Mobile Computing UNIT-8

UNIT-VIII
Mobile Wireless Short Range Networks
AND
Mobile Internet

Wireless Networking & Wireless LAN:
• We know that Local Area Network (LAN)
means a set of interconnected computers
with in a specific area which may include
some other computing systems.
• To form a LAN, we use the protocol suit
IEEE 802.x or 802.1y.
• All the units in local area network, has an
address, and with the help of address (IP)
they can communicate with each other.
• Now we discuss about wireless LANs, in
which each system may consists of smart
sensors, RFID labels, and have short range
communication capabilities.

•We know that the wireless LAN devices or
computers are using the IEEE 802.11
communication protocol.
• The implementation of IEEE802.11 leads to
WiFi – Wireless Fidelity. The WiFi is a
trademark of WiFi alliance, that certify the
products whose functions are based on
802.11 and used in WLANs. Thus interfaces,
devices, system and systems which are used
in wireless communication are WiFi enabled.
• Today a new technology in the market
known as “WiFi direct”, which is able to
connect with the existing WiFi networks and

gain the transmission speed up to 250Mbps.
• The WiFi direct devices may able to
advertise their presence and able to discover
another WiFi direct device.
• Generally establishment of wireless LANs
are a bit complex, the following diagram
shows an example for WLAN.
•

•The following are the some standards
recommended for WLAN in mobile
communication and for establishing
communication between mobile devices,
internet or other networks.
•2G: It enables digital encoding of voice and
enables mobile phone and SMS. It is based
on circuit switching.
•2.5G: It enables packet switching, Internet
and E-mail.
•3G: It enables wideband wireless
communication, video conferencing, video
calls and mobile TV.

• It supports data communication at
384kbps and 3 x 1.2288Mbps when using
three carriers of 1.2288Mbps each.
• 3.5G: It is a High speed Packet Access
Enhanced (HSPA) data communication at
28Mbps uplink and 56Mbps downlink.
•Pre-4G: It enables mobile WiMax using
IEEE 802.16e standard and very high data
rates using Long Term Evolution (LTE).
•4G: It enables multimedia news paper,
mobile TV of high resolution, IP telephony,
and 100Mbps data rates. It also uses mobile
WiMax IEEE 802.16m standard and
advanced LTE.

WLAN Configuration: Generally WLAN is a
peer-to-peer independent network. It
connects a set of computing systems, each
of which has a wireless interface (adaptors).
• Naturally two or more wireless interfaces
within the range of each other at an instant.
• The WLAN is formed on-demand, it should
not require administration and pre-configuration.
• There is another kind of configuration in
WLANs, which may known as a fixed
infrastructure network.

• In fixed infrastructure network, there are
multiple access points provide wireless
connectivity to the mobile computing
systems and also linked with wired
networks.
• The access point may form a micro cell or
PAN, which may have number of wireless
computing systems. The computing system’s
wireless interface (adaptor) sufficient
capabilities to establish connection with the
access point within a micro cell.
• Generally WLAN follows two types of
communication establishment techniques;

a) Spread spectrum.
b) Infrared WLAN.
The following are some important point that
should follow during configuration of
WLAN.
1. The range or coverage of WLAN may vary
from 30m to 125m.
2. A typical data transmission rate
(throughput) varies 1Mbps to 50Mbps.
3. It has interoperability with other wireless
infrastructure.
4. It also has interoperability with wired
infrastructure.

5. The WLAN has interference and
coexistence.
6. It should have the scalability.
7. Generally it is a ad-hoc network.
8. The WLAN should support security,
integrity and reliability.
9. It should have simplicity and ease of use.
10. It must be cost effective.
Advantages of WLANs:
1.Installation speed of wireless LANs are so
speed.
2.It is simple to install WLAN hardware.

3. WLANs has installation flexibility – The
WLANs are installed at anywhere, because
there is no need of wires and hubs and the
dynamic environment of network is
extendable.
4. WLANs provide improved services – The
WLAN user can interact with the network at
any time and able to access the real time
information through WiFi enabled handsets.
• The WLAN users can access internet
instead of expensive cellular services.
• Making secure phone call through VoIP
service.

