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UNIT NO 01 Basics of communication

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DATA COMMUNICATION FUNDAMENTAL

Concepts & Terminology:

Introduction1) Today computer is available in many offices and homes and therefore there is a need to share data and programs among various computers.2) With the advancement of data communication facilities the communication between computers has increased and thus it has extended the power of computer beyond the computer room. 3) Now a user sitting at one place can communicate with computers of any remote site through communication channel

Data Communication1) We all are acquainted with some sorts of communication in our day to day life. For communication of information and messages we use telephone and postal communication systems. 2) Similarly data and information from one computer system can be transmitted to other systems across geographical areas. Thus datatransmission is the movement of information using some standard methods.3) These methods include electrical signals carried along a conductor, opticalSignals along an optical fibers and electromagnetic areas.4) Suppose a manager has to write several letters to various clients. First he has to use his PC and Word Processing package to prepare the letter, if the PC is connected to all the client's PC through networking, he can send the letters to all the clients within minutes. 5) Thus irrespective of geographical areas, if PCs are connected through communication channel, the data and information, computer files and any other programs can be transmitted to other computer systems within seconds. 6) The modern form of communication like e-mail and Internet is possible only because of computer networking.



A Communication Model:1) The fundamental purpose of Communication System is the exchange of data between two parties.2) Following fig.(a) shows a simple model of communications and fig.(b) shows one particular example which is communication between a workstation and a server over a public telephone exchange.

Source system Destination System

Fig. (a)

Workstation Modem Public telephone network Modem server

Fig. (b)

Source: The sender (source) who creates the message to be transmitted Examples are telephones and personal computers.Transmitter:i) Usually the data generated by a source system are not transmitted in the form of in which they were generated .

Receiver

Destination

Source Transmitter

Transmission system



ii)Rather, a transmitter transform and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system.iii)for eg.a modem takes a digital bit stream from an attached device such as a personal computer and transform that bit stream into an analog signal that can be handled by the telephone network.Transmission System: This can be a single transmission line or a complex network connecting Source and Destination. Receiver:i)The Receiver accepts the signal from the transmission system and converts it into form that can be handled by the destination device. For eg.a modem will accept an analog signal coming from a network or transmission line and convert into a digital bit stream.Destination: Takes the incoming data from the receiver. In data communication four basic terms are frequently used.They are:Data : A collection of facts in raw forms that become information afterprocessing.Signals: Electric or electromagnetic encoding of data.Signaling: Propagation of signals across a communication medium.Transmission: Communication of data achieved by the processing of signals.

Data Transmission ModesThere are three ways for transmitting data from one point to another as shownin Fig. Simplex A to B only

Half-Duplex A to B or B to A

Full-Duplex A to B and B to A

A B

BA

BA



1. Simplex: In simplex mode the communication can take place in one direction. The receiver receives the signal from the transmitting device. In this mode the flow of information is Uni-directional. Hence it is rarely used for data communication.2. Half-duplex: In half-duplex mode the communication channel is used in both directions, but only in one direction at a time. Thus a half-duplex line can alternately send and receive data.3. Full-duplex: In full duplex the communication channel is used in both directions at the same time. Use of full-duplex line improves the efficiency as the line turnaround time required in half-duplex arrangement is eliminated. Example of this mode of transmission is the telephone line.Computer NetworkA computer network is interconnection of various computer systems located at different places. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communication data and sharing resources. The computer that provides resources to other computers on a network is known as server. In the network the individual computers, which access shared network resources, are known as nodes.Types of Networks

Local Area Networks:

Local area networks, generally called LANs, are privately-owned networks within a single building or campus of up to a few kilometers in size.

They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information. LANs are distinguished from other kinds of networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology.

LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance



Various topologies are possible for broadcast LANs. Figure 1-7 shows two of them. In a bus (i.e., a linear cable) network, at any instant at most one machine is the master and is allowed to transmit. All other machines are required to refrain from sending

Metropolitan Area Networks

Metropolitan area network, or MAN, covers a city. The best-known example of a MAN is the cable television network available in many cities.

