Chapter 4 - Ethernet Basics
The DIX Ethernet standard allowed computers to communicate with each other at a transfer rate of ____________________.
10 Mbps
What is the maximum speed at which 10BaseT Ethernet networks communicate?
10 Mbps
What is the maximum distance between a hub and a node on a 10BaseT network?
100 meters
What is the maximum number of nodes that can be attached to a 10BaseT segment or hub?
1024
10BaseFL is often simply called ____________________.
10BaseF
Which standard specifies multimode cabling?
10BaseFL
Which Ethernet cabling standard defines an Ethernet network that uses CAT 3 or better UTP ca-bling, operating at 10Mbps?
10BaseT
Which version of Ethernet was introduced in 1990?
10BaseT
What was the original maximum data transfer rate of the first Ethernet developed by Xerox?
3 Mbps
What is the minimum size of an Ethernet frame?
64 bytes
The IEEE ____________________ subcommittee sets the standards for the CSMA/CD access method used with Ethernet networks.
802.3
Explain why a 10BaseT Ethernet network cannot send and receive data simultaneously, even though it uses separate pairs of wires to send and receive data.
A 10BaseT network cannot both send and receive because of the CSMA/CD access method. Only one device can use the segment contained in the hub without causing a collision.
In terms of cabling, how is a 10BaseT network different from a 10BaseFL network?
A 10BaseT network uses UTP cabling, a 10BaseFL network uses fiber-optic cabling.
Describe a problem with an Ethernet hub that using an Ethernet switch would solve.
A classic 10BaseT network with a hub can only have one message on the wire at any time. When two computers send at the same time, the hub dutifully repeats both signals. A busy network becomes a slow network because all the computers share the same collision domain. An Ethernet switch looks like a hub, because all nodes plug into it. But switches don't function like hubs inside. Switches come with extra smarts that enable them to take advantage of MAC addresses, effectively creating point-to-point connections between two conversing computers. This gives every conversation between two computers the full bandwidth of the network.
Describe the wiring of a crossover cable in terms of TIA/EIA.
A crossover cable reverses the sending and receiving pairs on one end of the cable. One end of the cable is wired according to the TIA/EIA 568A standard, whereas the other end is wired according to the TIA/EIA 568B.
Explain why a bridge may be regarded as an intelligent device.
A newly installed Ethernet bridge initially behaves exactly like a repeater, passing frames from one segment to another. Unlike a repeater, however, a bridge monitors and records the network traffic, eventually reaching a point where it can begin to filter and forward. This capability makes the bridge more "intelligent" than a repeater. A new bridge usually requires only a few seconds to gather enough information to start filtering and forwarding.
Describe an easy trick to remember the difference between the TIA/EIA 568A and 568B wiring standards for 10BaseT networks.
An easy trick to remembering the difference between 568A and 568B is the word "GO." The green and orange pairs are swapped between 568A and 568B, whereas the blue and brown pairs stay in the same place.
Describe three items you should remember when connecting hubs.
Ans: When connecting hubs, remember the following: · You can only daisy-chain hubs. · Take time to figure out the uplink ports. · If you plug hubs in incorrectly, no damage will occur—they just won't work.
If Ethernet nodes detect that a collision has occurred, what do they do?
Both nodes immediately stop transmitting. They then each generate a random number to determine how long to wait before trying again. Whichever node generates the lowest random number begins its retransmission first, winning the competition to use the wire. The losing node then sees traffic on the wire and waits for the wire to be free again before attempting to retransmit its data.
What the meaning of the term "carrier sense" on an Ethernet network?
Carrier sense means that each node using the network examines the cable before sending a data frame. If another machine is using the network, the node detects traffic on the segment, waits a few milliseconds, and then rechecks. If it detects no traffic (the more common term is to say the cable is "free"), the node sends out its frame.
Originally, Ethernet used ____________________ cabling.
Coaxial Cable
What purpose does collision detection serve on an Ethernet network?
Collision detection is when nodes detect that a transmission did not complete.
An Ethernet network using an Ethernet switch minimizes or avoids which events?
Collisions
Describe an RJ-45 connector and explain how it is used.
Each pin on the RJ-45 connects to a single wire inside the cable; this enables devices to put voltage on the individual wires within the cable. The pins on the RJ-45 are numbered from 1 to 8.
Why are the wires color-coded in a UTP cable?
Each wire inside a UTP cable must connect to the proper pin inside the crimp. Manufacturers color-code each wire within a piece of four-pair UTP to assist in properly matching the ends.
How many pins does an RJ-45 connector have?
Eight
Explain how Ethernet determines which computer should use a shared cable at a given moment.
