TOLONG JEK PA PADEH KARENA INI YANG AKU KIRIM
Chapter 3 Review Questions
SECTIONS
3.1–3.3
R1 | Suppose the network layer provides the
following service. The network layer in
the source host accepts a segment of maximum size 1,200 bytes and a destination
host address from the transport layer. The network layer then guarantees to
deliver the segment to the transport layer at the destination host. Suppose
many network application processes can be running at the destination host.
a. Design
the simplest possible transport-layer protocol that will get application data
to the desired process at the destination host. Assume the operating system in
the destination host has assigned a 4-byte port number to each running
application process.
è We will call this protocol Simple Transport
Protocol (STP). The protocol then accepts from thesending process a chunk of
data not exceeding 1196 bytes, a destination host address, and adestination
port number. It adds a four‐byte header to each chunk and puts the port numberof the
destination process in this header. It then gives the destination host address
and theresulting segment to the network layer. The network layer delivers the
segment to STP at the
b. Modify
this protocol so that it provides a “return address” to the destination
process.
è The segment now has two header fields: a source
port field and destination port field. At thesender side, STP accepts a chunk
of data not exceeding 1192 bytes, a destination host address,a source port
number, and a destination port number. STP creates a segment which containsthe
application data, source port number, and destination port number. It then
gives thesegment and the destination host address to the network layer. After
receiving the segment,STP at the receiving host gives the application process
the application data and the source portnumber
c. In
your protocols, does the transport layer “have to do anything” in the core of
the computer network?
è No, the transport layer does not have to do
anything in the core; the transport layer “lives” inthe end systems.
P3.
UDP and TCP use 1s complement for their checksums. Suppose you have the
following three 8-bit bytes: 01010011, 01100110, 01110100. What is the 1s
complement of the sum of these 8-bit bytes? (Note that although UDP and TCP use
16-bit words in computing the checksum, for this problem you are being asked to
consider 8-bit sums.) Show all work. Why is it that UDP takes the 1s complement
of the sum; that is, why not just use the sum? With the 1s complement scheme,
how does the receiver detect errors? Is it possible that a 1-bit error will go
undetected? How about a 2-bit error?
UDP and TCP use 1's complement
for their checksums. Suppose you have thefollowing three 8-bit bytes: 01010011,
01100110, 01110100.
a. What is the 1's complement of the
sum of these 8-bit bytes? (Note thatalthough UDP and TCP use 16-bit words in
computing the checksum, for thisproblem you are being asked to consider 8-bit
sums.) Show all work.
01010011
+ 01100110
|
10111001
+01110100
|
One’s
Complement = 11010001
|
|
10111001
|
00101110
|
b. Why is it that UDP takes the 1's
complement of the sum; that is, why not justuse the sum?
è UDP takes the 1’s complement of the sum, because it
is easier to detecterrors.
c. With the 1's complement scheme, how does the
receiver detect errors? Is itpossible that a 1-bit error will go undetected?
How about a 2-bit error?
è The receiver knows if there are errors if the sum
contains a zero.It is notpossible for a 1bit error to go undetected.However, it
is possible for a2bit error to go undetected.
Chapter 6
Review Questions
SECTION
6.1
R1. What does it mean for a wireless network to
be operating in “infrastructure mode?” If the network is not in infrastructure
mode, what mode of operation is it in, and what is the difference between that
mode of operation and infrastructure mode?
è In infrastructure mode of operation, each wireless host is connected to the
larger network via a base station (access point). If not operating in
infrastructure mode, a network operates in ad-hoc mode. In ad-hoc mode,
wireless hosts have no infrastructure with which to connect. In the absence of
such infrastructure, the hosts themselves must provide for services such as
routing, address assignment, DNS-like name translation, and more.
R2. What are the four types of wireless networks
identified in our taxonomy in Section 6.1? Which of these types of wireless
networks have you used?
è a) Single hop, infrastructure-based
è b) Single hop, infrastructure-less
è c) Multi-hop, infrastructure-based
è d) Multi-hop, infrastructure-less
R9. Describe how the RTS threshold works.
è Each wireless station can set an RTS threshold such that the
RTS/CTS sequence is used only when the frame is longer than the threshold. This
ensures that RTS/CTS mechanism is used only for large enough frames.