This system grew from earlier community antenna systems used in areas with poor over-the-air television reception. In these early systems, a large antenna was placed on top of a nearby hill and signal was then piped to the subscribers' houses.

At first, these were locally-designed, ad hoc systems. Then companies began jumping into the business, getting contracts from city governments to wire up an entire city. The next step was television programming and even entire channels designed for cable only.



Often these channels were highly specialized, such as all news, all sports, all cooking, all gardening, and so on. But from their

inception until the late 1990s, they were intended for

A metropolitan area network based on cable TV

Wide Area Networks:

A wide area network, or WAN, spans a large geographical area, often a country or continent. It contains a collection of machines intended for running user (i.e., application) programs. We will follow traditional usage and call these machines hosts. The hosts are connected by a communication subnet, or just subnet for short.

Hosts are owned by the customers (e.g., people's personal computers), whereas the communication subnet is typically owned andoperated by a telephone company or Internet service provider. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener.

Separation of the pure communication aspects of the network (the subnet) from the application aspects (the hosts), greatly simplifies the complete network design

A short comment about the term ''subnet'' is in order here. Originally, its only meaning was the collection of routers and communication lines that moved packets from the source host to the destination host

In most wide area networks, the subnet consists of two distinct components: transmission lines and switching elements. Transmission lines move bits between machines.

They can be made of copper wire, optical fiber, or even radio links. Switching elements are specialized computers that connect three or more transmission lines. When data arrive on an incoming line, the switching element must choose an outgoing line onwhich to forward them.



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Wide Area Network

Basics of communicationBasics of communication

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Transmission impairments Signal received may differ from signal transmitted Analog Signals Degradation of signal quality Digital Signals Bit errors Classification

o Attenuation and Delay distortiono Noise

Attenuation:

Signal strength falls off with distance Depends on medium Designer needs to address problems:

Received signal strength: Must be enough to be detected Must be sufficiently higher than noise to be received without error Attenuation is an increasing function of frequency Equalizer circuit

Delay Distortion• Related to propagation speed • Propagation velocity varies with frequency• Different frequency components experience different delays• Eventually, arrive at different time

Noise Additional signals inserted between transmitter and receiver Thermal

o Due to thermal agitation of electronso White noiseo Upper bound on the performance

Intermediation Signals that are the sum and difference of original frequencies sharing a medium



Crosstalk A signal from one line is picked up by another

Unwanted electrical coupling between the transmission paths

Impulse Irregular pulses or spikes

External electromagnetic disturbance

Short duration

High amplitude

Analog & Digital data transmission Data

o Entities that convey meaningo Signalso Electric or electromagnetic representations of datao Transmissiono Communication of data by propagation and processing of signals

AnalogContinuous values within some intervale.g. sound, videoDigitalDiscrete valuese.g. text, integer

Analog Continuously variable Various media wire, fiber optic, space Speech bandwidth 100Hz to 7kHz Telephone bandwidth 300Hz to 3400Hz Video bandwidth 4MHz



Digital Use two DC components Advantage:

o Cheapero Less susceptible to Noise & Interference

Disadvantage:o Greater Attenuation

Pulses become rounded and smaller Leads to loss of information

Channel Capacity Data rate

o In bits per secondo Rate at which data can be communicated

Bandwidtho In cycles per second of Hertzo Constrained by transmitter and medium

Noiseo Introduce errors

Guided Transmission Media• Twisted Pair

• Analog transmission • Amplifiers every 5km to 6km

• Digital transmission• Use either analog or digital signals• repeater every 2km or 3km

• TP is Limited • Distance• Bandwidth • Data rate• Susceptible to interference and noise



• Easy coupling of electromagnetic fields•

Unshielded Twisted Pair (UTP)• Ordinary telephone wire• Less expensive• Weak immunity against noise and interference • Suffers from external EM interference

UTP Categories:Cat 3

upto 16MHzVoice grade found in most officesTwist length of 7.5 cm to 10 cm

Cat 4upto 20 MHz

Cat 5upto 100MHzCommonly pre-installed in new office buildingsTwist length 0.6 cm to 0.85 cm

