Cs 101 ( Module 61-70)

Combining Networks

• Networking involves connecting existing networks to form an extended communication system.
• This can be done by connecting networks of the same type using devices such as repeaters, bridges, and switches.
• Repeaters connect two buses, passing signals between them without considering the meaning of the signals.
• Bridges connect two buses, looking at the destination address of each message and forwarding only those destined for the other side.
• Switches are like bridges, but connect multiple buses, considering destination addresses and forwarding messages only to the intended spoke.

Internets and Routers

• When networks with incompatible characteristics are connected, a network of networks (internet) is formed.
• Routers are devices that connect networks, allowing each network to maintain its individuality while communicating with others.
• Routers forward messages based on internet-wide addressing, using routing tables to determine the direction of each message.

Client/Server and Peer-to-Peer Models

• The client/server model involves a client requesting services from a server, which provides the service.
• The peer-to-peer model involves processes providing services to and receiving services from each other.
• The client/server model is used in networks, such as print servers and file servers.
• The peer-to-peer model is used in applications such as instant messaging and file sharing.

Distributed Systems

• Distributed systems consist of software units executing as processes on different computers.
• Examples include cluster computing, grid computing, and cloud computing.
• Cluster computing involves multiple computers working together to provide high-availability and load-balancing.
• Grid computing involves loosely coupled systems working together to accomplish large tasks.
• Cloud computing involves allocating shared computing resources over the network, providing scalability and reliability.

Internet Architecture

• The Internet is a collection of connected networks, with Internet Service Providers (ISPs) operating and maintaining these networks.
• Tier-1 ISPs form the backbone of the Internet, with high-speed, high-capacity networks.
• Tier-2 ISPs are regional in scope and less potent than tier-1 ISPs.
• Access ISPs provide access to the Internet for individual users.

Internet Addressing

• The Internet uses IP addresses to identify devices and allocate addresses to ISPs.

• IP addresses were originally 32-bit patterns, but are being converted to 128-bit addresses.

• IP addresses can be written in dotted decimal notation, separating bytes with periods.

• The Internet has an alternative addressing system using mnemonic names, with domains registered with ICANN.### Domain Names and DNS

• A domain name is a mnemonic name used to identify a specific domain on the Internet (e.g., mu.edu)

• The suffix following the period in a domain name indicates the domain's classification (e.g., ".edu" for educational institutions)

• Top-level domains (TLDs) include .com, .gov, .org, .museum, .info, and .net

• Country-code TLDs represent specific countries (e.g., .au for Australia, .ca for Canada)

Subdomains and DNS

• A domain name can be extended to the left with multiple extensions, called subdomains, to organize names within a domain
• Subdomains often represent different networks within a domain's jurisdiction
• The dotted notation used in mnemonic addresses is not related to dotted decimal notation used to represent addresses in bit pattern form
• Messages are transferred over the Internet using IP addresses, which are converted from mnemonic addresses with the aid of name servers
• The Domain Name System (DNS) is an Internet-wide directory system that provides address translation services to clients

Establishing a Domain Presence

• An organization can establish and maintain its own name server containing all the names within its domain
• Alternatively, an organization can contract with an access ISP to create the appearance of a registered domain using the ISP's resources
• Many registered domains can reside within a single ISP, each occupying only a small portion of a single computer

Internet Applications

• Early applications on the Internet were separate, simple programs that each followed a network protocol (e.g., NNTP, FTP, Telnet, SSH)
• Web servers and browsers have made it possible to handle many traditional network applications via HTTP
• Examples of Internet applications include:
• Electronic Mail (Email)
• VoIP (Voice over Internet Protocol)
• Internet Multimedia Streaming (e.g., Netflix, YouTube)

Email

• Email is one of the oldest and most enduring uses of the Internet
• Email protocols include:
  • SMTP (Simple Mail Transfer Protocol) for text messages
  • MIME (Multipurpose Internet Mail Extensions) to convert non-ASCII to SMTP-compatible form
  • POP3 (Post Office Protocol Version 3) for storing messages on a local machine
  • IMAP (Internet Mail Access Protocol) for storing messages on a mail server machine

VoIP

• VoIP (Voice over Internet Protocol) uses the Internet infrastructure to provide voice communication similar to traditional telephone systems
• VoIP consists of two processes on different machines transferring audio data via the P2P model
• Existing VoIP systems come in four forms:
  • VoIP soft phones (e.g., Skype)
  • Analog telephone adapters
  • Embedded VoIP phones
  • VoIP systems that provide links to traditional telephone communication systems