Supporting Packet-Data QoS in Next-Generation Cellular Networks

1
Supporting Packet-Data QoS in Next-Generation
Cellular Networks

• R. Koodli and Mikko Puuskari
• Nokia Research Center
• IEEE Communication Magazine
• Feb, 2001

2
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

3
Introduction

• UMTS (Universal Mobile Telecommunication Systems)
  are defined by 3GPP (Third Generation Partnership
  Project) Release 1999
• Based on GPRS (General Packet Radio Service)

4
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

5
Network view of regular GPRS
6
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
  between the MS and GGSN
• includes an identifier (eg. IP), QoS parameters
  etc.
• establish a GPRS tunnel between GGSN and SGSN
  using GPRS Tunneling Protocol (GTP)

7
QoS Approach in current GPRS

• QoS profile (to each PDP context) consists of
• delay acceptable transfer time from one edge of
  GPRS system to the other edge
• service precedence drop preference during
  network abnormalities
• reliability tolerance for error rates and need
  for re-transmission
• mean throughput, peak throughput specify average
  rate and maximum rate

8
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)

9
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

10
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 in
  interpreting implementations, thus raising
  inter-operability concerns

11
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

12
UMTS Packet QoS Architecture

• UMTS packet data system includes
• MS
• UTRAN (UMTS Terrestrial Radio Access Network)
• 3G-SGSN
• GGSN
• HLR (home location register)
• SCp (service control point)
• BG (border gateway)

13
UMTS architecture
14
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
  application 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

15
UMTS vs. GPRS

• Table 1

16
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

17
UMTS bearer support
18
Layered bearer model

• TE (Terminal Equipment)
• laptop, PDA, or mobile phone
• UMTS bearer
• provides QoS inside UMTS network and perform QoS
  functions with interworking with external
  networks
• External bearer service
• QoS support available outside UMTS, including
  Differentiated Services, RSVP-based services, or
  simply best-effort service

19
UMTS bearer service

• Realizes QoS in UMTS network, and consists of
• radio access bearer
• RLC-U (Radio Link Controls 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
  network, e.g. between a SGSN and a GGSN
• based on UDP/IP datagram delivery

20
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

21
QoS components in reference architecture
22
UMTS QoS Management

• Admission Control
• admission control module in SGSN to accept or
  reject 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

23
UMTS QoS Management

• Resource Manager
• manages access to resources
• provides support for QoS required for a bearer
  service
• may achieve QoS by scheduling, bandwidth
  management, and power control
• Traffic Conditioner
• provide conformance of input traffic to
  specification agreed in the bearer service
• may achieve this by traffic shaping or traffic
  policing

24
UMTS QoS Management

• Packet Classifier
• In MS, assigns packets received from local bearer
  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

25
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

26
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

27
Traffic classes and QoS parameters

• Table 2

28
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