2. INTERFACES AND CABLES
SWITCHES provide many PORTS for connectivity (usually 24)
These PORTS tend to be RJ-45 (Registered Jack) ports.
WHAT IS ETHERNET?
- Ethernet is a collection of network protocols/standards.
Why do we need network protocols and standards?
- provide common communication standards over networks.
- provide common hardware standards to allow connectivity between devices.
Connections between devices operates at a set speed.
These speeds are measured in "bits per second" (bps)
A bit is a value of "0" or "1". A byte is 8 bits (0s and 1s)
| Size | # of Bits |
|---|---|
| 1 kilobit (Kb) | 1,000 |
| 1 megabit (Mb) | 1,000,000 |
| 1 gigabit (Gb) | 1,000,000,000 |
| 1 terabit (Tb) | 1,000,000,000,000 |
Ethernet standards are:
- Defined in the IEEE 802.3 standard in 1983
- IEEE = Institute of Electrical and Electronics Engineers
ETHERNET STANDARDS (COPPER)
| Speed | Common Name | Standard | Cable Type | Max Transmission Distance |
|---|---|---|---|---|
| 10 Mbps | Ethernet | 802.3i | 10BASE-T | 100m Max |
| 100 Mbps | Fast Ethernet | 802.3u | 100BASE-T | 100m Max |
| 1 Gbps | Gigabit Ethernet | 802.3ab | 1000BASE-T | 100m Max |
| 10 Gbps | 10 Gigabit Ethernet | 802.3an | 10GBASE-T | 100m Max |
BASE = refers to Baseband Signaling
T = Twisted Pair
Most Ethernet uses copper cables.
UTP or Unshielded Twisted Pair (no metallic shield) Twist protects against EMI (Electromagnetic Interference)
Most use 8 wires (4 pairs) however ...
10/100BASE-T = 2 pairs (4 wires)
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How do devices communicate via their connections?
Each ethernet cable has a RJ-45 plug with 8 pins on the ends.
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- PCs Transmit(TX) data on Pins #1-2
- Switches Receive(RX) data on Pins #1-2
- PCs Receive(RC) data on Pins #3,6
- Switches Transmit(TX) data on Pins #3,6
This allows Full-Duplex transmission of data.
What if a Router / Switch connect?
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- Routers Transmit(TX) data on Pins #1-2
- Routers Receive(RX) data on Pins #3,6
- Switches Transmit(TX) data on Pins #3,6
- Switches Receive(RX) data on Pins #1-2
Routers and PCs connect the same way with Switches.
The cable used to connect is called a "Straight-Through" cable.
What if we want to connect similar devices to each other?
We CANNOT use a "Straight-Through" cable. We MUST use a "Crossover" cable.
This cable swaps the pins on one end to allow connection to work.
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PIN#1 -----> PIN#3 PIN#2 -----> PIN#6
PIN#3 -----> PIN#1 PIN#6 -----> PIN#2
| DEVICE TYPE | TRANSMIT (TX) PINS | RECEIVE (RX) PINS |
|---|---|---|
| ROUTER | 1 and 2 | 3 and 6 |
| FIREWALL | 1 and 2 | 3 and 6 |
| PC | 1 and 2 | 3 and 6 |
| SWITCH | 3 and 6 | 1 and 2 |
Most modern equipment now has AUTO MDI-X which automatically detects which pins their neighbour is transmitting on and adjust the pins they receive data on.
1000BASE-T/10GBASE-T = 4 pairs (8 wires)
Each wire pair is bidirectional so can transmit/receive much faster than 10/100BASE-T.
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Fiber-Optic Connections:
- Defined in the IEEE 802.3ae standard
SFP Transceiver (Small Form-Factor Pluggable) allows fiber-optic cables to connect to switches/routers.
- Have separate cables to transmit / receive.
4 parts to a fiber-optic cable.
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There are TWO types of fiberoptic cable.
Single-Mode:
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- Narrower than multimode
- Lighter enters at a single angle (mode) from a laser-based transmitter.
- Allows longer cables than both UTP and multimode fiber.
- More expensive than multimode fiber (due to more expensive laser-based SFP transmitters)
Multimode:
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- Core is wider than Single-mode
- Allows multiple angles (modes) of light waves to enter core
- Allows longer cables than UTP but shorter than single-mode
- Cheaper than single-mode fiber (due to cheaper LED-based SFP transmitter)
Fiber Optic Standards:
| Speed | Standard | Connection Speed | Mode Support | Max Transmission Distance |
|---|---|---|---|---|
| 1000BASE-LX | 802.3z | 1 Gbps | Multimode / Single | 550 meters (Multi) / 5km (Single) |
| 10GBASE-SR | 802.3ae | 10 Gbps | Multimode | 400 meters |
| 10GBASE-LR | 802.3ae | 10 Gbps | Single | 10 kilometers |
| 10GBASE-ER | 802.3ae | 10 Gbps | Single | 30 kilometers |
UTP vs Fiber-Optic Cabling:
UTP are:
- Lower cost than fiber-optic.
- Shorter maximum distance than fiber-optic (~100m).
- Can be vulnerable to EMI (Electromagnetic Interference).
- RJ45 ports used with UTP are cheaper than SFP ports.
- Emit (leak) a faint signal outside of cable, which can be copied (security risk).
Fiber-Optic:
- Higher cost than UTP.
- Longer maximum distance than UTP.
- No vulnerability to EMI.
- SFP ports are more expensive than RJ45 ports (single-mode is more expensive than multimode).
- Does not emit any signal outside of the cable (no security risk).