Chapter 1
Lecture 1
Introduction to Computer Networks
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Outline
Internet history
Network terminology
Basic Network Communications
Network architecture
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Why do we need to know
the history of the Internet?
We need to know the past
to understand the present, in turn
to do better in the future.
Title: History of the Internet
URL: https://youtu.be/9hIQjrMHTv4
Video length: 8:09 minutes
Producer: Melih Bilgil
Learning focus:
Remote network connection (1:10)
Time-sharing processing (1:15)
The Cold War: Satellite Sputnik launched by Soviet Union in 1957 (1:32)
The basis of the Internet:The Advanced Research Projects Agency Network (ARPANET) by the US in 1958 (1:45)
Military, commercial network, scientific networks
Interface Message Processor (IMP) (2:50)
The 1st packet-switching network protocol – Network Control Protocol (NCP) (3:20)
Packet switching: file data packets file (3:50)
The Open Systems Interconnection (OSI) model
TCP/IP model
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Network Control Protocol (NCP)
The 1st standard operational packet-switching protocol on ARPANET and standardised the ARPANET network interface.
NCP allowed users to access and use computers and devices at remote locations and to transmit files between computers.
NCP provided the middle layer of the protocol stack, and enabled application services such as email and file transfer.
Robert Kahn and Vinton Cert built on NCP to develop the standard TCP/IP.
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Interface Message Processor (IMP)
IMP was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989.
The 1st generation of gateways, known as routers
The1st of a series of standardization documents published by the Internet Engineering Task Force (IETF).
An IMP was a Honeywell DDP-516 minicomputer with special-purpose interfaces and software
An IMP requires the connection to a host computer via a special bit-serial interface
The IMP software and the ARPA network communications protocol running on the IMPs was discussed in RFC1
The IMP routes the message to the destination host using protocols that were eventually adopted by Internet routers.
A Request for Comments (RFC) is a formal document from the Internet Engineering Task Force (IETF),
more detail from https://en.wikipedia.org/wiki/Request_for_Comments
Source: https://en.wikipedia.org/wiki/Interface_Message_Processor
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Internet History
In response to the launch of USSR’s first artificial earth satellite
The US formed the Advanced Research Projects Agency (ARPA), known as ARPANET, within the Department of Defense (DoD) to establish a US lead in science and technology in 1957
ARPANET was commissioned by the DoD in 1969
Information Message Processor (IMP)
Honeywell 516 mini-computer with 12K of memory
15 nodes (23 hosts) were on the ARPANET in 1971
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Internet History (continued)
“A Protocol for Packet Network Intercommunication” – the design for TCP, in 1974
ARPA established TCP/IP as the protocol suite for the ARPANET in 1982
The routing protocol, the External Gateway Protocol (RFC 827) specification was written in 1982
The Internet transitions from Network Control Protocol (NCP) to TCP/IP on 1 Jan 1983
The World Wide Web (WWW) was released in 1991
The 1st remotely operated machine to be hooked up to the Internet, the Internet Toaster in 1990.
The US White House came online with www.whitehouse.gov president Bill Clinton in 1993.
Pizza Hut offered on-line order using the WWW in 1994.
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Outline
Internet history
Network terminology
LAN, WAN, WAN and Internetwork
Packet, Frame, Bit
Basic Network Communications
Network architecture
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LANs, WANs, MANs and Internetworks
Local area network (LAN)
a network that interconnects devices within a limited geographic area, e.g. university campus, office.
Wide area networks (WANs)
use the services of third-party communication providers to carry network traffic from one location to another
Metropolitan area networks (MANs)
use WAN technologies to interconnect LANs in a specific geographic region, such as a county of city
Internetwork
is a networked collection of LANs tied together by devices such as routers
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Internet, Intranet and Extranet
Internet:
A worldwide public internetwork
Uses protocols such as TCP/IP and HTTP to transfer and view information
Intranet:
A private internetwork in which devices and servers are only available to those users connected to the internal network
Extranet:
An enterprise network that extends to external users (e.g. suppliers, vendors, partners, clients) to access internal resources
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Internet, Intranet, and Extranet
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Internet, Intranet, and Extranet
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Packets
Chunks of data sent across the network are usually called packets or frames, with packets being the more well-known term
Packet: a chunk of data with a source and destination IP address added to it
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Frames
Frame: a packet with the source and destination MAC addresses added to it
The packet is “framed” by the MAC addresses on one end and an error-checking code on the other
The process of adding IP addresses and MAC addresses to chunks of data is called encapsulation
Information added to the front of the data is called a header and information added to the end is called a trailer
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Bits
A bit is a binary digit, the smallest increment of data on a computer.
