Chapter 3 Flashcards
A physical topology is the
arrangement of cabling and how cables connect one device to another in a network
A logical topology is the
path data travels between computers on a network
All network designs are based on four basic physical topologies:
- Bus
- Star
- Ring
- Point-to-point.
Describe how the four basic physical topologies connect:
- Bus: a series of computers connected along a single cable segment.
- Star: Computers connected via a central device, such as a hub or switch, are arranged in a star topology.
- Ring: Devices connected to form a loop.
- Point to point: Two devices connected directly to each other.
Cons of a physical bus topology:
- 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.
3 key properties of a physical bus include:
- 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.
Describe signal propagation in a physical bus topology
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.
Describe signal bounce in a physical bus topology
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”).
Describe a terminator in a physical bus topology
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.
The physical star topology definition
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.
The extended star topology definition
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.
A physical ring topology definition
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).
Fiber Distributed Data Interface (FDDI).
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.
point-to-point topology definition
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.
Point to point pros and cons
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.
a wireless bridge definition
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.
a wireless bridge definition
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.
