Physical Layer

Moving Bits Across the Wire

24:34

Bit

The smallesr representation of data that a computer can understand; it's a one or zero

Modulation

A way of varying the voltage of this charge moving across the cable

aka. Line Coding

Twisted Pair Cabling and Duplexing

26:53

Duplex Communication

The concept that information can flow in both directions across the cable

≈ Simplex Communication - unidrectional

Full-Duplex - both devices speak at the same time

Half-Duplex - only one device speak at a time

Network Ports and Patch Panels

28:48

Network Ports are generally directly attached to the devices that make up a computer network.

RJ45 Port

• consists of 4 twisted pair cables - 8 cables
• has two LED lights : Link LED, Activity LED
  • Link LED : lights up when two devices that are powered on are properly connected.
  • Activity LED : flashes when data is actively transmitted across the cable
  • Recently internet speeds are so fast that the leds aren't that significant. Depending on its manufacturers, it might mean something else.

Patch Panel

• series of network ports
• containers of end points
• it is then connected to Switches or Routers

Ethernet and MAC Addresses

31:15

CSMA/CD

Used to determine when the communications channels are clear, and when a device is free to transmit data

MAC Address (Media Access Control Address)

A globally unique identifier attached to an individual network interface. It's 48-bit number normally represented by six groupings of two hexadecimal numbers.

Octet

In computet networking, any number that can be represented by 8 bits.

Hexadecimals can also be represented in octets.

• First Half of 48 Bits : OUI
• Second Half of 48 Bits : Vendor Assigned (NIC cards, Interfaces)

Organizationally Unique Indentifier (OUI)

The first three octets of a MAC address

These are assigned to individual manufacturers by the IEEE.

We can always identify the manufacturers of a network interface purely by its MAC address.

Last three octets of MAC address can be assigned in the way that the manufacturers would like with the condition that they assign each possible address once to keep all MAC Address globally unique.

Ethernet uses MAC address to ensure that the data it sends has both an address for the machine that sent the transmission, as well as the one the transmission was intended for.