Prepared referring Kaveh-Pahlavan-Prashant-Krishnamurthy-Principles-of-Wireless-Networks-A-Unified-Approach

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.

13. Physical Architecture

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.