Physical Components of the Internet Servers Networks Routers
Server Computer Answers requests for services. –Mail servers –Web servers –List servers (discussed in Ch. 10) –News servers (discussed in Ch. 10)
Network A computer system that uses communications equipment to connect two or more computers and their resources. Actual physical means for transporting data (packets of information)
Network Uses: –Copper wires -- electrical impulses. or –Fiber-optic cables - light waves. or –Radio Waves or –Microwaves or –Infrared light -- invisible light that carries a message through air.
Router Special-purpose computer Computer that directs data packets along the network.
Local Area Network (LAN) A network designed to share data and resources among several computers, usually personal computers in a limited geographical area, such as an office or a building. (compare to WAN)
Wide Area Network (WAN) A network of geographically distant computers and terminals. (compare to LAN)
Host The central computer in a network, to which other computers, and perhaps terminals, are attached. A personal computer with file-transfer software permits a user to download data files from the host or upload data files to the host.
Downloading a file means to retrieve it from another computer.
Uploading a file means to send a file to another computer.
Node A device, usually a personal computer, that is connected to a network.
Ring network topology Computers are connected in a circular fashion
Bus network topology Network is preserved if one computer fails
Benefits of a Network Used as a back up for files Resources, such as printers, can be shared Promotes an ease of communication through e-mail, transferring files and videoconferencing
Benefits of a Network (continued) It costs less to use several small computers connected to a network than to use a large computer. And several small computers connected to a network can offer more computing power than just using a single large computer.
Packet switching Transmitted data is divided into small packets of information. Each packet has the same destination but does not necessarily take the same path.
Advantages of packets Packets can be rerouted to a less congested area of the network if a particular area is congested. If the network experiences a failure, packets can be rerouted. If a packet is corrupted, only the corrupted packet needs to be resent.
What other information is contained in a packet? Info about the computer that sent it Info about the computer to which it is being sent A sequence number
TCP / IP Software managing the transmission of the individual packets. TCP / IP - Transmission Control Protocol / Internet Protocol Consists of many (approx. 100) different protocols Communication between networks is based on the TCP/IP suite.
TCP Places the data into packets and reassembles the packets.
IP Handles the addressing and sees to it that packets are routed across multiple computers.
Connecting to the Internet User connects to the ISP (Internet Service Provider) using either a modem or an ISDN (Integrated Services Digital Network) –Replaces a modem with a special adaptor. ISP connects to the NSP (Network Service Provider) networks through leased lines through the local phone company. TCP/IP then divides the message into packets and sends them over the lines.
Connecting to the Internet (continued) The router directs the packets to their destination. The packets are reassembled at their destination-computer which then responds to any request. A message is sent from the destination computer to the sending computer in order to request that any missing or corrupt packets be resent.
Internet Network of networks Used to: –View web pages (WWW) –Download files (ftp) Files located on a remote computer can be downloaded –Communicate through e-mail
Internet (another definition) Global information system linked together by a unique address space (DNS).
Domain Name System (DNS) Used to assign names to host computers.
Domain Name Symbolic name used to identify each computer on the Internet.
IP Address Numeric name used to identify each computer on the Internet. Consists of 32 bits (4 bytes)
Largest 8 bit number is 255. Smallest 8 bit number is 0 11111111 = 2 8 - 1 = 255 00000000 = 0
IP Address (continued) Consists of a network component and a host component. Ex. 220.127.116.11 01100110 = 102 10010110 = 150 00001000 = 8 01000100 = 68
Review URL entered –http://publications.UNL.edu/faculty/index.ht m Browser queries the DNS for the IP Address –Domain Name System IP address returned –18.104.22.168
TCP connection is established with 22.214.171.124 Browser then asks for the “what” part of the URL –index.htm The server, publications.UNL.edu, sends back the file index.htm.
TCP connection is then closed Browser renders the text portion of the HTML code contained in index.htm Steps are repeated in order to retrieve any in-line images within index.htm. –In-line image -- Image within a document.