gsm gprs edge overview
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Course 335
GSM 2.5G Migration:General Packet Radio Service GPRS
GSM 2.5G Migration:General Packet Radio Service GPRS
10-2001 5 - 1GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
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What’s GPRS All About? How Does It Fit In?
10-2001 5 - 2GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
GSM: Global System for Mobile Communication
• The world’s most widely used wireless phone technology
– Over 500,000,000 users worldwide!
– TDMA-based radio interface, 200 kHz.-wide signals
• But very limited data capability
– 9,600 or 14,400 bps maximum in circuit-switched mode
WCDMA / UMTS: The Long-Term 3G Data Solution• Uses spread-spectrum CDMA techniques, 4-MHz.-wide signals
• Provides both voice and high speed packet data access
• But not widely deployed and available until late 2004 or later
GPRS: General Packet Radio Service
• A packet-switched IP-capable way of using GSM radio infrastructure
• Defined in 1996, wide deployment beginning in 2001
• Provides both interim pre-WCDMA and long-term packet access
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Communications Technology Family History A Story of Births, Weddings and Funerals
Commercial telegraphy gave birth to telephony, then died
Telephony and Land Mobile Radio married, giving IMTS & Cellular
IP networks developed, their usage and bandwidth are increasing
The wedding of IP and Wireless is happening now in 3G!
1900s 2000s1800s10 20 30 40 50 60 70 80 90 10 20 3050 60 70 80 90
Commercial Telegraphy
Commercial Switched Telephony
Wireless Voice and IP Data
40 50
Digital Swiing
IMTS-Cellular-GSM-GPRS-WCDMA
IP NetworksThe Internet Voice over IP
Land Mobile RadioHF, VHF, UHF, Trunked
Extinction!
Extinction?
Extinction?
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GSM and GPRS
Background: GSM TechnologyThe Foundation of GPRSBackground: GSM TechnologyThe Foundation of GPRS
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The Beginnings of GSM
10-2001 5 - 5GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
1980’s: Europe used variety of first generation analog cellular systems: TACS, ETACS, NMT450, NMT900, Netz, etc.
• Operation was limited to various national boundaries
• Poor roaming capabilities, poor economies of scale in mfg.
In 1982, CEPT the Conference of European Posts and Telegraphscreated a group to study and define a 2G Pan-European system
• Group Spécial Mobile (GSM)• In 1989, administration of GSM was transferred to the
European Telecommunications Standards Institute (ETSI)
• In 1990, the GSM specification, Phase I, was published
GSM has become very popular due to many positive factors
• Non-proprietary: anyone can manufacture networks/handsets
• Thorough/integrated standard: well-defined RF air interface,
network architecture, call delivery and roaming features
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GSM World ACeptance
GSM commercial deployment beganin 1991
By 1993, there were 36 GSMnetworks in 22 countries
In 2000, there were over 200 GSMnetworks in over 110 countries
around the world• Operation in 900 MHz., 1800
MHz., and 1900 MHz. bands
The wide aCeptance of GSM has provided tremendous
economies of scale in network, handset, and test equipmentmanufacturing and distribution
Worldwide in 2001, GSM users have passed the 500 million mark
• One in 12 human beings uses a GSM phone!
The global dominance of GSM provides a large market for the2.5G and 3G enhancements GPRS and UMTS WCDMA
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GSM vs. North American Standards
10-2001 5 - 7GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
Two different approaches to wireless technology development!
• Americans: Invent cool new stuff driven by market forces, writestandards if it works and the market aCepts it
• Europeans: Study, Plan, build Standards, build Consensus, Plan,Review, build more Consensus, finally Deploy
The differences are visible in the resulting standards
• American: multiple interim standards necessary to define functionality
• Europeans: single integrated standard covers all functionality
Other Features
Air InterfaceRF Architecture
Network Architecture
Intersystem Roaming,Call Delivery, Handoff
The GSM StandardOne coordinated, uniformly
structured family of documents
IS-95/J-Std 008 CDMA
IS-634 A-interface
IS-41C, D, P
IS-637SMS
IS-683OTA
IS-707Data
Etc.
