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What's the Difference Between a Packet and a Frame?

Protocol Data UnitLayer 7 Application
Layer 6 Presentation
Layer 5 Session
SegmentLayer 4 Transport
PacketLayer 3 Network
FrameLayer 2 Data Link
BitsLayer 1 Physical

When speaking of the data in a network, people often call everything a packet. A more proper generic term would be protocol data unit or PDU. The specific name for a PDU depends on at what layer the data unit is in the OSI model.

At layer 5, 6, or 7 of the OSI model, the actual construction of the PDU depends upon the specific application. At these levels you could just call the PDU data.

At layer 4, the transport layer of the OSI model, if the protocol stack is TCP, the PDU is called a segment. This is because at the transport layer the data is segmented it into chunks, and a TCP header is added.

At layer 3, the Network layer of the OSI model, if the protocol stack is TCP, the PDU is called a packet. The Network layer encapsulates each TCP segment into an IP packet by adding a header that includes the destination IP address.

At layer 2, the Data Link layer, the PDU is called a frame. The Data Link layer encapsulates one or more packets into a frame by adding the physical address of the source and destination, and adds a frame sequence number.

At layer 1, the Physical layer, the PDU is the bit. The Physical layer is the electronic network circuitry and connection media like fiber optic cable. Its the layer where data is physically moved across the network.

More Networking Protocols and Standards:
• Networking and Internet Standards Organizations
• T-Carrier
• Free eBook: Introduction to 802.11 Wireless
• What's the Difference Between a Packet and a Frame?
• Video - The Upper Layers 5 Through 7 of the OSI Networking Model
• Looking at the OSI 7 Layer Reference Model
• IPv6 Packet Fragmentation
• Link Aggregation
• IPv6 Global Unicast Addresses
• Comparison of the Layers of the OSI and TCP/IP Models

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