Lec2a - EC E544: C m om unication Ne tworks-I I S pring...

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ECE544: Communication Networks-II Spring 2010 D. Raychaudhuri Lecture II Includes teaching materials from L. Peterson, J. Kurose
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Today’s Lecture Recap of network architecture & top- down design architecture paper discussion Shared media (MAC) protocols Ethernet Token ring IEEE 802.11
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Link Layer: Introduction Some terminology: hub/repeater (layer 1), bridge/LAN switch (layer 2), router  (layer 3), host (layers 1-3 + app) Links are communication channels that connect adjacent  nodes along communication path (point-to-point, shared, wired,  wireless) Layer-2 frame: encapsulates payload/datagram/IP  packet/service unit Router Switch Link Host Lin k LAN 1 LAN 2 Switch Link Host
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Link Layer Services Data-link layer:  transfer datagram from one  node to adjacent node over a link Framing: encapsulate datagram into frame, adding  header, trailer.  Identify what set of bits constitute a frame, that is,  determining the beginning and the end of a frame channel access if shared medium MAC addresses used in frame headers to identify source,  destination different from IP address! Reliable delivery between adjacent nodes Error detection  Error recovery: forward error correction code, retransmission  (ARQ)
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Link Layer Communication Link layer implemented in adaptor (NIC) and driver (Ethernet card,  WLAN card) Sending side: encapsulates higher layer payload in a frame, adds error  checking bits, flow control, etc. Receiving side: error detection, flow control, extracts payload, passes  to the receiving node CPU Cache Memory Control status register Bus interface Link interface Host NIC I/O bus Network Datagram Frame Adaptor Sending node Datagram Frame Adaptor Recv node Link layer protocol
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Layer 2 vs. Layer 3 Layer 2 switching Based on MAC  address Self configuring and  Transparent to  protocols above the  MAC layer  Fast and inexpensive Does not limit the  scope of broadcasts  Does not scale to  extremely large  networks  Layer 3 routing Based on IP address Must get IP address  (DHCP or manual assign) Easily connect LANs that  uses different link  protocols Scalable to large network  by subnet routing Broadcast limited only in  a subnet
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Link Layer Techniques Encoding (more Physical Layer stuff) ARQ Self study topics (see Ch2 & slides)
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Binary Encoding Binary Encoding:  turn the binary data (bits) into  signals to transmit on cable or optical fiber link  (physical layer stuff, but better to know) Baseband, not modulate to high frequency Nonreturn To Zero (NRZ):  1=high signal, 0=low signal
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This document was uploaded on 02/27/2010.

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Lec2a - EC E544: C m om unication Ne tworks-I I S pring...

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