North American CDMA GSM
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GSM Terminology
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Some terms have differentmeanings when used in GSMor North American practice!
Sector
β
Sector
α
Sector
γ
CELL Cell
β
Cell
α
Cell
γ
BTS
It’s a Sector! It’s a Cell!
Sector
β
Sector
γ
Cell
β
Cell
γ
That was a Handoff! That was a Handover!
The frequencies used
by each sector areits channel set.
The frequencies used
by each cell areits allocation.
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The Frequencies Used by GSM
GSM Uplink
124 ch.
GSM Downlink
124 ch.
1850
915 935 960
A
75 ch.
D
25
B
75 ch.
E
25
F
25
C1
25
C2
25
C3
25
1865 1885 1900 1910 1930 1945 1965 1975 1990
890
A
75 ch.
D
25
B
75 ch.
E
25
F
25
C1
25
C2
25
C3
25
Europe and International
North American PCS Licensed Blocks
MHz.
MHz.
GSM operates in a variety of frequency bands worldwide
GSM carrier frequencies are normally assigned in 200 KHz.Increments within the operator’s licensed block of spectrum
Spectrum is provided in “blocks”
• Base stations transmit in the upper block
• Mobiles transmit in the lower block
Each cell uses a certain number of carriers, called its “allocation”
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Channels in GSM: Repeating Patterns
10-2001 5 - 12GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
Channels of information in GSM oCupy physical timeslots of the GSMsignal in repeating patterns
• Similar to the way that classes and activities of a university oCupy the
physical classrooms on a defined schedule – Some classes meet daily, some only three days a week
– Some labs once or twice a week
– Meals daily in the cafeteria, movies on Friday nights
– Graduation ceremonies each semester
Dedicated channels (carrying traffic or control information for individualusers) oCur in a repeating 26-multiframe pattern 120 ms long
• 24 frames are used for traffic, one for SACH, one is unused
• Full-rate s oCur in each traffic frame
• Half-rate s (if used) oCur in alternating traffic frames
• 1/8 rate dedicated channels are defined for special purposes and arecalled SDCHs (Stand-Alone Dedicated Control Channels)
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A GSM Uplink Normal Burst
GSM is a TDMA system and a mobile’s transmission bursts are carefullyconstructed not to overlap with bursts from other mobiles
Different propagation delays of mobiles near and far mobiles the BTS are
compensated by automatically advancing mobile transmit timing Special training sequences are included in each uplink burst and downlink
timeslot to facilitate demodulation
During unused timeslots, a mobile measures the strength of surroundingbase stations to guide the handover process (this is called MAHO, Mobile
Assisted Hand Over)
10-2001 5 - 16GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
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GSM Bursts on the Uplink: 4 Types
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Stealing
Bit
Stealing
BitNormal Burst
Guard
BitsData Bits Training Bits Data Bits T a
i l
T a
i l
3 57 bits 1 26 bits 1 57 bits 3 8.25 bits
Guard
Bits T a i l
T
a i l
Data Bits Training Bits Data Bits
Synchronization Burst
3 39 bits 64 bits 39 bits 3 8.25 bits
Guard
Bits T a i l
T a i l
Fixed ‘0’ or Fill-in Bits
Frequency Correction Burst or Dummy Burst
3 142 bits 3 8.25 bits
ACess Burst
Tail
Bits
Guard
BitsTraining Bits Data Bits T
a i l
8 41 bits 36 bits 3 68.25 bits
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GSM Channels
DOWNLINK CHANNELS UPLINK CHANNELS
BCHBTS identity, channel allocation,
frequency hopping sequences
10-2001 5 - 18GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
FCH RACHProvides frequency referenceSlotted aloha channel used to
request network aCess
SCHDefines burst period boundaries
and time slot numbering
PCHCarries pages to mobiles,
alerting of incoming calls
SDCHStand Alone Dedicated
Control Channel AGCH Allocates SDCH to mobile to
obtain dedicated channel after
a request on the RACHTraffic Channel
BTS FACHFast Associated Control
Channel
SACHSlow Associated Control
Channel
F-TRAFFIC
SDCH
FACH
0 to many
SACH
Traffic Channel
Fast Associated Control Channel
Slow Associated Control Channel
Stand Alone DedicatedControl Channel
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The GPRS Timeslot Allocation
