Mme Selection; Packet Data Network Gateway (P-Gw) Selection; Serving Gateway (S-Gw) Selection - Cisco ASR 5000 Series Administration Manual

▀ Features and Functionality - Base Software
3GPP R8 Identity Support
Tracking Area List Management
Reachability Management

MME Selection

The MME selection function selects an available MME for serving a UE. This feature is needed for MME selection for
handover with minimal MME changes.
MME selection chooses an available MME for serving a UE. Selection is based on network topology, i.e. the selected
MME serves the UE‟s location and in case of overlapping MME service areas, the selection function may prefer MME‟s
with service areas that reduce the probability of changing the MME.

Packet Data Network Gateway (P-GW) Selection

Provides a straightforward method based on a default APN provided during user attachment and authentication to assign
the P-GW address in the VPLMN or HPLMN. The MME also has the capacity to use a DNS transaction to resolve an
APN name provided by a UE to retrieve the PDN GW address.
P-GW selection allocates a P-GW that provides the PDN connectivity for the 3GPP access. The function uses subscriber
information provided by the HSS and possibly additional criteria. For each of the subscribed PDNs, the HSS provides:
an IP address of a PDN GW and an APN, or
an APN and an indication for this APN whether the allocation of a PDN GW from the visited PLMN is allowed
or whether a PDN GW from the home PLMN shall be allocated.
The HSS also indicates the default APN for the UE. To establish connectivity with a PDN when the UE is already
connected to one or more PDNs, the UE provides the requested APN for the PDN GW selection function.
If the HSS provides an APN of a PDN and the subscription allows for allocation of a PDN GW from the visited PLMN
for this APN, the PDN GW selection function derives a PDN GW address from the visited PLMN. If a visited PDN GW
address cannot be derived, or if the subscription does not allow for allocation of a PDN GW from the visited PLMN,
then the APN is used to derive a PDN GW address from the HPLMN.

Serving Gateway (S-GW) Selection

The Serving GW selection function selects an available Serving GW to serve a UE. This feature reduces the probability
of changing the Serving Gateway and a load balancing between Serving Gateways The MME uses DNS procedure to
for S-GW selection.
S-GW selection chooses an available S-GW to serve a UE. The selection is based on network topology, i.e. the selected
S-GW serves the UE‟s location and in the case of overlapping S-GW service areas, the selection may prefer S-GWs
with service areas that reduce the probability of changing the Serving GW. If a subscriber of a GTP only network roams
into a P-MIP network, the PDN GWs selected for local breakout supports the P-MIP protocol, while P-GWs for home
routed traffic use GTP. This means the S-GW selected for such subscribers may need to support both GTP and PMIP, so
that it is possible to set up both local breakout and home routed sessions for these subscribers.
▄ Cisco ASR 5000 Series Mobility Management Entity Administration Guide
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MME in LTE/SAE Wireless Data Services
OL-22987-01