A network is a collection of computers and devices connected to each other. The network allows computers to communicate with each other and share resources and information. The Advance Research Projects Agency (ARPA) designed "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defence. It was the first computer network in the world in late 1960's and early1970's.
Why a Network?
Distribute pieces of computation among computers (nodes)
Remote Data/File Access , Remote I/O Devices
Personal communications (like e-mail, chat, audio/video conferencing)
World Wide Web
Computer Networks Network Classification
On the basis of
Based on their scale, networks can be classified as Local Area Network (LAN) , Wide Area Network (WAN) , Metropolitan Area Network (MAN) , Personal Area Network (PAN) , Virtual Private Network (VPN) , Campus Area Network (CAN) , Storage Area Network (SAN) , etc.
Connection Method such as Optical Fiber, Ethernet, Wireless LAN etc.
Network Architecture such as Client-Server or Peer to Peer
Topology- Bus, Star, Ring , Mesh, Tree, Hybrid
Types of Network
Personal Area Network (PAN)
Local Area Network (LAN)
Campus Area Network (CAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
Global Area Network (GAN)
Virtual Private Network (VPN)
a) Without Computer networks, Computers will be half the use.Comment.
b) What are the various topologies? Which one is the most secure?
c) Difference between Internet and Intranet.
d) Difference between Client Server and Work-group.
e) Wifi stands for?
f) What are the various types of networks? Discuss all of them
Uses of Computer Network
Client Server Architecture
Access to Remote Information
Person to Person Communication
Computer Networks Network Hardware
There are two types of transmission technology that are widespread in use-
Point to Point Link
What is Broadcasting, Multicasting & Unicasting?
What is Simplex, Half Duplex and Full Duplex mode?
LAN, MAN, WAN
Computer Networks Network Software
Protocol Hierarchies – To reduce the design complexity, most networks are organized as a stack of layers or levels, built one over the other.
They name of each layer, content and functions of each layer are different.
The purpose of each layer is to offer services to higher layer, shielding those layers from the details of how the offered services are actually implemented.
Protocol is an agreement between the communicating parties on how communication is to proceed.
Figure 1.13 from the text book
No data is directly transferred from layer n of 1 machine to the layer n of the other , instead they have to use the Physical Layer.
A Set of Layers and Protocols together is called network architecture.
Computer Networks Design Issues for the Layers
Every layer needs a mechanism for identifying senders and receivers
We need to identify with whom a machine wants to talk, i.e. some form of addressing mechanism is required.
Rules for Data transfer need to be established. In some cases data only travels one direction, in others both ways. Also need to find out how many logical channels?
Error Control :- Various error-detecting and error correcting codes are there that have to be used, also at times, the sequence in which data is sent is not the way in which it is received, hence reassembly also needs to be done.
Inability to receive long messages, we disassemble, transmit and then reassemble data
At times sending data packets separately is not efficient, in that case we use multiplexing and demultiplexing.
Connection-oriented service : Just like a telephone system, we establish a connection, use and then release the connection.
Firstly, negotiations take place about the parameters used, such as maximum message size, quality of service required and other issues.
Connectionless Service : Just like the postal system
A reliable service is ensured by having the receiver acknowledge the receipt of each message so that sender is sure that it arrived. This introduces overheads and delays.
Example of connection oriented and connection less service
Remote login- connection oriented
Request Reply – Database Query etc
Computer Networks Service Primitives A service is formally specified by a set of primitives ( operations) available to a user process to access the service. Send a message to the peer SEND Terminate a Connection DISCONNECT Block waiting for an incoming message RECEIVE Establish a connection with a waiting peer CONNECT Block waiting for an incoming connection LISTEN Meaning Primitive
Computer Networks Client Machine Server Machine 1)Connection Request 2)ACK 3)Request for Data 4)Reply 5)Disconnect 6)Disconnect How communication takes place?
Computer Networks Services & Protocols
A service is a set of primitives (operations) that a layer provides to the layer above it.
A service defines what operation the layer is prepared to perform but cannot tell how they will be performed.
A Protocol is a set of rules governing the format and meaning of the packers or messages that are exchanged by the peer entities within a layer.
1)What is broadcasting, multicasting and unicasting?
2)Justify the purpose behind the layered architecture, define service & protocol
3)What are the various design issues pertaining to Layers?
4) Differentiate Connection Less & Connection Oriented Service.
Computer Networks OSI Reference Model
Open System Interconnection model has seven layers.
The principles that were applied to arrive at the seven layers can be summarized as follows :
A layer should be created where a different abstraction is needed.
Each Layer should perform a well-defined function.
The function of each layer should be chosen with an eye toward defining internationally standardized protocols.
The layer boundaries should be chosen to minimize the information flow across the interfaces.
The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy.
Computer Networks Layers in OSI
Computer Networks Layers in OSI
Computer Networks The Application Layer
It is the spot where the User communicates with the Computer.
Example of IE.
It is also responsible for identifying and establishing the availability of the intended communication partner and determining whether sufficient resources for the intended communication exist.
