Upon completion of this chapter, you will be able to answer the following questions:
- What are the characteristics of physical and logical topologies?
- How do devices access a LAN in order to send frames?
This chapter uses the following key terms. You can find the definitions in the Glossary.
bus topology
Carrier sense multiple access with collision avoidance (CSMA/CA)
Carrier sense multiple access with collision detection (CSMA/CD)
extended star topology
full-duplex
half-duplex
Logical topology
Physical topology
ring topology
star topology
Introduction (31.0)
How will Halimah familiarize herself with the network at headquarters?
She will examine some topologies that have been created by the IT department. These will help her understand how the various end and intermediary devices are connected and what media is used to connect them. Logical topologies will help her understand the type of network framing and media access control that is being used. Physical topologies serve as a sort of map that tells Halimah what devices are found in which rooms of each of the buildings on campus.
Learning how to read topologies is a very important part of becoming an IT professional.
Let’s get going!
Nodes on a network can be interconnected in numerous ways. How these nodes are physically connected is described by the topology of the network. This topic will provide an overview of network topologies.
Physical and Logical Topologies (31.1.1)
As you learned in the previous topic, the data link layer prepares network data for the physical network. It must know the logical topology of a network in order to be able to determine what is needed to transfer frames from one device to another. This topic explains the ways in which the data link layer works with different logical network topologies.
The topology of a network is the arrangement, or the relationship, of the network devices and the interconnections between them.
There are two types of topologies used when describing LAN and WAN networks:
• Physical topology — Identifies the physical connections and how end devices and intermediary devices (i.e, routers, switches, and wireless access points) are interconnected. The topology may also include specific device location such as room number and location on the equipment rack. Physical topologies are usually point-to-point or star.
• Logical topology — Refers to the way a network transfers frames from one node to the next. This topology identifies virtual connections using device interfaces and Layer 3 IP addressing schemes.
The data link layer “sees” the logical topology of a network when controlling data access to the media. It is the logical topology that influences the type of network framing and media access control used.
Figure 31-1 displays a sample physical topology for a small sample network.
Figure 31-1 Example of a Physical Topology
Figure 31-2 displays a sample logical topology for the same network.
Figure 31-2 Example of a Logical Topology
Video – The Logical Topology (31.1.2)
Refer to the online course to view this video.