gprs tunneling protocol gtp
DESCRIPTION
GPRS basicsTRANSCRIPT
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GPRS architecture and GTP protocol
GPRS/UMTS Overview
GTP Overview
APNs
GTP Details
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ContentsGPRS and its Features
GPRS Network Architecture -
Role of SGSN & GGSN
GPRS Protocol Architecture -
Definition and functions of various protocol layers i.e. SNDCP, RLC-MAC, LLC, PHY
GPRS Session Management -
PDP context establishment, accept, negotiation
GPRS Mobility Management -
Network Attach\detach
Routing area update
GPRS Applications
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GSM networks Constraints
Data Rates too slowabout 9.6 kbps
Connection setup time too long
Inefficient resource utilization for bursty traffic
Proves expensive for bursty traffic utilization
No efficient method for packet transfers
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GSM GPRS
Data Rates 9.6 Kbps 14.4 to 115.2 Kbps
Billing Duration of connection Amount of data transferred
Access to HLR every MT call causes query to HLR no need to access HLR for everyGPRS packet
Flow of data Data transmission burstyContinuous flow of data in both
direction
Type of Connection
Circuit Switched =>
connection with circuit switchednetworks typically one call per hour,
average call 2 minutes
Packet - Switched
=>connection with external packetdata networks and can last for
several hours
PR o ers s gn cant
performance improvement over
GSM
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What is GPRS ?
General Packet Radio Service (GPRS) is a new bearer service forGSM that greatly improves and simplifies wireless access to packet
data networks
GPRS applies packet radio principal to transfer user data packets in
an efficient way b/w MS & external packet data network
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GSM network architecture
Base Station Controller (BSC):It controls a group of BTSs and manages their radioressources. A BSC is principally in charge of handoffs, frequency hopping,exchange functions and power control over each managed BTSs.
Base Transceiver Station (BTS) :it maps to transceivers and antennas used ineach cell of the network. It is usually placed in the center of a cell. Its transmitting
power defines the size of a cell. Each BTS has between 1-16 transceiversdepending on the density of users in the cell.
MS consists of :The Subscriber Identity Module (SIM) and Mobileequipment/terminal.
Network and switching subsystem (NSS) :Its main role is to manage thecommunications between the mobile users and other users, such as mobile users,ISDN users, fixed telephony users, etc. It also includes data bases needed in orderto store information about the subscribers and to manage their mobility. The
different components of the NSS: MSC, HLR,VLR, AuC, EIR.
MSC: the central component of the NSS. The MSC performs the switchingfunctions of the network. It also provides connection to other networks.
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Benefits of GPRS New Data Services
High Speed (Data Rate 14.4115 kbps)
Efficient use of radio bandwidth (Statistical Multiplexing)
Circuit switching & Packet Switching can be used in parallel
Constant connectivity
Billing based on volume of data transferred
Utilizes existing GSM authentication and privacy procedures.
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High Data Rate
GPRS uses radio channel i.e. 200 kHz wide
Radio channel carries digital data stream of 271 kbps
This rate is divided into 8 time slots each carrying 34 kbps per timeslot
Data rate 14 kbps per time slot achieved after corrections GPRS can combine upto 8 time slots giving data rate of 114 kbps
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GPRS Network Elements GPRS Architecture same as GSM except few hardware modifications
GPRS includes GSNs
SGSN : Serving GPRS Support Node
GGSN : Gateway GPRS Support Node
GPRS Register
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BSCBTS
GSM/GPRS AccessNetwork
Serving
GSN
PSTNMSC
BSC
BTS
BTS
BTS
Internet
Gateway
GSN
GPRS Network Architecture
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SGSNServing GPRS Support
Node
Delivers data packets to mobile stations & vice-versa
Detect and Register new GPRS MS in its serving area
Packet Routing, Transfer & Mobility Management
Authentication, Maintaining user profiles
Its location register stores location info. & user profiles
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GGSNGateway GPRS Support Node
Interfaces GPRS backbone network & external packet datanetworks
Converts the GPRS packets from SGSN to the PDP format
Converts PDP addresses change to GSM addresses of thedestination user
Stores the current SGSN address and profile of the user in its
location register
Performs authentication
Many-to- many relations among SGSNs & GGSNs
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GPRS Register
GPRS Register is integrated with GSM-HLR.
Maintains the GPRS subscriber data and Routing information.
