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diff --git a/OsmoBTS/chapters/architecture.adoc b/OsmoBTS/chapters/architecture.adoc new file mode 100644 index 0000000..aca5bb9 --- /dev/null +++ b/OsmoBTS/chapters/architecture.adoc @@ -0,0 +1,120 @@ +== OsmoBTS software architecture + +=== OsmoBTS PHY interface abstraction + +The OsmoBTS PHY interface serves as an internal abstraction layer +between given PHY hardware (as provided by the bts_model) and the actual +logical transceivers (TRXs) of a BTS inside the OsmoBTS code base. + + +==== PHY link + +A PHY link is a physical connection / link towards a given PHY. This +might be, for example, + +* a set of file descriptors to device nodes in the /dev/ directory + (sysmobts, litecell15) +* a packet socket for sending raw Ethernet frames to an OCTPHY +* a set of UDP sockets for interacting with OsmoTRX + +Each PHY interface has a set of attribute/parameters and a list of 1 to +n PHY instances. + +PHY links are numbered 0..n globally inside OsmoBTS. + +Each PHY link is configured via the VTY using its individual top-level +vty node. Given the different bts-model / phy specific properties, the +VTY configuration options (if any) of the PHY instance differ between +BTS models. + +The PHY links and instances must be configured above the BTS/TRX nodes +in the configuration file. If the file is saved via the VTY, the code +automatically ensures this. + + +==== PHY instance + +A PHY instance is an instance of a PHY, accessed via a PHY link. + +In the case of osmo-bts-sysmo and osmo-bts-trx, there is only one +instance in every PHY link. This is due to the fact that the API inside +that PHY link does not permit for distinguishing multiple different +logical TRXs. + +Other PHY implementations like the OCTPHY however do support addressing +multiple PHY instances via a single PHY link. + +PHY instances are numbered 0..n inside each PHY link. + +Each PHY instance is configured via the VTY as a separate node beneath each +PHY link. Given the different bts-model / phy specific properties, the +VTY configuration options (if any) of the PHY instance differ between +BTS models. + + +==== Mapping PHY instances to TRXs + +Each TRX node in the VTY must use the 'phy N instance M' command in +order to specify which PHY instance is allocated to this specific TRX. + +=== Internal control flow + +==== start-up / sequencing during OsmoBTS start + +.Control flow at OsmoBTS start-up procedure +[options="header",cols="10%,35%,55%"] +|=== +| section | function | description +| bts-specific | main() | Entering main() from glibc +| common | bts_main() | initialization of talloc contexts +| common | bts_log_init() | initialization of logging +| common | handle_options() | common option parsing +| bts-specific | bts_model_handle_options() | model-specific option parsing +| common | gsm_bts_alloc() | allocation of BTS/TRX/TS data structures +| common | vty_init() | Initialziation of VTY core, libosmo-abis and osmo-bts VTY +| common | main() | Setting of scheduler RR priority (if configured) +| common | main() | Initialization of GSMTAP (if configured) +| common | bts_init() | configuration of defaults in bts/trx/s object +| bts-specific | bts_model_init | ? +| common | abis_init() | Initialization of libosmo-abis +| common | vty_read_config_file() | Reading of configuration file +| bts-specific | bts_model_phy_link_set_defaults() | Called for every PHY link created +| bts-specific | bts_model_phy_instance_set_defaults() | Called for every PHY Instance created +| common | bts_controlif_setup() | Initialization of Control Interface +| bts-specific | bts_model_ctrl_cmds_install() | Install model-specific control interface commands +| common | telnet_init() | Initialization of telnet interface +| common | pcu_sock_init() | Initializaiton of PCU socket +| common | main() | Installation of signal handlers +| common | abis_open() | Start of the A-bis connection to BSC +| common | phy_links_open() | Iterate over list of configured PHY links +| bts-specific | bts_model_phy_link_open() | Open each of the configured PHY links +| common | write_pid_file() | Generate the pid file +| common | osmo_daemonize() | Fork as daemon in background (if configured) +| common | bts_main() | Run main loop until global variable quit >= 2 +|=== + + +==== At time of OML establishment + +.Control flow at time of OML establishment +[options="header",cols="10%,35%,55%"] +|=== +| section | function | description +| bts-specific | bts_model_oml_estab() | Called by core once OML link is established +| bts-specific | bts_model_check_oml() | called each time OML sets some attributes on a MO, checks if attributes are valid +| bts-specific | bts_model_apply_oml() | called each time OML sets some attributes on a MO, stores attribute contents in data structures +| bts-specific | bts_model_opstart() | for NM_OC_BTS, NM_OC_SITE_MANAGER, NM_OC_GPRS_NSE, NM_OC_GPRS_CELL, NMO_OC_GPRS_NSVC +| bts-specific | bts_model_opstart() | for NM_OC_RADIO_CARRIER for each trx +| bts-specific | bts_model_opstart() | for NM_OC_BASEB_TRANSC for each trx +| bts-specific | bts_model_opstart() | for NM_OC_CHANNEL for each timeslot on each trx +| bts-specific | bts_model_change_power() | change transmit power for each trx (power ramp-up/ramp-down) +|=== + +==== At time of RSL connection loss + +.Control flow at time of RSL connection loss +[options="header",cols="10%,35%,55%"] +|=== +| section | function | description +| bts-specific | bts_model_abis_close() | called when either one of the RSL links or the OML link are down +|=== |