Networking Week 9

After a collision, the hosts involved have to wait an additional length of time
controlled by the backoff timer before trying to retransmit. Why is this?

• Since the delay time is selected at random, it is unlikely that the hosts will
  retransmit at the same time and have another collision.

• The timer chooses times that ensure that the most urgent frame is retransmitted
  first.

• 
  The timer makes it more likely that the host that transmitted first will get
  priority for retransmission.

• 
  It makes sure that a host that was not involved in the collision will be the next
  host to transmit.

A host needs to find the MAC address corresponding to a known IP address. What
can it do?

• 
  Send an ARP request using a level 3 broadcast

• 
  Send an ARP request using a level 2 broadcast

• Send a DHCP request to the local server

• Send a MAC request to the switch

A host needs to send a message to a destination on another network. It sends out an ARP request giving the IP address of the destination. What reply does it get?

• The destination host will reply, giving its MAC address.

• The local router will reply, giving the MAC address of the remote host.

• The local router will reply, giving its own MAC address

• There will be no reply because the remote host will not get the message.

Ethernet is now operated on networks with physical topology that is a star or extended
star. What is the underlying logical topology of the original version of Ethernet?

• 
  Extended star

• Multi-access bus

• Ring

• Mesh

Host A has a packet to be sent to host B on a remote network. Host A encapsulates the
packet in a frame and transmits it. Which device will remove the frame header and
trailer?

• 
  The local switch on Host A's network

• The gateway router on Host A's network

• The gateway router on Host B's network

• The local switch on Host B's network

• 
  Host B

Host A has a packet to be sent to host B on a remote network. Host A encapsulates the
packet in a frame and transmits it. Which device will remove the packet header?

• The local switch on Host A's network

• The gateway router on Host A's network

• The gateway router on Host B's network

• The local switch on Host B's network

• 
  Host B

How big is an Ethernet frame?

• 
  32 to 64 bytes

• 
  64 to 128 bytes

• 
  64 to 1522 bytes

• 128 to 1522 bytes

How long is a MAC address? (Choose 3)

• 48 bits

• 6 bytes

• 12 hexadecimal digits

• 8 bytes

• 
  16 hexadecimal digits

If a host is transmitting and it detects a collision, what does it do?

• 
  Stops all transmission at once.

• Sends a jam signal

• 
  Retransmits as soon as the cable is clear.

• Makes a random choice of whether it or the other host will retransmit first.

In order for CSMA/CD to work, when must a transmitting host detect a collision?

• Before it starts transmitting the frame.

• Before it has finished transmitting the destination address field.

• 
  Before it has transmitted the first 64 bytes of the frame.

• 
  Before it has finished transmitting the frame.