1 / 14

Chap 8. Cellular Digital Packet Data (CDPD)

Chap 8. Cellular Digital Packet Data (CDPD). 네트워크 컴퓨팅 연구실 석사 1 학기 박호진 ( sanzini96@hotmail.com ). Introduction. CDPD (Cellular Digital Packet Data) Offers low-cost, ubiquitous, wireless data network Can be overlaid on AMPS and IS-136, and share its infrastructure

conway
Télécharger la présentation

Chap 8. Cellular Digital Packet Data (CDPD)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chap 8. Cellular Digital Packet Data(CDPD) 네트워크 컴퓨팅 연구실 석사1학기 박호진 ( sanzini96@hotmail.com )

  2. Introduction • CDPD (Cellular Digital Packet Data) • Offers low-cost, ubiquitous, wireless data network • Can be overlaid on AMPS and IS-136, and share its infrastructure • Transmits packet data over idle cellular voice channels • Automatically switches to another channel • Doesn’t communicate with underlying cellular network • 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

  3. CDPD Architecture • Two basic classes of network entities • End system (ES) • Intermediatesystem (IS)

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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 transferprocess 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

  9. 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

  10. 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 sealingor channel stealing • Timer • Dwell timer • Layout timer

  11. Channel hopping

  12. 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

  13. Roaming Management • Location registration procedure Registration directory service in the MSF Location directory service in MHF

  14. Roaming Management • NPDU forwarding procedure Redirection and forwarding service NPDU data routed Decapsulate and route : readdress service NPDU (network protocol data unit)

More Related