Information Systems Study Guide

Format: 20-30 MC; 6pages of short answers Review – labs  Travel over the internet; TCP/UDP is from end to end, IP is in the middle, between hops o Write email – this is data o Data is sent to the transport layer and is SEGMENTED, adds s/d PORT # and sequence number o Network layer turns these into packets with s/d ip address o Data link layer turns these into frames with s/d mac address for default gateway o Frames go to switch and switch checks source mac and learns it if it doesn’t o Switch checks destination mac (default gateway mac) and port floods if it doesn’t know  Switch does NOT OPEN frame; just reads frame because switch is same layer as frame o Switch forwards to router/default gateway o Router gets rid of frames and checks ip address, router REFRAMES with next hop dest. Mac address o Next device looks at dest mac address and see if mac address matches its mac address o Runs crc (cyclic redun. Check) and compares to fcf (frame check seq.), accepts frames and open them up o Packets are sent to network layer, sent to transport layer o Transport layer puts it in right order and passes to application layer Intro/chapter 1 o Data storage – stored in digital binary o 8 bits make 1 byte o Know how to translate binary! o ASCII only supports English char set (0-127) o Duo bit/Unicode supports other languages with bigger char sets  UTF 8/16;  ASCII and UTF share same codes for 0-127  Larger than 127: leading byte has two or more 1’s followed by 0’s, continuation bytes start with 10 o Data sizes – what’s here  8 bits = 1 byte (B)  1 kilobyte = 1024 B  1 megabyte = 1,048,576 B  1 gigabyte = 1,073,741,824 B  1 terabyte = 10^12 B  Peta, exa, zetta, yotta o Hardware  Cpu – processing unit  Modem – de/modulate; digital <> analog phone lines

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 Network interface card – connects to network  Sound/video car – expands capabilities of computer Buying a computer – starting to have more USB ports  Cpu speed – g/m/hz  Ram has starting and expandable; l1/2 another type of ram  Hard drive – magnetic (5400, 7200 rpm); ssd  Integrated/dedicated graphics card Windows os  Fat, fat32 not as stable as ntfs (common)  Disk defrag – digitally repackages disk storage to make it more efficient (continuous pieces instead of scattered fragments)  32 (86) v. 64 bit (do more instructions  Network account – domain account that has capabilities on a network Type of computers  Desktop; workstations (beefed up desktops)  Server – computer that can service requests from multiple client computers; shares processing needs of multiple clients; DHCP serves static ip addresses  Main frame – large scale computing; research labs Computer ports – know speeds?  Ethernet – rj-45; cat5; cat5e; cat6; goes into nic  Rj11 – phone line  Pcmcia card – extension/expansion Computer startup – bios (basic input output system); post (power on self test); OS boot up Connect two computers -??  Ethernet crossover cable (like devices) v. straight through cable  Specialized usb cables (with SW); not regular usb  Serial cable (null modem) or parallel peripheral cable Connect two or more: hub, switch, router; lan and Ethernet; wan and the internet Networks impact daily life: IM, weblogs, podcasting

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Data networking components  Devices – communicate with one another  Medium – how devices are connected together  Messages – information that travels over medium  Rules (protocols) – govern how messages flow across network  Converged network – type of network that carries voice, video, and data o Network architecture  Fault tolerance – if breaks, there is a way around it; packet switching; data is split into chunks  Scalability – can it keep up with growth; hierarchical, common standards and protocols; tier 1 = big boy ISPs; peering – contract to provide service if downtime occurs  Quality of service – maintain a SLA; prioritize bandwidth consumption according to type of data; all traffic not alike; video/audio > transactions > loading pages  Security Communication over the network o Network edge = end systems, access networks, links o Network core = circuit switching, packet switching, network structure o Internet  Devices – millions of devices; hosts are end systems running network apps (have an ip address)  Communication links – fiber, copper, radio, satellite; bandwidth = transmission rate; throughput = actual rate; access points, wired links  Routers – forward packets

