Transcript Chapter 3

Chapter 3
General Packet Radio Service
(GPRS)
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GSM
A Brief Introduction
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Architecture
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Components/ Elements
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Mobile Station (MS)
Base Station Subsystem (BSS)
• Base Transceiver Station (BTS)
• Base Station Controller (BSC)
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Mobile Switching Center (MSC)
Four databases
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Home Location Register (HLR)
Visitor Location Register (VLR)
Equipment Identity Register (EIR)
Authentication Center (AUC)
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Standard Interfaces
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Um:MS-BTS
Abis: BTS-BSC
A-interface:
BSC-MSC
SIM:
Subscriber
Identity
Module
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Physical Channel
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Physical Channel (Cont’d)
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Logical Channel
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Logical Channel (Cont’d)
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TCH (Traffic Channel)
• TCH/F
• TCH/H
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Signaling channels
• BCH (Broadcast CH)->3 CHs
• CCCH (Common Control CH)->3 CHs
• DCCH (Dedicated Control CH)->3 CHs
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GSM Data
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Evolution
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CSD:Circuit-Switched Data
SMS: Short Message Service
HSCSD: High-Speed CSD
EDGE: Enhanced Data rate for GSM Evolution
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Pre-GPRS Systems
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SMS in GSM
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Two-way non-blocking packet-mode messaging
service
• Allowing non-real-time (NRT) dialog between mobile
terminals
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Transmission on GSM’s signaling channel (e.g.,
SDCCH)
• Up to 160 bytes (PTP/broadcast)
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Offered message categories
• SMS-mobile-terminated PTP (stored intermediately in
the SMS service center (SMS-SC))
• SMS-mobile-originated PTP
• Cell broadcast SMS
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HSCSD
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Aggregation of multiple slots in a GSM
frame
• Speed ranges from 14.4 kbps to 64 Kbps
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Using the existing GSM infrastructure
Affects to GSM
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Channel allocation
Connection setup
Handoff procedures
Access to the fixed network
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GPRS
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About GPRS
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Initiated in 1994 by ETSI
Services offered: PTP and PTM
Systems adopted: GSM and IS-136
Speed
• Single slot->14.4 kbps
• Multiple slot->115.2 kbps
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Web page browsing and Internet surfing
Channel allocation
• Fixed/Static or dynamic
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GPRS Network Architecture
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Elements-SGSN
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Serving GPRS Support Node (SGSN)
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Functions similar to MSC/VLR
Monitors user location
Handles charging data
Provides security via A5 ciphering algorithm
Manages sessions, mobility, and logical
channels
• QoS management: policing and scheduling
• Network access control
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Elements-GGSN
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Gateway GSN (GGSN)
• Inter-works GPRS network with external
packet-switched networks
• Data formatting
• Address translation
• Protocol conversion
• Routing of packets
• Firewall, billing, and packet filtering
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GSN
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GSN includes SGSN and GGSN
A GPRS network consists of multiple
SGSNs but only one GGSN for
internetworking
GTP (GPRS Tunnel Protocol)
• Communication protocol between two
GSNs
• User data is encapsulated and tunneled
through the IP backbone network
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GPRS Coding Schemes
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Four schemes: CS-1~CS-4
Convolutional Code
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GPRS Protocol Stack (Data Trans.)