In conventional GSM, a channel is permanently allocated for a particular user during the entire call period (whether speaking or silent, whether transmitting data or not)
• In GPRS, the channels are only allocated when data packets aretransmitted or received, and they are released after the transmission
• For bursty traffic this results in much more efficient use of the scarceradio resources
• Multiple users can share one channel
BTS
GPRS allows a single mobile totransmit and/or receive on multiple
timeslots of the same frame (this iscalled multislot operation)
• This provides “bandwidth ondemand” in a very flexiblescheme
• One to eight timeslots per framecan be allocated to a mobile
• Uplink and downlink allocationscan be allocated separately,which efficiently supports
asymmetric data traffic (suitablefor web browsing, for example)
•This GPRS mobile is in “3+1” timeslot mode
•3 timeslots assigned on downlink
•1 timeslot assigned on uplink
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Allocation of GPRS Channels
10-2001 5 - 20GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
A cell supporting GPRS may allocate physical channels for GPRS traffic
Such a physical channel is denoted a Packet Data Channel (PDCH)
• The PDCHs are taken from the common pool of all channels available
in the cell• The radio resources of a cell are shared by all GPRS and all non-
GPRS mobiles in the cell
• The mapping of physical channels to either GPRS or GSM usage canbe performed dynamically, based on:
– Capacity on demand principle
– Depending on the current traffic load, priority of service, and themultislot class
A load supervision procedure monitors the PDCHs in the cell
The number of channels allocated to GPRS can be changed aCording tocurrent demand
• Physical channels not currently in use by conventional GSM can beallocated as PDCHs to increase the GPRS quality of service
• When there is a resource demand for services with higher priority,PDCHs can be de-allocated
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3 Steps to 3G: The GSM Transition
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3 Steps to 3G: The GSM Transition
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UTRAN
Core Network
Core Network
BSCBase
StationController
BSCBase
StationController PCU
BTSBase
Transceiver Stations
BTSBase
Transceiver Stations
SIM
MobileEquipment
Gateway
MSC
VLR
HLR
MSCMobile
Switching
Center
Gateway
MSC
VLR
HLR
MSCMobile
Switching
Center
GatewayGPRSSupport
node
ServingGPRSSupport
node
Core Network
Gateway
MSC
VLR
HLR
MSCMobile
Switching
Center
Gateway
GPRSSupportnode
Serving
GPRSSupportnode
UMTSSIM
MobileEquipment
RNCRadio
NetworkController
RNC
RadioNetworkController
Node B
Node B
Node B
Node B
Internet
ISDN
PLMN
PSTN
Internet
ISDN
PLMNPSTN Mobile
Station
SIM
MobileEquipment
MobileStation
2.5G: GSM + GPRS
GSM TODAY
Internet
ISDN
PLMNPSTN
User
Equipment
3G: UMTS, UTRA
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Architecture of a Phase-1 GSM Network
Core Network
Gateway
MSC
VLR
HLR
MSCMobile
Swiing
Center
BSCBase
StationController
BTSBase
Transceiver Stations
Internet
ISDN
PLMNPSTN SIM
MobileEquipment
MobileStation
EIR AuC Abis
Interface
A
Interface
Um
Interface
EIR - Equipment Identity Register
AuC - Authentication Center
HLR - Home Location Register
VLR - Visitor Location Register
BSC - Base Station Controller
BTS - Base Transceiver Station
SIM - Subscriber Identity Module
ME - Mobile Equipment
MS - Mobile Station
PLMN - Public Land Mobile Network
PSTN - Public SwiedTelephone Network
ISDN - Integrated Services Digital Network
GMSC - Gateway Mobile SwiingCenter
MSC - Mobile Swiing Center
GSM Functional Entities and Network Elements
The network elements and interfaces of GSM are standardized
This provides for inter-vendor participation in operators’ networks
• Competition improves quality, provides economies of scale
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GPRS B kb N t k
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GPRS Backbone Networks
Two kinds of GPRSbackbones:
• Intra-PLMN amongGSNs of same PLMN(private, IP-based)
• Inter-PLMN amongGSNs of differentPLMNs (roamingagreements)
Gateways between thePLMNs and the externalinter-PLMN backbone arecalled Border Gateways
• Border Gateways perform security functions to prevent unauthorizedaCess and attacks
