Suggest an editImprove this articleRefine the answer for “What errors does the data link layer detect?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**The data link layer** detects errors related to data corruption while a frame is transmitted over the physical medium - in other words, it checks whether the frame arrived without bit errors. **Key point:** the data link layer only detects errors via a checksum (FCS/CRC), it does not correct them or guarantee delivery - that is handled by the transport layer (TCP).Shown above the full answer for quick recall.Answer (EN)Image**The data link layer detects errors related to data corruption while a frame is transmitted over the physical medium**. Briefly and to the point: **L2 checks whether the frame arrived without bit errors**. --- ## Exactly which errors the data link layer detects ### 1. **Bit errors** The most fundamental type. They occur when: - the signal is distorted - interference flips a 0 to a 1 or vice versa The data link layer: - recalculates the checksum (FCS) - compares it with the received one - if they do not match, it considers the frame corrupted --- ### 2. **Frame corruption** If: - part of the frame is lost - the data is altered - the frame arrived incomplete The checksum: - will not match - the frame will be **discarded** --- ### 3. **Loss of frame integrity** The data link layer can detect: - errors in the payload - errors in the frame header Any change to the bits: - results in an FCS error --- ### 4. **Errors related to collisions** *(classic Ethernet)* On networks with CSMA/CD: - collisions corrupted frames - such frames failed the FCS check --- ## Which errors the data link layer does NOT detect Important for an interview: The data link layer: - does not understand logical errors (wrong address, wrong port, wrong protocol) - does not check delivery order - does not guarantee delivery - does not correct errors (it only detects them) Correction and retransmission are handled by: - the transport layer (TCP) - or logic above it --- ## How error detection actually happens Ethernet uses: - **CRC (Cyclic Redundancy Check)** - the value is recorded in the **FCS** field The receiver: 1. recalculates the CRC 2. compares it with the FCS 3. if they do not match: **discards the frame**For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.