From b26ddd7e44f23e712fe1cd3c72d5d5d3ca4dbbec Mon Sep 17 00:00:00 2001 From: Harald Welte Date: Thu, 12 Apr 2018 22:30:55 +0200 Subject: osmodevcon2018 LCLS --- 2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html | 4272 +++++++++++++++++++++ 1 file changed, 4272 insertions(+) create mode 100644 2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html (limited to '2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html') diff --git a/2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html b/2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html new file mode 100644 index 0000000..938f2ff --- /dev/null +++ b/2018/osmodevcon2018-lcls/osmodevcon2018-lcls.html @@ -0,0 +1,4272 @@ + + + + +3GPP LCLS (Local Call, Local Switch) + + + + + + + + +
+

Classic GSM User Plane

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+
    +
  • + +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 + +
    • +
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Problems with classic approach

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    +
  • + +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 + +
      • +
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    • +
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+

3GPP LCLS to the rescue

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+
    +
  • + +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 + +
      • +
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    • +
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+width=100% +
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3GPP LCLS problem domains

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    +
  • + +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, …)? + +
    • +
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3GPP LCLS early media

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+width=100% +
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3GPP LCLS early media

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+width=100% +
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3GPP LCLS tone / announcement

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+width=100% +
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3GPP LCLS: Negotiation in CN

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+
    +
  • + +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 + +
      • +
    +
    • +
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3GPP LCLS Negotiation results

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+
    +
  • + +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 + +
      • +
    +
    • +
+
+
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3GPP LCLS: Implications on A / BSSMAP

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+
    +
  • + +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 + +
        • +
      +
      • +
    +
    • +
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+

3GPP LCLS: Osmocom Plans

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+
    +
  1. + +Plan: support minimal sub-set without bi-casting + +
      +
    1. + +in OsmoBSC + +
        +
      1. + +requires us to add BSSMAP LCLS IEs/Messages + +
        2. +
      2. + +will use MGCP to re-configure the CN-side RTP connection on OsmoMGW + +
        3. +
      3. + +development will be test-driven (develop TTCN-3 tests first) + +
        4. +
      +
      2. +
    2. + +in OsmoMSC (only among RANs connected to single MSC) + +
        +
      1. + +requires us to permit/enable LCLS on AoIP + +
        2. +
      +
      3. +
    +
    2. +
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+

Further Reading

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+

EOF

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End of File

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