Network Layer Header Management

The Network Layer data unit, the packet, carries a Network Layer header which must serve many purposes.

The NL header is created in the source node, examined (and possibly modified) in intermediate nodes, and removed (stripped off) in the destination node.

The Network Layer headers typically contain (note that not all NL protocols will require or implement all of these fields or responsibilities):

• The source and destination node addresses,
• Packet size, if packets may be of more than one size,
• Message number, and possibly packet number within that message,
• Several control bits indicating if the packet is a 'user-data' packet or a control packet, whether or not fragmented, fixed or variable length,
• Flow control information, such as permission to send additional messages, or flags to change the rate of flow, and
• The packet priority.

Finally, the data portion (the payload) of the packet includes the 'user-data', control commands or network-wide statistics.