Terminology » Networking Basics » Segments, Packets, and Frames: Understanding Networking Data Units

Segments, Packets, and Frames: Understanding Networking Data Units

networking tcp/ip data unit segment packet frame data encapsulation

This article breaks down the differences between segments, packets, and frames in networking.

Segment vs Packet vs Frame Figure-1: Depicts simple TCP/IP stack with 5 layers.

Figure 1 illustrates a simplified TCP/IP stack with its five layers. Let’s explore how data transforms as it moves through these layers:

  • Segment: Data originating from the Application layer is divided into smaller segments by the Transmission Control Protocol (TCP). The size of these segments is determined by the Maximum Segment Size (MSS), which reflects the transport layer’s capacity. Each segment is assigned a unique sequence number. This segmentation happens at Layer 4 (Transport Layer).

  • Packet: These segments are then encapsulated with an IP header, typically ranging from 20 to 60 bytes in size. This IP header contains essential information such as the source and destination IP addresses, as well as the protocol field. This encapsulation occurs at Layer 3 (Network Layer), and the resulting data unit is called a packet.

  • Frame: At Layer 2 (Data Link Layer), a header and trailer are added to the Layer 3 packet. The header typically includes the source and destination MAC addresses, along with a type field. The trailer contains a Cyclic Redundancy Check (CRC) field, used for error detection. This complete unit is known as a frame.

In summary, the key distinction lies in the layer at which each data unit is formed and the specific header/trailer information added at each stage.