Diversity in the Grocery Store Professor Ramos Blog

Diversity in the Grocery Store It was the evening after my last day of school before winter break began. There I was, standing in line in the checkout at Albertsons with my mom after having tagged along with her to do our family’s weekly grocery shopping. Directly in front of us was a woman, who looked no older than thirty, trying to calm her crying baby along with her other young daughter who looked to be about 5 or 6. Her cart was, noticeably, barely full, or at least compared to ours which was almost overflowing with groceries. As she went to pay, the cashier looked visibly irritated, then tells her that there was an issue with her card. This was when the cashier, instead of privately attempting to flag down a manger, made an announcement over the intercom, something along the lines of, â€Å"I need help in checkout line _, a food stamps card didn’t go through.† This is when the woman looked as if she was beginning to tear up. Her shoulders began to droop as her demeanor suddenly changed fr om friendly to extremely uneasy. After an uncomfortably long amount of time, a manager finally made his way down to fix the problem and luckily had everything up and working again in under a minute. Everything went smoothly after that, however, the woman did still look like she was holding back tears. She quickly left, looking almost ashamed, as soon as it was our turn to check out. Being only eight years old at the time, I didn’t quite know what the issue was, but I felt absolutely horrible for her. After both my mom and I made it back to the car and loaded up all of the groceries in the trunk, she started the car and we began to make our way back home. Being a bit curious, I asked her for a bit more information on everything that had just went down inside the store. She then explained that when some people can’t afford to buy food, the government will provide it for them. â€Å"When some people don’t need that kind of help, they don’t really underst and what those who are struggling with that are going through. They don’t think it’s fair to everyone else and will treat other people who do have to rely on extra help from the government for food badly.†      I sat and thought about that for awhile. It seemed extremely unfair. Those who are struggling enough with money to need the government to step in don’t need the extra stress of having to deal with people who are not willing to even try to understand their situation. This was one of my more memorable experiences with diversity during my childhood. At that point, having lived most of my life in a predominately middle-income neighborhood, I had always been surrounded by people of the middle to upper-middle class. My family was always a bit less well-off than the families we were surrounded by, but we never truly knew what it was like to struggle, or at least financially. This was what I knew as normal, so as a result, that specific instance was one of my first (memorable) exposures I had to prejudice towards people of lower incomes. Although I now knew that this problem existed, I still did not know how much of a problem it really was- as well as how close to home of a problem it really was. This would not be the last time I would have to witness someone being treated so badly just because they could not afford to buy the basic necessities for themselves and their families to live. One Sunday when I was thirteen years old, I was at my grandparents’ house for a family gathering, just like we had every single other Sunday. I was sitting in the living room with all of the adults since none of my cousins who were my age had arrived yet. The conversation then turned to my aunt, who had just started a new job as a receptionist at a local gym. â€Å"I’m so glad you were able to find something stable. Does this mean you won’t need help from the government for much longer?† my grandma asked, then immediately bit her tongue, forgetting for just a second the kind of company we had at the time. My aunt looked a bit embarrassed but she answered, â€Å"Yep, that’s the plan†. This is when one of my uncles, with a smug smile on his face, decided to pipe up, â€Å"Welfare huh? Well how long have you been on that?†. Partly ignoring the question she attempted to correct him, â€Å"Well I mean it isn’t quite welfare, but I have been on the food stamps program.†. Brushing her off, he then says, â€Å"Same thing. Government handouts are government handouts† and just goes silent again. My aunt, who seemed understandably, very uncomfortable with the whole situation, didn’t take much longer to leave after that. For the rest of the night I sat there feeling angry about what I had just seen happen. This was when I began to remember an instance very similar to the exchange I’d witnessed. I recalled the instance I’d seen happen five years earlier with the woman in the grocery store, and imagined my aunt, who I love and care about, in the same exact position. It absolutely broke my heart to think about her being treated that way, and the fact that it was likely that she has been.   Ã‚  Many people will choose to confront diversity simply with hatred, especially when they are not quite able to relate to those who are different than them, whether that is in race, culture, gender, religion, or as my experiences have shown, in socioeconomic status. The two experiences I had regarding this have pushed me to be a more understanding and tolerant person, especially with what I had seen my aunt go through behind the scenes. Not only that, but over the past few years I’ve had to watch as close friends have had to go through financial struggles as well and from what I’ve seen, there is so much more to it than what is on the surface. The anxiety and stress of not knowing whether or not you will be able to eat can be crippling. Overall, what I took from this, is that life does not treat everyone the same, and despite this, everyone deserves to be treated with kindness and respect- no matter their circumstances.

