Basic Concepts

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Basic Concepts. EE 122, Fall 2013 Sylvia Ratnasamy http://inst.eecs.berkeley.edu/~ee122/. Administrivia. Instructional account forms have been sent by email to registered students (not wait list) you should have them by now email apanda@eecs and sylvia@eecs if you don ’ t - PowerPoint PPT Presentation

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  • Basic ConceptsEE 122, Fall 2013Sylvia Ratnasamyhttp://inst.eecs.berkeley.edu/~ee122/

  • AdministriviaInstructional account forms have been sent by email to registered students (not wait list)you should have them by nowemail apanda@eecs and sylvia@eecs if you dont

    Size of discussion sections raised to 45

    Reminder: sections start this Friday

  • TodayBasic concepts linkspacket delayscircuit switching packet (datagram) switching

    Layering (if we have time)

  • Nodes and LinksAB

  • Properties of LinksBandwidth (capacity): width of the link number of bits sent (or received) per unit time (bits/sec or bps)Latency (delay): length of the linkpropagation time for data to travel along the link (seconds)Bandwidth-Delay Product (BDP): volume of the link amount of data that can be in flight at any timepropagation delay bits/time = total bits in linkbandwidthLatencydelay x bandwidth

  • Examples of Bandwidth-DelaySame city over a slow link: BW~100MbpsLatency~0.1msecBDP ~ 10,000bits ~ 1.25KBytes

    Cross-country over fast link:BW~10GbpsLatency~10msecBDP ~ 108bits ~ 12.5GBytes

  • time=0Packet DelaySending a 100B packet from A to B?AB100Byte packet1Mbps, 1ms Packet Delay = Transmission Delay + Propagation DelayPacket Delay = (Packet Size Link Bandwidth) + Link Latency

  • Packet DelaySending a 100B packet from A to B?AB100Byte packet1Mbps, 1ms 1Gbps, 1ms?The last bit reaches B at (800x1/106)+1/103s= 1.8ms1GB file in 100B packetsThe last bit reaches B at (800x1/109)+1/103s= 1.0008msThe last bit in the file reaches B at (107x800x1/109)+1/103s= 8001ms107 x 100B packets

  • Packet Delay: The pipe viewSending 100B packets from A to B?time BW pkt tx time

  • Packet Delay: The pipe viewSending 100B packets from A to B?1Mbps, 10ms (BDP=10,000) time BW 10Mbps, 1ms (BDP=10,000) time BW 1Mbps, 5ms (BDP=5,000) time BW

  • Packet Delay: The pipe viewSending 100B packets from A to B?1Mbps, 10ms (BDP=10,000) time BW 200B?1Mbps, 10ms (BDP=10,000) time BW

  • Any questions?

  • Nodes and LinksAB

  • What if we have more nodes?One link for every node?Need a scalable way to interconnect nodes

  • What if I have more nodes?One link for all nodes?This is a broadcast network

  • Solution: A switched networkNodes share network link resourcesHow is this sharing implemented?

  • Two forms of switched networksCircuit switching (used in the telephone network) Packet switching (used in the Internet)

  • Circuit switching(1) Node A sends a reservation request(2) Interior switches establish a connection -- i.e., circuit(3) A starts sending data(4) A sends a teardown circuit message Idea: source reserves network capacity along a pathAB

  • Circuit Switching: Sharing a LinkTime-division Each circuit allocated certain time slotsFrequency-divisionEach circuit allocated certain frequenciestimefrequencytime

  • Time-Division Multiplexing/DemultiplexingTime divided into frames; frames into slotsRelative slot position inside a frame determines to which conversation data belongse.g., slot 0 belongs to orange conversationSlots are reserved (released) during circuit setup (teardown)If a conversation does not use its circuit capacity is lost!Frames012345012345Slots =

  • timeTiming in Circuit Switching

  • timeTiming in Circuit Switching

  • timeTiming in Circuit Switching

  • timeTiming in Circuit Switching

  • Circuit Establishment timeTiming in Circuit Switching

  • InformationCircuit Establishment Transfer timeTiming in Circuit Switching

  • InformationCircuit Establishment Transfer Circuit Teardown timeTiming in Circuit Switching

  • Circuit switching: pros and consProsguaranteed performance fast transfer (once circuit is established)

    Cons

  • InformationCircuit Establishment Transfer Circuit Teardown timeTiming in Circuit Switching

  • Circuit switching: pros and consProsguaranteed performance fast transfer (once circuit is established)

    Conswastes bandwidth if traffic is bursty

  • InformationCircuit Establishment Transfer Circuit Teardown timeTiming in Circuit Switching

  • InformationCircuit Establishment Circuit Teardown timeData transferTiming in Circuit Switching

  • Circuit switching: pros and consProsguaranteed performance fast transfers (once circuit is established)

    Conswastes bandwidth if traffic is burstyconnection setup time is overhead

  • Circuit switchingABCircuit switching doesnt route around trouble

  • Circuit switching: pros and consProsguaranteed performance fast transfers (once circuit is established)

    Conswastes bandwidth if traffic is burstyconnection setup time is overheadrecovery from failure is slow

  • Circuit switching: pros and consProsguaranteed performance fast transfers (once circuit is established)

    Conswastes bandwidth if traffic is burstyconnection setup adds delayrecovery from failure is slow[in the telephone network] designed for a specific app

  • Two forms of switched networksCircuit switching (e.g., telephone network) Packet switching (e.g., Internet)

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payload* Nick McKeown 200601000111100010101001110100011001Internet AddressAgeChecksum to protect headerHeaderDataheaderpayload

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payload*payload is the data being carriedheader holds instructions to the network for how to handle packet (think of the header as an interface!)

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payloadSwitches forward packets based on their headers

  • Switches forward packetsto MITto UWUCBto NYUForwarding Tableswitch#2switch#5switch#3switch#4

    Destination Next HopUCB4UW5MIT2NYU3

  • timeTiming in Packet SwitchingWhat about the time to process the packet at the switch?Well assume its relatively negligible (mostly true)

  • timeTiming in Packet SwitchingCould the switch start transmitting as soon as it has processed the header?Yes! This would be called a cut through switch

  • timeTiming in Packet SwitchingWe will always assume a switch processes/forwards a packet after it has received it entirely. This is called store and forward switching

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payloadSwitches forward packets based on their headers

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payloadSwitches forward packets based on their headersEach packet travels independentlyno notion of packets belonging to a circuit

  • Packet SwitchingData is sent as chunks of formatted bits (Packets)Packets consist of a header and payloadSwitches forward packets based on their headersEach packet travels independentlyNo link resources are reserved in advance. Instead packet switching leverages statistical multiplexing

  • Statistical Multiplexing

  • Data Rate 1Data Rate 2Data Rate 3Three Flows with Bursty TrafficTimeTimeTimeCapacity

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  • Data Rate 1Data Rate 2Data Rate 3When Each Flow Gets 1/3rd of CapacityTimeTimeTimeFrequent Overloading

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  • When Flows