Exam 2 Lecture Review Notes Flashcards
What information do hosts lack that can result in congestion?
Hosts are unaware of network congestion and the complete state of the network. They may continue to send packets into the network and this can result in lost packets and long delays.
What is a spurious retransmission?
When senders dont receive acknowledgments for packets in a timely fashion, they can spuriously retransmit those packets.
What are the two main goals of congestion control?
1) To use network resources efficiently 2) to ensure that all of the senders get their fair share of the resources.
What are two major approaches to adjusting packet-sending rate?
1) Window based: a sender uses acknowledgments from the receiver to clock the retransmission of new data. 2) Rate based: the sender monitors the loss rate and uses a timer to modulate the transmission rate.
What kind of workloads do datacenters typically experience?
High bandwidth and low latency workloads.
What is TCP incast?
TCP incast is a drastic reduction in application throughput that results when servers using TCP all simultaneously request data, leading to a gross underutilization of network capacity in many-to-one communication networks like a datacenter.
What is the barrier synchronization request pattern?
A client issues many requests from parallel threads and no forward progress can be made until all the responses for those threads are satisfied.
What are some solutions to TCP Incast?
1) Use fine-grained TCP retrasmisson lines. Reduce the retransmission timeout for TCP. 2) Reduce the network load by having the client acknoledge every other packet instead of every packet.
What does it mean to digitize an audio signal?
The audio signal is converted to a stream of bits.
How can we compress a single image?
Using spatial redundancy
How can we perform compression across images?
Using temporal redundancy
What is a playout buffer?
A playout buffer is a means by which the client stores data as it arrive from the server, and plays the data for the user in a continuous fashion.
Why is TCP not a good fit for congestion control when streaming audio/video?
TCP retransmists lost packets but retransmissions in the context of streaming media may not always be useful. TCP slows down its sending rate after packet loss, which may cause starvation of the client. TCP as a protocol also contains a certain amount of overhead. A TCP header of 20 bytes on every packet is large for audio samples.
How can QoS be performed for streams?
QoS can be performed by marking certain packet streams as higher priority than others.
What is weighted fair queueing?
A queueing strategy in which the queue containing the VoIP packets is serviced more frequently than the queue containing say for example, FTP packets.