Create, Parse and Manipulate XML Documents With Delphi

Create, Parse and Manipulate XML Documents With Delphi What is XML? Extensible Markup Language is a  universal language for data on the Web. XML gives developers the power to deliver structured data from a variety of applications to the desktop for local computation and presentation. XML is also an ideal format for server-to-server transfer of structured data. Using an XML parser, software evaluates the hierarchy of the document, extracting the structure of the document, its content, or both. XML is in no way limited to Internet use. In fact, XMLs main strength organizing information makes it perfect for exchanging data between different systems. XML looks much like HTML. However, whereas HTML describes the layout of content on a webpage, XML defines and communicates data, it describes the type of content. Hence, extensible, because it is not a fixed format like HTML. Think of each XML file as a self-contained database. Tags   the markup in an XML document, offset by angle brackets delineate the records and fields. The text between the tags is the data. Users  perform operations like retrieving, updating and inserting data with XML using a parser and a set of objects exposed by the parser. As a Delphi programmer, you should know how to work with XML documents. XML with Delphi For more information about pairing Delphi and XML, read: Learn how to store TTreeView component items to XML preserving the Text and other properties of a tree node and how to populate a TreeView from an XML file. Simple Reading and manipulating RSS feeds files with DelphiExplore how to read and manipulate XML documents with Delphi using the TXMLDocument component. See how to extract the most current In The Spotlight blog entries (RSS feed) from the About Delphi Programming  content environment, as an example. Create XML files from Paradox (or any DB) tables using Delphi. See how to export the data from a table to an XML file and how to import that data back to the table. If you need to work with dynamically created TXMLDocument component, you might get access violations after you try to free the object. This article offers a solution to this error message. Delphis implementation of the TXMLDocument component, which uses Microsoft XML parser by default, does not provide a way to add a node of the ntDocType (TNodeType type). This article provides a solution to this problem. XML in Detail XML W3CPeruse the full XML standard and syntax at the W3C site. XML.comA community website where XML developers share resources and solutions. The site includes timely news, opinions, features and tutorials.

People Resourcing Essay Example | Topics and Well Written Essays - 2500 words

People Resourcing - Essay Example With the stated objective of ‘protecting the rights of workers’, unions negotiate with the management of the company and other regulating bodies to extract the best possible solution for the problems arising from time to time. But the union will be able to negotiate the solution only if it is recognized the management and the regulatory bodies for the purpose. The first step towards recognition is to be acceptable amongst the workers. To seek recognition, the union has to be acceptable amongst the employees as well. This implies that the union will have to enrol good number of employees as its members. In general, the minimum number of employees to be enrolled by any union for recognition, is defined in the rulebook. It also needs to be emphasised that enrolment or affiliation of a member with union has to be purely voluntary and without any coercion. The recognition itself is a multistage process comprising of the following steps (OPSI, 2004);  Step-1: After ensuring support of the requisite minimum number of workers, the union writes to the employer/ management requesting recognition. For the request to be valid there must be at least 21 employees under the banner of the union. The management can grant the recognition on the basis of the request or it may wish to verify the claim or further negotiate it with the employees and the union. At times, the help of Advisory, Conciliation and Arbitration Service (ACAS) is also sought in case of some disagreements.  Step-2: In case of persistence of some difference, the matter can be referred to the Central Arbitration Committee (CAC) by the union (s). The CAC is supposed to decide on the matter within a fixed time period by taking into account the merits of the case and the percentage of employees being represented by the union. Representation of at least 10 percent of the total workforce is once such criterion which helps in deciding in favour of the union. Step-4: Once the bargaining unit is formed the union is granted recognition either directly or by carrying out a referendum amongst the workers to ascertain the validity of the claims being made by the union.

