3Gpp R8 Identity Support; Tracking Area List Management - Cisco ASR 5000 Series Administration Manual

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MME in LTE/SAE Wireless Data Services

3GPP R8 Identity Support

Provides the identity allocation of following type:
EPS Bearer Identity
Globally Unique Temporary UE Identity (GUTI)
Tracking Area Identity (TAI)
MME S1-AP UE Identity (MME S1-AP UE ID)
EPS Bearer Identity: An EPS bearer identity uniquely identifies EPS bearers within a user session for attachment to the
E-UTRAN access and EPC core networks. The EPS Bearer Identity is allocated by the MME. There is a one to one
mapping between EPS Radio Bearers via the E-UTRAN radio access network and EPS Bearers via the S1-MME interface
between the eNodeB and MME. There is also a one-to-one mapping between EPS Radio Bearer Identity via the S1 and
X2 interfaces and the EPS Bearer Identity assigned by the MME.
Globally Unique Temporary UE Identity (GUTI): The MME allocates a Globally Unique Temporary Identity (GUTI)
to the UE. A GUTI has; 1) unique identity for MME which allocated the GUTI; and 2) the unique identity of the UE
within the MME that allocated the GUTI.
Within the MME, the mobile is identified by the M-TMSI.
The Globally Unique MME Identifier (GUMMEI) is constructed from MCC, MNC and MME Identifier (MMEI). In
turn the MMEI is constructed from an MME Group ID (MMEGI) and an MME Code (MMEC).
The GUTI is constructed from the GUMMEI and the M-TMSI.
For paging, the mobile is paged with the S-TMSI. The S-TMSI is constructed from the MMEC and the M-TMSI.
The operator needs to ensure that the MMEC is unique within the MME pool area and, if overlapping pool areas are in
use, unique within the area of overlapping MME pools.
The GUTI is used to support subscriber identity confidentiality, and, in the shortened S-TMSI form, to enable more
efficient radio signaling procedures (e.g. paging and Service Request).
Tracking Area Identity (TAI): Provides the function to assign the TAI list to the mobile access device to limit
the frequency of Tracking Area Updates in the network. The TAI is the identity used to identify the tracking
area or group of cells in which the idle mode access terminal will be paged when a remote host attempts to
reach that user. The TAI consists of the Mobile Country Code (MCC), Mobile Network Code (MNC) and
Tracking Area Code (TAC).
MME S1-AP UE Identity (MME S1-AP UE ID): This is the temporary identity used to identify a UE on the
S1-MME reference point within the MME. It is unique within the MME per S1-MME reference point instance.

Tracking Area List Management

Provides the functions to allocate and reallocate a Tracking Area Identity (TAI) list to the UE to minimize the Tracking
Area updates.
The MME assigns the TAI list to a UE so as to minimize the TA updates that would be sent by the UE. The TAI list
should not be very long as this would mean that the paging load would be high. There is a trade-off between paging load
and Tracking Area Update procedures number.
To avoid ping-pong effect, the MME includes the last visited TAI (provided that the TA is handled by the MME) in the
TAI list assigned to the UE.
The tracking area list assigned to different UEs moving in from the same tracking area should be different so as to avoid
Tracking Area Update message overflow.
OL-22987-01
Cisco ASR 5000 Series Mobility Management Entity Administration Guide ▄
Features and Functionality - Base Software ▀
27

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