INTERNETWORKING III

(SEMESTER 3)

CHAPTER 2 STUDY GUIDE

1.     What does a host send out when it detects a collision?

The first host to detect the collision sends out a jam signal

2.     What can you do to relieve network congestion?

add more bandwidth.

3.     What is the definition of transmission time?

the time it takes a frame or packet to move from the data link layer to the physical layer.

4.     How can you extend the distance of LAN?

add internetworking devices, such as a repeater

5.     What is the definition of latency?

latancy (propogation delay) is the time it takes a frame to travel from the source to the destination

6.     How many wires does it take to make a full-duplex cable? How much of the bandwidth is available on a full-duplex network?

it takes two pairs for full duplex. 100% of the bandwidth in both directions is available on full-duplex because there is one pair of wires for sending and another for receiving data.

7.     How many wires does it take for a half-duplex cable? What is the main difference between a full-duplex and half-duplex network?

it takes only one pair of wires for half-duplex (although we use two pair). The difference between full- and half-duplex is that in full-duplex you have 100% of the available bandwidth for both sending and receiving, which can be accomplished at the same time; in half-duplex sending and receiving have to share the same wire, so they have to take turns. You can’t send and receive data at the same time on half-duplex. Ethernet is half-duplex (CSMA-CD).

8.     What is the main reason for LAN segmentation?

It improves the performance of shared media (cuts down on collision domain size)

9.     What device(s) can you use to segment a LAN?

bridge, switch, router

10.  What does a bridge use to forward data packets? How does it learn this information?

They use MAC address to forward/not forward data packets to another segment. They learn new MAC addresses from the source address in the header of a packet and add this info to a MAC table they build.

11.  What layer does a router operate at?

Layer 3

12.  What layer does a bridge operate at?

Layer 2

13.  What layer does a repeater operate at?

Layer 1

14.  How does a router make the decision to forward a packet?

Routers base forwarding decisions on the destination IP address of a packet.

15.  What is a microsegment? How is a LAN microsegmented?

single host segments (created by segmenting with a switch)

16.  Are there more or fewer collision domains in a microsegmented LAN? Why?

There are more collision domains in a microsegmented LAN because switches break a LAN down into smaller “LANs” by segmenting them. This makes smaller—but more—collision domains.

17.  What is one big advantage of microsegmenting a LAN?

Basically, a switch segments a LAN so that it looks like the LAN only has two hosts on it: the sending one and the receiving one. This gives the segment close to 100% of the available bandwidth.

18.  What piece of information does a bridge use to forward a data packet?

the destination MAC address in the incoming packet. It compares this to the MAC addresses in its table to determine which segment to send/not send the packet to.

19.  What piece of information does a switch use to forward a data packet?

the destination MAC address in the incoming packet.

20.  How does a switch learn MAC addresses? What happens when a switch adds a new MAC address to its table?

Switches learn MAC addresses from incoming packets. They add these addresses to their MAC tables so they can remember which segment hosts which nodes. Each new address is time stamped so the switch can determine which address are still good and which are old.

21.  What type of circuits does a switched LAN create? What is one advantage of using switches on a LAN?

virtual circuits. Switches create many small collision domains so collisions are almost totally avoided, thus speeding up transmission.

22.  What is the difference between a symmetric and asymmetric switch?

symmetric switches switch between like media (same bandwidth); asymmetric switches switch between unlike media (different bandwidths).

23.  Where does a switch store destination and transmission data?

memory buffer.

24.  What are the two methods of switching? What are the main difference between the two?

store-and-forward switching, cut-through switching. The main difference is that store-and-forward waits until the entire frame has been received before it sends it on its way; cut-through switching reads the destination MAC address on the incoming frame and immediately begins sending it on through (before the entire frame is received).

25.  What is a VLAN? How are they created (what device is used)?

Virtual LAN is a logical grouping of devices or users not physically restricted to the same switch segment. They are created with switches.

26.  What are the five Spanning Tree protocol states (in order)?

Blocking – no frames forwarded, BPDUs heard

Listening – no frames forwarded, listening for frames

Learning – no frames forwarded; learning addresses

Forwarding – frames forwarded; learning addresses