Network Fundamentals and Classifications

Network Fundamentals

• Network software facilitates information exchange and resource sharing among users
• Examples of content shared include music, videos, pictures, and text
• Software includes apps and operating systems
• Data storage facilities include Google Drive and Dropbox
• Network software has evolved into network-wide operating systems

Network Classifications: Scope

• Personal Area Network (PAN) covers a short range, typically a few meters
  • Examples: Wireless mouse, headset, and smartphone
• Local Area Network (LAN) covers a building or campus
  • It typically has computers in a single building or campus
• Metropolitan Area Network (MAN) serves a local community
• Wide Area Network (WAN) spans greater distances
  • It could be neighboring cities or opposite sides of the world

Network Classifications: Ownership

• Closed networks are owned by individuals or corporations
• Open networks are in the public domain and freely circulated
  • The Internet uses the TCP/IP protocol suite and has no playing fees or licensing agreements

Network Classifications: Topology (Configuration)

• Topology defines how machines are connected
• Bus: Uses a common communication line, like Ethernet
  • Fast Ethernet can work like a star network (Figure 4.1.a)
• Star: History in large central computers
  • Modern wireless networks use a central Access Point
  • Star networks can emulate bus networks (Figure 4.1.b)

Communication Protocols

• Protocols are rules governing activities on a network
  • For example, coordinating the transmission of messages to prevent simultaneous transmissions from all machines
• Protocols allows vendors to create compatible products with those from other vendors

Protocols for Transmitting Messages

• CSMA/Collision Detection is used in Ethernet
  • Machines send messages to all other machines, but only processes messages addressed to itself
  • Transmissions occur only when the bus is silent
  • If a collision is detected: Devices stop and wait for a random amount of time before retransmitting
• CSMA/Collision Avoidance is used in WiFi
  • It’s vital when not all machines can hear each other, known as the hidden terminal problem
  • Collisions cannot be detected
  • Machines that have been waiting longer are given priority
  • All machines send a request and need an acknowledgement before sending their message
  • All machines hear acknowledgements

Combining Networks

• Repeater: Passes all messages across two busses.
• Bridge: Passes only messages destined for computers on the other bus.
• Switch: Acts like a bridge, but with connections to multiple busses (Figure 4.4).
• Router: Connects two incompatible networks, resulting in a network of networks called an internet.
  • Internet (with a capital "I") is different from an internet. The former is only a larger network of networks.
  • Routers connect two WiFi networks and an Ethernet network (Figure 4.5)
  • Passes only messages destined to other networks
  • Contains a forwarding table with information on network destinations
  • A Router is a gateway to other networks

Methods of Process Communication

• Interprocess communication is required when processes on the same or different machines need to communicate
  • Required for coordinate action
• Client-server
  • Achieved with many clients and one server running continuously (Figure 4.6)
  • Server serves and satisfies requests from clients
  • Printer servers and file servers
• Peer-to-peer (P2P)
  • Has two processes communicating as equals and execute on a temporary basis (Figure 4.6)
  • Allows instant messaging, interactive games, and distribution of files via the Internet (swarm)

Distributed Systems

• Systems units that execute as processes on different computers and can be communication and security systems
• Cluster computing
  • Independent computers work closely together instead of a large machine
  • Requires a high-speed network and offers high-availability and load-balancing
• Grid computing
  • Loosely coupled network of computers work together to accomplish large tasks
  • Voluntary distributed grid includes computers available when not otherwise in use
• Cloud computing
  • Features huge pools of shared computers on the network that can be allocated for use of clients as needed
  • Examples: Amazon Elastic Compute Cloud (Amazon Web Services AWS), Google Drive and Google Apps, Microsoft Azure
  • Rental of virtual computers by the hour for data storage, collaboration, and building web services
  • Can provide different service models: IaaS, PaaS, SaaS while providing services and hiding the details
  • Provides reliability and scalability

The Internet

• The internet is a global network
• The original goal was to link a variety of networks into a connected system unaffected by local disasters
  • Originated as a DARPA project, later shifted to academic research
• Today, it is a commercial undertaking which links PANs, LANs, MANs, and WANs which involves millions of computers

Internet Architecture Includes ISPs

• Tier-1 (Internet backbone)
  • Features very high-speed, high-capacity, international for WANs
  • Operated by leading companies
• Tier-2 features regional WANs
  • Many pathways provide redundancy
• Tier-3 ISP
  • Provides connectivity to the Internet with a single authority
  • Supplies Internet access to homes and companies
  • Cable and telephone companies, universities, corporations
• End systems or hosts such as laptops, PCs, telephones, video cameras, automobiles, and home appliances
  • Connection by Hot spot (wireless), telephone lines, cellular, cable/satellite systems
  • Has "last mile" problems

