LAN Technologies LE SS O N 7 E X A M O B J E C T I V E M AT R I X TECHNOLOGY SKILL COVERED EXAM OBJECTIVE EXAM OBJECTIVE NUMBER LAN Technologies Compare and contrast different 3. • Types: • Ethernet • 10BaseT • 100BaseT • 1000BaseT • 100BaseTX • 100BaseFX • 1000BaseX • 10GBaseSR • 10GBaseLR • 10GBaseER • 10GBaseSW • 10GBaseLW • 10GBaseEW • 10GBaseT • Properties: • CSMA/CD • CSMA/CA Other LAN Concepts Compare and contrast different 3. • Properties: • Broadcast • Collision • Bonding • Speed • Distance Wireless LAN Technologies Given a scenario, install and 2.2 configure a wireless network. • WAP placement • Antenna types • Interference • Frequencies • Channels • SSID (enable/disable) 219 220 | Lesson 7 Given a scenario, implement 5.1 appropriate wireless security measures.
• Encryption protocols: • WEP • WPA • WPA2 • WPA Enterprise • MAC address filtering • Device placement • Signal strength SOHO Network Given a set of requirements, 2.6 Technologies plan and implement a basic SOHO network. • List of requirements • Cable length • Device types/requirements • Environment limitations • Equipment limitations • Compatibility requirements KEY TERMS ad hoc wireless network Ethernet bonding baseband Ethernet DIX bit Ethernet II bonding Ethernet SNAP broadband gigabits per second (gbps) broadcast infrastructure wireless network broadcast networking kilobits per second (kbps) Carrier Sense Multiple Access with Collision link aggregation Avoidance (CSMA/CA) MAC address filtering Carrier Sense Multiple Access with Collision megabits per second (mbps) Detection (CSMA/CD) Multilink trunking (MLT) channel Network Fault Tolerance (NFT) channel bonding Novell Ethernet collision port bonding collision domain Redundant Array of Independent contention-based access method Nodes (RAIN) distance Service Set Identifier (SSID) encryption Small Office Home Office (SOHO) Ethernet speed Ethernet_802.2 Synchronous Optical Network (SONET) Ethernet_802.3 terabits per second (tbps) LAN Technologies | 221 George is a network engineer at a local hospital. He has been tasked by his boss to come up with a way for all the records of a patient who is in the hospital to be accessed from anywhere in the hospital. The solution George comes up with must also ensure that all changes to a patient’s records be updated as soon as any changes are made to their record.
What technology can George use to accomplish this task? ■ LAN Technologies This section of Lesson 7 discusses some of the current LAN technologies that are available as well as some older technologies that are not in general use anymore. A particular THE BOTTOM LINE emphasis in this section is placed on Ethernet technologies and CSMA/CD, which is used by Ethernet to access a network. As has been previously discussed previously in this book, networking technologies come in two types, wide area network (WAN) and local area network (LAN) technologies. While there is beginning to be a convergence in these two technology areas, it is still in the very early stages.
For the time being, the two technologies are still very distinct and different from each other. Because of this, these technologies are discussed as separate topics in this book. This lesson concentrates on those technologies that are used in LAN networks. Lesson 8 deals with WAN technologies.
Ethernet Frames Ethernet is one of the oldest and the most widely used LAN technologies in use today. A group headed by Xerox Corporation first developed Ethernet between 1973 and 1975. Because of how old it is, initially there was not a set standard for Ethernet. The four types of Ethernet available are the result of different frame types that have been used for it over the years.
The most widely used Ethernet frame type is called Ethernet II or Ethernet DIX. The DIX stands for (DEC, Intel, and Xerox), which are the three companies that worked together to develop this Ethernet frame type. Ethernet II or DIX is the most commonly used Ethernet frame today, mainly because it can be used directly by the Internet Protocol (IP). Back when Xerox and company first developed Ethernet, Novell wanted to standardize it and CERTIFICATION READY What are the main types approached the IEEE to do so.
However, when the IEEE went to create an Ethernet standard, of Ethernet frames? they did not take into consideration the implementation already used by Xerox and company or Which type of Ethernet how the Ethernet standard was to work in the overall OSI Model. Put simply, they forgot, did frame is most commonly not consider, or simply overlooked the fact that a Layer 2 Data Link protocol needed a Layer used in modern 2 Data Link identifier to work. However, in their defense, Novell claims that at the time of the networks? development of the IEEE 802.3 standard, such an identifier was not needed. The end result 3.7 is that this standard became Ethernet standard IEEE 802.3 (raw), which is sometimes referred to Ethernet_802.
As a result of the way that Ethernet 802.3 was constructed, it can only run with Novell’s IPX packets, and because of that, some people have called it Novell Ethernet.3 does not have an identifier number to enable it to work with the Data Link sublayer of the OSI Model, IEEE had to modify their standard. This modification became known as the Ethernet IEEE 802.2 Logical Link Control (LLC) standard, which is sometimes referred to as Ethernet_802. Basically, what this standard does is add the capa- bility to the Ethernet_802.3 frame header that enables it to have an identifier so that it works with the Data Link sublayer of the OSI Model. This allows this Ethernet frame type to work with more than just the IPX protocol.
