1. Computer Networks
A network is a set of devices or nodes connected by communication links
A node can be a computer, printer or any other device capable of sending and receiving data generated by other nodes in the network.
A link can be a cable, air or optical fiber or any medium which can transmit signal carrying information
It is a collection of hardware and software which can share information.
Example: Sharing of printers

2. Computer Networks Distributed Processing
A task is divided among multiple computers and processed Network Criteria
Performance
Measured in terms of transit time and response time
Often evaluated by 2 metrics: Throughput and delay
Reliability
Accuracy of Delivery, Frequency of failure and time to recover
Security
Protecting data from unauthorized access, damage and development

3. Computer Networks Physical Structure
Type of connection: In a network one or more devices are connected through links
Point to point
Multipoint or multi-drop connection
Spatially shared: several devices uses the link simultaneously
Timeshared: Devices takes turns
Physical Topology: The way in which the network is laid out physically.

4. Classification of networks
Based on the size of the network it is divided into
(PAN)- Personal Area Network
LAN- Local Area Networks
WAN- Wide Area Networks
MAN- Metropolitan Area Networks

5. Classification of networks
Personal Area Network (PAN)
The interconnection of devices within the range of an individual person, typically within a range of 10 meters.
For example, a wireless network connecting a computer with its keyboard, mouse or printer is a PAN.
Another example of PAN is a Bluetooth.

6. Classification of networks
Local Area Network (LAN):
Privately-owned networks covering a small geographic area, like a home, office, building or group of buildings (e.g. campus).
They are widely used to connect computers in company offices and factories to share
resources (e.g., printers) and exchange information. LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance.
Knowing this bound makes it possible to use certain kinds of designs that would not otherwise be possible.
It also simplifies network management. Traditional LANs run at speeds of 10 Mbps to 100 Mbps, have low delay (microseconds or nanoseconds), and make very few errors.
Newer LANs operate at up to 10 Gbps.
Early LAN (Local Area Network) networks were formed using coaxial cable, coax is an electric cable and it is used to carry radio signals.
LAN (Local Area Network) setup is developed by connecting two or more than two computers with each other using a physical connection in order to share files and data overtime.

7. Classification of networks
Metropolitan Area Network (MAN): Covers a larger geographical area than is a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of LANs. Metropolitan Area Networks can span up to 50km, devices used are modem and wire/cable.
Most widely used technologies to develop a MAN (Metropolitan Area Network) network are FDDI (fiber distribution data interface), ATM (Asynchronous Transfer Mode) and SMDS (switched multi megabit data service).ATM (Asynchronous Transfer Mode) is the most frequently used of all. ATM (Asynchronous Transfer Mode) is a digital data transfer technology. It was developed in 1980 to improve the transportation of real time data over a single network. ATM (Asynchronous Transfer Mode) works just like cell relay system, where data is separated in the form of fixed equal sized packets and is transferred overtime. The purpose of ATM (Asynchronous Transfer Mode) was to access clear audio and video results during a video conferencing.

8. Classification of networks
Wide Area Networks (WAN): Computer network that covers a large geographical area, often a country or continent. (Any network 1 whose communications links cross metropolitan, regional, national boundaries). Less formally, a network that uses routers and public communications links. Routers will be discussed later.
WAN (Wide Area Network) networks are established often by seeking help from telecomm departments who provide the] facility of leased lines. Router is connected to the LAN at one side and a hub is attached at the other end.

9. Internet Interconnection of networks or internetwork
When 2 or more networks are connected, it is called as internet.
History of Internet
ISP- Internet Service Provider

10. Internet History of Internet
Mid 1960’s- Stand alone devices(multi-vendor systems that can not communicate with each other)
ARPA- (Advanced Research Projects Agency) found a way to connect these computers to share information
In 1967 ARPA introduced the idea of ARPANET
Each host computer attached to a specialized computer called Interface Message Processor(IMP) and the IMPs are connected to one another
In 1969 first physical network was construct

11. Internet History of Internet
Software called NCP(Network Control Protocol) provided communication between hosts
This is the first operational packet switching network
In 1972 introduced the concept of protocols to achieve end to end delivery of packets and the first program was created
The TCP concept is developed
During 1973 the development began on the protocol called TCP/IP

12. Internet
Most end users who wants the internet connection use the services of ISP (Internet Service Providers)
An Internet Service Provider (ISP) is a company that provides internet connectivity to home and business customers.
It provides access to the internet through a variety of intermediaries
Dial up modems
Wireless modem
Broadband
Cable modem

13. Protocol
For proper communication, entities in different systems must speak the same language
there must be mutually acceptable conventions and rules about the content, timing and underlying mechanisms
Those conventions and associated rules are referred as “PROTOCOLS”

14. Protocol A set of rules governing data Communications that defines
What is Communicated
How it is Communicated
When it is Communicated
Key elements are
Syntax
Semantics
Timing

15. Protocol Syntax : Refers to structure or format of the data
Data formats, Signal levels
Semantics:
Refers to meaning of each section of bits
control information, error handling information
Timing:
When and how fast the data can be sent
Speed matching and sequencing

16. Protocol
STANDARS
Enables national and international interoperability of data and telecommunication technology and process
2 Categories
De-facto- Not approved by an organization but wide spread
De jure- Standards approved by organizations like ISO, ITU-T, ANSI, IEEE

17. Protocol PROTOCOL ARCHITECTURE
Data exchange between 2 devices is a complex task
Protocol architecture is the layered structure of hardware and software that supports data exchange
There are a number of tasks to be performed in a data transfer application
These tasks are broken into subtasks and implemented separately
The modules are arranged in a vertical stack
Each layer in the stack performs a related subset of functions required to communicate with another system
Each layer provides services to the next higher layer

18. Protocol PROTOCOL ARCHITECTURE
Layers are designed in such a way that change in one layer do not affect the other layer
To enable communication between 2 systems the same set of layered functions must exist in 2 systems. The corresponding layers are called peers.

19. Protocol
LAYERED ARCHITECTURE

20. Protocol
A BASIC 3 LAYER MODEL

21. Protocol PROTOCOL ARCHITECTURE- 3 layer model Network Access Layer
Manages the exchange of data between the computer and network
Sending computer provides the address of destination
Dependent on the type of network used.
This layer may need specific drivers and interface equipment depending on type of network used.

22. Protocol PROTOCOL ARCHITECTURE- 3 layer model Transport Layer
reliable exchange of data
To make sure that all the data packets arrived in the same order in which they are sent out
Packets nor received or received in error are retransmitted
Independent of the network being used
Independent of the application

23. Protocol PROTOCOL ARCHITECTURE- 3 layer model Transport Layer
reliable exchange of data
To make sure that all the data packets arrived in the same order in which they are sent out
Packets nor received or received in error are retransmitted
Independent of the network being used
Independent of the application
Application Layer
Provides support for different user applications.
Example: , File Transfer

24. Protocol Protocol Data Units (PDU)
User data is passed from layer to layer
Control information is added/removed to/from user data at each layer
Header (and sometimes trailer)
each layer has a different header/trailer
Data + header + trailer = PDU (Protocol Data Unit)
This is basically what we call packet
each layer has a different PDU

25. Protocol