The Gn and GP interfaces are also defined between two SGSNs• This allows exchange of user profiles as mobiles move around
The Gf interface allows a SGSN to query the IMEI of a registering mobile
The Gi interface connects the PLMN to external public or private PDNs
• Interfaces to IPv4, IPv6, and X.25 networks are supported The Gr interface allows an SGSN to communicate with an HLR
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GPRS S i
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GPRS Services
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GPRS bearer services provide end-to-end packet-swied data transfer.There are two kinds:
PTP Point-to-Point Service, available now, has two modes:
• PTP Connectionless Network Service (PTP-CLNS) for IP
• PTP Connection-oriented network Service (PTP-CONS) for X.25
PTM Point-to-Multipoint Service (available in future releases)
• PTM-M Multicast Services broadcasts packets in certain geographicalareas; a group identified indicates whether the packets are intended
for all users or for a group• PTM-G Group Call Service addresses packets to a group of users
(PTM group) and are sent out in geographical areas where the groupmembers are currently located
SMS Short Message Services
Supplemental Call Services:
• CFU Call Forwarding Unconditional, CFNRc Call ForwardingSubscriber Not Reachable, CUG Closed User group
Non-Standard Services may be offered at GPRS service providers
• Database aCess, messaging, e-transactions, monitoring, telemetry
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Serving GPRS Support Node (SGSN) Functions
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Serving GPRS Support Node (SGSN) Functions
10-2001 5 - 34GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
The Serving GPRS Support Node(SGSN) is responsible for the followingto and from the mobile stations in itsservice area:
• Packet Routing and Transfer • Mobility management (attach/detach
and location management)
• Logical Link management
• Authentication and chargingfunctions, encryption
• Compression (optional)
• Location register of SGSN storeslocation (cell, vlr) and user profiles
A typical PLMN network will start withonly one SGSN
Each BSC has a PacketCommunications Unit, PCU
• Similar hardware provides thePCUSN function
Several models of the
Nortel Passport Swi
for SGSN and PCUSN service
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The MS-SGSN Interface
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The MS SGSN Interface
Physical BSC
Packet Controller functions are provided bythe PCU, which is implemented in aphysical PCUSN in the BSS
• The PCUSN handles the GPRS-
specific packet processing using framerelay protocols
• The PCUSN connects to the BSC withnetwork manufacturers’ proprietary Agprs
interfaces
• The PCUSN connects to the SGSN viathe standard-defined Gb interface
Although a PCUSN can optionally servemore than one BSC, all channels from one
BSC must pass through the same PCUSN
TRAU frames from the mobile pass throughthe BTS to the BSC and on into the PCUSN
SGSNBSC
BTS
MS
GbPCUSN
MSC
ATCU
Agprs
Ater
VLR
PCUSN and PCU Distinction
•A PCUSN (Packet Controller Unit ServingNode) is the hardware unit which implements
the PCU (Packet Controller Unit) function
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The Gn Interface: SGSN-GGSN
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n
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SGSN
GGSN
GGSN
BSCBTS
BTS
SMS-GMSC
SMS-IWMSC
MSEIR
MSCVLR
HLR
PDN
OTHER
GPRS PLMNGd
Gf
D
Gs Gr
Gn
Gc
GiGb
Gp The SGSN and GGSN are linked by aGPRS backbone using IP routing
The Gn interface creates and operates
through secure tunnels, using theGPRS Tunneling Protocol (GTP)
The GTP packet headers include
• Tunnel endpoint and group identity
• PDU type• QoS parameters
• Routing protocol identification
– Static, RIP2, OSPF
Beneath IP, any transport architecturecan be used
• Ethernet, Token-Ring, FDDI, ISDN, ATM
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The Gf Interface: SGSN-EIR
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SGSN
GGSN
GGSN
BSCBTS
BTS
SMS-GMSC
SMS-IWMSC
MSEIR
MSCVLR
HLR
PDN
OTHER
GPRS PLMNGd
Gf
D
Gs Gr
Gn
Gc
GiGb
Gp The Gf interface connects the SGSNand the Equipment Identity Register (EIR)
The Gs Interface: SGSN-MSC/VLR
