Chapter 1

Question 1

What is a network protocol?

Answer 1

A network protocol is a set of rules that define the format and order of messages exchanged between two or more communicating entities, as well as the actions taken on message transmission and reception.

Question 2

What is store-and-forward transmission

Answer 2

each packet switch receives an entire packet before forwarding it to the next hop.

Question 3

How is transmission delay in a packet-switched network calculated?

Answer 3

Transmission delay is the time required to push all bits of a packet onto the link and is calculated as:

TransmissionDelay = PacketLength(L)inbits/TransmissionRate(R)inbitspersecond

• For example, if a 1000-bit packet is transmitted on a 10 Mbps link, the transmission delay is 100 µs.

Question 4

Why does queueing delay occur in packet-switched networks?

Answer 4

Queueing delay occurs when a packet arrives at a router that is already processing other packets. It has to wait in a buffer (queue) until earlier packets are transmitted.

Question 5

What factors influence queueing delay in a packet-switched network?

Answer 5

• Traffic load – Higher traffic increases waiting time.
• Link capacity – If the link is slow, packets take longer to process.
• Packet arrival rate – If packets arrive faster than they can be transmitted, the queue builds up.

Question 6

Why does packet loss occur in a packet-switched network?

Answer 6

Packet loss occurs when a router’s buffer (queue) is full and cannot store any more packets, causing new incoming packets to be dropped.

Question 7

How do routing protocols impact forwarding?

Answer 7

Routing protocols (such as OSPF, BGP) help determine optimal paths for packets by exchanging information between routers. This information is used to update forwarding tables, ensuring packets take efficient routes.

Question 8

What are the four main components of end-to-end delay in a packet-switched network?

Answer 8

• Processing delay – Time for routers to process the packet header.
• Queueing delay – Time waiting in the router’s queue.
• Transmission delay – Time to push the packet onto the link.
• Propagation delay – Time for the packet to travel across the physical link.

Question 9

What are Access ISPs and what role do they play in the Internet?

Answer 9

Access ISPs provide end users (homes, businesses, and institutions) with connectivity to the Internet through wired or wireless technologies.

Question 10

What are Regional ISPs, and how do they fit into the Internet structure?

Answer 10

Regional ISPs connect multiple Access ISPs and provide an intermediate level of connectivity between Access ISPs and Tier-1 ISPs.

Question 11

What are Tier-1 ISPs, and why are they important?

Answer 11

Tier-1 ISPs (e.g., AT&T, Level 3) form the backbone of the Internet, interconnecting large regions and countries. They do not pay other ISPs for connectivity but instead peer with each other.

Question 12

What are Internet Exchange Points (IXPs)?

Answer 12

IXPs are physical locations where multiple ISPs interconnect to exchange traffic efficiently, reducing reliance on Tier-1 ISPs.

Question 13

What are Content Provider Networks, and how do they influence Internet traffic?

Answer 13

Companies like Google, Netflix, and Facebook build their own private networks to deliver content efficiently by bypassing traditional ISPs and connecting directly to IXPs and access ISPs.

Question 14

How do content providers reduce costs in the Internet structure?

Answer 14

By peering directly with ISPs and using CDNs (Content Delivery Networks) to cache content closer to users, reducing transit costs and improving speed.

Question 15

What are the types of delay in a packet-switched network?

Answer 15

Processing Delay, Queuing Delay, Transmission Delay, and Propagation Delay

Question 16

What is Processing Delay?

Answer 16

Time taken by a router to examine a packet’s header and determine where to forward it.

Question 17

What is Queuing Delay?

Answer 17

Time a packet spends waiting in a router’s queue before being transmitted.

Question 18

What is Transmission Delay

Answer 18

Time required to push all the packet’s bits onto the link.

Question 19

What is Propagation Delay

Answer 19

Time for a bit to travel from the sender to the receiver over the physical medium.

Question 20

Under what conditions does Processing Delay become more prominent?

Answer 20

Significant when packets require deep inspection or filtering (e.g., firewalls).