Schizophrenia Essay Example | Topics and Well Written Essays - 1250 words

Schizophrenia - Essay Example This difference in levels of cognition in various patients led to more research into other underlying pathologic pathways responsible for severe cognitive impairment in NPI patients but was apparently working fine in patients on NPNN category. Brain morphometry was used to analyze differences. Both groups were tested against each other on the basis of four tests to asses the attention and working memory (verbal and nonverbal) and were confirmed by California verbal learning test and degraded stimulus continuous performance test. The standard deviation within 0.5 was the cut off for near normal cognition whereas 1 standard deviation below normal rendered the patient cognitively impaired. They gray matter was found to be smaller in both the groups along with larger third ventricle. An additional pathology found in NPI was that along with the gray matter, their white matter was also decreased in volume. The lateral ventricle cavity was also enlarged. Whitford et al (2007) further invest igated the white matter abnormalities in schizophrenics and also studied whether the degenerative changes are progressive. T1 weighted magnetic resonance images (MRI) of 41 first- episode schizophrenics were compared against those of 47 normal comparable people for baseline volume of white matter using voxel-based morphometry in statistical parametric mapping- 2 (SPM2). The schizophrenics had decreased volume of white matter in frontal and temporal lobes. However there was an increase in white matter at frontoparietal junctions on both sides. The longitudinal changes at follow up after 2 to 3 years were compared using tensor based morphometry which showed decreased white matter bilaterally in middle and inferior temporal cortices of schizophrenics. The neural connection abnormalities were attributed to this progressive loss of white matter. The structural brain abnormalities at the time of first psychotic episode were studied by Fannon et al (2000) whose research involved 37 patient s going through their first episode of psychosis. T1 weighted steady brain scans of 1.5 mm contiguous sections were obtained and volumetric brain measurements were taken. The patients were found to have structural deviations and there was generalized reduction in brain volume, along with enlarged third and lateral ventricles. Cortical and temporal gray matter was found to be decreased. Schizophrenia is a chronic progressive mental disorder. It is associated with cognitive impairment and worsening interpersonal skills. The attacks are accompanied by hallucinations and delusions. Person feels that he is hearing different sorts of voices and has false beliefs and perceptions. There is extreme emotional instability and the patient may suffer from depression or social isolation. Cognitive decline involves memory impairment, decreased ability to pay attention and difficulty in functional execution of activities. The abnormalities are attributed to abnormal distribution and ratios of gray and white matter in the brain. Apart from that, increase in size of ventricular cavities as well as generalized reduction in brain volume also adds to affect the typical schizophrenic picture. The result is alterations in various brain functions owing to

Han Dynasty and Roman Empire Essay Example for Free

Han Dynasty and Roman Empire Essay Both the Han dynasty and the Roman Empire were bureaucratic. The central rulers all eventually became hereditary and both empires had rulers that oppressed the peasants in order to boost political control. However, the two empires differ in that the emperors had varying justifications for ruling and rose to power in different ways. The Han Dynasty and The Roman Empire both were able to expand and develop their empires with their distinctive governing methods and control. To China, the centerpiece that supervised everything was knows as Confucianism. With all dependability focused on the emperor and society serving as a family unit, Han Chinas political system was known for a centralized, closed unit. It was ruled by an emperor who greatly observed the Mandate of Heaven. The Han developed a supply of soldiers, which kept their borders secured and made them capable to exchange with others from time to time. On the other hand, Rome had a centralized, blended structure. The main focus points of the Roman Society were operated by a Roman Republic, which was more like a monarchy, who controlled their complex structure. The Roman Society had more residents and rights than the Hans, Romans political control lay in the hands of the wealthy, which then they were elected to a political seat. The governors were picked from family networks. The only way Romans could accomplish anything big in a certain time span was to make strong changes in their community. It was an enormous weight on Romes resources and power, when they had to stress over big wins. For example, when there was barely any food to support the developing empire. The Romans and the Hans both had their wealthiest people control over their peasants, which caused a social distribution to each and every one, and could have leaded to outbreaks in little battles, wars between the communities, and what not. This was entirely not beneficial on each empires part and especially their social interaction. The political structures of both Rome and Han China were based on bureaucratic systems with a strong monarchy set of succession. They strengthened their control by reducing the land holdings of old aristocratic families. However, the reversal of this process led to breakdown of authority in the central government. During its reign of power, the central bureaucracy promoted trading with neighboring societies. However, Rome was more aggressive with its role in trading in the Mediterranean verses Han China’s river trade. Rome’s trade led to a much greater technology, culture, and general transfer of knowledge in areas surrounding the Mediterranean which in turn led to a much longer lasting influence on the world. Under the Han Dynasty, the power of the emperor and bureaucracy were emphasized. The organized structure of government allowed such a large territory to be effectively governed, even though it was the largest political system in the world at the time. The Hans political framework stressed male dominated families. Han rulers didnt support local warrior-landlords, believing that they were corrupt. Because bureaucracy was so important, civil service exams were first given, a tradition that would be incorporated into modern politics. Not only did bureaucracy effectively govern, but it had a sort of checks and balance on the upper class. Chinese bureaucracy from the Han Dynasty lasted well into the twentieth century. The imperial government sponsored intellectual life, such as astronomy and mathematics. Han rulers promoted Confucianism, with the idea that they were in charge of their subjects beliefs. The administration also took part in the economy. It organized production, standardized currency and measures, sponsored public works like canal systems and irrigation, and tried to regulate agricultural supplies to control price increases. The Roman republic allowed all citizens to meet in assemblies to elect magistrates. The most important legislative body was the Senate, made up of aristocrats. Public service and participation, political ethics, uncorrupt government, and oratory were extremely important. Roman leaders were very tolerant of local customs and religions and believed that well-made laws could hold the lands together. Aristocratic leaders supported legal codes to protect private property as well as their poor subjects. It was a sort of check on the upper class. They believed that laws should evolve to keep up with the demands of the changing society. Imperial law codes also controlled property rights and trade. The law of the land was fair and equal for everyone, for the most part. The Roman government also supported public works like roads and harbors to facilitate transport and commerce. It also supported an official religion, but tolerated others as long as they didnt interfere with loyalty to the state. Unlike the Chinese, the Romans didnt emphasize as much on hierarchy, obedience, or bureaucracy, but more on participation. However, some of the Romans political writing did resemble Confucianism. Both governments also supported government funded public works.

