CST 311 Week 7

 Down to The Wire - Link Layer

Nearing the end of the journey in learning about networks, we are down to the wire. The link layer is the last layer where computer science logic applies. Below lies the physical layer; a savage realm of cables, connectors, and raw materials. To the hardware folks out there, I'm joking! Hardware requires the convergence of different disciplines like physics, chemistry, computer science and engineering.

What Does The Link Layer Do?

Think of the link layer like local streets and roads that connect neighborhoods to the main highway. It moves data from one device to another within the same network segment, eventually connecting to the broader network. The link layer is responsible for moving data across a single link at a time, ensuring that data is properly packaged, accessed, and delivered between directly connected devices.

Here’s a closer look at what the link layer does:

• Framing: The link layer puts the data from the network layer into units called frames. Frames contain the data and a header, which has extra information needed to help manage the data.
• Link Access: The link layer uses a set of rules called the Medium Access Control (MAC) protocol. These rules decide how devices share the same channel and avoid getting in each other's way when sending data.
• Reliable Delivery: The link layer can ensure that data is sent correctly without any errors. This is especially useful for unreliable links, where mistakes are more likely to happen.

Error Detection and Correction

When data is being sent, bits can get lost or changed by mistake. The link layer uses tools like Parity Checks and Cyclic Redundancy Checks (CRC) to detect and correct these errors, ensuring that the data stays accurate.

Ethernet and CSMA/CD

One of the most common link-layer technologies is Ethernet, which uses a method called CSMA/CD (Carrier Sense Multiple Access with Collision Detection). This helps devices detect if another device is sending data. If a collision happens, the devices will stop, wait, and try again later, making data transfer more efficient.

Wrap Up

The link layer is crucial for making sure data moves reliably from one point to another in a network. It manages how data is packaged, accessed, and checked for errors so that everything moves smoothly. Understanding the link layer is key to knowing how data travels across networks and how everything stays connected.