MME: Functions and Interfaces
Summary:
This
article deals with one of the important element of the EPC
architecture, MME (Mobility Management Entity). It also describes
some of the interfaces of the MME with the other network elements.
MME
(Mobility Management Entity):
The
MME is the key control-node for the LTE access-network. It is
responsible for idle mode UE (User Equipment) tracking and paging
procedure including retransmissions. It is involved in the bearer
activation/deactivation process and is also responsible for choosing
the SGW for a UE at the initial attach and at time of intra-LTE
handover involving Core Network (CN) node relocation.
It is
responsible for authenticating the user (by interacting with the
HSS).
The Non
Access Stratum (NAS) signaling terminates at the MME and it is
also responsible for generation and allocation of temporary
identities to UEs. It checks the authorization of the UE to camp on
the service provider’s Public Land Mobile Network (PLMN) and
enforces UE roaming restrictions.
The MME is the termination point in
the network for ciphering/integrity protection for NAS signaling and
handles the security key management. Lawful interception of signaling
is also supported by the MME.
The MME also provides the control plane
function for mobility between LTE and 2G/3G access networks with the
S3 interface terminating at the MME from the SGSN. The MME also
terminates the S6a interface towards the home HSS for roaming UEs.
MME is
the control plane entity within EPS supporting functions as listed
below.
Mobility
Management,
- NAS
signalling and security;
- Inter
CN node signalling for mobility between 3GPP access networks;
- Tracking
Area list management;
- PDN
GW and Serving GW selection;
- SGSN
selection for handovers to 2G or 3G 3GPP access networks;
- Roaming
;
- Authentication;
- Bearer
management functions including dedicated bearer establishment.
- Lawful
Interception of signalling traffic.
In
order to support 3GPP2 access, MME supports:
- HRPD
access node selection and maintenance for handovers to HRPD;
-
Transparent transfer of HRPD signaling messages and transfer of
status information between E-UTRAN and HRPD access.
The
procedures for information transfer between the SGSN, the MME and the
HSS are defined in TS 23.401 and TS 23.060.
The CS
fallback enabled MME supports the following additional functions
according to TS 23.272:
- Deriving
a VLR number and LAI out of the TAI
- Maintaining
of SGs association towards MSC/VLR for EPS/IMSI attached UE
- Initiating
IMSI detach at EPS detach
- Initiating
paging procedure towards eNodeB when MSC pages the UE for CS services
- Supporting
SMS procedures for CS Fallback.
- Support
CS Fallback interface and related functions for 1xRTT CDMA access.
When
the MME supports the interworking to 3GPP CS, the MME supports the
following functions as specified in TS 23.216 [83]:
- Performing
the PS bearer splitting function by separating the voice PS bearer
from the non-voice PS bearers.
- Handling
the non-voice PS bearers handover with the target cell as according
to Inter RAT handover procedure as defined in TS 23.401 [76].
- Initiating
the SRVCC handover procedure for handover of the voice component to
the target cell.
- Coordinating
PS handover and SRVCC handover procedures when both procedures are
performed,
- support
interworking and SRVCC related functions for 1xRTT CDMA access.
The
Basic Interfaces of MME:
1: Interface between MSC/VLR and MME (SGs-interface) for EPC
The
SGs interface is the reference point between the MME and MSC/VLR
which is used for the mobility management and paging procedures
between EPS and CS domain, and it is based on the Gs interface
procedures. The SGs interface is used to provide Fallback for
Location Services (LCS) and Call Independent Supplementary Services
(SS). The SGs interface is also used for the delivery of both mobile
originating and mobile terminating SMS over EUTRAN in case SMSIP is
not used.
CS
Fallback function and SMS delivery via the CS core network is
realized by reusing Gs interface mechanisms as defined in
3GPP TS 29.018 on the interface between the MME in the EPS
and the VLR. This interface is called SGs interface. The SGs
interface connects the databases in the VLR and the MME.
The
basis for the interworking between a VLR and an MME is the existence
of a SGs association between those entities per UE. The SGs
association is applicable to UEs with CS Fallback capability
activated and to UEs configured for SMS delivery via the CS core
network.
