Cloud computing. Their types of use. Discuss one of them with providing me with example. Compare this model with distributed computing.

Provide me with the pseudo-code for creating sockets by using UDP

Also provide me with correct code for client-side of this type of programming.

Cloud computing. Their types of use. Discuss one of them with providing me with example. Compare this model with distributed computing.

“Cloud computing is a style of computing where massively scalable IT-related capabilities are provided ‘as a service’ across the Internet to multiple external customers”

(ZDES NUJNO VYBRAT ODIN IZ NIH)

1)SaaS(Software as a Service) - Software delivery model

• Increasingly popular with SMEs

• No hardware or software to manage

• Service delivered through a browser

Advantages

• Pay per use

• Instant Scalability

• Security

• Reliability

• APIs

Examples

• CRM

• Financial Planning

• Human Resources

• Word processing

Commercial Services:

• Salesforce.com

• emailcloud

2)PaaS (Platform as a Service) - Platform delivery model

• Platforms are built upon Infrastructure, which is expensive

• Estimating demand is not a science!

• Platform management is not fun!

Popular services

• Storage

• Database

• Scalability

Advantages

• Pay per use

• Instant Scalability

• Security

• Reliability

• APIs

Examples

• Google App Engine

• Mosso

• AWS: S3

3)IaaS (Infrastructure as a Service) -Computer infrastructure delivery model

Access to infrastructure stack:

• Full OS access

• Firewalls

• Routers

• Load balancing

Advantages

• Pay per use

• Instant Scalability

• Security

• Reliability

• APIs

Examples

• Flexiscale

• AWS: EC2

Difference between cloud computing and distributed computing

Cloud computing is a technology that delivers many kinds of resources as services, mainly over the internet, while distributed computing is the concept of using a distributed system consisting of many self-governed nodes to solve a very large problem (that is usually difficult to be solved by a single computer). Cloud computing is basically a sales and distribution model for various types of resources over the internet, while distributed computing can be identified as a type of computing, which uses a group of machines to work as a single unit to solve a large scale problem. Distributed computing achieves this by breaking the problem up to simpler tasks, and assigning these tasks to individual nodes.

5.Explain the process of IMAP? How does it work? What for do we need this protocol?

Internet message access protocol (IMAP): It is a method of accessing e-mail messages on a server without having to download them to your local hard drive. This is the main difference between IMAP and another popular e-mail protocol called "POP3." POP3 requires users to download messages to their hard drive before reading them. The advantage of using an IMAP mail server is that users can check their mail from multiple computers and always see the same messages. This is because the messages stay on the server until the user chooses to download them to his or her local drive. Most webmail systems are IMAP based, which allows people to access to both their sent and received messages no matter what computer they use to check their mail.

What for do we need this protocol?

IMAP is a standard protocol for accessing e-mail from your local server. IMAP is a client/server protocol in which e-mail is received and held for you by your Internet server.

6. What are pipelining protocols? What for do we need them? What types of them do you know? Compare them.

Pipelining protocols allow the user to send multiple requests without waiting for each response. A server must send its responses to those requests in the same order that the requests were received. Pipelining protocols decrease transmission time comparing to stop-and-wait protocol.

Pipelining: sender allows multiple, “in-flight”, yet-to-be-acknowledged packets

• range of sequence numbers must be increased

• buffering at sender and/or receiver

Two generic forms of pipelined protocols: go-Back-N, selective repeat

Go-back-N:

• Sender can have up to N unacknowledged packets in pipeline

• Receiver only sends cumulative acknowledges

- Doesn’t acknowledge packet if there’s a gap

• Sender has timer for oldest unacknowledged packet

- If timer expires, retransmit all unacknowledged packets

Selective Repeat:

• Sender can have up to N unacknowledged packets in pipeline

• Receiver acknowledges individual packets

• Sender maintains timer for each unacknowledged packet

- When timer expires, retransmit only unacknowledged packet

7. What is SEO? How can we use this? Describe on-page optimization

Search engine optimization (SEO) is the process of improving the visibility of a website or a web page in search engines via the "natural" or un-paid ("organic" or "algorithmic") search results. In general, the earlier (or higher ranked on the search results page), and more frequently a site appears in the search results list, the more visitors it will receive from the search engine's users. SEO may target different kinds of search, including image search, local search, video search, academic search, news search and industry-specific vertical search engines.