Cat 5 E (Enhanced) –see tablesCat 6Cat 7

Shielded Twisted Pair (STP)• An extra metallic sheath on each pair• Relatively more expensive• Provide better performance than UTP

• Increased Data rate • Increased Bandwidth



Coaxial Cable

• Most commonly used medium• Telephone network

• Between house and local exchange (subscriber loop)



• Within buildings• To private branch exchange (PBX)

• For local area networks (LAN)• 10Mbps or 100Mbps

Applications

• Television (TV) signals distributiono Ariel to TVo Cable TV

• Long distance telephone transmissiono Can carry 10,000 voice calls simultaneouslyo Being replaced by fiber optic

• Short distance computer systems linkso Local area networks (LAN)o Metropolitan area network (MAN)

• Advantages• Less expensive • Easy to work with

• Disadvantages• Low data rate• Short range

• Optical Fiber



Optical Fiber - Transmission CharacteristicsGreater capacity

o Data rates of hundreds of Gbps o Smaller size & weighto Made up of extremely thin fibers

• Lower attenuationo Electromagnetic isolation

• Greater repeater spacingo 10s of km at least

• Operational range 1014 to 1015 Hz

o Light sourceo Light Emitting Diode (LED)

Cheaper Wider operating temperature range Last longer

o Injection Laser Diode (ILD) Operates on laser principle More efficient

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Greater data rate

Line Coding techniques:

Types of Digital to Digital Encoding

Basics of communication

Types of Digital to Digital Encoding


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Compared with its polar counterpart (see the next section), this scheme is very costly. As (power needed to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, this scheme is normally data communications today.


Compared with its polar counterpart (see the next section), this scheme is very costly. As we will see shortly, the normalized power (power needed to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, this scheme is normally


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we will see shortly, the normalized power (power needed to send 1 bit per unit line resistance) is double that for polar NRZ. For this reason, this scheme is normally not used in

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• AMI (alternate mark inversion)– The work mark comes from telegraphy and means – AMI means alternate 1 inversion– The neutral zero voltage represents binary 0.– Binary 1s are represented by alternating positive and negative voltages.

• Pesudotenary Same as AMI, but 1 bit is encoded as a zero voltage and the 0 bit is encoded as alternating positive and negative voltages.


comes from telegraphy and means 1.AMI means alternate 1 inversionThe neutral zero voltage represents binary 0.Binary 1s are represented by alternating positive and negative voltages.

but 1 bit is encoded as a zero voltage and the 0 bit is encoded as alternating positive and negative voltages.


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but 1 bit is encoded as a zero voltage and the 0 bit is encoded as alternating positive and negative voltages.

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B8ZS Encoding

Block Coding:

• Use redundancy to ensure synchronization and to provide some kind of inherent error detecting.

• In general, block coding changes a block of


Use redundancy to ensure synchronization and to provide some kind of inherent error detecting.

changes a block of m bits into a block of n bits, where n is larger than m.


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• Block coding is referred to as an mB/nB encoding technique.

• For example:

– 4B/5B encoding means a 4-bit code for a 5-bit group.

• Block coding is normally referred to as mB/nB coding;

• it replaces each m-bit group with an n-bit group.

–

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Signal-to-noise ratio:Signal-to-noise ratio (often abbreviated SNRdesired signal to the level of background noiseA ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. While SNR is commonly quoted for electrical sigbe applied to any form of signal (such as isotope levels in an

Signal-to-noise ratio is defined as the power ratio between a

signal):

where P is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within

the same system bandwidth.

Modulations systems

What is modulation ?


SNR or S/N) is a measure used in science and engineering that compares the level of noise. It is defined as the ratio of signal power to the noise power, often expressed in

A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. While SNR is commonly quoted for electrical sigbe applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells).

ratio between a signal (meaningful information) and the background

is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within


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) is a measure used in science and engineering that compares the level of a nal power to the noise power, often expressed indecibels.

A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can between cells).