Internet Addressing: The Use of IP

• IP (Internet protocol) address
  • Internet-wide addressing system using 32 or128 bits, represented in dotted decimal notation
  • Example: 192.207.177.133
• Mnemonic address: Readable for humans
  • Domain names, unique, operated by a single authority, registered with ICANN
  • Top-Level Domains: .edu (education), .org (non-profit organization), .gov (US government), .com (company), .mil (military), .net, .au (Australia), .ca (Canada), .biz (Business), .fi (Finland).
• Internet addressing uses a domain name system (DNS)
  • Name servers: directories that provide address translation services to clients
  • DNS (Domain name system) lookup hierarchically to other servers on upper levels
  • All domains do not need their own name servers, and use their ISP name server

Internet Corporation for Assigned Names & Numbers (ICANN)

• A non-profit corporation that coordinates Internet operation
• Allocations blocks of IP addresses to ISPs, who then assign those addresses within their regions
• Registration of domains and domain names are overseen

Early Internet Applications

• The initial applications were separate simple programs with a network protocol
• The first protocols included are listed below
  • Network News Transfer Protocol (NNTP): A Usenet news reader application (no longer in use)
  • File Transfer Protocol (FTP): Allowed listing and copying files across the network
  • Telnet and Secure Shell (SSH): Allowed user to access another computer
  • Hypertext Transfer Protocol (HTTP): Used to serve web pages
  • Electronic Mail (email): Transmitted email messages in the Internet
  • Simple Mail Transfer Protocol (SMTP): Transmitted email
• Domain mail server collects incoming/outgoing mail
• Mail server delivers collected incoming mail to clients via POP3 (Post Office Protocol) or IMAP (Internet Mail Access Protocol)

Recent Application

• Voice Over IP (VoIP):
  • Includes Skype, analog telephone adapters, 4G phone networks
• Internet Multimedia Streaming Includes:
  • N-unicast: Sending multimedia with a single sender to multiple receivers like an Internet radio station
  • Multicast: Transmitting server messages through routers
  • On-demand streaming allows users to listen to media at an arbitrary time, start, pause and rewind.
  • Content delivery networks (CDNs): The distribution of streaming copies via Groups of servers

World Wide Web

• Tim Berners-Lee 1990, CERN invented the world wide web
• Hypertext combines internet technology with linked-documents
  • Hyperlinks are embedded to other documents and uses protocol for transferring hypertext upon request
• Browsers presents materials requested from the webserver
  • Chrome, Firefox, Safari, Microsoft Edge are some examples
• Webservers provide access to documents using Hypertext Transfer Protocol HTTP
  • Apache, Microsoft IIS, Nginx are examples of these programs
• Documents are identified by URLs (Uniform Resource Locator)
  • Unique address of the hypertext document
  • HTTP protocol is used if the protocol is missing
  • The home page is returned if the filename is missing

Hypertext Markup Language (HTML)

• Encoded as a text file using ASCII or Unicode, and contains tags to communicate with the broswer
  • Appearance like <h1> to start level one or <p> starts a new paragraph
  • Other documents and content can be linked with <a href = . ..>
  • Images can be embedded in the file with <img src = …>
• W3C (World Wide Web Consortium) standard.

Extensible Markup Language (XML)

• Extensible Markup Language is a language for constructing markup languages similar to HTML
  • A descendant of the Standard Generalized Markup Language
  • Opens the door for to a World Wide Semantic Web
  • XML can be used to encode music

Client Side vs Server Side

• Client-side activities
  • Javascript
  • Java applets
  • Macromedia Flash
• Server-side activities
  • Common Gateway Interface (CGI)
  • Servlets
  • JavaServer Pages (JSP): Active Server Pages (ASP)
  • PHP

Cypersecurity

• Forms of Attack include Malware
  • Virus: Code inserted in a program and is executed with the program which is then able to degrade operating systems and erase mass storage
  • Worm: Autonomous program that copy themselves to other computers and performs extreme vandalism and overload networks
  • Trojan Horse: Virus disguise as a game or utility package which performs harmful effects.
  • Spyware: Sniffs and collects information about activities at the computer and also, it reports information to the instigator.
  • Phishing: Obtains information simply by asking for it with emails to numerous recipients with hopes that some will give up the information
• Denial of service (DoS)
  • Includes spam and is an overloading a system
• Spam
  • Common medium for delivering malware
• Protection and Cures include:
  • A firewall to filter traffic passing through a point, incoming and outgoing of a network and blocks messages from malicious clients (spam filters),
  • Antivirus software to detect and remove viruses, and filter spam via unwanted email to detect changes is traffic
  • Has the ability to learn from training.
  • Proxy Servers

Cryptography

• Designed for sending and receiving messages securely in the presence of adversaries
• HTTPS is for secure Internet access protocol using Transport Layer Security (TLS)
• Cryptography uses secure password keys to protect messages via symmetric encryption
• Public-key Encryption is asymmetric
  • Public keys can be used to encrypt messages
  • Private keys can be used to decrypt message
  • Certification is needed to maintain lists of public keys
  • Provides certificates to clients containing a parties name
  • Authenticates via with digital signatures