity_PR_pTMSIRAI (PS identity)
upon first registration to the network.

Recording the IMSI in hnbgw: we could use the subscriber list during paging, to
page a UE on only its last seen HNB. On the other hand, it doesn't hurt to
anyway always page to all HNBs connected to osmo-hnbgw. The paging procedure
does include a page-to-all-HNBs in case the first HNB paging fails. But we must
be aware that UEs that register by TMSI will simply not have an IMSI recorded
in the list of UE contexts, so a lookup based on IMSI may fail.

Patch-by: Harald Welte <laforge@gnumonks.org>, me
Change-Id: I87bc1aa3e85815ded7ac1dbdca48f1680b468589