Chapter 3 Flashcards

1
Q

A physical topology is the

A

arrangement of cabling and how cables connect one device to another in a network

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2
Q

A logical topology is the

A

path data travels between computers on a network

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3
Q

All network designs are based on four basic physical topologies:

A
  1. Bus
  2. Star
  3. Ring
  4. Point-to-point.
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4
Q

Describe how the four basic physical topologies connect:

A
  1. Bus: a series of computers connected along a single cable segment.
  2. Star: Computers connected via a central device, such as a hub or switch, are arranged in a star topology.
  3. Ring: Devices connected to form a loop.
  4. Point to point: Two devices connected directly to each other.
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5
Q

Cons of a physical bus topology:

A
  • Limit of 30 computers per cable segment.
  • The max total length of cabling is 185 meters (607 feet).
  • Both ends of the bus must be terminated.
  • Any break in the bus brings down the entire network.
  • Adding or removing a machine brings down the entire network temporarily.
  • Technologies using this topology are limited to 10 Mbps half-duplex communication because they use coaxial cabling, as discussed in Chapter 4.
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6
Q

3 key properties of a physical bus include:

A
  • Signal propagation
  • Signal bounce
  • A terminator

A logical bus is sometimes called a “shared media topology” because all stations must share the bandwidth the media provides.

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7
Q

Describe signal propagation in a physical bus topology

A

When copper wire is the medium, as in a typical physical bus, these signals are sent as a series of electrical pulses that travel along the cable’s length in all directions.

The signals continue traveling along the cable and through any connecting devices until they weaken enough that they can’t be detected or until they encounter a device that absorbs them.

This traveling across the medium is called signal propagation.

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8
Q

Describe signal bounce in a physical bus topology

A

When a signal hits the end of a cable and bounces back up the cable’s length, it interferes with signals following it, much like an echo.

The term used when electricity bounces off the end of a cable and back in the other direction is called signal bounce (or “reflection”).

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9
Q

Describe a terminator in a physical bus topology

A

To keep signal bounce from occurring, you install a terminator, which is an electrical component called a “resistor” that absorbs the signal instead of allowing it to bounce back up the wire.

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10
Q

The physical star topology definition

A

The physical star topology uses a central device, such as a hub or switch, to interconnect computers in a LAN.

Each computer has a single length of cable going from its NIC to the central device.

the central device can be a 1000 Mbps switch, which increases a physical bus’s top speed by 100 times and works in full-duplex mode, further increasing overall bandwidth.

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11
Q

The extended star topology definition

A

The extended star topology, is the most widely used.

This topology is a star of stars. A central device, usually a switch, sits in the middle.

Instead of attached computers forming the star’s arms, other switches are connected to the central switch’s ports. Computers and peripherals are then attached to these switches, forming additional stars.

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12
Q

A physical ring topology definition

A

A physical ring topology is like a bus, in that devices are daisy-chained one to another, but instead of terminating each end, the cabling is brought around from the last device back to the first device to form a ring.

This topology had little to no following in LANs as a way to connect computers. It was used to connect LANs to each other with a technology called Fiber Distributed Data Interface (FDDI).

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13
Q

Fiber Distributed Data Interface (FDDI).

A

FDDI was most often used as a reliable and fast network backbone, which is cabling used to communicate between LANs or between switches.

Technologies such as FDDI overcome some problems with a physical ring network by creating a dual ring, in which data can travel in both directions so that a single device failure doesn’t break the entire ring.

This technology is costly, and physical rings have mostly been supplanted by extended star Ethernet installations.

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14
Q

point-to-point topology definition

A

a point-to-point topology is a direct link between two devices.

It’s most often used in WANs, in which a device on a business’s network has a dedicated link to a telecommunication provider, such as the local phone company.

The connection then hooks into the phone company’s network to provide Internet access or a WAN or MAN link to a branch office.

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15
Q

Point to point pros and cons

A

The advantage of this topology is that data travels on a dedicated link, and its bandwidth isn’t shared with other networks.

The disadvantage is that it tends to be quite expensive, particularly when used as a WAN link to a distant branch office.

