Mobile Data Networks
- 1. Unit – V Mobile Data Networks Introduction Data oriented CDPD Network GPRS and higher data rates Short messaging service in GSM Mobile application protocol Wireless ATM & HIPERLAN: Introduction Wireless ATM HIPERLAN
- 2. Introduction • Mobile Data: –Mobile data networks refer to those services, technologies and standards over wide area coverage spanning more than local area or campus. –Mobile data networks are classified into three categories: • Independent • Shared • Overlay
- 3. Mobile Data Networks Independent Licensed bands Examples: ARDIS, Mobitex Unlicensed bands Examples: Metricom Ricochet Shared Example: CDPD Overlay Overlay on traffic channels Example: GPRS Overlay on signaling channels Example: SMS Figure: Classification of Mobile Data Networks
- 4. Independent Mobile Data • Independent networks have their own spectrum and infrastructure not shared with any other service. • First group uses independent spectrum in licensed bands. – Ex: ARDIS and Mobitex (first mobile data services that were introduced). – Not economically successful.
- 5. Independent Mobile Data • Second group uses independent spectrum in unlicensed bands. – Shared among variety of applications and users. – Ex: Metricom’s Ricochet service used 915 MHz unlicensed ISM band. – This service was deployed in airports and some metropolitan areas for internet services.
- 6. Shared Mobile Data • These networks share the spectrum and part of the infrastructure with an already existing analog voice- oriented service. • In addition to dedicated channels, these services can also use the available unused channels. • Initial deployment could be made in areas where there is subscriber demand. • Ex: CDPD service which shares spectrum and part of infrastructure with AMPS.
- 7. Overlay Mobile Data • These networks not only makes use of the spectrum allocated for another service but also the air-interface and MAC frames of an existing voice-oriented digital cellular network. • Ex: GPRS and GSM’s SMS are examples of such overlays. – They make use of free time slots available within the traffic channels and signaling channels in GSM. – Amount of infrastructure required is reduced to bare minimum.
- 8. Data-Oriented CDPD Network • CDPD is one of the longest surviving wide area mobile data technologies worldwide. • It is a shared mobile data network that shares part of the infrastructure and entire spectrum with AMPS in United States. • It is an open standard making its implementation easier and more widespread.
- 9. What is CDPD? • Design goals of CDPD included location independence and independence from service provider, so that coverage could be maximized. • CDPD used primitive RF technology for cost reasons and GMSK modulation scheme was chosen. • Raw signaling rate is 19.2 kbps with Reed-Solomon (RS) coding. • CDPD employs a technique called RF sniffing to detect whether an AMPS call is trying to access frequency channel – And hopping to move from such a band to another to give the voice call priority.
- 10. CDPD Services • Network services are the basic form of services offered by CDPD. – Supports for transfer of data from one location to another via standard network layer protocols. – CDPD supports connectionless layer 3 protocols (IP or connectionless network protocol - CLNP). • Network support services are services necessary to maintain the operation of mobile data network such as management, security etc. – These services include mobility and radio resource management, that are transparent to the user. • Network application services: – These are value added services such as limited size messaging that need explicit subscription.
- 11. Reference Architecture in CDPD
- 12. Reference Architecture in CDPD • There are three key interfaces that form logical boundaries for CDPD service provider’s network. • A-Interface: air link interface • E-Interface: – external interface by which CDPD operates with the rest of data network. – Protocols IP, CLNP and IPv6 will be supported. • I-Interface: Interservice provider interface – Supports E-interface protocols plus two CDPD specific protocols • MNLP: Mobile Network Location Protocol – by which mobile users from one system are supported by another system. • Network management protocols.
- 14. Physical Architecture 1. Mobile-End System (M-ES): • ultimate source and destination of PDUs. • Equipped with a CDPD radio and software. • Ex: telemetry devices, laptops, vending machines etc. • Can be full duplex or half duplex. • Employs variety of power sources such as internal batteries, laptop based PC card etc. • Has three functional units: i. Subscriber unit (SU) establishes and maintains data comm. ii. Subscriber identity module (SIM) is a repository of identity and authentication credentials. iii. Mobile application system (MAS) deals with higher layer protocols.
- 15. Physical Architecture 2. Mobile Data Base Station (MDBS): • Is the system end of the MAC sublayer over the air interface. • Communicates with M-ES through the A-interface. • Performs modulation of data bits and demodulation of RF signal. • Actively participates in the medium access scheme called digital sense multiple access (DSMA).
- 16. Physical Architecture 2. Mobile Data Intermediate System (MD-IS): • Is the focal point of CDPD mobility management and packet forwarding. • Has mobile serving function (MSF) that serves as a foundation for registration of a mobile. • Also performs accounting services. 3. Fixed-end system (F-ES): • Conventional network node that includes PCs, workstations etc. • Internal F-ES operates within the boundaries of CDPD network and is under the control of service provider.
