Networks Week 2 LBSC 690 Information Technology Computer Systems Hardware Types of hardware Storage hierarchy Moore s law Software Types of software Types of interfaces Types of Software Application programs e g Internet Explorer What you normally think of as a program Compilers and interpreters e g JavaScript Allow programmers to create new behavior Operating system e g Windows XP Moves data between disk and RAM lots more Embedded program e g BIOS Permanent software inside some device Installing Applications Copy to a permanent place on your hard drive From a CD the Internet Installs any other required programs DLL files can be shared by several applications Register the program s location Associates icons start menu items with it Configures the uninstaller for later removal Configure it for your system Where to find data files and other programs Discussion Point What s a Virus Characteristics Initiation Behavior Propagation Spyware Detection Network Computers and devices connected via Communication devices Transmission media Why Network Sharing data Sharing information Sharing hardware Sharing software Increasing robustness Facilitating communications Facilitating commerce Packet vs Circuit Networks Telephone system circuit switched Fixed connection between caller and called High network load results in busy signals Internet packet switched Each transmission is routed separately High network load results in long delays Packet Switching Break long messages into short packets Keeps one user from hogging a line Route each packet separately Number them for easy reconstruction Request retransmission for lost packets Unless the first packet is lost Networks of Networks Local Area Networks LAN Connections within a room or perhaps a building Wide Area Networks WAN Provide connections between LANs Internet Collection of WANs across multiple organizations Local Area Networks Within a campus or an office complex Short distance lines are fast and cheap Fast communications makes routing simple Ethernet is a common LAN technology All computers are connected to the same cable Ordinary phone lines can carry 10 Mb sec 100 Mb s connections require special cables 1 Gb s connections require special switches Every host broadcasts everything to all others Collisions limit throughput to about 50 utilization Shared Network All attach to the same cable Ethernet and cable modems Transmit anytime Collision detection Automatic retransmission Inexpensive and flexible Easy to add new machines Robust to computer failure Practical for short distances Half the bandwidth is wasted Switched Star Network All attach directly to a hub Switched Ethernet Digital Subscriber Lines DSL Higher cost Line from hub to each machine Hub must handle every packet Hub requires backup power Much higher bandwidth No sharing no collisions Allows disks to be centralized Local Area Networks CSS www rac2 rac3 rac4 ttclass PLS sam kim ann dove joe HBK Wireless Networks Radio based Ethernet Effective for a few rooms within buildings Access Point gateways to wired networks Available throughout most of the Maryland campus Commercial providers offer hot spots in airports etc Available in two speeds IEEE 802 11b 10Mbps good enough for most uses IEEE 802 11g 54Mbps required for wireless video http www tss northwestern edu wireless faq wir html Wide Area Networks Campus regional national or global scale Expensive communications must be used well Limiting to two hosts allows 100 utilization Routing is complex with point to point circuits Which path is shortest Which is least busy Internet routers exchange routing tables Which routes seem fast which seem slow Between a LAN and a WAN Ring Network Unidirectional transmission Used mostly for WANs Very high bandwidth No collisions Simple routing policies Complex management Changes must be coordinated Maryland s Campus Network Elsewhere in CSS www rac2 rac3 rac4 ttclass CSS 1410 sam kim ann dove joe HBK The Internet Global collection of public IP networks Private networks are often called intranets Independent Each organization maintains its own network Cooperating Internet Protocol IP address blocks Domain names World Wide Web Consortium W3C Computer Emergency Response Team CERT A Short History of the Internet 1969 Origins in government research Advanced Research Projects Agency ARPAnet Key standards UDP TCP DNS 1983 Design adopted by other agencies Created a need for inter network connections Key standards IP 1991 World Wide Web added point and click Now 150 million Internet hosts Key standards HTTP URL HTML XML Overview http www geog ucl ac uk casa martin atlas isp maps html Types of Internet Nodes Hosts Computers that use the network to do something Routers Specialized computers that route packets Gateway Routers that connect two networks Firewall Gateways that pass packets selectively An Internet Protocol IP Address Identifies a LAN IP address 216 183 103 150 Identifies a specific computer Routing Tables IP Prefix Next Router Estimated Delay 216 141 xxx xxx 120 0 0 0 18 ms 216 xxx xxx xxx 121 0 0 0 34 ms 101 42 224 xxx 120 0 0 0 21 ms xxx xxx xxx xxx 121 0 0 0 250 ms 45 0 2 10 121 0 0 0 120 0 0 0 Domain Name Service DNS Domain names improve usability Easier to remember than numeric IP addresses DNS coverts between names and numbers Written like a postal address general to specific Each name server knows one level of names Top level name server knows edu com mil edu name server knows umd umbc stanford umd edu name server knows wam glue ttclass wam umd edu name server knows rac1 rac2 IP Addresses and Domain Names IP address 216 183 103 150 Domain Name www howstuffworks com Hands on Learn About Your IP Address Find your IP address Select start on the taskbar then Run Type in cmd and click OK Type ipconfig all and press enter See who owns that address Use http whois godaddy com See how packets get to your computer Use http www traceroute org The TCP IP Protocol Stack Link layer moves bits Ethernet cable modem DSL Network layer moves packets IP Transport layer provides services to applications UDP TCP Application layer uses those services DNS SFTP SSH User Datagram Protocol UDP The Internet s basic transport service Sends every packet immediately Passes received packets to the application No delivery guarantee Collisions can result in packet loss Example sending clicks on web browser Transmission Control Protocol TCP Built on the network layer version of UDP Guarantees delivery all data