📘 CCNA 200-301 v1.1

1.3 Compare physical interface and cabling types

1.3.b – Connections (Ethernet Shared Media and Point-to-Point)

This topic explains how network devices are physically connected to each other in Ethernet networks.
It focuses on two types of connections:

1. Ethernet Shared Media
2. Point-to-Point Connections

Let’s understand both in detail.

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🧩 1. Ethernet Shared Media

Definition

A shared media connection means multiple devices share the same physical communication channel to send and receive data.

In simple terms — many devices are connected to the same network segment, and only one device can send data at a time.

How It Works

In shared media:

• All devices are connected to the same collision domain.
• Data sent by one device is “heard” by all others on that medium.
• If two devices send data at the same time, their signals collide (called a collision).
• Devices then use a method called CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to manage and recover from collisions.

CSMA/CD Process

1. Carrier Sense – Device checks if the cable is free (no other device is sending data).
2. Multiple Access – Many devices share the same connection.
3. Collision Detection – If two devices send data at the same time, they detect the collision.
4. Backoff – Each device waits for a random time and then tries again.

Shared Media Devices

• Hubs (Layer 1 devices): All ports share the same bandwidth.
• Bus topology networks (older networks using coaxial cables).
• Half-duplex connections (only send or receive, not both at the same time).

Shared Media Limitations

• Collisions: Reduce performance.
• Lower throughput: Because devices share bandwidth.
• Half-duplex only.
• Not scalable: More devices = more collisions.

Modern Use

• Not used in modern LANs anymore.
• Replaced by switches, which create point-to-point connections and eliminate collisions.

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🔗 2. Point-to-Point Connections

Definition

A point-to-point connection means a dedicated link between two network devices only.

For example:
A switch connected directly to another switch, or a router connected to a switch, using one cable — no other device shares that link.

How It Works

• Only two devices are on the link.
• No collisions, because no other device shares the cable.
• Supports full-duplex communication (both devices can send and receive data at the same time).

Point-to-Point Devices

• Switch-to-switch connections.
• Router-to-switch connections.
• Router-to-router connections (for WAN links).
• Access point-to-switch uplinks.

Duplex Modes

Mode	Description
Half-duplex	Data flows in one direction at a time. Used in shared media.
Full-duplex	Data can flow both ways at the same time. Used in point-to-point.

Modern Ethernet always uses full-duplex because of point-to-point connections.

Advantages

• No collisions.
• Faster performance (dedicated bandwidth per device).
• More secure (no one else “listens” on the same line).
• Easier troubleshooting.

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⚙️ Comparison Table

Feature	Shared Media	Point-to-Point
Number of devices per segment	Multiple devices share the same cable	Only two devices connected
Collision Domain	One large collision domain	Each link has its own collision domain
Duplex Mode	Half-duplex	Full-duplex
Performance	Slower due to collisions	Faster due to dedicated link
Media Access Control	Uses CSMA/CD	No CSMA/CD needed
Devices used	Hubs, coaxial cable networks	Switches, routers, fiber or Ethernet cables
Modern Use	Outdated	Standard in all modern networks

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💡 Exam Tips (CCNA 200-301 Focus)

1. Shared Media = Hubs = Collisions = Half-Duplex.
2. Point-to-Point = Switches = No Collisions = Full-Duplex.
3. CSMA/CD is used only in shared Ethernet (not in switched Ethernet).
4. Modern Ethernet networks use point-to-point links with switches.
5. Remember that each switch port creates its own collision domain.

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🧠 Key Terms to Remember

Term	Meaning
Collision Domain	Area where data collisions can occur.
Broadcast Domain	Area where broadcast frames are forwarded. (Not directly related here, but useful for exam context.)
Half-Duplex	Can send or receive, not both simultaneously.
Full-Duplex	Can send and receive data at the same time.
CSMA/CD	Method to detect and recover from collisions in shared media.

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🖧 Example in IT Context (No Non-IT Analogies)

• In an old network, multiple computers connected to a hub shared the same bandwidth. If one sent a large file, others had to wait — that was shared media.
• In a modern network, each computer connects to its own switch port. Each connection is independent and full-duplex — that’s point-to-point.

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✅ Summary

Concept	Shared Media	Point-to-Point
Connection Type	Many-to-one (shared cable)	One-to-one (dedicated cable)
Collisions	Yes	No
Duplex	Half	Full
Devices	Hubs, old Ethernet	Switches, routers, APs
Common Today?	No	Yes