How can we use this? SEO considers how search engines work, what people search for, the actual search terms typed into search engines and which search engines are preferred by their targeted audience.

Describe on-page optimization. SEO requires making your site search engine-friendly

There are many ways to optimize your site so that search engines will list your site higher in their rankings. Start with the following: Links from other sites: Search engine spiders move from site to site across the Internet by following hyperlinks. Internal links: Make sure your site is well-organized and easy to navigate. A site map will help visitors — and spiders — navigate your site. Meta tags: Meta tags are hidden HTML directions for Web browsers or search engines. They include important information such as the title of each page, relevant keywords describing site content, and the description of the site that shows up when a search engine returns a search. Make sure your meta tags accurately describe your content. Keywords: Consider likely words or phrases that users might type into search engines to find your site. Make sure your content contains those words or phrases, and include them in your title portions of your site and in relevant content.

8. What is GFS? Design of GFS? How players of GFS contact each other and what for do they do this?Write operation?(<--- netu otveta)

GFS is a proprietary distributed file system developed by Google Incorporation. for its own use. It is designed to provide efficient, reliable access to data using large clusters of commodity hardware.

Design

Files are divided into fixed-size chunks of 64megabytes, similar to clusters or sectors in regular file systems, which are only extremely rarely overwritten, or shrunk; files are usually appended to or read. It is also designed and optimized to run on Google's computing clusters, dense nodes which consist of cheap, "commodity" computers, which means precautions must be taken against the high failure rate of individual nodes and the subsequent data loss. Other design decisions select for high data throughputs, even when it comes at the cost of latency.

A GFS cluster consists of multiple nodes. These nodes are divided into two types: one Master node and a large number of Chunkservers. Each file is divided into fixed-size chunks. Chunkservers store these chunks. Each chunk is assigned a unique 64-bit label by the master node at the time of creation, and logical mappings of files to constituent chunks are maintained. Each chunk is replicated several times throughout the network, with the minimum being three, but even more for files that have high end-in demand or need more redundancy.

The Master server doesn't usually store the actual chunks, but rather all the metadata associated with the chunks, such as the tables mapping the 64-bit labels to chunk locations and the files they make up, the locations of the copies of the chunks, what processes are reading or writing to a particular chunk, or taking a "snapshot" of the chunk pursuant to replicate it (usually at the instigation of the Master server, when, due to node failures, the number of copies of a chunk has fallen beneath the set number). All this metadata is kept current by the Master server periodically receiving updates from each chunk server ("Heart-beat messages").

Permissions for modifications are handled by a system of time-limited, expiring "leases", where the Master server grants permission to a process for a finite period of time during which no other process will be granted permission by the Master server to modify the chunk. The modifying chunkserver, which is always the primary chunk holder, then propagates the changes to the chunkservers with the backup copies. The changes are not saved until all chunkservers acknowledge, thus guaranteeing the completion and atomicity of the operation.

Programs access the chunks by first querying the Master server for the locations of the desired chunks; if the chunks are not being operated on (e.g. no outstanding leases exist), the Master replies with the locations, and the program then contacts and receives the data from the chunkserver directly. As opposed to other file systems, GFS is not implemented in the kernel of an operating system, but is instead provided as a userspace library.

9.Suppose there are 15-car caravan.Each car propagates at 80 km/hour. There are 2 toll boths and the distance between them is 160 km. Toll booth takes 18 sec to service a car.(transmission time). How long does it take for caravan to line up before 2^nd toll booth?

Time for one to came from one tall booth to another:160km÷80km/hour=2 hours

Time serviced at first tall booth 18÷3600=0.005, 0.005*15 = 0.075

Because oh they move one by one in general for all 15 cars to line up at 2^nd tall booth needs 2+0.075 = 2.075hours

Дата добавления: 2015-11-16