(meaningful information) and the background noise (unwanted

is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within



• Modulation = Adding information to a carrier signal

• The sine wave on which the characteristics of the information signal are modulated is called a carrier signal

Digital Modulation

1.1 Pulse Code Modulation:

Digital Transmission of Analog DataDigitization – process of converting analog data into digital signal

• example: telephone system

human voice ↔ analog data ↔ analog signal ?!

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analog signal is sensitive to noise, especially over long

reconstructed)

solution:

(1) digitize the analog signal at the sender

(2) transmit digital signal

(3) convert digital signal back to analog data at the receiver

Example


analog signal is sensitive to noise, especially over long distance (cannot be perfectly

reconstructed)

solution:

digitize the analog signal at the sender

transmit digital signal

convert digital signal back to analog data at the receiver


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distance (cannot be perfectly



Pluse Code Modulation (PCM), consists of 2 steps

(1) sampling – obtain signal values at equal intervals (T)

(2) quantization – approximate samples to certain values

SamplingSampling –Pulse Amplitude Modulation (PAM)

1. “digitization in time” - sampling process results in signal that is discrete in time but analog in amplitude!

2. choice of sampling interval T is determined by how fast a signal changes, i.e. frequency content of the signal



PAM signal quantized signal



Quantization Error– by quantizing the PAM signal, the original signal is

now only approximated & cannot be 100% recovered

• effect known as quantizing error or quantizing noise

Quantization • PAM signal samples have amplitudes of ‘∞ precision” –

direct encoding of such amplitudes would require ∞

number of bits (digital pulses) per sample

• to convert PAM signal to digital signal (that is practical

for transmission), each sample has to be ‘rounded up’to the nearest of M possible quantization levels



Delta-Modulation – most popular alternative to PCM• analog signal is approximated by staircase function

• only a single binary digit is required for each sample

!!!

• at each sampling time (kT), the function moves up or down a constant amount δ (step size) – the staircase function attempts to track the original waveform as closely as possible

• at each sampling time, the analog input is compared to the most recent value of the approximating staircase function

• binary-1 is generated if the function goes

up, binary-0 otherwise





1)step size (δ) – should not be too small, nor too large

• small δ + signal changes rapidly � underestimation

• large δ + signal changes slowly � overestimation

(2) sampling time (T)

• smaller T increase overall accuracy

• but, small T increases output data rate, i.e. # of bps



What is DPCM?

Differential pulse code modulation (DPCM) is a procedure of converting an analog into a digital signal in which an analog signal is sampled and then the difference between the actual sample value and its predicted value (predicted value is based on previous sample or samples) is quantized and then encoded forming a digital value.

DPCM code words represent differences between samples unlike PCM where code words represented a sample value.

Basic concept of DPCM - coding a difference, is based on the fact that most source signals show significant correlation between successive samples so encoding uses redundancy in sample values which implies lower bit rate.

Realization of basic concept (described above) is based on a technique in which we have to predict current sample value based upon previous samples (or sample) and we have to encode the difference between actual value of sample and predicted value (the difference between samples can be interpreted as prediction error).Because it's necessary to predict sample value DPCM is form of predictive coding.

DPCM compression depends on the prediction technique, well-conducted prediction techniques lead to good compression rates, in other cases DPCM could mean expansion comparing to regular PCM encoding.

ADPCM (adaptive differential pulse-code modulation)



Short for Adaptive Differential Pulse Code Modulation, a form ofpulse code modulation (PCM) that produces a digital signal with a lower bit rate than standard PCM. ADPCM produces a lower bit rate by recording only the difference between samples andadjusting the coding scale dynamically to accommodate large and small differences. Some applications use ADPCM to digitize avoice signal so voice and data can be transmitted simultaneously over a digital facility normally used only for one or the other.

Multiplexing

• Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

• A Multiplexer (MUX) is a device that combines several signals into a single signal.

• A Demultiplexer (DEMUX) is a device that performs the inverse operation.





Frequency-division Multiplexing (FDM)

• FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.

• In FDM signals generated by each device modulate different carrier frequencies. These modulated signals are combined into a single composite signal that can be transported by the link.