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Protocol Description
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Layer 1/ Physical layer
• PLL (Physical Link sub-Layer)
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Data unit framing
Data coding
Error detection and correction
• RFL (Radio Frequency sub-Layer)
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Conforms to GSM 05 series recommendations
Performs modulation and demodulation
Specifies carrier freq., radio channel structures, raw
channel data rates, transceiver characteristics,
performance requirements
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Protocol Description (Cont’d)
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Layer 2/ Data link layer
• LLC (Logical Link Control)
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Supports PTM transmission
Provides secure logical pipe between MS and
SGSN
• RLC (Radio Link Control)/ MAC (Medium
Access Control)
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Provides access signaling
Resolves access contentions
Provides link level ARQ
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Protocol Description (Cont’d)
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Relay function
• In the BSS, relays LLC PDUs between
the Um and Gb interfaces
• In the SGSN, it relays packet data
protocol (PDP) PDUs between the Gb
and Gn interfaces
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Protocol Description (Cont’d)
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SNDCP (Sub-Network-Dependent
Convergence Protocol)
• Handles TCP/IP headers and data
compression
• Deals with multiplexing, encryption, and
segmentation
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BSSGP (BSS GPRS Protocol)
• QoS
• Routing between BSS and SGSN
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GPRS QoS Issues
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Access delay: 4 classes (Um~Gi)
Priority: 3 classes
Reliability: 5 classes
Mean throughput: 31 classes
Peak throughput: 9 classes (Gi~R)
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Access Delay
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The Others
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Priority classes: high, medium, and low
Reliability classes: relates to prob. Of
corruption, loss, mis-sequencing,
duplication of packets
Mean throughput classes: class 1
(0.22bps)~class 30 (111kbps), class 31
(best effort)
Peak throughput classes: 8 kbps~2048
kbps
<Remark>: delay class and mean
throughput are used by the SGSN for
scheduling and admission control
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MSDRA MAC Protocol
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MSDRA: Master-Slave Dynamic Rate
Access
Channel concept
• PDCH (Packet Data CHannels)
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Channels are dedicated to packet mode
transfer
Uplinks and downlinks are basically used as
independent channel resources
Further divided into MPDCH (Master PDCH)
and SPDCH (Slave PDCH)
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Channel Concept (Cont’d)
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SPDCHs: the channels on which user data
and signaling is transferred
• Packet Traffic Channels (PTCHs)
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Dedicated to one MS or a group of MSs used for user
data transfer
• Packet-Associated Control Channels (PACCHs)
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Transport signaling info related one MS
• Packet Data Broadcast Channels (PDBCHs)
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Downlink to broadcast user data
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Channel Concept (Cont’d)
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MPDCHs: accommodate Common Control
Channels (CCHs) that carry the signaling
information required to initiate packet transfer
• PRACH (Packet Random Access CH)
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Uplink to initiate data transfer of the MS
• PPCH (Packet Paging CH)
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Downlink to inform MSs about incoming packets
• PPRCH (Packet Paging Response CH)
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Uplink to respond to paging
• PAGCH (Packet Access Grant CH)
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Downlink to send CH reservation info to an MS
• PBCCH (Packet Broadcast Control CH)
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Downlink to broadcast all GPRS-specific info.
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Phases of MAC
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MAC is based on a slotted ALOHA
reservation protocol which has three
phases on the uplink
• Contention phase
• Notification
• Transmission
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Two phases on the downlink
• Notification
• Transfer
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PRACH Performance Analysis
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RACH and PRACH: slotted ALOHA
with retransmission (# of max.
retrx.=7)
Assumption
• Equal new call arrival rates
• System is memoryless
• Capture effect is considered
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Performance Analysis (Cont’d)
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For infinite number of users, PDF of
interfering packets is Poisson
where G is total access attempts
 Pc(Su|n): the prob of success of a test
packet given n interfering packets
 PC(Su|n)=Pr(Pt>zPn), z is the capture
ratio
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Performance Analysis (Cont’d)
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Pc(Su|n) is given
by
Pc(Su) is given by
The access
throughput is
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Performance Analysis (Cont’d)
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The prob that a
packet will be
successfully
exactly k
transmissions
Average number of
transmissions
needed for a
successful
reception
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Performance Analysis (Cont’d)
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Channel Allocation for GPRS
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Packet Data Traffic
CH (PDTCH)
Packet Common
Control CH (PCCCH)
Packet Dedicated
Control CH (PDCCH)
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Allocation Algorithms
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Fixed resource allocation (FRA)
Fixed resource allocation with queue
capacity (FRAQ)
Dynamic resource allocation (DRA)
Dynamic resource allocation with
queue capacity (DRAQ)
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EGPRS (EDGE)
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Initiated in 1997
Using the GPRS core network but a
new air interface with 8 coding
schemes
8-PSK modulation
Max data rate: 384 kbps
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References
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Book: Wireless Personal Communications
Systems by D. J. Goodman
Paper: GPRS-features and packet random
access channel performance analysis by A.
Gyasi-Agyei et al.
Paper: Concepts, services, and protocols
of new GSM phase 2+ General Packet
Radio Service by G. Brasche et al.
Paper: Channel allocation for GPRS by
Phone Lin et al.
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