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SGSN
GGSN
GGSN
BSCBTS
BTS
SMS-GMSC
SMS-IWMSC
MSEIR
MSCVLR
HLR
PDN
OTHER
GPRS PLMNGd
Gf
D
Gs Gr
Gn
Gc
GiGb
Gp The Gs interface is optional
• Provides simultaneous GPRS andGSM operation between SGSN and
MSC/VLR (same as BSSMAP butoptional)
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Quality of Service
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ReliabilityProbability of
Class LostPacket
Dupli-cated
Packet
Out-of SequencePackets
Corrupt-ed
Packets
1 109 109 109 109
2 104 105 105 106
3 102 105 105 102
Service Precedence
High
Medium
Low
10-2001 5 - 54GSM 2.5G Migration: GPRS v1.28 (c)2001 Scott Baxter
Mobile packet applications have a wide range of reliability expectations --real-time multimedia, Web browsing, email transfer
QoS Classes settable per session are a very important feature
• Service Precedence
– Priority of a service in relation to other services
• Reliability
– Required transmission characteristics (3 classes defined)
• Delay
– Maximum values for mean delay and 95-percentile delay
• Throughput
– Maximum-Peak bit rate and the mean bit rate
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Mobile Classes and Simultaneous Usage
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In a GSM network, two classes of service can run concurrently:• Circuit-Swied Services (speech, data, and SMS)
• Packet-Swied Services (GPRS)
Three Classes of Mobile Stations are defined:
• Class A mobiles
– Support simultaneous operation of GPRS and conventional GSMservices, but two separate radio chains are required
• Class B mobiles
– Able to register with the network for both GPRS and conventionalGSM services simultaneously, but can only use one of the twoservices at a given moment - voice can pre-empt data
• Class C mobiles
– Able to attach for either conventional GSM or GPRS, manuallyswied
– Simultaneous registration (and usage) is not possible, except for SMS messages which can be received and sent at any time
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GPRS
Session Management
Mobility ManagementRouting
Session Management
Mobility ManagementRouting
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Location Management
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The main task of location management is to keep track of theuser’s current location
• This allows incoming packets to be routed to the MS
The MS frequently sends location update messages to its SGSN• If the mobile sends updates infrequently, its location is not
known and paging is necessary for each downlink packet(adding considerable delay)
• If the mobile sends updates frequently, its location is wellknown and data packets can be delivered with no paging delay
• Location updates consume battery power and uplink radiocapacity, so a balance is required to optimize resource usage
To optimize the location management function in GPRS, a statemodel has been created and applied
The GPRS Location Management State Model
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A mobile can be in any of three statesdepending on its current traffic level
• Location update frequency is dependent
on the MS state In IDLE state, the mobile is not reachable
Performing a GPRS attach, the mobileenters the READY state
With a GPRS detach the mobile maydisconnect from the network and fall backinto the IDLE state
• all PDP contexts will be deleted
The STANDBY state is reached when a MSdoes not send any packets for a long period
• The READY timer expires
IDLE
READY
STANDBY
GPRSdetach
GPRSattach
Trans-mission
of apacket
S T A N D B Y T i m e r E x
p i r e d
READYtimer
Expired or Forced toStandby
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Inter-SGSN Routing Area Updates
MS BSS SGSN
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Routing area update request[Old RAI, old P-TMSI signature,
Update type]
Security functions
Routing area update aCept[P-TMSI, PTMSI signature)
Routing area update complete[P-TMSI] (optional)
Routing area update request[Old RAI, old P-TMSI signature,
Update type, CI]
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The new RA is administered by a different SGSN than the old RA The new SGSN realizes that the MS has changed to its area and
requests the old SGSN to send the PDP contexts of the user
