Transport Layer Flashcards
What is a TCP(Transmission Control Protocol)?
TCP provides reliable, ordered, and error-checked delivery of bytes between applications.
What is a UDP(User Datagram Protocol)?
Quick, connectionless communication
What is Multiplexing and Demultiplexing?
Multiplexing (at sender)- how servers handle data from multiple sockets, Multiplexers add the transport header.
Demultiplexers(at receiver)- use header info to deliver segments to the correct socket
What is a UDP checksum?
Used to detects errors (e.g., flipped bits)
What is the Stop and Wait protocol
When the sender sends a packet, and then waits for the receiver to respond, this means that we can have a one-bit sequence number.
What’s the difference between the demultiplexing process in UDP vs TCP?
UDP only looks at the destination port
TCP looks at a combination of the source IP addr. and port number dest. IP addr. and port number.
Name 3 uses of UDP
- SNMP
- Streaming Multimedia
- DNS
Is it possible to have a UDP connection that’s reliable?
Yes, this can be implemented in the application layer
What’s rdt1.0?
Reliable transfer over a reliable channel
What’s rdt2.0?
Transfer with bit errors. Repeats transfer to recover these errors after getting control messages(ACKs, NACKs).
How does rdt2.0 handle ACK/NACK corruption/duplication?
Stop and Wait protocol is implemented, this is where the sender adds a sequence number to each packet and waits for the receiver response.
What is a Pipeline protocol?
Sender allows multiple packets to be sent, they don’t have to be acknowledged packets. e.g. Go Back N, Selective Repeat
What’s the difference between Selective repeat and the Go-Back-N protocols?
In Selective repeat the rcvr sends an individual ack for each packet and the sndr has a timer for each unacked packet.
MEANWHILE…
In Go-Back-N the rcvr sends a cumulative ack and has a timer for the oldest unacked packet.
What is a method of increasing utilization?
Pipelining
Does TCP use cumulative or individual acknowledgements?
Cumulative, similar to GBN
Why does TCP use a 3 way handshake instead of a 2 way handshake?
- Message loss
- Variable delays
Whats Flow Control?
The sender won’t overrun the receiver’s buffers by transmitting too much, too fast.
How does the receiver in flow control advertise free space?
Including the rwnd value in the TCP header.
What are the 4 costs of congestion?
(1) Lost packets
(2) Long delays
(3) Unneeded retransmission
(4) Upstream transmission capacity is wasted
WHat’s congestion control?
This is when too many sources are sending too much too fast for the network to handle. Congestion control is different to flow control.
What are the 2 approaches to congestion control?
- End to end congestion control
- Network assisted congestion control
How does TCP sender deal with perceived end to end congestion?
Using the TCP slow start algorithm.
What is TCP slow start?
When connection begins, the sender increases rate exponentially until loss event. Once loss event occurs, increase congestion window per ACK message received.
How is loss detected in the TCP congestion control process?
1 Timeout
How does TCP react to loss in the congestion control process?
- TCP RENO cuts congestion window in half
- TCP TAHOE sets congestion window to 1
What is the TCP fairness goal?
if K TCP sessions share the same bottleneck link of bandwidth R, each should have a rate of R/K (router capacity)
Why do multimedia apps usually use UDP instead of TCP?
They don’t want rate throttled by TCP congestion control.
What does the transport layer do?
Provides process-process data transfer
