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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 packetswitched 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 errorprone 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 circuitswitched 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-toend 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: ecommerce, 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