The new SGSN informs the involved GGSNs of the users new
routing context The HLR (and if needed, the MSC/VLR) are informed about the
user’s new SGSN
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Uplink Channel Allocation
MS BSS
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PRACH or RACH
PRAGCH or AGCH
PACH
PACH
Packet channel
request
Packet immediate
assignment
Packet resource
request
Packet resource
assignment
(Optional)
(Optional)
Mobile requests radio resources for uplink transfer by sending a“packet channel request” on the PRACH or RACH
The network answers on the PAGCH or AGCH, telling the mobile
which PDCHs it may use An uplink state flag is transmitted on the downlink telling the
mobile whether the uplink is free
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GPRS
Channel CodingChannel Coding
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GPRS
Protocol ArchitectureProtocol Architecture
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GPRS PROTOCOL ARCHITECTURE
Application
MS BSS SGSN GGSN
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NetworkLayer
(IP, X.25
SNDCP
LLC
RLC
MAC
PLL
RFL
Data Link
Layer
Physical
Layer
Um Gb Gn Gi
SNDCP Subnetwork dependent convergence protocol
LLC Logical link control
RLC Radio link control
MAC Medium aCess control
PLL Physical link layer
RFL Physical RF layer
BSSGP BSS GPRS application protocol
GTP GPRS tunneling protocol
TCP Transmission control protocol
UDP User datagram protocol
IP Internet Protocol
RLC
MAC
PLL
RFL
BSSGP
NetworkService
Phy.Layer
RelayBSSGP
NetworkService
Phy.Layer
LLC
SNDCP
Phy.Layer
IP
Data LinkLayer
TCP/UDP
GTP
Relay
Phy.Layer
IP
Data LinkLayer
TCP/UDP
GTP
NetworkLayer
(IP, X.25
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GPRS Backbone: SGSN GGSN
User data packets are encapsulated within the GPRS backbone network
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• GPRS tunneling protocol tunnels user data packets and relatedsignaling information between the GPRS support nodes (GSNs)
The protocol is defined for two instances:
• between GSNs of one PLMN (Gn interface)
• Between GSNs of different PLMNs (Gp interface) In the transmission plane, GTP uses a tunnel mechanism to transfer user
data packets
In the signaling plane, GTP specifies a tunnel control and managementprotocol
• The signaling is used to create, modify, and delete tunnels
GTP packets carry the user’s IP or X.25 packets
• Below GTP, the standard protocols TCP or UDP are used to transportthe GTP packets within the backbone network
• X.25 expects a reliable data link, so TCP is used• UDP is used for aCess to IP-based packet data networks, which do
not expect reliability in the network layer or below
• IP is used in the network layer to route packets through the backbone
• Ethernet, ISDN, or ATM-based protocols may be used below IP
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GPRS Downlink/Uplink Segmentation
PDU
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FH
BH Info Field BCS BH Info Field BCS BH Info Field BCS
Normal Burst Normal Burst Normal Burst Normal Burst
Information Header FCS
PDULLCFrame
LLCLayer
RLC/MACLayer
PhysicalLayer
RLCBlocks
FH: Frame Header
FCS: Frame Check Sequence
BH: Block Header
BCS: Block Check Sequence
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Air Interface - Data Link Layer RLC/MAC
Th RLC/MAC l i l d t f ti
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The RLC/MAC layer includes two functions:
• Reliable link between the MS and BSS
– Includes segmentation and reassembly of LLC frames into
RLC data blocks and ARQ of uncorrectable codewords• Medium ACess Control MAC layer controls the aCess attempts
of the MS on the radio channel shared by several MSs
– Algorithms for contention resolution, multiuser multiplexing
on a PD, scheduling and prioritization based on thenegotiated QoS
– Uses Slotted Aloha principle
– Both acknowledged and unacknowledged modes aresupported
Air Interface Physical Layer
The physical layer is divided into two sublayers:
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The physical layer is divided into two sublayers:
The Physical Link Layer PLL
• Provides a physical channel between the MS and the BSS
• Tasks include: – Channel coding, detection of errors, forward error
correction (FEC), indication of uncorrectable codewords,interleaving, and detection of physical link configuration
