Cisco Cisco ASR 5000
SGSN-MME Combo Optimization
▀ Feature Description
▄ SGSN Administration Guide, StarOS Release 18
Feature Description
The SGSN and MME can be enabled simultaneously in the same chassis and, though co-located, they each behave as
independent nodes. This Combo Optimization feature enables the co-located SGSN and MME to co-operate with each
other in order to achieve lower memory and CPU utilizations and to reduce signaling towards other nodes in the
network. When functioning as mutually-aware co-located nodes, the SGSN and the MME can share UE subscription
data between them.
independent nodes. This Combo Optimization feature enables the co-located SGSN and MME to co-operate with each
other in order to achieve lower memory and CPU utilizations and to reduce signaling towards other nodes in the
network. When functioning as mutually-aware co-located nodes, the SGSN and the MME can share UE subscription
data between them.
Important:
This feature is supported by both the S4-SGSN and the Gn-SGSN. For the feature to apply
to a Gn-SGSN, the Gn-SGSN must be configured to connect to an HSS. Combo Optimization for an SGSN-
MME node is a licensed Cisco feature. Contact your Cisco account representative for detailed information on
specific licensing requirements. For information on installing and verifying licenses, refer to the Managing
License Keys section of the Software Management Operations chapter in the System Administration Guide.
MME node is a licensed Cisco feature. Contact your Cisco account representative for detailed information on
specific licensing requirements. For information on installing and verifying licenses, refer to the Managing
License Keys section of the Software Management Operations chapter in the System Administration Guide.
Overview
The load on S6d/S6a interfaces towards an HSS is reduced effectively by utilizing the resources in a co-located SGSN-
MME node scenario. Requests for subscription data in Update Location Request (ULR) are skipped by setting the 'skip-
subscriber-data' bit in the ULR flags; this, in turn, reduces the load on the HSS. The Skip Subscriber Data AVP is used
and the subscriber data is shared across the SGSN and the MME services.
MME node scenario. Requests for subscription data in Update Location Request (ULR) are skipped by setting the 'skip-
subscriber-data' bit in the ULR flags; this, in turn, reduces the load on the HSS. The Skip Subscriber Data AVP is used
and the subscriber data is shared across the SGSN and the MME services.
As per 3GPP TS 29.272, setting the 'skip-subscriber-data' bit in the ULR indicates that the HSS may skip sending
subscription data in Update Location Answer (ULA) to reduce signaling. If the subscription data has changed in the
HSS after the last successful update of the MME/SGSN, the HSS ignores this bit and sends the updated subscription
data. If the HSS skips sending the subscription data, then the GPRS-Subscription-Data-Indicator flag can be ignored.
subscription data in Update Location Answer (ULA) to reduce signaling. If the subscription data has changed in the
HSS after the last successful update of the MME/SGSN, the HSS ignores this bit and sends the updated subscription
data. If the HSS skips sending the subscription data, then the GPRS-Subscription-Data-Indicator flag can be ignored.
Important:
The SGSN supported the Skip-Subscription-Data bit prior to Release 18.0. Support for this
functionality was added to the MME in Release 18.0.
Ensuring that packets are routed internally reduces network latency for S3/Gn interface messages.This is achieved by
configuring the SGTP and EGTP services in the same context for the SGSN and the MME configurations.
configuring the SGTP and EGTP services in the same context for the SGSN and the MME configurations.
For outbound Inter-RAT SRNS Relocations, the MME gives preference to the co-located SGSN, irrespective of the
order/priority or preference/weight configured for the SGSN entry in DNS Server. When Inter-RAT handovers take
place between the co-located MME and the SGSN, the new call arrives at the same Session Manager that hosted the call
in the previous RAT. If the subscription data is available for a given UE at the co-located SGSN, then the MME does
not need to request this data from the HSS and provides UE subscription data obtained from the SGSN. This optional
function can be turned on or off through the MME Service configuration.
order/priority or preference/weight configured for the SGSN entry in DNS Server. When Inter-RAT handovers take
place between the co-located MME and the SGSN, the new call arrives at the same Session Manager that hosted the call
in the previous RAT. If the subscription data is available for a given UE at the co-located SGSN, then the MME does
not need to request this data from the HSS and provides UE subscription data obtained from the SGSN. This optional
function can be turned on or off through the MME Service configuration.
Combo Optimization is available for subscribers with an EPC-enabled UE and an EPC subscription configured at the
HSS. During handoff from 4G to 3G or 4G to 2G, the EPC subscription will be copied from the MME. Combo
Optimization is also applicable for Non-EPC subscribers if core-network-interface is selected as S4 for the EPS-
subscription.
HSS. During handoff from 4G to 3G or 4G to 2G, the EPC subscription will be copied from the MME. Combo
Optimization is also applicable for Non-EPC subscribers if core-network-interface is selected as S4 for the EPS-
subscription.