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Chapter 1 Flashcards

(42 cards)

1
Q

What is a network protocol?

A

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.

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2
Q

What is store-and-forward transmission

A

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

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3
Q

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

A

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.
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4
Q

Why does queueing delay occur in packet-switched networks?

A

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.

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5
Q

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

A
  • 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.
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6
Q

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

A

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

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7
Q

How do routing protocols impact forwarding?

A

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.

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8
Q

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

A
  • 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.
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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

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

A

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.

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12
Q

What are Internet Exchange Points (IXPs)?

A

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

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13
Q

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

A

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.

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14
Q

How do content providers reduce costs in the Internet structure?

A

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

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15
Q

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

A

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

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16
Q

What is Processing Delay?

A

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

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17
Q

What is Queuing Delay?

A

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

18
Q

What is Transmission Delay

A

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

19
Q

What is Propagation Delay

A

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

20
Q

Under what conditions does Processing Delay become more prominent?

A

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

21
Q

Under what conditions does Queuing Delay become more prominent?

A

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

22
Q

Under what conditions does Transmission Delay become more prominent?

A

Higher for large packets on low-bandwidth links.

23
Q

Under what conditions does Propagation Delay become more prominent?

A

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

24
Q

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

A

-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.

25
How is the end-to-end delay calculated in a packet-switched network?
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
26
How does the traceroute tool work under the hood?
- 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.
27
What is throughput?
The actual rate at which data is transferred over a network.
28
What is Instantaneous Throughput?
Rate at a given moment.
29
What is Average Throughput?
Rate over a long period.
30
What is a Bottleneck Link
The slowest link in the network path that limits throughput.
31
What is End-to-End Throughput determined by?
Determined by the link with the smallest bandwidth capacity.
32
What is a layered architecture in computer networks?
A structured design where network functions are divided into separate layers. Each layer provides services to the layer above.
33
What are the layers of the Internet protocol stack?
Application Layer, Transport Layer, Network Layer, Link Layer, and Physical Layer
34
What does The Application Layer do?
Provides network services to applications (e.g., HTTP, SMTP, FTP).
35
What does The Transport Layer do?
Ensures data delivery between hosts (TCP for reliability, UDP for speed).
36
What does The Network Layer do?
Routes data packets between networks (IP addressing and routing).
37
What does The Link Layer do?
Moves packets between directly connected nodes (Ethernet, Wi-Fi).
38
What does The Physical Layer do?
Transmits raw bits over physical media (fiber, copper, radio waves).
39
What is encapsulation in the Internet layered architecture?
- 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).
40
Describe the encapsulation process in the Internet protocol stack.
- 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).
41
How is Propagation Delay calculated?
Propagation Delay = distance between routers / speed of the link
42
How is Queuing Delay caclulated?
Queuing Delay = (N-1)L/2R - where N is the number of packets in the system.