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Computer Networks Lecture Notes 01
1. B.Tech IV Sem CSE ‘C’; Scheme 2017; AY: 2020_21
COMPUTER NETWORKS
Dr. C. Sreedhar
2. Unit 1
Introduction:
Data Communications, Networks, Protocols and Standards
OSI Model TCP/IP Protocol Suite
Addressing: Physical, Logical, Port
Physical Layer and Transmission Media
Analog and Digital: Data; Signals
Digital Signals: Bit rate, Bit length, Transmission of digital signals
Transmission Impairments: Attenuation, Distortion, Noise
Performance: Bandwidth, Throughput, Latency, Jitter
3. Unit 2
Data Link Layer
Error detection: Block coding
Error correction: Hamming distance,
minimum hamming distance, CRC, Checksum
Framing
Flow and error control
4. Unit 3
Design Issues
Store and forward; Services to Transport layer
Connectionless and connection oriented services
Comparison of virtual circuits; Datagram subnets
Routing Algorithms
Optimality principle
Shortest Path Routing, Flooding
Distance Vector Routing, Link State Routing; Hierarchical Routing
Broadcast and Multicast Routing
5. Unit 4
Congestion Control
Principles, congestion prevention policies
Congestion control in virtual circuits and datagram subnets
Load shedding, Jitter control
Internetworking
Concatenated virtual circuits, Connectionless internetworking
Tunnelling, Internetwork routing; Fragmentation, IP :Protocol,
Address; Internet Control Protocols
Gateway routing protocols: OSPF, BGP
6. Unit 5
UDP;
TCP:
Service model, protocol, segment header,
connection management; Transmission policy
Congestion control and timer management
Application Layer
DNS Namespace; Resource Records
Name Servers
7. Unit 1
Data Communications
Definition
Components of DC
Data representation
Data flow
Networks
Network criteria
Types of connections
Categories of topology
Network Models
Protocols and
Standards
Definition
Standards
8. Data Communication: Definition
Data communications are the exchange of data
between two devices via some form of transmission
medium such as a wire cable.
9. Data Communication
The effectiveness of a data communications system
depends on four fundamental characteristics:
Delivery: deliver data to the correct destination
accuracy: system must deliver the data accurately
Timeliness: system must deliver data in a timely manner
Jitter: refers to the variation in the packet arrival time
10. Data Communication: Components
Five components
1. Sender
2. Message
3. Transmission media
4. Protocol
5. Receiver
Protocol is a set of rules that govern data communications.
It represents an agreement between the communicating devices.
11. Data Communication: Components
Five components
1. Sender
2. Message
3. Transmission media
4. Protocol
5. Receiver
Protocol is a set of rules that govern data communications.
It represents an agreement between the communicating devices.
12. Data Representation
Text:
Text is represented as a bit pattern.
Unicode uses 32 bits to represent a symbol or character
Numbers
Numbers are also represented by bit patterns.
number is directly converted to a binary number
Images
Images are also represented by bit patterns.
image is composed of a matrix of pixels
each pixel is assigned a bit pattern.
Audio and Video
Sampling rate
Analogue signal
Time
Amplitude
14. Network
A network is a set of devices (nodes) connected by
communication links.
A node can be a computer, printer, or any other
device capable of sending and/or receiving data
generated by other nodes on the network.
A link can be a cable, air, optical fiber, or any
medium which can transport a signal carrying
information.
15. Network Criteria
Performance:
Measured: transit time and response time
Transit time: time required for a message to travel from AB
Response time: elapsed time between inquiry and response
Evaluated using two metrics:
throughput and delay (more throughput and less delay).
Reliability:
measured by the frequency of failure
Security
Network security issues include protecting data from unauthorized access
16. • Point to Point - single transmitter and receiver
Ex: Television remote control
• Multipoint - multiple recipients of single transmission
• Ex: Telephone Line
Types of Connections
18. Mesh topology
every device has a dedicated point-to-
point link to every other device.
Total no. of connections??? n(n-1)/2
Advantages
Manages high amounts of traffic
Withstands failure of link.
