49 lines
1.9 KiB
Plaintext
49 lines
1.9 KiB
Plaintext
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GSM Paging implementation in OpenBSC
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== Code structure ==
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The code is implemented in the libbsc/paging.c file. The external
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interface is documented/specified in the include/openbsc/paging.h
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header file. The code is used by the NITB and BSC application.
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== Implementation ==
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Paging can be initiated in two ways. The standard way is to page by
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LAC. Each BTS has its own list/queue of outstanding paging operation.
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When a subscriber is paged one "struct paging_request" per BTS will
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be allocated and added to the tail of the list. The BTS is supposed
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to be configured to not repeat the paging.
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A paging_request will remain in the queue until a paging response or at
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the expiry of the T3113. Every 500 milliseconds a RSL paging command is
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send to the BTS. The 500 milliseconds is a throttling to not crash the
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ip.access nanoBTS. Once one paging_request has been handled it will be
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put at the end of the queue/list and the available slots for the BTS
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will be decreased.
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The available slots will be updated based on the paging load information
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element of the CCCH Load indication. If no paging slots are considered
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to be available and no load indication is sent a timer is started. The
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current timeout is 500 milliseconds and at the expiry of the timer the
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available slots will be set to 20.
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OpenBSC has the " paging free <-1-1024>" configuration option. In case
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there are less free channels than required no paging request will be
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sent to the BTS. Instead it will be attempted to send the paging request
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at the next timeout (500 milliseconds).
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== Limitation ==
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The paging throughput could be higher but this has lead to crashes on the
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ip.access nanoBTS in the past.
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== Configuration ==
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=== ip.access nanoBTS ===
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The current CCCH Load indication threshold is 10% and the period is 1 second.
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The code can be found inside the src/libbsc/bts_ipaccess_nanobts.c inside the
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nanobts_attr_bts array.
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