Transcript 知识管理的IT实现 IBM知识管理解决方案

Passage Two.
Networking Hardware and Topology
Training target:
In this part，our target is to train your reading
speed. You should pay more attention to” word group”.
Treating a group of words as a whole unit is a short cut
to save your time. We have underlined the word groups
in some sentences，and the rest can be practiced by
yourself. If there are some new words，you may cover
the note area with a piece of paper and try to guess
their meanings without looking them up in the
dictionary.
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 1.Networking hardware
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Networking hardware includes all computers，peripherals，interface
cards and other equipments needed to perform data-processing and
communications within the network. Let’s look some networking
hardwares.
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 （1）Network Interface Card（NIC）:The network interface card
provides the physical connection between the network and the
computer workstation. Most NICs are internal，with the card fitting
into an expansion slot inside the computer. NIC is a major factor in
determining the speed and performance of a network. It is a good
idea to use the fastest network card available for the type of
workstation you are using.
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（2）Switch（concentrator）:A switch is a device that provides a
central connection point for cables from workstations，servers and
peripherals. In a star topology，twisted-pair is run from each
workstation to a central switch. Switches electrically amplify the
signal as it moves from one device to another. Switches no longer
broadcast network packets as hubs did in the past，they memorize
the addresses of computers and send the information to the correct
location directly.
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（3）Repeater: Since a signal loses strength as it passes along a
cable，it is often necessary to boost the signal with a device called a
repeater. The repeater electrically amplifies the signal it receive
 s and rebroadcasts it. Repeaters can be separate devices or they can
be incorporated into a concentrator. They are used when the total
length of your network cable exceeds the standards set for the type
of cable being used.
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 （4）Bridge: A bridge is a device that allows you to segment a large
network into two smaller，more efficient networks. Bridges can be
used to connect different types of cable，or physical topologies. They
must，however，be used between networks with the same protocol.
Bridges are store-and-forward devices. A bridge accepts an entire
frame and passes it up to the data link layer where the checksum is
verified. Then the frame is sent down to the physical layer for
forwarding on a different network. Bridges can make minor changes to
the frame before forwarding it，such as adding or deleting some
fields from the frame header.
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 A bridge monitors the information traffic on both sides of the network
so that it can pass packets of information to the correct location. Most
bridges can “listen” to the network and automatically figure out the
address of each computer on both sides of the bridge. You might say
that the bridge is like a traffic cop at a busy intersection during rush. It
keeps information flowing on both sides of the network，but it doesn’t
allow unnecessary traffic through.
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 （5）Router: A router translates information from one network to
another; it is similar to a super intelligent bridge. Routers can direct
traffic to prevent head-on collisions. Routers know the addresses of
computers，bridges and other routers on the network. Based on the
destination address and origin，routers can even “listen” to the entire
network to determine which sections are busiest，then select the
best path to route a message.
 （6）Gateway: A gateway can translate information between different
network data formats or network architectures. It can translate
TCP/IP to AppleTalk so computers supporting TCP/IP can
communicate with Apple brand computers. Most gateways operate at
the application layer，but can operate at the network or session layer
of the OSI model.
 2.Network topology

Every network has a “shape” which is normally referred to as its
topology. There are five major topologies in use today: Bus，Ring，
Star，Tree，and Mesh . Each is used for specific network types，
although some network types can use more than one topology.
 （1）Bus:The simplest topology to understand is the Bus.In a Bus，
all the devices on the network are connected to a common
cable.Normally，this cable is terminated at either end，and can
never be allowed to form a closed loop.Pic6.4shows an example of a
Bus network.
Pic6.4 Bus network
 （2）Ring:A Ring topology is very similar to a Bus.In a Ring，all the
devices on the network are connected to a common cable which
loops from machine to machine.After the last machine on the network，
the cable then returns to the first device to form a closed
loop.Pic6.5shows an example of a Ring network.
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Pic6.5 Ring Topology
 （3）Star: A Star topology is completely different from either a Bus
or a Ring. In a Star，each device has its own cable run connecting
the device to a common hub or concentrator. Only one device is
permitted to use each port on the hub.Pic6.6shows an example of a
Star network.
 Pic6.6 Star Topology
 （4）Tree: A Tree topology can be thought of as being a “Star of
Stars ”network. In a Tree network，each device is connected to its
own port on a hierarchical concentrator in the same manner as in a
Star. However，concentrators are connected together in a
hierarchical manner.
 Pic6.7shows a
 Tree network.
 （5）Mesh: A Mesh topology consists of a network where every
device on the network is physically connected to every other device
on the network. This provides a great deal of performance and
reliability，however，the complexity and difficulty of creating one
increases geometrically as the number of nodes on the network
increases.Pic6.8shows an example of a four-node Mesh network.
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Pic6.8a four-node Mesh
 network geometrically
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Key words
NIC网卡
bridge网桥
repeater中继器
topology拓扑结构
Ring network环型网络
Tree network树型网络
switch交换机
router路由器
gateway网关
Bus network 总线型网络
Star network 星型网络
Mesh network网型网络
 OSI:Open System Interconnection开放系统互联（一种网络体系结构）
 TCP/IP:Transmission Control Protocol/Internet Protocol传输控制协议
/网际协议（一个协议集、一种网络体系结构）
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The End