Focus Questions

Focus Questions

1. Compare and contrast four different Ethernet LAN devices in increasing

order of complexity (and typically cost).

Repeaters Repeaters regenerate and retime signals, thereby increasing the

distance that signals can travel and still be clearly interpreted at the destination.

Repeaters deal only with packets at the bit level; therefore, they are Layer 1

devices. Repeaters are internetworking devices that exist at the physical layer

(Layer 1) of the OSI model.

Hubs Hubs combine connectivity with the amplifying and retiming properties

of repeaters. It is typical to see 4, 8, 12, and up to 24, ports on multiport

repeaters. This allows many devices to be cheaply and easily interconnected.

Bridges Bridges are devices that connect and pass packets between two

network segments that use the same communications protocol. Bridges operate

at the data link layer (Layer 2) of the OSI reference model. In general, a bridge

will filter, forward, or flood an incoming frame based on the MAC address of that

frame.

Switches 1) Switches are network devices that filter, forward, and flood

frames based on the destination address of each frame. The switch operates at

the data link layer of the OSI model. 2) Switch is a general term applied to an

electronic or mechanical device that allows a connection to be established as

necessary and terminated when there is no longer a session to support.

2. What are some of the characteristics of shielded twisted-pair (STP)?

Shielded twisted-pair cable combines the techniques of shielding and

cancellation via the twisting of wires. Each pair of wires is wrapped in metallic

foil. The four pairs of wires are wrapped in an overall metallic braid or foil. (It is

normally 150-ohm cable.) STP reduces electrical noise originating inside the

cable (crosstalk) and outside the cable (electromagnetic interference [EMI] and

radio frequency interference [RFI]). Shielded twisted-pair cable shares many of

the advantages and disadvantages of unshielded twisted-pair (UTP) cable. STP

affords greater protection from all types of external interference, but it is more

expensive and difficult to install than UTP.

3. What are some of the characteristics of unshielded twisted-pair (UTP)?

Unshielded twisted-pair cable is a four-pair wire medium used in a variety of

networks. Insulating material covers each of the eight individual copper wires in

the UTP cable. In addition, each pair of wires is twisted around each other. This

type of cable relies solely on the cancellation effect, produced by the twisted wire

pairs, to limit signal degradation caused by EMI and RFI. To further reduce

crosstalk between the pairs in UTP cable, the number of twists in the wire pairs

varies. Like STP cable, UTP cable must follow precise specifications as to how

many twists or braids are permitted per foot of cable.

4. What are some of the characteristics of coaxial cable?

Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a

single inner wire conductor.the two conductors are separated by insulation. In

the center of the cable is a single copper wire. A layer of flexible insulation

surrounds it. Over this insulating material, a woven copper braid or metallic foil

acts as the second of two wires in the circuit. It also acts as a shield for the inner

conductor. This second layer, or shield, helps reduce the amount of outside

interference. The cable jacket covers this shield.

5. What is the difference between STP and UTP?

UTP cable relies solely on the cancellation effect, produced by the twisted wire

pairs, to limit signal degradation caused by EMI and RFI. To further reduce

crosstalk between the pairs in UTP cable, the number of twists in the wire pairs

varies. UTP uses 100 ohm of resistance; whereas, STP generally has 150 ohms

of resistance. STP, unlike UTP cabling, has a metallic braid or foil that adds

additional protection against EMI and RFI.

6. What is the difference between STP and coaxial cable?

Both STP and coaxial cable use a metallic braid or foil for added insulation. STP

has individual shielding around each individual pair of wires. STP can transfer

data at 100 Mbps; whereas, coaxial is limited to 10 Mbps. Coax is terminated

using a BNC or AUI connector; whereas, STP cabling is usually terminated with

an RJ connector.

7. What is the advantage of fiber-optic cable?

Fiber-optic cabling allows for increased distance while also having the capability

of transferring data at a much faster rate than other types of media. Single-mode

fiber will support 10 Gbps transmission speeds. Fiber-optic cabling is more

secure because data cannot be extracted from the cable inductively. Fiber-optic

cabling is also unaffected by RFI and EMI.

