Assignment on Distributed Computation

ASSIGNMENT-1

Ques-1 Write short note on

(a) Domain Name System

DNS stands for Domain Name System (or Service or Server),The Domain Name System (DNS) is a hierarchical decentralized naming system for computers, services, or other resources connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. The Domain Name System has been an essential component of the functionality of the Internet since 1985.

It is an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

Every computer, node, device or resource on the internet has a unique name and unique IP address. There are millions of such devices or resources. Computers communicate on the internet using the machine-readable IP addresses. Imagine if we are to remember the IP addresses of all the pages we needed to visit or resources we needed to access. Browsing the internet would be anything but fun.

Well, the DNS is what makes our lives so easy. It makes navigating this complex network of IP addresses user-friendly. It is the internet's address book/directory. It is the footman of our internet requests! The World Wide Web depends on the DNS to function as we know it today. Yes! DNS is that important!

The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

(b) URL'S

URL stands for Uniform Resource Locator that identifies a particular Internet resource. URL help the user to locate web page, gopher service, library catalog and image or text file locations. URLs are the standard addressing system of the www. A complete URL provides the web client with all the information it needs to contact a server and make a request for information.

It is Also known as a Universal Resource Locator (URL) or Web address. A URL is a type of uniform resource identifier (URI). In common practice, the term URI isn't used, or is used synonymously with URL, even though this is technically incorrect.

Tim Berners-Lee and the Internet Engineering Task Force working group is credited with developing the URL in 1994. It is formally specified in RFC 1738.

All URLs are presented in the following order:

Scheme name
Colon and two slashes
Location of the server
The port (optional) and the location of the resource on the server
Fragment identifier (optional)

So, the format will look like this:

scheme://location:port/file-on-server.htm?querystring=1

This looks more complex that it is. The most common schemes (protocols) are HTTP and HTTPS, which any WWW user will recognize. The location of the server is generally a domain name. Given this, the following URLs are much more simple to understand:

http://www.google.com/default.htm
https://www.google.com/default.htm

Both these URLs indicate that there is a file named default.htm on a server with the address of "google.com". One uses regular HTTP, while the other uses a secure version of this scheme.

Two common elements of confusion about URLs:

The "www" is not actually part of the technical protocol. Websites just started using this to indicate the user is using the World Wide Web. This is why if you go to http://google.com, it redirects to http://www.google.com.
Most users access the Internet via a Web browser, which inserts port 80 on HTTP connections behind the scenes. This is why if you go to http://www.google.com:80, you will see the same website as if there were no port number.

Finally, the following URL demonstrates a fragment identifier, more commonly known as a querystring:

http://www.google.com/some-page?search=hello

This is saying that to use the HTTP protocol to send a request to the website at google.com (over port 80) and to ask for "some-page" and send in the search variable "hello". This is why you'll sometimes see an extremely long URL as many variables are being sent to the Web server in more interactive Web applications.

(c) HTTP

HTTP stands for Hypertext (Hypertext is text which contains links to another document or texts) Transfer Protocol. It is the set of rules for transferring files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. As soon as a Web user opens their Web browser, the user is indirectly making use of HTTP. HTTP is an application protocol that runs on top of the TCP/IP suite of protocols (the foundation protocols for the Internet).It is used to access data on the WWW (World Wide Web). It is a protocol which governs the communication between the client and server.

There are three important features of HTTP:

i. HTTP is Connectionless

After a request is made, the client disconnects from the server and waits for a response. The server must re-establish the connection after it processes the request.

ii. HTTP is Media Independent

Any type of data can be sent by HTTP as long as both the client and server know how to handle the data content.

iii. HTTP is Stateless

This is a direct result of HTTP being connectionless. The server and client are aware of each other only during a request. Afterwards, each forgets the other. For this reason neither the client now the browser can retain information between different requests across the web pages.

Working:

i. A browser contacts a server to establish a TCP connection with it.

ii. The HTTP software on the client sends a request to the server. The HTTP software on the server interprets this request and sends the response to the client.

iii. HTTP Commands:

a. GET : Request by a client to obtain a web page from the server.

b. PUT : Request by a client to store a web page on the server.

c. POST : Request by a client to update contents of a web page on the server.

d. DELETE: Request by a client to remove a web page from the server.

Ques-2 Explain Remote procedure call & write the protocols used in Remote procedure call for communication purpose.

A remote procedure call is an interprocess communication technique that is used for client-server based applications. It is also known as a subroutine call or a function call.

A client has a request message that the RPC translates and sends to the server. This request may be a procedure or a function call to a remote server. When the server receives the request, it sends the required response back to the client. The client is blocked while the server is processing the call and only resumed execution after the server is finished.

The sequence of events in a remote procedure call are given as follows:

The client stub is called by the client.
The client stub makes a system call to send the message to the server and puts the parameters in the message.
The message is sent from the client to the server by the client’s operating system.
The message is passed to the server stub by the server operating system.
The parameters are removed from the message by the server stub.
Then, the server procedure is called by the server stub.

A diagram that demonstrates this is as follows:

Advantages of Remote Procedure Call

Some of the advantages of RPC are as follows:

Remote procedure calls support process oriented and thread oriented models.
The internal message passing mechanism of RPC is hidden from the user.
The effort to re-write and re-develop the code is minimum in remote procedure calls.
Remote procedure calls can be used in distributed environment as well as the local environment.
Many of the protocol layers are omitted by RPC to improve performance.

Disadvantages of Remote Procedure Call

Some of the disadvantages of RPC are as follows:

The remote procedure call is a concept that can be implemented in different ways. It is not a standard.
There is no flexibility in RPC for hardware architecture. It is only interaction based.
There is an increase in costs because of remote procedure call.

Ques-3 Discuss multicast communication in detail.
Multicast is a communication method and data delivery scheme in which a single source sends the same data to multiple receivers simultaneously. It is similar to broadcasting but more secure because it has an added bonus of receiver discretion, where the data is received by specific users or hosts.

The multicast process involves a single sender and multiple receivers. versus systems that are designed to be connection-dependent, like a client-server system. User datagram protocol (UDP) is the most common protocol used with multicasting.

Email is the best example of multicast, where a user can choose to send mail to many different addresses, rather than a complete contact list. Another example is the one-to-many multicasting of a streaming video toward many users from a single server. Another good example is Internet protocol (IP) multicasting, where network nodes, like switches and routers, handle data packet replication through multicast groups.

Non-IP based multicast implementations include Internet Relay Chat (IRC), which is well scaled for large numbers of small groups.

Multicast

Ques-4 How the communication between distributed objects takes place ? Discuss shared memory approaches in java RMI.

Ques-5 Make a sketch for CORBA and Discuss various components of this architecture.

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