Single-mode fiber, multimode fiber, copper

📘 CCNA 200-301 v1.1

1.3 Compare Physical Interface and Cabling Types

1.3.a – Single-mode fiber, Multimode fiber, Copper

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.

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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.

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2. Multimode Fiber (MMF)

Definition:

By Original by Bob Mellish, SVG derivative by Benchill – derivative work by uploader, CC BY-SA 3.0, https://commons.wikimedia.org/w/index

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.

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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.

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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

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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.

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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.

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✅ Summary for CCNA 200-301

Media Type	Medium	Signal Type	Typical Use	Distance	Connector
SMF	Glass (9 µm)	Laser	Long-distance WAN or backbone	Up to 40 km+	LC/SC
MMF	Glass (50/62.5 µm)	LED	Short-distance LAN/campus	Up to 550 m	LC/SC
Copper	Twisted copper wires	Electrical	Device-to-switch connections	Up to 100 m	RJ-45

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