122 lines
3.1 KiB
Plaintext
122 lines
3.1 KiB
Plaintext
Re-introducing E1 in OsmoBSC
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============================
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:author: Harald Welte <laforge@gnumonks.org>
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:copyright: 2018 by Harald Welte (License: CC-BY-SA)
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:backend: slidy
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:max-width: 45em
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== Intro
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* OpenBSC (later OsmoNITB) started with E1 BTS
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* until NITB Split, E1 support remained present
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* even old OsmoBSC (sccplite) never had E1 BTS suport
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* new OsmoBSC also has no E1 BTS support
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* let's change that!
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== Classic OsmoNITB with E1-BTS + ext MNCC
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image::osmo-userplane1_e1_mncc.svg[width="100%"]
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* Abis/E1 with 16k sub-slots in 64k slots
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* E1 device offers 64k timeslots only
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** 16k sub-channel mux/demux done in software
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* TRAU frames in 16k sub-slots decoded (to FR/EFR codec frames)
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* passed next to MNCC signaling over MNCC socket
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== Classic OsmoNITB with E1-BTS + ext MNCC + RTP
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image::osmo-userplane2-e1_rtp.svg[width="100%"]
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* just like previous example, but we generate RTP from TRAU frames
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* MNCC interface is signaling only
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* user voice frames handled via RTP
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== Classic OsmoNITB with IP-BTS + ext MNCC + RTP proxy
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image::osmo-userplane3-rtp_proxy.svg[width="100%"]
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* Abis/IP BTS use RTP transport for speech frames
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* OsmoNITB is asked to provide RTP proxy functionality
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== Classic OsmoNITB with IP-BTS + ext MNCC + direct RTP
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image::osmo-userplane4-rtp_direct.svg[width="100%"]
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* Abis/IP BTS use RTP transport for speech frames
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* OsmoNITB rtp_proxy is disabled
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* RTP data passes directly from BTS to external PBX and vice-versa
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== IP-BTS User Plane in post-NITB
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When using IP-based BTS like OsmoBTS, this looks like this:
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[graphviz]
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----
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digraph G {
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rankdir=LR;
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BSC [label="OsmoBSC"];
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MSC [label="OsmoMSC"];
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MGWb [label="OsmoMGW\n(BSC)"];
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MGWm [label="OsmoMGW\n(MSC)"];
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{ rank=same; BSC; MGWb; };
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{ rank=same; MSC; MGWm; };
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BTS -> BSC [label="A-bis/IP (RSL+OML)"];
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BSC -> MSC [label="A (BSSAP)"];
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BTS -> MGWb [label="RTP"];
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MGWb -> MGWm [label="RTP"];
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MSC -> PBX [label="MNCC"];
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MGWm -> PBX [label="RTP"];
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BSC -> MGWb [label="MGCP"];
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MSC -> MGWm [label="MGCP"];
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}
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----
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* RTP to/from the BTS is handled by the BSC-colocated OsmoMGW
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== E1-BTS User Plane in post-NITB
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When using E1-based BTS, it should look like this:
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[graphviz]
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----
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digraph G {
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rankdir=LR;
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BSC [label="OsmoBSC"];
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MSC [label="OsmoMSC"];
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MGWb [label="OsmoMGW\n(BSC)"];
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MGWm [label="OsmoMGW\n(MSC)"];
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{ rank=same; BSC; MGWb; };
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{ rank=same; MSC; MGWm; };
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BTS -> BSC [label="A-bis/E1 (RSL+OML)"];
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BSC -> MSC [label="A (BSSAP)"];
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BTS -> MGWb [label="TRAU-Frames\nover E1"];
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MGWb -> MGWm [label="RTP"];
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MSC -> PBX [label="MNCC"];
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MGWm -> PBX [label="RTP"];
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BSC -> MGWb [label="MGCP"];
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MSC -> MGWm [label="MGCP"];
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}
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----
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* TRAU frames in 16k E1 sub-slots to/from the BTS are handled by the BSC-colocated OsmoMGW
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* OsmoMGW needs real media gateway functionality from E1 sub-slots to RTP
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* E1 driver needs to support single E1 span (line) that
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** opens RSL/OML LAPDm signaling on one TS from OsmoBSC
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** opens TRAU on other TS from OsmoMGW
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* `osmo-bsc.cfg` states which Um TS maps to which E1 TS/SS
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* `osmo-bsc` uses MGCP EP naming scheme like `E1/Line1/TS4/SS2@mgw`
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== EOF
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End of File
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