• They are able to access local files of an
enterprise.
5. WLANs reduce the cost of ownership –
The initial investment of WLAN are higher
compared to wired LAN, but the cost of
maintaining over the whole life is low.
6. WLANs are scalable – We know that,
WLAN network is independent or Fixed
infrastructure or peer-to-peer network. The
WLANs are configured in various topologies
depending on need of specific applications.

WLAN Architecture:
• An addressable node in WLAN is called a
station. The following diagram shows a Basic
Service Set (BSS) of a particular station in
WLAN architecture.
•

• The BSS can have number of computing
systems and those are interconnected with
access point by using 802.11.
• The devices in a station of WLAN may use
same frequencies and interconnection of
stations done only through access point.
• Each node of a station use same frequency
band if it is at a tolerable distance from
another station or a node may use different
frequency bands if its distance not enough
from other stations.
•

•So a particular node at a station can
communicate directly to the access point
and to the other node at another station
through the access point.
• The nodes of a station can communicate
among themselves by forming an ad-hoc or
any other type of network, using same
frequency band by each node.
•Independent Basic Service Set (IBSS): An
IBSS having no access point for the
connectivity of distributed systems. The
IBSS has set of nodes those can
communicate among themselves within its
boundary.

The following diagram shows an IBSS;
• There are several devices at a station,
which are networked by using 802.11
protocol.
• In the diagram an IBSS has three stations,
STAB, STAC, and STAD, the stations in IBSS

does not connected to any access point.
Here the devices are communicate directly
with one another or communicate among
themselves after forming a ad-hoc network.
• All the nodes in a particular station can
considered as a single addressable unit. The
nodes among them are interact through
peer-to-peer communication manner.
• Here 802.11 protocol does not specify any
protocols for communication among the
nodes, for data routing, exchanging and
support for exchange of network topology
information.

• So in IBSS, the exchange of information
among the node can use Bluetooth and
these are ZigBee devices.
Distributed System: The wireless BSS may
or may not provide sufficient service over the
specified coverage area. So IEEE 802.11
provides the facility to integrate multiple
BSSs which have number of distributed
systems.
The following diagram shows distributed
systems interconnected by wireless access
points;

• The distributed systems provides flexible
functionality to the WLAN architecture
component. Here the wireless medium
802.11 is logically separates from the
distributed system medium (DSM).

• The following are the main functions of the
Distributed systems in WLAN.
1.Perform address-to-destination mapping.
2.Seamless integration of multiple mobile
devices in the BSS.
•An access point in WALN support the
following services
1.It physically connects the distributed
systems with access point and access those
systems.
2.The access point can provide distributed
system services.

3. The access point functions as a station
within BSS.
4. The access point bridge and extends the
services of the network.
5. It provide address for the connectivity.
Extended service set (ESS): The distributed
system can create a wireless network of
arbitrary size and complexity. It also from
a network which defines an extended
service set (ESS).

The following diagram shows WLAN access
points of distributed systems networked
using ESS.
•

• Here the access points A, B, C, D, E, F and
G networked together and form an ESS.
Generally an ESS have an ID known as
ESSID.
• Suppose to gent the internet I at each
WLAN DS, then establish a connection
between internet I and ESS.
• The ESS access point may exist or
implemented at a base station or gateway
and the access point may have multi point
relay node.
•The ESS can able to interconnect with a
cellular network.

•At this stage the 802.11 can facilitate only
the ESSID, but it not define or provide any
protocols that support distributed system.
• The protocols used in ESS may or may not
be TCP/IT or IPv6, these usage of protocols
may depend upon the how the BSS is
interoperate in a service provider servicing
setup.

IEEE802.11 Protocol Layers:
• 802.11 protocol layers means those are the
physical and data link layers.
• We know that there is a need of multiple
layers each of which may consists of various
protocols are for establishing
communication network.
• Generally these protocols can send the bits
to the above and bellow layers and some of
the layers may communicate with
neighboring node layers.

