DPNHTW

Welcome to Alaska!By Nicholas

Holley,Travis Warren,& David Paul

This presentation will be “BRRRRRRRy” exciting!

HTTPWait, I’m

confused already.

Alas-wha?HTT-huh?Browsawhoo?

Alaska.gov HTTP Latency is the

between the sending of the get request and the time at which the HTTP response is completely received by the client.

Test one (Chrome): Using wireshark and http 1.1

Total HTTP Time

Summary

Summary (cont.) Just chose to do the first few and total as there are 30+ total http

requests. I measured arrival times between the get and responses.

First GET at: Apr 28, 2013 14:59:41.944717000, response: Apr 28, 2013 14:59:42.660135000. Latency .715 seconds.

GET main2.css at: Apr 28, 2013 14:59:42.448113000 , response: Apr 28, 2013 14:59:42.876539000. Latency .4284 seconds.

GET home.css at: Apr 28, 2013 14:59:42.449129000, response: Apr 28, 2013 14:59:42.873624000. Latency .4245 seconds.

GET jquery.js at: Apr 28, 2013 14:59:42.449517000, response: Apr 28, 2013 14:59:43.248560000. Latency .7990 seconds.

GET soa.js at: Apr 28, 2013 14:59:42.449800000, response: Apr 28, 2013 14:59:42.655950000. Latency .2062 seconds.

Between First get and last 200 OK: 2.881 seconds.

Test 2

Summary

Summary (cont.)

First GET at: Apr 28, 2013 15:47:05.020728000, response: Apr 28, 2013 15:47:06.523220000. Latency 1.5025 seconds.

GET main2.css at: Apr 28, 2013 15:47:05.207500000, response: Apr 28, 2013 15:47:06.440409000. Latency 1.2329 seconds.

GET home.css at: Apr 28, 2013 15:47:06.685392000, response: Apr 28, 2013 15:47:07.631714000. Latency .9463 seconds.

GET jquery.js at Apr 28, 2013 15:47:06.685395000, response: Apr 28, 2013 15:47:08.667395000. Latency 1.982 seconds.

GET soa.js at Apr 28, 2013 15:47:06.969326000, response: Apr 28, 2013 15:47:07.606148000. Latency .6368 seconds.Between First get and last 200 OK: 6.205 seconds. (With favicon)without fav icon (Only used by browser, not part of downloading the site), 5.784

IE had more TCP retransmissions.

Same request could have different retransmissions if sent at multiple different times.

One difference could be that IE waits less time before sending another retransmissionso it sends more before it is sure that all data has been recieved.

DNS

DNS nslookup

The first command tells us the address we received the result from as well as the address of the server www.alaska.gov

The second command tells us the primary name server for alaska.gov

DNS nslookup• This time by

calling nslookup on alaska.gov we get the list of name servers as well as their addresses

DNS Local Network Server

• The highlighted numbers are all the same because the command is retrieving the DNS responses from a local DNS Server

DNS Wireshark

DNS Response• The response for

the DNS query to www.alaska.gov first sends the canonical name for the server, then sends the address for the server

DNS Query

DNS LatencyThe total latency is the difference in

time between the query and the associated response

The result is .334909 seconds for the initial query to www.alaska.gov

Because we only see the results retrieved from the local name server, we cannot see the latency between the intermediate steps

TCP

Compare to TCP Slides

Done at ITS

FIN, ACK RST, ACK

FIN (1 bit) – No more data from sender◦ Serves as a connection termination

RST (1 bit) – Reset the connection

FIN,ACK “[ACK] is the acknowledgement that the previously sent

data packet was received. [FIN] is sent by a host when it wants to terminate the connection; the TCP protocol requires both endpoints to send the termination request”

RST,ACK Either your service is not running on the host, or possibly it

has been firewalled.

Internet Control Message Protocol version 6 (ICMPv6)

HTTP Continuation◦no such thing as an

HTTP Continuation message – this is Wireshark’s way of indicating that there are multiple TCP segments being used to carry a single HTTP message.

TCP Traceroute from New York

ExplanationsRound-trip time (RTT), also called round-trip

delay, is the time required for a signal pulse or packet to travel from a specific source to a specific destination and back again.

But David, I don’t understand! What would even affect the RTT at different times?◦ The data transfer rate of the source's Internet

connection◦ The nature of the transmission medium

(copper, optical fiber, wireless or satellite)◦ The physical distance between the source and the

destination◦ The number of nodes between the source and the

destination