What's the Difference Between a Packet and a Frame?
By Stephen Bucaro
| Protocol Data Unit | Layer 7 Application |
| Layer 6 Presentation |
| Layer 5 Session |
| Segment | Layer 4 Transport |
| Packet | Layer 3 Network |
| Frame | Layer 2 Data Link |
| Bits | Layer 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:
• How to Set Up FTP (File Transfer Protocol)
• Understanding IP Routing
• Networking and Internet Standards Organizations
• IEEE 802.11.x Wireless Standards
• Networking Routing Believability and Administrative Distance
• Internet Protocol versions IPv4, IPv5 and IPv6
• IPv6 Global Unicast Addresses
• T-Carrier - A Complete and Comprehensive Guide
• OSI Transport Layer
• An Introduction to the Types of VPNs
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