• In open system interconnectivity the order
of the layers are, Physical (L1), Data link (L),
Network (L3), Transport (L4), Session (L5),
Presentation (L6) and Application (L7) layers.
• Suppose the transceiver send the signals
then the order of the layers are L7 to L1,
when it receiving signals, the order is L1 to
L7.
• But during the communication, the
transceiver may not use the services of
seven layers and the functions of the layers
are also divide among the sub layers.

• Generally the physical layer, does the
sequencing and formatting of data bits, it
also do multiplexing, modulating and
demodulating. Addition and deletion of some
control bits are also takes place at physical
layer.
• The data link layer does the control
functions of addressing, access
coordination, frame sequencing and logical
links.

The following is the description of 802.11
protocol layers
IEEE 802.x: The IEEE 802.x is a set of
protocols defined for networking of
computers. Here x=1 specifies the bridge
between LLC (Logical Link Control) and MAC
(Medium Access Control) sub layers and
802.1 also have some management function
of layer 1 and 2. If X=2 especially specifies
the LLC at the layer 2.
• The 802.1 and 802.2 specifications are
common for all 802.x standard.

• 802.3 specifies the functionalities of MAC
at the layer 2 and physical layer
functionalities in wired networks.
• In 802.x all upper layers have some
common protocols up to 802.10, specifies
security mechanisms.
IEEE 802.1y: IEEE 802.1y when y=1 means
802.11 series protocols, which are the
specifications for WLANs.
• Here each station in WLAN has a logical
architecture as per the 802.11 standard and
consists of a single MAC and one multiple
physical sub layers.

• The 802.11 may include the previous
specifications of 802.x (x= 1-10). So the
nodes using 802.11 may access the network
either wired or through wireless, because
the higher layers of 802.11 are identical to
802.x.
The following diagram shows the physical
and MAC functions in 802.11

• Here the physical layer, which transmit or
receives the signals through wireless
communication or through wire, fiber or
microwave after formatting, multiplexing,
modulating, the following three options of
physical layer is called Physical Media Data
(PMD).
•1The physical layer in 802.11 using
Frequency Hopping Spread Spectrum
(FHSS) or Direct Sequence Spread Spectrum
(DSSS) or using Diffused Infra Red for the
signaling.

2. It also using Orthogonal Frequency
Division Multiple Access (OFDM), which is
capable of multiplexing 6Mbps to
54Mbps.
3. The physical layer may also includes,
Physical Layer Convergence Protocol
(PLCP) and Complementary Code Keying
(CCK) sub layers.
In the diagram, the goal of MAC is to provide
access control functions. These functions
may be addressing, access coordination,
and Frame sequence checking for shared
medium in support of LLC layer.

•The following diagram shows the basic
protocol layers at the transmitter and
receiver in 802.11

• Here MAC service Data Units (MSDUs) are
sent between two entities on the network.
The 802.11 also specifies the services that
required by the LLC.
• The following are the general MAC
functions supported by 802.11 at layer 2.
1.Station services – which include MSDU
delivery, Privacy, Authentication, and de-authentication.
2.Distribution system services –
Distribution, Integration, association,
disassociation and re-association.

Wireless Application Protocol: We know that
wired environment has HTTP for accessing
the websites.
• The HTTP browser is installed at the client
side. The client sends a request to the web
server and server responds to the client
through the internet.
• The following diagram shows web access
architecture based on HTTP

• Coming to the wireless environment,
packet losses and disconnections has the
major problem, so wireless environment
require new web access architecture.
• WAP is an open international standard,
which defines industry oriented
specifications for developing the service
applications.
• Now a days WAP is used in smart phones
and in mobile devices for web browsing and
supporting innovative applications. So WAP
is a powerful framework to support such an
applications.

• There are several services are accessed
through WAP such as, email, downloading
music, sending MMS, receiving news, and
other web services.
• The WAP transmission physical layer
contains, High Speed Circuit Switched Data
(HSCSD), SMS, General Packet Radio
Service (GPRS), GSM, Cellular Digital Packet
Data (CDPD) and 3G bearer services.
• The main objective of WAP is to facilitate
browsing and used of wired internet, in
protocol independent environment.

