In OSI 7 layer model, the Physical layer defines the Networking hardware pertaining to transmitting the electrical (or optical) signals. A major component in this layer is the physical medium that carries the data. This Physical medium is typically a Network cable with appropriate connector.
Digital & Analog Signaling:
Digital: Data is transmitted in pulses (electrical signals on/off)
Analog: Data is transmitted through continues wave with variations in amplitude, frequency and Phase.
Baseband & Broadband Signaling:
Baseband: This is the common signaling mechanism in LAN. It uses a single channel to transmit digital signals.
Boradband: Uses multiple channels to transmit Analog signals with varying frequency. It can carry voice,data and video.
Network Cables
Four major types:
- Coaxial
- Twinaxial
- Twisted Pair
- Fiber Optic
- Coaxial
Construction:
Single, solid copper wire core, surrounded by an insulator (Teflon or Plastic), braided metal shielding and metal foil wrap, all covered with Plastic sheath.
Usage:
Broadband networks, Satellite and Cable TV Receivers
Advantages:
Durable construction.
Less Electro Magnetic and Radio Frequency interference
Two types:
-
Thick Net
Also known as RG8 or RG11. Uses a screw type connector known as Attachment Unit Interface (AUI)
-
Thin Net
Uses BNC connector (Bayonet Neill-Concelman connector). Also known as RG58
- Twinaxial
Construction:
Similar to Coaxial but has two solid copper wire cores.
Usage:
SAN (Storage Area Network) and to connect critical routers and switches.
Advantages:
Very high throughput over short distance (10Gbits/Sec).
Lower Transceiver latency.
Lower Power Consumption.
Lower Bit Error Ration
- Twisted Pair
Construction:
Consists of four pairs of copper wire that are twisted together. Tighter the twisted pair, better the transmission speed.
It can be shielded (STP) or unshielded (UTP). UTP is more common because it is less expensive.
Usage:
Ethernet, Analog phone lines.
Advantages:
Cheap, Easy maintenance, light.
Cable types:
| Category | Data Type | Speed |
| Cat 1 | Voice only | – |
| Cat 2 | Data | 4 Mbits/Sec (Token Ring Networks) |
| Cat 3 | Data and Voice | 10 Mbits/Sec (Ethernet) |
| Cat 4 | Data | 20 Mbits/Sec |
| Cat 5 | Data | 100 Mbits/Sec (Ethernet) |
| Cat 5e | Data | 1000 Mbits/Sec at 100 MHz (Ethernet) |
| Cat 6 | Data | 1000 Mbits/Sec at 250 MHz (Ethernet) |
| Cat 6a | Data | 10 Gbits/Sec at 500 MHz (Ethernet) |
| Cat 7 | Data | 10 Gbits/Sec at 600 MHz, upto 100 meters (Ethernet) |
| Cat 7a | Data | 100 Gbits/Sec at 1000 MHz upto 15 meters (Ethernet |
Connector types:
RJ11 – Used for analog telephone lines
RJ45 – Used for Ethernet
RJ49 – Use for ISDN (Integrated Services Digital Network) and WAN interfaces
- Fiber Optic
Construction:
Glass core surrounded by cladding and protected by PVC or Teflon outer sheath. Fiber Optic cable carries data as light signals rather than electrical signals.
The cable is terminated with SC, ST or LC type connectors.
It can be shielded (STP) or unshielded (UTP). UTP is more common because it is less expensive.
Usage:
FDDI and Backbone Networks.
Advantages:
High Speed. Resistance to interception and interference. Long Distances.
Ethernet Designations:
Ethernet designations identifies the characteristics of the Network
Consider couple of examples as shown below.
- 10Base-2
- 10 refers to the speed, i.e 10 MBits/Sec
- Base refers to the band, i.e Baseband
- 2 refers to the maximum distance this cable supports, i.e 200 meters
- 100Base-T
- 100Mbits/Sec
- BaseBand
- Twisted Pair cable
- 100Base-F
- 100MbitsSec
- BaseBand
- Fiber Optic Cable
EMI (Electro Magnetic Interference)/RFI (Radio Frequency Interference) resistance rating
The following table shows the EMI/RFI rating for various types of cables
| Cable | EMI/RFI Resistance |
| Coaxial Thinnet | Good |
| Coaxial Thicknet | Better |
| Twisted Pair UTP (Unshielded) | Poor |
| Twisted Pair UTP (Shielded) | Fair to Good |
| Fiber Optic | Best |