The Film Camila :: movie films movies

Camila Camila is an Argentinean film set in the mid 19th century, during the Rosas regime. The film focuses on the lives of a young girl, Camila, and her Jesuit priest Ladislao Gutierrez. Camila and Ladisalo fall in love and the film follows their troubles. Through following the events that happen with Camila and Ladisalo, the director shows how restrictive and devout followers of Rosas were and of the resentment against him.   Ã‚  Ã‚  Ã‚  Ã‚  The unjust ways of the Rosas regime were illustrated passively. Instead of having Rosas a central character issuing orders to be carried out, Rosas was instead placed in the background of the film. You would see Rosas through the actions of the church, military, and of the common people. His picture adorned the towns, everyone was to wear a red ribbon symbolizing their loyalty to Rosas. His supporters spoke of him proudly while those against him had to hide in silence. To illustrate the inherent problems of the Rosas era, the director chose to show the injustices through the ordeals of Camila and Ladislao.   Ã‚  Ã‚  Ã‚  Ã‚  First of all, in everyday life, Rosas demanded public showings of loyalty. Every citizen had to wear a bright red ribbon symbolizing their faith in their leader. Slaves, commoners, and even priests had to wear this ribbon. Through the execution of the bookseller, the tyranny of the Rosas regime is clear. He will tolerate to questions to his authority or allow anyone with a dissenting opinion to speak without fear of retribution. At the end of the film when the two young lovers are captured, Rosas rears his head again. Wishing to set an example to inspire terror into the masses, he doesn't hold Camilas execution even with the knowledge that she is pregnant. To further illustrate this point, the film makes it appear that Rosas is operating directly in contrast with the blessings of god.   Ã‚  Ã‚  Ã‚  Ã‚  While never specific in

