What Does the Data Link Layer Do in Computer Networks? | Lec-22

TL;DR

The data link layer handles hop-to-hop delivery while also providing flow, error, and access control between consecutive network nodes. It is the second OSI layer from the bottom, positioned between the network and physical layers, and uses methods such as Stop-and-Wait, Go-Back-N, Selective Repeat, CRC, CSMA/CD, and ALOHA. Read on to understand how each responsibility supports reliable node-to-node communication.

Transcript

Hello friends, Welcome to Gate Smashers the topic is data link layer and data link layer in OSI model is 2nd layer from bottom. You can also call it as a layer in between network layer and physical layer. It takes data from network layer and provides data to physical layer and then the physical layer sends that data further in the network so that i... Read More

Key Insights

• The data link layer is the second layer from the bottom of the OSI model, located between the network layer and the physical layer. It receives data from the network layer and supplies that data to the physical layer for further transmission.
• Hop-to-hop delivery is the primary responsibility of the data link layer. It moves a message from one node or router to the next node, while the network layer handles the broader task of moving data from the original source to the final destination.
• Communication within one network can be provided by the data link layer using a MAC address or physical address. When data must cross different networks, routers connect those networks, and the message advances through consecutive hops before reaching the receiver.
• Flow control is the process of regulating how quickly a source sends messages to the next node. It prevents a router or other node from becoming filled with messages when the sender produces data faster than the receiving node can accommodate.
• Data-link flow control operates from node to node, while transport-layer flow control operates from source to destination. The data link layer considers the capacity of each intermediate node, whereas the transport layer considers the capacity and message acceptance of the final destination machine.
• Stop-and-Wait, Go-Back-N, and Selective Repeat are three algorithms used for flow control at the data link layer. These methods regulate transmission across individual hops so that messages can move through intermediate nodes without exceeding their receiving capacity.
• Error control at the data link layer detects errors on individual hops, including single-bit changes and burst errors involving multiple bits. Detecting an error at an intermediate node can reduce the distance traveled before the damaged message must be sent again.
• Access control determines how multiple devices use a shared communication channel within a network. Methods named for this responsibility include CSMA/CD, Ethernet, ALOHA, Slotted ALOHA, Token Ring, and Token Bus, particularly when several devices connect through one high-bandwidth wire.

Questions & Answers

Q: What does the data link layer do in computer networks?

The data link layer provides hop-to-hop, or node-to-node, delivery across each consecutive link in a message’s path. It also performs flow control, error control, and access control. Within one network, it can support communication using MAC addresses, also called physical addresses.

Q: Where is the data link layer located in the OSI model?

The data link layer is the second layer from the bottom of the OSI model. It sits between the network layer and the physical layer, taking data from the network layer and providing it to the physical layer for transmission.

Q: What is hop-to-hop delivery in the data link layer?

Hop-to-hop delivery means moving a message from one node or router to the next node along its route. The data link layer manages each consecutive link rather than the complete journey from the original source to the final destination.

Q: How does the data link layer support communication within a LAN?

Within one network or LAN, the data link layer can provide communication between connected devices. It uses a MAC address, also called a physical address, to support this local delivery.

Q: How does flow control work at the data link layer?

Flow control regulates the speed at which a sender transmits messages to the next node. It prevents a router or other node from becoming filled when messages arrive faster than its buffer can accommodate.

Q: Which flow-control algorithms does the data link layer use?

The three identified flow-control algorithms are Stop-and-Wait, Go-Back-N, and Selective Repeat. They regulate transmission between nodes so the sender does not overwhelm the next node’s receiving capacity.

Q: How does data-link flow control differ from transport-layer flow control?

Data-link flow control operates node to node and considers the capacity of each intermediate node. Transport-layer flow control operates from the source to the final destination and considers the destination machine’s capacity and ability to accept messages.

Q: What error-control and access-control methods are associated with the data link layer?

CRC is associated with data-link error checking, including detecting single-bit and burst errors. Access-control methods for shared channels include CSMA/CD, Ethernet, ALOHA, Slotted ALOHA, Token Ring, and Token Bus.

Summary & Key Takeaways

• The data link layer is the second layer from the bottom of the OSI model, positioned between the network and physical layers. It accepts data from the network layer and passes it to the physical layer. Its central delivery responsibility is moving data between consecutive nodes or hops along a communication path.

• Flow control at the data link layer prevents a node from receiving messages faster than its capacity allows. It operates separately on each hop, unlike transport-layer flow control, which considers the final destination. Stop-and-Wait, Go-Back-N, and Selective Repeat are identified as important algorithms for controlling this node-to-node message flow.

• Error control allows intermediate nodes to detect damaged data before it travels all the way to the destination. CRC is associated with data-link error checking, while checksum is associated with transport-layer checking. Access control addresses shared-channel communication through methods including CSMA/CD, ALOHA, Slotted ALOHA, Token Ring, and Token Bus.