SGs
interface is a logical interface between the MME and the VLR.
All the SGsAP messages described require an SCTP association between
the MME and the VLR.
The
signaling on this interface uses SCTP. The SGs interface is defined
in TS 23.272 and TS 29.118.
2: Interface between 3GPP MSC Server and MME or SGSN (Sv-interface)
The Sv
reference point provides SRVCC support for functions like sending
Forward Relocation Message between MME or SGSN and 3GPP MSC Server.
This interface is specified in TS 29.280.The
Sv messages are based on GTP. The Sv application defines a set of
messages between the MME/SGSN and MSC Server to provide SRVCC as
defined in 3GPP TS 23.216 . The Sv message header is defined in 3GPP
TS 29.274.
The message format is coded as per GTP in 3GPP TS 29.274.
3: Interface between MME and E-UTRAN (S1-MME-interface)
Reference
point for the control plane protocol between E-UTRAN and MME. This
interface is defined in the TS 36.41x-series of Technical
Specifications and in TS 24.301.
The
non-access stratum (NAS) protocols form the highest stratum of the
control plane between the user equipment (UE) and MME. NAS protocols
support the mobility of the UE and the session management procedures
to establish and maintain IP connectivity between the UE and a PDN
GW. They define the rules for a mapping between parameters during
inter-system mobility with 3G networks. They also provide the NAS
security by integrity protection and ciphering of NAS signaling
messages. EPS provides the subscriber with a "ready-to-use"
IP connectivity and an "always-on" experience by linking
between mobility
management
and session management procedures during the UE attach procedure.
Complete
NAS transactions consist of specific sequences of elementary
procedures with EPS Mobility Management (EMM) and EPS Session
Management (ESM) protocols.
EMM
(EPS Mobility Management): The EPS Mobility Management (EMM) protocol
provides procedures for the control of mobility when the User
Equipment (UE) uses the Evolved UMTS Terrestrial Radio Access Network
(E-UTRAN). It also provides control of security for the NAS
protocols.
EMM
involves different types of procedures such as:
1:=
EMM common procedures -- can always be initiated whilst a NAS
signalling connection exists. The procedures belonging to this type
are initiated by the network. They include GUTI reallocation,
Authentication, Security mode control, Identification, EMM
information.
2:=
EMM specific procedures -- specific to the UE only. At any time only
one UE-initiated EMM specific procedure can run. The procedures
belonging to this type are Attach and combined attach, Detach or
combined detach, Normal tracking area update and combined tracking
area update (S1 mode only), Periodic tracking area update (S1 mode
only).
3:=
EMM connection management procedures -- manage the connection of UE
with network:
ESM
(EPS Session Management): The EPS Session Management (ESM) protocol
provides procedures for the handling of EPS bearer contexts. Together
with the bearer control provided by the access stratum, it provides
the control of user plane bearers. The transmission of ESM messages
is suspended during EMM procedures except for the attach procedure.
1:=
EPS bearer contexts procedures -- initiated by the network and are
used for the manipulation of EPS bearer contexts, including Default
EPS bearer context activation, Dedicated EPS bearer context
activation, EPS bearer context modification, EPS bearer context
deactivation.
2:=
Transaction related procedures -- initiated by the UE to request for
resources, i.e. a new PDN connection or dedicated bearer resources,
or to release these resources. They include PDN connectivity
procedure, PDN disconnect procedure, Bearer resource allocation
procedure, Bearer resource modification procedure.
4:= Interface between MME and HSS (S6a-interface)
This
interface is used to exchange the data related to the location of the
mobile station and to the management of the subscriber. The main
service provided to the mobile subscriber is the capability to
transfer packet data within the whole service area. The MME informs
the HSS of the location of a mobile station managed by the latter.
The HSS sends to the MME all the data needed to support the service
to the mobile subscriber. Exchanges of data may occur when the mobile
subscriber requires a particular service, when he wants to change
some data attached to his subscription or when some parameters of the
subscription are modified by administrative means.
The
S6a interface enables the
transfer of subscriber
related data between the MME
and the HSS.
Signaling
on this interface uses Diameter S6a/S6d Application as specified in
TS 29.272.