A bit can hold only one of two values: 0 or 1, corresponding to the electrical values of off or on, respectively.
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Packets and Frames
Computers transfer information across networks in shorts bursts of about 1500 bytes of data
Reasons data is transferred this way:
Pauses between bursts allows other computers to transfer data during pauses
Allows the receiving computer to process received data
Allows the receiving computer receive data from other computers at the same time
Gives the sending computer an opportunity to receive data from other computers and perform other processing tasks
If an error occurs during transmission of a large file, only the chunks of data involved in the error needs be resent.
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Outline
Internet history
Network terminology
Basic Network Communications
Hardware and software
Network architecture
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The Fundamentals of Network Communication
A computer network consists of two or more computers connected by some kind of transmission medium
Such as a cable or air waves
In order to access the Internet, a computer has to be able to connect to a network
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Hardware component
Network Interface Card (NIC)
Network Medium
Interconnecting device
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Network Interface Card (NIC)
An add-on card plugged into a motherboard expansion slot that provides a connection between the computer and the network
The main two types of network cards:
Wired
Wireless
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Network medium
An Ethernet cable is used to attach to the NIC of a computer for connecting to a wired network.
A wireless NIC translates data into radio signals and then transmits these signals through the use of an antenna for the wireless connection.
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Interconnecting device
To allow two or more computers to communicate on the network without having to be connected directly to one another
A router is used for connecting multiple networks together
A switch is used for connecting multiple computers within a network.
An access point (AP) allows wireless devices to connect to a wireless network.
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Network Connectivity
Peer-to-Peer
Wired connection
Wireless connection
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Network Components
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Network Connectivity
Star Topology
Wireless connection
Wired connection
AP
Switch
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Software Components
Network clients and servers
Network client software requests information stored on another network computer or device
Network server software allows a computer to share its resources
Protocols
define the rules and formats a computer must use when sending information across the network
NIC driver
receives data from protocols and forwards this data to the physical NIC
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Steps of Network Communication
Application tries to access a network resource by sending a message
Client software formats the message and passes the message on to the network protocol
Protocol packages the message in a format suitable for the network and sends it to the NIC driver
NIC driver sends data in the request to the NIC card to be converted into necessary signals to be transmitted on the network
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Layers of the Network Communication Process
Each step required for a client to access network resources is referred to as a “layer”
Each layer has a task and all layers work together
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Outline
Internet history
Network terminology
Basic Network Communications
Network architecture
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Network Architecture
It is the design of a communication network
It is a framework for the specification of
a network’s physical components and their functional organization and configuration, its operational principles and procedures, as well as data formats use.
Reference: https://en.wikipedia.org/wiki/Network_architecture
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Two Reference Models
Two models reference models:
TCP/IP protocol suite
Open System Interconnection (OSI) model
To describe the layers of hardware and software necessary to transmit data between two points or for multiple devices/applications to interoperate
Divided into separate and achievable function-based layers/modules,
Each layer/module is easier to manage and maintain
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Structure of the OSI and TCP/IP models
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Structure of the OSI Model
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The Open Systems Interconnection (OSI) reference model
The OSI is proposed by the International Organization for Standardization (ISO) provides a common framework for developers and students of networking to work with and learn from
It is not specific to any protocol suite and can be applied to most networking protocols
It is well known and acknowledged as a baseline for categorization of network communication functions and assessment
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Structure of the OSI Model
It is a seven-layer organization of how data travels from place to place on any given network
Each layer provides services to the next higher layer until the data reaches the Application layer
Application layer has the job of providing services to user applications
Each layer on one computer behaves as though it were communicating with the same layer on the other computer
This is known as peer communication between layers
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Structure of the OSI Model
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Encapsulation in Networking
At each layer, control information is either added or removed, depending on whether the data is leaving or arriving at a computer
To add additional control information to a data unit as it moves through the layers is called encapsulation.
Encapsulation process takes place in the sending computer while the de-encapsulation process takes place in the receiving computer.
Protocol information can be added before and after the data. If information is added before the data, it is known as header. If information is added after the data, it is known as trailer.
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An Example of Data Encapsulation
Encapsulation is often illustrated with placing a letter into an envelope.
On the envelope, we have sender’s and receipt’s names and addresses. They are the control information, not the contents of the letter.
The sender places the letter into an envelop, which can be illustrated as encapsulation
The recipient removes the envelop, which can be illustrated as de-capsulation.
