add osmocon2018-lcls talk
This commit is contained in:
parent
87dac5161d
commit
aabd18f4ce
Binary file not shown.
After Width: | Height: | Size: 128 KiB |
Binary file not shown.
After Width: | Height: | Size: 119 KiB |
Binary file not shown.
After Width: | Height: | Size: 86 KiB |
Binary file not shown.
After Width: | Height: | Size: 120 KiB |
|
@ -0,0 +1,120 @@
|
|||
3GPP LCLS (Local Call, Local Switch)
|
||||
====================================
|
||||
:author: Harald Welte <laforge@gnumonks.org>
|
||||
:copyright: 2018 by Harald Welte (License: CC-BY-SA)
|
||||
:backend: slidy
|
||||
:max-width: 45em
|
||||
|
||||
== Classic GSM User Plane
|
||||
|
||||
* user plane joins signaling plane at all times
|
||||
* voice circuit between two phones in same BTS
|
||||
** goes from BTS to BSC (Abis) where a BSC-colocated TRAU is located
|
||||
** goes from BSC to MSC (A, typiclaly G.711))
|
||||
** returns from MSC to same BSC
|
||||
** returns from same BSC to same BTS
|
||||
* this is of course far from optimal
|
||||
|
||||
== Problems with classic approach
|
||||
|
||||
* works great with low-latency, land-based/wired TDM network
|
||||
* works not well with remote sites connected via satellite (VSAT)
|
||||
** maritime sector
|
||||
** rural BTSs in areas where no other back-haul is available
|
||||
* various vendors have implemented proprietary solutions
|
||||
** conveniently creating vendor lock-in
|
||||
|
||||
== 3GPP LCLS to the rescue
|
||||
|
||||
* official 3GPP standard appears to solve the problem in interoperable fashion
|
||||
* underlying principle quite simple:
|
||||
** each call gets a _Global Call Reference_ on A inerface
|
||||
** this allows BSC to identify two legs of same call
|
||||
** this enables BSC to locally switch the user plane between such calls
|
||||
|
||||
image::lcls-overview.png[width=100%]
|
||||
|
||||
== 3GPP LCLS problem domains
|
||||
|
||||
* early media / alerting phase
|
||||
* what about playback of voice announcements ("your prepaid account is low")?
|
||||
* what about lawful interception?
|
||||
* what about hand-over implications (intra-BSC, inter-BSC, inter-MSC, inter-RAT, ...)?
|
||||
|
||||
== 3GPP LCLS early media
|
||||
|
||||
image::lcls-conn_model_1.png[width=100%]
|
||||
|
||||
== 3GPP LCLS early media
|
||||
|
||||
image::lcls-conn_model_2.png[width=100%]
|
||||
|
||||
== 3GPP LCLS tone / announcement
|
||||
|
||||
image::lcls-announcement.png[width=100%]
|
||||
|
||||
== 3GPP LCLS: Negotiation in CN
|
||||
|
||||
* don't blindly activate LCLS, but _negotiate_ it
|
||||
** all calls start non-locally switched
|
||||
* LCLS negotiation on Nc interface (ISUP, BICC, SIP-I) between MSCs
|
||||
* LCLS negotiation only succeeds if all CN (MSC) support it
|
||||
** LCLS-Negotiation-Request IE
|
||||
** LCLS-Negotiation-Response IE
|
||||
** LCLS-Configuration-Preference IE
|
||||
|
||||
== 3GPP LCLS Negotiation results
|
||||
|
||||
* variety of different possible media configurations (examples)
|
||||
** classic non-local (non-LCLS)
|
||||
** connected both-way in BSS (basic LCLS)
|
||||
** connected both way in BSS _and_ bi-casted UL to CN
|
||||
** connected both way in BSS _and_ send access DL from CN
|
||||
*** BSS may combine or replace local DL data with DL data from CN
|
||||
** connected both way in BSS _and_ send access DL from CN, block local DL
|
||||
|
||||
== 3GPP LCLS: Implications on A / BSSMAP
|
||||
|
||||
* BSS is instructed about media configuration in BSSMAP
|
||||
** during call establishment
|
||||
*** BSSMAP ASSIGNMENT REQ with GCR + LCLS-Config IEs
|
||||
*** BSSMAP ASSIGNMENT COMPLETE with LCLS-BSS-Status IE
|
||||
** during handover
|
||||
*** BSSMAP HANDOVER COMPLETE with LCLS-BSS-Status IE
|
||||
** at any other time
|
||||
*** BSSMAP LCLS-NOTIFICATION from BSS -> MSS
|
||||
*** BSSMAP LCLS-CONNECT-CONTROL message MSS -> BSS
|
||||
|
||||
== 3GPP LCLS: Osmocom Support
|
||||
|
||||
. minimal sub-set without bi-casting
|
||||
.. in OsmoBSC
|
||||
... added BSSMAP LCLS IEs/Messages
|
||||
... use MGCP to re-configure the CN-side RTP connection on OsmoMGW
|
||||
... development was test-driven (TTCN-3 tests written first)
|
||||
.. in OsmoMSC
|
||||
... currently not implemented yet
|
||||
|
||||
== 3GPP LCLS: Osmocom Restrictions
|
||||
|
||||
. RTP audio looping is done in BSC-colocated MGW
|
||||
.. saves RTP on A interface between BSC and MSC
|
||||
.. doesn't save RTP round-trip on Abis between BTS and BSC
|
||||
. In deployments with a centralized BSC, that's insufficient
|
||||
.. you want true RTP loop-back betwen the BTSs involved in locally switched call
|
||||
. implementation pending, should happen rather soon
|
||||
|
||||
|
||||
== Further Reading
|
||||
|
||||
* 3GPP TS 23.284 http://www.3gpp.org/DynaReport/23284.htm
|
||||
* 3GPP WI 430001 (LCLS-CN) http://www.3gpp.org/DynaReport/WiCr--440021.htm
|
||||
* 3GPP WI 440021 http://www.3gpp.org/DynaReport/WiCr--440021.htm
|
||||
* http://osmocom.org/projects/cellular-infrastructure/wiki/Local_Call_Local_Switch
|
||||
* Osmocom tickets
|
||||
** http://osmocom.org/issues/1602
|
||||
** http://osmocom.org/issues/2487
|
||||
|
||||
== EOF
|
||||
|
||||
End of File
|
Loading…
Reference in New Issue