5:= Interface between MME and S-GW (S11-interface)
This
interface is used to support mobility and bearer management between
the MME and S-GW. This interface is specified in TS 29.274.
6:= Interface between MME and MME (S10-interface)
This
interface is used to support user information transfer and MME
relocation support between the MMEs. This interface is specified in
TS 29.274.
7:= Interface between MME and EIR (S13-interface)
This
interface is used between MME and EIR to exchange data, in order that
the EIR can verify the status of the IMEI retrieved from the Mobile
Station.
The
S13 interface shall enable
the ME
Identity
check procedure between the
MME and the
EIR
as described in the 3GPP
TS 23.401.
This
Mobile Equipment Identity Check Procedure
shall be used between the MME
and the EIR
and between
the SGSN
and the EIR
to check the Mobile Equipment's identity status (e.g. to check that
it has not been stolen, or, to verify that it does not have faults).
Signaling
on this interface uses the Diameter S13 Application in TS 29.272.
8:= Interface between MME and SGSN (S3-interface)
This
interface enables user and bearer information exchange for inter 3GPP
access network mobility in idle and/or active state. This interface
is specified in TS 29.274.
4:= Interface between MME and HSS (S6a-interface)
This
interface is used to exchange the data related to the location of the
mobile station and to the management of the subscriber. The main
service provided to the mobile subscriber is the capability to
transfer packet data within the whole service area. The MME informs
the HSS of the location of a mobile station managed by the latter.
The HSS sends to the MME all the data needed to support the service
to the mobile subscriber. Exchanges of data may occur when the mobile
subscriber requires a particular service, when he wants to change
some data attached to his subscription or when some parameters of the
subscription are modified by administrative means.
The
S6a interface enables the
transfer of subscriber
related data between the MME
and the HSS.
Signaling
on this interface uses Diameter S6a/S6d Application as specified in
TS 29.272.
5:= Interface between MME and S-GW (S11-interface)
This
interface is used to support mobility and bearer management between
the MME and S-GW. This interface is specified in TS 29.274.
6:= Interface between MME and MME (S10-interface)
This
interface is used to support user information transfer and MME
relocation support between the MMEs. This interface is specified in
TS 29.274.
7:= Interface between MME and EIR (S13-interface)
This
interface is used between MME and EIR to exchange data, in order that
the EIR can verify the status of the IMEI retrieved from the Mobile
Station.
The
S13 interface shall enable
the ME
Identity
check procedure between the
MME and the
EIR
as described in the 3GPP
TS 23.401.
This
Mobile Equipment Identity Check Procedure
shall be used between the MME
and the EIR
and between
the SGSN
and the EIR
to check the Mobile Equipment's identity status (e.g. to check that
it has not been stolen, or, to verify that it does not have faults).
Signaling
on this interface uses the Diameter S13 Application in TS 29.272.
8:= Interface between MME and SGSN (S3-interface)
This
interface enables user and bearer information exchange for inter 3GPP
access network mobility in idle and/or active state. This interface
is specified in TS 29.274.
9:= Reference point between HRPD AN and MME (S101-reference point)
The
S101 interface supports procedures for Pre-Registration, Session
Maintenance and Active handovers between E UTRAN and HRPD networks.
This is based on tunneling over S101 signaling of one technology
while the UE is in the other technology as specified in TS 23.402.
The HRPD air interface messages tunneled over S101 in E UTRAN to HRPD
mobility are defined in 3GPP2 C.S0087 0.
10:= Reference point between 3GPP2 1xCS IWS and MME (S102-reference point)
The
S102 reference point provides a tunnel between MME and 3GPP2 1xCS IWS
to relay 3GPP2 1xCS signaling messages in order to support SRVCC as
specified in TS 23.216 and CS Fallback as specified in
TS 23.272. 1x CS signaling messages are those messages that are
defined for A21 interface as described in 3GPP2 A.S0008-C.
In
case of CS Fallback to 1x CS network as specified in TS 23.272,
S102 Tunnel Redirection Procedure is used when the UE perform
Tracking Area Update with MME change (as specified in TS 23.402
in case of S101 tunnel redirection) while the UE is registered with
the 1xRTT CS domain and the S102 session exists between the MME and
the 1xCS IWS.