The Physical RF Layer RFL• The RFL operates below the PLL
• Its main roles are modulation and demodulation
BSS SGSN Interface
• The BSS GPRS Application Protocol (BSSGP) delivers routingand QoS information between BSS and SGSN
• The underlying Network Service (NS) protocol is based on theFrame Relay protocol
Signaling Plane
The protocol architecture of the signaling plane includes protocols
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The protocol architecture of the signaling plane includes protocolsfor control and support of the functions of the transmission plane:
• GPRS attach and detach
• PDP context activation• Control of routing paths
• Allocation of network resources
Between MS and SGSN, the GPRS Mobility Management andSession Management (GMM/SM) is used
Signaling architecture between SGSN and HLR, VLR, and EIR arethe same as used in conventional GSM with a few additions
Interworking with IP Networks
GPRS supports both IPv4 and IPv6
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GPRS supports both IPv4 and IPv6
• The Gi interface is the interworking point with IP networks
• From outside, the GPRS network looks like any other IP subnetwork,and the GGSN looks alike a usual IP router
Each registered user who wants to exchange data packets with the IPnetwork gets an IP address
• The IP address is taken from the address space of the GPRS operator
• In order to support a large number of mobile users, it is essential touse dynamic IP address allocation (in IPv4)
– DHCP server is installed; the address resolution between IP andGSM is performed by the GGSN using the appropriate PDPcontext
To protect the PLMN from unauthorized aCess, a firewall is installed
between the private GPRS network and the external IP network With this configuration, GPRS can be seen as a wireless extension of the
Internet all the way to a mobile station or mobile computer. The mobileuser has direct connection to the Internet!
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Nortel GPRS-UMTS Integration
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Nortel Managed Packet WAN
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GPRS Enhancements:
A Closer Look at EDGE A Closer Look at EDGE
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Steps in the EDGE Evolution
Best effort IP packet data on EDGE
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Voice over IP on EDGE circuit bearers
Voice over IP with statistical radio resource multiplexing
Network based intelligent resource assignment
Smart antennas & adaptive antennas
Downlink speeds at several Mbps based on wideband OFDM and/or multiple virtual channels
Edge Updates - April, 2001
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Credit RCR News,
April 9, 2001
www.rcrnews.com
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Two EDGEs: Compact and Classic
Fundamental difference is the frequency reuse and minimum startupspectrum: Compact (1/3 and 2x 600 kHz) and for Classic (4/12 and 2x 2 4
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spectrum: Compact (1/3 and 2x 600 kHz) and for Classic (4/12 and 2x 2.4MHz)
Classic is specified by ETSI SMG2
Compact is specified by the PDFG of the UWC Compact achieves 4/12 reuse on control channels by combining 4/4 time
reuse with 1/3 space reuse
Compact achieves 2x spectral efficiency of Classic on traffic channels bycombining 1/3 reuse with partial loading
EDGE Modulations
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Scheme Modulation Maximum
rate [kb/s]
Code Rate Family
MCS-9 59.2 1.0 A
MCS-8 54.4 0.92 A
MCS-7 44.8 0.76 B
MCS-6 29.6 / 27.2 0.49 A
MCS-5
8PSK
22.4 0.37 B
MCS-4 17.6 1.0 C
MCS-3 14.8 / 13.6 0.80 A
MCS-2 11.2 0.66 B
MCS-1
GMSK
8.8 0.53 C
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The EDGE Multi-Mode Radio Link
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Scheme Modulation Maximum
rate [kb/s]
Code Rate Header CodeRate
Blocksper 20 ms
Family
MCS-9 59.2 1.0 0.36 2 A
MCS-8 54.4 0.92 0.36 2 A
MCS-7 44.8 0.76 0.36 2 B
MCS-6 29.6 / 27.2 0.49 1/3 1 A
MCS-5
8PSK
22.4 0.37 1/3 1 B
MCS-4 17.6 1.0 0.53 1 C
MCS-3 14.8 / 13.6 0.80 0.53 1 A
MCS-2 11.2 0.66 0.53 1 B
MCS-1
GMSK
8.8 0.53 0.53 1 C
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EDGE Payload Format
37 o ctets 37 octets 37 octets37 octets
