The Internet Encyclopedia (Volume 3)

P1: C-167

Guizani WL040/Bidgolio-Vol I WL040-Sample.cls July 16, 2003 10:7 Char Count= 0

818 WIRELESSCOMMUNICATIONSAPPLICATIONS

to send, IP will fragment the packets in order to fit the

network.

Transmission Control Protocol (TCP)

As a transport layer protocol, TCP ensures that data for

which IP finds a destination host will be propagated to

the right application. File transfer protocol (FTP) and hy-

pertext transfer protocol (HTTP) applications might be

running on the same host, and the TCP port number in-

dicates which is the target application. TCP also ensures

that packets of data are delivered reliably and in order.

Packets that have traveled different routes in order to

get to the same destination need to be assembled in the

right order. Finally, TCP provides flow control functional-

ity, which makes sure that the sender and receiver agree

on a suitable speed of data delivery. Covering the lost of

packets and the maintenance of flow control are the two

features that affect wireless performance the most.

Hypertext Transfer Protocol (HTTP)

HTTP is a protocol that handles the transfer of Web pages

and relies on TCP on the transport layer for the reliable,

in-order delivery of individual packets. HTTP is a stateless

protocol, and it has a number of different requests that a

client can use from a server.

Each request is sent as regular ASCII text, and the

server responds with an object. The object returned can

either be a simple Web page or a MIME response contain-

ing several objects, such as images. When fetching each

object of a Web page separately, a new HTTP request must

be performed for every object. Because of the high latency

of those networks, fetching each part of a Web page with a

separate request might cause significant delay. While this

situation might not matter much when you are using a

desktop computer that has a broadband connection, it is

a significant advantage when you are developing for wire-

less networks.

File Transfer Protocol (FTP)

Like HTTP, FTP is an application layer protocol. FTP is

a connection-oriented file transfer between two hosts us-

ing TCP as transport. The only issue with FTP when run-

ning over wireless is greed. A client that fetches a file via

FTP will start one TCP session and keep it throughout the

transmission.

Before we get into the discussion of the different types

of wireless networks/systems, Table 1 shows the compar-

isons between wireless and wireline network systems.

CELLULAR PHONE GENERATION

The first radiotelephone service was introduced in the

United States at the end of the 1940s, and was meant

to connect mobile users in cars to the public fixed net-

work. In the 1960s, a new system launched by Bell

Systems, called “improved mobile telephone service”

(IMTS), brought many improvements like direct dialing

and higher bandwidth. The first analog cellular systems

were based on IMTS and developed in the late 1960s and

early 1970s. The systems were “cellular” because coverage

areas were split into smaller areas, which are served by a

low-power transmitter and receiver.

First Generation (1G)

First generation (1G) phones are analog. It sends informa-

tion as a continuously varying waveform, and can only

be used for voice and have highly variable call quality.

The disadvantage is it is very insecure. Snoopers can lis-

ten in on call or charge calls to another person’s account.

Two key improvements were made during the 1970s—the

invention of the microprocessor and the digitization of

the control link between the mobile phone and the cell

site.

Second Generation (2G)

Second generation (2G) phones cover all speech into digi-

tal code, resulting in a clearer signal that can be encrypted

for security. These systems digitized not only the control

link but also the voice signal. The new system provided

better quality and higher capacity at lower cost to con-

sumers. It includes some kind of messaging, as well as

support for Centrex-style services such as voice mail and

caller ID. Most popular is GSM (global system for mobile

communication), which can send data only at less than

10 Kbps (kilobits per second).

Second^1 / 2 Generation (2.5G)

Most operators are upgrading their 2G networks to higher

data speed using fast modems. This term applies to tech-

nology such as WAP, which uses a compressed version

of the Web to fit into a mobile phone’s slow data rate and

small screen. 2.5G networks, such as GPRS (global packet

radio service), are already available in some parts of

Europe.

Third Generation (3G)

Third generation (3G) systems promise faster communi-

cations services, including voice, fax, and Internet, any-

time and anywhere with seamless global roaming. The

ITU’s IMT-2000 global standard for 3G is expected to en-

able innovative applications and services (e.g., multime-

dia entertainment, infotainment and location-based ser-

vices, among others). Instead of a phone, many terminals

will be small computers or PDAs (personal digital assis-

tants). It will cover not only the connection between a

mobile terminal and its base stations, called a WAN (wide

area network), but also the LAN (local area network). The

vision behind it is mobile multimedia to all at the price of

today’s fixed telephony.

Fourth Generation

Fourth generation networks are already in the labs, tar-

geted for deployment beginning in 2010. It will provide

data rates of up to 100 Mbps, enough for telepresence.

This is a type of virtual reality, defined as full stimulation

of all senses required to provide the illusion of actually

being somewhere else—an illusion that cannot be distin-

guished from the real thing (Anderson, 2001; CDMA, n.d.).