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Introduction to Computer Networks

What is a Network?

• In its simplest form, a network is nothing more than “two connected computers sharing resources with one another.”

• Technically speaking, it is composed of two main aspects:

  • Physical Connection (wires, cables, wireless media)

  • Logical Connection (data transporting across the physical media)

Some Basic Networking Rules

• The computers in a network must use the same procedures for sending and receiving data. In computer networks, we call these communication protocols.

• Data must be delivered uncorrupted. If it is corrupted, it is useless. (There are exceptions; e.g., phone calls where it is more important to have noisy connection than connection fail. So it depends on the types of communication.)

• Computers in a network must be capable of determining the origin and destination of a piece of information, i.e., it’s IP and Mac Address.

Types of Computer Networks (by Size)

• Personal Area Network (PAN)

  Ultra-small networks used for personal use to share data from one device to another.

  Examples:

  • Smartphone to laptop

  • Smartwatch to smartphone

  • Smartphone hands free car calling

  • Heart rate monitor to smartphone

• Local Area Network (LAN)

  A computer network within a small geographical area, such as a single room, building or group of buildings.

  Examples:

  • Home network

  • Small office network

• Wireless Local Area Network (WLAN)

  A LAN that’s fully dependent on wireless connectivity.

  Examples:

  • Most home networks are WLANs.

    • e.g., Personal computers, smartphones, tablets wirelessly connected to home LAN.

• Campus Area Network (CAN)

  A computer network of multiple interconnected LANs in a limited geographical area, such as a corporate business park, government agency, or university campus.

• Metropolitan Area Network (MAN)

  A computer network that interconnects users with computer resources in a city.

  Larger than a CAN, but smaller than a WAN.

• Wide Area Network (WAN)

  A computer network that extends over a large geographical distance, typically multiple cities and countries.

  Examples:

  • The “Internet”

  • Google offices in different states

Network Architecture

• Peer-to-Peer (Decentralized Architecture)

  • All computers on the network are peers.

    • No dedicated servers

    • There’s no centralized control over shared resources (no dedicated servers)

  • Any device can share its resources as it pleases

  • All computers can act as either a client or a server

  • Easy to setup, and common in homes and small business

  • Common in homes and small businesses

• Client-Server (Centralized Architecture)

  • The network is composed of clients and servers.

    • Servers provide resources

    • Clients receive resources

  • Servers provide centralized control over network resources (files, printers, etc.)

  • Centralizes user accounts, security, and access controls to simplify network administration

    • A huge benefit of the client-server architecture

  • More difficult to setup and requires an IT administrator

  • Common in medium to large businesses

Why Build a Computer Network?

• Before computer networks, people sent and received information by hand, using the postal service. This is slow and can be unreliable.

• Computer networks enable faster, more efficient modes of communication, i.e., email, video conferencing, etc.

• Computer networks and the sharing of electronic data encourage the use of standard policies and precedures.

• Computer networks provide backup and recovery support for our data, i.e., redundancy.

• Computer networks lead to cost savings.

Computer Networking Protocols

• Computers communicate with each other with network protocols.

• Protocols are rules governing how machines exchange data and enable effective communication.

• Everyday examples of protocols:

  • When you call somebody, you pick up the phone, ensure there is a dial tone, and if there is, you dial the number.

  • When you drive your car, you obey the rules of the road.

• Protocols define the interfaces between the layers in the same system and with the layers of peer system.

• Protocols are building blocks of a network architecture.

• Physical protocols describe the medium (wiring), the connections (RJ-45 port), and the signal (voltage level on a wire).

• Logical protocols are pieces of software controlling how and when data is sent and received to computers, supporting physical protocols.

• Computer networks depend on many different types of protocols in order to work properly.

• Example of common TCP/IP suite of protocols:

  • Web communication: HTTP

  • E-mail: POP3, SMTP, IMAP

  • File transfers: FTP

Duplex Communication (Half vs. Full Duplex Communication)

• Network communication will occur in either full or half duplex mode:

  • Half Duplex

    Can send and receive data, but not at the same time.

  • Full Duplex

    Can send and receive data simultaneously.

Network Transmission Types

• The general way in which we can communicate from one system to the other systems on a network.

  • Unicast (One-to-One)

  • Multicast (One-to-Many)

    Communicating within the Multicasting Group

  • Broadcast (One-to-All)

    Used very commonly on the Local Area Network (LAN)