Networking stuff

1. Questions & Exercises
(Chapter 1)

2. Question 1
What is the difference of between connection-oriented and connectionless delivery services?
 Connection-oriented service involves the creation and termination of the
connection for sending the data between two or more devices.
 In contrast, connectionless service does not require establishing any connection
and termination process for transferring the data over a network
Answer

3. Question 2
List four Internet access technologies.
Answer
 Digital subscriber line (DSL)
 Cable Internet access (TV cable)
 Fiber to the home (FTTH)
 Cellular 4G

4. Question 3
What are the main categories of communication physical media? Give examples of each one
Answer
guided media and unguided media
- Guided media include:
- fiber-optic cable,
- twisted-pair copper wire (unshielded twisted pair (UTP), shielded twisted pair (STP))
- coaxial cable
- Unguided media: electromagnetic waves (radio waves, infrared waves, …)

5. Question 4
What are the two approaches to moving packets in networks?
Answer
circuit switching and packet switching
 In circuit-switched networks, a connection (i.e., a physical path) is first
established between source and destination, then data is exchanged following
the same path. Once data exchange is finished, the connection is torn down.
Connection establishment means that the resources needed along a path
(buffers, link transmission rate) to provide for communication between the end
systems are reserved for the duration of the communication session between
the end systems. Tearing a connection down means releasing the reserved
resources.

6.  In packet-switched networks, there is no connection establishment or resource
reservation, rather data chunks or packets are provided with the destination
address, and packets might follow different paths to the destination depending
on the resources available to routers that process the packets.

7. Question 5
What are the main functions of a packet switch (a router)? Explain.
Answer
There are two main functions: packet forwarding and routing.
Packet Forwarding means that a packet switch moves a packet arriving on one
of its attached links to an appropriate output of its attached links.
Routing means determining the appropriate (or least-cost, or good) path that
packets follow from a source to a destination.

8. Exercise 6
Suppose there is exactly one packet switch between a sending host and a receiving host. The
transmission rates between the sending host and the switch and between the switch and the
receiving host are R1 and R2, respectively. Assuming that the switch uses store-and-forward
packet switching, what is the total end-to-end delay to send a packet of length L? (Ignore
queuing, propagation delay, and processing delay.)
Answer
 the end-to-end delay is L/R1 + L/R2
 At time t0 the sending host begins to transmit. At time t1 = L/ R1, the sending host
completes transmission and the entire packet is received at the router (no
propagation delay). Because the router has the entire packet at time t1, it can begin
to transmit the packet to the receiving host at time t1. At time t2 = t1 + L/ R2, the
router completes transmission and the entire packet is received at the receiving host.
Thus, the end-to-end delay is L/R1 + L/R2

9. Question 7
When does packet queuing occur?
Answer
when an output link onto which arriving packets need to be transmitted is found
busy with the transmission of another packet (this queuing happens on output
links of a router, however, queuing might occur on input links of a router).
Generally, Queueing occurs when packets arrive faster than they can be
serviced.

10. Question 8
When does packet loss occur?
Answer
When buffers are completely full (or even in some situation before they become
full as to make storage space available to important packets).

11. Exercise 9
Consider sending a packet from a source host to a destination host over a fixed route. List
the delay components in the end-to-end delay. Which of these delays are constant and
which are variable?
Answer
The delay components are: processing delays, transmission delays, propagation
delays, and queuing delays.
All of these delays are fixed (for a given packet and distance), except for the
queuing delays, which are variable.

12. Exercise 10
How long does it take a packet of length 1,000 bytes to propagate over a link of distance 2,500
km, propagation speed 2.5 x 108 m/s, and transmission rate 2 Mbps? More generally, how long
does it take a packet of length L to propagate over a link of distance d, propagation speed s
Answer
2,500 km / 2.5 x 108 [m/s] = 2500000 / 2.5 x 108 = 10 [ms]
d/s where d is the distance between the sender and receiver, and s is the
propagation speed.

13. Suppose Host A wants to send a large file to Host B. The path from Host A to
Host B has three links, of rates R1 = 500 kbps, R2 = 2 Mbps, and R3 = 1 Mbps.
a) Assuming no other traffic in the network, what is the throughput for the file
transfer?
Min (R1, R2, R3) = 500 kbps
b) Suppose the file is 4 million bytes. Dividing the file size by the throughput,
roughly how long will it take to transfer the file to Host B?
(4000000 * 8) / 500000= 64 [s]
Exercise 11