umts basic funct ix 0405 - 1-4-5.netdmm/ngn/umts_basic_funct_ix_0405.pdfws 04/05, tkn tu berlin,...

WS 04/05, TKN TU Berlin, Cornelia Kappler Course UMTS Networks, IX. Basic Functionalities 1

Course Overview• Motivation• Standardization issues• UMTS architecture basics• UMTS radio link

– Physical layer– Signaling

• UE, UTRAN, PS Domain, CS Domain • Basic functionalities:

– Accessing the network– Transferring data– Detaching from the network– Information storage

• Mobility• QoS• Security• Charging

• IMS

• Example signaling flows

• UMTS Evolution: from R99 to Rel7

• Beyond UMTS


• Functionality overview• Accessing the network• Transferring data• Detaching from the network• Identities• Information storage

cf. TS 23.003 „Numbering, addressing and identification“TS 23.060 "General Packet Radio Service (GPRS)“TS 23.107 „Quality of Service (QoS) concept and architecture”TS 25.331 “Radio Resource Control (RRC) Protocol Specification”

Basic Functionalities


Functionality overview• Accessing the network

– Finding the access point– Localizing UE – Establishing connectivity for signaling– Registration

• Authentication and authorization (-> security)

– Establishing connectivity for data transfer• Admission control (-> QoS)

– Paging (-> Mobility)

• Transferring data – Routing, encapsulating and tunneling– Address translation– Ciphering and encryption (-> security)– Compression– Charging– Resource management (-> QoS)

• Mobility Handling• Detaching from the network


• Functionality overview• Accessing the network

– Finding the access point– Localizing the UE – Establishing connectivity for signaling (RRC connection set-up)– Registration (GPRS Attach)– Establishing connectivity for data transfer (PDP context activation)

• Transferring data• Detaching from the network• Identities• Information storage




Accessing the network -Finding the access point I

Upon being switched on the UE…

• …scans all possible frequencies (time slots), in order to find elegible cells

– elegible = UMTS technologie, e.g. UTRA FDD

• …synchronizes, and finds scrambling code

– As described in lecture on UTRA

– Now it is able to receive cell-specific broadcast information• Sent by RNC on BCCH


Accessing the network -Finding the access point II

• …prioritizes PLMNs(if more than one is available)– PLMN „Public Land Mobile Network“

mobile telecommunication network under the control of a single operator

– PLMN identity broadcasted on P-CCPCH• in regular intervals

– PLMN identified by MCC-MNCMobile Country Code – Mobile Network Code

– UE prioritizes PLMNs according to a preference list stored on the USIM

• Always prefer „home PLMN“• Availability of better PLMN is checked on a regular basis


Accessing the network -Finding the access point III

• …looks for suitable cells– Suitable = acceptable radio conditions

• Signal to noise ratio is above threshold both uplink and downlink

• …finally picks cell– Listens on the BCCH for general

cell configuration information, e.g. localization• UE is responsible for tracking its location

– Only now UE makes its presence known to the network


Accessing the network - Localization of the UE I

• Hierarchical organization

…not exchanging data in CS („idle“)…several RAsLA – LocationArea

Accuracy with which location of UE is knownwhen. . .

May contain. . .Name

…not exchanging data in PS („idle“)…several URAsRA – Routing Area

…sporadically exchanging data in PS (II)(unless using (I))

…several cellsURA - UTRAN Registration Area

…continuously exchanging data(both CS and PS)…sporadically exchanging data in PS (I)(unless using (II))

Cell

SGSN 2

SGSN 1


Accessing the network -Localization of the UE II

• Identification of Localization– LAI – Location Area Identity = MCC + MNC + LA Code

– RAI – Routing Area Identity = LAI + RA Code

– URA Identity

– CGI – Cell Global Identity = LAI + cell identity

• Globally unique identifiers


Now a signaling connection needs to be established in order to perform signaling for registration:

RRC connection set-up• UE sends a RRC Connection Request to RNC

– using the CCCH / RACH– containing

• USIM specific identity IMSI– IMSI = MCC + MNC + MSIN

– The RNC does not authenticate user, but a unique ID as address for thetransaction is needed

• Routing Area Identifier RAI• Measurement report, e.g. power levels• …

Accessing the network -Establishing signaling connectivity I

PLMN identifier


Accessing the network -Establishing signaling connectivity II

• RNC signals to Node B that resouces are to be allocated– Depending on the type of session, a dedicated or a common

channel is used

– Node B is informed of • Codes to be assigned

• Power level

• Transport format to use for Transport Channel– Length of data blocks transmitted

– Time allowed to transmit data block

– Details of error correction

• …

• RNC informs UE that radio connection is established– Code, power level, transport format,…


