Suggest an editImprove this articleRefine the answer for “What is a segment (segment)?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**A segment** is a unit of data at the transport layer (L4). The transport layer transmits data between applications precisely in the form of segments. A segment is a piece of application data packaged by the transport layer for transmission over the network. **Key point:** a segment is encapsulated into an IP packet, and routers work with packets, not with segments.Shown above the full answer for quick recall.Answer (EN)Image**A segment** is a **unit of data at the transport layer (L4)**. It is precisely in the form of segments that the transport layer transmits data **between applications**. In short: **a segment is a piece of application data packaged by the transport layer for transmission over the network**. --- ## Why a segment is needed Applications often transmit **large amounts of data**. The transport layer does not send it all at once, instead it: - splits the data into **small parts** - packages each part as a **segment** - sends the segments over the network - **reassembles** the data on the receiver's side --- ## What a segment consists of A segment consists of two parts: ### 1. The transport layer header It holds service information, for example: - source port - destination port - service fields (numbers, flags, and so on) The header is needed to: - deliver data to the **right application** - manage the transfer --- ### 2. The payload This is: - the application's data - the reason the whole transfer happens --- ## Segments and protocols Important for the interview. - **TCP**: - uses segments - a segment contains: - sequence numbers - acknowledgments - service flags - provides reliability - **UDP**: - also transmits data in segments (often called a "UDP datagram") - without acknowledgments or ordering --- ## Relationship to other layers When data is transmitted: - **Transport layer** → segment - **Network layer** → packet - **Data link layer** → frame - **Physical layer** → bits Each layer adds its own header. --- ## What is important to remember - a segment is **L4** - a segment is **encapsulated** into an IP packet - routers work with packets, **not with segments** - a segment exists only **between the end nodes** --- ## In short, for the interview > **A segment** is a unit of data at the transport layer, containing an L4 header and application data, used to transmit information between applications in an end-to-end connection.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.