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Application Layer
The Application layer (Layer 7) provides interfaces for applications to access network services
File sharing, message handling, and database access
Common protocols found at Layer 7 include Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP)
Possible problems at this layer include missing or misconfigured client or server software and incompatible or obsolete commands used to communicate between a client and server
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Presentation Layer
The Presentation layer (Layer 6) handles data formatting and translation
For outgoing messages
Converts data into a format specified by the Application layer
For incoming messages
Reverses the conversion if required by the receiving application
Encryption/decryption can be done at this layer
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Session Layer
Session layer (Layer 5) permits two computers to hold ongoing communications, called a “session”
This layer handles communication setup ahead of data transfers and session teardown when the session ends
Common network functions at this layer:
Name lookup, user logon and logoff
Manages the mechanics of ongoing conversations such as identifying which side can transmit data when and for how long
Checkpointing is performed at this layer
Example: keeping the audio in sync with video
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Transport Layer
The Transport layer (Layer 4) manages data transfer from one application to another across a network
By breaking data down into smaller chunks called “segments”
Segmenting data is important because every network technology has a maximum frame size called the maximum transmission unit (MTU)
Includes flow control and acknowledgements to ensure reliability
Handles re-sequencing segments into the original data on receipt
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Transport Layer
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Transport Layer
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Network Layer
The Network layer (Layer 3):
Performs logical addressing,
Maps between logical network addresses (IP addresses) into physical addresses,
Performs routing (i.e. selects the best path)
Routers operate at this layer
Protocols related this layer include:
Internet Protocol (IP),
Address Resolution Protocol (ARP)
Internet Control Message Protocol (ICMP)
IP, ARP and ICMP see more details in later lectures
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Network Layer
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Network Layer
Problems that can occur at the Network layer often include:
Incorrect IP addresses or subnet masks
Incorrect router configuration
Router operation errors
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Data Link Layer
The Data Link layer (Layer 2) works with frames and is the intermediary between the Network layer and Physical layer
Defines how computers access the network medium)
Media Access Control (MAC) address is defined at this layer
A layer 2 frame consists of both a header and a trailer
Trailer component is labeled “FCS” (frame check sequence) and contains a Cyclic Redundancy Check (CRC) code
A CRC is an error-detecting code commonly used in network communications
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Data Link Layer
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Data Link Layer
The software component operating at this layer is in the network interface card (NIC) driver
Hardware components that operate at this layer include NICs and switches
Problems at this layer include collisions and invalid frames
Can be caused by collisions, poor network design, environmental interferences, line noise, or NIC driver problems
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Physical Layer
The Physical layer (Layer 1) converts bits into signals for outgoing messages and signals into bits for incoming messages
Wire media uses electrical pulses, fiber-optic uses light pulses and wireless media uses radio waves
Details for creating a physical network connection are specified at this layer
Example: type of connectors used to attach the medium to the NIC
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Physical Layer
Encoding (representing 0s and 1s by a physical signal) happens at this layer
Such as electrical voltage or a light pulse
Components at this layer include all the cable and connectors used on the medium, repeaters and hubs
Problems occurring here are often related to:
Incorrect media termination
Electromagnetic interference or noise that scrambles the signals
NICs and hubs are misconfigured or malfunctioning
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Summary of the OSI Model
Table 7-2 OSI model summary
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Summary of the OSI Model
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Why layering in network?
Why do we learn reference models?
Do we need to learn them by heart?
Purposes of network layering
It can be clearly divided into separate and achievable function-based modules/layers
Each module/layer is easier to manage and control, i.e., one module/layer can be changed without affecting other module/layers
It facilitates in protocol implementation and troubleshooting
…
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Summary
The layers of the network communication process can be summarized as user application, network software, network protocol, and network interface
The four terms used to describe networks of different scope are LAN, Internetwork, WAN, and MAN
Packets and frames are the units of data handled by different network components
Packets have the source and destination IP address added and are processed by the network protocol
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Summary
A summary of the OSI Model layer functions:
Application – Provides access to network resources
Presentation – Handles data formatting and translation
Session – Manages ongoing conversations between two computers
Transport – Breaks long data streams into smaller chunks (segments)
Network – Provides best path selection and IP addressing
Data Link – Defines how computers access the media
Physical – Converts bits into signals and defines media and connectors
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Title: Warriors of the Net – IP for Peace (1999)
URL: https://www.youtube.com/watch?v=7rR8p6gsExY
Video length: 12:57 minutes
Producer: Ericsson
Learning concepts:
TCP segment
ICMP packet
UDP segment
Router and switch
Network security: ping of death, firewall
Internet of Things (IoT)
Addressing and routing
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Practical 1 – from Week 1
Introduction to Wireshark
Wireshark is one of open-source packet analyzers
It can be used to capture network packets and display that packet data
Lecture 2
Network media and network interface cards (NICs)
Wired and Wireless technologies
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