BCS - 041 - 000 PDF

Preview

Summary

000...

Description

IGNOU BCA(4): BCS – 041 Solved Assignment

2019-2020

Q1. Assuming that all routers and hosts are working properly and that all software in both is free of all errors, is there any chance, however small, that a packet will be delivered to the wrong destination? Solution: Yes. A large noise burst could garble a packet badly and would be able to undetected using checksum. With 2-k bit checksum, there is a probability of 2-k that the error is undetected.. So if destination address or VCI fields go undetected, the packet will be delivered to the wrong destination. Take the case where the physical media that the data is transferred over has an error. If the destination address field of the packet gets error during transmission, and this error it not detected by the checksum, then the packet would be delivered to the incorrect destination. Traditionally, a data packet holds between 46 and 1,522 bytes of data. However, different packets impact the speed of the connection. Smaller packet sizes result in slower effective data rates, while larger packets are effectively faster. A network packet is a formatted unit of data carried by a packet itched network. A packet consists of control information and user data, which is also known as the payload. Control information provides data for delivering the payload, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers. In packet switching, the bandwidth of the communication medium is shared between multiple communication sessions, in contrast to circuit switching, in which circuits are reallocated for the duration of one session and data is typically transmitted as a continuous bit stream. IP packets are composed of a header and payload. The header consists of fixed and optional fields. The payload appears immediately after the header. An IP packet has no trailer. However, an IP packet is often carried as the payload inside an Ethernet frame, which has its own header and trailer. Many networks do not provide guarantees of delivery, non duplication of packets, or in-order delivery of packets, e.g., the UDP protocol of the Internet. However, it is possible to layer a transport protocol on top of the packet service that can provide such protection; TCP and UDP are the best examples of layer 4, the Transport Layer, of the seven layered OSI model.

Q2. Suppose that you want to send an MP3 file to a friend, but your friend’s ISP limits the size of each incoming message to 1 MB and the MP3 file is 4 MB. Is there a way to handle this situation by using RFC 5322 and MIME? Are there any other ways. Solution: Yes, it's possible to simply utilize the message body subtype and send it by means of encoded form. Internet Message Format (basic format of an email message), previously RFC 822 and RFC 2822. RFC 5322 capacity=998 × 8 = 7984 bytes

www.learningscience.co.in

Page 3

IGNOU BCA(4): BCS – 041 Solved Assignment

2019-2020

ISP Limit=1024 × 8=8192 bytes Image size=4 × 1024 × 8=32768 bytes Encoded data can be transferred in 4 to 5 instance RFC 1521 describes a mechanism for denoting textual body parts which are coded in various character sets, as well as methods for encoding such body parts as sequences of printable ASCII characters. This memo describes similar techniques to allow the encoding of non-ASCII text in various portions of a RFC 822 message header, in a manner which is unlikely to confuse existing message handling software. While it is unfortunate that these programs do not correctly interpret RFC 822 headers, to "break" these programs would cause severe operational problems for the Internet mail system. The extensions described in this memo therefore do not rely on little-used features of RFC 822. Instead, certain sequences of "ordinary" printable ASCII characters (known as "encoded-words") are reserved for use as encoded data. The syntax of encoded-words is such that they are unlikely to "accidentally" appear as normal text in message headers. Furthermore, the characters used in encodedwords are restricted to those which do not have special meanings in the context in which the encodedword appears. Generally, an "encoded-word" is a sequence of printable ASCII characters that begins with "=?” ends with "? =", and has two "?"S in between. It specifies a character set and an encoding method, and also includes the original text encoded as graphic ASCII characters, according to the rules for that encoding method. A mail composer that implements this specification will provide a means of inputting non-ASCII text in header fields, but will translate these fields (or appropriate portions of these fields) into encoded words before inserting them into the message header The basic format of Internet email is defined in RFC 5322, which is an updated version of RFC 2822 and RFC 822. These standards specify the familiar formats for text email headers and body and rules pertaining to commonly used header fields such as "To:", "Subject:", "From:", and "Date:". MIME defines à collection of email headers for specifying additional attributes of a message including content type, and defines a set of transfer encodings which can be used to represent 8-bit binary data using characters from the 7-bit ASCII character set. MIME also specifies rules for encoding non-ASCII characters in email message headers, such as "Subject:” allowing these header fields to contain non-English characters. The goals of the MIME definition included requiring no changes to existing email servers and allowing plain text email to function in both directions with existing clients. These goals were achieved by using additional RFC 822-style headers for all MIME message attributes and by making the MIME headers optional with default values ensuring a non-MIME message are interpreted correctly by a MIME-capable client. A simple MIME text message is therefore likely to be interpreted correctly by a non-MIME client even if it has email headers which the non-MIME client won't know how to interpret. Similarly, if the quoted printable transfer encoding is used, the ASCII part of the message will be intelligible to users with non MIME clients. Image can be transferred using MIME protocol.

www.learningscience.co.in

Page 4...