WAP 1.1 Architecture: We know that WAP
defines a set of protocols. There are mainly
three protocol layers in WAP which
facilitates the wireless data transmission
and reception.
• These three protocol layers are, Transport,
Transaction and Session layers. Here
Wireless Datagram Protocol (WDP) is used
for transmitting and receiving the datagram
over the network.
The following diagram shows functions of
Wireless Application Environment (WAE)

• Here WAE at the layer-7, which supports
the web services, and Wireless Markup
Language (WML). The following are WAE
functions at the (client) Mobile computing
system.
1.WAP supports WML (Wireless Markup
Language) and WML script.
2.It also support WAP binary XML (WBXML).
3.It support Wireless Telephony Applications
(WTA).
4.It is able to maintain user agent profiles.

5. It supports the data formats vCard2.1,
vCalender1.0, address book, pictogram, and
other picture formats (jpg, gif, etc..).
6. It is able to pre configuring the remote
service provider.
WAP 1.1 Gateway:
• A WAP1.1 gateway is required for protocol
conversions between the mobile client and
HTTP server.
• The gateway converts WAE1.1, WSP, WTP,
WTLS and UDP layers encoded data packets
into HTTP and Transport Layer Security
(TLS) formats.

• The gateway also getting the data from the
clients and encoded in UDP format, when
device transmit the data to the server. It also
decoding in the reverse path that the server
sends the data to the client through the
gateway.
• The WAP gateway is able to access the both
wired and wireless networks. Over the
wireless networks it builds the cashes to
procure the data due frequent
disconnections. It also ensures the security
in wired and wireless environment.

• We know that the HTTP environment can
only provide the PULL mode of services – the
client sends the request and pull the data
from the server as a response.
• The WAP gateway support both PUSH and
PULL mode of services.
• The WAP gateway also has WML encoder-decoder,
so that the application written in
WML is converted into HTML, when the
client who using WAE, sends a request to
HTTP server and response from the server to
the client is also decoded into WML formats.

• One more important function of gateway is
iWML Script compilation. The script written
in Common Gateway Interface (CGI) runs at
the HTTP server and then the server
generates the HTML responses to the client.
Wireless Datagram Protocol (WDP):
• The WDP (wireless datagram protocol) a
connectionless protocol over the wireless
environment, so the data transmitted by
using WDP in connection less way like UDP
in wired environment.
• The WDP datagram's provide independent
and stateless information. That is the data

in one datagram is no way to related to data
in another datagram.
• WDP supports the multicasting of the
datagram's over the network. It also uses the
Wireless Control Message Protocol (WCMP)
which functions like an ICMP in wired
environment.
• The WCMP is a connectionless protocol, it
is used when sending the messages, to know
the queuing information, reporting errors,
and for route address advertisement. It also
used for route seeking (soliciting) messages.

• The following diagram shows the WDP
header

• The WDP can enable the adaptation of
datagram's over the wireless environment.
The WDP datagram header is received from
the upper layers at the client device.
• The WDP header consists of source port,
destination port, source IP address,
destination IP address (it is optional), length
of data, and checksum fields.
• The WDP datagram may also has error code
to report errors to the upper layers at client.

Wireless Transport Layer Security (WTLS):
• We know that the Transport Layer Security
is used in wired internet for secure
networking of transport layer data.
• In wired networks the TLS is an optional
one and also TLS maps to Secure Socket
Layer (SSL) in HTTPS (HTTP with SSL).
• In wireless networks also the WTLS is an
optional one, which provide security to the
networked data getting from the transport
layer.

• The following diagrams shows data
exchanges by using WTLS

The following are the WTLS services;
1.It assures integrity when data transactions
occurs between client and gateway.
2.It ensures the privacy of transactions.
3.It maps SSL to HTTPS.
4.It supports TCP, WDP, and WCMP.
5.It serves as a layer, above the WDP and
provide security to datagram's when required.