Accessing the network – Registration I• Registration in PS Domain is called GPRS Attach

• Registration changes the Mobilty Management State (MM State) of UE at UE and SGSN – From PMM-Detached to PMM-Connected

• Mobility Management State Machine (Fig. 16 of 23.060):

PMM DETACHED

GPRS Attach

Iu SignallingConnection Release

Iu SignallingConnection Establish

GPRS

Detac

h

PMM-CONNECTEDPMM-IDLE

Detach,GPRS Attach Reject,RA Update Reject

GPRS

Detac

h

PMM-CONNECTED

Serving RNCrelocation

SGSN Mobility Management StatesUE Mobility Management States

Detach,GPRS Attach Reject,RA Update Reject

Iu SignallingConnection Establish

Iu SignallingConnection Release

PMM-IDLE

PMM DETACHED

GPRS Attach


Accessing the network – Registration II• UE registers with SGSN, using

– GMM / RANAP protocol between UE and SGSN

– MAP protocol between SGSN and HLR

• Sequence of events

– UE sends SGSN identity and location information (IMSI, IMEI, RAI)

– SGSN checks identity with information obtained from HLR (-> authentication)

– UE and SGSN activate encryption

– SGSN ensures that equipment is not stolen with EIR

– SGSN informs HLR is is handling this UE and in return receives information on what services this user is allowed to use(-> authorization)

– SGSN informs user if request has been granted and assigns temporary ID: P-TMSI (Packet Temporary subscriber identity)

• For security reasons TMSI is only used for registration


Accessing the network – Registration III• GPRS attach is denied by SGSN when

– Identity of user could not be confirmed

– Equipment or USIM are listed as stolen• This USIM is henceforth listed as forbidden in TE,

– No other GPRS attach will be initiated with this USIM

– No roaming agreement between this PLMN and homePLMN, or user not allowed to switch PLMNs

• This PLMN is henceforth listed as „forbidden“ in USIM

– …


Establishing connectivity for data transfer Bearer Services I

• In order to send or receive data, a so-calledBearer Service needs to be set-up

• A Bearer Service– is offered by one service layer to the upper layer

– extends across a well-defined domain• E.g. UMTS Bearer Service from UE to GGSN

– offers data transport, mobility and QoS

– to do so may use services of lower-layer Bearers


Establishing connectivity for data transfer Bearer Services II

TE MT RAN SGSN GGSN TE

UMTS

End-to-End Service

TE/MT LocalBearer Service

UMTS Bearer Service External BearerService

UMTS Bearer Service

Radio Access Bearer Service CN BearerService

BackboneBearer Service

RAN AccessBearer Service

Radio BearerService

Physical Radio Bearer Service

Physical Bearer Service

Fig. 1 from 23.107


Establishing connectivity for data transfer PDP context activation I

• I.e. for the UE to use a service (send or receive data), it needs to signal for UMTS Bearer Service establishment

– The UMTS Bearer is specific to the service used– This is called PDP context activation

• PDP – Packet Data Protocol– A PDP context is characterized by

• Beginning: PDP address of UE• End: Terminating GGSN • QoS specific to service

– UE is assigned a dynamic PDP address, unless static PDP address exists

• This is an IPv4 or IPv6 address– Terminating GGSN depends on end-point of session;

UE must name APN (Access Point Name)• Is it a session internal to this PLMN?• Is an external network addressed? Which one?

– UE can establish more than one PDP context simultaneously(„secondary PDP context“)

• When UE uses two applications with different QoS requirements,it would establish two PDP contexts

– Changes PDP state from Inactive to Active• Only possible if mobility management state is PMM-idle or PMM-

Connected– PMM-IDLE then must change to PMM-CONNECTED

Deactivate PDP Contextor

Mobility Management state changes to IDLEor PMM-DETACHED

Activate PDPContext

INACTIVE

ACTIVE

PDP State Model:

Fig. 61 from 23.060


Establishing connectivity for data transferPDP context activation II

• PDP context activation uses GMM / RANAP, GTP-C• PDP context activation sequence of events

– UE asks SGSN to establish PDP context with• NSAPI – Network Service Access Point Identifier

– Identifies PDP context at UE

• Static PDP address of UE or request to be assigned dynamic PDP address• APN – Access Point Name• PDP context characteristics, e.g. QoS (bandwidth, real-time?,…)• Traffic descriptor (TFT – Traffic Flow Template)• …

– SGSN • determines GGSN suitable for this APN• May check resource availability in PS domain (admission control)• May reserve resources in PS domain

– SGSN asks GGSN to create PDP context with specific QoS• Identified by TEID (Tunnel Endpoint Identifier) which is mapped to NSAPI + IMSI

– SGSN invokes set-up of Radio Access Bearer (RAB) with specific QoS• Assignment of resources in RAN

