Intranetwork Devices
To create a LAN, we need to select the appropriate devices to connect the end device to the network. The two most common devices used are hubs and switches.
Hub
A hub receives a signal, regenerates it, and sends the signal over all ports. The use of hubs creates a logical bus. This means that the LAN uses multiaccess media. The ports use a shared bandwidth approach and often have reduced performance in the LAN due to collisions and recovery. Although multiple hubs can be interconnected, they remain a single collision domain.
Hubs are less expensive than switches. A hub is typically chosen as an intermediary device within a very small LAN, in a LAN that requires low throughput requirements, or when finances are limited.
Switch
A switch receives a frame and regenerates each bit of the frame on to the appropriate destination port. This device is used to segment a network into multiple collision domains. Unlike the hub, a switch reduces the collisions on a LAN. Each port on the switch creates a separate collision domain. This creates a point-to-point logical topology to the device on each port. Additionally, a switch provides dedicated bandwidth on each port, which can increase LAN performance. A LAN switch can also be used to interconnect network segments of different speeds.
In general, switches are chosen for connecting devices to a LAN. Although a switch is more expensive than a hub, its enhanced performance and reliability make it cost effective.
There is a range of switches available with a variety of features that enable the interconnection of multiple computers in a typical enterprise LAN setting.
To meet user requirements, a LAN needs to be planned and designed. Planning ensures that all requirements, cost factors and deployment options are given due consideration.
When selecting a device for a particular LAN, there are a number of factors that need to be considered. These factors include, but are not limited to:
1. Cost
2. Speed and Types of Ports/Interfaces
3. Expandability
4. Manageability
5. Additional Features and Services
Factors to Consider in Choosing a Switch
Although there are many factors that must be considered when selecting a switch, the next topic will explore two: cost and interface characteristics.
Cost
The cost of a switch is determined by its capacity and features. The switch capacity includes the number and types of ports available and the switching speed. Other factors that impact the cost are its network management capabilities, embedded security technologies, and optional advanced switching technologies.
Using a simple "cost per port" calculation, it may appear initially that the best option is to deploy one large switch at a central location. However, this apparent cost savings may be offset by the expense from the longer cable lengths required to connect every device on the LAN to one switch. This option should be compared with the cost of deploying a number of smaller switches connected by a few long cables to a central switch.
Another cost consideration is how much to invest in redundancy. The operation of the entire physical network is affected if there are problems with a single central switch.
Redundancy can be provided in a number of ways. We can provide a secondary central switch to operate concurrently with the primary central switch. We can also provide additional cabling to provide multiple interconnections between the switches. The goal of redundant systems is to allow the physical network to continue its operation even if one device fails.
Speed and Types of Ports/Interfaces
The need for speed is ever-present in a LAN environment. Newer computers with built-in 10/100/1000 Mbps NICs are available. Choosing Layer 2 devices that can accommodate increased speeds allows the network to evolve without replacing the central devices.
When selecting a switch, choosing the number and type of ports is a critical decision. Ask yourself these questions: Would you purchase a switch with:
Just enough ports for today's needs?
A mixture of UTP speeds?
Both UTP and fiber ports?
Consider carefully how many UTP ports will be needed and how many fiber ports will be needed. Likewise, consider how many ports will need 1 Gbps capability and how many ports only require 10/100 Mbps bandwidths. Also, consider how soon more ports will be needed.
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