What we’ve learned so far Ch. 6 Ch. 7 Ch. 8 Ch. 10 Ch. 11

Where we are now

What’s next? Layer 2: Network Interface – How to use the physical media to send packets?

Packets and Frames

5 Circuit Switching Circuit switching: Establishing a physical path between a sender and a receiver

6 Circuit Switching Three-step process analogous to placing a phone call – a circuit is established between two parties – the two parties use the circuit to communicate – the two parties terminate use

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Manual service exchanges To connect the call, an operator plug the ringing cord into the jack on the switchboard of the requested number

Electromechanical switches Telephones were equipped with a dial by which a caller transmitted the destination telephone number to the automatic switching system. 9

Digital switches 10 Nowadays, instead of having each circuit corresponding to a physical path, multiple circuits are multiplexed over shared media – Virtual circuit The interior of a modern telephone system is digital

11 Packet Switching Divide each message into blocks of data that are known as packets Chief advantage: the lower cost – To provide communication among N computers A circuit-switched network: at least N/2 independent paths A packet-switching network: only requires one path that is shared

12 Packet Switching A packet switching system uses statistical multiplexing

13 Packet Identification & MAC Addresses Each packet specifies an intended recipient with an identifier. – Demultiplexing uses the identifier known as an address. IEEE (Institute for Electrical and Electronic Engineers) allocates a unique address for each piece of network interface hardware, i.e., a network interface card (NIC) Media Access Control (MAC) address – A computer may have multiple MAC addresses depending on how many network interface cards it has.

14 48 bits in hexadecimal number

15 MAC Addresses Composition – Vendor ID + NIC ID VV:VV:VV:NN:NN:NN – IEEE assigns a vendor ID Organizationally Unique ID (OUI) – The vendor assigns a unique NIC value to each device

Exercise: Find MAC address of your computer 1.Start Command Prompt (Start  Run  cmd) and type ipconfig /all 2.Do a google search to find the vendor name of the NIC of your computer