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16
Q

a wireless bridge definition

A

Point-to-point topologies are also used with wireless networks in what is called a wireless bridge. This setup can be used to connect two buildings without using
a wired network (see Figure 3-5) or to extend an existing wireless network.

They aren’t commonly used in LANs; they’re used more often in WANs and large internetworks.

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16
Q

a wireless bridge definition

A

Point-to-point topologies are also used with wireless networks in what is called a wireless bridge. This setup can be used to connect two buildings without using
a wired network (see Figure 3-5) or to extend an existing wireless network.

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17
Q

A mesh topology definition

A

A mesh topology connects each device to every other device in a network. You can look at a mesh topology as multiple point-to-point connections for the purposes
of redundancy and fault tolerance.

18
Q

What is network technology

A
  • a network interface uses to access the medium and send data frames, and the structure of these frames.
  • Other terms include network interface layer technologies, network architectures, and Data Link layer technologies.
  • Your network uses Ethernet, 802.11 wireless (Wi-Fi), or some combination of these and other technologies to move data from device to device in your network.
19
Q

Unshielded Twisted Pair (UTP)

A
  • the most common media type in LANs.
  • consists of four pairs of copper wire, with each pair tightly twisted together and contained in a plastic sheath or jacket
  • UTP comes in numbered categories, and is up to Category 8 as of this writing. The higher the category number is, the higher the cable’s bandwidth potential.
20
Q

Most common category of UTP

A

Category 5 Enhanced (Cat 5E) and Category 6 (Cat 6) are the most common in wired LANs, allowing speeds up to 10 Gbps.

21
Q

UTP cabling is used in?

A

UTP cabling is used in physical star networks

22
Q

the maximum cable length from NIC to switch for UTP is?

A

the maximum cable length from NIC to switch is 100 meters (328 feet) in LAN applications.

23
Q

UTP cabling is susceptible to?

A

UTP cabling is susceptible to electrical interference, which can cause data corruption, so it shouldn’t be used in electrically noisy environments.

24
Q

Fiber-optic Cabling definition

A

Fiber-optic cabling uses extremely thin strands of glass to carry pulses of light long distances and at high data rates.

25
Q

Fibre-optic cabling is usually used in?

A

large internetworks to connect switches and routers and sometimes to connect high-speed servers to the network.

Because of its capability to carry data over long distances (several hundred to several thousand meters), it’s also used in WAN applications frequently.

Fiber-optic cabling isn’t susceptible to electrical interference, so, unlike UTP, it can be used in electrically noisy environments. In most cases, two strands of fiber are needed to make a network connection: one for transmitting and one for receiving.

26
Q

Coaxial cable definition

A

Best known for its use in cable TV, coaxial cable is obsolete as a LAN medium, but it is used as the network medium for Internet access via cable modem.

Coaxial cable was the original medium used by Ethernet in physical bus topologies, but its limitation of 10 Mbps half-duplex communication made it obsolete for LAN applications after star topologies and 100 Mbps Ethernet became the dominant standard. Coaxial cable in LANs can be about 200 meters long.

27
Q

Network technologies can use media to transmit signals in two main ways:

A

broadband and baseband

28
Q

Baseband definition

A
  • sends digital signals in which each bit of data is represented by a pulse of electricity (on copper media) or light (on fiber-optic media).
  • These signals are sent at a single fixed frequency, using the medium’s entire bandwidth. In other words, when a frame is sent to the medium, it occupies the cable’s entire bandwidth, and no other frames can be sent along with it— much like having cable TV that carries only a single channel.

LAN technologies, such as Ethernet and token ring, use baseband transmission. If cable TV used baseband signaling, you would need one cable for each channel!

29
Q

Broadband

A
  • Instead of digital pulses, broadband systems use analog techniques to encode binary 1s and 0s across a continuous range of values.
  • Broadband signals move across the medium in the form of continuous electromagnetic or optical waves rather than discrete pulses.
  • On broadband systems, signals flow at a particular frequency, and each frequency represents a channel of data. That’s why broadband systems, such as cable TV and Internet, can carry dozens or hundreds of TV channels plus Internet access on a single cable wire: Each channel operates at a different frequency.
  • In addition, incoming and outgoing Internet data use separate channels operating at different frequencies from TV channels.
30
Q

Define Ethernet networks

A
  • the most popular LAN technology
  • advantages include ease of installation, scalability, media support, and low cost.
  • It supports a broad range of transmission speeds, from 10 Mbps to 10 Gbps.
  • can operate in a bus or star physical topology and a bus or switched logical topology.

