Transport Layer Flashcards
Implications of best effort
drop messages, out of order messages, duplicates, finite message size, delays
End to end services
guarantee message delivery, in order, at most 1 copy, large messages, synchonization, receive flow control sender, multiple application processes on hosts
How can processes on different systems get the right messages?
Ports
Ports
numeric locators which enable messages to be demultiplexed to proper process
Ports are typically implemented as
messages queues
Simplest function of the transport layer
multiplexing/demultiplexing of messages
transport layer functions
connection control, error detection, in order delivery, flow control, congestion control
What is UDP?
user datagram protocol
unreliable unordered datagram service
Does UDP have flow or congestion control?
No
Does UDP have reliability?
optional checksum
What does UDP do?
adds multiplexing/demultiplexing
How are end points identified in the transport layer?
Ports
What does the UDP demultiplexer do?
extends host-to-host delivery service of the underlying network into a process-to-process communication service
UDP Checksum computer over?
UDP header + body + pseudoheader
What does the UDP psuedoheader consist of?
Protocol number (UDP or TCP), IP src, IP dst, UDP length
What is TCP?
2 way, reliable, byte stream oriented end-to-end protocol
TCP Features:
Connection oriented, full duplex, flow control, congestion control, byte stream, reliable data transfer
what is in the acknowledgement field?
next expected bye in reverse direction
advertised winow
amount of room to receive data
Each connection identified with a 4-tuple
SrcPort, SrcIpAddr, DsrPort, DestIPAddr
Sequence numbers
each packet has a sequence number, wrap around supported, initial number selected at connection time
ACK indicates what?
next bye expected
TCP’s sliding window serves what purposes?
1) guarantees reliable delivery of data
2) ensures in order delivery
3) enforces flow control between sender and receiver
window
upper bound on unACKed frames
