network+ review guide 3.7

Compare and contrast different LAN technologies

Today's businesses rely on many types of LAN connections to provide for the transfer of data throughout their networks. The type of LAN connections that you choose will depend on the properties of that specific solution and how they align with the goals of the business. In the following sections, I'll discuss the main types of LAN connections and their specific properties.

Types

Generally what users have always needed is more speed. Network administrators needed more speed but also the ability to run a link for farther distances without the need for the amplification of signal. This gives them options in regard to network designs and other decisions about which most users are unaware. Over the years, LAN technology types have continued to evolve to meet the needs of users and network administrators. Table 3.3 categorizes many LAN technology types and their major properties of transmission media, speed, and distance.

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Table 3.3: LAN technology types
Open table as spreadsheet

Types	Transmission media	Speed	Distance
Ethernet	Copper (first coax then twisted-pair)	10Mbps	100m
10BaseT	Twisted-pair copper	10Mbps	100m
100BaseT	Twisted-pair copper	100Mbps	100m
100BaseTX	Twisted-pair copper	100Mbps	100m
100BaseFX	Multimode fiber	100Mbps	400m
1000BaseT	Twisted-pair copper	1Gbps	100m
1000BaseX	Singlemode fiber	1Gbps	Overall standard for 1Gbps on fiber
10GBaseSR	Multimode fiber	10Gbps	26m-82m
10GBaseLR	Singlemode fiber	10Gbps	25km (about 16 miles)
10GBaseER	Singlemode fiber	10Gbps	40km (about 25 miles)
10GBaseSW	Multimode fiber	10Gbps	26m-82m
10GBaseLW	Singlemode fiber	10Gbps	25km
10GBaseEW	Singlemode fiber	10Gbps	40km
10GBaseT	Twisted-pair cable	10Gbps	100m

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Note

You may have noticed that the distance limitations for SW, LW, and EW are the same as for SR, LR, and ER, respectively. That is because they are basically the same standard except that the first group uses SDH frames, whereas the second uses SONET frames.

Properties

The following are the properties of LAN connections:

CSMA/CD    In the past, we had networks that contained devices called hubs. Most of these are gone, and you would probably be hard-pressed to find a hub to buy today (maybe on eBay). These hubs created what we called a shared network. That meant each computer that communicated in the network had equal access to the same electrical paths as the others. Since the paths could carry only one communication at a time, the computers had to “take turns” accessing the wire.

A protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) was developed for this purpose. Each computer using CSMA/CD must sense the “wire” to determine whether current is fluctuating and therefore whether some other computer is using it. If another computer has the wire, then the first computer must wait until the wire is not in use before it can send its data. As you can imagine, if two computers see that the wire is not busy and decide to send at the same millisecond, then the electrical signals will cancel each other out. This is referred to as a collision. Once the collision is detected by the protocol, each computer will be given a set time to go based on a back-off algorithm created by the protocol. In this way, the computers will be kept from creating subsequent collisions.

The main problem with using CSMA/CD is that it doesn't work well for networks that are large--like today's networks. Because of this, newer technologies have been developed that do not require the use of CSMA/CD. In most of today's networks, this media access method is effectively disabled due to the wide use of switches instead of hubs.

CSMA/CA    Your LAN can also have wireless communications between computers and devices. When you use wireless, the CSMA/CD protocol cannot be used because the wireless protocols do not provide for any collision detection circuit. Instead, your wireless connections use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The main purpose of this protocol is to assure that the data to be transmitted can be transmitted and received successfully between the two devices. It does this by first listening and then using additional frames to negotiate the network access.

Broadcast    Essentially, there are three types of network communication on IPv4 networks. These are unicast, multicast, and broadcast. Unicast communication consists of a packet that has one source address and one destination address. Multicast communication also has one source address, but it has multiple destination addresses that have to be detected by each host to determine whether the data is for them. Broadcast communications are from one source but go to any destinations in the area where the data is allowed to flow.

A broadcast address at layer 2 will be flooded by switches, in other words, sent out of all the ports except for the one that it came in. Layer 3 broadcasts can be received by all the hosts on a network or subnet. Some network protocols, such as ARP and DHCP, use broadcasts as part of their normal operation. As a network administrator, one of your goals is to keep broadcast traffic to a minimum, with the exception of the broadcast traffic required by the network protocols.

Collision    Generally speaking, a collision domain is part of a network in which collisions could occur if more than one communication were allowed to take place at the same time. In the case of an old network that uses hubs, all the hosts connected to the hub share the same collision domain. A collision then occurs when two or more devices attempt to communicate at the same time in the same collision domain.

The counterintuitive part of this is that when you have more collision domains, you will actually have fewer collisions. When you deploy a network with only switches (no hubs), then each communication is contained in its own collision domain, and there is no possibility for collisions.

Bonding    Let's say you have a couple of 10Gbps interfaces, but what you really need is a 20Gbps link. Could you combine the two physical interfaces into one logical interface? You better bet you could! The process of combining more than one physical interface into one logical interface is called bonding. Ether channel links are one type of bonding that allows administrators flexibility and more options in regard to bandwidth allocation.

Speed    Just as with WAN links, the speed of a LAN is a product of available bandwidth. Available bandwidth is what's left over for the users after you take out your overhead to provide the network services. We tend to think that the network is there for our amusement and experimentation, but the truth is that it's really there so “Bob and Mary” can collaborate on a spreadsheet or just check their email. Bob and Mary don't know anything about the network, but they should be able to do their jobs quickly, and the network should be rather transparent for them. Speed is a relative factor, but your job is to provide as much speed as possible with the network connections and equipment available to you.

Distance    This goes full circle back to Table 3.3. Based on the type of transmission media you use, there will be distance limitations for your network segments. Anything with a T in it (100BaseT, for example) will have a distance limitation of 100m before it needs to hit another switch or device to amplify the signal. Fiber optics can span much greater distances because their signal does not attenuate as quickly. You should use the appropriate media to span the distance you need.

Exam Essentials

Be able to categorize LAN technologies    Be able to categorize the major LAN technologies from 10BaseT through 10GBaseEW in regard to speed, transmission media, and distance.

Know the properties of LAN technologies    Understand the main properties of LAN technologies, including the CSMA/CD, broadcast communications, collisions, bonding connections, speed differences, and distance limitations.