Mid-Sem Examples Flashcards
Name the 7 OSI Layers, from Lowest to Highest
Application, Presentation, Session, Transport, Network, Data Link Physical
List 2 advantages and 2 disadvantages of strictly conforming to a layered networking standard, such as OSI/ISO model
- (A) Layer corresponds to a different level of abstraction
- (A) Each layer corresponds to a well defined, independent function
- (A) Assures that users networking software will connect to other vendor’s system and software
- (D) Doesn’t allow creativity of other techniques
- (D) Exploitable for DoS hacks
Which two layers would you employ encryption in for the OSI model?
Employ encryption at the lowest two levels because they’re the easiest to cause a DoS for.
A system uses n-layer protocol hierarchy. Appl generates messages of M bytes each. At each layer, a header of h bytes is added. What fraction of the network B/W is filled with headers?
(n.h)/(m+n.h)
Provide 3 distinct reasons why a stream of data is broken into frames by the DL layer?
- Easier to send small chunks of data in frames
- Can control the f;pw pf frames depending on traffic
- Detecting and correcting higher-level transmission errors from the network layer
Reason for piggy-backed ACKs in the DL layer?
Used to decrease the number of frames sent back from the receiver to sender, by combining data and ACK in to one frame
Why does the checksum only cover headers?
Without the header, the data is useless as it has no destination or source so would never be received by dest.
Why is ACK preferred to NACk in stop-and-wait protocol?
- Timeouts would have to be longer to account for busy routes/lots of traffic
- ACK preferred as shorter timeout and sender knows sooner whether to resend data
- Less frames wasted if data is retransmitted quicker
For the sliding window protocol, is it meaningful for the receiver’s max window size to be larger than the sender’s max window size?
Receiver’s window size should be constant so that the receiver doesn’t pick up unwanted frames as well as sender knowing when it sold receive ACK from receiver, knowing that the frames are in order
Primary difference between Eth hub and Eth switch?
Hub receives packet and broadcasts to all outgoing ports but switch is more intelligent and only retransmits to correct/most efficient outgoing port.
List 3 tasks a network bridge must perform connecting dissimilar hardware technologies
- Buffering of frames to allow for varying bit rates
- Data link reformatting for the 3 different standards of 802.3, 802.4 and 802.5
Why must IEEE 802.3 employ collision avoidance instead of collision detection?
Wireless NIC cannot transmit and receive at the same time, therefore cannot detect a collision if transmitting. Employs a scheme to avoid collisions, MACA (multiple access with collision avoidance) using both physical and virtual channel sensing.
Why are all MAC addresses in 802.11 NICs unique?
Unique identifier for a particular device
Why is registering only wanted MAC addresses for an AP ineffective against a determined intruder?
Hackers are able to create fake MAC addresses so would be able to passively listen to packets to find out which MAC address is registered.
Provide 2 distinct motivations for the NL to employ sequencing numbers
- Make sure all packets are received at dest from src for routing purposes so that the routing arg can be improved because nodes know which packet has been seen before
- In load shedding, better to discard higher seq num frames to descrease the num of frames kept in buffer.