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Protocols – control sending receiving of msgs; TCP, ip, http, skype, Ethernet; every protocol has a RFC  ALL communication activity in internet governed by protocols  Define format, order of msgs sent and received among network entities, and actions take on msg transmission/receipt  Protocols are channel specific  Internet = network of networks; loosely hierarchical; public internet v. private intranet  Internet standards – rfc request for comments; ietf – internet engineering task force Function of network protocols  Allow devices to communicate successfully; define behavior in certain situations Network structure  Network edge = applications and hosts  Access networks, physical media – wired, wireless communication links  Network core = interconnected routers, network of networks  End systems (hosts) – run application programs  Client/server model – client host requests, receives service from always on server  Peer to peer model – minimal or no use of dedicated servers; bittorrent; skype Dial up – uses existing telephony infrastructure; 56kbps; home is connected to central office  Modem translates between digital and analog over phone  Hump is 0; valley is a 1 Digital subscriber line (DSL) – uses existing telephone infrastructure; 8/1 mb dl; 1/256 m/kb ul; dedicated physical line to telephone central office Ethernet access – used in companies and universities, etc  10, 100, 1gb, 10gb wired ethernet; gigabit; fe = fast Ethernet  End systems typically connect into Ethernet switch Wireless access networks  Shared wireless access network – connects end system to router via base station/access point  Wireless lan – 802.11b/g/n; 11/54 mbps  Wider-area wireless access; provided by telco; wimax 10mbps over wide area Home networks – dsl/cable model, router/firewall/nat; Ethernet; wireless access pt Physical media  Bits – propagate between transmitter/rcvr pairs  Physical link – what lies between transmitter and receiver  Guided media – signals propagate in solid media; copper, fiber, coax  Unguided media – signals propagate freely; radio

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Twisted pair (tp) – two insulated copper wires; cat 3- traditional phone wires, 10mbps Ethernet; cat 5 100mbps Ethernet  Network media – channel over which message travels  Coax – two concentric copper conductors; street  Fiber optic – glass fiber carrying light pulses, each pulse a bit; highway  Radio – signal carried in electro magnetic spectrum; bidirectional; propagation environment effects (reflection, object obstruction, interference)  Lan/wifi 11/54mbps; widearea cellular 3g1mbps; satellite kbps to 45 mb Network core – mesh of interconnected routers  Circuit switching – dedicated circuit per call; telephone net  End/end resources reserved for call; dedicated resources and no sharing; guaranteed performance, call setup required; pay whether use circuit or not; PSTN public switched telephone network  Packet switching – data sent through in discrete chunks  Breaks transmission into messages; packet received at router, it must decide which of several paths to use to send packet; complex and made at each router  Multiplexing – saves $; packets from many transmissions mixed over each transmission line; only pay for line CAPACITY; now radio, tv, music, film all digitalized Real internet delays/routes – watch video! – review lab for this  Traceroute – provides delay measurement from source to router along end-end internet path towards destination  sends 3 packets that will reach router “i” on path towards destination  router i will return packets to sender  sender times interval between transmission and reply  “tracert <ip address or website url>”  Ping -> “ping <ip address or website url>”  Ip is used from router to router; tcp at end nodes, to reorder Protocol layers – many pieces (hosts, routers, media links, apps, protocols, h/sw; layers gives organization to structure  Each layer implements a service, via its own internal layer actions, relying on services provided by layer below  Modularization eases maintenance, updating of system; change of implementation of layer’s service transparent to rest of system  Changes in one layer do not affect other layers Internet protocol stack  Application – supporting network applications – ftp; smtp; http  Transport – process-process data transfer – tcp, udp  Network – routing of datagrams from source to destination – ip, routing protocols

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 Data link – data transfer between neighboring network elements- ppp, Ethernet  Physical – bits on the wire  Tcp/ip v. osi; app, presentation, session are in application  Encapsulation from message, segment, datagram, frame o Lans separated by geographic distance are connected by WAN o Network structure  Lans – Ethernet  Wan – internet  Client/server – humans/processes at each end  P2p – humans/processes at each end Application layer – ch 3 o Its protocols provide means for generating and receiving data that can be transporting on the network o Application – you are running, service – windows machine is running, system operations – supports running the machine  Multiprocessing – one programing running several times each in its own process o Client server applications – daemon: program usually continuously running in bg of server that responds to certain requests; process name often ends in d; webserver is a http daemon o DNS – resolves ip address for human friendly internet addresses; provides name resolution, using name daemon “named”  Dns server stores different types of resource records, used to resolve names  Ipconfig /displaydns, /flushdns, nslookup (query) o http – stateless protocol (connection not maintained), not secure; https; get/post(put)  200 – ok; 404 – doc not found; 501 – youre being bad o Mail  Mua – mail user agent (outlook) that is used to access mail  Pop – post office protocol – used by mua to retrieve mail from server  Imap – internet msg access protocol - more feature rich than pop3 o Mail  Mua  Smtp – simple mail transfer protocol – standard for email msg transfer  Mta – forwards mail when dest isn’t local  Mda – delivers email to local email account mailbox  Mail is then accessed by recipient with a mua using pop/imap o Emails using mime – multipurpose internet mail extensions is internet standard that extends format of email to support chars other than ascii, nontext attachments, message bodies with multiple parts, nonascii header info, binary o ftp – upload/download files from servers; two connections – one for control traffic one for data o dhcp (port 67/68) – how you get ip address; leases network information to hosts in network