Stores current SGSN address
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MS and SGSN Signaling messages protocol stack
GSM RF
GMM\SM
Um Gb
MAC
RLC
LLC LLC
GSM RF
Frame
Relay
MAC
RLC BSSGP
L1bis
BSSGPFrame
Relay
LLC
GMM\SM
L1bis
MS BSS (PCU) SGSN
BSSGP-Base station system GPRS protocol
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User Data Protocol Stack
GSM RF
SNDCP
IP / X.25
Application
Um GnGb
MAC
RLC
LLC
IP / X.25
GTP
L1
L2
LLC
GSM RF
Frame
Relay
MAC
RLC BSSGP
L1bis
BSSGP
Frame
Relay
LLC
SNDCP GTP
L1bis L1
L2
IP
MS BSS (PCU) SGSN GGSN Gi
IP
UDP/
TCP
UDP/
TCP
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SNDCP - Sub Network Dependent Convergence Protocol
Used to transfer data packets (TCP/IP) between SGSN and MS.
Converting and segmenting external network formats (N-PDUs) into sub-
network formats (SN-PDUs). In the opposite direction, SNDCP layer
receives SN-PDUs from LLC and converts them back into network data
packets.
Managing multiple PDP context sessions ensuring that N-PDUs fromeach PDP context are txed to LLC layer in sufficient time to maintain
QOS for each PDP context.
Compression and decompression of user data and header information
Negotiating the compression parameters to be used between MS and
network.
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GiGn
Gc
Gp
Signalling and Data Transfer
Signalling Interface
TEPDN
Iu
UTRANTE MT
Gr or Gc
HLR
Other PLMN
SGSN GGSN
SGSN
GTP-MAPprotocolconverting
GSN
Gn
IuTE MT UTRAN
SGSN
Gn
BSSGb
TE MT
Gn
GPRS/UMTS Logical Architecture
U Pl f GPRS/UMTS
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User Plane for GPRS/UMTS
Relay
Network
Service
GTP-U
Application
IP / X.25
SNDCP
LLC
RLC
MAC
GSM RF
SNDCP
LLC
BSSGP
L1bis
RLC
MAC
GSM RF
BSSGP
L1bis
Relay
L2
L1
IP
L2
L1
IP
GTP-U
IP / X.25
Um Gb Gn GiMS BSS SGSN GGSN
Network
Service
UDP /
TCP
UDP /
TCP
L1
RLC
PDCP
MAC
IP,
PPP,
OSP
Application
L1
RLC
PDCP
MAC
ATM
UDP/IP
GTP-U
AAL5
Relay
L1
UDP/IP
L2
GTP-U
IP,
PPP,
OSP
3G-SGSNUTRANMS
Iu-PSUu Gn Gi
3G-GGSN
ATM
UDP/IP
GTP-U
AAL5
L1
UDP/IP
GTP-U
L2
Relay
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GPRS Higher Layer Signalling
OverviewApplication Layer
SM LayerSet up data calls,
negotiates QoS
GMM- Registration, authentication, attach,
location management
LLCProvides Highly reliable data link
RLC- MAC
PHY
AM radio link UM radio link
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GPRS Identities
IMSI=> International Mobile Subscriber Identity-is the identity number of the SIM. MS send to NWduring attach.
(not more than 15 digits)
3 digits 2-3 digits
P-TMSI =>Packet Temporary Mobile Subscriber Identity
P-TMSI is sent during GMM attach , if the network does not recognize the P-TMSI (incase of roaming) ,it will ask MS to send IMSI for authentication purposes. SGSN selects a P-TMSI from a store of randomnumbers and sent to MS in ciphered mode which uses P-TMSI to generate TLLI.
PDP (Packet Data Protocol) addresses=> MS is identified with IMSI. IMSI will have related PDPaddresses for the services subscribed to. These addresses can be temporary or permanent and mustconfirm to the standards of external networks.
MCC- mobile country code , MNC- PLMN network code , MSIN- mobile subscriber identity code
MCC MNC MSIN
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GTP
GTP specifies a tunnel control and management protocolwhich allows the SGSN toprovide GPRS network access for an MS. In the transmission plane, GTP uses a tunnellingmechanism to provide a service for carrying user data packets. The choice of path isdependent on whether the user data to be tunnelled requires a reliable link or not.
The GTP protocol is implemented only by SGSNs and GGSNs. No other systems need tobe aware of GTP. GPRS MSs are connected to a SGSN without being aware of GTP.
It is assumed that there will be a many-to-many relationship between SGSNs and GGSNs.An SGSN may provide service to many GGSNs. A single GGSN may associate with manySGSNs to deliver traffic to a large number of geographically diverse mobile stations.
