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Answer Section
MULTIPLE CHOICE
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51
SHORT ANSWER
51. ANS:
Store-and-forward switching requires that the switch read the entire frame into its buffers before forwarding
it. The switch first examines the frame’s frame check sequence (FCS) field to be sure the frame contains no
errors before it’s forwarded. If an error is found, the switch discards the frame. The store-and-forward
switching method has the advantage of conserving bandwidth when many frames contain errors. The
disadvantage is that the entire frame must be read,stored in memory,and examined before it can be forwarded.
This process takes time and slows the network somewhat.
PTS: 1
REF: 486-487
52. ANS:
Also known as a linear bus, the physical bus topology is by far the simplest and at one time was the most
common method for connecting computers. Inherent in this simplicity, however, is a weakness: A single cable
break can halt the entire network. All components of the bus topology connect via a backbone, a single cable
segment that (theoretically) interconnects all the computers in a straight line. A physical bus topology is no
longer a practical choice because technology has moved past this obsolete method of connecting computers,
but your understanding of bus communications aids your general understanding of how computers
communicate with each other across a network. Two properties inherent on a physical bus are signal
propagation and signal bounce. In addition, to understand physical bus topologies fully, you must be familiar
with cable termination and what happens when a cable breaks.
PTS: 1
REF: 43
53. ANS:
On its way down the stack, as data gets passed from one layer to the next, it’s divided into data units
appropriate for the layer. Each unit of information is called a protocol data unit (PDU), which is passed as a
self-contained data structure from one layer to another on its way up or down the protocol stack. In the
preceding discussion, it’s more accurate to say that an outgoing PDU for the sender at any layer should agree
with the incoming version of that PDU on the receiver. At each layer in the stack, the software adds its own
formatting or addressing to the PDU to allow successful delivery of its payload across the network. This
special formatting or addressing added to the PDU is referred to as a “header,” and the process of adding this
header is called encapsulation.Remember the mail delivery analogy in which the sender must put the letter
(data) into an envelope (encapsulation) and address the envelope.
PTS: 1
54. ANS:
REF: 167
Collisions are the only type of error for which Ethernet automatically attempts to resend the data involved in
the collision. Another type of error that can occur happens when data is altered as it travels across the
medium. This error is usually caused by noise or faulty media connections. As explained in Chapter 5, an
Ethernet frame trailer consists of the frame check sequence (FCS) field, which contains the Cyclical
Redundancy Check (CRC) value. When the destination computer receives a frame, the CRC is recalculated
and compared against the CRC value in the FCS. If the two values match, the data is assumed to be okay. If
the values don’t match, the data was corrupted. In the event of a CRC error, the destination computer discards
the frame.No notice is given to the sender that this error has occurred. It’s up to the upper-layer protocols,
primarily TCP if the TCP/IP protocol suite is used, to detect that not all the data that was sent actually arrived
at its destination and to resend that data.
PTS: 1
REF: 249
55. ANS:
The following list summarizes the advantages of server-based networking:
- Centralized user accounts, security, and access controls simplify network administration.
- More powerful equipment means more efficient access to network resources.
- Server hardware design is generally more robust, providing features such as fault-tolerant hardware and
redundant systems.
- A single password for network logon delivers access to network-wide resources as specified in access
controls.
- Server-based networking makes the most sense for networks with 10 or more users or any networks where
resources are used heavily.
PTS: 1
REF: 13
56. ANS:
For any computer, a network interface card (NIC) performs two crucial tasks:
- Establishes and manages the computer’s network connection.
- Translates digital computer data into signals (appropriate for the networking medium) for outgoing
messages and translates signals into digital computer data for incoming messages.
In other words, the NIC establishes a link between a computer and a network, and then manages that link on
the computer’s behalf.
PTS: 1
REF: 124