Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
Features and Functionality ▀
SGSN Administration Guide, StarOS Release 18 ▄
cannot be achieved. Note that GTPv2 to GTPv1 conversions (for QoS and Context IDs) are lossy data conversions, so a
subscriber doesn’t encounter a similar type of network behavior while in 2G/3G and 4G networks.
subscriber doesn’t encounter a similar type of network behavior while in 2G/3G and 4G networks.
S4-SGSN Support for “Higher Bit Rates than 16 Mbps”Flag
As per 3GPP R9 specifications, the SGSN can now be aware if the UE is capable of supporting extended R7 bit rates.
The “higher bit rates than 16 Mbps” flag is used for this purpose. This flag is sent by the RNC in the Initial UE message
or Re-location Complete message or by Peer S4-SGSN / MME in Forward Relocation Request / Context Response
message. The SGSN also supports sending "higher Bit Rates than 16 Mbps flag" as part of MM Context in Context
response/Forward Relocation request/Identification request during Old ISRAU/SRNS handover procedures.The SGSN
stores the UE capability in the MM-context. During PDP context activation, the per bearer bit rate or APN-AMBR is
capped based on the flag's value. If the RNC is not 3GPP R9 compliant, the SGSN does not receive this flag. A new CLI
keyword
The “higher bit rates than 16 Mbps” flag is used for this purpose. This flag is sent by the RNC in the Initial UE message
or Re-location Complete message or by Peer S4-SGSN / MME in Forward Relocation Request / Context Response
message. The SGSN also supports sending "higher Bit Rates than 16 Mbps flag" as part of MM Context in Context
response/Forward Relocation request/Identification request during Old ISRAU/SRNS handover procedures.The SGSN
stores the UE capability in the MM-context. During PDP context activation, the per bearer bit rate or APN-AMBR is
capped based on the flag's value. If the RNC is not 3GPP R9 compliant, the SGSN does not receive this flag. A new CLI
keyword
sm ue-3gpp-compliance-unknown restrict-16mbps
is introduced under the sgsn-service to support
this functionality. When the CLI is configured, the SGSN caps the APN-AMBR for non-GBR bearers to “16” Mbps and
rejects activation of GBR bearers with GBR higher than “16” Mbps. If not, APN-AMBR and GBR higher than “16”
Mbps are allowed.
rejects activation of GBR bearers with GBR higher than “16” Mbps. If not, APN-AMBR and GBR higher than “16”
Mbps are allowed.
Consider the scenarios where UE 3GPP compliance is not known and the CLI is configured to restrict bitrate to 16
Mbps or it is known that UE is not capable of supporting bitrates higher than 16Mbps; the Session Manager uses the
flag to perform the following actions:
Mbps or it is known that UE is not capable of supporting bitrates higher than 16Mbps; the Session Manager uses the
flag to perform the following actions:
1. The APN-AMBR is restricted to “16” Mbps during PDP activation of non-GBR bearers, particularly the default
bearer.
2. If the PGW upgrades the APN-AMBR in Create Session Response during non-GBR bearer activation, then the
APN-AMBR is retained as “16” Mbps and same is indicated to the UE in an Activate Accept.
3. If the PGW upgrades APN-AMBR in Update Bearer Request for non-GBR bearer, then the APN-AMBR is
restricted to “16” Mbps and only if the APN-AMBR changes, the PGW init bearer modification procedure is
continued. In case APN-AMBR does not change, then Update Bearer Response is sent immediately.
continued. In case APN-AMBR does not change, then Update Bearer Response is sent immediately.
4. For GBR bearers, Update Bearer Request with GBR/MBR higher than “16” Mbps is rejected with “No resources
available”.
5. Activation of GBR bearers with MBR/GBR higher than “16” Mbps in Create Bearer Request is rejected with
cause “No resources available”.
6. After S3 SRNS, Modify Bearer Command is initiated to modify the APN-AMBR to “16” Mbps for Non-GBR
bearers having bitrates higher than 16 Mbps.
7. After S3 SRNS, GBR bearers having bitrates higher than “16” Mbps are de-activated.
For more information on the CLI command see, Command Line Interface Reference.
S6d and Gr Interface Support
The S4-SGSN supports the Diameter based S6d interface to the HSS, in addition to the legacy Gr interface to the HLR
(used by an SGSN configured to use the Gn/Gp interfaces). This is a license-enabled feature.
(used by an SGSN configured to use the Gn/Gp interfaces). This is a license-enabled feature.
The S6d / Gr interface enhancements allow operators to consolidate the HLR/HSS functions into a single node, which
improves operational efficiency and other overhead. With the deployment of the EPC core, many operators may
consolidate the HLR/HSS functions into a single node. Until then, the S4-SGSN still supports the MAP-based Gr and
the Diameter based S6d interfaces.
improves operational efficiency and other overhead. With the deployment of the EPC core, many operators may
consolidate the HLR/HSS functions into a single node. Until then, the S4-SGSN still supports the MAP-based Gr and
the Diameter based S6d interfaces.
The SGSN selects the Gr interface / S6d interface based on the MAP or HSS service associated with the configured
SGSN and/or GPRS services. If both the services are associated, then SGSN will use the following order of selection:
SGSN and/or GPRS services. If both the services are associated, then SGSN will use the following order of selection:
1. Select the appropriate interface based on any operator policy preference for S6d / Gr.
2. If no operator policy is present, then by use the Gr interface by default.
2. If no operator policy is present, then by use the Gr interface by default.
The S4-SGSN sets the following initiate UGL messages on a change of HSS service: