The Physical Layer

Physical Layer

• 
• Responsible for getting bits from one place to another.
• The physical layer comprises the devices on a network and the cables used to connect them together.

Coaxial Cables

• 
• A centre core conductor lies within a shield separated by an air gap.
• Typically used for video, cable TV and broadband.

Twisted Pairs

• 
• Also known as CAT 5/6.
• Typically used for carrying audio and HDMI video over long distances.

Noise Rejection

• 
• Electromagnetic noise is present almost everywhere.
• Unshielded Twisted Pairs rely solely on noise rejection properties of twisted pairs.
• Shielded Twisted Pairs have an additional grounded shield to reduce noise.

Straight and Crossovers

• 
• Straight-through cables connect PCs to a hub or switch.
• AKA Patch cable.
• Crossover cables connect PCs to each other.

Connectors

• 
• Cables can be terminated into a:
• RJ45 Connector
• RJ45 Wall Socket
• Patch Panel

Ethernet

• Almost all Ethernet is based on twisted pair cabling.
• Ethernet (10 Mbps) - original standard
• Fast Ethernet (100 Mbps) - still common
• Gigabit Ethernet (1 Gbps) - new standard