Week 12: TCP & Congestion Control Flashcards
TCP is a protocol on which layer?
Layer 3 - Transport
UDP is a protocol on which layer?
Layer 3 - Transport
List characteristics of UDP
- Connectionless
- Low header Overhead
- No Flow, Error, or Congestion Control
True or False: In UDP, the source port number is used in demultiplexing
False, in UDP the source port number is not used in demultiplexing
List characteristics of TCP
- Reliable
- Connection-Oriented
- High header overhead
- Error, Flow, & Congestion Control
List some applications that are used with UDP
- DNS
- RIP
- SNMP
List some applications that are used with TCP
- HTTP
- SMTP
- FTP
- TELNET
- POP3
How many tuples is TCP specified by?
4 Tuples:
- Source IP
- Source Port
- Destination IP
- Destination Port
What is a Stream Data Transfer?
A contiguous stream of bytes across the network with no indication of boundaries
What does a Stream Data Transfer do?
- group bytes into segments
- Sequence & Acknowledgement numbers guarantees reliable delivery
What is the Sequence number for a segment?
the Byte-stream number for the first byte in the segment
What is the Acknowledgement number for a segment?
The sequence number of the next byte expected from the other side
True or False: In TCP Flow Control, the Receiver doesn’t control the sender
False, in TCP flow control, the Receiver controls the sender so the receiver’s buffer isn’t overflowed by too much too quickly
When does congestion in TCP occur?
When total arrival rate from all packet flows exceeds R over a sustained period of time
What occurs when TCP congestion occurs?
Buffers at multiplexer will fill & packets will be lost
In TCP, what maintains the Congestion Window?
The sender (determines how many bytes can be sent out at any time)
True or False: cwnd is a static function of network congestion
False, cwnd is a dynamic function of perceived network congestion
How does the TCP Congestion algorithm change the congestion window dynamically?
- Slow Start
- Congestion Avoidance
- Fast Retransmit
What happens in Slow Start TCP Congestion Control?
Congestion Window size is increased by one segment per ACK received
Congestion window increases exponentially until first loss event
What happens in Congestion Avoidance for TCP Congestion Control?
Algorithm progressively sets a congestion threshold
What happens in Fast Retransmit for TCP Congestion Control?
When three duplicate ACK’s arrive before timeout expires, retransmit lost segment immediately