8. What are the disadvantages of fiber-optic cable?

The cost of fiber cabling and fiber equipment is significantly greater than that of

twisted-pair cabling. Fiber is also very fragile and breaks easily during installation

or thereafter. Termination and installation cost is more than double that of

twisted-pair cabling.

9. What is the medium for wireless communication?

Wireless signals are electromagnetic waves that can travel through the vacuum

of outer space and through media, such as the air in our atmosphere. Therefore,

no cable medium is necessary for wireless signals.

10. What are TIA/EIA standards?

The TIA/EIA standards specify the minimum requirements for multiproduct and

multivendor environments. They allow for the planning and the installation of

LAN systems without dictating the use of specific equipment giving LAN

designers the freedom to create options for improvement and expansion.

11. What are patch panels?

Patch panels are convenient groupings of RJ-45 jacks. They come in 12, 24, and

48 ports, and typically are rack mounted. The front sides are RJ-45 jacks; the

back sides are punch-down blocks that provide connectivity or conducting paths.

They are classified as Layer 1 components.

12. How many conductors does an RJ-45 jack have?

An RJ-45 jack/connector is made up of eight conductors, four individual pairs.

13. What is a shared media environment?

A shared media environment occurs when multiple hosts have access to the

same medium. If several PCs are attached to the same physical wire or optical

fiber, or share the same airspace, for example, they all share the same media

environment. Occasionally, you might hear someone say .all the computers are

on the same wire.. It means they all share the same media even though the

.wire. might be CAT 5 UTP, which has four pairs of wire.

14. Where on a network do collisions occur?

If, for example, only one cable interconnects all the devices on a network, the

possibility of conflicts with more than one user sending data at the same time is

high. The same is true if only non-filtering devices, such as repeaters, connect

segments of a network. Ethernet allows only one data packet to access the cable

at any one time. If more than one node attempts to transmit at the same time, a

collision occurs, and the data from each device suffers damage.

15. What is a collision domain?

The area within the network from where the data packets originated and collided

is called a collision domain. All shared media environments are collision

domains. One wire might be connected to another wire through patch cables,

transceivers, patch panels, repeaters, and hubs. All these Layer 1

interconnections are part of a collision domain.

16. What happens to the signal in a collision?

When a collision occurs, the data packets that are involved are destroyed, bit by

bit. In a collision, the signals interfere, or collide, with each other and create a

third and invalid state.

17. How do you recognize a collision domain?

If you connect several computers to a single medium that has no other

networking devices attached, you have a shared-access situation and you have

a single collision domain. Depending on the particular technology used, this

situation limits the number of computers that can use that portion of the medium,

also called a segment.

18. How do repeaters extend collision domains?

Repeaters regenerate and retime bits, but they cannot filter the flow of traffic that

passes through them. Signals that arrive at one port of a repeater are sent out

on all other ports. The network on both sides of the repeater is one large collision

domain.

19. How do hubs extend collision domains?

The extended collision domain introduced by a hub results in diminished network

performance. The degradation in performance depends on the degree of usage

of the network by the computers on that network. The hub operates just like the

repeater with the addition of numerous nodes, thus increasing the collision

domain.

20. Do repeaters filter network traffic?

Both repeaters and hubs are Layer 1 devices; therefore, they perform no filtering

of network traffic.

21. What is the four-repeater rule?

The four-repeater rule in Ethernet states that no more than four repeaters or

repeating hubs can be installed between any two computers on the network. If

followed, the rules guarantee that if a collision occurs, every node in the collision

domain knows it has occurred. This is crucial to the successful operation of the

network protocol

22. How can the segmentation of collision domains be achieved?

You can reduce the size of collision domains by using intelligent networking

devices that break up the domains. Examples of this type of networking device

are bridges, switches, and routers.

23. What is linear bus network topology?

The bus topology has all its nodes connected directly to one link, and has no

other connections between nodes. Each host is wired to a common wire. One

advantage of this topology is that all hosts are connected to each other, and thus

can communicate directly. One disadvantage of this topology is that a break in

the cable disconnects hosts from each other.