• FDM is an analog multiplexing technique that combines signals



•

•

• In FDM signals generated by each device modulate different carrier frequencies. These modulated signals are combined into a single composite signal that can be transported by the link.

• Carrier frequencies are separated by enough bandwidth to accommodate the modulated signal.

• These bandwidth ranges arte the channels through which various signals travel.

• Channels must separated by strips of unused bandwidth (guard bands) to prevent signal overlapping.



Example

• Five channels, each with a 100-KHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 KHz between the channels to prevent interference?

For five channels, we need at least four guard bands. This means that the required bandwidth is at least

• 5 x 100 + 4 x 10 = 540 KHz,

Wave-division Multiplexing (WDM)

• Wave-division multiplexing is conceptually the same as FDM, except that multiplexing and demultiplexing involve light signals transmitted through fiber-optic channels.



• The purpose is to combine multiple light sources into one single light at the multiplexer and do the reverse at the demultiplexer.

• Combining and splitting of light sources are easily handled by a prism.



Time-division Multiplexing (TDM):

• Time-division multiplexing (TDM) is a digital process that can be applied when the data rate capacity of the

transmission medium is greater than the data rate required by the sending and receiving devices.



• TDM can be implemented in two ways: synchronous TDM and asynchronous TDM.

• In synchronous time-division multiplexing, the term synchronous means that the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

• Frames

Time slots are grouped into frames. A frame consists of a one complete cycle of time slots, including one or more slots dedicated to each sending device.

TD-SCDMA

Time Division Synchronous Code Division Multiple Access (TD-SCDMA) or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate (LCR) : is an air interface[ found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA.

Together with TD-CDMA, it is also known as UMTS-TDD or IMT 2000 Time-Division (IMT-TD).



TD-SCDMA uses the S-CDMA channel access method across multiple time slots.

Traditional Connectivity

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Virtual Private Network

Virtual Private Network is a type of private network that uses public telecommunication, such as the Internet, instead of leased lines to communicate.

Became popular as more employees worked in remote

Terminologies to understand how VPNs work.

Basics of

Page

Virtual Private Network is a type of private network that uses public telecommunication, such as the Internet, instead of leased lines to communicate.

Became popular as more employees worked in remote locations.

Terminologies to understand how VPNs work.

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Virtual Private Network is a type of private network that uses public telecommunication,

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Employees can access the network (Intranet) from remote locations.

Secured networks.

The Internet is used as the backbone for VPNs

Saves cost tremendously from reduction of equipment and maintenance cos

Brief Overview of How it Works

Basics of

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Employees can access the network (Intranet) from remote locations.

The Internet is used as the backbone for VPNs

Saves cost tremendously from reduction of equipment and maintenance costs.

Brief Overview of How it Works

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Two connections – one is made to the Internet and the second is made to the VPN.

Datagrams – contains data, destination and source information.

Firewalls – VPNs allow authorized users to pass through the firewalls.

Protocols – protocols create the VPN tunnels.

Four Critical Functions

Authentication – validates that the data was sent from the sender.

Access control – limiting unauthorized users from accessing the network.

Confidentiality – preventing the data to be read or copied as the data is being transported.

Data Integrity – ensuring that the data has not been altered

Tunneling A virtual point-to-point connection made through a public network. It transports encapsulated datagrams.

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VPN Encapsulation of Packets

Basics of

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LTE: Long Term Evolution

The successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services.

In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.

There has been a rapid increase in the use of data carried by cellular services, and this increase will only become larger in what has been termed the "data explosion". To cater for this and the increased demands for increased data transmission speeds and lower latency



ZigBee

• ZigBee is a technological standard designed for control and sensor networks



• Based on the IEEE 802.15.4 Standard

• Created by the ZigBee Alliance

• Operates in Personal Area Networks (PAN’s) and device-to-device networks

• Connectivity between small packet devices

• Control of lights, switches, thermostats, appliances, etc.

