Quiz 1

1) Contact the network expert at your school or place of work. Find out which topology, communication links, and configuration are used in the network. IS it a LAN, MAN, or WAN?
* The topology, communication links, and configuration of roseclyde internet café is the LAN (Local Area Network).
2.) Discuss the primary difference between a bridge and a gateway and give real life example that uses each one?
*A bridge joins two similar types of networks so that they look like one network. The word transparent is often used with bridges because network clients do not know the bridge is even in place. A bridge must look at every packet on the network, not just those addressed to it. Thus it is possible to overload a bridge by putting it on a very busy network, even if very little traffic is actually going through the bridge.
*A gateway joins two dissimilar networks. There can be a lot of protocol conversion work to do. Often the gateway needs to be configured on client systems where communications are directed to the gateway and then some address mapping is provided to get the message to the recipient on the other side. Gateways have their own advantages and disadvantages. In general a gateway is more complex to design and to administer than a bridge. A gateway must participate in all of the protocols that it is designed to forward. For example, an IP gateway must respond to ARP requests. The IP standards also require it to completely process the IP header, decrementing the time to live field and obeying any IP options.
3.) Name three commercially-available operating systems for LANs and their vendor names. Explain the topology that each designed to manage and describe the access protocol it uses.
*The three commercially-available operating systems for LANs are the Windows 2000, Windows XP, Windows Server 2003, Windows Vista. This operating systems are created by the Microsoft Windows Corporation.
*Windows Vista’s network map uses the Link Layer Topology Discovery (LLTD) protocol to determine the network’s topology. The cool thing about it is that this is the same discovery topology used by XBOX 360. Microsoft automatically enables network mapping on home (private) networks, so if you happen to have an XBOX 360 on your home network, it should show up on the network map. Unfortunately, mapping is disabled on domain networks and public networks by default.
4.) Explain the similarities and differences between a file infector virus and a macro virus, including the types of files each infects.
*File infector viruses infect program files. These viruses normally infect executable code, such as .com and .exe files. The can infect other files when an infected program is run from floppy, hard drive, or from the network. Many of these viruses are memory resident. After memory becomes infected, any noninfected executable that runs becomes infected. Examples of known file infector viruses include Jerusalem and Cascade.
* Macro viruses these types of viruses infect data files. They are the most common and have cost corporations the most money and time trying to repair. With the advent of Visual Basic in Microsoft's Office 97, a macro virus can be written that not only infects data files, but also can infect other files as well. Macro viruses infect Microsoft Office Word, Excel, PowerPoint and Access files. Newer strains are now turning up in other programs as well. All of these viruses use another program's internal programming language, which was created to allow users to automate certain tasks within that program. Because of the ease with which these viruses can be created, there are now thousands of them in circulation. Examples of macro viruses include W97M.Melissa, WM.NiceDay and W97M.Groov.

5.) Give three examples of inadequate passwords and explain why each would be a poor choice to protect a system from unauthorized users.
* One of the best ways to protect information or physical property is to ensure that only authorized people have access to it. Verifying that someone is the person they claim to be is the next step, and this authentication process is even more important, and more difficult, in the cyber world. Passwords are the most common means of authentication, but if you don't choose good passwords or keep them confidential, they're almost as ineffective as not having any password at all. Many systems and services have been successfully broken into due to the use of insecure and inadequate passwords, and some viruses and worms have exploited systems by guessing weak passwords.


Sources: http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,295199,sid63_gci981843,00.html
http://en.wikipedia.org/wiki/Windows_NT
http://www.us-cert.gov/cas/tips/ST04-002.html

Exercises 1 - 6

1. Deadlock
-> deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. “When two trains approach each other at a crossing, both shall come to a full stop and neither shall start up again until the other has gone.”

*Starvation - describes a situation where a thread is unable to gain regular access to shared resources and is unable to make progress. This happens when shared resources are made unavailable for long periods by "greedy" threads.
*Race is a synchronozation problem between two processes vying for the same resources.
2. *Deadlock example : Alphonse and Gaston are friends, and great believers in courtesy. A strict rule of courtesy is that when you bow to a friend, you must remain bowed until your friend has a chance to return the bow. Unfortunately, this rule does not account for the possibility that two friends might bow to each other at the same time.
*Example of starvation suppose an object provides a synchronized method that often takes a long time to return. If one thread invokes this method frequently, other threads that also need frequent synchronized access to the same object will often be blocked.

3. Necessary Conditions for a Deadlock:
1.) Mutual exclusion - Each resource is either currently allocated to exactly one process or it is available. (Two processes cannot simultaneously control the same resource or be in their critical section).
2.) Hold and Wait - processes currently holding resources can request new resources
3.) No preemption - Once a process holds a resource, it cannot be taken away by another process or the kernel.
4.) Circular wait - Each process is waiting to obtain a resource which is held by another process.

4. Algorithm for prevention of deadlock and starvation:
-> public boolean tryAcquire( int n0, int n1, ... ) { if ( for all i: ni ≤ availi ) { // successful acquisition availi -= ni for all i; return true; // indicate success } else return false; // indicate failure}init) Semaphore s = new Semaphore(1,1);Thread A Thread B-------- --------s.acquire(1,0); s.acquire(0,1);s.acquire(0,1); s.acquire(1,0);Thread B--------while(true) {s.acquire(0,1);if ( s.tryAcquire(1,0) ) // if second acquisition succeedsbreak; // leave the loopelse {s.release(0,1); // release what is heldsleep( SOME_AMOUNT); // pause a bit before trying again}}run action s.value--- ------ -------(1,1)A s.acquire(1,0) (0,1)B s.acquire(0,1) (0,0)A s.acquire(0,1) A blocks on secondB s.tryAcquire(1,0) => falseB s.release(0,1) (0,1)A s.acquire(0,1) (0,0) A succeeds on second.

6. a. This is not a deadlocked.
b. There is no blocked processes.
c. P2 can freely request on R1 and R2.
d. P1 can freely request on R1 and R2.
e. Both P1 and P2 have requested R2.1. P1 will wait after the request of P2.2. P2 will wait after the request of P1.

Apple's Leopard OS certified for Unix 03 standard

November 20, 2007 (Computerworld) -- Enterprise IT shops looking for more options in computer operating systems now have another choice to evaluate -- Apple Inc.'s Mac OS X Leopard client software and Mac OS X Leopard Server have both been officially certified as meeting the latest Unix 03 standards.
On Monday, the San Francisco-based open standards and interoperability consortium, The Open Group, announced that it had awarded certificates of conformance to the Unix 03 standards to both versions of Leopard. The certifications mean that the software meets the latest UNIX product standards developed by The Open Group Platform Forum for the Single UNIX Specification version 3, according to the group.
"For over 10 years, the Single UNIX Specification has consistently provided both scalability and stability to end users -- one hallmark of a tried and true technology standard," Allen Brown, president and CEO for The Open Group, said in a statement. "Operating platforms conforming to the UNIX 03 standard assures enterprises with industrial strength products, as well as an opportunity to avoid limited choice in vendor partnership. In achieving UNIX 03 certification, Apple has shown true commitment to its customers in providing open solutions that are warranted and fully supported."
Adding both Mac desktop and server OSes to the list of compliant systems allows a popular desktop OS to be included on the list of available options for enterprise users, according to the group.
Mac OS X is also the first operating system derived from the open source BSD Unix project to meet the certification requirements, according to the group.

Source:http://www.computerworld.com