This document provides an overview of a presentation on HTTP latency and DNS lookups in Alaska. It includes the results of tests measuring HTTP response times for various resources on Alaska's website using Chrome and IE browsers. It also demonstrates DNS queries and lookups using nslookup and Wireshark. The results show latency variations between browsers and differences in TCP retransmissions between IE and Chrome. Round-trip times are also measured for traceroutes between New York and Alaska.

1. Welcome to Alaska!
 By Nicholas Holley,
 Travis Warren,
 & David Paul
 This presentation
will be
“BRRRRRRRy”
exciting!

3. HTTP
 Wait, 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

5. Total HTTP Time

6. Summary

7. 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.

8. Test 2

9. Summary

10. 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
retransmission
so it sends more before it is sure that all
data has been recieved.

11. DNS

12. 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

13. DNS nslookup
• This time by
calling nslookup
on alaska.gov we
get the list of
name servers as
well as their
addresses

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

15. DNS Wireshark

16. 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

17. DNS Query

18. DNS Latency
 The 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

19. TCP

21. Compare to TCP Slides

22. Done at ITS

23.  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.

24.  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.

25. TCP Traceroute from New
York

26. Explanations
 Round-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