1. Application Layer Part 1
Daniel Graham PhD

2. Application Layer
Our Goals:

3. Examples of Application Layer

4. Creating a network App application transport network data link
physical
application
transport
network
data link
physical
application
transport
network
data link
physical

5. Application Architectures

6. Client Server Architecture

7. Pure P2P Architectures
peer-peer

8. Hybrid client-server/P2P

9. Process Communication
application
application
controlled by
app developer
process
process
transport
transport
network
controlled
by OS
network
link
Internet
link
physical
physical
Application Layer

10. Process Communication

11. Address Processing

12. Application Layer Protocol Define

13. Transport service requirements: common apps
application
file transfer
Web documents
real-time audio/video
data loss
no loss
loss-tolerant
throughput
elastic
audio: 5kbps-1Mbps
video:10kbps-5Mbps
time sensitive no
yes, 100’s msec
Application Layer

14. Web and HTTP www.someschool.edu/someDept/pic.gif path name host name
Application Layer

15. HTTP overview PC running Firefox browser server running Apache Web
iphone running
Safari browser
Application Layer

16. HTTP overview (continued)
Application Layer

17. HTTP connections
Application Layer

18. Nonpersistent HTTP suppose user enters URL: time
time
Application Layer

19. Non-persistent HTTP: response time
Application Layer

20. Persistent HTTP
non-persistent HTTP issues:
persistent HTTP:

21. HTTP request message GET /index.html HTTP/1.1\r\n
Host: www-net.cs.umass.edu\r\n
User-Agent: Firefox/3.6.10\r\n
Accept: text/html,application/xhtml+xml\r\n
Accept-Language: en-us,en;q=0.5\r\n
Accept-Encoding: gzip,deflate\r\n
Accept-Charset: ISO ,utf-8;q=0.7\r\n
Keep-Alive: 115\r\n
Connection: keep-alive\r\n
\r\n

22. HTTP request message: general format
method sp
URL sp
version cr lf cr lf
value
header field name ~ ~ cr lf
value
header field name cr lf ~
entity body ~
Application Layer

23. Uploading form input
Application Layer

24. Method types
HTTP/1.0:
HTTP/1.1:
Application Layer

25. HTTP response message HTTP/1.1 200 OK\r\n
Date: Sun, 26 Sep :09:20 GMT\r\n
Server: Apache/ (CentOS)\r\n
Last-Modified: Tue, 30 Oct :00:02 GMT\r\n
ETag: "17dc6-a5c-bf716880"\r\n
Accept-Ranges: bytes\r\n
Content-Length: 2652\r\n
Keep-Alive: timeout=10, max=100\r\n
Connection: Keep-Alive\r\n
Content-Type: text/html; charset=ISO \r\n
\r\n
data data data data data ...
Application Layer

26. HTTP response status codes
200 OK
301 Moved Permanently
400 Bad Request
404 Not Found
505 HTTP Version Not Supported

27. Trying out HTTP (client side) for yourself
1. Telnet to your favorite Web server:
For Macs you will have
to brew install telnet
telnet 80
2. type in a GET HTTP request:
GET /~dgg6b/ HTTP/1.1
Host:
3. look at response message sent by HTTP server!
(or use Wireshark to look at captured HTTP request/response)

28. User-server state: cookies
example:
many Web sites use cookies
four components:
Application Layer

29. Cookies: keeping “state” (cont.)
client
server
ebay 8734
Amazon server
creates ID
1678 for user
create
entry
cookie file
ebay 8734
amazon 1678
backend
database
cookie-
specific
action
access
cookie-
specific
action
access
one week later:
ebay 8734
amazon 1678

30. Cookies (continued) what cookies can be used for: how to keep “state”:
aside
what cookies can be used for:
cookies and privacy:
cookies permit sites to learn a lot about you
how to keep “state”:
Application Layer

31. Lets Build a webserver Live coding