Module 10: Application Layer Multicast and Link Layer Services Flashcards
Application Layer Multicast (ALM)
What are the advantages of ALM?
No need for changes to IP or routers
No need for ISP cooperation
End hosts can prevent other hosts from sending
Easy to implement reliability: use hop-by-hop retransmissions
What are the disadvantages of ALM?
lack of knowledge about network:
-does not have direct access to unicast routing
-does not know about network topology
stretch: ratio of latency in the overlay to the latency in the underlying network
How is the disadvantage of Stress in ALM solved?
stress: number of duplicate packets sent over by the same physical link
solution: periodically probe overlay neighbors to pick best neighbor that meets application-level utility function (e.g. latency, available bandwidth, both)
DHT multicast tree formation
group is associated with key
root of group is node that owns key
any node that wants to joins ends message to root, leaving forwarding state along path
In a multicast tree, if the root wants to broadcast to n leaves of a subtree, it has to send n messages to the root of that subtree.
false
ISO OSI Reference Model for Layers
Which of the following layers use end-to-end protocols?
Transport (TCP) and Application
Adaptors communicating
Link Layer Servives
Encoding
Framing
Error detection
Flow control
Encoding
problem with simple approach to encoding
simple approach to address the long strings of 0s and 1s
encoding alternatives (NRZI and Manchester)
encoding alternatives (4B/5B)
Framing
More Framing
What is a potential downside with the counter-based approach?
count field gets corrupted
Error Detection
Techniques for error detection
parity checking
checksum
cyclic redundancy check
Parity Check
link-layer broadcast media
Methods to handle contention in end-to-end layers is similar to that in the link layer.
True
Multiple Access Protocol
Single shared broadcast channel
- avoid having multiple nodes speaking at once
- otherwise, collisions
MAP
- distributed algo for sharing the channel
- algo determines which node can transmit
classes of techniques
channel partitioning
taking turns
random access
Which of the following is false about TDMA?
packet transmission can span multiple slots
true stuff:
Each machine can only occupy one time slot at a time
Transmission channel gets partitioned into fixed length slots
channel partitioning: FDMA
Taking Turns MAC protocols
used in bluetooth
Which of the following MAC protocols utilize the technique of “taking turns”?
Token Passing
key ideas of random access
Which of the following is incorrect about random access concepts?
Carrier sense means that the receiver should check if anyone else is already sending data to it before accepting data sent from a source
correct stuff:
Collision detection means that when a node discovers that other nodes are sending data after its data is sent out, it stops sending data and retries at a later time
Randomness refers to nodes backing off and restarting after a random amount of time
aloha transmissions strategy
variation: slotted aloha
slotted aloha example
efficiency of slotted aloha
ethernet uses CSMA/CD
Explain CSMA/CD Random Access: exponential backoff
ethernet frame structure
Minimum Packet Size
Limitations on Ethernet Length
