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

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

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 in 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 Network) –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 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

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 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

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 network, 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 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

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

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

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 s 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