2. ICC Module 3 Lesson 4 – Networking 1 / 8 © 2015 Ph. Janson Information, Computing & Communication Networking – Clip 4 – Switching School of Computer Science & Communications Ph. Janson, W. Zwaenepoel

3. ICC Module 3 Lesson 4 – Networking 2 / 8 © 2015 Ph. Janson Outline ►Computer communication basics  Clip 1 – Protocols & messages Clip 1  Clip 2 – Protocol layers Clip 2  Clip 3 – Protocol encapsulation Clip 3  Clip 4 – Switching Clip 4 ►Internet basics  Clip 5 – Internet topology & interfaces Clip 5  Clip 6 – Internet addressing & routing Clip 6  Clip 7 – Internet route calculation Clip 7  Clip 8 – Internet protocols Clip 8 ►Computer network paradigms  Clip 9 – Network paradigms Clip 9 Intro clipPrevious clipNext clip

4. ICC Module 3 Lesson 4 – Networking 3 / 8 © 2015 Ph. Janson Layer 3: Switching The case of telephony ►Information throughput / flow is quasi constant over time time throughput

5. ICC Module 3 Lesson 4 – Networking 4 / 8 © 2015 Ph. Janson ►One builds and reserves a dedicated electronic connection between speakers ►The connection is busy during the entire conversation time, incl. silences Layer 3: Circuit switching The case of telephony circuit avec reserved capacity C C time throughput

6. ICC Module 3 Lesson 4 – Networking 5 / 8 © 2015 Ph. Janson Layer 3: Circuit switching The case of telephony SDM = space-division multiplexing of physical circuits (analog telephony) TDM = time-division multiplexing of physical circuits (digital / mobile phones) FDM = frequency-division multiplexing of physical circuits (radio, TV) In all cases the reservation of the circuit blocks it (the line is busy)

7. ICC Module 3 Lesson 4 – Networking 6 / 8 © 2015 Ph. Janson Layer 3: Switching The case of computer networks ►Information flow is asymmetrical, jerky, with variable-intensity bursts separated by “silences” time throughput

8. ICC Module 3 Lesson 4 – Networking 7 / 8 © 2015 Ph. Janson Layer 3: Packet switching The case of computer networks ►Reserving high-throughput circuits would be inefficient ►Reserving low-throughput circuits would be slow ►One does not reserve any circuits; instead one sends information in high-speed “packets” ►Lines and switches remain free for other packets during “silences” Which throughout to consider? In any case it is inefficient time throughput

9. ICC Module 3 Lesson 4 – Networking 8 / 8 © 2015 Ph. Janson Payer 3: Packet switching The case of computer networks B A D B BC A B C B D BC C ►Modelled after the postal instead of the telephone system => Packets can get lost or arrive out of order Protocols (e.g. retransmission) are there to accommodate such “hiccoughs” and it even works for telephony (Skype)