Chapter 10: The Internet

INTRODUCTION

During the late 1960s, US government called the Advanced Research Projects Agency (ARPA) created one of the country's first wide area packet-switched networks, the ARPAET. Select research universities, military bases and government labs were allowed to access to the ARPANET. In 1983, the Department of Defense broke the ARPANET into two similar networks: the original ARPANET and MILNET, which was for military use only. During the time the ARPANET was phasing out and replacing with newer technology, the National Science Foundation funded the creation of a new high speed, cross-country network backbone called the NSFNET. The backbone is the main telecommunications line through the network, connecting major router sites across the country. In 1990s, the government essentially withdrew all direct support for the internet and turned it over to private industries and universities. There was no longer one single backbone but multiple supported by different businesses and organizations

INTERNET PROTOCOLS

The internet depends on many protocols, several commonly used are:

• Internet Protocol (IP)
• Transmission Control Protocol (TCP)
• Address Resolution Protocol (ARP)
• Dynamic Host Configuration Protocol (DHCP)
• Network Address Translation (NAT)

Recall that the Internet with all its protocols follows the TCP/IP protocol suite (Internet model)An application, such as e-mail, resides at the highest layerA transport protocol, such as TCP, resides at the transport layerThe Internet Protocol (IP) resides at the Internet or network layerA particular media and its framing resides at the network access (or data link) layer

1. The Internet Protocol

• Provides a connectionless data transfer service over heterogeneous networks by passing and routing IP datagrams
• IP datagrams or packets that are passed down from the transport layer to the network layer are encapsulated with an IP header that contains the information necessary to transmit the packet

• There are currently two versions of IP
• Version 4, which has been in existence for many years
• Version 6, which has been available for several years but is only now starting to see a substantial move towards replacing version 4

IPv4 Diagram and Format

• Makes routing decision based on the 32-bit destination address
• May have to fragment the datagram into smaller datagrams using Fragment Offset
• May determine that current datagram has been hopping the network too long and delete it (time to live)

IPv4 Addresses

• All devices connected to Internet have a 32-bit IP address
• Think of the IP address as a logical address (possibly temporary), while the 48-bit address on every NIC is the physical, or permanent address
• Computers, networks and routers use the 32-bit binary address, but a more readable form is the dotted decimal notation
• When IP addresses were originally created, they were called classful addresses
• That is, each IP address fell into particular class
• A particular class address has a unique network address size and a unique host address size
• There are basically five types of IP addresses: Classes A, B, C, D and E

• Each IP address can consist of three parts:
• A 1-, 2-, 3- or 4-bit identifier field (beginning bit pattern)
• A net ID, which indicates a particular network
• A host ID, which indicates a particular host, or computer on that network
• IP multicasting : the capability of a network server to transmit a data stream to more than one host at a time
• IP multicasting suffers from lack of security
• Subnet masking: take the host ID portion of an IP address and divide it into a subnet ID and host ID. each subnet can support a smaller umber of hosts
• Today, IP addresses are considered classless addresses
• With classless addressing, companies (users) do not apply for particular class of addresses 
• Instead, company will get its IP addresses from an Internet service provider (ISP)
• Most ISPs have already applied for a large number of IP addresses and are willing to lease those addresses to companies
• The addresses are not identified by any class – they are simply a contiguous block of IP addresses
• Classless addressing has led to a much more efficient allocation of the IP address space
• A company can lease only as many addresses as it needs 
• An IP address in slash notation has all the info we need about the block of addresses assigned to a user/company

Internet Protocol Version 6

• IPv6 was created as the demand o the internet began to grow
• Main feature include:
• Simple header
• 128-bit IP address
• Priority levels and quality of service parameters
• No fragmentation

IPv6 Adresses

• IPv6 addresses are 128-bits in size (2128)
• They are also classless addresses, similar to IPv4 addresses
• Because of their size, a number of conventions have been adopted
• Binary addresses are written using the short-hand hexadecimal form:
• 0110 1010 0011 1110 1011 1010 ... 1110 1111
• 6A3E : BA91 : 7221 : 000 : 01FC : 922C : 877B : FFEF
• Four hex 0s in a row are truncated as:
• 6A3E : BA91 : 0 : 01FC : 922C : 877B : FFEF
• Longer strings of 0s can be abbreviated further:
•  6A3E : BA91 : 0 : 0 : 0 : 0 : 877B : FFEF
• Can be abbreviated as 
• 6A3E : BA91 : : 877B : FFEF

