[ntpwg] ntp extension

[Greg Dowd]

NTP Extensions Field


 

TLV = Type, Length and Value

 

 

Autokey is currently using ALL 65,535 types.  This violates the TLV
principle.  The reason for this is that Autokey has redefined the Type
field as a structure containing version and flag fields along with the
original type id.  

 

Current type definition in the NTP document

The Field Type field is specific to the defined function and is not
elaborated here.  

 

Suggested definition in NTP document.

The Field Type field is specific to the defined function and is not
elaborated here.  TLV types are IANA registered numbers.  

 

Current type definition in the Autokey document

The 8-bit Code field specifies the request or response operation,
while the 4-bit Version Number (VN) field is 2 for the current
protocol version.  There are four flag bits: bit 0 is the Response
Flag (R) and bit 1 is the Error Flag (E); the other two bits are
presently unused and should be set to 0.  The remaining fields will
be described later.

 

If we take the presently unused flag bits and force them to 0, we could
recover some space for future use.

 

Note that the 48000 TLVs currently in use by Autokey support about 20
commands.  This is wasting 99.96% of the allocated space.  This is due
to Autokey's usage of the Type field as a compound structure
incorporating not only commands but also a version and flags field. 

 

Types currently in use by Autokey (if flag fields are capped)

 

0x0000 - 0x0FFF

0x4000 - 0xFFFF

 

Available for future use (if flag fields are capped)

 

0x1000 - 0x3FFF

 

Result is that at least 25% of the space will be available for
extensions of the protocol, which will be backwards compatible with the
current proposed version.

 

 

 
  
Greg Dowd
gdowd at symmetricom dot com (antispam format)
Symmetricom, Inc.
www.symmetricom.com <blocked::http://www.symmetricom.com/> 
"Everything should be made as simple as possible, but no simpler" Albert
Einstein
 
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