Network communication depends on physical cables that connect devices such as routers, switches, servers, and end-user computers. In CCNA, you must understand the three main types of physical media:
Single-mode fiber (SMF)
Multimode fiber (MMF)
Copper cables (Twisted-pair cables like Ethernet cables)
Each cable type is designed for different distances, speeds, and environments. Let’s explain each in detail.
1. Single-Mode Fiber (SMF)
Definition:
Single-mode fiber uses a very thin glass core (about 9 microns in diameter) that allows only one light signal (mode) to travel through the cable.
Key Points:
Uses laser light as the light source (because lasers are focused and powerful).
Designed for long-distance communication — often used in WANs, data centers, or between buildings.
Provides very high bandwidth and low signal loss (attenuation).
Characteristics:
Property
Description
Core size
~9 microns
Light source
Laser
Distance range
Up to 40 km or more (depending on equipment)
Speed
1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps, and beyond
Color of jacket (outer cover)
Yellow (for identification)
Cost
More expensive than MMF (laser-based transceivers are costly)
Usage Example in IT:
Connecting two core switches between data centers several kilometers apart.
Internet Service Providers (ISPs) use SMF to link their main network backbone connections.
2. Multimode Fiber (MMF)
Definition:
Multimode fiber uses a larger glass core (about 50 or 62.5 microns in diameter) that allows multiple light signals (modes) to travel through it at the same time.
Key Points:
Uses LED light sources instead of lasers.
Designed for shorter distances — typically within a building or campus.
Multiple light paths (modes) can cause signal dispersion, meaning the light signals spread out and lose clarity over longer distances.
Characteristics:
Property
Description
Core size
50 or 62.5 microns
Light source
LED
Distance range
Up to 550 meters (depending on standard and speed)
Speed
1 Gbps, 10 Gbps, 40 Gbps (short-range)
Color of jacket
Orange (OM1/OM2) or Aqua (OM3/OM4)
Cost
Cheaper than SMF (LED equipment is cheaper)
Usage Example in IT:
Connecting switches in the same building (for example, between floors).
Server rooms and local data centers where high speed is needed but distance is limited.
3. Copper Cables (Twisted-Pair Ethernet Cables)
Definition:
Copper cables use electrical signals (not light) to transmit data through pairs of twisted copper wires.
Key Points:
Used for short-distance connections, such as connecting computers to switches or switches to routers.
Most common type in LAN environments.
Twisting helps reduce electromagnetic interference (EMI) from nearby cables or devices.
Main Types of Twisted-Pair Cables:
Type
Full Name
Shielding
Typical Use
Max Distance
UTP
Unshielded Twisted Pair
No shielding
Office networks, general use
100 meters
STP
Shielded Twisted Pair
Has foil/braided shielding
High-interference environments
100 meters
S/FTP
Shielded/Foiled Twisted Pair
Extra shielding per pair
Data centers, sensitive equipment
100 meters
Cable Categories (Ethernet Standards):
Category
Speed
Max Distance
Common Use
Cat5e
Up to 1 Gbps
100 m
Common in small offices
Cat6
Up to 10 Gbps (short distance ~55m)
100 m
Modern LANs
Cat6a
10 Gbps
100 m
High-speed networks, data centers
Cat7/Cat8
40 Gbps (short distance)
30–50 m
Specialized or backbone cabling
Connector Type:
RJ-45 connector is used at the ends of copper Ethernet cables.
Color of Jacket:
Varies (blue, gray, yellow, etc.) — no standard color like fiber optic cables.
4. Comparing the Three Cable Types
Feature
Single-Mode Fiber
Multimode Fiber
Copper (Twisted Pair)
Medium
Glass
Glass
Copper wire
Signal type
Light (Laser)
Light (LED)
Electrical
Distance
Long (up to 40 km+)
Medium (up to 550 m)
Short (up to 100 m)
Bandwidth
Very High
High
Limited
Interference
Immune
Immune
Prone to EMI
Cost
Expensive
Moderate
Cheap
Common Use
WAN links, long-distance connections
LAN or campus backbone
End-user connections, LAN
Connector
LC or SC
LC or SC
RJ-45
5. Connectors Used in Fiber Optic Cables
Connector
Description
LC (Lucent Connector)
Small form factor; common in modern networks
SC (Subscriber Connector)
Push-pull design; older but still in use
ST (Straight Tip)
Used in older fiber systems (twist-and-lock style)
For CCNA exam purposes, remember LC and SC are most common today.
6. Key Points to Remember for the Exam
Single-mode fiber = Laser, long distance, small core (9 µm), yellow cable.
Multimode fiber = LED, short distance, large core (50/62.5 µm), orange or aqua cable.
Copper = Electrical signals, short range (up to 100 m), uses RJ-45 connectors.
Fiber = immune to EMI, Copper = affected by EMI.
SMF used in WAN or backbone, MMF used in LAN/campus, Copper used for end devices.
Know cable categories (Cat5e, Cat6, Cat6a) and maximum speeds/distances.
