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 Fox
