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1 Topics Midterm Review EECS University of California Berkeley Network Architecture Network hierarchy Layering Performance Link Layer Ethernet Wi-Fi Network Layer Addressing Routing EECS Midterm Review Review: Network WAN Review: Network WAN MAN MAN LAN EECS Midterm Review EECS Midterm Review 4 Review: Network WAN Layers & Protocols Application Data Transport TH Data HTTP, FTP, UDP - TCP Application Transport LAN Network Asynchronous routed path Asynchronous routed path Network PH Data PH Data IP Network EECS Midterm Review 5 Data Link Control Physical Interface Asynchronous reliable bit pipe FH Data Data Link Control Eth. Synchronous unreliable bit pipe Physical Interface Fiber, Wires, WL Physical Link Asynchronous reliable bit pipe Data Link Control Synchronous unreliable bit pipe Physical Interface Physical Link End Node Router End Node EECS Midterm Review 6 FH Data EECS

2 Timing: Queuing Link: R bps P bits Q T seconds Timing: Store & Forward - Multiple System: Mbps 5Mbps Mbps Mbps Q/R Q/R = queuing delay (load-dependent) T P/R Time EECS Midterm Review 7 EECS Midterm Review 8 Performance Metrics Throughput Delay Jitter Connection Throughput Connection: Send W bits (window size) Wait for ACKs Repeat Assume that the round-trip time is RTT seconds Throughput = W/RTT bps Source RTT K Destination Numerical Example: W = 64KBytes = 5 kbits = 5x,4 = 54,88 bits RTT = ms Throughput = W/T =.6Mbps RTT Time K EECS Midterm Review 9 EECS Midterm Review N Little s Result S D S = area X(t) T(N) T(N - ) Ethernet Random Multiple Access Switching Bridged Ethernet 8. S = T() + + T(N) = integral of X(t) S T() + + T(N) N X(t)dt = =. T T N T T Average occupancy = (average delay)x(average arrival rate) EECS Midterm Review EECS Midterm Review EECS

3 Random Multiple Access How to share a channel? Multiple Access Multiplexing ALOHA: First random multiple access system Efficient for many users, each with low utilization Try; If collide, wait random time then repeat (CD) Analysis: Slotted Aloha efficiency /e = 6% Random Multiple Access Ethernet: First version CSMA/CD Wait until channel is idle; try; if collide, stop, wait, repeat Idea: CS should improve efficiency if fast enough Wait random multiple of 5 bit times (exponential back off) Analysis: Efficiency /( + 5a), a = PROP/TRANS A p, indpdt. Slot N nodes P(success) = Np( p) N- /e if p = /N B EECS Midterm Review EECS Midterm Review 4 Switching Ethernet: Later versions Switched Larger aggregate throughput VLANs: partition in disjoint logical LANs Link Aggregation Each port is in its own collision domain as opposed to a hub where all ports are in the same collision domain Fast, GE, GE Improved modulation schemes Bridged Ethernet Flat Addressing Learning Watch source addresses Avoiding Loops Spanning Tree Protocol (ID, presumed root ID, distance to presumed root ID) Note: Not very efficient; Not very fast EECS Midterm Review 5 EECS Midterm Review 6 Spanning Tree Example Ethernet B B [ ] 4 [ ] [ ] B B4 B6 6 [6 ] 5 [ ] B5 [5 ] Service? Operations: Addresses, MAC, Hub, Switch, Learning, Spanning Tree MAC: Why not Aloha? Why Switch? Why Loops? Format: [my ID presumed root ID distance to presumed root] EECS Midterm Review 7 EECS Midterm Review 8 EECS

4 8. a - 5GHz, up to 54Mbps b -.5GHz, up to Mbps g -.5GHz, up to 54Mbps MAC: CSMA/CA with or without RTS/CTS Distributed (DCF): CSMA/CA using different Interframe Gaps maintain network allocation vector Centralized (PCF): access point polls nodes 8. Basic mode: Wait until idle; Transmit (cannot listen while transmitting) If collision, backoff (exponential; decrements when idle) RTS/CTS mode: (Hidden & Exposed Terminal) RTS / CTS / DATA / ACK R C 4 R = RTS: silences C = CTS: silences 4 NAV: time until completion of exchange R/C/D/A EECS Midterm Review 9 EECS Midterm Review 8. MAC If medium is idle for DIFS interval after a correctly received frame and backoff time has expired, transmission can begin immediately If previous frame contained errors, medium must be free for EIFS If medium is busy, access is deferred until medium is idle for DIFS and exponential backoff Backoff counter is decremented by one if a time slot is determined to be idle Unicast data must be acknowledged as part of an atomic exchange 8. Virtual Carrier Sensing Virtual Carrier Sensing using Network Allocation Vector (NAV) EECS Midterm Review EECS Midterm Review 8. Layers: IP Internet Protocol Why not CSMA/CD? Objectives of new MAC? Why RTS/CTS? How does NAV work? Why different IFS? Why more than addresses? Why different PHYs? Why multiple channels? Internetworking Subnets Addressing Class-Based Classless: CIDR Routing EECS Midterm Review EECS Midterm Review 4 EECS

