Supporting Packet-Data QoS in Next-Generation Cellular Networ

ks

R. Koodli and Mikko Puuskari

Nokia Research Center

IEEE Communication Magazine

Feb, 2001

Introduction

• Traditional circuit-switched networks that support basic voice are now to support packet-switched data services

• 3G: evolution of cellular network architectures are to be multi-service platforms supporting voice, video and data services

• QoS is crucial issue for packet data services, especially in bandwidth-constrained and error-prone environment

Introduction

• UMTS (Universal Mobile Telecommunication Systems) are defined by 3GPP (Third Generation Partnership Project) Release 1999

• Based on GPRS (General Packet Radio Service)

Background• UMTS phase one encompasses both circuit-

switched networks (GSM) and packet-switched networks (GPRS) evolution

• SGSN (Serving GPRS support node)– handles terminal mobility and authentication

functions– is connected to BSS (base station subsystem) and to

GGSN over an IP backbone network

• GGSN (Gateway GPRS support node)– handles accounting of resource usage– edge IP router

Network view of regular GPRS

GPRS Operation and PDP Contexts

• MS (mobile station) initiates a GPRS attach procedure, known to the SGSN

• Once attached, activate a Packet Data Protocol (PDP) context to send or receive packet data

• PDP context: – network layer protocol, is a virtual connection betwe

en the MS and GGSN– includes an identifier (eg. IP), QoS parameters etc.– establish a GPRS “tunnel” between GGSN and SGS

N using GPRS Tunneling Protocol (GTP)

QoS Approach in current GPRS

• QoS profile (to each PDP context) consists of:– delay: acceptable transfer time from one edge of G

PRS system to the other edge– service precedence: drop preference during networ

k abnormalities– reliability: tolerance for error rates and need for r

e-transmission– mean throughput, peak throughput: specify averag

e rate and maximum rate

Current GPRS QoS

• GPRS performs admission control based on QoS profile requested in PDP Context Activate message and availability of resources

• actual algorithms used for admission control are not specified (can be vendor- or operator-specific)

Current GPRS QoS

• When PDP Context Activate succeeds:– SGSN maps QoS profile into appropriate Radio

Link Control (RLC)/Medium Access Control (MAC) priority level to indicates the use in uplink access

– SGSN also maps accepted QoS profile into an appropriate IP QoS procedure (e.g. marking in Differentiated Services for QoS provisioning over core networks

Limitations of Current GPRS QoS

• Limitations make current GPRS infeasible for supporting real-time tranffic– For a given PDP address, only one QoS profile

can be used: all application flows share same PDP context, and no per-flow prioritization is possible

– do not allow QoS re-negotiation – QoS parameters are too vague and ambiguous i

n interpreting implementations, thus raising inter-operability concerns

Limitations of Current GPRS QoS

– GPRS is designed for best-effort traffic only– In GPRS phase 1, BSS does not perform clever

resource management or simply reserving resources for higher priority flows

UMTS Packet QoS Architecture

• UMTS packet data system includes:– MS– UTRAN (UMTS Terrestrial Radio Access Networ

k)– 3G-SGSN– GGSN– HLR (home location register)– SCp (service control point)– BG (border gateway)

UMTS architecture

UMTS vs. GPRS

• UMTS is evolved from GPRS

• But, some differences in QoS approach

• 2 main QoS-related enhancements:– PDP context mechanism can support multiple a

pplication flows and provide a more flexible QoS negotiation and setup

– BSS (known as UTRAN) can support QoS for application flows with extension of GTP tunnels to RNC

UMTS vs. GPRS

• Table 1

Overview of Different Levels of QoS

• Bearer service defines characteristics and functionality established between communicating end-points for end-to-end services– UMTS control plane signaling is used to set up

an appropriate bearer that complies with end-to-end QoS of applications within UMTS

– once bearer is established, user plane transport and QoS management functions provide actual bearer service support

UMTS bearer support

Layered bearer model• TE (Terminal Equipment):

– laptop, PDA, or mobile phone

• UMTS bearer– provides QoS inside UMTS network and perfor

m QoS functions with interworking with external networks

• External bearer service– QoS support available outside UMTS, includin

g Differentiated Services, RSVP-based services, or simply best-effort service

UMTS bearer service

• Realizes QoS in UMTS network, and consists of:– radio access bearer:

• RLC-U (Radio Link Control’s User-plane) layer between RNS and MS support radio bearer service

• Iu-bearer service provides transport services between RNS can SGSN

– core network bearer• provides transport services within UMTS core netw

ork, e.g. between a SGSN and a GGSN

• based on UDP/IP datagram delivery

UMTS QoS Management Functions for Bearer Support

• Provide end-to-end QoS for each PDP context

• Control-plane and data-plane components of this architecture– admission control– bearer service manager– resource manager– traffic conditioner– packet classifier

QoS components in reference architecture

UMTS QoS Management

• Admission Control– admission control module in SGSN to accept or r

eject the PDP context activation and requested QoS

– GGSN and UTRAN verify whether they can support the bearers associated with QoS profile

• Bearer Service Manager– coordinates control plane signaling to establish,

modify, and maintain the bearer service

UMTS QoS Management• Resource Manager

– manages access to resources – provides support for QoS required for a bearer s

ervice– may achieve QoS by scheduling, bandwidth ma

nagement, and power control

• Traffic Conditioner– provide conformance of input traffic to specific

ation agreed in the bearer service– may achieve this by traffic shaping or traffic po

licing

UMTS QoS Management

• Packet Classifier– In MS, assigns packets received from local bear

er service manager to correct UMTS bearer based on DSCp, transport layer port numbers, security parameter, etc.

– In GGSN, assigns packets received from external bearer service manager to appropriate UMTS bearer

QoS Traffic Classes and Parameters• Conversation class

– conversational real-time applications: video telephony

– supported by fixed resource allocation– constant bit rate services

• Streaming class– streaming media applications: video

downloading– certain amount of delay variation is tolerable– variant of constant bit rate and real-time

variable bit rate services

QoS Traffic Classes and Parameters• Interactive class

– for services requiring assured throughput: e-commerce, interactive Web

– supported by traffic flow prioritization

• Background class– traditional best-effort services: background

download of emails and files, etc– lowest priority

Traffic classes and QoS parameters

• Table 2

QoS Negotiation and Setup

• QoS profile for a PDP context may consist of values for:– traffic class– transfer delay– traffic handling priority– etc

• per-PDP QoS provisioning

• Both MS and GGSN maintain separate filters for packet classification