RFC 1106 (rfc1106) - Page 2 of 13
TCP big window and NAK options
Alternative Format: Original Text Document
RFC 1106 TCP Big Window and Nak Options June 1989
over high bandwidth*delay networks is still very poor. It appears
that no algorithm changes alone will make any significant
improvements over high bandwidth*delay networks, but will require an
extension to the protocol itself. This RFC discusses two possible
options to TCP for this purpose.
The two options implemented and discussed in this RFC are:
1. NAKs
This extension allows the receiver of data to inform the sender
that a packet of data was not received and needs to be resent.
This option proves to be useful over any network path (both high
and low bandwidth*delay type networks) that experiences periodic
errors such as lost packets, noisy links, or dropped packets due
to congestion. The information conveyed by this option is
advisory and if ignored, does not have any effect on TCP what so
ever.
2. Big Windows
This option will give a method of expanding the current 16 bit (64
Kbytes) TCP window to 32 bits of which 30 bits (over 1 gigabytes)
are allowed for the receive window. (The maximum window size
allowed in TCP due to the requirement of TCP to detect old data
versus new data. For a good explanation please see [2].) No
changes are required to the standard TCP header [6]. The 16 bit
field in the TCP header that is used to convey the receive window
will remain unchanged. The 32 bit receive window is achieved
through the use of an option that contains the upper half of the
window. It is this option that is necessary to fill large data
pipes such as a satellite link.
This RFC is broken up into the following sections: section 2 will
discuss the operation of the NAK option in greater detail, section 3
will discuss the big window option in greater detail. Section 4 will
discuss other effects of the big windows and nak feature when used
together. Included in this section will be a brief discussion on the
effects of congestion versus noise to TCP and possible options for
satellite networks. Section 5 will be a conclusion with some hints
as to what future development may be done at NASA, and then an
appendix containing some test results is included.
2. NAK Option
Any packet loss in a high bandwidth*delay network will have a
catastrophic effect on throughput because of the simple
acknowledgement of TCP. TCP always acks the stream of data that has
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