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67 lines
2.1 KiB
Markdown
67 lines
2.1 KiB
Markdown
---
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title: "22-LAN-physical-layer"
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aliases:
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tags:
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- cosc203
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- lecture
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---
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# LAN vs WAN
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Local area network
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- a network connecting computers within a limited geographic area
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- e.g., building, school, home etc
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- wired or wireless
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Wide Area network
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- a network that extends over a large area such as town, country, region or the world
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- used to connec LANs and other types of networks together
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- often established with leased telecommunication circuits (e.g., chorus)
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## ethernet
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dominant wired tech
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- first used LAN tech
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- simple cheap
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- IEEE 802.3 standard
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- kept up with speed race: 10 Mbps - 400 Gbps
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- physical topology
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- bus: all nodes in the same collision domain can collide (old)
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- switched: active link-layer switch in center (new)
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frame structure
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- encapsulates IP datagram (or other network layer protocol packet) in ethernet frame
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- 
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- preamble: used to sync reciever and sender clock rates
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- 7 bytes of 10101010 followed by one byte of 10101011
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- addresses: 6 bytes source, destination MAC addr
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- if adapter recieves frame with matching MAC destination address, it passes data in frame to network layer protocol, otherwise adapter discards frame
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- type
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- most IP but other possible: e.g., Novell IPX, Appletalk
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- used to demultiplex up at reciever
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- CRC: cyclic redundancy check at reciever
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- error detected: frame is dropped
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- it can correct but doesn't because just dropping and resending is faster
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# ARP
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Address resolution protocol
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arp table: each IP node on lan has table
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- IP/MAC mappings for some LAN nodes
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- mapping is forgotten after TTL is exceeded (usually 20min)
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# Switch vs Router
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switch:
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- link layer deivce
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- takes an active role
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- store and foward ethernet frames
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- examine incoming frame's MAC addr, selectively forward frame to one-or-more outgoing links when frame is to be fowarded on segment, uses CSMA/CD
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- transparent
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- hosts unaware of presence of switches
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- plug and play, self-learning
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- switches do not need to be configured
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multiple simultaneous transmissions
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- hosts have direct connection to sw
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# All layers together |