What Happens on the LAN? — TechKnowSurge

About this interactive

On a hub, everything one device sends reaches every other device, so if two devices send at the same moment their signals collide. Ethernet expects this and handles it with CSMA/CD: carrier sense, multiple access, collision detection. Multiple access: many devices share the same network. Carrier sense: before sending, a device listens, and if someone else is sending, it waits. Collision detection: if a device detects a collision while sending, it stops. Both frames are ruined, no matter who started first, and both must be sent again. Each device then picks a random number and counts down. The one with the smaller number sends first; the other, when its count ends, hears the line in use and waits until it is free. If both waited the same fixed time, they would just collide again. A broadcast is a frame for every device on the network. Its destination is the MAC address FF:FF:FF:FF:FF:FF, all 1s, and every device that receives it processes it. The area where devices can collide is a collision domain. Replacing the hub with a switch does away with collisions (each device gets its own link to the switch), and with much of the security worry of a hub. Broadcasts remain: a switch still sends them out of every port. A local area network is all the devices that reach each other directly like this, and it ends at the router. Collisions and broadcasts stop there. That is why networks are split into LANs: one network the size of the internet would drown in broadcasts. Count the LANs by counting the networks each router separates.

What you'll learn

Predict what happens on a hub when devices talk at once: carrier sense before sending, collision detection, and a random backoff before trying again
Predict how far a broadcast and a collision reach: every device on the LAN, stopping at the router that marks the LAN's edge

Aligned to

Cisco CCNA

1.13 Describe switching concepts

CompTIA Network+

1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.

1.6 Compare and contrast network topologies, architectures, and types.

Cisco CCST Networking

1.1 Identify the fundamental conceptual building blocks of networks

1.3 Differentiate between LAN, WAN, MAN, CAN, PAN, and WLAN

CompTIA A+ Core 1

2.7 Compare and contrast Internet connection types, network types, and their features.

Key terms

Carrier Sense Multiple Access with Collision Detection: The media access control method used in traditional Ethernet where devices listen before transmitting and detect collisions if two devices transmit simultaneously, then retransmit after a random backoff period. CSMA/CD is defined for half-duplex Ethernet and is not used in full-duplex switched networks.
Random Backoff Algorithm: A collision recovery mechanism in which each device waits a randomly selected period of time before attempting to retransmit, reducing the chance of repeated collisions.
Collision Domain: A network segment where data packets can collide with each other when transmitted simultaneously.
Broadcast: A transmission type in which one device sends a single packet that is delivered to every other device on the local network segment simultaneously. Broadcast traffic is contained within a broadcast domain and does not cross router boundaries.
Local Area Network: A network that connects devices within a limited geographic area such as a home, office floor, or building, where all devices share the same broadcast domain and communicate at high speeds with low latency. A router defines the boundary of a LAN by separating it from other networks.
Broadcast Domain: A network segment in which a broadcast sent by one device is received by all other devices within that segment; routers define the boundaries of broadcast domains by not forwarding broadcast traffic.
Router: A network device that forwards data packets between networks based on IP addresses.
Switch: A network device that connects devices within a LAN and forwards traffic based on MAC addresses.
Half Duplex: A communication mode that allows data to be transmitted in both directions but only one direction at a time.

Topics

Carrier Sense Multiple Access With Collision Detection Collision Domain Broadcast Local Area Network Interactive Predict

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