CPSC614:Graduate Computer Architecture Network 2: Protocols, Routing, Wireless Prof.Lawrence RauchwergerReview: Network BasicsReview: Performance MetricsReview: InterconnectionsCompare MediaInterconnect IssuesConnecting Multiple ComputersConnection-Based vs. ConnectionlessSlide 9Routing MessagesDeterministic Routing ExamplesStore and Forward vs. Cut-ThroughCut-Through vs. Store and ForwardCongestion ControlProtocols: HW/SW InterfaceProtocol Family ConceptSlide 22TCP/IP packet, Ethernet packet, protocolsExample NetworksConnecting NetworksComparing NetworksSlide 27Slide 28Packet FormatsWireless NetworksIssues in WirelessReliability of Wires Transmission2 Wireless ArchitecturesCellular TelephonyCellular Telephony IIPractical Issues for Inteconnection NetworksSlide 37Practical IssuesCross-Cutting Issues for NetworkingCrosscutting: Smart Switch vs. Smart Network Interface CardSummary: NetworkingCPSC614:Graduate Computer Architecture Network 2: Protocols, Routing, WirelessProf.Lawrence RauchwergerBased on lectures by Prof. David A. PattersonUC BerkeleyReview: Network Basics•Link made of some physical media–wire, fiber, air•with a transmitter (tx) on one end–converts digital symbols to analog signals and drives them down the link•and a receiver (rx) on the other–captures analog signals and converts them back to digital signals•tx+rx called a transceiver01100110Review: Performance MetricsSenderReceiverSenderOverheadTransmission time(size ÷ bandwidth)Transmission time(size ÷ bandwidth)Time ofFlightReceiverOverheadTransport LatencyTotal Latency = Sender Overhead + Time of Flight + Message Size ÷ BW + Receiver OverheadTotal Latency(processorbusy)(processorbusy)Includes header/trailer in BW calculation?Review: Interconnections•Communication between computers•Packets for standards, protocols to cover normal and abnormal events•Performance issues: HW & SW overhead, interconnect latency, bisection BW•Media sets cost, distanceCompare Media•Assume 40 2.5" disks @ 25 GB (1 TB), Move 1 km•Compare Cat 5 (100 Mbit/s), Multimode fiber (1000 Mbit/s), single mode (5000 Mbit/s), and car•Cat 5: 1000 x 1024 x 8 Mb / 100 Mb/s = 23 hrs•MM: 1000 x 1024 x 8 Mb / 1000 Mb/s = 2.3 hrs•SM: 1000 x 1024 x 8 Mb / 5000 Mb/s = 0.5 hrs•Car: 5 min + 1 km / 50 kph + 10 min = 0.25 hrs•Car of disks = high BW mediaInterconnect Issues•Performance Measures•Network Media•Connecting Multiple ComputersConnecting Multiple Computers•Shared Media vs. Switched: pairs communicate at same time: “point-to-point” connections•Aggregate BW in switched network is many times shared–point-to-point faster since no arbitration, simpler interface•Arbitration in Shared network?–Central arbiter for LAN?–Listen to check if being used (“Carrier Sensing”)–Listen to check if collision (“Collision Detection”)–Random resend to avoid repeated collisions; not fair arbitration; –OK if low utilization(A. K. A. data switching interchanges, multistageinterconnection networks,interface message processors)Connection-Based vs. Connectionless•Telephone: operator sets up connection between the caller and the receiver–Once the connection is established, conversation can continue for hours•Share transmission lines over long distances by using switches to multiplex several conversations on the same lines–“Time division multiplexing” divide B/W transmission line into a fixed number of slots, with each slot assigned to a conversation•Problem: lines busy based on number of conversations, not amount of information sent•Advantage: reserved bandwidthConnection-Based vs. Connectionless•Connectionless: every package of information must have an address => packets –Each package is routed to its destination by looking at its address–Analogy, the postal system (sending a letter)–also called “Statistical multiplexing”–Note: “Split phase buses” are sending packetsRouting Messages•Shared Media–Broadcast to everyone•Switched Media needs real routing. Options:–Source-based routing: message specifies path to the destination (changes of direction)–Virtual Circuit: circuit established from source to destination, message picks the circuit to follow–Destination-based routing: message specifies destination, switch must pick the path»deterministic: always follow same path»adaptive: pick different paths to avoid congestion, failures»Randomized routing: pick between several good paths to balance network load•mesh: dimension-order routing–(x1, y1) -> (x2, y2)–first x = x2 - x1,–then y = y2 - y1,•hypercube: edge-cube routing–X = xox1x2 . . .xn -> Y = yoy1y2 . . .yn–R = X xor Y–Traverse dimensions of differing address in order•tree: common ancestor•Deadlock free?Deterministic Routing Examples001000101100010110111011Store and Forward vs. Cut-Through•Store-and-forward policy: each switch waits for the full packet to arrive in switch before sending to the next switch (good for WAN)•Cut-through routing or worm hole routing: switch examines the header, decides where to send the message, and then starts forwarding it immediately –In worm hole routing, when head of message is blocked, message stays strung out over the network, potentially blocking other messages (needs only buffer the piece of the packet that is sent between switches). –Cut through routing lets the tail continue when head is blocked, accordioning the whole message into a single switch. (Requires a buffer large enough to hold the largest packet).Cut-Through vs. Store and Forward•Advantage–Latency reduces from function of:number of intermediate switches X by the size of the packet to time for 1st part of the packet to negotiate the switches + the packet size ÷ interconnect BWCongestion Control•Packet switched networks do not reserve bandwidth; this leads to contention (connection based limits input)•Solution: prevent packets from entering until contention is reduced (e.g., freeway on-ramp metering lights)•Options:–Packet discarding: If packet arrives at switch and no room in buffer, packet is discarded (e.g., UDP)–Flow control: between pairs of receivers and senders; use feedback to tell sender when allowed to send next packet»Back-pressure: separate wires to tell to stop»Window: give original sender right to send N packets before getting permission to send more; overlaps latency of interconnection with overhead to send & receive packet (e.g., TCP),