Tutorial 4 and Tutorial 5

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Data Comm. and Netwrking



ANSWERS:1. "Reliability is not of primary importance in applications such as echo, daytime, BOOTP, TFTP and SNMP. In custom software, reliability can be built into the client/ server applications to provide a more reliable, low overhead service." 2. By using UDP, a segment will be delivered correctly to the specified application because UDP uses source and destination ports while raw IP packet does not include ports. That is, a segment cannot be delivered to a specified application as a raw IP packet. No,IP packets contain IP addresses, which specify a destination machine. Once such a packet arrived, how would the network handler know which process to give it to. UDP packets contain a destination port. 3. No! The IP layer will properly reassemble fragments and ensure that the datagrams are correctly ordered. However the datagrams themselves may arrive out of order (or be lost) and it is up to the TCP layer to rectify this. 4. Two Reasons are..:-

(1) Process ID is not static. Since process ID is assigned dynamically to the process when a process is created (forked), it cannot be used for well-known service such as HTTP. (2) In some situations, one process manages multiple sockets on different TSAPs. If process ID is use d, it cannot be implemented since one process can have one process ID.

5. When a timeout occurs, three things happend. First, slow start will be initiated. Second, the congestion window would start at 1. Third, the threshold will be reset to 18KB/2=9KB. If the next four transmission are all successful, then 1st transmission: 1 segment, 1KB 2nd transmission: 2 segments, 2KB 3rd transmission: 4 segments, 4KB 4th transmission: 8 segments, 8KB After these four successful transmissions, the window size is supposed to be 16. However, since the threshold is 9KB, the window size can only be 9KB.


ANSWERS:1. FTP does not need a message format because there is no need to send additional information back and forth aside from the commands and responses, which use the control connection.


3. (Ache se shivani mai diya hua hai,,data compressin k naam seagar

usme na mile then write this one..)

Data compression, source coding or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be either : a. Lossy Lossy compressionLossy compression, as opposed to lossless compression, eliminates some information in order to achieve the best possible compression ratio, while keeping a result which is as close as possible to the original data. It is the case, for example, of certain image or sound compressions, such as MP3 or the Ogg Vorbisformat. Since this type of compression removes information contained in the data that is to be compressed, it is usual to speak of irreversible compression methods.

b. Lossless

Loseless Compression:- :Lossless data compression algorithms usually exploit statistical redundancy to represent data more concisely without losing information. Lossless compression is possible because most real-world data has statistical redundancy. For example, an image may have areas of colour that do not change over several pixels; instead of coding "red pixel, red pixel, ..." the data may be encoded as "279 red pixels". This is a basic example of run-length encoding; there are many schemes to reduce file size by eliminating redundancy.

4. Since p and q must both be prime and n = 3599 = 15961, we can assume p=59 and q=61, and: (n) = (p-1)(q-1) = (59-1)(61-1) = 3480 d = (1 + k (n))/e = (1 + 3480k)/31 = -13921/31 = -449 (for k = -4) d = -449 (mod 3480) = 3031 (mod 3480)


Simple Network Management Protocol (SNMP) is an "Internet-standard protocol for managing devices on IP networks". Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more. It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention. SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force (IETF). It consists of a set of standards for network management, including an application layer protocol, a database schema, and a set of data objects