6 - Delay Flashcards
What is ASCII?
American Standard Code for Information Interchange
What are the Internet Protocol Stack layers?
Applic. - message Transp. - segment Net. -datagram Link - frame Physical -bits
Give Application layer examples
HTTP, FTP, SMTP
Transport Layer Examples
TCP, UDP
Netowkr Layer example
IP
Link Layer example
Ethernet
Define Bandwidth
Measure of rate or capcity of a link
What is bandwidth units?
Size/time - bytes/second etc
What are the four types of packet delay?
Transmission
Propagation
Queuing
Processing
Transmission delay
n = packet length (size in bits) B = bandwidth
n/B is time to send
Propagation Delay
n = length of physical link (metres) s = propagation speed in medium (~2x10^8 m/sec)
delay = n/s
Processing delay
check bit errors
Examine packet headers and determine output link
Queuing Delay
Time waiting at output link
If a router puts a 1500Byte packet onto a 10Mb/s link what is the transmission delay?
(15008)/(10^7) = 1.210^-3 s
Transmission delay for 500byte packet on 512kb/s cable?
(5008)/(51210^3) = 7812us
Transmission delay for a 100b packet on a 2Mb/s link?
100/(2x10^6) = 0.00005seconds
Define propagation delay as a concept
The time needed for the signal to travel from one end of the wire to the other
Normally use 2*10^8
Propagation delay on a 100m cable in seconds?
100/(210^8) = 510^-7 seconds
Propagation delay on a 40km fibre?
(4010^3)/(210^8) = 2*10^-4 seconds = 0.2ms
A packet of 650 byte is sent
A-> R = 10Mb/s and 5metres
R -> B = 2Mb/s and 10km
What is the transmission delay at A?
(6508)/(10^7) = 5.210^-4
A packet of 650 byte is sent
A-> R = 10Mb/s and 5metres
R -> B = 2Mb/s and 10km
What is the propagation delay A to R?
5/(210^8) = 2.510^-8 s
A packet of 650 byte is sent
A-> R = 10Mb/s and 5metres
R -> B = 2Mb/s and 10km
What is transmission delay at R?
(6508)/(210^6) = 2.6*10-3s
A packet of 650 byte is sent
A-> R = 10Mb/s and 5metres
R -> B = 2Mb/s and 10km
What is propagation delay at R?
(10^4)/(210^8) = 510^-5 s = 50 micro seconds
What is the formula for Queuing delay?
I/R
I = average num of bits arriving per second
R is bandwidth
if more than 1, cannot function
else there is no queue
traffic intensity
packet length (bits) * average arrival rate all divided by bandwidth in bps
WHat happens to larger messages?
Split into smaller packets
Each packet has a transmission/propagation delay
What is the total delay for larger messages?
one transmission delay for each packet plus the propagation delay for the last
Stop and wait protocol
Next packet cannot be sent until an acknowledgement was received for the current one
RTT
Round Trip Time
delay between sending packet and receiving the acknowledgement
if RTT = 20ms and the 600 packet message uses stop and wait, how long would it need?
20ms x 600 = 12s
If the delay from A to B is 30ms, what is the estimated RTT?
60ms
Throughput
Amount of data per second that can be transferred
L/RTT
Efficiency
Ratio between actual performance and max theoretical performance.
packets of L bits over link of bandwidth R
L/(R*RTT)