One of the main limitations of Ethernet_802.2_LLC is that its header can only support 128 protocols. While this is a large number, in point of fact there are more than protocols than that in the TCP/IP Protocol Suite. In order for a network to use Ethernet_802.2_LLC it had to 222 | Lesson 7 be limited to 128 protocols on a single network. This did not sit well with the Internet com- munity, so Ethernet_802.2_LLC was modified to allow a larger number of protocols to run on the network.
This became known as Ethernet SNAP or Ethernet Subnetwork Access Protocol. Ethernet Communications Methods We have just finished discussing the different frame types available for Ethernet. The next topic of discussion is how Ethernet transfers data on a network. There are generally two main ways that Ethernet does this.
One method is called Carrier Sense Multiple Access with Collision Detection (CSMA/CD), and the other is called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). Both methods are considered contention-based access methods. In a contention-based access method, the different nodes on the network segment compete to see which node is able to send out its packet first. Both methods are very much first-come, first-serve methods of access.
The first node to get its packet on the network is the one to send its packet first. The next two sections of Lesson 7 will discuss these two methods. CARRIER SENSE MULTIPLE ACCESS WITH COLLISION DETECTION (CSMA/CD) Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is the primary method that Ethernet uses to access wired LANs. Ethernet uses a different method to access wireless LANs.
When Ethernet was first created it was intended for bus-based networks. As a result, it needed to have a way to access a bus-based network without having packets constantly colliding into each other. To accomplish this, CSMA/CD was developed. The way that CSMA/CD works is as follows.
CERTIFICATION READY Figure 7-1 illustrates the process that is used when Ethernet sends data across a LAN using What does CSMA/CD CSMA/CD. When a computer or node on a network needs to send a packet to another com- stand for? What is puter or node on the network, the first thing it does is listen to the network to make sure that CSMA/CD? How does another node is not in the process of sending a packet. If a different node is in the process it work? What happens of sending a packet, it waits for a time and listens again. If no other node is sending on the when CSMA/CD detects network, the node that needs to send a packet sends it.
This part of the process is the Carrier a collision? Sense Multiple Access part of sending a packet on an Ethernet network using CSMA/CD.7 Figure 7-1 Computer 1 Computer 2 Computer 3 Bus-based network using CSMA/CD to send a packet A. Computer 1 needs to send a packet to Computer 3. Computer 1 listens to the network to see if there is any traffic on the network. If there is traffic, Computer 1 waits a certain amount of time and checks again until there is no traffic.
If there is no traffic Computer 1 Computer 4 Computer 5 sends the packet. There is one main weakness with CSMA/CD as a means of accessing a network. That weakness is that more than one computer can send data across the network at one time. This happens when two different computers need to send data at the same time.
Both computers will listen to the network and neither computer will hear any activity on said network. This leads both LAN Technologies | 223 computers to conclude that it is clear for them to send data. The result is that both computers end up sending data packets simultaneously; however, because only one data packet can be on the network cable at one time, a collision occurs. The collision results in a power spike on the network as well as the data in the two different packets being destroyed.
Figure 7-2 shows what this collision looks like. In Figure 7-2 Computers 1 and 5 send data packets at the same time resulting in the collision that is symbolized by the starburst where the two data paths meet. Figure 7-2 Computer 1 Computer 2 Computer 3 Bus-based network using CSMA/CD to send a packet when a collision occurs Computer 4 Computer 5 Fortunately, CSMA/CD has a mechanism in place for collisions. When the power spike that results from the two packets colliding occurs, all the computers on the affected network segment are able to “hear” it.
When the computers on the network segment hear a collision on the network, they all immediately activate something called a hold down timer. A hold down timer is a clock that activates in each NIC on the network and starts counting down from a randomly set point of time. While the clock on a particular NIC is counting down, it is unable to send any packets. As each computer on the network segment finishes its random countdown it is able to begin listening to the network again in order to find an open point where it can begin to send its data packet.
Figure 7-3 shows a network segment immediately after a collision has occurred. Each computer on the segment has its hold down timer set for a random amount of time from which it will begin to count down before it can send its data. Figure 7-3 Computer 1 Computer 2 Computer 3 Bus-based network using CSMA/CD immediately after a collision Computer 4 Computer 5 224 | Lesson 7 CARRIER SENSE MULTIPLE ACCESS WITH COLLISION AVOIDANCE (CSMA/CA) Like CSMA/CD, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a method used by Ethernet to access a local area network. Where CSMA/CD is most com- monly used for wired networks, CSMA/CA is most commonly used for wireless networks.
Figure 7-4 illustrates how CSMA/CA works. CSMA/CA and CSMA/CD are very similar in operation; however, CSMA/CA adds another step. Instead of immediately sending its data packet after listening to the network, CSMA/CA first sends out a warning message letting all the other computers on the network know that a data packet is coming. After this warning is sent out, then the actual data packet is sent.