The Internet: Protocols, Addressing, and Services

Chapter Ten: The Internet

Introduction

  • The Internet is a vast collection of thousands of networks and attached devices.
  • It originated as ARPANET in the 1960s.
  • ARPANET initially consisted of a high-speed backbone connecting universities, government, and research sites.
  • The backbone supported transmission speeds of 56 \, \text{kbps}.
  • The National Science Foundation (NSF) eventually financed ARPANET.

Internet Protocols

  • Many protocols support the Internet and its services.
  • Key protocols include:
    • Internet Protocol (IP)
    • Transmission Control Protocol (TCP)
    • Address Resolution Protocol (ARP)
    • Dynamic Host Configuration Protocol (DHCP)
    • Network Address Translation (NAT)
  • The Internet follows the TCP/IP protocol suite (Internet model).
  • The layers of the TCP/IP model are:
    • Application Layer: E.g., e-mail
    • Transport Layer: E.g., TCP
    • Internet/Network Layer: IP
    • Network Access/Data Link Layer: Media and framing

The Internet Protocol (IP)

  • IP prepares packets for transmission across the Internet.
  • The IP header is encapsulated onto a transport data packet.
  • The IP packet is passed to the next layer for further network information encapsulation.
  • Two versions of IP are currently in use:
    • IPv4: The older version
    • IPv6: The newer version, gradually replacing IPv4

IPv4

  • With IPv4, a router:
    • Makes routing decisions based on the 32-bit destination address.
    • May fragment datagrams into smaller units using Fragment Offset.
    • May delete datagrams that have been hopping around the network for too long (Time to Live).

IPv4 Addresses

  • All devices connected to the Internet have a 32-bit IP address.
  • IP addresses are logical and possibly temporary, while MAC addresses on NICs are physical and permanent (48-bit).
  • Computers, networks, and routers use the 32-bit binary address, but dotted decimal notation is more readable.
  • Example: The binary address 10000000 10011100 00001110 00000111 translates to 128.156.14.7 in dotted decimal notation.
  • Originally, IP addresses were classful, with each address belonging to a specific class (A, B, C, D, and E).
  • Each class has a unique network address size and host address size.
  • The first decimal value in dotted decimal notation indicates the class:
    • Class A: 0 - 127
    • Class B: 128 - 191
    • Class C: 192 - 223
    • Class D: 224 - 239
    • Class E: 240 - 255
  • Class A:
    • 128 networks
    • 16,777,216 hosts per network.
    • All Class A addresses were assigned a long time ago.
    • Impractical due to the large number of computers per network.
  • Class B:
    • 16,384 network IDs
    • 65,536 host IDs per network.
  • Class C:
    • 2,097,152 network IDs
    • 256 host IDs.
    • Too small for most networks.
  • Class D:
    • Used for multicasting of messages.
    • IP multicasting allows a network server to transmit a data stream to multiple hosts simultaneously.
  • Subnet masking allows a company to break its IP addresses into subnets for easier network management.
    • The host ID portion of an IP address is divided into a subnet ID and a host ID.
    • ISPs and companies can break down large numbers of host IDs into smaller subnets.

Classless IPv4 Addresses

  • Today, IP addresses are classless.
  • Companies obtain IP addresses from an Internet service provider (ISP).
  • ISPs lease addresses to companies.
  • Instead of applying for two Class C addresses, a company can lease 512 IP addresses from an ISP.
  • Classless addressing has led to a more efficient allocation of IP address space.
  • Companies can lease only as many addresses as needed.
  • In slash notation: 167.199.170.82/27
    • 27 bits for the network ID, 5 bits for the host ID.
    • The network mask is 255.255.255.224.
    • The block contains 2^5 = 32 addresses.
  • Example: ISP gives 512 addresses to a company: 162.48.128.0/23.
    • 162.48.128.0 is the beginning address.
    • /23 indicates that the first 23 bits are for the network ID, leaving 9 bits for the host ID.
    • With a 9-bit host ID, there are 2^9 = 512 host IDs.

