1. Suppose that web browsers at 128.255.23.45 port 52000, 129.129.100.200 port 5

Question

1. Suppose that web browsers at 128.255.23.45 port 52000, 129.129.100.200 port 55900, and 130.57.56.60 port 62222 open concurrent, persistent connections to a public web server at 173.194.77.103, and suppose further that these are the web server’s only connections.
(a) List the inbound (client-server) and outbound (server-client) four-tuple labels for any one of these three web server connections.

(b) How many sockets will be in use by the web server once the three connections have been set up? To how many ports are these sockets bound? Justify your answers.

(c) Is it possible for the web browser at 128.255.23.45 to open a second, parallel connection to the web server from port 52000? What about the web browser at 130.57.56.60?

Explanation / Answer

Considering TCP as the protocol used for communication between server and client,

(a) Inbound(Client-server)

The tuple is formed of five elements:

(protocol, source IP address, source port, destination IP address, destination port)

So, considering connection between web browser 128.255.23.45:52000 and web server 173.194.77.103:80

(TCP, 128.255.23.45, 52000, 173.194.77.103, 80) , since the default port of HTTP is 80 and given in the question that the conection is between a web browser and web server, so HTTP protocol is used for web pages communication.

Similarly, you can try other web browser as the source and rest will be same, considering TCP is the protocol and destination port as 80.

Outbound (Server-client):

(TCP, 173.194.77.103, 80, 128.255.23.45, 52000) in the same way as the logic described above.

(b) 1 socket will be in use by the web server

IP address + port number = socket; since the web server is using only one port number i.e 80 and one IP address i.e. 173.194.77.103 for all the three connections to the web browser.

The socket on Web server is bound to 3 ports on the three different web browsers.

128.255.23.45 + 52000 = 1 socket

129.129.100.200 + 55900 = 1 socket

130.57.56.60 + 62222 = 1 socket

So, in total 3 sockets of web browser are bounded to one socket of web server.

(c) It is completely possible to open a second, parallel connection to the web server from a web browser

There are list of browser that support parallel connection:

Browser    HTTP/1.1    HTTP/1.0

IE 6,7         2                  4

IE 8            6          6

Firefox 2    2                 8

Firefox 3    6                 6

For complete list please refer to web. So, it depends completely on the web browser for a second, parallel connection.

All the three web browsers mentioned in the question can have a second, parallel connection to the web server.

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