63 lines
2.3 KiB
Plaintext
63 lines
2.3 KiB
Plaintext
[[gb-sgsn-pool]]
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== Gb interface in SGSN Pooling
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SGSN Pooling is a modern optional extension of the 3GPP GERAN
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architecture. It is officially referred-to as _Intra Domain Connection
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of RAN Nodes to Multiple CN Nodes_. It requires The use of IP-SNS and
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does not support legacy or non-standard Gb variants.
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Without this optional feature, a given PCU/BSS always connects to one
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SGSN via a Gb interface. All traffic is handled through that one
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interface.
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While the NS-level load sharing function and the _weights_ of the IP-SNS
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allow for load distribution between different user plane entities, there
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was demand for additional scalability and fail-over capabilities leading
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to the SGSN pooling feature.
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The major changes introduced to the Gb interface by SGSN pooling are as
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follows:
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* There is a separate NSE in the BSS for each of the SGSNs in the pool,
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creating a 1:1 relationship between BSS-NSE and SGSN.
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* Each of those per-SGSN NSEs has it's own NS-VCGs and NS-VCs, unrelated
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to those of the other NSEs
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* Each of those per-SGSN NSEs has it's own Signaling BVC
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* Each Cell in the BSS has one PTP BVC _per SGSN in the pool_
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This relationship is illustrated in <<fig-gb-pool>> below.
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[[fig-gb-pool]]
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.Gb interface concepts when SGSN pooling feature is used (from 3GPP TS 48.016)
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image::./common/images/gb-concepts-pool.pdf[]
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Looking strictly at the Gb interface, this means that there is a completely
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separate Gb interface between each BSS and each pool member SGSN. All of the
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procedures explained in <<gb-ip-sns>> hence occur N number of times to N number
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of SGSN pool members.
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=== Status of SGSN Pool support in Osmocom
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==== osmo-pcu
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There is currently no direct support for SGSN pooling in `osmo-pcu`
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itself. However, as of December 2020, `osmo-gbproxy` is being extended
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with SGSN pooling support.
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This means that SGSN pooling can be added to any `osmo-pcu` based
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deployment by introducing `osmo-gbproxy` between `osmo-pcu` and the SGSN.
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The use of `osmo-gbproxy` also has the added benefit that all Gb
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interfaces from various PCUs are aggregated into one Gb interface
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towards (each) SGSN. Most deployments are used to such a _one interface
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per BSS_ approach as they are used to the BSC-colocated PCU architecture
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and not to the BTS-colocated PCU architecture as implemented in Osmocom.
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==== osmo-gbproxy
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FIXME
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==== osmo-sgsn
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FIXME
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