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