Chapters 14 Midterm Review

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Chapters 1-4Midterm Review

• Professor Rick Han
• University of Colorado at Boulder
• rhan_at_cs.colorado.edu

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Announcements

• HW 1, 2, 3 see profs office hours
• Solutions to HW 2 and 3 online
• Solutions to HW 4 online by tonight
• Programming Assignment 3 due after Spring Break
• Best practices code
• TCP/IP Sockets in C Practical Guide for
  Programmers Michael Donahoo and Kenneth
  CalvertThird edition of Peterson and Davie
• Im trying to obtain free evaluation copies of
  both will have more say later

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Midterm

• Midterm March 13
• Through Chapter 4 Network Layer
• Excluding 2.9 (network adaptors), 3.4 (switching
  hardware)
• 75 minutes
• In class
• Closed book
• Calculator OK
• 3-4 multipart questions (multiple sections)
• maybe some short-answer/multiple-choice questions
• About 20 minutes for each long question

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Potential Topics for Midterm

• List is not all-inclusive some topics may appear
  on midterm not listed here
• How does ___ work? Why is it used?
• Physical
• Propagation delay, bandwidthdelay product
• Byte stuffing
• Error detection/correction, e.g. checksums
• Data-link
• Reliable protocols
• Stop-and-Wait
• Go-Back-N cumulative ACKs, window-based
  flow-control
• Selective Repeat selective ACKs

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Potential Topics for Midterm (2)

• MAC
• Aloha, Slotted Aloha
• CSMA Listen before talk
• CSMA/CD Ethernet Listen while talk
• exponential backoff
• CSMA/CA wireless Ethernet
• Token Ring
• Ethernet Hubs/Repeaters
• Ethernet Bridges/Switches
• How do bridges build their forwarding tables?
• How are Spanning Trees constructed?

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Potential Topics for Midterm (3)

• Network
• Virtual circuit routing
• IP
• Addressing, CIDR
• ARP
• First, Broadcast on Ethernet
• DHCP
• DHCP Relay to a DHCP Server
• ICMP
• How do ping and traceroute use ICMP?

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Potential Topics for Midterm (4)

• Network
• IP
• Distance-vector routing (RIP)
• Distributed Bellman-Ford
• Bouncing effect, counting-to-infinity, split
  horizon
• Link-state routing (OSPF)
• Flooding of LSPs Dijkstra
• Link-state cost metrics
• Inter-domain routing (BGP)
• Path vector exchanged between ASs

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Sample Problems

• Reliable protocols
• Suppose a host X wishes to transmit packets to a
  host Y using a reliable protocol. Assume that
  the propagation delay is D in each direction, the
  bandwidth is B bits/sec in each direction, and
  there are no other delays in the network or
  endpoints. Assume the speed of light C is 3108
  m/s. Suppose a stop-and-wait protocol reliably
  sends packets of fixed size P from X to Y, and
  that each packet arrives without error at host Y
  and is ACKnowledged immediately. Each ACK is of
  fixed size A and is sent from Y to X, arriving
  without error at host X. Assume that P and A are
  both much less than the bandwidthdelay product
  of the link.
• (a) What is the roundtrip time of the link,
  beginning from the time the first bit of packet P
  is sent to the time the last bit of ACK A is
  received, expressed as a function of A, B, C, D
  and P?
• Answer RTT forward delay reverse delay (D
  P/B) (D A/B) 2D (PA)/B (assuming full
  duplex)

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Sample Problems (2)

• Reliable protocols
• (b) What is the fraction of each roundtrip time
  that the stop-and-wait protocol spends waiting
  before it can send new data packets P, expressed
  as a function of A, B, C, D, and P? Hint its
  a ratio of expressions, not numbers
• Answer fraction of each RTT devoted to waiting
  1 - P/B / RTT
• 1 - P / 2DB P A
• 2DB A / 2DB P A (assuming full
  duplex)

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Sample Problems (3)

• Ethernet bridges
• For the Figure above, fill in the bridge
  forwarding table after each of the following
  sequence of events. The table should expand
  along with the events.

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Sample Problems (4)

• Ethernet bridges

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Sample Problems (5)

• Ethernet bridges (answer)

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Sample Problems (6)

• Link state routing
• Suppose now that link-state routing is applied to
  the above network topology (all links are up and
  running). Assume that all link information has
  been reliably flooded via LSPs to all nodes.
  Assume that node B is the root node of the
  shortest path tree. Fill in the table below that
  iteratively adds nodes onto the shortest path
  tree using Dijkstras shortest path algorithm
  with B as the root. Here is Dijkstras algorithm

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Sample Problems (7)

• Link state routing
• Initialize shortest path tree SPT B
• For each n not in SPT, C(n) l(s,n)
• While (SPTltgtN)
• SPT SPT U w such that C(w) is minimum for all
  w in (N-SPT)
• For each n in (N-SPT), C(n) MIN (C(n), C(w)
  l(w,n))
• where N set of nodes in graph, l(i,j) link
  cost between i,j ( infinity if not neighbors),
  SPT set of nodes in shortest path tree thus
  far, B source node, C(n) cost of path from B
  to node n. In case of ties in cost, choose the
  node with the lowest id, AltBltCltDltEltF.

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Sample Problems (8)

• Link state routing

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Sample Problems (9)

• Link state routing (answers)