Suggest an editImprove this articleRefine the answer for “What is a packet?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**A packet** is the unit of data transmission at the network layer (L3). It is in the form of packets that data is transmitted between different networks. **Key point:** a packet is data packaged according to the rules of the network layer so that it can be routed.Shown above the full answer for quick recall.Answer (EN)Image**A packet** is the **unit of data transmission at the network layer (L3)**. It is in the form of packets that data is transmitted **between different networks**. Short version: **a packet is data packaged according to the rules of the network layer so that it can be routed**. --- ## Why a packet is needed The data link layer can only deliver data **inside a single network**. A packet is needed to: - transmit data **through several networks** - indicate the **IP address of the sender and the receiver** - allow routers to decide **where to send the data next** --- ## What a packet consists of ### 1. **Packet header (IP header)** The service part, which contains: - the source IP address - the destination IP address - routing information - auxiliary fields (for example, TTL, protocol type) Routers analyze **only the header**, not the data itself. --- ### 2. **Payload** Inside a packet is data from the **transport layer**: - a TCP segment or UDP datagram - application data (indirectly, inside the segment) The network layer: - **does not check** the content of this data - **does not guarantee** its delivery --- ## What is important to understand - a packet is **L3** - a packet **does not contain MAC addresses** - a packet can be: - transmitted - fragmented - dropped by a router --- ## Relationship with other layers - transport layer → segment - **network layer → packet** - data link layer → frame - physical layer → bits During transmission: - the packet stays the same - frames change at every segment of the network --- ## What a packet does NOT do Important for an interview A packet: - does not guarantee delivery - does not control speed - does not track transmission order - does not correct errors That is handled by the **transport layer**. --- ## In short, for an interview > **A packet** is a unit of network layer data containing an IP header and a payload, used for transmitting data between networks and for routing.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.