internet general working principles

Question 1

which are the components of internet and what do they do

Answer 1

• hosts = end systems = connected computing devices running network apps at Internet’s “edge”
• routers and switches that forward packets (=chunks of data)
• communication links (fiber, copper, radio, satellite)
• network = collection of devices, routers, links, managed by an organization

Question 2

end systems

Answer 2

• they are the network edge
• also colled hosts
• can be client or server
• server are usually in data centers

Question 3

what is the network core?

Answer 3

• interconnected routers
• network of networks

Question 4

network core has 2 functionalities

Answer 4

• forwarding (aka switching, it’s a local action, consists in moving packets arriving in the router input links to the appropriate output link)
• routing (it’s a global action, consists in determining the path taken by packets from source to destination, uses algorihms to find the optimal path)

Question 5

model of a switch

Answer 5

• Each link has its own capacity
• Input packet arrival is
  asynchronous
• Output packets can have a time
  conflict
• Need a buffer to analyze packet header and handle output conflicts
• queues can form if there are input links faster than output links
• if buffer is full we start loosing packets

Question 6

network metrics

Answer 6

• throughput ( = amount of data per second that can be transferred between end systems)
• transmission time ( = time T required to transmit L bits, which depends on the throughput R)

Question 7

different types of delays

Answer 7

• Nodal processing delay = Time required to examine the packet’s header and determine where to direct the packet
• Queuing delay = Waiting time in the queue
• Transmission delay = amount of time required for the router to push out the packet; it is a function of the packet’s length and the transmission rate of the link
• Propagation delay = It is the time W requested to reach the receiver end system from the transmitter. It depends on the distance D [m] and propagation speed v [m/s].
• processing delay (nowadays can be neglected)

Question 8

different transmission logics

Answer 8

• Store-and-forward: the packet must be fully received before being transmitted
• Cut-through: the packet can be transmitted right after the header is decoded