• Before transmission of the data over the
wireless network, a secure session is
established between the nodes by using the
upper layer protocols, such as WTP, WSP,
WAE.
• The following specifications can takes place
during WTLS establishing secure session;
1.Source device generate a message to
create a secure channel consists the
following information;
a.Source address and source port number.
b.Destination address and destination port
number.

c. Either RSA or ECC algorithms for key
exchange.
d. IDEA or DES algorithms for ciphering the
data.
e. Compression method used for data
compression.
2. The destination side messages for secure
channel establishment conformation
consists the following information.
a.Sequence number.
b.How many times the key is refreshed and
exchanged again

C. Identification of session after
establishment of session.
d. RSA or ECC algorithm for key exchange.
e. IDEA or DES algorithm for ciphering of
text.
f. A compression method for data
compression.
3. After getting the request from the
destination the source generates the secure
channel public key authentication by a
client certificate.
4. Source device generate message to
commit the request.

5. The destination generate the message for
commit conformation request.
Wireless Transaction & Session Layers:
Introduction:
• We know that the TCP getting the problem
of loss of packets in wireless environment,
so we need Wireless Transaction Protocol
(WTP) for sending and receiving of
information in wireless environment.
• In wired networks, first we establish
session (connection) and then transmit the
data as per the TCP segment numbers (here
the maximum segment number is 232 ),

but the wireless environment has frequent
loss of connectivity, so the wireless
environment require compressed codes and
suitable encoding mechanism.
• Here encoding means adding additional
bits for error detection and correction.
• The Wireless Session Protocol (WSP) can
also used compressed binary codes for
establishing wireless sessions.
Wireless Transaction Protocol (WTP):
• Wireless Transaction Protocol (WTP) is an
upper layer of Wireless Transaction Layer
Security (WTLS), so it transmits the data to

WTLS for secure transmission.
•The WTP has also able to directly transmit
the data to Wireless Datagram Protocol
(WDP) or to Wireless Control Message
Protocol (WCMP) without transmit the
information to WTLS.
• WTP supports the joining of messages and
enables asynchronous data transmissions.
• Suppose the transmission is aborted in the
middle of transmission, then the WTP
facilitates set back the whole transaction to
the initial state.
• WTP also indicate the success or failure of
transactions.

• The WTP act as an interface for reliable
transmission and it has three WTP services
classes such as 0, 1 and 2.
1.Class-0: Here the source send the
messages to destination and it should not
expect any response from the destination.
2.Class-1: This class represents reliable data
transfer. Here source start the transaction
with a request.
•Now the destination device obtain the
request then generate the conformation of
invocation.

• After getting the invocation from the
destination, the source responds with data
transmission.
• Finally the device sends the
acknowledgement to the source.
• Here the source takes the responsibility to
remove the duplicate data, provide
retransmission and transaction identifier.
• The total process comes under the PUSH
service, in which there is no
acknowledgement for user’s data except
conformation invocation.

3. Class-2: This class also represents the
reliable data transmission. Here also the
source start the transaction with a request.
• Now the destination device gets this
request and send back the
acknowledgement to the source.
• Now the source responds by transmitting
the information to the destination. Again the
device send the acknowledgement to source.
• Here also the source takes the
responsibility of removing the duplicate
data, retransmission and transmitting
transaction ID.

• Here two acknowledgements, one is
acknowledgement generated by the user and
another is automatic acknowledgement.
• The following diagram shows WTP header
and WTP invocation

Wireless Session Protocol:
• The Wireless Session Protocol support
stateless data transfers, so the client browser
get the packets in any sequence from the
server.
• Here Synchronization Markup Language (Sync
ML) in WSP is used to connect the particular
node to the internet (server). Here the
synchronizations can also takes place between
the client and server by using Sync ML at WAP
application layer.
•The WSP transmit the data to the WTP for
reliable data transmissions other wise the WSP
is also able to transmit the data directly to the
WDP or WCMP.

The following diagram shows WSP protocol
session, it has establishing connection,
receiving and response headers.

• WSP can considered as a compressed
binary encoded version and as a extended
version HTTP.
• The WSP also supports, asynchronous
exchange of data, multiple requests from
clients, push and pull mechanism of data
dissemination, capability negotiation and
content encoding.
• The following is the session management of
WSP.
1. First the session is established by using
the functions of agreed common protocols.

2. In WSP, an established session can be
suspended and then resumed from the point
at which it was suspended.
3. A session can be terminated.
• The WSP having the three service classes
such as 0,1 and 2.
Class-0: This class indicating the source
sending unconfirmed push. It support
session suspension, resumption, and
management. The messages sent from the
source do not get any response from
destination.