- 17. Mobility Support in CDPD • Mobility Management: • Mobility Management Service manages network roaming and tracks the location of each CDPD subscriber, as well as keep the serving MD-IS informed of that location down to the specific cell site. • In a wireless mobile data network, the endpoints of the data connections can be located anywhere in the network coverage area, and the location of these endpoints can change over time thus mobility management is important. • Like voice cellular networks, CDPD supports roaming. CDPD devices have a home sub-domain usually the home city of the subscriber. One may travel from a sub-domain registered as one’s home area to a new serving area.
- 18. Mobility Support in CDPD (cont…) • Mobility Management: • The CDPD network’s Mobility Management Service handles the routing of packets for all visiting M-ESs in its serving area. • The home area is that in which the CDPD subscriber has registered their device with a CDPD service provider. If the subscriber travels to another area, the mobility management services maintain information about their current serving area. • Mobility management services in the new serving area regularly notify the subscriber’s home-area CDPD network of the subscriber’s new location. Therefore, a CDPD subscriber can travel throughout the country and still obtain CDPD network services.
- 19. Mobility Support in CDPD (cont…) • Mobility Management:
- 20. Mobility Support in CDPD (cont…) • Mobility Management: • CDPD mobility management is based on principles similar to mobile-IP. The MD-IS is the central element in the process. • An MD-IS is logically separated into a home MD-IS and serving MD-IS. A home MD-IS contains a subscription database for its geographic area. Each subscriber is registered in his home. MD-IS associated with his home area. • The IP address of a subscriber points to his home MD-IS. At the home MD-IS, MHF maintains information about the current location of MHS associated with that home MD-IS. • The MHS also encapsulates any packet that is addressed to an M- ES homes with it directing it to an MSF associated with the serving MD-IS, whose serving area the M-ES is currently visiting
- 21. Mobility Support in CDPD (cont…) • Mobility Management: • A serving MD-IS manages one serving MD-IS, whose MSF contains information about all subscribers currently visiting the area and registered with it. • The MSF employs the mobile network location protocol (MNLP) to notify the MHF about the presence of the M-ES in its service area. The channel stream in which a subscriber is active is also indicated. The MSF decapsulates forwarded packets and routes them to the correct channel stream in the cell.
- 22. Mobility Support in CDPD (cont…) • Handoff procedure in CDPD: • Handoff in CDPD occurs when the M-ES moves from one cell to another or if the CDPD channel quality deteriorates, the current CDPD channel is requested by an AMPS voice call, or if the load on the CDPD channels in the current cell is much more than the load on the channels in an overlapping cell. • The physical layer of CDPD provides the ability to tune to a specific RF channel, the ability to measure the received signal strength of the received signal, the ability to set the power of the M-ES transmitted signal to a specified level and the ability to suspend and resume monitoring of RF channels in the M-ES.
- 23. Mobility Support in CDPD (cont…) • Handoff procedure in CDPD: • The handoff is mobile controlled. The M-ES always measures the signal strength of the reference channel. M-ES scans for the alternative channels when its signal deteriorates. • Because certain cells may have large shadowing effects within them the operator can set a RSSI scan value to determine when a M-ES should scanning for alternative channels. M-ES will ignore a drop in signal level if the RSSI scan value is large enough or start scanning for alternative channels if it is small. • This value is also useful when the signal strength does not drop even the M-ES has moved well into a neighbouring cell.
- 24. Mobility Support in CDPD (cont…) Handoff procedure in CDPD
- 25. Mobility Support in CDPD (cont…) • Handoff procedure in CDPD: • When additional threshold for RSSI hysteresis block error rate (BLER) and symbol error rate (SER) are reached, the M-ES will go through a list of channels of adjacent cells that the current BS is broadcasting and tune in to the one with the best signal strength. • The M-Es informs the new BS that it has entered its cell. • The mobile serving function of the new MD-IS uses a redirect- request and redirect-confirm procedure with the mobile home function of M-ES. • Depending on the nature of handoff the delay of registration and traffic redirection will vary.
- 26. Mobility Support in CDPD (cont…) • Security: • Security functions in CDPD are limited to data link confidentiality and M-ES authentication. • CDPD authentication is performed by the mobile network registration protocol management entity (MME) that exists in both MD-IS and M-ES. • It uses network entity identifier (NEI)along with an authentication sequence number (ASN) and an authentication random number (ARN) for authentication. • CDPD confidentiality is based on encrypting all data using a secret key that is different for each session.
- 27. Mobility Support in CDPD (cont…) • Security: • The usual concept of using public key for exchanging keys and secret keys for block data encryption is employed. • The session key generation is based on “Diffie-Hellman” key exchange with 256 bit values. RC-4 is used for block data encryption. • There are no mechanisms for data integrity, nonrepudiation or traffic flow confidentiality.
- 28. Mobility Support in CDPD (cont…) • Radio Resource Management (RRM): • RRM is handled by a management layer in CDPD and contains the procedure to handle dynamically changing RF environment. • It takes care of: – Acquiring and releasing channels due to competition between CDPD and AMPS. – Handoff from one cell to another or from one channel to another. • Its function is to provide best possible RF channel between M-ES and the fixed network. • Also ensures that the transmission powers are set dynamically to minimize co-channel interference.