5.3. Packet Size and Overhead
5.3. Packet Size and Overhead
Some readers will worry about the increase in packet size due to new headers, padding, and the Message Authentication Code (MAC). The minimum packet size is in the order of 28 bytes (depending on negotiated algorithms). The increase is negligible for large packets, but very significant for one-byte packets (telnet-type sessions). There are, however, several factors that make this a non-issue in almost all cases:
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The minimum size of a TCP/IP header is 32 bytes. Thus, the increase is actually from 33 to 51 bytes (roughly).
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The minimum size of the data field of an Ethernet packet is 46 bytes [RFC0894]. Thus, the increase is no more than 5 bytes. When Ethernet headers are considered, the increase is less than 10 percent.
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The total fraction of telnet-type data in the Internet is negligible, even with increased packet sizes.
The only environment where the packet size increase is likely to have a significant effect is PPP [RFC1661] over slow modem lines (PPP compresses the TCP/IP headers, emphasizing the increase in packet size). However, with modern modems, the time needed to transfer is in the order of 2 milliseconds, which is a lot faster than people can type.
There are also issues related to the maximum packet size. To minimize delays in screen updates, one does not want excessively large packets for interactive sessions. The maximum packet size is negotiated separately for each channel.