7. Transmission of the information can be analog or digital .therefore we have four possibilities:
1. Analog information transmitted as an analog signal.
2. Analog information transmitted as a digital signal.
3. Digital information transmitted as an analog signal.
4. Digital information transmitted as a digital signal
When a signal carrying information is transmitted, it looses its energy and strength and gathers
some interference (noise) as it propagates away from the
BOOSTED / AMPLIFIED
Boost energy and strength of a signal, it must be amplified (in case of analog signals)
rebuilt (in case of digital signals)
NOISE AMPLIFICATION in Analog Signal
8. Why Digital Signal is preferred over Analog Signal in communication?
• FILTERED OUT of noise in Digital Signal
• processing of information for error detection and correction, applying encryption and
decryption techniques to sensitive information.
9. COMPUTER NETWORKS
Interconnection of computers.
The interconnection forms a facility that provides reliable and efficient means of
communication among users and other devices.
Computer networks are also referred to as computer communication networks.
Interconnection among computers may be via wired or wireless transmission
Two broad categories
1. Wide area networks
2. Local/metropolitan area networks
10. (a) A typical WAN. (b) A typical local/metropolitan area network. (c) A typical
local/metropolitan area communication ring network
11. • Users will be sharing the transmission link to exchanging their information.
Users will also share
• the processing power of the computers.
• buffering capacity to store the information.
• and any other resources that are connected to the computer network.
• The information from one user to another may need to pass through several switching
nodes and transmission links before reaching its destination.
• If one path is not available, not feasible, or not functional, some other path may be used
• Exchange of Large Quantity of Information via a Packets of information.
12. TRANSPORTION OF NFORMATION :
Major aspects are
Addressing mechanism to identify users.
Addressing mechanism for information packets to identify their source and destination
Establishing a connection between sender and receiver and maintaining it
Choosing a path or a route to carry the information from a sender to a receiver
Implementing a selected route or path.
Checking information packets.
Encryption and decryption of information
Controlling the flow of information.
Informing the sender.
Billing for the use of resources
Ensuring that different computers running different applications and operating systems can exchange
Preparing information appropriately for transmission .
13. OSI (open system interconnection) Model
The International Organization for Standardization (ISO) established the Open
Systems Interconnection (OSI) Reference Model
Each layer deals with a particular aspect of network communication.
14. WIDE AREA COMPUTER NETWORKS:
A WAN consist of switching nodes and transmission links.
Layout of the switching nodes and transmission links is based on the traffic pattern and expected
volume of traffic flow from one site to another site.
When a user is ready to transmit information
1. Connection oriented service
2. connectionless service
16. BISDNs (Broadband Integrated Services Digital
Transmit voice, video and data at the same time over fiber optic telephone lines.
Broadband ISDN can support data rates of 1.5 million bits per second (bps)
Asynchronous transfer mode (ATM) is expected to be used as a transfer mechanism
in BISDNs where information is transmitted into the form of the cell
17. LOCAL & METROPOLITAN AREA NETWORK
LOCAL AREA NETWORK
Limited geographical scope(few kilometers)
Limited to building or an organization
METROPOLITAN AREA NETWORK
Large transmission area (150 km)
High data rates
TRANSMISSION IN LOCAL & METROPOLITAN AREA NETWORKS
18. CATAGORIES OF MAC(medium access control)PROTOCOL
Controlled Access Protocols.
Contention based protocols.
CONTROLLED ACCESS PROTOCOLS.
• Users take TURNS.
• Only one user is allowed to transmit info. at a time.
CONTENTION BASED ACCESS PROTOCOLS
• Don't take turns.
• User makes own decision to transmit information.
• Example: carrier sense multiple access with collision detection (CSMA/CD)
19. WIRELESS AND MOBILE COMMUNICATION
The devices used for wireless communication require certain features
Low power consumption
worldwide communication ability.
Access to a communication network is wireless so that the end users remain free to move.
Range of wireless communication is always limited.
Range of user mobility is also limited.
20. To overcome this limitations:
A geographical region is divided into smaller regions called CELLS.
• Each cell has a fixed communication device that serves all mobile devices within that
• As a mobile Device moves out of one cell and into another cell, service of that
connection is transferred from one cell to another. This is called the handoff process.
• Low power consumptions.
21. RESOURCE ALLOCATION TECHNIQUES
Two approaches for allocation of resources among the users.
Static Allocation of resources
Dynamic allocation of resources
STATIC ALLOCATION OF RESOURCES
• Quantity of resources is allocated to each user.
• If user doesn't use his allocated resources , no one else can
DYNAMIC ALLOCATION OF RESOURCES
• Desired quantity of resources is allocated to users on the basis of their demands and for
the duration of their need.
• Once the need is satisfied, the allocation is retrieved.
• Someone else can use these resources if needed.
22. CHALLENGES AND ISSUES
Propagation Delay (the time for a signal to propagate from one end to another)
Integrations of different services in the same networks & Each type of service has its own
requirements to achieving a desired level of quality of service
Maintaining security and integrity of information.