MCS-3
MCS-6
Fa mily A
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MCS-9
28 o ctets 28 o ctets 28 o ctets28 o ctets
MCS-2
MCS-5
MCS-7
Family B
22 octets22 octets
MCS-1
MCS-4
Family C
34+3 octets34+3 octets
MCS-3
MCS-6Fa mily A
padding
MCS-8
34 o ctets 34 o ctets 34 o ctets34 o ctets
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Carriers,Frames,Timeslots& Channels for Classic & Compact
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A GSM carrier’s time is divided into frames
A frame is divided into 8 timeslots and each is designated atimeslot number, TN0 …TN7
All timeslots of a carrier’s timeslot number are considered a singlephysical channel
Control/Traffic logical channels map to parts of the physicalchannels
GSM Carriers and TDMA Frames for EDGE Classic and Compact
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1/3 Frequency Re-use (EDGE Compact)
• 3 x 200 kHz carrier, reused in every site
1MH 2 i i i l d l
• 3 x 200 kHz carrier, reused in every site• <1MHz x 2 initial deployment
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• <1MHz x 2 initial deployment
• 3 sectors per site
p y
• 3 sectors per site
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Reuse in Time for EDGE Compact
TN0 TN1 TN2 TN3 TN4 TN5 TN6 TN7
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OFF OFF OFFTraffic Control Traffic Traffic Traffic
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Base Station Frame Synchronization - so that all base stations can be swiedon/off synchronously to achieve reuse in time
Modified air-interface protocols - to be able to handle the resultingdiscontinuous nature of transmissionsse is in space only
Reuse for control and reuse for traffic channels are independent of each other
The actual reuse employed - for traffic or control - is operator controlled and
limited only by the available spectrum Typically, 4/12 is used for control and 1/3 for traffic. However, other
combinations are also possible subject to performance requirements,environment and spectrum availability.
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0 1 2 3 4 5 6 7
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1 timeslot 577 µs
1 frame 4.515 ms
210 643
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5. Collect the Configuration Messages!
BTS
W1
W32
W0
PAGING
SYNC
PILOT
SYN SYN SYN
ACK
SYN SYN SYN SYN SYN SYN SYN SYN SYN SYN SYNSYNSYN
ChASN ACK GPAGChASN ACK
SYN
SYS CHN XSYS NBR GSRM APM
PN 168
Ref Time
Collect all the Configuration Messages
(all config.messages are repeated every 1.28 sec)
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Rake Receiver
Collect all the Configuration Messages
Absorb and store al l their parameters.
#1 PN168+0 W1
#2 PN168+2 W1
#3 PN168+9 W1
#4 PN168+5 W1
Pilot Searcher
S y s t em
P ar am
e t er s
M e s s
a g e
* * C
DMA
C h a
nn el
L i s t M
e s s a g e
E x t en d e d
S y s t e
m
P ar am e
t er s
M e s s a
g e
N ei gh
b or
* * L i s t
M e s s a
g e
Gl o b al
S er v i c e
* * R e d
i r e c t i on
M e s
s a g e
A C e s s
P ar am e
t er s
M e s s a
g e
TIME
S t a y L o c k e d !
The Configuration Messages tell the mobile everything it needs to know tosuCessfully operate on the system
• ACess Parameters Message (how to behave on the aCess channel)
• System Parameters Message (registration, handoff, window settings)
• Extended System Parameters Message (how to identify; packet details)• Channel List Message (list of all carrier frequencies on this sector)
• Neighbor List Message (list of nearby sectors to wa out for)
• Global Service Redirection Message (“don’t stay here - go over there”)
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A GSM Uplink Normal Burst
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GSM is a TDMA system and a mobile’s transmission bursts are carefullyconstructed not to overlap with bursts from other mobiles
Different propagation delays of mobiles near and far mobiles the BTS arecompensated by automatically advancing mobile transmit timing
Special training sequences are included in each uplink burst and downlinktimeslot to facilitate demodulation
During unused timeslots, a mobile measures the strength of surroundingbase stations to guide the handover process (this is called MAHO, Mobile
Assisted Hand Over)
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