the LAN 5.1.9 Bridges There are times when it is necessary to break up a large LAN into smaller, more easily managed segments. This decreases the amount of traffic on a single LAN and can extend the geographical area past what a single LAN can support. The devices that are used to connect network segments together include bridges, switches, routers, and gateways. Switches and bridges operate at the Data Link layer of the OSI model. The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network. When a bridge receives a frame on the network, the destination MAC address is looked up in the bridge table to determine whether to filter, flood, or copy the frame onto another segment. This decision process occurs as follows: If placed strategically, a bridge can greatly improve network performance. Web Links Bridge http://searchsecurity.techtarget.com/ sDefinition/0,,sid14_ gci211705,00.htm
Content 5.1 Cabling the LAN 5.1.10 Switches A switch is sometimes described as a multiport bridge. While a typical bridge may have just two ports linking two network segments, the switch can have multiple ports depending on how many network segments are to be linked. Like bridges, switches learn certain information about the data packets that are received from various computers on the network. Switches use this information to build forwarding tables to determine the destination of data being sent by one computer to another computer on the network. Although there are some similarities between the two, a switch is a more sophisticated device than a bridge. A bridge determines whether the frame should be forwarded to the other network segment based on the destination MAC address. A switch has many ports with many network segments connected to them. A switch chooses the port to which the destination device or workstation is connected. Ethernet switches are becoming popular connectivity solutions because, like bridges, switches improve network performance by improving speed and bandwidth. Switching is a technology that alleviates congestion in Ethernet LANs by reducing the traffic and increasing the bandwidth. Switches can easily replace hubs because switches work with existing cable infrastructures. This improves performance with a minimum of intrusion into an existing network. In data communications today, all switching equipment performs two basic operations. The first operation is called switching data frames. Switching data frames is the process by which a frame is received on an input medium and then transmitted to an output medium. The second is the maintenance of switching operations where switches build and maintain switching tables and search for loops. Switches operate at much higher speeds than bridges and can support new functionality, such as virtual LANs. An Ethernet switch has many benefits. One benefit is that an Ethernet switch allows many users to communicate in parallel through the use of virtual circuits and dedicated network segments in a virtually collision-free environment. This maximizes the bandwidth available on the shared medium. Another benefit is that moving to a switched LAN environment is very cost effective because existing hardware and cabling can be reused. Lab Activity Lab Exercise: Purchasing LAN Switches This lab is to introduce the variety and prices of network components in the market. Web Links Switch http://searchnetworking.techtarget.com/ sDefinition/0,,sid7_ gci213079,00.html
Content 5.1 Cabling the LAN 5.1.11 Host connectivity The function of a NIC is to connect a host device to the network medium. A NIC is a printed circuit board that fits into the expansion slot on the motherboard or peripheral device of a computer. The NIC is also referred to as a network adapter. On laptop or notebook computers a NIC is the size of a credit card. NICs are considered Layer 2 devices because each NIC carries a unique code called a MAC address. This address is used to control data communication for the host on the network. More will be learned about the MAC address later. As the name implies, the network interface card controls host access to the medium. In some cases the type of connector on the NIC does not match the type of media that needs to be connected to it. A good example is a Cisco 2500 router. On the router an AUI connector is seen. That AUI connector needs to connect to a UTP Cat 5 Ethernet cable. To do this a transmitter/receiver, also known as a transceiver, is used. A transceiver converts one type of signal or connector to another. For example, a transceiver can connect a 15-pin AUI interface to an RJ-45 jack. It is considered a Layer 1 device because it only works with bits, and not with any address information or higher-level protocols. In diagrams, NICs have no standardized symbol. It is implied that, when networking devices are attached to network media, there is a NIC or NIC-like device present. Wherever a dot is seen on a topology map, it represents either a NIC interface or port, which acts like a NIC. Web Links Network Interface Card http://searchsystemsmanagement.techtarget.com/ sDefinition/0,,sid20 _gci212660,00.html
Content 5.1 Cabling the LAN 5.1.12 Peer-to-peer By using LAN and WAN technologies, many computers are interconnected to provide services to their users. To accomplish this, networked computers take on different roles or functions in relation to each other. Some types of applications require computers to function as equal partners. Other types of applications distribute their work so that one computer functions to serve a number of others in an unequal relationship. In either case, two computers typically communicate with each other by using request/response protocols. One computer issues a request for a service, and a second computer receives and responds to that request. The requestor takes on the role of a client, and the responder takes on the role of a server. In a peer-to-peer network, networked computers act as equal partners, or peers. As peers, each computer can take on the client function or the server function. At one time, computer A may make a request for a file from computer B, which responds by serving the file to computer A. Computer A functions as client, while B functions as the server. At a later time, computers A and B can reverse roles. In a peer-to-peer network, individual users control their own resources. The users may decide to share certain files with other users. The users may also require passwords before allowing others to access their resources. Since individual users make these decisions, there is no central point of control or administration in the network. In addition, individual users must back up their own systems to be able to recover from data loss in case of failures. When a computer acts as a server, the user of that machine may experience reduced performance as the machine serves the requests made by other systems. Peer-to-peer networks are relatively easy to install and operate. No additional equipment is necessary beyond a suitable operating system installed on each computer. Since users control their own resources, no dedicated administrators are needed. As networks grow, peer-to-peer relationships become increasingly difficult to coordinate. A peer-to-peer network works well with 10 or fewer computers. Since peer-to-peer networks do not scale well, their efficiency decreases rapidly as the number of computers on the network