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smb – samba – method for accessing unix file space as drive letter maping in windows, mac, linux, etc transport layer – ch 4 o transport layer preps/moves data between applications on devices in network  segments data and manages separation of data for different applications; each tab on browser will have own port #; manages transport to EACH application o segmentation is very important o TCP headers contain more info/bytes than UDP header o UDP (user datagram protocol) – connection less; doesn’t care if packets are lost; fast; low overhead; delivers data as it arrives; ip telephony, streaming video o TCP (transmission control protocol) – reliable, acknowledge data, resends lost data, delivers data in order sent; http, smtp/pop o Three functions  Multiplexing – send data from multiple computers  Segmentation and reassembly (only tcp does lateR)  Error checking (only tcp) o Socket = port # and ip address o Tcp is 3 way handshake – send syn, send syn acknowledgement, ok established o Port addressing – 25 smtp; 80 web; source/dest port # switch from client to server o Well known ports  ftp data – 20; ftp control 21  telnet – 23  smtp – 25  tftp – 69; udp  http – 80; https - 443  pop3 – 110  irc – 194  rip – 530; udp Network layer – ch 5 o Local area network – connects computers in limited area such as home, school, lab, office building  Every line out of a router = 1 subnet/lan segment/network interface  Sending frames outside of local subnet, need router/DEFAULT GATEWAY o Subnet mask – identifies network portion and host portion o Broadcast domain – each local network is a broadcast domain; too many hosts on single broadcast domain can be problematic/excessive traffic  router does not pass broad cast message; each line of router is a network; each line out of router is a broadcast domain and collision domain o Ip address on packets (ip header)  App data -> tcp segment -> network packet - > link layer frame  Ethernet frame tacks on header and trailer o Roles network layer

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Addressing – end device only becomes host when given ip address Encapsulation – takes TCP segment and adds network headers (s/d ip address) making a packet  Routing – intermediary network devices that connect networks (ie routers)  Decapsulation – opening frame to get packet to check IP and pass up Ip stack to transport and application layers  Ip v4/6, appletalk  Ipv4 – connectionless, best effort/unreliable (does not guarantee packet delivery), media independent  Source/dest ip address doesn’t change! o Dividing networks – geographic, purpose, ownership; routers optimize network to avoid broadcast overload o Default gateway is way outside of network = ip address of router; only know the addresses of devices in my network, so send unknown ones to default gateway o Maximum transmittable unit – network and datalink layer collaborate on max size of packet (mtu); packet may have to be split as it travels from one end host to another end host -> fragmentation from hop to hop Data link layer – ch 7/9 o Need ip address and subnet mask to ID comp on network o Peer networking – 2 computers want to share resources o Clients (dynamic/dhcp) and servers (static) o Physical topology – how devices are linked via media o Logical topology – hierarchy of ip addresses; group hosts by how they use the network o Ethernet protocol is dominant for lan; bob Metcalf and Ethernet (standardization of protocols) o Ethernet speeds (fe = 100mbps; gigabit = 1000mbps; 1gb, 10gb) o Addresses  Ip = 32 bit; 4 bytes 192.168.1.2; first 3 are network, 4th is host  Mac = 6 bytes, physical address, given at time of manufacture of NIC; bia; find using ipconfig; hexadecimal o Hexadecimal = 1 byte = 2 nibbles; 1 nibble can be represented in hexadecimal  ALL F’s IS BROADCAST ADDRESS  Decimal = 88; hexadecimal = 0x88  Hexadecimal – 10111001  First four are 11; Second four are 9  Hex is from 0-9, then A-F; second four is B -> 0xB9 o Message patterns – uni (one to one computer; mac address of one host); multi (one to few; mac address and ip range); broad (all computers; ff:ff:ff:ff:ff:ff)  if ff’s reach a switch, will switch just forward to everyone except source? o Hub is dumb and will send a unicast msg to ALL connected devices, except source, creates unnecessary traffic o Lan communication – ARP RELATED TO LAN