Computer Networks Essay

I. Internet and layered protocol architecture: Q1. (5 points) In the layered protocol architecture the transport layer functionality includes congestion control and error recovery (e.g., retransmission). One suggested that this functionality should be done strictly at the end points (i.e., at the hosts) without aid from the network. Do you agree? Why? Elaborate showing the design trade-offs. Answer: (5 points) In general, error recovery (e.g., re-transmission) is specific to application needs. Some applications require 100% packet recovery, even with delays and jitters (such as TCP-based applications, http, ftp and telnet traffic). Other applications may be tolerant to loss but less tolerant to delays and jitter, such as voice applications. Re-transmissions and packet recovery add to the jitters and the delays and hence may not be desirable for realtime or voice applications. Hence it is not a good idea, in general, to include error recovery at the network layer (that is not aware of application needs) and it is better to implement such functionality at the transport layer end-to-end. In cases of lossy channels in the network (such as X.25 in the early networking days, or wireless links) it may be desirable to reduce the bit error rates on those links by including error recovery at the end points of those links. [In general, most links nowadays have very low BER, and for wireless links the MAC (such as IEEE 802.11) layer provides Ack’ed delivery]. For congestion control, a similar argument may be given. That is, congestion reaction may be application specific and is better implemented end-to-end. Congestion notification, on the other hand, may provide useful information to the end points to react appropriately. Since losses in the network may be due to congestion or other factors, a signal from the network to the end point may help distinguish congestion errors from other errors. Only congestion errors should trigger ‘back off’ or rate cut at the end points. So, network assistance in congestion notification may help in some scenarios. [extra: In other scenarios network assistance may prevent synchronization effects of congestion control, e.g., RED, or may prevent/isolate misbehavior, e.g., WFQ.]. Q2. (5 points) What advantage does a circuit-switched network have over a packetswitched network? How can it establish such advantage? Answer: A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. Circuit-switched networks use admission control, and reserve a circuit (in TDM it is done in the form of an assigned time slot per source that no other source can use). The allocated resources are never exceeded. Q3. (10 points) What are the advantages and disadvantages of having a layered protocol architecture for the Internet? (mention at least 3 advantages and 2 disadvantages) Answer: Is it true that the change in any of the layers does not affect the other layers? (support your answer/arguments with examples) Advantages: Allows an explicit structure to identify relationships between various pieces of the complex Internet structure, by providing a reference model for discussion. Provides a modular design that facilitates maintenance, updating/upgrading of protocols and implementations (by various vendors) at the various layers of the stack. Supports a flexible framework for future advances and inventions (such as mobile or sensor networks). Disadvantages: overhead of headers, redundancy of functions (sometimes not needed) [such as reliability as the transport layer and the link layer, or routing at the network layer and some link layer protocols (such as ATM)] It is true in many cases that the change in one layer does not affect the change in the other layers, but not always. Examples of change that did not affect the other layers: change from FDDI to token ring, to Ethernet at the MAC layer. Examples of change that affected other layers: wireless vs. wired (performance of TCP and routing degraded drastically). Introduction of 802.11 for wireless and ad hoc networks (a change in the physical and MAC layers), does affect in a major way routing at the network layer and the transport layers. In that case, many of the protocols needed re-design. Q4. (10 total points) Design parameters: In order to be able to analyze performance of the Internet protocols a researcher needs to model some parameters, such as number of nodes in the network, in addition to many other parameters. a. Discuss 4 different main parameters one would need to model in order to evaluate the performance of Internet protocols. [Elaborate on the definition of these parameters and their dynamics] b. Discuss 2 more parameters for mobile wireless networks [these two parameters are not needed for the wired Internet] Answer: a. Traffic model temporal and spatial (packet arrival processes, session/flow arrival processes, spatial distribution of traffic (src-dst) pair distribution across the topology), topology/connectivity model, node failure model, membership dynamics (for multicast) spatio-temporal models. [Any reasonable 4 parameters are ok, with 1.5 points per parameter] b. For mobile wireless networks there is a need to model ‘mobility’ (spatio-temporal), and wireless channel dynamics/loss/bandwidth since it changes with time much more drastically than the wired Internet (in which virtually the max bandwidth of a channel/link is static) [Any 2 reasonable parameters are ok, with 2 points per parameter] II. Statistical multiplexing and queuing theory Note: You may want to make use of the following equations: M/D/1: queuing delay ; Ts is service time & Ï  is link utilization