1. COMPUTER NETWORKS
CS610
Lecture-21
Hammad Khalid Khan

2. Review Lecture 21 Virtual Private Networks (VPNs)
Guaranteeing Absolute Privacy
Service Paradigm
Connected-Oriented Service
Connectionless Service
Address and Connection Identifiers

3. Network Performance Characteristics Delay Throughput

4. Delay Important quantitative property of networks.
Delay is a measure of how long it takes for a bit of data to travel across the network from one computer to the other.
Measured in seconds or fractions of seconds (milliseconds).
Maximum and Average Delay.

5. Types of Delay Propagation delay - time to travel across medium.
Switching delay - time for network. component (hub, bridge, packet switch) to forward data.
Access delay - time to get control of medium (CSMA/CD, token).
Queuing delay - time enqueued in packet switches.

6. Throughput
Throughput is a measure of the rate at which data can be sent through the network.
The throughput capability of the underlying hardware is called bandwidth.

7. Throughput
Because each frame contain headers the effective throughput is less than the hardware bandwidth.
Networking professional often use the term speed as a synonym for throughput.

8. Relationship between Delay and Throughput
If a packet switch had a queue of packets waiting when a new packet arrives the new packet will be placed on the ail of the queue and will need to wait while the switch forward the previous packets.
D = D0
(1-U)
D = Effective Delay
D0 = Delay when the network
is idle
U = Value between 1 and denoting the current utilization

9. Relationship between Delay and Throughput
Throughput and delay are not completely independent.
As traffic in a computer network increase, delays increase; a network that operates at close to 100% of its throughput capacity experiences severe delay.

10. Delay-Throughput Product
Computed as delay time multiplied by effective throughput.
Measures amount of data that can be present in the network.
In fast networks with long delay times, sending computer can generate large amounts of data before destination receives first bit.

11. Jitter The amount of delay that a network introduces.
A network with zero jitter takes exactly the same amount of time to transfer each packet.
A network with high jitter takes much longer to deliver some packets than others.

12. Summary Delay Throughput Relationship between Delay and Throughput
Delay-Throughput Product
Jitter