Packet switching concepts

Mahmoud Farid

Contents• Brief introduction.• GPRS network structure.• Mobility management.• Session management.• EPC overview.

What is packet switching?

• Packet switching is a digital networking communications method that groups all transmitted data into suitably sized blocks, called packets, that are transmitted via a medium that may be shared by multiple simultaneous communication sessions.

• Packet switching increases network efficiency, robustness and enables technological convergence of many applications operating on the same network.

Evolution of mobile generation GSM (2G): Circuit switching with data rate 9.6 Kb/s. HSCSD(2.15G): Circuit switching with data rate 14.4 Kb/s. GPRS (2.5G): the first generation to introduce the packet

switching, with a data rate up to 21.4 Kb/s per physical channel, also it introduced the new extension to the network with the new nodes i.e. (SGSN, GGSN, and CG).

EDGE (2.75G): data rate up to 69.2 Kb/s. UMTS (3G): data rate up to 2 Mb/s. HSPA: 14 Mb/s. HSPA+: 84 Mb/s. LTE: 150 Mb/s. LTE+: 1 Gb/s.

GPRS network structure

GPRS network structure (SGSN)• Important Entity Function: SGSN

– Mobility management• The MM functions are used to keep track of the current

location of an MS within the PLMN or within another PLMN.– Session management

• SM function manages the PDP context of MS.– Routing and transfer

• SGSN performs routing and forwarding of service data between MS and GGSN.

– Charging• SGSN can generate, store, convert and send CDRs.

– NTP

GPRS network structure (GGSN)

• Important Entity Function : GGSN

– Session management

• SM function manages the PDP context of MS.

– Routing and transfer

• GGSN performs routing and forwarding of service data between MS and internet.

– Charging

• GGSN can generate, store, convert and send CDRs.

– Dynamic IP allocation

– Service management

• Manage APN

GPRS network structure (CG)

• Important Entity Function: CG

– Real-time collection of GPRS CDRs

– Temporary storage and buffering of GPRS CDRs

– Pre-processing of GPRS CDRs

– Sending GPRS CDRs to the billing center

GPRS network structure (DNS)

• Resolve the APN to a GGSN IP in the PDP active procedure

• Resolve the RAI to a SGSN IP in the inter-SGSN RAU procedure

• Resolve the RNCID to a SGSN IP in the relocation procedure (UMTS)

Mobility management

GPRS mobility management statesGPRS attach and detachSecurity function

Mobility management states(GSM)

Mobility management states(UMTS)

GPRS Attach

GPRS Detach-MS initiated

Depending on the type

GPRS detach• Results after any Detach procedure:

– The SGSN shall not service the detached MS, unless reattach– The MS is in idle or PMM-DETACHED state

• The MS is detached either explicitly or implicitly: – Explicit detach: The network or the MS explicitly requests detach – Implicit detach: The network detaches the MS, without notifying the

MS, a configuration-dependent time after the mobile reachable timer expired, or after an irrecoverable radio error causes disconnection of the logical link.

Security functionAuthentication

• Authentication types:

– GSM Authentication

• Using triplet: RAND, SRES, Kc

• Using GPRS Encryption Algorithm (GEA)

– UMTS Authentication

• Using quintet: RAND, XRES, AUTN, CK, IK

– AUTN: for UE authenticate network

– IK: for data integrity function

• Using UMTS Encryption Algorithm (UEA)

Security functionAuthentication

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1a. Send Authentication Info

2a. Authentication and Ciphering Request 1b . Send Authentication Info ack

2b. Authentication and Ciphering Response

MS BSS/UTRAN HLR/Auc SGSN

Security function-Identity Check

• Function– Get IMSI from MS– Check the IMEI

Page18

1. Identity Response 2. Check IMEI

1. Identity Request

2. Check IMEI Ack

MS BSS/UTRAN EIRSGSN

Security functionP‑TMSI Reallocation

• Function– The SGSN may reallocate the P TMSI at any time‑ – The reallocation procedure can be performed by the P TMSI Reallocation ‑

procedure – The P TMSI can be included in the Attach or Routeing Area Update ‑

procedures.