2. The Transmission Control Protocol (TCP)

• primary function is to turn an unreliable network (such as the one created in IP) into a reliable network that is free from lost and duplicate packets
• Performs 6 following functions:
• Create a connection
• release a connection
• Implement flow control
• Establish multiplexing
• Perform error recovery
• Establish priority

3. The Internet Control Message Protocol

• ICMP used by routers and nodes
• Perform error reporting for the Internet Protocol

4. User Datagram Protocol

• No frills transport protocol that does not establish connections, does not attempt to keep data packets in sequence and does not watch for datagrams that have existed for too long
• Its header contains 4 fields: Source port, Destination port, Length, and Checksum and is used by a small number of network services such as DNS that do not establish connection before sending data

5. The address Resolution Protocol

• Takes an IP address in an IP datagram and translates it into the appropriate medium access control layer address for delivery on a local area network
• When an IP packet has traversed the Internet and encounters the destination LAN, how does the packet find the destination workstation?
• Even though destination workstation may have an IP address, a LAN does not use IP addresses to deliver frames
• ARP translates IP address into MAC layer address so frame can be delivered to proper workstation

6. Dynamic Host Configuration Protocol

• An IP address can be assigned to a workstation permanently or dynamically
• Dynamic IP address assignment is a more efficient use of scare IP addresses
• When DHCP client issues an IP request, DHCP server looks in its static table
• Of no entry exists, server select an IP address from available pool
• The address assigned by DHCP server is temporary
• Part of agreement includes specific period of time
• DHCP clients may negotiate for a renewal before the time expires

7. Network Address Translation

• NAT lets router represent entire local area network to Internet as single IP address
• All traffic leaving LAN appears as originating from global IP address
• All traffic coming into this LAN uses this global IP address
• A level of security has been added because the outside world never sees any of the IP addresses used within the corporate network
• Company doesnt need to use purchased IP addresses
• A number of IP addresses have been designated as "phony" IP addresses
• NAT allows multiple workstations to access the internet with only one IP address

8. Tunneling Protocols and Virtual Private Networks 

• Virtual Private Network (VPN) is a data network connection that makes use of the public telecommunications infrastructure but maintains privacy through the use of a tunneling protocol and security procedures
• Tunneling protocol such as the Point-to-Point Tunneling Protocol (PPTP) is the command set that allows an organization to create secure connections using public resources such as the Internet
• Point-to-Point Protocol (PPTP) is used for communication between two computers using a serial connection such as DSL or cable modem connection between user's workstation and an internet service provider

THE WORLD WIDE WEB

• the world wide web (WWW) is a vast collection of electronic documents that are located on may different web servers, and contain text, images, videos and more that can be accessed by simple clicking links within a browser's web page
• Hypertext Markup Language (HTML) can be generated manually with a text-based editor such as Notepad, or through the use of a web page authoring tool
• Hypertext Transfer Protocol (HTTP) is an application layer protocol to transfer a web page

Locating A Document on The Internet

• Every document on the internet has a unique Uniform Resource Locator (URL)
• To find the document, part of the object's URL has to be translated into the IP address that identifies the web server where the object is stored
• This translation is performed by the domain name system (DNS)

Uniform Resource Locator:

• Uniquely identifies files, web pages, images or any other types of electronic documents that reside on the internet
• All URL consists of 4 parts:
• Service type: identifies the protocol that is used to transport the requested document
• Domain Name: specifies a particular server at a particular site that contains the requested item
• Directory or Subdirectory Information: specifies that the requested item is located in the subdirectory
• Filename: the document title

Domain Name System:

• is a large, distributed database of internet addresses and domain names
• The first operation performed by DNS is to query a local database for URL/IP address information
• If local server does not recognize address, the server at next level will be queried
• Eventually root server for URL/IP addresses will be queried
• If root server has answer, results are returned
• If root server recognizes domain name but not extension in front of domain name, root server will query server at domain name’s location
• When domain’s server returns results, they are passed back through chain of servers (and their caches)

INTERNET SERVICES

Electronic Mail (email)

