Suggest an editImprove this articleRefine the answer for “What is a frame?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**A frame** is the unit of data transmission at the data link layer (L2), packaged according to that layer's rules for transmission within a single network. **Key point:** a frame exists only within a single local network, and when it passes through a router, the old frame is discarded and a new one is created.Shown above the full answer for quick recall.Answer (EN)Image**A frame** is the **unit of data transmission at the data link layer (L2)**. It is data **packaged according to the rules of the data link layer** so it can be transmitted **within a single network**. Simply put: **a frame is an "envelope"** in which the data link layer places data and writes **who it is from and who it is going to**. --- ## Why a frame is needed The physical layer can only transmit **bits (0 and 1)**. A frame is needed to: - know **where the data starts and where it ends** - indicate **who the data is intended for** - check **whether it got corrupted along the way** --- ## What a frame consists of (using Ethernet as an example) A typical frame contains: 1. **Destination MAC address** who the frame is sent to 2. **Source MAC address** who sent the frame 3. **Data type** what is inside (for example, an IP packet) 4. **Payload** higher-level data (usually an IP packet) 5. **Checksum (FCS)** error check --- ## What is inside a frame Inside a frame there is usually: - a **network-layer packet (IP packet)** The data link layer **does not analyze** this packet: it simply **carries it**. --- ## An important distinction for an interview - **Bit** - physical layer - **Frame** - data link layer - **Packet** - network layer A very common mistake is confusing a frame with a packet. --- ## Where a frame "lives" - a frame exists **only within a single local network** - when passing through a router: - the old frame **is discarded** - a **new frame** is created for the next network --- ## Simple analogy Mail: - a frame is a **box with addresses** - an IP packet is the **letter inside** - the road is the **physical layer** --- ## Short answer for an interview > **A frame** is a data-link-layer unit of data that contains MAC addresses, service information, and a payload, and is used to transmit data within a single network.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.