Four Important Addresses

  • Network Address / Subnet ID: The first address in the subnet.
  • Broadcast Address: The last address in the subnet.
  • First Available host address: One more than the network address.
  • Last available host address: One less than the broadcast address.

IPv6

  • Several notable differences between IPv6 and IPv4.
    • IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses.
    • IPv4 addresses ran out in 2011.
    • Significant changes to the IP header: Version 4 has 14 fields, while version 6 has 8 fields.
  • IPv6 addresses are 128 bits in size (2^{128} is a very large number!).
  • They are also classless, similar to IPv4.
  • Due to their size, certain conventions have been adopted for representation.
  • Binary addresses are written using hexadecimal form:
    • 0110 1010 0011 1110 1011 1010 ... 1110 1111 becomes 6A3E : BA91 : 7221 : 0000 : 01FC : 922C : 877B : FFEF
    • Four hex 0s in a row are truncated: 6A3E : BA91 : 7221 : 0 : 01FC : 922C : 877B : FFEF
    • Longer strings of 0s can be abbreviated further: 6A3E : BA91 : 0 : 0 : 0 : 0 : 877B : FFEF becomes 6A3E : BA91 :: 877B : FFEF

The Internet Protocol

  • IP is one of the most important communication protocols.
  • It interconnects networks of virtually any type.
  • Its primary objective is to get data through one or more networks.
  • It is not responsible for creating an error-free, end-to-end connection.
  • IP relies on the Transmission Control Protocol (TCP).

The Transmission Control Protocol (TCP)

Functions

  • Creates a connection between sender and receiver using port numbers.
    • The port number identifies a specific application on a device (IP address).
  • Releases a connection after all data has been sent and received.
  • Establishes Multiplexing: Multiple connections (using port numbers) over a single IP connection.

Continued

  • Implements flow control: Prevents the sending station from overwhelming the receiving station with too much data (Window value).
  • Performs error recovery: Checksum.
  • Establishes priority: Urgent Pointer.

Internet Control Message Protocol (ICMP)

  • Used by routers and nodes for error reporting in the Internet Protocol.
  • Reports errors such as an invalid IP address, invalid port address, and excessive packet hops.

User Datagram Protocol (UDP)

  • A transport layer protocol used as an alternative to TCP.
  • While TCP supports connection-oriented applications, UDP is used with connectionless applications.
  • UDP encapsulates a header onto an application packet, which is simpler than TCP's (16-bit source port, 16-bit destination port, 16-bit length of entire packet, 16-bit checksum).

Multiprotocol Label Switching (MPLS)

  • An additional layer often added above TCP.
  • Used to move Internet packets more quickly through routers.
  • By using the MPLS label, the router doesn't have to delve as deeply to retrieve the IP address.
  • The 20-bit Label field is the key identifier that connects the packet with a specific flow of packets.

Address Resolution Protocol (ARP)

  • When an IP packet encounters the destination LAN, how does it find the destination workstation?
  • Although the destination workstation has an IP address, LANs use MAC layer addresses.
  • ARP translates IP addresses into MAC layer addresses, enabling delivery to the correct workstation.

Dynamic Host Configuration Protocol (DHCP)

  • IP addresses can be assigned statically or dynamically.
  • Dynamic IP address assignment is a more efficient use of IP addresses.
  • When a DHCP client issues an IP request, the DHCP server checks its static table.
  • If no entry exists, the server selects an IP address from an available pool.
  • The IP address assigned by the DHCP server is temporary.
    • The agreement includes a specific time period.
    • If no time period is specified, the default is one hour.
    • DHCP clients may negotiate for renewal before the time period expires.

