Chapter 33

When using UTP cabling, what is the maximum cable length that can be used from the NIC to a hub or switch?

100 meters

Which of the following is NOT a component of an Ethernet frame header?

4-byte frame check sequence

What is the IEEE standard governing wireless networking?

802.11

What are the advantages and disadvantages of a physical star topology?

A physical star is the easiest topology to setup and expand. You are only limited by your available ports. You can easily expand the number of ports by adding yet another device and forming an extended star. The centralized design makes monitoring and managing network traffic easier. With a bus, the bandwidth is limited to 10Mbps and half-duplex mode. A star can operate at much higher speeds and, if a switch is used, is capable of operating in full-duplex mode. There is only one main disadvantage that is that the central device represents a single point of failure. One other small disadvantage is that it takes more cable to implement a star than it does a bus.

What media access method does Wi-Fi use, and how is it different from Ethernet s?

A station that is trying to transmit on a wireless network has a unique problem. Because it is not connected to a physical medium, it cannot hear whether any other station is transmitting.  Instead of trying to detect another signal, as stations must do in an Ethernet network with physical cabling, a wireless station must try to avoid another signal. This access method is called CSMA/CA, which is carrier sense multiple access with collision avoidance. For each frame sent, the transmitting station must wait for an acknowledgement before it can transmit again. If no acknowledgement is received, the frame is retransmitted. In some configurations, the transmitting station must send a message saying that it has data it would like to transmit.  This message is called an RTS, request to send . Then it must wait for a CTS message from the receiving station or device a clear to send message.

What type of topology, both physical and logical, is implemented in a token ring network, and how does it work?

A token ring network uses a physical star topology all the stations are connected to a central device called a multistation access unit, or MAU. The logical topology however forms a logical ring, which means that the data is passed along from one station to the next until it reaches its destination. This ring is implemented using the electronics inside the MAU. When a station wants to transmit data in a token ring network, it must wait until it receives a special frame called the token, then it can transmit. The token is passed around the ring to each station. If a station receives the token but has no data to transmit it, it simply passes the token to the next computer. In a token ring network, the token is the media access control. Only the device with the token can transmit or receive, so there are no collisions.q50

Describe the structure of an Ethernet frame.

An Ethernet frame is composed of three parts. The first part is called the header. It contains the source and destination MAC addresses along with a 2-byte type field. The type field is a code that tells what network protocol is being used in the data portion of the frame. The second part of the frame is the data portion, which is referred to as the payload. This is the actual data that an application is sending across the network. The part also includes the header from the network protocol. The last part of a frame is the FCS, which contains an error-checking code called a CRC. It is the result of applying a mathematical formula to the data portion of the frame. It is used to verify that the frame was not damaged in transmission.

In wireless networks, what type of media access control is used?

CSMA/CA

What is the media access method used by Ethernet?

CSMA/CD

What is CSMA/CD and how does it work?

CSMA/CD is the media access method used by Ethernet, which is a set of rules that govern how and when a device can transmit on an Ethernet network. When two devices transmit a signal at the same time, they cause a collision to occur. Then the devices must try to transmit again, and again, causing a bottleneck. To avoid these collisions, CSMA/CD says that a device must first listen to see whether it can detect any other signal on the medium. If no other signal is detected, then the device can transmit. If another device transmits at the same time and a collision occurs, then both transmitting stations must wait for a random period before they can try to transmit again.

The most popular LAN technology used today is ____________.

Ethernet

What is the Ethernet frame type that is used by TCP/IP?

Ethernet II

A collision can occur on a switch only if the switch is operating in full-duplex mode.

False

The physical bus topology is no longer used because it required extra cable to connect all the computers and required a central device.

False

What is the main disadvantage of cable modem networking?

It uses a bus topology.

Which of the following is the physical topology that is daisy-chained like a bus and in which the cabling is brought around from the last device to the first device?

physical ring

What are the four primary physical topologies? Briefly describe each one.

