cellular digital packet data(cdpd)
DESCRIPTION
PRESENTATION ON cdpd TECHNOLOGYTRANSCRIPT
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Cellular Digital Packet Data
(CDPD)
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SUBMITTED TO-MR.
SUBMITTED BY-
Bhanu Pratap Singh (Roll No.)
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INTRODUCTION
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CDPD (Cellular Digital Packet Data)Offers low-cost, ubiquitous, wireless data
networkCan be overlaid on AMPS and IS-136, and
share its infrastructureTransmits packet data over idle cellular
voice channelsAutomatically switches to another channelDoesn’t communicate with underlying
cellular network
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CDPD (Cellular Digital Packet Data)
Takes advantage of its knowledge of channel assignment algorithms for cellular system
Predicts the channels available for CDPD use
Serve as the wireless extension to a PSDN or other data networks such as the Internet
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CDPD Architecture• Two basic classes of network entitiesES & IS
• Though physical location if M-ESs may change from time to time, continuous network access is maintained.
Mobile End System (M-
ES)
• Mobile Database StationMDBS
• Mobile Data-intermediate System .MD-IS
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Architectures in brief
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MD-IS MD-IS
AMPSMSC
M-ES
MDBS
MDBS
AMPS BS
AMPS BSAMPSBase
Station
MobileData Base
Station
Mobile Station
To other intermediate systems
CDPD Architecture
Two basic classes of network entities ◦ End system (ES)◦ Intermediate system (IS)
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CDPD Architecture (2)
Mobile End System (M-ES)
◦ Though physical location if M-ESs may change from time to time, continuous network access is maintained
◦ Consists of three parts Subscriber unit
– used to access the radio interface Subscriber identity module
– contains information to identify a subscriber Mobile application subsystem
– provides M-ESs application functionality
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CDPD Architecture (3) Mobile Database Station (MDBS)
◦ Control of the radio interface radio channel allocation interoperation radio media access control
◦ Consists of several modem-transceivers, each of which supports one channel pair
◦ User data received by the modem-transceiver are processed by control computer
◦ M-ES can communicate only with outside world through MDBS
Mobile Data-intermediate System (MD-IS)◦ Connects to several MDBSs via wired links or via microwave◦ Consists of frame relay switch, packet router, and
workstation◦ Receives data from one network and forwards it to another
network◦ Supports user mobility – CDPD-specific mobile network
location protocol
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CDPD Air Interface
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CDPD Air Interface
CDPD channel streams - 19.2Kbps raw duplex wireless link
Use idle cellular RF channels CDPD transmission must not interfere with
cellular voice Forward link - link from MDBS to M-ES
◦ MD-IS sends frames to the MDBS on the forward link
◦ MDBS broadcasts frames in its radio coverage area
◦ Only M-ESs that have valid NEI (network entity identifiers) can decode the received data
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CDPD Air Interface (2)
Reverse link - link from M-ES to MDBS◦ Uses DSMA (digital sense multiple access)
MDBS broadcasts the availability of the reverse link by an idle/busy control flag
If there are no transmission on the reverse channel, MDBS sets the control flag “idle”
M-ES may transmit the data on the reverse link at idle status
◦ If M-ES detects a “busy” status Waits for a random period of time Rechecks the status of the control flag
◦ If two M-ESs detect the “idle” status, and try to access the reverse link at the same time Collision occurs Exponential backoff procedure for retransmission
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CDPD Air Interface (3)
To prevent Channel-hogging situation◦ Maximum time period is defined between two bursts
When M-ES in communication moves from one cell to another◦ Radio link transfer process is required to reconnect the
M-ES in the new cell◦ CDPD link transfer process is controlled by the M-ES◦ M-ES monitors the radio link quality
If the quality falls below the thresholds M-ES initiates link transfer New MD-IS updates its registration directory
If the old MDBS and the new MDBS connected to different MD-ISs Transport layer retransmission is required to reestablish
the end-to-end connection
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CDPD Air Interface (4) Sleep mode operation
◦ An idle M-ES shut off power for predefined period◦ To “wake up”
MD-IS periodically broadcasts a notification message M-ES periodically activate its receiver If its name is found in the list,
MD-IS leaves sleep mode Sends a notification message to the MD-IS
◦ TEI (temporary equipment identifier) assignment procedure TEI is dynamic assigned MDLP address Sleep mode operation is requested T203 – element inactivity timer T204 – TEI notification timer
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Radio Resource Allocation
◦ CDPD use channel sniffing and channel hopping◦ MDBS periodically scans/monitors the channels
If a communication link is exit between cellular system and CDPD If an communication link is not exit – sniffing is used
◦ MDBS Generates a candidate list of available channels ◦ List is then forwarded to the MD-IS◦ MD-IS collects channel lists from all the associated MDBSs◦ Determines the CDPD channel streams based on its knowledge
of the voice channel allocation algorithm◦ Periodical channel switching timed hop or planned hop
to avoid channel sealing or channel stealing◦ Timer
Dwell timer Layout timer
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Channel hopping
Channel 5
Channel 6
VOICE CDPD
VOICEChannel
7
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Roaming Management
◦ Is achieved by two functions MHF (Mobile Home Function) MSF (Mobile Serving Function)
◦ M-ES is identified by a distinct NEI◦ Every NEI is associated with home MD-IS ◦Home MD-IS maintains a location directory
Is called the location directory service in the MHF Record the address of the current serving MD-IS for each
of its homed M-ESs
◦ Visited MD-IS maintains a registration directory Is called the registration directory service in the MSF Keep track of all visiting M-ESs
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Roaming Management Location registration procedure
M-ES
OldMD-IS
HomeMD-IS
NewMD-IS
Old MDBSNew MDBS
Registration
Cacellation
Registration directory service in the MSF
Location directory service in MHF
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Roaming Management NPDU forwarding procedure
Dataforwarding
MD-IS
HomeMD-IS
NewMD-IS
M-ES New MDBS
Step 1 Step 2
Step 3
Step 4
NPDU (network protocol data unit)
NPDU data routed
Redirection and forwarding service
Decapsulate and route :
readdress service
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