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GPRS Tunneling Protocol is
The protocol between GPRS Support Nodes
Includes both the GTP signaling (GTP-C) & data transfer
(GTP-U) proceduresIs defined for the Gn interface, i.e. the interface between GSNs
within a PLMN &
For the Gp interface between GSNs in different PLMNs
Allows multi-protocol packets to be tunneled through theUMTS/GPRS backbone
GTP Overview
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GTP Overview (Cont.)
GTP-C is
the signaling plane and specifies a tunnel control and
management protocol
is used to create, delete modify tunnels.
GTP-U is
the transmission plan & uses a tunneling mechanism
(GTP-U) to provide a service for carrying user data packets
Definitions
T-PDUOriginal data packet
G-PDUOriginal data packet (T-PDU) + GTP header
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GTP Header
Version PT (*) E S PN
Message Type
Length (1stOctet)
Length (2ndOctet)
Tunnel Endpoint Identifier (1stOctet)
Tunnel Endpoint Identifier (2ndOctet)
Tunnel Endpoint Identifier (3rdOctet)
Tunnel Endpoint Identifier (4thOctet)
Sequence Number (1st
Octet)
Sequence Number (2ndOctet)
N-PDU number
Next Extension Header Type
8 7 6 5 4 3 2 1Octets1
2
3
4
56
7
8
910
11
12SGSN
specific
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GTP Messages
GTP defines a set of messages. These are classified into
Path Management messages
Tunnel Management messages
Location Management messages
Mobility Management messages
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Call set up and tear down
Create PDP Context req.
Create PDP Context resp.
G-PDU (data transfer)
Delete PDP Context req.
Delete PDP Context resp.
SGSN GGSN
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Tunnel Management Messages
Create PDP Context RequestCreate PDP Context Response
Delete PDP Context Request
Delete PDP Context Response
Update PDP Context request
Update PDP Context Response
PDU Notification request
PDU Notification response
PDU Notification reject request
PDU Notification reject response
Used for n/w initiated PDP context
Used for SGSN handoff
DHCP relay of PDP address
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Access Point Name
An APN identifies a PDN that is configured on and accessible from
A GGSN. APN has two parts.
APN Network Identifier
APN Operator Identifier
The APN network identifier must correspond to a fully qualified
name in DNS e.g. cisco.com
The access Points that are supported by the GGSN are preconfigured
on the GGSN.
APN is sent in the create PDP context request message to GGSN.
APN has several attributes associated with its configuration
which specify how the user can access the network at the entry point.
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APN Attributes
Some of the attributes are
- APN Network Identifier- Access ModeTransparent (no authentication) / Non-transparent
- IP address pool
- Primary DHCP server
- Secondary DHCP server- DHCP gateway address
- RADIUS server
- Backup RADIUS server
- IP address of the next hop for the Gi interface
Attributes to get logs
- Current allocated IP address count
- Current PDP context count
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Path Management Messages
Path management messages can be sent between any type of GSNs.
Echo RequestNo elements
Echo ResponseRecovery
Version not supportedNo elements
Supported Extension Header NotificationsExtension header
type list
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Echo Request/Response Message
Echo request is send on a path to another GSN to find out if the Peer
GSN is alive.
The periodicity is implementation dependent but is > 60 secs.
The Echo response is sent with the local restart counter of the GSN.
The GSN receiving the response would compare the restart countervalue to the previous stored value to check if the GSN has restarted.
The receiving GSN clears off all the PDP context belonging to the
restarted GSN.
Every GSN maintains its own restart counter in non-volatile memoryand its peers restart counters in volatile memory.
Tunnel Management Messages (cont )
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Tunnel Management Messages (cont.)Create PDP Context Request
IMSI(identify a subscriber by the operator. ) Conditional
Recovery Optional
Selection Mode Conditional
Tunnel End Point Identifies Data 1 Mandatory
Tunnel Endpoint Identifier Control Plan Conditional
NSAPI Mandatory
Linked NSAPI Conditional
Charging Characteristics Optional
Trace Reference Optional
Trace Type Optional
End User Address Conditional
Access Point Name Conditional
Protocol Configuration Options Conditional
SGSN Address for signaling Mandatory
SGSN Address for user traffic Mandatory
MSISDN( for routing call , number to dialin) Conditional
Quality of service Profile Mandatory
TFT Conditional
Trigger ID Optional
OMC identity OptionalPrivate Extension Optional
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Tunnel Management Messages (cont.)
