COMP 361  -- Week 15

Chapter  5

 

Problem 1:

Consider three LANs interconnected by two routers, as shown in the diagram below.

  1. Redraw the diagram to include adapters.
  2. Assign IP addresses to all of the inter faces. For LAN 1 use addresses of the form 111.111.111.xxx; for LAN 2 uses addresses of the form 122.222.222.xxx; and for LAN 3 use addresses of the form 133.333.333.xxx.
  3. Assign LAN addresses to all of the adapters.
  4. Consider sending an IP datagram from host A to host F. Suppose all of the ARP tables are up-to-date. Enumerate all the steps as done for the single router example in Section 5.4.2.
  5. Repeat (d), now assuming that the ARP table in the sending host in empty (and the other tables are up-to-date).

Problem 2

Suppose nodes A, B, and C each attach to the same broadcast LAN (through their adapters). If A sends thousands of frames to B with each frame addressed to the LAN address of B, will C's adapter process these frames? If so, will C's adapter pass the IP datagrams in these frames to C (that is , the adapter's parent node)? How will your answers change if A sends frames with the LAN broadcast address?

Problem 3:

Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination LAN address?

Problem 4:

Recall that with a CSMA/CD protocol,  the adaptor waits K X 512 bit times after a collision, where K is drawn randomly.  For K=100, how long does the adaptor wait until returning to step 2 (p. 461 of the book) for a 10Mbs  Ethernet?  For a 100Mbps Ethernet?

Problem 5:

Suppose nodes A and B are on the same 10 Mbps Ethernet segment and the propagation delay between the two nodes is 225 bit times. Suppose A and B send frames at the same time, the frames collide, and then A and B choose different values of K in the CSMA/CD algorithm. Assuming no other nodes are active, can the retransmissions from A and B collide? For our purposes, it suffices to work out the following example. Suppose A and B begin transmission at t=0 bit times. They both detect collisions at t=225 bit times. They finish transmitting a jam signal at t=225+48=273 bit times. Suppose KA=0 and KB=1. At what time does B schedule its retransmission? At what time does A begin transmission? (Note: The nodes must wait for an idle channel after returning to Step 2 --see protocol.) At what time does A's signal reach B? Does B refrain from transmitting at its scheduled time?

 

Problem 6:

Consider a 100 Mbps 100BaseT Ethernet. In order to have an efficiency of 0.50, what should be the maximum distance between a node and hub?

Assume that bits propagate through the Ethernet cable  at  1.8 *108  m/sec (this is around .6 of the speed of light which is a reasonable value for the standard Ethernet media), a frame length of 72 bytes and that there are no repeaters. Does this maximum distance also ensure that a transmitting node A will be able to detect whether any other node transmitted while A was transmitting ? Why or why not ? How does your maximum distance compare to the actual 100 Mbps standard?

Problem 7:

In the following CSMA/CD 10 BaseT network calculate the worst case time needed by the transmitting station A to learn about the collision caused by the transmission at the station C. Assume that length of each twisted pair is 50m and that signal propagation speed in the twisted pair is 2*108 m/s. Also assume that  one way propagation delay through hub is 0.1µs .

Problem 8:

Consider hosts X, Y, Z, and W, and learning bridges B1, B2, B3 with initially empty forwarding tables as below:

 

 

•  Suppose X sends to Z, which bridges learn where X is?

•  Does Y's network interface see this frame and why

•  Suppose Z now sends to X. Which bridges learn where Z is?

•  Does Y's network interface see this frame and why

•  Suppose Y now sends to X. Which bridges learn where Y is?

•  Does Z's network interface see this frame and why

•  Finally, suppose Z sends to Y. Which bridges learn where Z is?

•  Does W's network interface see this frame and why