M/D/1: average queue length or buffer occupancy M/M/1: queuing delay , buffer occupancy: Q5. (8 points) Consider two queuing systems, serving packets with lengths that have exponential distribution, and the packet arrival process is Poisson. The first queuing system (system I) has a single queue and a single server, and hence the packet arrival rate is X, and the server speed is Y. The second queuing system (system II) has two queues and two servers, and hence the packet arrival rate is X/2, and the server speed is Y/2. Derive a relation between the delays in each of these systems. What conclusion can you make? Answer: (8 points) We use the M/M/1 queue (because the question states Poisson arrival and exponentially distributed service time). For the first system (I): Tq=Ts/(1-Ï )=1/M(1-ÃŽ »/M)=1/Y(1-X/Y), For the second system (II): Tq=2/Y(1-X/Y)=2Tq (of system I) That is, using ‘1’ queuing system performs better than using ‘2’ queues with half of the arrival rate and half of the output link capacity. Q6. (5 points) In an Internet experiment it was noted that the queuing performance of the switches/routers was worse than expected. One designer suggested increasing the buffer size in the routers drastically to withstand any possible burst of data. Argue for or against this suggestion, and justify your position. A6. Increasing the buffer size allows switches to store more packets (which may reduce loss). However, it does not alleviate the congestion. If this was the only cure proposed, then we expect the queues to build up, increasing the buffer occupancy, and increasing the delays. If the build up persists (due to lack of congestion control for example) the queues shall incur losses and extended delays. Delays may lead re-transmission timers to expire (for reliable protocols, such as TCP) leading to re-transmissions. Also, the TTL value in the header of each packet is reduced based on time (and hop count). So, many of the TTLs may expire leading to the discard of packets. So, in ge neral, only increasing the buffer sizes does not help improve the queuing performance. Q7. (7 points) Describe the network design trade-off introduced by using statistical multiplexing and define and describe a metric that captures this trade-off. A7. (7 points: 3.5 for the link between stat muxing and congestion and 3.5 for the trade off metric (network power) and its description). Statistical multiplexing allows the network to admit flows with aggregate capacity exceeding the network capacity (even if momentarily). This leads to the need for buffering and the ‘store and forward’ model. Subsequently, queuing delays and build up may be experienced as the load on the network is increased. Two major design goals of the network is to provide maximum throughput (or goodput) with least (or min) delay. However, these two goals are conflicting. In order to increase the throughput, the congestion increases and so does the delay. In order to reduce the queuing delays then we need to reduce the load on the network and hence the goodput of the flows would decrease. This is the throughput-delay trade off in network design. One metric that captures both measures is the network power=Tput/Delay, as the Tput increases, so does the network power, and when the delay decreases the network power increases. Q8. (8 points) Flows in the Internet vary widely in their characteristics. Someone suggested that in order to be fair to the various heterogeneous flows then we need the different flows to experience the same delay at the different queues. Argue for or against this suggestion. A8. (8 points: 4 points for the constant ratio and the link to the fluid flow model, 4 points for the unfairnes/greed description) In order to provide the same delay for the various flows we need to maintain the rate/capacity ratio constant (this is based on the fluid flow model we introduced in class). Hence, if the different flows arrive at various rates, then the capacity allocation should reflect such variation. The allocation leading to same delays would favor (i.e., allocate more capacity to) flows with higher rates at the expense of flows with low rates. This strategy encourages greed in the network and cannot achieve fairness, where the existence of high rate (large) flows in the network would adversely affect low rate (small) flows in the network by increasing the overall delay experienced by all the flows. Q9. (12 total points) Consider a network that uses statistical multiplexing. The network has ‘N’ number of ON/OFF sources, each sending at a rate of R packets per second when ON. All the sources are multiplexed through a single output link. The capacity of the output link is ‘M’. – A. (3 points) What is the condition on N, R and M in order to stabilize this network? – When the number of sources to be supported is increased from R to 10R, there were two suggestions to modify the network: Suggestion I is to replicate the above system 10 times. That is, create 10 links, each with capacity of ‘M’ handling R sources. – Suggestion II is to replace the link with another link of capacity ’10 M’ B. (9 points) Which suggestion do you support and why? [Argue giving expressions for the delay/buffer performance of each system. Give both the advantages and disadvantages of each case] Answer: ÃŽ ±=ÃŽ »Ã  A. (3 points) The conditions for a stable network are N.R. ÃŽ ± < M, N.R > M, where ÃŽ ± is the fraction of the time the sources are ON (on average) If ‘N.R. ÃŽ ± > M’, then this leads to constant build up of the queue with no change of recovering from congestion (and draining the queue), which would lead to unstable system. B. (9 