Important Descriptive Questions For Internet And Web Technology

Q1: What are the main differences between OSI and TCP/ IP reference models?Explain briefly. 

Ans:We will be focusing only on the key differences between the two references models.Three concepts are central to OSI model : services, interfaces and protocols. OSI model makes the clear distinction between these three concepts.The TCP/ IP model did not originally clearly distinguish between services,interface, and protocol .For example the only real services offered by the Internet layer are SEND IP packet and RECEIVE IP packet .The OSI reference model was devised before the protocols were invented.This ordering means that model was not biased towards one particular set of protocols, which made it quite general .With TCP/IP reverse was true: the protocol came first , and the model was really just a description of the existing protocols. So problem was model did not fit for any other protocol stack. Another difference is in the area of connectionless versus connection orientated communication. OSI model supports both connectionless and connection oriented communication in network layer , but only connection oriented in the transport layer . The TCP/ IP model has only connection less mode in network layer but supports both the mode in transport layer .

Q2: How optimization is achieved in DNS? 

Ans:There are two primary optimizations used in DNS: replication and caching. Each root server is replicated; many copies of the server exist around the world. When a new site joins the internet, the site configures its local DNS server with a list of root server . The site server uses whichever root server is most responsive at a given point of time. In DNS caching each server maintains a cache of names. Whenever it looks up a new name, the server places a copy of the binding in its cache. Before contacting another server to request a binding , the server checks its cache, if the cache contains the answer the server uses the cached answer to generate a reply.

Q3: When web pages containing emails are sent out they are prefixed by MIME Header. Why?

Ans:Initially email consisted messages containing simple text written in English and expressed in ASCII. Now a days on world wide internet messages can be sent in languages with accents like French and German, languages without alphabet like Chinese and Japanese etc. the basic idea of MIME is to add structure to message body and define encoding rule for non- ASCII messages.

MIME defines five additional message headers to the RFC 822 format .

Header	Meaning
MIME Version	Identifies the MIME version
Content Description	Readable string telling about message
Content - ID	Unique Identifier
Content transfer encoding	How the body is wrapped for transmission
Content Type	Nature of the message

Q4: What is CIDR?

Ans: CIDR is a new addressing scheme for the internet which allows for more efficient allocation of IP addresses than old class A, B, and C addressing scheme. Instead of being limited to network identifier (or prefixes) of 8, 16, or 24 bi ts, CIDR currently uses prefixes any where from 13 to 27 bi ts. Thus, block of addresses can be assigned to a network as small as 32 hosts or to those with 500,000 hosts. This allows for address assignments that much more closely fit an organization’s specific need. A CIDR address includes the standard 32- bit address and also information on how many bits are used for the network prefix. For example in CIDR address 206.13.01.48/25, the /25 indicates that the first 25 bits are used to identify unique network leaving the remaining bits to identify the specific host.

Q5: What is HDLC - High Level Data Link Control ?

Ans: Protocol Overall Description:

Layer 2 of the OSI model is the data link layer. One of the most common layer 2 protocols is the HDLC protocol. The basic framing structure of the HDLC protocol is shown below: HDLC uses zero insertion/deletion process (commonly known as bit stuffing) to ensure that the bit pattern of the delimiter flag does not occur in the fields between flags. The HDLC frame is synchronous and therefore relies on the physical layer to provide method of clocking and synchronizing the transmission and reception of frames.The HDLC protocol is defined by ISO for use on both point-to-point and multipoint (multidrop) data links. It supports full duplex transparent-mode operation and is now extensively used in both multipoint and computer networks. HDLC has three operational modes:

1. Normal Response Mode (NRM)

2. Asynchronous Response Mode (ARM)

3. Asynchronous Balanced Mode (ABM)

Q6:  What is POP (Post Office Protocol)?

Ans: The Post Office Protocol provides remote access to an electronic mail box. The protocol allows a user’s mailbox to reside on a computer that runs a mail server, and allows the user to access items in the mailbox from another computer.This protocol requires an additional server to run on the computer with the mailbox. The additional server uses the POP protocol . A user runs email software that becomes a client of POP server to access the contents of the mail box.

Q7:  What is SNMP (Simple Network Management Protocol )

Ans:When SNMP is used the management stat ion sends a request to an agent asking it for information or commanding it to update its state. SNMP defines seven messages that can be sent . The following six messages form an initiator.

Get - request - requests the value of one or more variables

Get -next- request – requests the value of next variable

Get -bulk-request – used for large transfer like tables

Set- request – updates one or more variables

Inform- request – allows the manager to update an agent ’s variables SnmpV2-trap – Agent to manager trap report .

Q8:  What is UDP?

Ans: UDP (User Datagram Protocol) uses a connectionless communication paradigm. That is, an application using UDP does not need to pre establish a connection before sending data, nor does application need to terminate communication when finished. Furthermore, UDP allows application to delay an arbitrarily long time between the transmissions of two messages. UDP does not use any control messages. Communication consists only of the data messages themselves.

Q9:  What is Sliding Window Protocol ?

Ans:To obtain high throughput rates, protocols use a flow control technique known as sliding window. The sender and receiver are programmed to use a fixed window size, which is the maximum amount of data that can be sent before an acknowledge arrives. For example, the sender and receiver might agree on a window size of four packets.

(a) still unsent window

(b) already acknowledged window

Q10:  What is Digital Signature?

Ans: This technique is used to authenticate the sender of a message. To send a message, the sender encrypts the message using a key known only to the sender. The recipient uses the inverse function to decrypt the message.The recipient knows who sent the message because only the sender has the key needed to perform the encryption. To ensure that encrypted messages are not copied and resent later , the original message can contain date and time it was sent.A public key system can be used to provide a digital signature.To sign a message, a user encrypts the message using his or her own private key. To verify the signature, thee recipient looks up thee user ’s public key, only the user can encrypt a message that can be encoded with

the public key.

Q11:  What is Wireless Application Protocol (WAP)  ?

Ans: WAP is a global, open standard that gives mobile users access to Internet services through handled devices. WAP Gateway proves to be the perfect answer to the growing demand for wireless mobile services across the world.The WAP Gateway is a very unique product providing semi-automatic redirection of HTML documents to WAP compatible mobile phones.The WAP Gateway acts as a bridge between the Internet world and the mobile world and offers services such as end-user authentication, encoding of WML script compiling. WAP uses the underlying web structure to render more efficient communication between content providers and mobile devices. The wireless protocol employs Wireless Markup Language (WML) for application contents instead of Hypertext Markup Language (HTML) .