IETF-93 Proceedings

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Timing over IP Connection and Transfer of Clock (tictoc) (WG)

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Charter (as of 2008-03-06):

The Timing over IP Connections and Transfer Of Clock (TICTOC) WG is
concerned with highly accurate time and frequency distribution over
native IP and MPLS-enabled IP Packet Switched Networks (PSNs). While
this need arises from a variety of sources (see
draft-bryant-tictoc-probstat-01.txt), the application areas of focus for
this WG are:

(1) Network infrastructures with the need for highly accurate time and
frequency distribution within well-engineered service provider or
enterprise campus networks. On-path support with specialized hardware
may be expected to be available at one or more hops on a given path.

(2) Individual hosts and devices on the public Internet requiring
functionality or performance not currently available in NTP. On-path
support may be utilized if available, but is not expected. This
application brings additional requirements beyond improved accuracy, for
example, the traceable and authenticated distribution of UTC time,
including correct handling of leap seconds.

The NTP Working Group is currently standardizing the fourth version of
NTP for time distribution over IP networks. The NTP WG has focused its
deliverables largely on standardizing the currently deployed NTPv4,
while collecting requirements for future extensions. These requirements
will transition to the tictoc WG for further development. Meeting those
requirements may include revision of the protocol to a new version
level. However, in all cases backwards compatibility and coexistence
with currently deployed NTPv4 is a paramount concern. An applicability
statement will describe the use cases for which any extension of NTP is

The IEEE Test and Measurement Society is in the closing stages of
standardizing a second version of IEEE1588. This is unofficially known
as IEEE1588v2 and is expected to be published as IEEE1588-2008.
IEEE1588v2 is emerging as a viable solution for time transfer over
service provider and campus Ethernet networks, and for which on-path
hardware support is becoming available. IEEE1588v2 specifically
encourages other standards organizations to adapt it to their
requirements, and provides guidelines for doing so. TICTOC will
determine whether a profile for IEEE1588v2 over IP or MPLS-enabled IP
networks would be suitable for (1), and if so will produce a profile
within the guidelines provided in the IEEE1588v2 specification. An
applicability statement will describe the use cases for which any
profile of IEEE1588v2 is targeted.

Time and Frequency distribution is considered by many to be a complex
and often esoteric subject area. The WG will develop a modular framework
in order to map out components within the solution space, define
terminology, and identify common areas of protocol work that can be
capitalized upon.

TICTOC will also consider the co-existence of IEEE1588v2 and NTP in the
same network. In doing so, TICTOC will first verify that the data model
of NTP can be accommodated by IEEE1588v2 protocol operation and document
any deficiencies compared to NTP. If there is a need to map the data
models, it will produce a specification for how to utilize IEEE 1588 in
a localized region as one portion of an NTP-based system.

TICTOC protocols will be applicable to a variety of link layer
technologies. To get the highest quality time and frequency transfer the
user should take advantage of two types of on-path service where they
are available: Link based frequency transfer, and hop-by-hop delay
correction (for time). Examples of link based frequency support are
SONET/SDH, TDM, Synchronous Ethernet and DSL with timing reference
support. The main types of support that can be provided by a network
element are boundary clock (where the clock is regenerated at the node
in a multistage master slave relationship) and transparent clock where
corrections are applied to time transfer packets as they pass through to
compensate for the queuing delay, and where known for asymmetry in the
link delay. Transparent clock (queue delay correction) requires
routers to identify a time transfer packet, record the queuing delay,
and either apply an on the fly correction to the packet, or to generate
a follow-up packet with the necessary time correction information.
TICTOC will ensure that any transparent clock design is acceptable in an
Internet environment. On-path support is not a given, and TICTOC will
investigate methods for automatically discovering when this support is
available and when it is not.

TICTOC will transfer time and frequency over both IP and IP enabled MPLS
PSNs. One of the major users of TICTOC technology is the service
provider community, where MPLS enabled IP networks are common. If
necessary, TICTOC may take advantage of the path control properties of
MPLS and the ability to signal modifications to per packet forwarding

The security of time transfer, including the authentication of the time
reference is an important consideration and must be designed in from the

The ultimate system-level accuracy of time and frequency transfer
depends on a number of factors outside the scope of the protocols
themselves. Thus, even if it is possible for TICTOC to make a number of
improvements at the protocol level to facilitate more accurate time and
frequency transfer, it is impossible for the WG to provide system-level
accuracy guarantees on its own.

The TICTOC WG will co-ordinate with the PWE3 and NTP WGs in the IETF, as
well as IEEE1588, IEEE 802.1AS and ITU-T SG15 Q13. 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

First phase Objectives:

- To develop a time and frequency distribution requirements document for
the two cases listed above, including coexistence of the two as appropriate.

- To develop a document defining the modular breakdown of functionality
within the solution space.

- To determine the extent to which these requirements can be satisfied
using IEEE1588v2 and NTPv4 within each use case, along with an
associated gap analysis for what requirements are not met without
adaptation or extension of these protocols.

- To develop an IEEE1588v2 profile as necessary for time and frequency
distribution, with primary focus on (1). This profile will include a MIB
module for IEEE1588v2.

- To develop extensions to NTPv4 as necessary for time and frequency
distribution, with primary focus on (2).

- If required, to develop mechanisms for coexistence of IEEE1588v2 and NTP.

- To document threat analyses and security mechanisms for all protocols
developed by the WG.

- To document media mappings for link layer technologies of interest.

Second phase Objectives (requiring re-charter of the WG):

To propose and document algorithms, protocols and mechanisms for
transport, frequency acquisition, ranging, and packet selection/discard,
master clock selection, path selection, OAM, synchronization status
messaging, performance monitoring, security, and network management.