< draft-irtf-dtnrg-sdnv-02.txt		draft-irtf-dtnrg-sdnv-03.txt >
	Network Working Group W. Eddy		Network Working Group W. Eddy
	Internet-Draft Verizon		Internet-Draft Verizon
	Intended status: Informational May 22, 2009		Intended status: Informational August 18, 2009
	Expires: November 23, 2009		Expires: February 19, 2010
	Using Self-Delimiting Numeric Values in Protocols		Using Self-Delimiting Numeric Values in Protocols
	draft-irtf-dtnrg-sdnv-02		draft-irtf-dtnrg-sdnv-03
	Status of this Memo		Status of this Memo
	This Internet-Draft is submitted to IETF in full conformance with the		This Internet-Draft is submitted to IETF in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
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	skipping to change at page 1, line 32 ¶		skipping to change at page 1, line 32 ¶
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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	This Internet-Draft will expire on November 23, 2009.		This Internet-Draft will expire on February 19, 2010.
	Copyright Notice		Copyright Notice
	Copyright (c) 2009 IETF Trust and the persons identified as the		Copyright (c) 2009 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	Provisions Relating to IETF Documents in effect on the date of		Provisions Relating to IETF Documents in effect on the date of
	publication of this document (http://trustee.ietf.org/license-info).		publication of this document (http://trustee.ietf.org/license-info).
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 8, line 42 ¶		skipping to change at page 8, line 42 ¶
	again. Repeat Recursion Step.		again. Repeat Recursion Step.
	This encoding algorithm can easily be seen to have time complexity of		This encoding algorithm can easily be seen to have time complexity of
	O(log_2 n), since it takes a number of steps equal to ceil(n/7), and		O(log_2 n), since it takes a number of steps equal to ceil(n/7), and
	no additional space beyond the size of the result (8/7 log_2 n) is		no additional space beyond the size of the result (8/7 log_2 n) is
	required. One aspect of this algorithm is that it assumes strings		required. One aspect of this algorithm is that it assumes strings
	can be efficiently appended to new bytes. One way to implement this		can be efficiently appended to new bytes. One way to implement this
	is to allocate a buffer for the expected length of the result and		is to allocate a buffer for the expected length of the result and
	fill that buffer one byte at a time from the right end.		fill that buffer one byte at a time from the right end.
			If, for some reason, an implementation requires an encoded SDNV to be
			some specific length (possibly related to a machine word), any
			leftmost zero-padding included needs to properly set the high-order
			bit in each byte of padding.
	3.2. Decoding Algorithm		3.2. Decoding Algorithm
	Decoding SNDVs is a more difficult operation than encoding them, due		Decoding SNDVs is a more difficult operation than encoding them, due
	to the fact that no bound on the resulting value is known until the		to the fact that no bound on the resulting value is known until the
	SDNV is parsed, at which point the value itself is already known.		SDNV is parsed, at which point the value itself is already known.
	This means that if space is allocated for decoding the value of an		This means that if space is allocated for decoding the value of an
	SDNV into, it is never known whether this space will be overflowed		SDNV into, it is never known whether this space will be overflowed
	until it is 7 bits away from happening.		until it is 7 bits away from happening.
	(Initial Step) Set the result to 0. Set a pointer to the beginning		(Initial Step) Set the result to 0. Set a pointer to the beginning
	skipping to change at page 10, line 5 ¶		skipping to change at page 9, line 25 ¶
	This decoding algorithm takes no more additional space than what is		This decoding algorithm takes no more additional space than what is
	required for the result (7/8 the length of the SDNV) and the pointer.		required for the result (7/8 the length of the SDNV) and the pointer.
	The complication is that before the result can be left-shifted in the		The complication is that before the result can be left-shifted in the
	Recursion Step, an implementation needs to first make sure that this		Recursion Step, an implementation needs to first make sure that this
	won't cause any bits to be lost, and re-allocate a larger piece of		won't cause any bits to be lost, and re-allocate a larger piece of
	memory for the result, if required. The pure time complexity is the		memory for the result, if required. The pure time complexity is the
	same as for the encoding algorithm given, but if re-allocation is		same as for the encoding algorithm given, but if re-allocation is
	needed due to the inability to predict the size of the result, in		needed due to the inability to predict the size of the result, in
	reality decoding may be slower.		reality decoding may be slower.
			These decoding steps include removal of any leftmost zero-padding
			that might be used by an encoder to create encodings of a certain
			length.
	4. Comparison to Alternatives		4. Comparison to Alternatives
	This section compares three alternative ways of implementing the		This section compares three alternative ways of implementing the
	concept of SDNVs: (1) the TLV scheme commonly used in the Internet		concept of SDNVs: (1) the TLV scheme commonly used in the Internet
	family, and many other families of protocols, (2) the old style of		family, and many other families of protocols, (2) the old style of
	SDNVs (both the SDNV-8 and SDNV-16) defined in an early stage of		SDNVs (both the SDNV-8 and SDNV-16) defined in an early stage of
	LTP's development [BRF04], and (3) the current SDNV format.		LTP's development [BRF04], and (3) the current SDNV format.
	The TLV method uses two fixed-length fields to hold the Type" and		The TLV method uses two fixed-length fields to hold the Type" and
	Length elements that then imply the syntax and semantics of the		Length elements that then imply the syntax and semantics of the
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	4 lines changed or deleted		13 lines changed or added
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