nas
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NASTRANSCRIPT
10/12/2015 NAS
http://www.3gpp.org/technologies/keywordsacronyms/96nas 1/3
The Mobile Broadband Standard
NASAuthor: Frédéric Firmin, 3GPP MCC
This article gives an overview of the NonAccess Stratum (NAS) and its protocols EMM and ESM.
The NonAccess Stratum is a set of protocols in the Evolved Packet System. The NAS is used to convey nonradio signallingbetween the User Equipment (UE) and the Mobility Management Entity (MME) for an LTE/EUTRAN access.
NASFrom a protocol stack perspective, the NAS is the highest stratum of the control plane, as shown in figure 1.
Figure 1: EPS control plane for EUTRAN accessThe NAS procedures are grouped in two categories:
the EPS Mobility Management (EMM), andthe EPS Session Management (ESM).
EPS Mobility Management
The EPS Mobility Management protocol refers to procedures related to mobility over an EUTRAN access, authentication andsecurity. It is the equivalent in EPS of MM in GSM and GMM in GPRS.
3GPP specifications make distinction between EMM common, specific and connection management procedures:
EMM common procedures
EMM common procedures refer to various networkinitiated mechanisms.
GUTI (Global Unique Temporary ID) reallocationAuthenticationSecurity mode controlIdentificationEMM information
EMM specific procedures
EMM specific procedures are UEinitiated.
These procedures define attach/detach (to/from the EPC) mechanisms. They also introduce the Tracking Area Update (TAU)mechanism, which update the location of the UE within the network. Tracking Area is the equivalent in EPS of Location Areain GSM and Routing Area in GPRS.
In EPS, a UE initiates a Tracking Area Update when it detects that it enters into a new Tracking Area. EMM specificprocedures also define periodic Tracking Area Update.
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10/12/2015 NAS
http://www.3gpp.org/technologies/keywordsacronyms/96nas 2/3
Figure 2: tracking areasEPS also introduces the concept of Tracking Area List (TAL), which allows the provision of lists of Tracking Areas in UEs. A UEdoes not need to initiate a TAU if it enters a Tracking Area which is included in its TAL.
Provisioning different lists to the UEs within the network avoid signalling peaks for instance when all UEs on a train cross a TAborder.
EMM connection management procedures:
(also known as ECM: “EPS Connection Management“)
EMM connection management procedures provide several functions to support the connection of the UE to the network (seeESM procedures below):
Service request: initiated by the UE to start the establishment of NAS signalling connectionPaging: initiated by the network in case of downlink NAS signalling to indicate to the UE to start a service requestTransport of NAS messages: used for SMS (CS fallback)Generic transport of NAS messages: Various other applications (e.g. LCS)
EPS Session Management
The EPS Session Management protocol offers support to the establishment and handling of user data in the NAS.
In EPS, two concepts are introduced to define the IP connectivity between a UE and a packet data network (PDN):
PDN connection, andEPS bearer
As shown in figure 3, a PDN connection is composed of a default EPS bearer and possibly additional ones called "dedicatedbearers".
Figure 3: PDN connection and EPS bearerA default bearer is created upon establishment of a PDN connection. If a service (e.g. video streaming) requires specifichandling in terms of quality of service (QoS), dedicated bearers can be established.
Within a PDN connection, all EPS bearers share a same UE IP address and an APN.
EPS supports multiple simultaneous PDN connections. For instance, a UE can have a PDN connection to the Internet (withjust a default EPS bearer) and one to the operator’s IMS (with additional dedicated bearers, if required by the service).
ESM procedures are grouped into two categories:
EPS bearer procedures, which are networkinitiated and provide mechanisms for activation, deactivation or modification of EPSbearers, andTransactionrelated procedures, which are UEinitiated and provide mechanisms for:requests for PDN connection establishment and disconnection,requests for bearer resources allocation and modification, and
10/12/2015 NAS
http://www.3gpp.org/technologies/keywordsacronyms/96nas 3/3
release requests
Further reading:
General:
The 3GPP website contains all 3GPP specifications. They can be downloaded for free at www.3gpp.org/specifications
Descriptions of all 3GPP releases can be found at ftp://ftp.3gpp.org/Information/WORK_PLAN/Description_Releases/
An overview of the EPC can be found at: http://www.3gpp.org/TheEvolvedPacketCore
NAS:
3GPP TS 23.401 defines the architecture of the EPC for an LTE access3GPP TS 24.301 defines the protocol details of the NAS3GPP TS 24.008 defines intersystem mobility between LTE and 2G/3G3GPP TS 24.303 defines intersystem mobility between LTE and non3GPP accesses.
RAN 70 Sitges 0710 Dec 2015SA 70 Sitges 0911 Dec 2015GERAN 69 Malta 1519 Feb 2016CT 71 Gothenburg 0708 Mar 2016RAN 71 Gothenburg 0710 Mar 2016SA 71 Gothenburg 0911 Mar 2016GERAN 70 China 2327 May 2016CT 72 SOUTH KOREA 1314 Jun 2016RAN 72 SOUTH KOREA 1316 Jun 2016SA 72 SOUTH KOREA 1517 Jun 2016GERAN 71 Goteborg 2226 Aug 2016CT 73 US 1920 Sep 2016RAN 73 US 1922 Sep 2016SA 73 US 2123 Sep 2016GERAN 72 US 1418 Nov 2016CT 74 Vienna 0506 Dec 2016
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LTEAdvancedLTECarrier Aggregation ExplainedHetNet/Small CellsNASThe Evolved Packet CoreHSPAUMTSWCDMAGPRS & EDGE