1. NTP and PTP Random Thoughts on Trade-offs and Scalability
IETF 68
TICTOC BOF
Karen O’Donoghue

2. Objective As requested by the BOF organizers:
Kickoff a discussion on the tradeoffs between NTP and PTP (IEEE 1588), in particular as related to scalability
Thought provoking slides?
As revised by the speaker:
Identify some basic metrics for scalability
Propose a possible way ahead
Rationale for revision:
May be a bit premature to discuss specific NTP/PTP tradeoffs (suffice it to say they exist…)
15 March 2007

3. Characteristics of Scalability
What are scalability requirements?
Number of clients/slaves supported
Number of servers/masters available
Number of network or infrastructure devices
Clock (tod and/or freq) aware (e.g. transparent clocks)
Non-clock (tod and/or freq) aware
Mixture
Number and types of networks traversed
Logical and Geographic distance
Available bandwidth
If a potential WG is limited to infrastructure networks, how can the requirements be narrowed/clarified?
15 March 2007

4. Impacts to Scalability
What impacts scalability?
Client/server approach versus Master/slave approach
Server/master complexity
Client/slave complexity
Hardware requirement
Network design
Communications model
Unicast versus Multicast
Protocol Operations
Modes of operation (NTP)
Types of devices (PTP)
Algorithm complexity
Edge cases
Master/server selection and redundancy
15 March 2007

5. Clock Standardization Activities At a Glance
IETF (NTP)
Pros
Scalable and robust
Subnet technology independent
Represents the generic computing equipment market
Wide scale deployment and years of experience
Cons
Does not address high end synchronization requirements in an open standard manner
IEEE 1588 (PTP)
Pros
Designed for high precision applications
Industrial automation and telecom industries have real time requirements
Cons
Lacks the robustness and deployment experience of NTP
Currently represents a niche market relative to generic computing equipment and enterprise deployments
IEEE 802.1AS
Pros
Hardware time stamp capability available in every Ethernet NIC (mass market availability)
Cons
Immature at this point
Targets consumer market (may not be suitable for enterprise or telecom infrastructures)
Note: Each of these solutions has some overlap and addresses some unique aspects of the problem (not an apples to apples comparison).
15 March 2007

6. Given that:
There are various solutions addressing parts (but not all) of the problem space
There is a significant investment in this problem space represented by NTP and PTP
There is an expectation that both NTP and PTP will be encountered in the future
Perhaps:
There are aspects of both that can be identified and leveraged for a next generation solution
At the very least, an interface between the two should be considered
15 March 2007

7. Possible TICTOC Way Ahead
Clarify requirements
Both time and frequency
Define a modular architecture
Analyze/Decompose existing solutions in terms of this architecture
Identify existing components that can be leveraged in the new modular architecture
Identify any enhancements required to these existing components
Define new components needed to complete the architecture
Don’t reinvent the wheel
15 March 2007

8. Discussion?
15 March 2007