data communication and networking 연습문제 솔루션

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data communication and networking 4판
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Review Questions
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. IP and UDP are both connectionless and unreliable protocols. The main difference
in their reliability is that IP only calculates a checksum for the IP header and
not for the data while UDP calculates a checksum for the entire datagram.
3. Port addresses do not need to be universally unique as long as each IP address/port
address pair uniquely identify a particular process running on a particular host. A
good example would be a network consisting of 50 hosts, each running echo server
software. Each server uses the well known port number 7, but the IP address,
together with the port number of 7, uniquely identify a particular server program
on a particular host. Port addresses are shorter than IP addresses because their
domain, a single system, is smaller than the domain of IP addresses, all systems on
the Internet.
4. Ephemeral is defined as short-lived or transitory. Ephemeral port numbers are
only used for the duration of a single communication between client and server, so
they are indeed short-lived.
5. The minimum size of a UDP datagram is 8 bytes at the transport layer and 28 bytes
at the IP layer. This size datagram would contain no data–only an IP header with
no options and a UDP header. The implementation may require padding.
6. Since the length of a datagram must be contained in a 2 byte field, the maximum
size of a UDP datagram is 65,535 bytes (header plus data). However, given that the
IP layer must also store the total length of the packet in a 2 byte field, the maximum
length would be 20 bytes less than this, or 65,515 bytes, to leave room for the
IP header. The implementation may impose a smaller limit than this.
7. The smallest amount of process data that can be encapsulated in a UDP datagram

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