EE 122 Introduction To Communication Networks Fall 2007 WF 4 5 30 in Cory 277 Vern Paxson TAs Lisa Fowler Daniel Killebrew Jorge Ortiz http inst eecs berkeley edu ee122 Materials with thanks to Jennifer Rexford Ion Stoica and colleagues at Princeton and UC Berkeley 1 Some Questions Answers Q Is the class full or can I enroll A Class size increased Welcome to Daniel Killebrew our new TA New section added M 4 5PM 299 Cory But not next week holiday Do attend one of the other sections next week socket programming Q Will the class be webcast A No 2 1 Goals for Today s Class Type of Networks And the key concept of multiplexing What s a Protocol 3 What Global non digital Communication Network Do You Use Every Day Roughly speaking how does it work 4 2 What s Another Such Network That You Use Every Day 5 Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Co m m u n ic a t io n Ne t w o rk 6 3 Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Co m m u n ic a t io n Ne t w o rk Bro a d c a s t Co m m u n ic a t io n Ne t w o rk 7 Broadcast Communication Networks Information transmitted by any node is received by every other node in the network Examples Usually in LANs Local Area Networks E g Ethernet classical WiFi E g lecture What problems does this raise Problem 1 limited range Problem 2 privacy of communication Problem 3 coordinating access to the shared communication medium Multiple Access Problem 8 4 Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Co m m u n ic a t io n Ne t w o rk Sw it c h e d Co m m u n ic a t io n Ne t w o rk Bro a d c a s t Co m m u n ic a t io n Ne t w o rk 9 Switched Communication Networks Information transmitted along a path of intermediary nodes switches or routers Basic issue how the switches figure out the next hop along the path 10 5 Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Co m m u n ic a t io n Ne t w o rk Sw it c h e d Co m m u n ic a t io n Ne t w o rk Bro a d c a s t Co m m u n ic a t io n Ne t w o rk Circ u it Sw it c h e d Co m m u n ic a t io n Ne t w o rk 11 Circuit Switching e g Phone Network Establish source creates circuit to destination Nodes along the path store connection info Nodes generally reserve resources for the connection If circuit not available Busy signal Transfer source sends data over the circuit No destination address since nodes know path Teardown source tears down circuit when done 12 6 Circuit Switching Node switch in a circuit switching network incoming links Node outgoing links How does the node connect the incoming link to the outgoing 13 Telephone Network Alexander Graham Bell 1876 Demonstrates the telephone at US Centenary Exhibition in Philadelphia 7 Circuit Switching With Human Operator 15 Telephone Network Almon Brown Strowger 1839 1902 1889 Invents the girl less cuss less telephone system the mechanical switching system 8 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 time 17 Timing in Circuit Switching Host 1 Circuit Establishment Switch 1 Switch 2 Host 2 propagation delay between Host 1 and Switch1 time 18 9 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 Transmission delay propagation delay between Host 1 and Switch1 Circuit Establishment time 19 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 Transmission delay Circuit Establishment propagation delay between Host 1 and Switch1 time 20 10 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 Transmission delay propagation delay between Host 1 and Switch1 Circuit Establishment propagation delay between Host 1 and Host 2 time 21 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 Transmission delay propagation delay between Host 1 and Switch1 Circuit Establishment Transfer propagation delay between Host 1 and Host 2 Information time 22 11 Timing in Circuit Switching Host 1 Switch 1 Switch 2 Host 2 Transmission delay propagation delay between Host 1 and Switch1 Circuit Establishment propagation delay between Host 1 and Host 2 Transfer Information time Circuit Teardown 23 Circuit Switching Node switch in a circuit switching network incoming links Node outgoing links How do the black and orange circuits share the outgoing link 24 12 Circuit Switching Multiplexing a Link Time division Frequency division Each circuit allocated certain frequencies frequency Each circuit allocated certain time slots time time 25 Time Division Multiplexing Demultiplexing Frames Slots 0 1 2 3 4 5 0 1 2 3 4 5 Time divided into frames frames into slots Relative slot position inside a frame determines to which conversation data belongs E g slot 0 belongs to orange conversation Requires synchronization between sender and receiver surprisingly non trivial In case of non permanent conversations Need to dynamically bind a slot to a conversation How to do this If a conversation does not use its circuit the capacity is lost 26 13 5 Minute Break Questions Before We Proceed 27 Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Co m m u n ic a t io n Ne t w o rk Sw it c h e d Co m m u n ic a t io n Ne t w o rk Circ u it Sw it c h e d Co m m u n ic a t io n Ne t w o rk Bro a d c a s t Co m m u n ic a t io n Ne t w o rk Pa c ke t Sw it c h e d Co m m u n ic a t io n Ne t w o rk 28 14 Packet Switching Data sent as chunks of formatted bit sequences Packets Packets have following structure Data Header Trailer sometimes Header and Trailer carry control information e g destination address checksum Each packet traverses the network from node to node along some path Routing based on header info Usually once a node receives the entire packet it stores it hopefully briefly and then forwards it to the next node Store and Forward Networks 29 Packet Switching Node in a packet switching network incoming links Node outgoing links Memory 30 15 Packet Switching Multiplexing Demultiplexing …
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