What differs in ethernet variations are the cabling, speed of transmission, and method by which bits are encoded on the medium. Because the frame formatting is the same, however, Ethernet variations are compatible with one another. That’s why you often see NICs and Ethernet switches described as 10/100 or 10/100/1000 devices. These devices can support multiple Ethernet speeds because the underlying technology remains the same, regardless of speed.

31
Q

Ethernet pros

A

Ethernet Addressing
Every Ethernet station must have a physical or MAC address. As you learned in Chapter 2, a MAC address is an integral part of network interface electronics and consists of 48 bits expressed as 12 hexadecimal digits. When a frame is sent to the network medium, it must contain both source and destination MAC addresses. When a network interface detects a frame on the media, the NIC reads the frame’s destination address and compares it with the NIC’s own MAC address. If they match or if the destination address is the broadcast MAC address (all binary 1s or FF:FF:FF:FF:FF:FF in hexadecimal), the NIC reads the frame and sends it to the network protocol for further processing.

32
Q

A 14-byte frame header composed of these three fields:

A

° A 6-byte Destination MAC Address field
° A 6-byte Source MAC Address field
° A 2-byte Type field
* A Data field from 46 to 1500 bytes
* A frame trailer (frame check sequence [FCS]) of 4 bytes

33
Q

Ethernet frame

A

A frame is the unit of network information that NICs and switches work with. It’s the NIC’s responsibility to transmit and receive frames and a switch’s responsibility to forward frames out the correct switch port to get the frame to its destination.

34
Q

Ethernet networks can accommodate frames between

A

64 bytes and 1518 bytes.

35
Q

Collision Detection (CSMA/CD).

A

The media access method that Ethernet uses in half-duplex mode is Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

Ethernet detects, or “hears,” the other station transmit, so it knows a collision has occurred.
The NIC then waits for a random period before attempting to transmit again. Ethernet repeats the “listen before transmitting” process until it transmits the frame without a collision.

36
Q

a collision domain.

A

The extent to which signals in an Ethernet bus topology network are propagated is called a collision domain.

37
Q

Ethernet Error Handling

A

One reason for Ethernet’s low cost and scalability is its simplicity. It’s considered
a best-effort delivery system, meaning that when a frame is sent, there’s no acknowledgment or verification that the frame arrived at its intended destination. Ethernet relies on network protocols, such as TCP/IP, to ensure reliable delivery of data. It’s similar to the package delivery guy at a company. His job is to take what he’s given to its intended destination; it’s the package receiver’s job to verify its contents and let the sender know it was received.

38
Q

Cyclic Redundancy Check (CRC)

A

Ethernet can also detect whether a frame has been damaged in transit. The error- checking code in an Ethernet frame’s trailer is called a Cyclic Redundancy Check (CRC), and is the result of a mathematical algorithm computed on the frame data. The CRC
is calculated and placed in the frame trailer before the frame is transmitted. When the frame is received, the calculation is repeated. If the results of this calculation don’t match the CRC in the frame, it indicates that the data was altered in some way, possibly from electrical interference. If a frame is detected as damaged, Ethernet simply discards the frame but doesn’t inform the sending station that an error occurred (because it’s
a best-effort delivery system). Again, it’s the network protocol’s job to ensure that
all expected data was actually received. The network protocol or, in some cases, the application sending the data is responsible for resending damaged or missing data, not Ethernet.

39
Q

100BaseTX Ethernet

A

the most common Ethernet variety. It runs over Category 5e or higher UTP cable and uses two of the four wire pairs: one to transmit data and the other to receive data.

40
Q

What does MAC stand for

A

The acronym for “media access control” is MAC, which is where the term “MAC address” comes from.

41
Q

The media access method that Ethernet uses in half-duplex mode is

A

Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

42
Q

1000BaseT

A

1000BaseT - half and full duplex 250mbps