24. What is ring network topology?

A ring topology is a single closed ring consisting of nodes and links, with each

node connected to only two adjacent nodes. The topology shows all devices

wired directly to each other in what is called a daisy-chain.

25. Are the rings of a dual-ring network topology connected?

The two rings are not connected. A dual-ring topology is the same as a ring

topology, except that a second, redundant ring connects the same devices.

26. Where is the node of a star network topology located?

A star topology has a central node with all links to other nodes radiating from it

and allows no other links.

27. From a mathematical perspective, where does each node link in an

extended star network topology?

An extended star topology has a core star topology, with each of the end nodes

of the core topology acting as the center of its own star topology.

CCNA Exam Review Questions

The following questions help you prepare for the CCNA exam. Answers also appear in

Appendix A, .Answers to the CCNA Exam Review Questions,. from the Cisco

Networking Academy Program: Engineering Journal and Workbook, Volume I, Second

Edition.

1. What type of fiber-optic cable is required by the TIA/EIA-568B standard for

horizontal cabling?

a. Two pair of 100-ohm cable

b. Two pair of 150-ohm cable

c. Two fibers of 62.5/125 um multimode cable

d. Four fibers of 62.5/125 um multimode cable

2. How can you determine which category of UTP cable any cabling belongs

to?

a. By looking at the end connectors

b. By reading the UL marking

c. By measuring the cable diameter

d. By the color of the cable sheathing

3. Why do networks need to use an access method?

a. To regulate access to the networking media equitably

b. To regulate the access of data into certain parts of networking media

c. To keep unwanted, foreign users from having access to the network

d. To prioritize data transmissions so that important items have greater

access

4. Which of the following best describes an access method?

a. The method used by software to access network file servers

b. The method used to verify users as authorized for access to the network

c. The way users access the network

d. The way network devices access the network medium

5. Ethernet uses what access method?

a. Token header transmission protocol

b. Ethernet does not use an access method

c. Carrier sense multiple access collision detect

d. Ethernet transmission carrier collision detect

6. Which of the following best describes a collision?

a. The frames from two devices impact and are damaged when they meet

on the physical media.

b. Two nodes transmit at the same time and one data packet has priority, so

it obliterates the lesser packet.

c. Two data transmissions cross paths on the network media and corrupt

each other.

d. A data transmission is corrupted due to an energy spike over the network

media.

7. Which of the following best describes a backoff algorithm?

a. A process wherein the network holds up some data so that other, more

important data can get through

b. The retransmission delay enforced when a collision occurs

c. The signal that a device on the network sends out to tell the other devices

that data is being sent

d. A mathematical function performed by networking software that prioritizes

data packets

Questions 8.13 are supplemental and are not found in the Engineering Journal and

Workbook.

8. What is most important when considering the type of networking media to

use in an installation?

a. Management.s wishes

b. Availability of networking media from local sources

c. Applicable fire, building, and safety codes

d. Your experience and expertise

9. Which grade of UTP cabling described in the TIA/EIA-568B standard is

used for running CDDI and can transmit data at speeds up to 100 Mbps?

a. Category 2

b. Category 3

c. Category 4

d. Category 5

10. Which grade of UTP cabling described in the TIA/EIA-568B standard is the

one most frequently recommended and implemented in installations

today?

a. Category 2

b. Category 3

c. Category 4

d. Category 5

11. What is Category 5 UTP cabling suitable for?

a. Transmitting data at speeds up to 10 Mbps

b. Transmitting data at speeds up to 100 Mbps

c. 10BaseT networks

d. Token Ring networks

12. What type of STP cable is required by the TIA/EIA-568B standard for

horizontal cabling?

a. Two pairs of 100-ohm cable

b. Two pairs of 150-ohm cable

c. Four pairs of 100-ohm cable

d. Four pairs of 150-ohm cable

13. What type of UTP cable is required by the TIA/EIA-568B standard for

horizontal cabling?

a. Two pairs of 100-ohm cable

b. Two pairs of 150-ohm cable

c. Four pairs of 100-ohm cable

d. Four pairs of 150-ohm cable