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daniel gerrit-no-reply at lists.osmocom.orgdaniel has submitted this change. ( https://gerrit.osmocom.org/c/osmo-sgsn/+/22495 ) Change subject: manuals/gbproxy: MSC -> SGSN for pooling chapter ...................................................................... manuals/gbproxy: MSC -> SGSN for pooling chapter Mostly just change the chapter so it makes sense for gbproxy. Some todos are still left Change-Id: I905835c2be7be43fe376fbc9d743107948c7e6d4 Related: SYS#5115, SYS#5005 --- M doc/manuals/chapters/gbproxy-sgsnpool.adoc 1 file changed, 85 insertions(+), 104 deletions(-) Approvals: Jenkins Builder: Verified lynxis lazus: Looks good to me, approved pespin: Looks good to me, but someone else must approve diff --git a/doc/manuals/chapters/gbproxy-sgsnpool.adoc b/doc/manuals/chapters/gbproxy-sgsnpool.adoc index 923a088..c600bcf 100644 --- a/doc/manuals/chapters/gbproxy-sgsnpool.adoc +++ b/doc/manuals/chapters/gbproxy-sgsnpool.adoc @@ -1,96 +1,87 @@ -== MSC Pooling +== SGSN Pooling -MSC pooling is described in 3GPP TS 23.236 <<3gpp-ts-23-236>>, and is supported -by OsmoBSC since mid 2020. +SGSN pooling is described in 3GPP TS 23.236 <<3gpp-ts-23-236>>, and is supported +by OsmoGbProxy since early 2021. -The aim of MSC pooling is to distribute load from a BSC across multiple MSCs, +The aim of SGSN pooling is to distribute load from a BSS across multiple SGSNs, which are equivalent and redundant infrastructure for the same core network. -The main mechanism for MSC pooling is the TMSI identity, which an MSC hands out -to its attached subscribers. Typically 10 bits of the TMSI are designated as a -Network Resource Identifier (NRI) that identifies the originating MSC, and -allows OsmoBSC to direct a subscriber back to the same MSC instance that -previously negotiated the IMSI Attach procedure. Typically, the full NRI value -range available is divided into N even ranges, where each MSC is assigned one +The main mechanism for SGSN pooling is the TLLI/P-TMSI, which an SGSN hands out +to its attached subscribers. Typically 10 bits of the P-TMSI are designated as a +Network Resource Identifier (NRI) that identifies the originating SGSN, and +allows OsmoGbProxy to direct a subscriber back to the same SGSN instance that +previously negotiated the Attach procedure. Typically, the full NRI value +range available is divided into N even ranges, where each SGSN is assigned one NRI range. -Subscribers attaching without a TMSI identity, or those with unknown NRI value, -are evenly distributed across MSC instances. OsmoBSC uses a round-robin -approach to distribute load across all connected MSCs. +Subscribers attaching without a TLLI, or those with unknown NRI value, +are evenly distributed across SGSN instances. OsmoGbProxy uses a hash-based +approach to distribute load across all connected SGSNs. -A Paging Response from a subscriber is always returned back to whichever MSC +A Paging Response from a subscriber is always returned back to whichever SGSN initiated the Paging, regardless of the Mobile Identity used. -Finally, a NULL-NRI is a special NRI value that indicates that the MSC wishes -to offload this subscriber to a different MSC. A NULL-NRI is an arbitrary NRI -value that is chosen distinctly for each PLMN served by a BSC, so that a +Finally, a NULL-NRI is a special NRI value that indicates that the SGSN wishes +to offload this subscriber to a different SGSN. A NULL-NRI is an arbitrary NRI +value that is chosen distinctly for each PLMN served by a BSS, so that a subscriber can be reassigned within that PLMN. Upon (periodic) Location -Updating, an offloading MSC hands out a NULL-NRI value in the assigned TMSI, +Updating, an offloading SGSN hands out a NULL-NRI value in the assigned TLLI, along with a non-broadcast LAI. The subscriber will notice the LAI mismatch, -and immediately re-attempt the attach using the TMSI