Module 7 Flashcards
A channel partitioning protocol has which of the following characteristics:
all of the above
In slotted ALOHA with N active nodes, the probability that no node transmits in a given slot is
(1-p)^N
An ARP query packet is encapsulated in
a link-layer broadcast frame
Ethernet provides which of the following services to the network layer
error detection
For Ethernet, if an adapter determines that a frame it has just received is addressed to a different adapter
it discards the frame without sending an error message to the network layer
In the Ethernet CSMA/CD protocol, suppose a node constructs a frame and then senses the channel as busy. Then
the adapter waits until it senses the channel idle and then begins to transmit the frame.
In CSMA/CD, after the 3rd collision, what is the probability that the value of K that a node chooses is 2?
.125
A 10BaseT Ethernet LAN has
a star topology
When a switch transmits an Ethernet frame, the Ethernet frame has
none of the above
The switch poisoning attack involves:
sending many packets to the switch with different bogus source MAC addresses
A cut-through switch has which of the following properties:
all of the above
TF: All link layer protocols that support IP have the same frame structure (i.e., length of frame, number and length of header fields).
False
TF: CRC error detection, as used in Ethernet, is always able to detect whether there is an error in a frame.
False
TF: The even parity bit scheme can correct single bit errors.
False
TF: With CDMA, each sender uses the same code, cm, m=1,…,M.
False
TF: Each LAN adapter has a unique LAN address.
True
TF: Consider a router with multiple ARP tables, one for each of its interfaces. No two of these ARP tables can contain the same LAN address.
True
TF: Consider a twisted-pair Ethernet in which all nodes are 50 meters from the hub. The time it takes for a bit to propagate from hub to node for a 10BaseT Ethernet is ten times longer then for a 100BaseT Ethernet.
False
TF: The entries in a switch table need to be configured by the network administrator.
False
TF: PPP excludes certain bit patterns in the network-layer packets that it carries.
False
TF: Consider the switched LAN architecture in Figure 5.24. Assuming all links are full duplex, there are never collisions in this LAN.
True
TF: Consider a computer network consisting of several interconnected 10BaseT hubs, but which does not include any bridges or routers. Then this network has only one collision domain.
True
Which of the following services may be implemented in a link-layer protocol? Select one or more statements.
Reliable data transfer between directly connected nodes.
Coordinated access to a shared physical medium.
Bit-level error detection and correction.
Multiplexing down from / multiplexing up to a network-layer protocol.
Flow control between directly connected nodes.
Which of the following statements is true about a two-dimensional parity check (2D-parity) computed over a payload?
2D-parity can detect any case of a single bit flip in the payload.
2D-parity can detect any case of two bit flips in the payload.
2D-parity can detect and correct any case of a single bit flip in the payload.
Which of the following statements is true about channel partitioning protocols?
Channel partitioning protocols can achieve 100% channel utilization, in the case that all nodes always have frames to send.
There can be times when the channel is idle, when a node has a frame to send, but is prevented from doing so by the medium access protocol.
Which of the following statements is true about both Pure Aloha, and CSMA (both with and without collision detection?
Pure Aloha and CSMA can achieve 100% utilization, in the case that there is only one node that always has frames to send
There can be simultaneous transmissions resulting in collisions.
Which of the following statements is true about polling and token-passing protocols?
These protocol can achieve close 100% utilization, in the case that there is only one node that always has frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions)
These protocol can achieve close to 100% channel utilization, in the case that all nodes always have frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions)
Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols are collision-free (e.g., collisions will never happen)?
TDMA and FDMA
Polling
(This and the other three similar questions all have the same answers as above.)
Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols requires some form of centralized control to mediate channel access?
TDMA and FDMA
Polling
(This and the other three similar questions all have the same answers as above.)
Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is the maximum channel utilization 1 (or very close to 1)?
TDMA and FDMA
Polling
(This and the other three similar questions all have the same answers as above.)
Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is there a maximum amount of time that a node knows that it will have to wait until it can successfully gain access to the channel?
TDMA and FDMA
Polling
(This and the other three similar questions all have the same answers as above.)
(A) We’ve now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of MAC addresses (and therefore is not a property of IPv4 addresses - careful!).
This is a 48-bit address.
This is a link-layer address.
This address remains the same as a host moves from one network to another.
(B) We’ve now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of IPv4 addresses (and therefore is not a property of MAC addresses - careful!).
This is a 32-bit address.
This is a network-layer address.
This address is allocated by DHCP.
(C) We’ve now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is a property of both IPv4 addresses and MAC addresses.
This address must be unique among all hosts in a subnet.
Use the pulldown menus below to match the name of the field with the function/purpose of a field within an Ethernet frame.
- Cyclic redundancy check (CRC) field
- Source address field
- Data (payload) field
- Type field
- Sequence number field
- Used to detect and possibly correct bit-level errors in the frame.
- 48-bit MAC address of the sending node.
- The contents of this field is typically (bit not always) a network-layer IP datagram.
- Used to demultiplex the payload up to a higher level protocol at the receiver.
- This field does not exist in the Ethernet frame
Suppose an Ethernet frame arrives to an Ethernet switch, and the Ethernet switch does not know which of its switch ports leads to the node with the given destination MAC address? In this case, what does the switch do?
Flood the frame on all ports except the port on which the frame arrived.
Which of the following statements are true about a self learning switch?
A self-learning switch will age-out (forget) a self-learned association of a MAC address x and switch port y if it doesn’t see a frame with MAC address x incoming on switch port y after some amount of time.
A self-learning switch frees a network manager from a least one configuration task that might be associated with managing a switch
A self learning switch associates the source MAC address on an incoming frame with the port on which it arrived, and stores this matching in a table. The switch has now learned the port that leads to that MAC address.
Consider the simple star-connected Ethernet LAN shown below, and suppose the Ethernet switch is a learning switch, and that the switch table is initially empty. Suppose C sends an Ethernet frame address to C’ and C ‘ replies back to C. How many of these two frames are also received at B’s interface?
1
Consider the simple star-connected Ethernet LAN shown below, and suppose the switch table contains entries for each of the 6 hosts. How will those entries be removed from the switch table?
An entry for a host will be removed if that host doesn’t transmit any frames for a certain amount of time (that is, table entries will timeout).
Which of the following statements are true about MAC (link-layer) addresses? Select one or more statements below.
Has 48 bits.
Generally stays unchanged as a device moves from one network to another.
Generally does not change, and is associated with a device when it is manufactured/created.
An ARP query packet is encapsulated in
a link-layer broadcast frame
Which one of the statements below is not true about how entries in a switch forwarding table are created?
Entered manually
Created by the routing algorithm