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Arp – address resolution protocol – broadcast to find mac address for given ip address  Arp cache – arp –a command; stores mac address for given ip address o Lan network/hosts  192.168.1.4/24; first 3 network, 4th host; what is /24? 24 bits for network 8 for host o Ethernet wired (csma/cd)  Carrier sense multiple access/collision detection – wireless uses  Carrier sense – devices listen before transmitting  Multiple access – multiple hosts can transmit on same line; can write when they want  Collision detection – when frames collide, all devices are notified with jam signal o Hub is just a dumb repeater – layer 1 device; takes signal and sends it to all attached devices except source  Shared bandwidth devices; 100 mb -> if 10hosts, then 10mb each  Half duplex – one host can either receive or send at same time; not both at same time  1 hub -> 1 collision domain (those notified of collision)  2 hubs connected to each other with devices -> 1 collision domain Data link layer – ch 7/9 o Port 22 is for ssh, telnet is unsecure version of ssh  Ssh: secure remote access to machine; client-server; telnet is not secure and plaintest; need ssh client and daemon, daemon listens on port 22 o Frames and media – different frames for different media o Logical link control – frames network layer packet; id’s network layer protocol o Encoding – writing bits to layer o Controlled access – only one station transmit at a time; devices wait their turn, no collisions; token ring, fddi o Contention based access – fighting to write onto line; stations transmit any time, collisions exist; resolving contention = csma/cd for Ethernet; csma/ca for wireless  Csma/cd: carrier sense (devices listen before sending), multiple access (multiple hosts can transmit on same line), collision detection – when frames collide, jam signal – random backoff timing, hosts try again) o Mac addresses – 6 bytes; first 3 are organization unqiue number; second 3 are vendor assigned; ethernet communicates through mac addresses o Arp – cache contains ip address/mac address translation; if doesn’t know mac address then do arp broadcast domain o Ethernet frame – sender runs cyclic redundancy check and stores in frame check sequence in frame; router will open up frame and read mac addresses, if not match then adds on new frame with new mac addresses o Hubs and collision domains; hubs don’t break up collision domains; more collision domains the few collisions happen

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Switches – don’t forward to all ports; use mac table to find which port to send frame too; efficient! Smart forwarder  Clients send out arp broadcasts to find mac addresses of local computers to their subnet, then store mac/ip address in arp cache  Switches introspect frames and sent to it and learn mac addresses of computer connected to switch and stores mac address and SWITCH port in mac table  Switch flooding – flood frame to all connected ports except source to update mac table; acts as a hub on first communication; port flooding  Every line out of switch is a collision domain  Dedicated bandwidth to each port; full duplex operation (bandwidth not shared)  Learn (stores mac/port, look at source mac first); age (will forget and relearn); flood (to learn); selective forwarding (once mac/port learn will not repeat to all); filtering ? – selectively send it on Switches and collision domains  Hubs notify all hosts in collision domain (including switch) by repeating jam signal; but switch is smart and does not forward; every port on switch creates separate collision domain Broadcast domains  Hubs/switches DO NOT breakup broadcast domains Hub v. switch  Layer 1 v. 2  Do not break up cd v. does  No frame introspection v. yes to learn mac ad  Repeats to all except source v. selectively forwards  Repeats to all except source c. only floods except source first time  Shared v. full bandwidth  No temp/dedicated channel/circuit v. yes unshared temp circuit; collisions avoided  Repeats broadcast to all connected hosts v. forwards to all except source Gratuitous arp – not required by arp; arp reply when no arp request made; when new device comes online  Detect ip conflicts; let switch know about mac/port change; update other device arp tables; let devices know when ip interface on computer had link up event (Ethernet cable attached, or after reboot) Switches and hubs  When hub is attached to switch; switch associates mac address of all hosts on hub with single port that attaches hub to switch  Collisions can occur on hub, hub will repeat jam to all connected devices including switch; switch wont forward to other ports Collision domains and broadcast domains