Create PDP Context response
Information Element Presence required
Cause Mandatory
Reordering required Conditional
Recovery Optional
Tunnel Endpoint Identifier Data 1 Conditional
Tunnel Endpoint Id. control Plane Conditional
Changing ID Conditional
End User Address Conditional
Protocol Configuration Options Optional
GGSN Address for Control Plane Conditional
GGSN Address for Use Traffic Conditional
Quality of Service profile Conditional
Charging Gateway Address Optional
Private Extension Optional
* Private extension contains vendor or operator specific info
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Tunnel Management Messages (cont.)
Cause: Indicates if the PDP context was created. Some of the
values are
- Request accepted
- No resource available
- All dynamic PDP addresses are occupied- No memory available
- Missing or unknown APN etc.
If the PDP context request fails the SGSN tries to create the PDPcontext with the next GGSN in its GGSN list.
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Tunnel Management Messages(cont)
Error Indicationmsg.
Information Element Presence
Tunnel Endpoint Identifier data Mandatory
GSN Address Mandatory
Private extension Optional
Sent from GSN if no active PDP context exists for the received
G-PDU.
When an error indication is received, the receiving GSN deletes the
corresponding PDP context.
The elements TEID and GSN address are derived from the data
message and uniquely specify the PDP context.
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Location Management Messages
Used for network initiated PDP context request when there is no
SS7 MAP interface at the GGSN
Gn+
UDP
L2IP
GGSN
L1L2IP
UDP
SGSN
GTP
L1MTP2MTP3SCCPTCAPMAP
L1MTP2MTP3SCCP
HLR
TCAP
MAP
L1
GTP
Gc
GTP-MAP Interworking
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Location Management Messages (cont)
Send Routing Information for GPRS Request
Send Routing Information for GPRS Response
Failure Report Request
Failure Report Response
Note MS GPRS Present Request
Note MS GPRS Present Response
Mobility Management Messages:Sent between SGSNs at the GPRS attach and Inter SGSN routing
update procedures.
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Reliable Delivery of Signaling Messages
Each path maintains a queue with Signaling msg. to be sent
A request (with a response) shall be sent with a sequence number
and shall be held in a path list till the response comes.
Each path has its own listThe sequence number is unique for each outstanding req. msg.
T3-Response timerMax time a requesting entity would wait before retransmission
N3-Requests timesMax number of retransmissions allowed.
these two are configurable parameters on the stack.
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Handling of Sequence Number (optional)
For GTP-C
Used in request-response type of signaling messages as transactionIdentity. In the response message the seq. no. of request message is
copied.
For GTP-U
An increasing number of T-PDUs are transmitted via GTP-U tunnel
when transmission order must be preserved.
The receiving GGSN would reorder the incoming T-PDUs in seq. if
the reordering required flag in the PDP context is set. In this case if
required the GGSN would maintain a window and a timers to makesure that a G-PDU was lost.
The sequence number is kept unchanged irrespective of the tunnels it
travels before the destination.
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Session Management SM Layer is sandwiched between Network Layer and GMM layer. It provides service
by establishing a PDP context when asked to do so by network layer
To set up session for transfer of SN-PDUs and to de-activate the session wheninstructed
To modify QOS and Radio priority given to a PDP context when the network instructs itto do so.
It relies upon the services provided by GMM layer and will check that it is GPRSattached and then send PDP context activation request asking the GMM layer to deliver itto SGSN SM layer.
MS will receive from the network PDP context activation accept (or reject!) . This is theinformation SNDCP is waiting for and now accepts the N-PDUs from application layer.
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Cont.PDP context activation is a data call set-up for GPRS operations. Unlike circuitswitched call where set-up is removed when call is completed but PDP contextactivations remains valid when the call or session which caused the Context iscompleted.
For each session PDP context following parameters are exchanged :
PDP type
NSAPI APN Access Point Name MS may use this to specify which external network
it wishes to access
Requested PDP address- may be X.121, IPv4 or IPv6 address
QOS
Radio priority
Protocol configuration Options
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PDP Context Activation
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PDP Context DeactivationInitiated by :
Network- if PDP context is not used for some time
Mobile- QOS not accepted or Insufficient resources
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GMM GPRS M bilit
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GMM - GPRS Mobility
Management
Attaching to the GPRS network when requested by SM or
application layer. This attach process alerts the network to MS
presence and allows network to authenticate it and give
information required for encryption.