• Computerized version of writing a letter and mailing it at the local post office
• Most email programs offer the following services:
• Create an email message
• Sending an email message to one or multiple recipients
• Receiving, storing, replying and forwarding email messages
• Attaching a file
• Multipurpose Internet Mail Extension (MIME) is used to send e-mail attachments
• Simple Mail Transfer Protocol (SMTP) is used to transmit e-mail messages
• Post Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrieve e-mail messages

The File Transfer Protocol

• The first services offered on the internet
• allow user to download a file from a remote site to the user's computer and to upload a file from the user's computer to a remote site
• The three most common ways to access an FTP site are:
• Through a browser
• Using a canned FTP program
• Issuing FTP commands at a text-based command prompt

Remote Login (Telnet)

• A terminal emulation program for TCP/IP networks such as the Internet that allows users to log in to a remote computer
• the Telnet program runs on your computer and connects the workstation to a remote server on the internet
• once connected to a server or host, you can enter command through Telnet program and those commands will be executed as if your were entering them directly at the terminal of the remote computer

Voice Over IP

• The transfer of voice signals using a packet-switched network and the IP protocol
• Voice over IP (VoIP) can be internal to a company (private VoIP) or can be external using the Internet
• VoIP consumes many resources and may not always work well, but can be cost-effective in certain situations
• Three basic ways to make a telephone call using VoIP:
• PC to PC using sound cards and headsets (or speakers and microphone)
• PC to telephone (need a gateway to convert IP addresses to telephone numbers)
• Telephone to telephone (need gateways)
• Three functions necessary to support VoIP:
• Voice must be digitized (PCM, 64 kbps, fairly standard)
• 64 kbps voice must be compressed
• Once the voice is compressed, the data must be transmitted 
• ENUM
• A protocol that supports VoIP
• Converts telephone numbers to fully qualified domain name addresses
• Example – telephone number (312) 555-1212 will be converted to 2.1.2.1.5.5.5.2.1.3.1.e164.arpa

Listservs

• A popular software program used to create and manage internet mailing lists
• When an individual sends an email to a listserv, the program sends a copy of the message to all listserv members
• Listservs can be useful business tools for individuals trying to follow a particular area of study 

Streaming Audio And Video

• The continuous download of a compressed audio or video file, which can be heard or viewed on the user’s workstation
• Streaming audio and video consume a large amount of network resources
• Real-Time Protocol (RTP) and Real-Time Streaming Protocol (RTSP) support streaming audio and video

Instant Messaging, Tweets, and Blogs

• IM allows a user to see if people are currently logged in on the network and to send short messages in real time
• Consumes less resources than e-mail, and faster
• Tweets occur when you Twitter.  Max 140 character messages
• Blogs are online web logs that people maintain

THE INTERNET AND BUSINESS

• E-Commerce – the buying and selling of goods and services via the Internet
• Many agree that e-commerce consists of four major areas:
• E-retailing:  the electronic selling and buying of merchandise using the web
• Electronic data interchange (EDI): electronic commercial transaction between two or more companies
• Micro-marketing: gathering and use of the browsing habits of potential and current customers
• Internet security: security systems that support all internet transactions

Cookies and State Information

• A cookie is data created by a Web server that is stored on the hard drive of a user’s workstation
• This state information is used to track a user’s activity and to predict future needs
• Information on previous viewing habits stored in a cookie can also be used by other Web sites to provide customized content
• Many consider cookies to be an invasion of privacy

Intranets and Extranets

• An intranet is a TCP/IP network inside a company that allow employees to access the company’s information resources through an Internet-like interface
• When an intranet is extended outside the corporate walls to include suppliers, customers, or other external agents, the intranet becomes an extranet

THE FUTURE OF THE INTERNET

• Various internet committees are constantly working on new and improved protocols
• Some committees and groups include:
• The internet society (ISOC)
• The internet architecture Board (IAB)
• The internet engineering task force (IETF)
• the internet research task force (IRTF)
• the world wide web consortium (W3C)
• Internet Corporation for assigned names and numbers (ICANN)
• A new form of the Internet is being developed by a number of businesses and universities
• Internet2 will support very high-speed data streams
• Applications might include:
• Digital library serviceS
• Tele-immersion
• Virtual laboratories