Network Address Translation (NAT)

  • NAT allows a router to represent an entire local area network to the Internet as a single IP address.
  • All traffic leaving the LAN appears to originate from this global IP address.
  • All traffic entering the LAN uses this global IP address.
  • This provides security by hiding workstation IP addresses from the Internet.
  • When a user sends a packet to the outside, the NAT interface changes the user’s inside address to the global IP address; this is stored in a cache.
  • When the response comes back, NAT looks in the cache and switches the addresses back.
  • If there is no NAT, the packet is dropped.
  • Unless NAT has a service table of fixed IP address mappings, this service table allows packets to originate from the outside.

Tunneling Protocols and Virtual Private Networks (VPNs)

  • The Internet is not normally a secure system.
  • VPNs can create a secure connection through the Internet by using a tunneling protocol.
  • VPNs create secure connections from user homes into the corporate computer system.

The World Wide Web

  • The World Wide Web (WWW) is the most popular service on the Internet, consisting of an immense collection of web pages and other resources that can be downloaded and displayed on a workstation via a web browser.
  • Basic web pages are created with Hypertext Markup Language (HTML).
  • Hypertext Transfer Protocol (HTTP) is used to transfer web pages.

Locating a Document on the Internet

  • Every object on the Internet has a unique English-based address called its Uniform Resource Locator (URL).
  • The Internet does not recognize URLs directly.
  • Part of the object's URL has to be translated into the IP address that identifies the Web server where the document/object is stored.
  • This translation from URL to IP address is performed by the Domain Name System (DNS).

Uniform Resource Locator (URL)

  • All URLs consist of four parts:
    • Service type
    • Host or domain name
    • Directory or subdirectory information
    • Filename

Domain Name System (DNS)

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

Internet Services

  • The Internet provides many types of services including:
    • Electronic mail (e-mail)
    • File transfer protocol (FTP)
    • Remote login (Telnet)
    • VoIP (Voice over IP)
    • Listservs
    • Streaming audio and video
    • Instant Messaging, Tweets, and Blogs

Electronic Mail (e-mail)

  • E-mail programs can create, send, receive, and store e-mails, as well as reply to, forward, and attach non-text files.
  • 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.

File Transfer Protocol (FTP)

  • Used to transfer files across the Internet.
  • Users can upload or download files.
  • The URL for an FTP site begins with ftp://.
  • 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)

  • Allows a user to remotely log in to a distant computer site.
  • Users usually need a login and password to access the remote computer site.
  • Users save money on long-distance telephone charges.

Voice Over IP (VoIP)

  • The transfer of voice signals using a packet-switched network and the IP protocol.
  • VoIP can be internal to a company (private VoIP) or 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)

Listservs

  • A popular software program used to create and manage Internet mailing lists.
  • When someone sends an e-mail to a listserv, the listserv sends a copy to all listserv members.
  • Listservs can be useful business tools for following a particular area of study.
  • Examples: Mailserv, majordomo, and almanac.

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.
  • Real-Time Protocol (RTP) and Real-Time Streaming Protocol (RTSP) support streaming audio and video.
  • Streaming audio and video consume a large amount of network resources.

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 fewer resources than e-mail and is faster.
  • Tweets occur when you Twitter, with a maximum of 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.
  • E-commerce consists of four major areas:
    • E-retailing
    • Electronic data interchange (EDI)
    • Micro-marketing
    • Internet security

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 information is used to track a user’s activity and 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 allows 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.
  • Examples include:
    • Internet Printing Protocol
    • Internet fax
    • Extensions to FTP
    • Common Name Resolution Protocol
    • WWW Distributed Authoring and Versioning

Internet2

  • A new form of the Internet being developed by businesses and universities.
  • Internet2 will support very high-speed data streams.
  • Applications might include:
    • Digital library services
    • Tele-immersion
    • Virtual laboratories

The Internet In Action: A Company Creates a VPN

  • A company wants to allow 3500 workers to work from home.
  • If all 3500 users used a dial-in service, the telephone costs would be very high.
  • Instead, the company will require each user to access the Internet via their local Internet service provider.
  • This local access will help keep telephone costs low.
  • Then, once on the Internet, the company will provide software to support virtual private networks.
  • The VPNs will create secure connections from the participants' homes into the corporate computer system.