Module 2: Data-Link Layer
Module Objective: Explain how media access control in the data-link layer supports communication across physical and logical networks.
| Topic Title | Topic Objective |
| Topologies | Compare the characteristics of physical and logical topologies. |
| Media Access Control Methods | Explain how devices access a LAN IOT send frames. |
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| Module 2: Data-Link Layer |
2.1.1 Physical and Logical Topologies
The Data-Link layer prepares network data for the physical network.
The Data-Link layer must know the logical topology of a network IOT be able to determine what is needed to transfer frames from one device to another.
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.
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| Physical Topology Example |
- 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.
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| Logical Topology Example |
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
2.1.3 WAN Topologies
The three most common physical WAN topologies are:
- Point-to-Point
- The simplest and most common WAN topology.
- Consists of a permanent link between two endpoints.
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| Point-to-Point Topology |
- Hub and Spoke
- WAN version of the star topology in which a central site interconnects branch sites through the use of point-to-point links.
- Branch sites cannot exchange data w/ other branch sites w/o going through the central site.
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| Hub and Spoke Topology |
- Mesh
- Provides high availability but requires that every end system is interconnected to every other system.
- The administrative and physical costs can be significant.
- Each link is essentially a point-to-point link to the other node.
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| Mesh Topology |
A hybrid is a variation or combination of any topologies.
