94 lines
4.1 KiB
Plaintext
94 lines
4.1 KiB
Plaintext
== Channel allocation
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Radio resource management is one of the main tasks of the Base Station Controller.
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This involves selection, activation, and deactivation of logical channels, which
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are maintained by connected Base Stations. The number of usable logical channels
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is limited by total number of radio carriers and may vary depending on the physical
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channel combinations assigned to their timeslots. Thus a major goal of the this
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task is to manage all the available resources in an efficient way, shifting the
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balance between service quality and the overall capacity.
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=== Channel allocation parameters
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OsmoBSC's channel allocator can be configured via the VTY interface. All
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relevant parameters are limited by the scope of a BTS node they belong to.
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There is currently no way to define global configuration for all BTS.
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All parameters with their respective default values are listed below:
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----
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network
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bts 0
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channel allocator mode chan-req ascending
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channel allocator mode assignment ascending
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channel allocator mode handover ascending
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channel allocator avoid-interference 0
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channel allocator tch-signalling-policy always
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----
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==== Channel allocation modes
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Currently only the following two simple channel allocation modes are supported:
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- ascending (default): allocates channels in ascending order,
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starting from timeslot 0 of the first TRX (also called C0, the BCCH carrier);
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- descending: allocates channels in descending order,
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starting from timeslot 7 of the last TRX.
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NOTE: Regardless of the chosen mode, logical channels (sub-slots) are always
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selected in ascending order. For example, if a timeslot is configured as SDCCH/8
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and all 8 sub-slots are not in use, then the first SDCCH(0) sub-slot will be
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selected in both ascending and descending modes.
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The allocation mode to be used can be configured using the following VTY command:
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----
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OsmoBSC(config-net-bts)# channel allocator mode ? <1>
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set-all Set a single mode for all variants
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chan-req Channel allocation for CHANNEL REQUEST (RACH)
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assignment Channel allocation for assignment
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handover Channel allocation for handover
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OsmoBSC(config-net-bts)# channel allocator mode set-all ? <2>
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ascending Allocate Timeslots and Transceivers in ascending order
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descending Allocate Timeslots and Transceivers in descending order
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----
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<1> It's optionally possible to configure different allocation modes for
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different allocation causes, e.g. `ascending` for `chan-req` and `descending`
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for both `assignment` and `handover`.
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<2> `set-all` is equivalent to the old (deprecated) command syntax:
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`channel allocator (ascending|descending)`.
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==== Interference aware channel allocation
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The channel allocator can be configured to prefer logical channels with least
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interference, based on interference measurements periodically sent by the BTSs
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(see <<interf_rep>>). This is an optional feature, which is disabled by default.
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----
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OsmoBSC(config-net-bts)# channel allocator avoid-interference ?
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0 Ignore interference levels (default). Always assign lchans
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in a deterministic order.
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1 In channel allocation, prefer lchans with less interference.
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----
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NOTE: Interference levels are compared within the scope of the whole BTS. This
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means that the selection logic may pick channels on the other TRXes, if they are
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better according to the interference reports from the BTS. This feature makes
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the allocation order non-deterministic and therefore nullifies the meaning of
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channel allocation modes described above.
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==== TCH sigalling policy
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By default, in a situation when all SDCCHs are exhausted, OsmoBSC will be using TCH
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channels for signalling (e.g for Location Updating or call establishment). This
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behavior can be restricted to certain kinds of signalling or disabled completely.
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----
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OsmoBSC(config-net-bts)# channel allocator tch-signalling-policy ?
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never Never allow TCH for signalling purposes
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emergency Only allow TCH for signalling purposes when establishing an emergency call
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voice Allow TCH for signalling purposes when establishing any voice call
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always Always allow TCH for signalling purposes (default)
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----
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