HW2 Answers
1.
Layer
Example
Application
HTTP, email
Transport
TCP, UDP
Network
Routers, IP, Packets
Data Link
Frames, Switches, Ethernet
Physical
Hubs, NICS, Cable, UTP
Description
The application layer protocol
that powers the web. The
network process to application
and provides services that can
be used by other applications.
Ensures that messages are
delivered error-free, in
sequence, and with no loses or
duplications. Transmits data
using transmission protocols.
Can offer reliability,
detect/recover from errors, and
provide flow controls.
Address the use signaling to
transmit bits. Start path
determination. Provides
connectivity and path selection
between two end systems.
Router live here.
Provides reliable transfer of
data across media. Responsible
for physical addressing,
network topology, error
notification and flow control.
Uses signaling to transmit bits.
Concerned with the
transmission and reception of
the uninstructed row bit stream
over the physical medium.
2. A web client (i.e., browser) will initiate a reliable connection (TCP connection) with a
web server. The client will then send an HTTP request for a particular webpage or web
resource to the server. The server will respond with the requested object, if found. This
process may need to be repeated several times until all of the embedded resources on
a web page have been delivered to the client.
Request

A request line to get a required resource, for example a request GET
/fac/lpress/demo.htm is requesting a resource called /fac/lpress/demo.htm from
the server.



Headers (Example – Accept-Language: EN).
An empty line.
A message body which is optional.
Response




HTTP Status Code HTTP/1.1 200 OK (has not moved)
Headers (Example – Content-Type: html)
An empty line.
A message body which is optional.
All the lines should end with a carriage return and line feed. The empty line should only
contains carriage return and line feed without any spaces.
a) What is the URL of the document requested by the browser?

/fac/lpress/demo.htm
b) What browser does run on the client?

Mozilla/4.0
c) What web server does the server use?

Microsoft-IIS/6.0
d) How big is the returned document?

142
e) When was the returned document last modified?

Fri, 01 Jul 2005 06:25:24 GMT
f) What port does the Web server listen on for clients’ requests?

Default port for html 80



Host A to Host B: SYN seqno [w=1]
Host B to Host A: SYN/ACK seqno [x=1] ackno [y=2346 (2345+1)]
Host A to Host B: ACK ackno [z= 7778 (7777+1)
3.
4.
a. How many assignable IP addresses are there?
a. 1022
b. What is the assignable IP address range?
a. 168.2.44.1 to 168.2.47.255
c. What is the subnet mask?
a. 22 = 255.255.252.0
5.
Channel partitioning: Multiple-access method in which the available bandwidth of link is shared
in time, frequency, or through code. Divide channel into pieces (time slots, frequency). Allocate
piece to node for exclusive use. Share channel efficiently at high load.
Random Access: Allow collisions and recover from collisions. Efficient at low load, single node
can fully utilize channel. High load, collision overload. Has the right to the medium without
controlled by any other station.
Token ring: IEEE 802.5, shared ring medium and all nodes see all frames. A special 3 byte
pattern circulates around the ring perpetually and represents the "right to transmit". A station
cannot send unless it has been authorized by other stations.