11:= Interface between GMLC and MME (SLg-interface)
The
SLg interface is used by the GMLC to communicate with MMEs. The SLg
interface is defined in TS 29.172.
12:= Interface between MME and E-SMLC (SLs-interface)
The
SLs interface is used
to convey LCS-AP messages and
parameters between the MME to
the E-SMLC. It
is also used for tunneling LTE
Positioning Protocols (LPP between
the E-SMLC and
the target UE, LPPa between
the E-SMLC and the eNB), which are transparent
to the MME as described in 3GPP TS 36.305.
The
SLs interface is defined in TS 29.171.
SCTP
(see IETF RFC 4960) shall be supported as the transport layer of
LCS-AP
messages. The MME shall
establish the SCTP association.
The
port number (9082) and the
payload protocol
identifier
(29) for LCS-AP
is assigned by IANA.
(http://www.t1shopper.com/tools/port-number/9082/
and http://www.iana.org/assignments/sctp-parameters)
13:= Interface between the CBC and MME (SBc Interface)
Reference
point between CBC and MME for warning message delivery and control
functions. This interface is specified in TS 29.168.
SBc-AP
interface is a logical interface between the MME and the CBC.
All the SBc-AP
messages require an SCTP association between the MME and the CBC.
Multiple
local SCTP endpoints may be supported. Multiple remote SCTP endpoints
shall be supported. When multiple local or remote SCTP endpoints are
configured, several simultaneous SCTP associations shall be supported
between MME and CBC.
The
CBC shall establish the SCTP association. The registered port number
for SBc-AP is 29168.The registered payload protocol identifier for
SBc-AP is 24.
This is a short description of the interfaces that the MME handles.
References:
TS 23.401: 3rd Generation Partnership Project;
Technical Specification Group Services and System Aspects;
General Packet Radio Service (GPRS) enhancements for
Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access
,
Technical Specification Group Services and System Aspects;
General Packet Radio Service (GPRS) enhancements for
Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access
,
TS 23.402 : 3rd Generation Partnership Project;
Technical Specification Group Services and System Aspects;
Architecture enhancements for non-3GPP accesses
Technical Specification Group Services and System Aspects;
Architecture enhancements for non-3GPP accesses
TS 36.300: 3rd Generation Partnership Project;
Technical Specification Group Radio Access Network;
Evolved Universal Terrestrial Radio Access (E-UTRA)
and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN);
Overall description;
Stage 2
Technical Specification Group Radio Access Network;
Evolved Universal Terrestrial Radio Access (E-UTRA)
and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN);
Overall description;
Stage 2
TS 23.002: 3rd Generation Partnership Project;
Technical Specification Group Services and Systems Aspects;
Network architecture
Technical Specification Group Services and Systems Aspects;
Network architecture
TS
29.274: 3rd Generation Partnership Project;
Technical Specification Group Core Network and Terminals;
3GPP Evolved Packet System (EPS);
Evolved General Packet Radio Service (GPRS)
Tunnelling Protocol for Control plane (GTPv2-C);
Stage 3
Technical Specification Group Core Network and Terminals;
3GPP Evolved Packet System (EPS);
Evolved General Packet Radio Service (GPRS)
Tunnelling Protocol for Control plane (GTPv2-C);
Stage 3
TS 29.276:3rd Generation Partnership Project;
Technical Specification Group Core Network and Terminals;
3GPP Evolved Packet System (EPS);
Optimized Handover Procedures and Protocols between
E-UTRAN access and cdma2000 HRPD Access;
Stage 3
TS 29.171: 3rd Generation Partnership Project;Technical Specification Group Core Network and Terminals;
3GPP Evolved Packet System (EPS);
Optimized Handover Procedures and Protocols between
E-UTRAN access and cdma2000 HRPD Access;
Stage 3
Technical Specification Group Core Network and Terminals;
Location Services (LCS);
LCS Application Protocol (LCS-AP) between the
Mobile Management Entity (MME) and
Evolved Serving Mobile Location Centre (E-SMLC);
SLs interface
No comments:
Post a Comment