IGNOU MCA MCS-022 Solved Assignments 2010Course Code Course Title Assignment Number Maximum Marks Weightage Last Date of Submission : : : : : : MCS-022 Operating System Concepts and Networking Management MCA(2)/022/Assign/09 100 25% 15th October, 2009 (for July, 2009 session) 15th April, 2010 (for January, 2010 session)
This assignment has five questions. Answer all questions. Rest 20 marks are for viva voce. You may use illustrations and diagrams to enhance the explanations. Please go through the guidelines regarding assignments given in the Programme Guide for the format of presentation. Answer each part of the question should be confined to about 300 words. Question 1: a) Describe the structure of 5 classes of IP address. Also draw the network configuration of your study centre/organisation showings IP addresses assigned your organization by ISP. How do these classes differ? How do you identify a particular classes? (5 Marks) b) How does DNS improve the name resolution? c) What is real time OS? How it is different from the traditional OS. (5 Marks) (5 Marks)
Answer 1 : In the original Internet routing scheme developed in the 1970s, sites were assigned addresses from one of three classes: Class A, Class B and Class C. The address classes differ in size and number. Class A addresses are the largest, but there are few of them. Class Cs are the smallest, but they are numerous. Classes D and E are also defined, but not used in normal operation. To say that class-based IP addressing in still used would be true only in the loosest sense. Many addressing designs are still class-based, but an increasing number can only be explained using the more general concept of CIDR, which is backwards compatible with address classes. Suffice it to say that at one point in time, you could request the Internet NIC to assign you a class A, B or C address. To get the larger class B addresses, you might have to supply some justification, but only the class A was really tough to get. In any case, NIC would set the network bits, or n-bits, to some unique value and inform the local network engineer. It would then be up to the engineer to assign each of his hosts an IP address starting with the assigned n-bits, followed by host bits, or h-bits, to make the address unique.
Internet routing used to work like this: A router receiving an IP packet extracted its Destination Address, which was classified (literally) by examining its first one to four bits. Once the address's class had been determined, it was broken down into network and host bits. Routers ignored the host bits, and only needed to match the network bits to find a route to the network. Once a packet reached its target network, its host field was examined for final delivery. Summary of IP Address Classes Class A - 0nnnnnnn hhhhhhhh hhhhhhhh hhhhhhhh First bit 0; 7 network bits; 24 host bits Initial byte: 0 - 127 126 Class As exist (0 and 127 are reserved) 16,777,214 hosts on each Class A Class B - 10nnnnnn nnnnnnnn hhhhhhhh hhhhhhhh First two bits 10; 14 network bits; 16 host bits Initial byte: 128 - 191 16,384 Class Bs exist 65,532 hosts on each Class B Class C - 110nnnnn nnnnnnnn nnnnnnnn hhhhhhhh First three bits 110; 21 network bits; 8 host bits Initial byte: 192 - 223 2,097,152 Class Cs exist 254 hosts on each Class C Class D - 1110mmmm mmmmmmmm mmmmmmmm mmmmmmmm First four bits 1110; 28 multicast address bits Initial byte: 224 - 247 Class Ds are multicast addresses Class E - 1111rrrr rrrrrrrr rrrrrrrr rrrrrrrr First four bits 1111; 28 reserved address bits Initial byte: 248 - 255 Reserved for experimental use b) Answer: A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts. DNS Root Servers DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top level of the hierarchy, so-called root servers store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers that
have become somewhat famous for their special role. Maintained by various independent agencies, the servers are aptly named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in London, UK and one in Stockholm, Sweden. DNS resolution Resolution occurs when a client queries a name server to obtain the IP address with which it wants to connect. If a name server in the local domain cannot resolve a client's request, it queries other servers to locate a server that can. There are two types of resolution: by iteration by recursion Iterative queries By default, a name server queries ``iteratively'' (or non-recursively). This means that it queries several name servers in turn until it finds an answer. It starts by consulting a known name server within the domain hierarchy that contains the destination machine. If it does not already know of a suitable server to ask, it first asks a server in the root domain. Each server responds by referring to a name server in the domain name hierarchy that is closer to the one containing the destination machine. The local server then repeats its query to the name server whose name and IP address it has just been given. In this way, the local server traverses the domain name space until it reaches a name server for the domain that contains the destination machine. This name server should be able to provide the IP address of the destination machine. ``Obtaining an IP address by iterative query'' illustrates how a client in the domain reseau.co.fr might obtain the IP address of the remote host missouri.rivers.mynet.com. Obtaining an IP address by iterative query The steps taken to resolve missouri.rivers.mynet.com to its IP address are: 1. The local client asks the local name server for the IP address of missouri.rivers.mynet.com. 2. The local name server does not know the IP address of Missouri .rivers .mynet.com . It also does not know the IP address of the name servers for rivers.mynet.com or mynet.com so it asks a root name server for the IP address of missouri.rivers.mynet.com. 3. The root name server does not know the IP address of Missouri .rivers .mynet.com, but it does know the IP address of the name server for mynet .com so it tells this to the local name server.
4. The local name server asks mynet.com's name server for the IP address of issouri.rivers.mynet.com. 5. mynet.com's name server does not know the IP address of Missouri .rivers.mynet.com, but it does know the IP address of the name server for rivers.mynet.com so it tells this to the local me server. 6. The local name server asks rivers.mynet.com's name server for the IP address of missouri.rivers.mynet.com. 7. rivers.mynet.com's name server is authoritative for its zone so it can supply the IP address of missouri.rivers.mynet.com c) A real-time operating system (RTOS) is an operating system that guarantees a certain capability within a specified time constraint. For example, an operating system might be designed to ensure that a certain object was available for a robot on an assembly line. In what is usually called a "hard" real-time operating system, if the calculation could not be performed for making the object available at the designated time, the operating system would terminate with a failure. In a "soft" real-time operating system, the assembly line would continue to function but the production output might be lower as objects failed to appear at their designated time, causing the robot to be temporarily unproductive. Some real-time operating systems are created for a special application and others are more general purpose. Some existing general purpose operating systems claim to be a real-time operating systems. To some extent, almost any general purpose operating system such as Microsoft's Windows 2000 or IBM's OS/390 can be evaluated for its real-time operating system qualities. That is, even if an operating system doesn't qualify, it may have characteristics that enable it to be considered as a solution to a particular real-time application problem. In general, realtime operating systems are said to require: multitasking Process threads that can be prioritized A sufficient number of interrupt levels Real-time operating systems are often required in small embedded operating systems that are packaged as part of microdevices. Some kernels can be considered to meet the requirements of a real-time operating system. However, since other components, such as device drivers, are also usually needed for a particular solution, a real-time operating system is usually larger than just the kernel. The key difference between general-computing operating systems and real-time operating
systems is the need for " deterministic " timing behavior in the real-time operating systems. Formally, "deterministic" timing means that operating system services consume only known and expected amounts of time. In theory, these service times could be expressed as mathematical formulas. These formulas must be strictly algebraic and not include any random timing components. Random elements in service times could cause random delays in application software and could then make the application randomly miss real-time deadlines a scenario clearly unacceptable for a real-time embedded system. Many non-realtime operating systems also provide similar kernel services. General-computing non-real-time operating systems are often quite non-deterministic. Their services can inject random delays into application software and thus cause slow responsiveness of an application at unexpected times. If you ask the developer of a nonreal- time operating system for the algebraic formula describing the timing behavior of one of its serv