Characteristics

• Low cost

• Low power consumption

• Low data rate

• Relatively short transmission range

• Scalability

• Reliability

• Flexible protocol design suitable for many applications



ZigBee and Bluetooth Comparison

Feature(s) Bluetooth ZigBee

Power Profile days years

Complexity complex Simple

Nodes/Master 7 64000

Latency 10 seconds 30 ms – 1s

Range 10m 70m ~ 300m

Extendibility no Yes

Data Rate 1 Mbps 250 Kbps



Security 64bit, 128bit 128bit AES and Application Layer

Wireless Broadband Technologies

Standard Family Downlink(Mbps)

Uplink(Mbps)

Coverage

WiFi 802.11 11/54/150/300 100m

WiMAX 802.16e 144 35 10km



UMTS (3G)/HSPA (3.5G)

3GPP 14.4 5.76 30km

LTE (4G) 3GPP 360 80 30km

Wireless Technology Trends

• WiFi

– More hotspots, higher speed (802.11 a/b/g -> 802.11 n)

• WiMAX

– Bill Payne (CTO, Motorolla), said WiMAX will finally evolve into LTE.

• LTE

– Good coverage and high throughput (with offloading)

• What is WiFi



– Short for “Wireless Fidelity”

– A trademark of the Wi-Fi Alliance

– The brand name for products using the IEEE 802.11 family of standards

– Commonly used for “wireless local area network” (WLAN)

Comparison Between Similar Technologies

Bluetooth Wi-Fi

Maximum Operating

Range

100 m 100 m

Operating Frequency

2.4 GHz 2.4/5 GHz (802.11n)



Directional Communication

Two way Two way

Bit Rate 22 Mbps 144 Mbps

Potential Uses Communicate between phones,

peripheral devices

Wireless internet

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Topologies Relevant for Wireless

Basics of

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Topologies Relevant for Wireless Networking

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• Star- Yes, standard wireless topology• Tree -Yes (a combination of star and line)• Line -Yes, with two or more elements (PtP)• Mesh- Yes, mainly partial mesh• Ring- Possible, but rarely found• Bus -Not applicable. Why?

Wireless Networks

Need: Access computing and communication services, on the move Infrastructurebased Networks traditional

cellular systems (base station infrastructure)

Wireless LANs

– Infrared (IrDA) or radio links (Wavelan)

– very flexible within the reception area; adhoc networks possible

– low bandwidth compared to wired networks (110 Mbit/s)

Ad hoc Networks

– useful when infrastructure not available, impractical, or expensive

– military applications, rescue, home networking

Cellular WirelessSingle hop wireless connectivity to the wired world

– Space divided into cells

– A base station is responsible to communicate with hosts in its cell



– Mobile hosts can change cells while communicating – Handoff occurs when a mobile host starts communicating via a new base station

MultiHop Wireless

May need to traverse multiple links to reach destination



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Mobile Ad Hoc Networks (MANET)

Host movement frequent Topology change

frequent

A B A B

No cellular infrastructure. Multihop wireless links. Data must be routed via intermediate

nodes.

Why Ad Hoc Networks ?

Setting up of fixed access points and backbone infrastructure is not

always viable

– Infrastructure may not be present in a disaster area or war zone

– Infrastructure may not be practical for shortrange radios; Bluetooth (rang~ 10m)

Ad hoc networks:

– Do not need backbone infrastructure support

– Are easy to deploy

– Useful when infrastructure is absent, destroyed or impractical

Personal area networking

– cell phone, laptop, ear phone, wrist watch

Military environments

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Prof. Sunil Deokule Page 57

– soldiers, tanks, planes

Civilian environments

– taxi cab network

– meeting rooms

– sports stadiums

– boats, small aircraft

Emergency operations

– searchandrescue

– policing and fire fighting

·· Limitations of the Wireless Network

· packet loss due to transmission errors · variable capacity links · frequent disconnections/partitions · limited communication bandwidth · Broadcast nature of the communications

· Limitations Imposed by Mobility · dynamically changing topologies/routes · lack of mobility awareness by system/applications

· Limitations of the Mobile Computer · short battery lifetime · limited capacities

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