• Table of contents
• Local Call Local Switch
  • Affected messages
    • BSSMAP ASSIGNMENT REQUEST
    • BSSMAP ASSIGNMENT COMPLETE
    • BSSMAP HANDOVER REQUEST
    • BSSMAP HANDOVER REQUEST ACK
    • BSSMAP HANDOVER COMPLETE
    • BSSMAP HANDOVER PERFORMED
    • BSSMAP INTERNAL HANDOVER CMD
    • BSSMAP LCLS CONNECT CONTROL
    • BSSMAP LCLS CONNET CONTROL ACK
    • BSSMAP LCLS NOTIFICATION
  • Implementation Ideas
    • Information storage
    • check_and_enable_lcls()
    • MGW bits
      • LCLS_CFG_both_way
      • LCLS_CFG_both_way_and_bicast_UL
      • LCLS_CFG_both_way_and_send_DL
      • LCLS_CFG_both_way_and_send_DL_block_local_DL
      • LCLS_CFG_both_way_and_bicast_UL_send_DL
      • LCLS_CFG_both_way_and_bicast_UL_send_DL_block_local_DL
  • Spec references
  • Other references

Local Call Local Switch¶

In the classic 3GPP architecture, all calls go from BTS to BSC to MSC, only then to go back all the same way in case the second call leg is also in the same cell. Particularly in case of statellite or other expensive/slow back-haul this is far from ideal.

Using LCLS, a BSC can know which of the two call legs belong to one call, and can then directly bridge the RTP/media locally.

Affected messages¶

BSSMAP ASSIGNMENT REQUEST¶

This message may contain the following, LCLS related IEs:

• Global Call Reference
• LCLS Configuration
• LCLS Connection Status Control
• LCLS Correlation Not Needed

Using those LCLS related IEs, the MSC can grant the BSS to elect to use LCLS for this call [leg].

BSSMAP ASSIGNMENT COMPLETE¶

• LCLS BSS Status

Using this, the BSC can inform the MSC on whether or not LCLS was enabled.

BSSMAP HANDOVER REQUEST¶

• Global Call Reference
• LCLS Configuration
• LCLS Connection Status Control

Request from MSC to target BSC. The MSC specifies which kind of LCLS (if any) is permitted and/or requested.

BSSMAP HANDOVER REQUEST ACK¶

• LCLS BSS Status

Acknowledgement from targe BSC to MSC in response to a BSSMAP HANDOVER REQUEST.
The LCLS BSS Status contains the [possibly modified] LCLS status for the call.

BSSMAP HANDOVER COMPLETE¶

• LCLS BSS Status

Informs the MSC that the MS has successfully accessed the target cell. The LCLS BSS Status contains the [possibly modified] LCLS status for the call.

BSSMAP HANDOVER PERFORMED¶

• LCLS BSS Status

unilateral notification from BSC to MSC about an internal (intra-BSC) hand-over having been performed. The LCLS BSS Status contains the [possibly modified] LCLS status for the call.

BSSMAP INTERNAL HANDOVER CMD¶

• LCLS Connection Status Control

This is sent in AoIP from MSC to BSC in response to am earlier BSMAP INTERNAL HANDOVER REQUIRED. We don't implement this in OsmoBSC.

BSSMAP LCLS CONNECT CONTROL¶

• LCLS Configuration
• LCLS Connection Status Control

Sent by MSC to BSC in order to change the configuration/permission of LCLS during an ongoing call.

BSSMAP LCLS CONNET CONTROL ACK¶

• LCLS BSS Status

Sent by BSC to MSC in response to a BSSMAP LCLS CONNECT CONTROL, indicating the [possibly updated] LCLS status.

BSSMAP LCLS NOTIFICATION¶

• LCLS BSS Status
• LCLS Break Request

This message is sent from the BSC to the MSC to inform it about some changes in the LCLS status. This could e.g. be the case after a BSS-internal hand-over where the new BTS/channel doesn't support LCLS.

Implementation Ideas¶

Information storage¶

Each bsc_subscr_conn should contain

• uint8_t lcls_config (4 bit field + presence 1/0)
• uint8_t lcls_csc (4 bit field + presence 1/0)
• uint8_t gcr¹⁵
• uint8_t gcr_len;

Every time we receive LCLS CFG or CSC, we have to update this state in the bsc_subscr_conn and (as needed) change the user plane switching via MGCP

check_and_enable_lcls()¶

1. does own CFG + CSC permit LCLS?
2. do we have another call with same Global Call ID?
3. does other leg CFG + CSC permit LCLS?
   • activate LCLS, update state variables
   • send NOTIFY for other leg to MSC

MGW bits¶

LCLS_CFG_both_way¶

the easiest option: connect own MGCP EP to other MGCP EP

• requires MGCP MDCX on our side + other side

LCLS_CFG_both_way_and_bicast_UL¶

LCLS_CFG_both_way_and_send_DL¶

LCLS_CFG_both_way_and_send_DL_block_local_DL¶

• connect other MGCP EP to local MGCP EP (using MDCX)
• switch other MGCP EP into recvonly mode, discarding whatever it sends
• TBD

LCLS_CFG_both_way_and_bicast_UL_send_DL¶

• TBD

LCLS_CFG_both_way_and_bicast_UL_send_DL_block_local_DL¶

• TBD

Spec references¶

• http://www.3gpp.org/DynaReport/23284.htm
  • 3GPP TS 23.284 Rel 14
• http://www.3gpp.org/DynaReport/WiCr--440021.htm
• http://www.3gpp.org/DynaReport/WiCr--430001.htm

Other references¶

• OsmoDevCon 2018 video: https://media.ccc.de/v/DVE7UU
• OsmoDevCon 2018 slides: https://pretalx.sysmocom.de/media/osmodevcon2018-lcls.pdf

Virtual GSM Load Testing¶

This is about development of Load Testing Setup to demonstrate OsmoBSC functionality and performance at >= 200 TRX, >= 100 BTS and thousands of MS.

• Development of primitive-based asynchronous interface to OsmocomBB âmobileâ program, together with script language (e.g. LUA) bindings for cellselection, location update, SMS and voice calls.
• Development of voice frame support to OsmocomBB virt_phy, OsmocomBB mobile and osmo-bts-virtual to simulate voice/user plane in addition to control/signaling plane.
• Development of software to manage (configure, start, monitor, stop) thousands of OsmocomBB mobile instances as well as hundreds of osmo-bts-virtual instances
• Creation + Documentation of corresponding test suite for automatic execution of load testing