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2. P-TMSI Reallocation Complete

1. P-TMSI Reallocation Command

MS BSS/UTRAN SGSN

Session management

Important concepts PDP context activation/modification/deactivation

Important concepts- PDP Context– The PDP context is Packet Data Protocol context – PDP context contains all the information needed to transfer user data

between MS and GGSN.– The context includes parameters such as Routing, QoS (Quality of

Service), Charging ID etc.– PDP context exists in MS, SGSN, GGSN and RNC.

Important concepts – PDP state

Deactivate PDP Contextor

MM state change to IDLEor PMM-DETACHED

Activate PDPContext

INACTIVE

ACTIVE

PDP state inactive： cannot transmit data active： can transmit data

Important Concepts __ QoS

QoS is quality of serviceIt is a group of parameters that can define the network ability, such as the bit rate for downlink or uplink data transmission and the reliability class and so on

Important Concept __ APN

APN structure: APN_NI+APN_OI

ericsson.com.cn.mnc<MNC>.mcc<MCC>.gprs

APNNetwork ID

APNOperator ID

PDP activation in 2G

PDP activation in 3G

PDP deactivation

EPC overview

EPC highlightsEPC network structure

Evolution from 3G to LTE

nodeB

nodeB

RNC

RNC

SGSN

SGSN

GGSN

GGSN

PDN

PDN

3GPP Rel-99

3GPP Rel-7

User plane traffic through all nodes

User plane outside of SGSN

EnodeB

MMESAE GW

PDN

3GPP Rel-8 User plane directly between RAN and GW for all LTE traffic.

EPC Highlights

Separation

All IP

Bandwidth

Access

Separation of control plane from user plane, thus providing a flattened architecture with less latency on the user plane and less cost to scale whether it’s more bandwidth or more users required, We have seen how the control plane and user plane have been separated: MME becoming a sole signaling node and the eNodeB connecting directly to the Serving GW for the user plane.

All IP, non-existent CS domain in core network. The interfaces in the EPC are all IP, there are no ATM, Frame Relay, SS7 interfaces. It’s a entirely data centric architecture.

Maximum downlink rate > 400Mbps, with the introduction of LTE-Advanced. Access agnostic, supporting multiple access modes of 3GPP and non-3GPP.

We now have a Packet Core architecture that can communicate and talk to many access types…from our usual 3GPP networks such as 3G/LTE and non-3GPP networks like Wi-Fi for example.

EPC Highlights

EPC TerminologyEPS – Evolved Packet System

LTE – Long Term Evolution

EPC – Evolved Packet Core

SAE – System Architecture Evolution

LTE/EPC Architecture

LTE/EPC interfaces

Voice service overview in LTE network

Voice service overview in LTE network SVLTE (Simultaneous Voice and LTE):The UE supports CS and LTE at same time. CS provides voice service, LTE provides data services. CS is at 2G/3G network, so in SVLTE, UE both attach in 2G/3G and 4G. this method all depends on UE capacity, network side has no requirement. CSFB (circuit switched fall back):The UE fall back to 2G/3G for MO (Mobile Originated) and MT (Mobile Terminated) voice service. VoLTE and SRVCC(Single Radio Voice Call Continuity ):UE establishes LTE bearer and IP connection to IMS domain. The service is between UE and IMS, includes establishment, modification, release. Besides voice between Mobile subscribers, IMS can provide mobile voice to traditional fixed voice, different operators voice call too.The 4G doesn’t cover all areas, During voice call, the SRVCC or eSRVCC support handover from 4G to 2G/3G. OTT (Over The Top):The web browsing, video in mobile network is all OTT service. From the encapsulation view, PS is a tunnel and all service is in it.

CSFB quick look

Thank you..