Perform Routing area updates
Perform cell updates when MS is in ready state and reselects a
cell
Detaching from the network
Authentication
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GMM states
Idle MS is not attached to GPRS
Standby
Subscriber is attached to GPRS mobility management
MS performs RA and cell selection locally, reports RA changes Data, signaling or page response move the MS to READY
Detach procedures moves the state to Idle
Ready
Information on cell selection is reported
Cell selection may be done locally or by network control
State supervised by a timer
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Flow for GPRS attach procedure GMM is requested by SM layer to attach. Then GMM sendsAttach Request
(PTMSI, RAI,TLLI, cksn, QOS, Cause, Radio priority) down to LLC layer. From the PTMSI and cksn , the network operator will have a decision making processto authenticate MS or to go immediately in encryption mode, by passing authentication.
MS receives Authentication and Encryption commandfrom network, it extractsRAND, passes it to SIM card which produces SRES, and encryption key Kc .
GMM layer puts SRES into Authentication and Encryption response and passesthis Kc key to LLC for encryption procedures.
When GMM layer received Attach Accept(Ra update timer, RAi, PTMSi, PMTSIsig, new TLLI ), the authentication process is completed.
The GMM accepts the PTMSI and other information and send an Attach completemessage to the network.
RAND-Random number related to IMSI in the SGSN.
SRES-signed response
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Routing Area Update
RAU is performed when MS is GPRS attached and RLC indicates achange in routing area. The RA reported to GMM layer is continously
compared to RA stored in SIM card. When these differ an RA update to
GPRS network is initiated by GMM layer.
GSM Location Area(LA) is divided into several Routing Areas(RA)
RA consists of several cells SGSN is informed when MS moves to a new RA
MS sends a Routing Area Update Request to its assigned SGSN
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Routing Area Updatecontd.
Whenever an MS moves to a new RA, it sends a routing area update request to itsassigned SGSN. The message contains the routing area identity (RAI) of its old RA. Thebase station subsystem (BSS) adds the cell identifier (CI) of the new cell, from which theSGSN can derive the new RAI. Two different scenarios are possible:
Intra-SGSN routing area update: The MS has moved to an RA that is assigned to thesame SGSN as the old RA. In this case, the SGSN has already stored the necessaryuser profile and can assign a new packet temporary mobile subscriber identity (P-TMSI)
to the user (routing area update accept). Since the routing context does not change,there is no need to inform other network elements, such as GGSN or HLR.
Inter-SGSN routing area update: The new RA is administered by a different SGSN thanthe old RA. The new SGSN realizes that the MS has changed to its area and requeststhe old SGSN to send the PDP contexts of the user. Afterward, the new SGSN informsthe involved GGSNs about the users new routing context. In addition, the HLR and (i fneeded) the MSC/VLR are informed about the users new SGSN.
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Routing Area Update
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Applications of GPRS Web browsing
Corporate & Internet Email
Vehicle Positioning
Remote LAN Access
Home Automation
Document Sharing/Collaborative working
Virtual private network (VPN):With VPN, companies will be able to let their remote workers wirelessly access to
corporate resources and stay in touch with their work teams.
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ADDITIONAL SLIDES
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Data Link layer Divided into two sub layers :
LLC layer (between MS-SGSN)
RLC/MAC (between MS-BSS)
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LLC-Logical Link Control Establishes highly reliable logical link between MS & its assigned SGSN using
TLLI as the mobile station address.
Works either in connection mode (acknowledged) which is high reliability link
or connectionless mode (unacknowledged) for high delivery of SN-PDUs .
Data confidentiality is ensured by ciphering and deciphering functions
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Radio Link Control(RLC) Establish a reliable link between MS & BSS
Segmentation and reassembly of LLC frames into RLC data blocks
To allow ordered transfer of LLC PDUs between MAC and LLC.
Medium Access Control(MAC)
To allow shared use of radio medium (physical channels) betweenmultiple mobile stations or incase of a single MS between differentPDP contexts.
Allow contention resolution
To allow queuing and scheduling for MS terminating calls.
To control TBF for carrying data packets
RLC/MAC Layer
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Physical Layer
Divided into two sub layers :
Physical Link Layer (PLL)
Physical RF Layer (RFL)
PLLProvides a physical channel between MS and BSS
Channel coding, interleaving, detection ofphysical link congestion, neighboring cellmeasurements, Handovers (Cell changeorders), Measurement Reports, Cell re-selection.
RFL - Operates below PLL