– SGSN informs UE of PDP context establishment success / reject• PDP address assigned• Possibly downgraded resources

Not

in s

tand

ard


Establishing connectivity for data transfer Sequence chart for PDP context activation

GGSN

9. Activate PDP Context Accept

4. Create PDP Context Response

4. Create PDP Context Request

1. Activate PDP Context Request

SGSNRANMS

5. Radio Access Bearer Setup

C1

C2

6. Invoke Trace

8. Update PDP Context Response

8. Update PDP Context Request

Fig. 64 from 23.060


• Functionality overview• Accessing the network• Transferring data

– Routing – Encapsulating and tunneling– Address translation– Compression

• Detaching from the network• Identities• Information storagecf. TS 23.003 „Numbering, addressing and identification“TS 23.060 "General Packet Radio Service (GPRS)“TS 23.107 „Quality of Service (QoS) concept and architecture”TS 25.331 “Radio Resource Control (RRC) Protocol Specification”



Transferring Data –Routing, Encapsulation and Tunneling

• each user packet is assigned to a PDP context by GGSN / RNC– When more than one PDP context exists for this UE,

pick one based on associated traffic descriptors (TFT)

– Encapsulate packet with • GTP-U header (TEID)

– Allows assigning packets to PDP context at RNC / GSNs

– Masks upper layer protocol (may not be IP)

• “lower” IP header with GGSN as destination address

• Etc

⇒Routing in UMTS network controlled by operator- Using IETF protocols


Transferring Data –Address Translation; Compression

• PDP address is UE’s externally visible IP address

• Within PLMN, UE may use different IP address

⇒GGSN may perform address translation

• Redundant header information may be compressed in order to save resources on the UTRA


Detaching from the network• For example triggered by…

– … UE (e.g. switching it off)– …SGSN, when no Routing Area Update is received from UE (soft state)

• …involves– PDP context deactivation

• PDP State becomes “inactive”• Triggered actively by UE or… • …GSNs

– Triggered by Mobility Management State becoming IDLE (by time-out) or PMM-DETACHED (by performing GPRS Detach)

– Triggered by switching off UE

• Results in deletion of PDP context information at RNC and GSNs

– GPRS Detach• Mobility Management State becomes PMM-Detached• Triggered actively by UE or…• …SGSN when no periodic location update received • Results in deletion of user data in SGSN, and message to HLR

– Release of RRC Connection


Detaching from the network:Sequence Chart for user-initiated GPRS Detach

3. IMSI Detach Indication

2. Delete PDP Context Response

1. Detach Request 2. Delete PDP Context Request

5. Detach Accept

MS BSS/UTRAN GGSNSGSN MSC/VLR

4. GPRS Detach Indication

6. PS Signalling Connection Release

C2

C1


Identities Summary• Identities concerned with location

– PLMN identity = MCC + MNC– LAI = MCC + MNC + LA Code– RAI = MCC + MNC + LA Code + RA Code– URA identity– CGI = MCC + MNC + LA Code + cell identity

• Identities concerned with user– IMSI = MCC + MNC + MSIN

• Unique USIM ID– P-TMSI

• Temporary USIM ID when using PS Domain– IMEI

• Equipment identity– MS-ISDN

• “telephone number” for addressing UE via CS domain• Only unique, permanent, publicly known UE identifier

– PDP address (may be temporary) = IPv4 or IPv6 address• For addressing via PS domain

• Identification of PDP context– NSAPI (at UE)– TEID (in network)

• Identification of destination network and consequently GGSN– APN

Cf. 23.060 Sec. 14 and 23.003


Information Storage• UE maintains

– Mobility Management State

– PDP State

• SGSN maintains for each UE attached– Mobility Management State

– PDP State

• GGSN maintains for each PDP context– PDP State

• HLR maintains– Static user subscription data

– Current SGSN

Cf. 23.060 Sec. 13


Summary• Accessing the network

– Finding the access point

– Localizing UE

• Hierarchical organization of localization information– LA, RA, URA; cell

– Establishing connectivity for signaling: RRC Connection Set-up

– Registration: GPRS attach

– Establishing connectivity for data transfer: PDP context activation

• PDP context characterized by PDP address, APN and QoS

• Transferring Data

– Each packet assigned to a PDP context

• Detaching from network

– PDP context deactivation, GPRS detach, RRC Connection release

• UMTS end-to-end services are organized into layered Bearer services

• UE is always in one of three Mobility Management States

– PMM-detached – PMM-idle - PMM connected

• UE is always in one of two PDP states

– Active or inactive

umts basic funct ix 0405 - 1-4-5.netdmm/ngn/umts_basic_funct_ix_0405.pdfws 04/05, tkn tu berlin,...

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