Review for Exam 4 School of Business Eastern Illinois University © Abdou Illia, Fall 2005

The Internet School of Business Eastern Illinois University

3 The Internet addressing system n Network deliver messages based on network addresses – The Internet has two addressing systems for hosts n IP addresses. Example: n Host names (or domain names or Unique Resource Locators). Example: eiu.edu Host

4 IP Address n IP addresses – Are really strings of 32 bits (1s and 0s) n Example: – Usually represented by four number segments separated by dots: dotted decimal notation n Example: – Official addresses for hosts

5 Assigning Parts n Most Organizations have multiple Segments within the Organizational Network n So, usually Local Part is broken in two parts – a Segment Part to represent each segment – Remaining Bits are the Host Part, designating a particular station on that segment Network PartSegment Part IP Address (32 bits total) Host Part Local Part

6 IP address Place Value (2 N ) BitDecimal Position (N) Binary = Decimal 163 Note: Starts with 0

7 Network classes n The value of the first octet in an IP address determines the Network class Class A Class B Class C 0.x.x.x to 127.x.x.x x.x to x.x x to x ClassAddress range 0xxx 10xx 110x Leftmost bits 8 bits 16 bits 24 bits Network Part Length Place Value (2 N ) BitDecimal Position (N) ) For each of the following IP addresses, give the class and the network bits ) To which class belong Eastern’s network? (Net. Part =139.67)

8 Summary Questions 1. a) Distinguish between IP address and host name. b) Which is the official address of a host? c) Does a server host need an IP address? d) Does your home PC need an IP address when you are on the Internet? e) Does a server host need a host name? f) Does your home PC need a host name when you are on the Internet? 2. Using the conversion system on slide #10, convert the following IP address to dotted decimal notation: (Spaces are included to facilitate reading.)

9 Summary Questions 3. a) What are the three parts in IP addresses? b) What part(s) do border routers look at to determine whether the destination host is within the network or outside of it? 4. a) Who assigns the Network part? b) The Segment part? c) The Host part? 5. a) When do we need DNS? b) What information do you send in a DNS request message? c) What information do you receive in a DNS response message? 4. a) What is autoconfiguration? b) What information do we get back, at a minimum, in an autoconfiguration response message? c) What other information may we get back?

10 Other questions n Make sure you are able to answer questions in Internet exercises available in the Notes’ section of the course web site. You can get the files containing these questions through the following links: n InternetExercise.doc InternetExercise.doc n IPAddressExercise1.doc IPAddressExercise1.doc n IPAddressExercise2.doc IPAddressExercise2.doc

Network Management

12 Availability n Availability: probability that a particular component or system will be available during a fixed time period n Availability is function of: – Mean time between failures (Given by manufacturer or generated based on past performance) – Mean time to repair (Found in studies or in our archives) n Mean time between failures (MTBF) is the average time a device or system will operate before it fails. n Mean time to repair (MTTR) is the average time necessary to repair a failure

13  Standard equation: A(t) = a/(a+b) + b/(a+b) x e -(a+b)t in which:a = 1/MTTR b = 1/MTBF e = natural log function t = the time interval  Approximation equation: Availability% = (Total available time – Downtime)/Total available time Availability

14 Suppose we want to calculate the availability of a modem that has a MTBF of 3000 hours and a MTTR of 1 hour. The availability of this modem for an 8-hour period is: a = 1/1 b = 1/3000 = A(8 hours) =1/( ) /( ) x e -( )8 = x = Availability Q: What will be the availability of the modem if the Approximation equation is used? A(t) = a/(a+b) + b/(a+b) x e -(a+b)t

15 Availability n A component has been operating continuously for three months. During that time, it has failed twice, resulting in downtime of 4.5 hours. Calculate the availability of the component during that three- month period using the Approximation method.

16 Availability n To calculate the availability of a system of components: – Calculate the availability of each component – Find the product of all availabilities n Example: If a network has tree devices with availabilities of 0.992, 0.894, and 0.999, the availability of the network is: x x = 0.886

17 Reliability n Reliability: probability that a component or system will be operational for the duration of a transaction time t. n Reliability is function of: – Mean time between failures – Transaction time n Mean time between failures (MTBF) is the average time a device or system will operate before it fails. n Transaction time is the time interval of operation to complete a given transaction.

18 Reliability Reliability is defined by the equation: R(t) = e -bt in which:b = 1/MTBF t = the time interval of the operation

19 Reliability What is the reliability of a modem if the MTBF is 3000 hours and a transaction takes 20 minutes, or 1/3 of an hour (0.333 hours): R(t) = e -bt b = 1/MTBF = 1/3000 t = R(0.333 hours) = e -(1/3000)(0.333) = e = Q: If a component has a MTBF of 500 hours and a transaction takes 4 seconds, calculate the reliability of the component