points) Write down the equations, M/D/1: queuing delay ; Ts is service time & Ï  is link utilization M/D/1: average queue length or buffer occupancy M/M/1: queuing delay , buffer occupancy: The buffer occupancy depends on Ï  only. If Ï  is the same (i.e., the load on the queue server is the same) then the buffer occupancy is the same, Ï  = ÃŽ ». Ts = ÃŽ ±. N. R / M Increasing the bandwidth of the link to 10M means that we can get the same average buffer occupancy in the two systems. In system I we would need 10 times the buffer size as in system II, so system II is advantageous in that sense. (more sharing and statistical multiplexing) In addition, the queuing delay will be decreased drastically (by a factor of 10) where Tq=Ts. f(Ï ) (6 points for the above argument) (3 points) On the other hand the std deviation/fluctuation around the average in the queue size will be higher since it is shared by more number of flows, and hence the jitter will be relatively higher. III. Application layer and related issues Q10. (5 points) (Stateful vs. Stateless) Discuss one advantage and one disadvantage of having a ‘stateful’ protocol for applications. Advantage: The protocol can now maintain state about (i.e., remembers) users preferences (e.g., shopping preferences as in browser cookies), Disadvantage: when failure occurs the state needs to be reconciled (more complexity and overhead than stateless) [other correct and reasonable answers are accepted] Q11. (5 point) (Web Caching) Describe how Web caching can reduce the delay in receiving a requested object. Will Web caching reduce the delay for all objects requested by a user or for only some of the objects? Why? Ans. Web caching can bring the desired content â€Å"closer† to the user, perhaps to the same LAN to which the user’s host is connected. Web caching can reduce the delay for all objects, even objects that are not cached, since caching reduces the traffic on links. Q12. (1 0 points) Discuss three different architectures of the peer-to-peer applications. Give examples of real applications for each architecture and discuss the advantages and disadvantages of each architecture. Ans. 1. Centralized directory of resources/files, as in Napster. Advantage is that search for resources is simple with min overhead (just ask the centralized server). The disadvantages are: single point of failure, performance bottleneck and target of lawsuit. 2. Fully distributed, non-centralized architecture, as in Gnutella, where all peers and edges form a ‘flat’ overlay (without hierarchy). Advantages: robustness to failure, no performance bottleneck and no target for lawsuit. Disadvantages is that search is more involved and incurs high overhead with query flooding. 3. Hierarchical overlay, with some nodes acting as super nodes (or cluster heads), or nodes forming loose neighborhoods (sometimes referred to as loose hierarchy, as in BitTorrent). Advantages, robust (no single point of failure), avoids flooding to search for resources during queries. Disadvantages, needs to keep track of at least some nodes using the ‘Tracker’ server. In general, this architecture attempts to combine the best of the 2 other architectures. Q13. (7.5 points) Push vs. Pull: A. Give examples of a push protocol and a pull protocol B. Mention three factors one should consider when designing pull/push protocols, discuss how these factors would affect your decision as a protocol designer (give example scenarios to illustrate). Answer: A. An example of a push protocol is: http. An example of a pull protocol: SMTP B. The factors affecting the performance of a pull/push protocol include (but are not limited to): 1. access pattern: how often is this object cached and how often is it accessed (example: a push mechanism for a very popular video that is pushed closer to a large population that is going to frequently watch it, would be better than a pull mechanism), 2. delay: what is the delay to obtain the object, and 3. object dynamics: how often/soon does the information in the object expires (example: in a sensor network where the information sensed is constantly changing, but is queried once in a while would be better ‘not’ to push it, but to pull it when needed only). Q14. (7.5 points) We refer to the problem of getting users to know about each other, whether it is peers in a p2p network or senders and receivers in a multicast group, as the â€Å"rendezvous problem†. What are possible solutions to solve the rendezvous problem in p2p networks (discuss three different alternatives and compare/contrast them. Answer: The possible solutions for the rendezvous problem include: 1. Using a centralized server: advantages: simple to search, little communication overhead. Disadvantages: single-point-of-failure (not robust), bottleneck, doesn’t scale well 2. Using a search technique for discovery, perhaps using a variant of a flood (or scoped-flood) or expanding-ring search mechanism. Advantages: avoids single-point-of-failure and bottlenecks. Disadvantages: may be complex, incurs high communication overhead and may incur delays during the search. 3. hybrid (or hierarchy): where some information (e.g., pointers to potential bootstrap neighbors, or pointers to some resources) are kept at a centralized (or replicated) server or super-nodes, then the actual communication is peer-topeer. Advantage: if designed carefully can avoid single-point-of-failure, bottlenecks, and achieve reasonable overhead and delay. Disadvantage: need to build and maintain the hierarchy (can trigger costly re-configuration control overhead in case of highly dynamic networks and unstable super-nodes).