[ Pobierz całość w formacie PDF ]
.When such acollision occurs, the two stations stop transmitting and try again later after a randomly chosendelay period.Although an Ethernet network can be built using one common signal wire, such an arrange-ment is not flexible enough to wire most buildings.Unlike an ordinary telephone circuit,Ethernet wire cannot be spliced to connect one copper wire to another.Instead, Ethernetrequires a repeater, a simple station that is connected to two wires.When the repeater 20 2496 Ch17 8/30/00 1:21 PM Page 420420 CHAPTER 17 NETWORKINGreceives data on one wire, it repeats the data bit-for-bit on the other wire.When collisionsoccur, the repeater repeats the collision as well.In buildings that have two or more types ofEthernet cable, a common practice is to use repeaters to convert the Ethernet signal fromone type of wire to another.FDDIFiber Distributed Data Interface (FDDI) is a standard for data transmission on fiber-opticlines in a LAN that can extend up to 200km (124 miles).The FDDI protocol is based on thetoken-ring protocol.In a token-ring network, all the computers are arranged schematicallyin a circle.A token, which is a special bit pattern, travels around the circle.To send a mes-sage, a computer catches the token, attaches a message to it, and then lets it continue totravel around the network to be delivered.In addition to being large geographically, anFDDI local area network can support thousands of users.FDDI also allows for larger packetsizes than lower-speed LANs using Ethernet.An FDDI network can contain two token rings: a primary token ring and a secondary tokenring for possible backup in case the primary ring fails.The primary ring offers up to100Mbps capacity.If the secondary ring is not needed for backup, it can also carry data,doubling the capacity to 200Mbps.Network HardwareThe network hardware is the physical part of the network you can actually see.The physi-cal components connect the systems and include the NIC, host, cabling, connectors, hubs,and routers, some of which I will discuss here.NICThe computer hardware that lets you connect it to a network is known as a NetworkInterface Card (NIC) or network adapter.The network interface can support one or morecommunication protocols to specify how computers use the physical medium the networkcable to exchange data.Many computers come with a preinstalled network interface (suchas Sun workstations); others require you to purchase it separately (such as PCs).Each LAN media type has its own associated network interface.For example, if you want touse Ethernet as your network medium, you must have an Ethernet interface installed in eachhost that is to be part of the network.The connectors on the board to which you attach theEthernet cable are referred to as Ethernet ports.The same is true if you plan to use FDDI,and so on. 20 2496 Ch17 8/30/00 1:21 PM Page 421NETWORK FUNDAMENTALS 421HostIf you are an experienced Solaris user, you are no doubt familiar with the term host, oftenused as a synonym for computer or machine. From a TCP/IP perspective, only twotypes of entities exist on a network: routers and hosts.When a host initiates communication,it is called a sending host, or the sender.For example, a host initiates communications whenthe user types ping or sends an email message to another user.The host that is the target ofthe communication is called the receiving host, or recipient.Each host has a hostname, Internet address, and hardware address that help identify it to itspeers on the network.These are described in Table 17-2.Table 17-2 Host InformationIdentity DescriptionHostname Every system on the network has a unique hostname.Hostnames let users referto any computer on the network by using a short, easily remembered name ratherthan the host s network IP address.Internet address Each machine on a TCP/IP network has an Internet address (or IP address) thatidentifies the machine to its peers on the network.Hardware address Each host on a network has a hardware address that also identifies it to itspeers.The manufacturer physically assigns this address to the machine s CPU ornetwork interface.Each hardware address is unique.HubEthernet cabling is run to each system from a hub.The hub does nothing more than connectall the Ethernet cables so that the computers can connect to one another.It does not boostthe signal or route packets from one network to another.When a packet arrives at one port,it is copied to the other ports so that all the computers on the LAN can see all the packets.Hubs can support from two to several hundred systems.A passive hub serves as a conduit for the data, allowing it to go from one device, or segment,to another.Intelligent hubs include additional features that let an administrator monitor thetraffic passing through the hub and to configure each port in the hub.Intelligent hubs arealso called manageable hubs
[ Pobierz całość w formacie PDF ]
