lect12b_addressing_Ross

lect12b_addressing_Ross - Network Layer II Lecture 12b...

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Network Layer II Lecture 12b ELEC300U * The slides are adapted from ppt slides (available from “Computer Networking: A Top-Down Approach,” 4 th edition, by Jim Kurose and Keith Ross, Addison-Wesley, July 2007. Part of the materials are also adapted from MIT 6.02 and Virginia Tech course notes. • concept of throughput • IP addressing and subnets
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Data Link Physical Ethernet, WiFi, … Framing, coding, [limited] rxmits, channel access Modulation/demodulation Application HTTP, DNS, SMTP… Transport TCP, UDP End-to-End Layer Layering in the Internet Network IP (and addressing) Everything else! Reliability, integrity, ordering, jitter ctrl, congestion response, … Today
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Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous :rate at given point in time average: rate over long(er) period of time server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec pipe that can carry fluid at rate R s bits/sec) pipe that can carry fluid at rate R c bits/sec) server sends bits (fluid) into pipe
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Throughput R s < R c What is average end-end throughput? R s bits/sec R c bits/sec ± > R What is average end-end throughput? R s bits/sec R c bits/sec link on end-end path that constrains end-end throughput bottleneck link
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Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec R s R s R s R c R c R c R per-connection end-end throughput: min(R c ,R s ,R/10) in practice: R c or R s is often bottleneck
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Forwarding: It’s All in the Header Packet header is crucial: switches look at this info to decide what to do E.g., to send a letter via USPS, the “To” (and “From”) fields are crucial Header depends on network layer protocol Generally has dst address , src address, demultiplexing info (which higher layer should get packet) Also packet length, hop limit (or “time to live”), type-of- service (e.g., priority level), checksum Switch
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IP Addresses Application data TCP Header Ethernet Header Ethernet Trailer Ethernet frame IP Header version (4 bits) header length Type of Service/TOS (8 bits) Total Length (in bytes) (16 bits) Identification (16 bits) flags (3 bits) Fragment Offset (13 bits) Source IP address (32 bits) Destination IP address (32 bits) TTL Time-to-Live (8 bits) Protocol (8 bits) Header Checksum (16 bits) 32 bits how much overhead with TCP? ± 20 bytes of TCP ± 20 bytes of IP ± = 40 bytes + app layer overhead
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What is an IP Address? An IP address is a unique global address for a network interface An IP address: -is±a± 32 bit long identifier - encodes a network number ( network prefix ) and a host number
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The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network). How do we know how long the network
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This note was uploaded on 01/28/2011 for the course ELEC 300U taught by Professor Rossmurchandaminebermak during the Fall '08 term at HKUST.

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lect12b_addressing_Ross - Network Layer II Lecture 12b...

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