Application Layer acts as an interface between the actual application programs. This means that Microsoft Word, for e.g. does not reside at the Application Layer but instead interfaces with the Application Layer Protocols.
Computer Networks The Presentation Layer
It presents Data to the Application Layer and is responsible for Data translation and Code Formatting.
This layer is essentially a translator and provides coding and conversion functions.
By providing translation services, the Presentation Lauer ensures that data transferred from the Application Layer of one system can be read by the Application Layer of another one.
Tasks like Data Compression, Decompression, Encryption and Decryption are associated with this layer.
Computer Networks The Session Layer
Responsible for setting up, managing and then tearing down sessions between Presentation Layer entities.
It also provides Dialogue control between devices and nodes.
Simplex, Half Duplex or Full Duplex mode? The choice is made here
It keeps different application’s data separate from other application data.
Computer Networks The Transport Layer
Data is in the form of segments here.
The Transport Layer segments and reassembles data into data stream.
They provide end-to-end data transport services and can establish a logical connection between sending host and destination host on an inter network.
Both TCP and UDP work at this Layer, TCP is reliable service and UDP is not. (reliable means acknowledgements, sequencing and flow control be used.)
Connection Oriented Communication
Computer Networks The Transport Layer ( Cont…)
Connection Oriented Communication is reliable, a device that wants to transmit sets up a connection-oriented communication with a remote device by creating a session.
A session is established after a 3-way handshake.
While information is being transferred between hosts, the two machines periodically check in with each other, communicating through their protocol software to ensure that all is going well.
What happens when a machine receives a flood of datagrams too quickly to process?
It stores them in a memory section called buffer, if the buffer even gets full, transport layer sends a “Not Ready” indicator to the sender.
A service is considered to be connection-oriented if it has following characteristics –
A virtual circuit is set up.
It uses sequencing.
It uses acknowledgements.
It uses flow control.
The Transport Layer ( Cont…)
Computer Networks Windowing: The quantity of data segments (in bytes) that the transmitting machine is allowed to send without receiving an acknowledgement for them is called window. Acknowledgments: Non-duplication of data is achieved through positive acknowledgement with re transmission. The sender documents each segment it sends and waits for this acknowledgement before sending the next segment. It starts a timer and retransmits if it expires before an acknowledgement is returned from receiving end. The Transport Layer ( Cont…)
It manages device addressing, tracks the location of devices on the network and determines the best way to move data, which means that the NL must support transport traffic between devices that aren’t locally attached.
Routers are specified at the NL and provide the routing services
How does it work?
Two type of packets are used :
Data Packets (Routed Packets) & Route Update Packets.
The Routing Table consist of the following information :
The Network Layer
Computer Networks The Network Layer ( Cont…)
Computer Networks The Data Link Layer
The DLL provides Physical Transmission of the Data and handles error notification, network topology and flow control. That means that DLL will make sure that the messages are delivered to proper device on a LAN using hardware address and will translate messages from the Network Layer into bits for the Physical Layer to transmit.
Data is in the form of Frames here.DLL adds a custom header containing the Hardware Destination and Source Address.
The DLL consists of two sublayers :-
MAC (Media Access Control)
LLC ( Logical Link Control)
Bridges and Switches work at DLL
Collision Domain / Broadcast Domain
Computer Networks The Physical Layer
The Physical Layer does 2 things –send bits and receive bits.
The Physical Layer communicates directly with the various types of actual communication media.
Different type of media can be used to represent bit value. Some use audio tones, while others use State Transitions- Change in voltage from high to low and vice versa.
The Physical Layer specifies the electrical, mechanical, procedural and functional requirements for activating, maintaining & deactivating a physical link between end systems.
Interface between DCE and DTE is identified here. DCE is usually located at the service provider and DTE is attached device.
Hubs and Repeaters work at Physical Layer.
Computer Networks The TCP/IP Model
Computer Networks The TCP/IP Model
TCP/IP model is also called DOD Model
It has the following Layers
Process / Application Layer
Network Access Layer
TCP/IP Protocol Suite
Computer Networks The Process/Application Layer
It has the following Protocols
Computer Networks The Host-to-Host Layer
The main purpose of this layer is to shield the upper-layer applications from the complexities of the network
It consists of 2 protocols
TCP takes large blocks of information from an application and breaks them into segments.
It numbers and sequences each segment so that the destination’s TCP can put the segments back into the order.
Before sending, it establishes a connection, a virtual circuit, provides reliable service and works in a full-duplex mode.
It also waits for an acknowledgement from the receiver.
Computer Networks The Host to Host Layer TCP/IP Segment Format
Computer Networks The Host-to-Host Layer
UDP on the other hand, is a scale-down model.
It does not sequence the segments and does not care in which order the segments arrive at the destination.
UDP does not create a virtual circuit either.
Computer Networks The Host-to-Host Layer The Internet Layer
Computer Networks The Network Layer
The Physical Connectivity & actual Transmission of data takes place here.