1. Explain the circumstances under which a token-ring network is more effective than an Ethernet network.
Well, in Token Ring, there is a token. Only the machine with the Token may transmit. This is collision avoidance. While a station is transmitting, it holds the token and no-one else on the ring can transmit. After that station is finished, and the last frame makes a complete ciruit of the ring, the Token is passed on; everyone gets a chance to transmit eventually and the problem of collision is avoided.
There is also all kinds of complicated shit to do with priorities, requesting the token, and beaconing which I'm not going into here. You can look it up if you really want. The data is still broadcast to everyone on the ring (see: Network Topologies) although, as with Ethernet, only the NIC to whom it is addressed need read it. Each machine on the ring accepts the frame, passing it to the next logical machine in the ring.
Traditionally, Token Ring is slow. Up until a couple of years ago, you had a choice of 4 or 16 Mbps (while Ethernet was happily operating at 100 Mbps. Today, 100 Mbps Token Ring exists, but Ethernet is up to 1 Gigabit. Plus, as someone already mentioned in this node, Ethernet is cheap.
Hence, Token Ring is clever, yet unpopular.
It was the classical IBM vs. Digital Equipment Corp. battle taken to the network theatre.
Two computing behemoths each lining up behind competing LAN architectures: IBM advocating Token-Ring and DEC endorsing Ethernet.
Pioneered by IBM scientist Olof Soderblom in the 1960s, Token-Ring was initially successful for IBM – as most IBM-endorsed technologies are. But beyond IBM, it never garnered much support among top-tier vendors, which gravitated toward Ethernet, the preferred LAN technology of research institutions and manufacturing companies.
Token-Ring began its downward spiral soon after the emergence of 10Base-T Ethernet, an inexpensive, 10Mbps transmission technology than ran across telephone grade unshielded twisted-pair copper media. Matters were not helped when Soderblom began demanding royalties from the few Token-Ring vendors and chip makers, driving prices higher.
http://www.networkworld.com/news/2007/102607-arguments-ethernet-token-ring.html?nwwpkg=50arguments
2. Although security issues were not mentioned in this chapter, every network owner must consider them. Knowing that open networks all data to pass to every node, describe the posssible security concerns of open network achitectures. include the implicatiions of passing logon procedures, user IDs, and passwords openly on the network.
In the development of computer networks, the spread of malicious network activities poses great risks to the operational integrity of many organizations and imposes heavy economic burdens on life and health. Therefore, risk assessment is very important in network security management and analysis. Network security situation analysis not only can describe the current state but also project the next behaviour of the network. Alerts coming from Firewall and other security tools are currently growing at a rapid pace. Large organizations are having trouble keeping on top of the current state of their networks. The implicatiions of passing logon procedures, user IDs, and passwords openly on the network are great risk to protect critical information on the network. Appropriate access controls assist to protect information processed and stored in computer systems. The organisation's system security policy must clearly define the needs of each user or group to access systems, applications and data. The file-access rights should be configured according to business requirements and the "need to know" principle. Formal procedures should control how access is granted to information-system services or how such access is changed, so as to prevent unauthorised access to data or system resources. Access control can start by allowing access to everything, and then revoking access to whatever systems, applications or data repositories a user does not need. However, it is better to start by denying access to everything, and then explicitly granting access to just the specific resources a user needs. Secure logon procedures can control access to host-based information systems. Logon procedures should reveal minimal information about the system, to deter unauthorised use.
3. Remembering the discussion of deadlocks, if you were designing a networked system, how would you manage the treat of deadlocks in your network? Consider all of the following: prevention, detection, avoidance, and recovery.
Deadlock Prevention
Difference from avoidance is that here, the system itself is build in such a way that there are no deadlocks.
Make sure at least one of the 4 deadlock conditions is never satisfied.
This may however be even more conservative than deadlock avoidance strategy.
Attacking Mutual condition
never grant exclusive access. but this may not be possible for several resources.
Attacking pre-emption
not something you want to do.
Attacking hold and wait condition
make a process hold at the most 1 resource at a time.
make all the requests at the beginning. All or nothing policy. If you feel, retry. eg. 2-phase locking
Attacking circular wait
Order all the resources.
Make sure that the requests are issued in the correct order so that there are no cycles present in the resource graph. Resources numbered 1 ... n. Resources can be requested only in increasing order. ie. you cannot request a resource whose no is less than any you may be holding.
Detection and Recovery process
Is there a deadlock currently?
One resource of each type (1 printer, 1 plotter, 1 terminal etc.)
check if there is a cycle in the resource graph. for each node N in the graph do DFS (depth first search) of the graph with N as the root In the DFS if you come back to a node already traversed, then there is a cycle. }
Multiple resources of each type:
Detection and Recovery process
Is there a deadlock currently?
One resource of each type (1 printer, 1 plotter, 1 terminal etc.)
check if there is a cycle in the resource graph. for each node N in the graph do DFS (depth first search) of the graph with N as the root In the DFS if you come back to a node already traversed, then there is a cycle. }
Multiple resources of each type:
m resources, n processes
Max resources in existence = [E1, E2, E3, .... Em]
Current Allocation = C1-n,1-m
Resources currently Available = [A1, A2, ... Am]
Request matrix = R1-n,1-m
Invariant = Sum(Cij) + Aj = Ej
Define A <= B for 2 vectors, A and B, if Ai <= Bi for all i Overview of deadlock detection algorithm, Check R matrix, and find a row i such at Ri <>
Deadlock Avoidance
Avoid actions that may lead to a deadlock.
Think of it as a state machine moving from 1 state to another as each instruction is executed.
Safe State
Safe state is one where
It is not a deadlocked state
There is some sequence by which all requests can be satisfied.
http://homepages.uel.ac.uk/u0214248/Harriet4.htm
4. Assuming you had sufficient funds to upgrade only one component for a system with which you are familiar, explain which component you would choose to upgrade to improve overall performance, and why?
I will upgrade the memory of my computer
Random-access memory (usually known by its acronym, RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1]
This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.
The word RAM is mostly associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. However, many other types of memory are RAM as well (i.e. Random Access Memory), including most types of ROM and a kind of flash memory called NOR-Flash.
http://en.wikipedia.org/wiki/Random_access_memory