5 Internetworking Goal: Connect different networks a c.. X. a a b.. Y. b. c ROUTER. d. f. e d f.. X Router looks at IP addresses (., ) EECS Midterm Review 5 Each network uses local addresses (e.g., a, b, c, ) Subnets /4 IP H e H IP e e4 H: Is H on same subnet as I am? Yes if IP/4 = IP/4 Yes Ethernet frame to destination No Ethernet frame to R Use ARP to find needed MAC addresses e.g., [all e who is IP6?] [e e4 I am IP6] 8..4./4 IP R /4 IP /4 EECS Midterm Review 6 R e5 IP /4 e H Internetworking Direct Delivery Internetworking Indirect Delivery e5 e I am IP e e IP H e IP IP X e H e4 e IP H e IP IP X e H H IP e e e: e I am IP all e e: Who is IP? e4 R R e5 IP H IP e e4 SH IP IP X R R e5 IP e e5 IP IP X all e5 Who is IP? Note: Fragmentation may be required at R EECS Midterm Review 7 EECS Midterm Review 8 Class-base Addressing Addressing reflects internet hierarchy bits divided into parts: Class A Class B Class C 8 network host 6 network host 4 network host ~ million nets 56 hosts Classless Internet Domain Routing Suppose fifty computers in a network are assigned IP addresses Range is to They share the first 6 bits of 8..9.: Convention: 8..9./6 = prefix There are -6=6 bits for the 5 computers 6 = 64 addresses EECS Midterm Review 9 EECS Midterm Review EECS

6 IP: Routing BGP 4 4 RIP 6 B 5 7 IntraDomain 8 IntraDomain IntraDomain Interdomain IGRP BGP OSPF C Path Vector, Policies 6 Intradomain Formulate the routing problem as a Shortest Path Problem Link State v/s Distance Vector EECS Midterm Review Both work reasonably well in a well engineered network Route Computation Dijkstra: Link State Use a flooding protocol to discover the entire topology Find the shortest paths in order of increasing path length from node i. Bellman Ford: Distance Vector D(i,d) = min jεn(i) {c(i,j) + D(j,d)} Finds the shortest path of up to n hops increasing values of n BGP: Path Vector Policy routing: Receive and advertise entire routes AS numbers describe the path to a CIDR address EECS Midterm Review Algorithms LINK STATE ) Exchange Link States ) Each node computes BB A: [B, ], [C, ] the shortest paths to B: [A, ], [D, ] the others AA DD C: [A, ], [D, ] CC D: [B, ], [C, ] DISTANCE VECTOR BB BB BB AA DD AA DD AA DD CC CC CC PATH VECTOR B,D Don t like B BB D BB BB AA DD AA DD AA DD CC D CC CC C,D EECS Midterm Review TOC IP Routing Types Overview Network Structure BGP C C{,,} C{,,} D 4 5 AC {,,} AD {4,5} A D{4,5} DC{,,} E EECS Midterm Review 4 B BAC{,,} BAD{4,5} Transit; Peering Agreements; Customer-Provider F IP Service? Operations: Addresses, Routing Glue L/L: ARP Addressing: Why CIDR? How? Why DHCP, NAT? Routing: Why Domains? Why different algorithms? Pros/Cons of each algorithm? Class-base Addressing Addressing reflects internet hierarchy bits divided into parts: Class A Class B Class C 8 network host 6 network host 4 network host ~ million nets 56 hosts EECS Midterm Review 5 EECS Midterm Review 6 EECS

7 Classless Internet Domain Routing Suppose fifty computers in a network are assigned IP addresses Range is to They share the first 6 bits of 8..9.: Convention: 8..9./6 = prefix There are -7=6 bits for the 5 computers 6 = 64 addresses CIDR b Longest prefix match routing a c,, d,, Dest., a 4 b c d EECS Midterm Review 7 EECS TOC IP Notes - CIDR Midterm Review 8 NAT Trick: Use TCP port to distinguish computers There are 64k port numbers, the first k are reserved [IPa IPx TCPb TCPn ] [IPb IPx TCPm TCPn ] IPa [IPx IPa TCPn TCPb ] IPx [IPx IPb TCPn TCPm ] IPb NAT IPc [TCPb IPb, TCPm] EECS Midterm Review 9 Multicast Ethernet NIC knows if it is member of group Switches flood multicast packets With IGMP: router sends requests; report suppression Tree pruned tree of shortest paths Forward if on shortest path Shared tree in sparse mode Group Management Join group G Soft state (refresh before timeout) Reliability Many proposals EECS Midterm Review 4 Multicast Multicast Tree of shortest paths: weight = 6 Least weight spanning tree = 5 EECS Midterm Review 4 EECS Midterm Review 4 TOC IP Multicast Approaches Tree Computation EECS

8 Check List Network hierarchy Layering Performance: Timing & Metrics Layer Ethernet MAC Wi-Fi MAC Repeaters, hubs, bridges, switches, routers Internet addressing Routing Review: Check List Big Picture Layers Network Structure (L, L) Where protocols are implemented Switching Techniques Models Link rate; throughput; delay (mean, jitter) Store-and-forward; W/RTT Little s Result Ethernet CSMA/CD Learning bridge; Spanning tree EECS Midterm Review 4 EECS Midterm Review 44 Review: Check List 8. Hidden and Exposed Terminal RTS/CTS; NAV Network Class-Based; Classless Addressing; Subnets DHCP; NAT Dijkstra; Bellman-Ford Hierarchical routing Multicating: tree; group management; prune shortest paths EECS Midterm Review 45 EECS

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