Adding nodes easily added
Can avoid problems, malicious users
Disadvantages
amount of cabling
number of I/O ports
installation and reconnection are difficult
practical example: connection
of telephone regional offices
19. A star topology
each device needs only one link
and one I/O port to connect it to
any number of others
Advantages
less expensive than a mesh topology.
robust: If one link fails, only that link is
affected
Disadvantages
If the hub goes down, the whole system
goes down.
The star topology is used in local-
area networks (LANs)
20. bus topology
Nodes are connected to the bus cable by drop lines and taps
A drop line is a connection running between device and main cable.
A tap is a connector
One long cable acts as a backbone to link all the devices in a network
Advantages
bus uses less cabling than mesh or star topologies
Disadvantages
•difficult reconnection and fault isolation
•Signal reflection at the taps can cause degradation
•a fault or break in the bus cable stops all transmission
22. Ring Topology
Each device has a dedicated point to point connection with only two devices
on either side of it.
Signal is passed along the ring in one direction till it reaches destination
Each device has a repeater
When a device receives signal to be passed, its repeater regenerates bits
and passes along.
Advantages
Easy to install and reconfigure
Fault isolation is simple
Disadvantages
Unidirectional traffic
Break in the ring disables entire network; solved by dual ring
23. A hybrid topology: a star backbone with three bus networks
Main Star topology with each branch connecting several
stations in a bus topology
24. Standards
Set of rules for data communication that are needed for exchange
of information guaranteeing national and international
interoperability of data.
Two standards:
De facto:
By fact or by convention
Ex: Google, IBM
De Jure:
By law or by regulations
Ex: ANSI, ISO, IEEE
25. Standard Committees
International Standards Organization (ISO):
Ex: ISO 9000 family: Quality Management; ISO 6: Camera film speed
International Telecommunications Union (ITU)
Ex: ISDN, WDM, DSL
American National Standards Institute (ANSI)
ANSI C; ANSI Z1.4: Sampling Plan
Institute of Electrical and Electronics Engineers (IEEE)
IEEE 802.11: WLAN; IEEE 802.8: Fiber optic; IEEE 802.3: Ethernet
Internet Engineering Task Force (IETF)
RFC; IPR
26. Protocol
Protocol is a set of rules that govern all aspect of
data communication between computers on a
network.
regulate the following characteristics of a network:
access method, allowed physical topologies, types of
cabling, and speed of data transfer.
Ex: HTTP, FTP, IP, UDP, PPP, TCP, ARP, RARP
27. Protocol
The key elements of a protocol are syntax,
semantics and timing.
64 bits
8 bits 8 bits
Sender
address
Receiver
address
data
28. Network Models
OSI Model
TCP/IP Model
OSI Model:
The Open Systems Interconnection reference model.
Introduced in 1984 by International Standards Organization (ISO).
TCP/IP
Transmission Control Protocol/Internet Protocol
Developed in the year 1970s, adopted as protocol standard for
ARPANET (predecessor of internet) in 1983
33. Data link Layer: Functions
Moving frames from one hop to the next hop
Framing
Physical Addressing
Flow control
Error control
Access control
Hop to Hop Delivery
37. Layer 3: Network Layer
Responsibilities:
Delivery of individual packets from Actual source to final
destination.
Logical addressing
Routing
Source-to-destination delivery(End-to-End).
38. Layer 4: Transport Layer
The transport layer is responsible for:
Service point or Port addressing
Segmentation and reassembly : a message is divided into
transmittable segments each segment containing a sequence
no.
Connection Control: connection oriented or connectionless.
Flow control
Error control
43. Flow Control at Transport Layer
Segments
Error Control
Error Control at Transport Layer
44. Layer 5: Session Layer
Dialog control: allows two systems to start communication with each
other in half-duplex or full-duplex.
Synchronization: allows a process to add checkpoints or
synchronization points to a data stream.
45. Layer 6 :Presentation Layer
Design to the handle the syntax and semantic of the
information exchanged between 2 systems.
Data translation, encryption, decryption, and
compression.
46. Layer 7: Application Layer
The application layer is responsible for providing
services to the user.
Mail services
File transfer, access and management
Remote log-in or network virtual terminal
Accessing the World Wide Web
Directory service