containing the NULL-NRI. -The BSC recognises the NULL-NRI and redirects the subscriber to one of the -other MSCs. A prerequisite for this to work well is that the particular MSC is -previously marked as not accepting new subscribers, in the BSC's configuration. +and immediately re-attempt the attach using the TLLI containing the NULL-NRI. +OsmoGbProxy recognises the NULL-NRI and redirects the subscriber to one of the +other SGSNs. A prerequisite for this to work well is that the particular SGSN is +previously marked as not accepting new subscribers, in OsmoGbProxy's configuration. The mechanisms described above make up the NAS node selection function -implemented in the BSC. +implemented in OsmoGbProxy. -3GPP TS 23.236 also defines that an offloading MSC hands subscriber information -to the newly assigned MSC, which takes place outside the scope of the BSC. +3GPP TS 23.236 also defines that an offloading SGSN hands subscriber information +to the newly assigned SGSN, which takes place outside the scope of OsmoGbProxy. -=== Configuring MSC Pooling +=== Configuring SGSN Pooling -The NRI ranges assigned to each MSC must match in the BSC and the MSC -configuration. If MSC and BSC had inconsistent NRI value ranges configured, -attached subscribers would be redirected MSC instances that did not perform the +The NRI ranges assigned to each SGSN must match in the OsmoGbProxy and the SGSN +configuration. If inconsistent NRI value ranges are configured, +attached subscribers would be redirected to SGSN instances that did not perform the attach, possibly rendering the core network unusable. -==== Connecting Multiple MSCs - -The `cs7 instance` configuration defines the SCCP addresses to reach the MSCs -at. In addition, each MSC is configured by its own `msc` section in the -configuration. An example osmo-bsc.cfg serving three MSCs: +==== Connecting Multiple SGSNs ---- -cs7 instance 0 - # SCCP address book entries for the three MSCs - sccp-address my-msc-0 - point-code 0.23.0 - sccp-address my-msc-1 - point-code 0.23.1 - sccp-address my-msc-2 - point-code 0.23.2 - -# assign each MSC configuration its remote SCCP address -msc 0 - msc-addr my-msc-0 -msc 1 - msc-addr my-msc-1 -msc 2 - msc-addr my-msc-2 - +# Configure the Network Service +ns + bind udp sgsn + listen 10.0.0.1 23000 + nse 1 + ip-sns 10.0.1.1 23000 + ip-sns 10.0.1.1 23001 + nse 2 + ip-sns 10.0.1.2 23000 + nse 3 + ip-sns 10.0.1.3 23000 # configure NRI value ranges -network +gbproxy nri bitlen 10 nri null add 0 -msc 0 +sgsn 1 nri add 1 341 -msc 1 +sgsn 2 nri add 342 682 -msc 2 +sgsn 3 nri add 683 1023 ---- ==== NRI Value Bit Length -In OsmoBSC, the NRI value's bit length is freely configurable from 1 to 15 -bits. 3GPP TS 23.236 suggests a typical bit length of 10, which is OsmoBSC's -default. The NRI bit length must be identical across the entire MSC pool. +In OsmGbProxy, the NRI value's bit length is freely configurable from 0 to 15 +bits. 3GPP TS 23.236 suggests a typical bit length of 10. Setting the length +to 0 disables SGSN pooling, this is also the default. +The NRI bit length must be identical across the entire SGSN pool. -Change the NRI value bit length in OsmoBSC's VTY configuration like this: +Change the NRI value bit length in OsmoGbProxy's VTY configuration like this: ---- -network +gbproxy nri bitlen 10 ---- @@ -100,9 +91,9 @@ ==== NULL-NRI -Since OsmoBSC supports serving only one PLMN, NULL-NRI are configured globally. +Since OsmoGbProxy supports serving only one PLMN, NULL-NRI are configured globally. Even though 3GPP TS 23.236 indicates that there is a single NULL-NRI per PLMN, -OsmoBSC allows configuring multiple NULL-NRI values. +OsmoGbProxy allows configuring multiple NULL-NRI values. ---- network @@ -110,9 +101,9 @@ nri null add 423 ---- -==== Assigning NRI Ranges to MSCs +==== Assigning NRI Ranges to SGSNs -Each MSC configured in OsmoBSC must be assigned a distinct NRI value range. +Each SGSN