Ethernet networks use a system called carrier sense multiple access/collision detection (CSMA/CD) to determine which computer should use a shared cable at a given moment. Carrier sense means that each node using the network examines the cable before sending a data frame. If another machine is using the network, the node detects traffic on the segment, waits a few milliseconds, and then rechecks. If it detects no traffic - the more common term is to say the cable is "free"- the node sends out its frame.
What are some challenges that Ethernet's designers faced?
Ethernet's designers faced the same challenges as the designers of any network: how to send data across the wire, how to identify the sending and receiving computers, and how to determine which computer should use the shared cable at what time.
A repeater also functions as an amplifier.
F
An Ethernet frame must have 1500 bytes of data, so padding is used if the actual data is less than this size.
F
The Ethernet networking technology standard was based on a ring topology.
F
The hub of a 10BaseT network analyzes the MAC address to see to which port it should forward the packet.
F
When a collision occurs on an Ethernet network, the cable is restricted to the nodes whose data col-lided until they have finished retransmitting.
F
What kind of cabling does the 10BaseFL standard specify?
Fiber-optic
Explain two ways that the use of frames improves network communication
First, frames prevent any single machine from monopolizing the shared bus cable. Second, they make the process of retransmitting lost data more efficient.
How many wires does the 10BaseT specification require in the cabling used?
Four Page: 70
Although the terms frame and packet are sometimes used interchangeably, use the OSI model to explain the differences between these two terms.
Frames are based on MAC addresses; packets are generally associated with data assembled by the IP protocol at Layer 3 of the OSI seven-layer model.
Identify three names hub makes may give their uplink ports.
Hub makers give their uplink ports many different names, such as crossover, MDI-X, and OUT.
On an Ethernet network, what is the likely result when the collision domain gets too large?
If the collision domain gets too large, you'll start running into traffic problems that manifest as general network sluggishness.
What happens if you mess up your crossover connections between two PCs?
If you mess up your crossover connections, you will not cause any damage, but the connection will not work.
____________________ is the organization that now controls Ethernet standards.
Institute of Electrical and Electronics Engineers (IEEE)
Which company was involved in the 1979 introduction of the DIX Ethernet standard?
Intel
What is an advantage of fiber-optic cabling over Unshielded Twisted Pair (UTP)?
It has a longer maximum distance.
Which of the following statements best describes the preamble of an Ethernet frame?
It includes a 7-byte series of alternating ones and zeroes followed by a 1-byte Start Frame.
What does it mean if a NIC runs in promiscuous mode?
It processes all frames.
Which of the following is true of an Ethernet hub?
It reads a signal coming in from one port and repeats the signal out to the other ports.
Most UTP cables come with stranded ____________________ fibers to add strength to the cable.
Kevlar
A bridge filters and forwards traffic between segments based on the ____________________ of the computers on those segments.
MAC addresses
What basis do bridges use to determine whether to forward traffic?
MAC addresses
What is the meaning of the "10" in 10BaseT?
Maximum speed of 10 Mbps
What is the meaning of the term "multiple access" on an Ethernet network?
Multiple access means that all machines have equal access to the wire. If the line is free, any Ethernet node may begin sending a frame. From Ethernet's point of view, it doesn't matter what function the node is performing: it could be a desktop system running Windows 8 or a high-end file server running Windows Server or Linux. As far as Ethernet is concerned, a node is a node is a node and access to the cable is assigned strictly on a first-come, first-served basis.
Explain the difference between half-duplex mode and full-duplex mode.
NICs that can communicate in only one direction at a time run in half-duplex mode. Later advances enabled NICs to send and receive at the same time, thus running in full-duplex mode.
What is a sniffer program?
Network diagnostic programs, commonly called sniffers, can order a NIC to run in promiscuous mode. When running in promiscuous mode, the NIC processes all the frames it sees on the cable, regardless of their MAC addresses. Sniffers are valuable troubleshooting tools in the right hands, but Ethernet provides no protections against their unscrupulous use.
What would happen if a standard Ethernet cable connected two hubs that do not have special ports to interconnect them?
No communications would take place. A standard cable cannot be used to connect two hubs without using an uplink port because both hubs will attempt to send data on the second pair of wires (3 and 6) and will listen for data on the first pair (1 and 2).
When a collision occurs on a network relying on the CSMA/CD access method, what alerts the net-work interface cards (NICs)?
Overlapping signals
A 10BaseT network uses ____________________ connectors.
RJ-45
Which statement is an accurate comparison between repeaters and bridges?
Repeaters retransmit all packets, while bridges examine the destination MAC address to determine which packets to forward onto the next segment.
10BaseFL uses multimode fiber-optic cabling with ST or ____________________ connectors.
SC
Including the preamble, how many basic pieces of information does an Ethernet frame contain?
Seven
All networking technologies use frames.
T
An Ethernet network uses the CSMA/CD access method.
T
Ethernet identifies the NICs on a network using special 48-bit (6-byte) binary addresses known as MAC addresses.
