Subject: [TICTOC] RE: Draft TICTOC WG charter

From: "Jeremy Bennington" <[email-masked]>
Date: Thu, 18 Jan 2007 08:41:58 -0800

Stewart,

The draft charter is excellent.  I am glad that we are still considering
time and frequency in the same WG at this point.  While the accuracy
requirements may differ, I believe we will be doing a disservice by
creating two different approaches.  

I know Ron and others have volunteered to present 1588.  Someone from
Symmetricom would be happy to present what we have accomplished with NTP
and what extensions we have investigated.  

Best Regards,

Jeremy B.

----------------------------------------------------------------------

Message: 1
Date: Thu, 18 Jan 2007 16:29:33 +0000
From: Stewart Bryant <[email-masked]>
Subject: [TICTOC] Draft TICTOC WG charter
To: [email-masked]
Message-ID: <[email-masked]>
Content-Type: text/plain; charset=us-ascii; format=flowed

Description of Working Group:

There is an emerging need to distribute highly accurate time and
frequency information over IP and over MPLS packet switched networks
(PSNs).

Network transport service providers and their users are seeking to
rationalize their networks by migrating their existing services and
platforms onto IP or MPLS enabled IP packet switched networks (PSN). In
some cases this migration is only possible if the user equipment can be
provided with the high quality frequency service to replace the timing
(frequency) service provided to all users of TDM networks. These
applications include the TDM emulation techniques developed by the PWE3
WG, and the radio systems used in mobile phone networks.

There are applications that need require time with a greater precision
than can be achieved with the current version of NTP. These applications
span a range of
industries: telecommunications, financial, test and measurement,
government, industrial etc. The early work in these areas indicates that
the availability of high accuracy time as a commodity allows the use of
techniques that were previously impossible. High quality time is
therefore an enabler for new distributed technology. The best-known
example of an application that requires high quality time in the
telecommunications sector is the need to measure one-way packet delay.
Another network example is the need to synchronize device operation of
media types at the MAC layer.

The TICTOC WG will be responsible for identifying and satisfying the
time and frequency needs of the various services that need to be
supported over IP and MPLS PSNs.

The TICTOC WG will co-ordinate with the PWE3 and NTP WGs.

WG Objectives:

The objectives of a WG are:

To compile the time and frequency requirements of various services that
need to be supported over the PSN.

To research the influence of measurable network characteristics on the
achievable performance of clock distribution.

To propose algorithms that approach optimal clock recovery performance
over existing networks, and yet may take advantage of network upgrades
(should these be available).

To propose a suitable clock distribution protocol that can run over the
existing network architecture.
This protocol may have different operational modes, depending on whether
time or frequency distribution is required.

Goals and Milestones:
XXXX	  	TICTOC WG started
XXXX            TICTOC requirements published
XXXX            TICTOC architecture published

Other goals to be established

Internet-Drafts:

RFCs:

------------------------------

_______________________________________________
TICTOC mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/tictoc

End of TICTOC Digest, Vol 6, Issue 25
*************************************

_______________________________________________
TICTOC mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/tictoc

---

From: "Jeremy Bennington" <[email-masked]>
Date: Mon, 22 Jan 2007 18:18:47 -0800

See comments below, thanks!  -Jeremy B. 

Marshall & Stewart wrote:

>> I am fuzzy about the "one way delay".
>> 
>> "The best-known example of
>> 
>>> an application that requires high quality time in the 
>>> telecommunications sector is the need to measure one-way packet 
>>> delay."
>> 
>> 
>> I do not know of a good way to measure one way delay through the 
>> network unless both ends have independent time coming from, e.g.,  
>> GPS, due to the possibility of network asymmetries.  (Taking the RTT

>> and dividing by two is not sufficient.)
>> 
>> Do we plan to
>> 
>> - enable network paths with, say, GPS at both ends to determine the  
>> one way delay through the network (which sounds fairly easy) or to
>> 
>> - do this entirely autonomously, solving the problem of network 
>> asymmetry. If so, how ? Send references, please.

While we may focus on packet techniques to transport time & frequency,
there are very precise time and frequency references including GPS.
The most recent development in this area is ITU-T J.211 / CableLabs DTI.
This new synchronization architecture distributes time, frequency, phase
and location within a Headend, CO, Local Exchange.  Similar to BITS in
the telecom industry J.211/DTI uses a dedicated Cat5 connection between
a server and client to transfer Stratum 1 frequency, 100ns Time-Of-Day,
5ns local time and GPS location.   ITU-T SG15 may also consider this
technology for telecom under the name of UTI or TTI.   If you want more
information the J.211 spec. is available from the ITU, but you can also
download the sister spec for free at:
http://www.cablemodem.com/downloads/specs/CM-SP-DTI-I04-061222.pdf  I
was one of the authors of this spec., if you have any questions let me
know.

One of the uses for DTI in cable is for DOCSIS TDMA/CDMA timeslot
synchronization.  It is also used for one-way delay measurements between
devices on the IP network. 

As I mentioned earlier my colleagues and I would be happy to make a
presentation on high-accuracy NTP.   

Thanks!

-Jeremy B.