Download TICTOC - IETF - 73 17 Nov. 2008

IRTF Timing RG
TICTOC - IETF - 73
17 Nov. 2008
Yaakov (J) Stein
The issue
Charter language
our charter says the following :
It is also expected that active individuals in the TICTOC WG
will propose the formation of an IRTF RG to study more
advanced aspects of time and frequency distribution.
there have been no discussions on topics for such a RG
We could call it - Sync Your Network Clock
In the following slides I will mention possible topics of interest
Non-goals
We would probably not want to tackle :
• BCP(s) about design of particular algorithms (IPR issues)
• comparison of particular algorithms in various scenarios
• things already being carried out by TICTOC
• characterization / test scenarios (being done in ITU SG15)
PDV and clock recovery performance
The most common question asked by nonexperts is
given a PDV how good will my clock recovery be ?
The truth is that this question is not well enough defined
Even if the network is stationary (no reroutes or load changes)
a single number PDV is insufficient to predict
In general we need the full PDV distribution and its full spectrum
However, in certain cases the question is answerable
In the Gaussian, IID, white-noise case the answer is easily obtained
(assuming a PLL-like mechanism)
For other cases of interest, simulation using existing algorithms
can provide guidelines
PDV characterization
PDV is usually defined with certain applications in mind
for example - sizing of playout buffers for real-time media
The usual percentile-based definition reflects the intended use
RFC 3393 discusses the PDV's median PDF/CDF
but not its spectrum
In addition, RFC 3393 discusses having locked clocks
It would be useful to specify how and what to measure
(coordination with ITU, to avoid duplication, will be needed)
Time as a commodity
There is speculation that ubiquitous high-quality time
may transform application and protocol design
In many cases this has not been sufficiently explored
IxTF documentation of the implications would be useful
In particular, it would be useful to research
• performance measurement when network elements have time
• interaction between routing and timing
• interaction between DNS and timing
• database cache coherency
• others ?
Applications to security
There may be improved security mechanisms that rely on
high-quality time at various points in the network
Public-key cryptography and Autokey mechanisms are
presently used to secure timing streams,
but perhaps are not ideal - are there better mechanisms ?
New timing distribution topologies
It has been suggestions in the literature that time can be
distributed in non-hierarchical fashion
(e.g. classless time distribution)
This means that we need not know a trusted server a-priori
It is unclear if this can be extended to frequency distribution
due to the problem of timing loops
There may be other novel non-client/server topologies
Other suggestions
• high-quality time in mobile devices
• improving time in existing IP protocols (ICMP, …)
• distributing time over networks with very long delay