T
Regardless of the implementation of an Ethernet network, the design of the frames remains the same.
T
The preamble is added by the sending network interface card (NIC).
T
The ____________________ defines the industry standard for correct crimping of four-pair un-shielded twisted pair (UTP) for 10BaseT networks.
Telecommunications Industry Association/Electronics Industry Association (TIA/EIA)
What is an acceptable maximum collision rate on a properly running Ethernet network?
Ten percent
What information would be included in the data portion of an Ethernet frame on an IP network?
The IP addresses of the sending and receiving systems
Describe how to extend an Ethernet segment by using a connection device called a coupler.
The couplers—female connectors on both ends—enable you to connect a machine in a location not originally envisioned when a network was installed. These simple connectors make working with older networks a snap. You can find couplers of all stripes: BNC couplers, UTP couplers, and so on. Get the one for the network you support.
What is a shared attribute of all members of the Ethernet family of networking technologies?
The network access method
What is the biggest differentiator among Ethernet hubs?
The number of ports
Including the preamble, what are the seven basic pieces of information contained in an Ethernet frame?
The seven basic pieces of information contained in an Ethernet frame are: · the preamble · the MAC address of the destination computer · the MAC address of the sender · the type of data · the data itself · a pad · a frame check sequence
What information is identified in a cabling specification such as 10BaseT?
The signal type
What does "Base" mean in cabling standards such as 10BaseT?
The word "Base" refers to the signaling type: baseband. Baseband means that the cable only carries one type of signal.
What is the purpose of a crimper?
To connect a RJ-45 connector to the cable
What does it mean to filter and forward bridge traffic?
To filter traffic means to stop it from crossing from one network to the next; to forward traffic means to pass traffic originating on one side of the bridge to the other.
How many pairs of pins in an RJ-45 connector does a 10BaseT device actually use?
Two
Which type of cabling does the 10BaseT standard specify?
Unshielded Twisted Pair (UTP)
____________________ ports enable you to connect two hubs using a straight-through cable.
Uplink
What happens if the frame check sequence at the receiving machine does not match the one calcu-lated by the sending machine?
When creating an Ethernet frame, the sending machine runs the data through a special mathematical formula and attaches the result, the frame check sequence, to the frame. The receiving machine opens the frame, performs the same calculation, and compares its answer with the one included with the frame. If the answers do not match, the receiving machine asks the sending machine to retransmit that frame.
Explain why knowing how to make your own Ethernet cables is a real plus for a network techni-cian
With a reel of CAT 5e, a bag of RJ-45 connectors, a moderate investment in a crimping tool, and a little practice, you can kiss those mass-produced cables goodbye! You can make cables to your own length specifications, replace broken RJ-45 connectors that would otherwise mean tossing an entire cable—and, in the process, save your company or client's time and money.
What company developed the original Ethernet networking technology in 1973?
Xerox developed the original Ethernet network technology in 1973.
The signal type of a 10BaseFL network is ____________________.
baseband
In an Ethernet network, the process called ____________________ determines when each ma-chine should have access to the cable.
carrier sense multiple access/collision detection (CSMA/CD)
A(n) ____________________ is a group of nodes that have the capability of sending frames at the same time as each other, resulting in collisions.
collision domain
An RJ-45 connector is usually called a(n) ____________________.
crimp
In a pinch, you can use a(n) ____________________ to connect two computers together using 10BaseT NICs with no hub between them at all.
crossover cable
To connect more than two hubs, you must ____________________ your hubs by using one uplink port and one regular port.
daisy-chain
The cabling type that is most difficult to tap into is ____________________.
fiber-optic
If you ever run into a situation on a 10BaseT or later network in which none of the computers can get on the network, always check the ____________________ first.
hub
The classic 10BaseT network consists of two or more computers connected to a central ____________________.
hub
The single point of failure that can down an entire 10BaseT network is the ____________________.
hub
Fiber-optic cabling transmits data packets using pulses of ____________________.
light
Because 10BaseT and 10BaseFL use different types of cable, you can use a(n) ____________________ to interconnect different Ethernet types.
media converter
All Ethernet frames begin with a(n) ____________________, a 7-byte series of alternating ones and zeroes followed by a 1-byte Start Frame.
preamble
A(n) ____________________ reads the incoming signal and sends new copies of that signal out to every connected port on the hub.
repeater
10BaseT devices use pins 1 and 2 to ____________________ data.
send
10BaseT networks use the ____________________ hybrid topology.
star-bus
The maximum speed of a 10BaseFL network is ____________________ Mbps .
ten
The maximum length for a 10BaseFL cable is up to ____________________ kilometers, depend-ing on how you configure it.
two
Never connect two hubs by their ____________________ with a straight-through cable.
uplink ports
