Frame

Definition

A Frame is the Protocol Data Unit (PDU) at the Data Link Layer (Layer 2). It is formed when an IP packet is combined with a Layer 2 header and trailer (Ethernet information).

What Problem It Solves

It allows data to be delivered correctly within a local network (LAN) using MAC addresses and provides error detection for reliable transmission over a single hop.

What Happens If Not Used

Without frames, devices on a local network would not know how to format data for transmission or detect errors, leading to unreliable or failed communication.

Easy Wording

A frame is a packet wrapped with Ethernet information so it can travel inside a local network.

Layman Example

It’s like putting a letter (packet) into an envelope that also includes sender/receiver details and a seal for checking if it was damaged.

Technical Example

At Layer 2 (Ethernet):

• An IP packet is received from Layer 3
• An Ethernet header is added:
• Source MAC address
• Destination MAC address
• Type field
• An Ethernet trailer is added:
• FCS (Frame Check Sequence) for error detection The result is called an Ethernet Frame, which is sent over the local network to the next device (switch, router, or host).