<> Reference links
* CSKAOYAN.COM
<> LAN
LAN （Local Area Network）： abbreviation LAN, It refers to the computer group interconnected by multiple computers in a certain area , Use broadcast channel
characteristic 1： Small geographical coverage , Inlining only in a relatively independent local scope , Such as in one or several buildings
characteristic 2： Use specially laid transmission media （ Twisted pair , Coaxial cable ） Networking , High data transmission rate （10Mb/s~10Gb/s）
characteristic 3： Short communication delay time , Low bit error rate , High reliability
characteristic 4： All stations are equal , Shared transmission channel
characteristic 5： Distributed control and broadcast channel are mostly used , Can broadcast and multicast
The main factors that determine the LAN are ： Network topology , Transmission media and media access control methods
<> LAN topology
<> Star topology
The central node is the control center , The communication between any two nodes only needs two steps at most , Fast transmission rate , And the network configuration is simple , Easy to build network , Easy to control and manage . But this network system , Low network reliability , Poor network sharing ability , Single point of failure
<> Bus topology
High network reliability , Fast response between network nodes , Strong ability to share resources , Less equipment investment , Low cost , Easy to install and use , When a workstation node fails , Little impact on the whole network system
<> ring topology
Communication equipment and lines in the system are relatively economical . Single point of failure ; Because the loop is closed , Therefore, it is not convenient to expand , System response delay longer , And the efficiency of information transmission is relatively low
<> Tree topology
Easy to expand , Easy to isolate faults , It is also prone to single point of failure
<> LAN media access control method
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CSMA/CD. Commonly used in bus LAN , Also used in tree networks
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Token bus . Commonly used in bus LAN , Also used in tree networks . It is to put each workstation in a bus or tree network in a certain order , If by interface address size , Arrange to form a logical ring . Only the token holder can control the bus , Have the right to send information
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Token ring . For ring LAN , Such as token ring network
<> Classification of LAN
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Ethernet . Ethernet is the most widely used LAN , Including standard Ethernet （10Mbps）, Fast Ethernet （100Mbps）, Gigabit Ethernet （1000Mbps） and 10G Ethernet , They all match IEEE802.3 Series standard specifications . Logical topology master line , Physical topology is star or extended star . use CSMA/CD
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Token ring network . Star topology is adopted physically , Logically, it is a ring topology . Already “ chrysanthemums after the double ninth festival ”
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FDDI network （Fiber Distributed Data Interface）. Physically, a double ring topology is adopted , Logically, it is a ring topology
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ATM network （Asynchronous Transfer Mode）. Relatively new cell switching technology , use 53 Byte fixed length units are exchanged
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Wireless LAN （Wireless Local Area Network, WLAN） Adopted IEEE802.11 standard
<>IEEE 802 standard
IEEE 802 Series standard is IEEE 802
LAN/MAN LAN developed by the Standards Committee , Technical standard of man . One of the most widely used is Ethernet , Token ring , Wireless LAN, etc . Each sub standard in this series of standards is in the charge of a special working group in the Committee
IEEE 802.3： Ethernet media access control protocol （CSMA/CD） And physical layer technical specifications
IEEE 802.5： Token ring network （Token-Ring） Media access control protocol and physical layer technical specification of
IEEE 802.8： Optical fiber technical advisory group , Provide technical consultation on optical fiber networking
IEEE 802.11： Wireless LAN （WLAN） Media access control protocol and physical layer technical specification of
<>MAC Sublayer and LLC Sublayer
IEEE 802 The LAN reference model described in the standard only corresponds to OSI Data link layer and physical layer of reference model , It divides the data link layer into logical link layer and media access control MAC Sublayer
LLC Sublayer ： Responsible for identifying network layer protocols , Then they are encapsulated .LLC The header tells the data link layer that once the frame is received , How should packets be handled . Provide services for the network layer ： No confirmation no connection , Connection oriented , No connection with confirmation , High speed transmission
MAC Sublayer ：MAC The main functions of the sublayer include the encapsulation of data frames / Unloading , Addressing and recognition of frames , Frame receiving and sending , Link management , Frame error control, etc .MAC The existence of sub layers masks the differences of different physical link types
<> Ethernet
<> summary
Ethernet （Ethernet） Means by Xerox Company created by Xerox,Intel and DEC Baseband bus LAN specification jointly developed by the company , It is the most common communication protocol standard adopted by the existing LAN . Ethernet usage CSMA/CD technology
Ethernet is the dominant technology in LAN ：
* Low cost （ Ethernet network card is not available 100 block ）
* Is the most widely used LAN technology
* Token ring network ,ATM Internet is cheaper , simple
* Meet network speed requirements ：10Mb/s~10Gb/s
Ethernet two standards ：
* DIX Ethernet V2： The first LAN product （ Ethernet ） Statute
* IEEE 802.3：IEEE 802 committee 802.3 The first one developed by the working group IEEE Ethernet standard of .802.3 LAN is Ethernet
<> Ethernet provides no connection , Unreliable service
No connection ： No communication between sender and receiver “ Handshake process ”
unreliable ： No data frame number of the sender , The receiver does not confirm to the sender , Error frames are discarded directly , Error correction is the responsibility of senior management . Ethernet only realizes error free reception , No reliable transmission
<> Ethernet transmission medium
Thick coaxial cable => Thin coaxial cable => Twisted pair + Hub
<> Ethernet topology
Ethernet using hub is still a bus network in logic , Each station shares the bus on logic , Used or CSMA/CD agreement . Ethernet topology ： Logical master line , Physically star shaped
<>10BASE-T Ethernet
10BASE-T It is a twisted pair Ethernet that transmits baseband signals ,T Indicates twisted pair , present 10BASE-T Unshielded twisted pair is used （UTP）, The transmission rate is 10Mb/s
Adopt star topology physically , The maximum length of each twisted pair is 100m. Adopt Manchester coding . use CSMA/CD Media access control
<> Adapter and MAC address
The link between the computer and the external LAN is through the communication adapter . The adapter is equipped with processor and memory （ include RAM and ROM）.ROM Computer hardware address on MAC address
In LAN , Hardware address is also called physical address , or MAC address
MAC address ： Each adapter has a globally unique 48 Bit binary address , front 24 Representative manufacturers （ from IEEE regulations ）, after 24 Designated by the manufacturer . Commonly used 6 Hexadecimal number representation
<> Ethernet MAC frame
Most commonly used MAC Frame is Ethernet V2 Format of ：
And IEEE 802.3 Differences between ：
* The third field is length / type
* When length / Type field value is less than 0x0600 Hour , Data fields must be loaded LLC Sublayer
<> High speed Ethernet
rate ≥100Mb/s The Ethernet of is called high-speed Ethernet
<>100BASE-T Ethernet
Transmission on twisted pair 100Mb/s Star topology Ethernet of baseband signal , Still use IEEE 802.3 of CSMA/CD agreement
Support full duplex and half duplex , It can work in full duplex mode without conflict
<> Gigabit Ethernet
Transmission on optical fiber or twisted pair 1Gb/s signal
Support full duplex and half duplex , It can work in full duplex mode without conflict
<>10 Gigabit Ethernet
10 Gigabit Ethernet over optical fiber 10Gb/s signal
Only full duplex is supported , No contention problem
<>IEEE 802.11
IEEE 802.11 It is the general standard of wireless LAN , It is made by IEEE Defined standards for wireless network communication
<>802.11 of MAC Frame header format
<> Classification of wireless LAN
* Wireless LAN with fixed infrastructure
* Self organizing network without fixed infrastructure WLAN
Technology