Class-1: This class represents the source
sending the confirmation push.
Class-2: This class represents source
support for session invocation, suspension,
and resumption.
The following diagram shows WSP
invocation and request for results;

Wireless Application Environment:
• The Wireless Application Environment
consists of the following components;
1.WML
2. WML Script.
3. WBXML – Wireless Binary XML.
4. WTA - Wireless Telephony Application.
5. Data formats.

• The WML is also a XML based language
which takes the following mobile devices
constraints into account while programming
an application for running on the device.
• These are the constraints of mobile devices;
1.Narrow band network connection with
intermittent loss of connectivity.
2.String parameterization and state
management.
3.Limited user input and output facility.
4.Limited computational resources and
memory.

WML: We know that XML and how to create
applications in XML based languages. Here
tags are used to markup the code.
• The WML is a webpage markup language
for wireless environment internet. There are
two versions of WML those are WML2.x and
WML1.x . The WML2.x may also include
Extensible Hyper Text Markup Language
Mobile Profile( XHTML-MP).
• Generally, the WAP also has the functions
and WML methods at the server for pre
configuration of mobile device.

WML Card:
• WML is used to create the cards for mobile
applications. Here a card represents an
interaction between the user and the deck
contains the cards.
• In WML all the information collected and
managed in the form of deck and cards. The
WML deck is save with file extension .wml.
• Let us consider the deck is a WML file and
cards are records with in the file.
•In WML a scaled down set of procedural
elements are used to control navigation
between the cards and WML parser parses
the information within deck of cards.

• A WML card has the following features;
1.It provide content – programs, data,
commands, strings, or images.
2.It support wide variety of formatting
commands and layout commands.
3.It provides user interface for mobile
devices with constraints as mentioned in the
WML code.
4.Organizing similar deck of cards.
• A WML card is first validated against its
declared document type by using Document
Type definition (DTD) before parsing.

WML Script:
• WML script is a scripting language is used
in wireless environment. It is similar to CGI
script in HTML at server side.
• The WML script is used to retrieving the
application required data from the server
and enables the server response for clients
request.
• In WML script each line of code is loaded
into computer and executed at run time only

• At the client side the WML script is similar
to JavaScript and it does not require to
communicate with the server by sending a
request and waiting for the response.
• WML script is embedded markups within
WML, WAP browser displays the page having
WML script.
• The WML script does not require any pre
compilation, so it is executed very fast and it
is compiled at gateway, only byte code is
sent to the client.

WBXML:
• The Wireless application protocol provides
communication between the client and the
gate way by using the WBXML.
• General XML and WML data formats are
not compact to establish communication
between the client and gateway.
• WBXML represents any information in
binary format, so the data is transmitted to
the gateway in compact format.
• In WBXML we use a binary number
instead to represent a tag.

• The binary codes causes the compact
transmission, but there is no change in
contents, code functionality, and semantic
information.
• WBXML also support and keep the
structure of elements which are used in
XML intact. But metadata information,
document type definitions, conditional
sections are removed when the XML
document is converted into binary format.
• The WBXML browser does not take
unknown elements or attributes from the
gateway.

WTA:
• The specific telephonic features are defined
by the WAT interface (WATI) by using the
WML browser.
• A WTA server can push the script and WTA
event handler can handle the events,
persistent storage can help to data storage
on device.
• WTA can also provide security interface,
only authorized gateway can access the data
at the server.

User agent Profile:
• User agent is a software used by the user
to give inputs using Voice User Interface
(VUI) or Graphic User Interface (GUI) and
also interact with mini browser.
• User agent executes the WMLscript at the
client and displays the result. It also
displays the responses from the server.
• User agent support the small screen device
characteristics and profile enhances, such
as font, display capabilities, touch
characteristics etc.

Data Formats:
• The data displayed on mobile devices is in
special data format.
• vCard2.1 is format for visiting card,
vCalendar 1.0 is the format for calendar. The
mobile devices also support pictogram,
which display small pictures of low
resolution.
END OF UNIT VIII

Mobile Computing UNIT-8

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