The four most common physical topologies are bus, star, ring, and point-to-point. In a physical bus, all the devices are attached to a single line, with each computer connected to the next to form a daisy-chain. A physical star begins with a central device. All the stations are then connected to that device through individual ports, thus giving it the appearance of a star a central mass with rays of light streaming outward. A ring looks just as it sounds. The end of the cable loops around and connects to the beginning, forming a ring. The devices on a physical ring are connected in the same fashion as a bus, daisy-chained, each device connected to the next. Finally, a point-to-point is again, just as it sounds. One device connected straight to another device.

What are the four wireless standards, and how are they different?

The four standards for wireless communication are 802.11a, 802.11b, 802.11g, and 802.11n.  The first difference is the frequency at which they operate. 802.11b, 802.11g, and 802.11n all operate in the 2.4 GHz frequency range, while 802.11a operates in the 5GHz frequency range. The second difference is really only among the standards in the 2.4 GHz frequency.  These differ by the speed at which they can transmit. 802.11b can transmit at 11Mbps; 802.11g can transmit at 54Mbps; and 802.11n can achieve up to 600 Mbps. These three standards are all backward compatible because they operate in the same frequency range.  802.11a operates at 54Mbps.

What is the difference between a network's physical topology and its logical topology?

The physical topology of a network refers to the way that all devices are physically connected. It takes into account the way that the computers are cabled together and whether they have a central connecting device or not. The logical topology of a network refers to the way that the signals travel from one network device to another. Although all the devices may appear to pass data in certain direction, the actual path the data takes may be different often it depends on the interconnecting device such as a hub, switch, or MAU.

A network's logical topology often depends on the central device's electronics.

True

A network's physical topology refers to the arrangement of the cabling and how the devices connect to each other.

True

A point-to-point topology is typically used for WAN connections.

True

What is the best way to eliminate the possibility of collisions in a network?

Use higher speed hubs, Use NICs that operate in full-duplex mode.

What is the difference between operating in half-duplex mode or full-duplex mode and why does it eliminate collisions?

When a station is operating in half-duplex mode, the station cannot transmit and receive a signal at the same time. It must first wait for the medium to be clear of activity, and then it can transmit. When a station is operating in full-duplex mode, it can transmit and receive data at the same time. Because a hub repeats its signal to all ports, it can only operate in half-duplex mode. However, when using a switch, the communication on each port is isolated, and the switch decides where to send the signal. Therefore, a switch can operate in full-duplex mode, sending and receiving data at the same time, thus eliminating collisions. If a switch is set to operate in half-duplex mode, then a collision is possible if the station starts to transmit at the same time that the switch sends a signal to the station.

In a physical bus topology, why do the ends of the cable have to be terminated?

When data is sent onto the network in a physical bus topology, it continues to travel the length of the network until it loses strength or until it is absorbed by a device. Once the signal reaches the end of the cable, it will bounce back and interfere with the other signals that follow it. To eliminate this signal distortion, the ends are terminated with a material that absorbs the signal so that it cannot bounce back.

When a wireless computer uses a peer-to-peer connection to directly connect to another wireless computer, it is operating in what mode?

ad hoc

What does the frame trailer consist of in an Ethernet frame?

cyclic redundancy check

What is the main advantage of a point-to-point topology?

data travels on a dedicated link

In a large network, in which several switches need to be connected together, usually one device is placed at the center, forming a(n) ____________ star.

extended

When a wireless computer connects with an AP before it connects with other devices, it is operating in ____________ mode.

infrastructure

The way that data travels in a network is referred to as the network s ____________ topology.

logical

What type of logical topology does a Wireless LAN use?

logical bus

What type of logical topology is at work when using an Ethernet hub?

logical bus

A ___________ topology is fully redundant and is the most expensive to implement.

mesh

In a token ring network, what is the central device called?

multistation access unit

Which of the following is NOT a characteristic of Unshielded Twisted Pair cabling?

operates in half-duplex only

Which of the following is NOT an advantage of a physical star?

provides redundancy and fault tolerance

In a physical bus topology, both ends of the medium must be terminated in order to prevent what?

signal bounce

What is the most common topology and technology combination in use today?

switched / Ethernet

When discussing Ethernet standards, what does the XBaseY terminology refer to?

the transmission speed, the type of transmissions, and the length or type of cabling