1. New Timing Distribution Mechanism TICTOC WG, IETF 71th Philadelphia, USA draft-ji-tictoc-new-timing-distribution-mechanism-00.txt Kuiwen Ji (jikuiwen@huawei.com)

2. Background Route Technique using for timing distribution Agenda

3. Background Synchronization is typically distributed from one central office to another using the SONET/SDH signal for optical networks. Each node has two synchronization sources - a primary and secondary source. this provides a degree of protection for the synchronization network As a last line of defense, clock hold-over provides minimum service quality for a given time period.

4. Typical Master-Slave Synchronization Example

5. Todays Network Synchronization planning and distribution is administered manually base on SSM (G.781) usually. SONET/SDH networks are primarily implemented in linear and rings architectures. Now with the introduction of the network controlled by GMPLS and synchronous Ethernet, it is probable that the transport architecture will shift from linear/ring to mesh architecture. Mesh networks will provide more paths/combinations for synchronization distribution.

6. Using of SSM The SSM (G.781) has been used for a long time in Sync network. A synchronization coordinator usually determines how best to implement synchronization to each piece of equipment in the network and configure the priority of reference sources to each. We are careful to avoid timing-loops when planning there synchronization networks. Not every bi- directional link can be used even if they are available in the ring.

7. Limitation of SSM 3 1 2 Source 1 2 1 1 1 3 3 2 2 Source 2 3 1 2 Source 1 2 1 1 1 2 2 Source 2 3 1 2 Source 1 2 1 1 1 2 2 Source 2 : Nodes : Main timing tracing path : Backup timing tracing path # # : priority of reference sources A(×) B() C()

8. Another simple example 1 2 3 Source 1 4 3 1 1 2 2 Source 2 5 4 2 1 1 1 2 2 : Nodes : Main timing tracing path : Backup timing tracing path # # : priority of reference sources Clock source 1 is assumed to be a higher priority clock than clock source 2 for this example. Probably we can plan the synchronization like this.

9. Multiple failures 1 2 3 Source 1 4 3 1 1 2 2 Source 2 5 4 2 1 1 1 2 2 : Nodes : Main timing tracing path : Backup timing tracing path # # : priority of reference sources If the source 1 fails and a failure occurs between node 1 and 2, node 1 will go to holdover. Node 1 can get the synchronization from blue link but it cant use it now. We can change the priority of each node to make another configuration of course. But for preventing timing- loop we still cant use every link bi- direction even if it would be possible to use them. The point is that no one configuration is best for every type of possible failure condition. There is still limitation. X X Holdover

10. Normal mesh network How could the synchronization be setup? Whats the best configuration? We need to be very careful to avoid timing-loop. Thus, we have to give up many of the bi-directional links. : Nodes : Main timing tracing path : Backup timing tracing path Source 1 Source 3 Source 2

11. Background Route Technique using for timing distribution Agenda

12. Information distribution # : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 With the GMPLS control plane, its possible to know the network topology and the state and condition of links. And the reference source attribution, like priority, quality can be distributed through route protocol OSPF. So all nodes know the network topology and which source output to be used and traced as the primary timing source.

13. Calculating the traceability paths : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # Each node calculates the timing tracing path to the master clock source based on the topology and the primary source. From the root of the primary reference, simple calculating algorithm like Dijkstra can be used to establish a shortest path tree. The synchronization distribution algorithm would be like a tree structure to prevent timing loop.

14. Building a timing tree : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # A ready message is sent when timing traceability path is setup and operational. Each node will not switch to a new synchronization source until it knows the new synchronization source is ready. After a node traces to a new timing source successfully, the node will send a message to the next to show it is ready. M M M

15. Building a timing tree : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # A ready message is sent when timing traceability path is setup and operational. Each node will not switch to a new synchronization source until it knows the new synchronization source is ready. After a node traces to a new timing source successfully, the node will send a message to the next to show it is ready. M M M

16. Building a timing tree : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # A ready message is sent when timing traceability path is setup and operational. Each node will not switch to a new synchronization source until it knows the new synchronization source is ready. After a node traces to a new timing source successfully, the node will send a message to the next to show it is ready. M M

17. Building a timing tree : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # A ready message is sent when timing traceability path is setup and operational. Each node will not switch to a new synchronization source until it knows the new synchronization source is ready. After a node traces to a new timing source successfully, the node will send a message to the next to show it is ready.

18. Failure occurs between nodes 3 and 7 disrupting the sync path : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path X #

19. A second failure occurs between nodes 6 and 7 : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path X # X

20. Source 1 Fails : Node Source 1 Source 2 1 4 2 3 7 5 6 8 9 : Timing tracing path # X

21. SSM=PRC Interworking with existing networks BITS 1 : Node which doesnt use automatic techniques : Main timing tracing path : Node which use automatic techniques : Backup timing tracing path Source1 SSM=PRC PRC SSM=SSU PRC SSM=PRC PRC DNU PRC BITS 4 BITS 2 BITS 3 1 1 2 1 2 2 1 1 1 1 2 2 2 PRC All blue nodes could be viewed as one node which use traditional SSM at the boundary to interwork with others.

22. Benefits Can be used in future network like Synchronous Ethernet, 1588 or any network with GMPLS. Provide survivability (sync traceability) for multiple failures. Possibly ease requirements on clock holdover mode by providing traceability in event of multiple failures (i.e., maintain service quality). Easy planning and maintenance. People dont need to do complex work in Synchronization scheme and configuration. More…

23. Next Step Timing distribution is very important for synchronization. Comments from the group are always appreciated Working with CCAMP with respect to the GMPLS extensions, which supports this feature.