Question 21

Under what conditions does Queuing Delay become more prominent?

Answer 21

High when traffic intensity (utilization) is high and link congestion occurs.

Question 22

Under what conditions does Transmission Delay become more prominent?

Answer 22

Higher for large packets on low-bandwidth links.

Question 23

Under what conditions does Propagation Delay become more prominent?

Answer 23

Dominates in long-distance links (e.g., satellite communication).

Question 24

How is traffic intensity defined, and how does it relate to queuing delay?

Answer 24

-Traffic Intensity (I) = (La) / R, where:
L = packet length (bits)
a = average packet arrival rate (packets/sec)
R = transmission rate

-Relation to Queuing Delay:
If I < 1, queuing delay is low.
If I approaches 1, queuing delay increases significantly.
If I > 1, the queue builds up indefinitely, leading to packet loss.

Question 25

How is the end-to-end delay calculated in a packet-switched network?

Answer 25

End-to-End Delay = N * (d_proc + d_queue + d_trans + d_prop) Where: N = number of network nodes d_proc = processing delay d_queue = queuing delay d_trans = transmission delay d_prop = propagation delay

Question 26

How does the traceroute tool work under the hood?

Answer 26

- Sends ICMP or UDP packets with increasing TTL (Time-To-Live) values. - Each router that receives the packet decreases TTL by 1. - When TTL reaches 0, the router sends back an ICMP Time Exceeded message. - This allows measuring the round-trip time (RTT) to each router along the path.

Question 27

What is throughput?

Answer 27

The actual rate at which data is transferred over a network.

Question 28

What is Instantaneous Throughput?

Answer 28

Rate at a given moment.

Question 29

What is Average Throughput?

Answer 29

Rate over a long period.

Question 30

What is a Bottleneck Link

Answer 30

The slowest link in the network path that limits throughput.

Question 31

What is End-to-End Throughput determined by?

Answer 31

Determined by the link with the smallest bandwidth capacity.

Question 32

What is a layered architecture in computer networks?

Answer 32

A structured design where network functions are divided into separate layers. Each layer provides services to the layer above.

Question 33

What are the layers of the Internet protocol stack?

Answer 33

Application Layer, Transport Layer, Network Layer, Link Layer, and Physical Layer

Question 34

What does The Application Layer do?

Answer 34

Provides network services to applications (e.g., HTTP, SMTP, FTP).

Question 35

What does The Transport Layer do?

Answer 35

Ensures data delivery between hosts (TCP for reliability, UDP for speed).

Question 36

What does The Network Layer do?

Answer 36

Routes data packets between networks (IP addressing and routing).

Question 37

What does The Link Layer do?

Answer 37

Moves packets between directly connected nodes (Ethernet, Wi-Fi).

Question 38

What does The Physical Layer do?

Answer 38

Transmits raw bits over physical media (fiber, copper, radio waves).

Question 39

What is encapsulation in the Internet layered architecture?

Answer 39

- The process of adding headers and sometimes trailers as data moves down the protocol stack. - Each layer packages data from the layer above it into a protocol data unit (PDU). - Example: An HTTP message (Application Layer) → Encapsulated in a TCP segment (Transport Layer) → Placed inside an IP packet (Network Layer) → Sent as an Ethernet frame (Link Layer).

Question 40

Describe the encapsulation process in the Internet protocol stack.

Answer 40

- Application Layer – Generates data (e.g., an HTTP request). - Transport Layer – Wraps it into a segment (adds TCP/UDP headers). - Network Layer – Wraps the segment into a packet (adds IP headers). - Link Layer – Encapsulates the packet into a frame (adds MAC addresses). - Physical Layer – Converts the frame into bits for transmission. -The process is reversed at the destination (de-encapsulation).

Question 41

How is Propagation Delay calculated?

Answer 41

Propagation Delay = distance between routers / speed of the link

Question 42

How is Queuing Delay caclulated?

Answer 42

Queuing Delay = (N-1)L/2R - where N is the number of packets in the system.