Cs 101 ( Module 61-70)

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.

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.

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 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.

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.

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)

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

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

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 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 (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