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Devices notified in lan when two frames collide v. hosts in lan when any hosts uses ffx6 for dest mac Switches/routers break up v. routers Performance improves when broken up v. performance improves when routers break up

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Oop o Objects of different types that communicate with each other to get task done o Class = blueprint and create instances of it called objects o Class models states and behaviors o Have a simple interface to mask complex implementation Java – how to code each type of example o Benefits: platform independent; huge standard utility library; most developed in terms of features; supports Unicode, similar to c++ (not as buddy, memory leak problems, etc) o Java code -> compiler -> class (byte code) -> jvms for os’s o Java environment  Java sdk – all libraries, utilities, compiler, jvm (java virtual machine that runs compiled byte code files)  Jre – java runtime environment; allows to execute java code on web page;  To run java code need java jre; to develop need java sdk (which contains jre) o Javac to compile, java to run class without .class; will look for “public static void main (string [] args) {}  A file can only have one public class; name of file should be name of class with .java extension o Structure of class  Package declaration – optional  Import statement – access to java libraries not in java.lang  Class declaration, instance data declaration, constructor – gives initial values, method declarations/signatures o Variable scope – variable declared in a code block is accessibly by any code in that code block and any nested code blocks; variable inside code block is not accessible to outer code blocks o Method signatures  Public/private  Void/data type – what type of data return  Name of method  Parameters (); still need if none; finally {} o Method access directives  Public – accessible by everyone  Protected – accessibly by sub classes  Package – accessible by other classes in package  Private – accessibly to objects of same class o Class = user defined datatype; udt

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 Classes are types; objects are instances of a type  Classes are another datatype, except they define data AND BEHAVIOR Objects – use new to construct new object fro class Interface v. implementation  Interface – use public keyword, what object reveals to world  Implementation is how it may be doing things behind the scenes  Encapsulation – technique used to create well designed classes; separates out interface and implementation  Data is private to an object and other objects can modify an objects data though well defined interfaces Constructors – called when object is instantiated; one object can have multiple constructors; used to give an object an initial state  Name is same as class and no return type; ex: public animal (){}  There is a default constructor if none specified This operator – refers to current object instance Static v. nons-static blocks  static (class) methods; don’t need an object instance to use them  Dog d = new Dog();  D.doSomething();  Dosomething can be static or instance method  Dog.doSomething(); <- this is a class reference/static reference!  Countofaccounts example (when making new accounts, add to countofaccounts; kind of shared by whole class) Exception handling – specify how to throw an exception; try catch block Inheritance – implementing common state and behavior at a general level; java has single inheritance  Can be reused among a family of classes; keyword extends  All classes inherit object class  Inheritance does not need to implement all its superclass for it to be concrete Upcasting – moving up object hierarchy; always safe; using a superclass reference to access subclass; can only use superclass portion of object  Animal a=new dog(); -> cant use a.bark because bark is not in animal superclass Downcasting – going down object hierarchy; when you want to assign superclass to subclass reference; not always safe  Cat c = new animal(); not all animals are cats! Polymorphism – each subclass can respond differently to same message  Superclass has makeSound; sub class has distinct makeSounds (subclasses override superclass)  vet will handle animal; animal a a.handle(); uses a superclass reference, but response is taken care of by subclass Abstract classes – classes not fully implemented

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Some methods will not have a body and will be declared abstract Class with ANY abstract methods has to be abstract class Abstract class cannot be instantiated; can have a constructor  Cannot do animal a = new animal();  Put methods that are subclasses are required to have in respective superclass (abstract)  Good way to specify general state and behavior information in a class; animal would never be instantiated; what does an animal look like? Interfaces – like abstract classes in that it leaves out ALL implementation  Abstract classes can implement some methods  Solely serve to specify method signatures  Polymorphic benefits; end in –“able”  Public class something implements somethingable, something2able  Instead of vet accepting pet, it will accept treatable JAVA – make a class, make a method, constructor, etc

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Common commands Four steps to making a bash script:  #!/bin/bash is first line of code  <do whatever script does> echo “hello world”  Chmod 5 or 7, 00 <name>.sh; executable by me  Call it by “./<name>.sh” Go over chmod values