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 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

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