Supporting Packet-Data QoS in Next-Generation Cellular Networks R. Koodli and Mikko Puusk ari Nokia Research Center IEEE Communication Magazi ne Feb, 2001
Dec 21, 2015
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
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 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
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
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
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