configured in OsmoGbProxy must be assigned a distinct NRI value range. Overlapping NRI value ranges will cause failure to serve subscribers. NRI values are typically configured in ranges, here dividing a 10bit range @@ -120,18 +111,18 @@ as NULL-NRI: ---- -msc 0 +sgsn nsei 1 nri add 1 341 -msc 1 +sgsn nsei 2 nri add 342 684 -msc 2 +sgsn nsei 3 nri add 685 1023 ---- NRI can also be assigned in single values: ---- -msc 0 +sgsn nsei 1 nri add 23 ---- @@ -139,75 +130,65 @@ configurations, here a contrived example: ---- -msc 0 +sgsn nsei 1 nri add 0 342 nri del 23 nri del 42 235 nri add 1000 1023 ---- -To view the current NRI config in a running OsmoBSC instance, use the -`show nri` command, here showing the result of the contrived example: +On the VIEW and ENABLE VTY nodes, `show nri all` shows all SGSNs: ---- -OsmoBSC(config-msc)# show nri -msc 0 - nri add 0 22 - nri add 24 41 - nri add 236 342 - nri add 1000 1023 ----- - -On the VIEW and ENABLE VTY nodes, `show nri` shows all MSCs: - ----- -OsmoBSC> show nri -msc 0 +OsmoGbProxy> show nri all +sgsn nsei 1 nri add 1 341 -msc 1 +sgsn nsei 2 nri add 342 684 -msc 2 +sgsn nsei 3 nri add 685 1023 ---- -When configuring overlapping NRI value ranges across MSCs, the telnet VTY warns -about it, and starting OsmoBSC with such a configuration will fail: +When configuring overlapping NRI value ranges across SGSNs, the telnet VTY warns +about it, and starting OsmoGbProxy with such a configuration will fail: ---- -msc 0 +sgsn nsei 1 nri add 1 511 -msc 1 +sgsn nsei 2 nri add 512 1023 -msc 2 +sgsn nsei 3 nri add 500 555 ---- This results in: ---- -$ osmo-bsc -DMSC ERROR msc 2: NRI range [500..555] overlaps between msc 2 and msc 0. For overlaps, msc 0 has higher priority than msc 2 -DMSC ERROR msc 2: NRI range [500..555] overlaps between msc 2 and msc 1. For overlaps, msc 1 has higher priority than msc 2 +$ osmo-gbproxy +% Warning: NSE(00003/SGSN): NRI range [500..555] overlaps between NSE 00003 and NSE 00001. For overlaps, NSE 00001 has higher priority than NSE 00003 +% Warning: NSE(00003/SGSN): NRI range [500..555] overlaps between NSE 00003 and NSE 00002. For overlaps, NSE 00002 has higher priority than NSE 00003 ---- -==== MSC Offloading +==== SGSN Offloading -To effectively offload a particular MSC, it must be marked as no longer taking -new subscribers in OsmoBSC. This can be achieved in the telnet VTY by: +To effectively offload a particular SGSN, it must be marked as no longer taking +new subscribers in OsmoGbProxy. This can be achieved in the telnet VTY by: ---- -msc 0 +sgsn nsei 1 no allow-attach ---- -This MSC will, as long as it is connected, continue to serve subscribers -already attached to it: those that yield an NRI matching this MSC, and those -that are being paged by this MSC. But OsmoBSC will no longer direct new -subscribers to this MSC. +This SGSN will, as long as it is connected, continue to serve subscribers +already attached to it: those that yield an NRI matching this SGSN, and those +that are being paged by this SGSN. But OsmoGbProxy will no longer direct new +subscribers to this SGSN. -To re-enable an MSC for attaching new subscribers: +TODO: Is paging response relevant for SGSN? + +To re-enable an SGSN for attaching new subscribers: ---- -msc 0 +sgsn nsei 1 allow-attach ---- -- To view, visit https://gerrit.osmocom.org/c/osmo-sgsn/+/22495 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-sgsn Gerrit-Branch: master Gerrit-Change-Id: I905835c2be7be43fe376fbc9d743107948c7e6d4 Gerrit-Change-Number: 22495 Gerrit-PatchSet: 3 Gerrit-Owner: daniel <dwillmann at sysmocom.de> Gerrit-Reviewer: Jenkins Builder Gerrit-Reviewer: daniel <dwillmann at sysmocom.de> Gerrit-Reviewer: lynxis lazus <lynxis at fe80.eu> Gerrit-Reviewer: pespin <pespin at sysmocom.de> Gerrit-MessageType: merged -------------- next part -------------- An HTML attachment was scrubbed... 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