IETF Minneapolis- Nov 2008 On-Path-Support Jean-Loup Ferrant Michel Le Pallec

Different type of On-Path-Support On path support: –Transport of frequency on a Physical layer –QOS? –Etc This presentation addresses the transport of frequency

2 main modes for 1588V2 End-to-End mode -frequency useful at the end of the 1588V2trail With intermediate nodes processing 1588V2 –A clock is useful at the intermediate nodes –And at the end of the 1588V2 trail

OSI layers OSI model: Protocol layers “communicate” to a peer layer. Intermediate Network elements are not visible. Time protocol PHY layer The only information provided by the physical layer at the termination of the Time Protocol path is related to the last physical section.

Example on the physical layer Time protocol PHY layer QL x QLy LOS End Equipment End Equipment Intermediate Equipment QLx QLy

Management of physical layer Physical layer information LOS, AIS QL No way for upper layer to know the status of the OPS (PHY layer here) as shown on the following examples –E.g. if Qly=QLx, the OPS failure is hidden –Phase transients might occur –Timing Loops are hidden

Should, can, time and frequency follow the same path? Frequency transport belongs to a synchronization network where equipments must be locked to a reference clock Transport of time is defined between a source and an application F ref T serv BCTC F ref 2 End user interface

Risk of change of reference F ref T serv F ref 2 A failure may decorrelate time and frequency if both sources are PRC, i.e. almost 2 µs phase error per day if one source is an SSU in holdover, 1µs phase eror in 7 minutes -5*10 -8 for a SEC in holdver, i.e. 1 µs in 15 seconds -The effect of this failure has a terrible effect on time, although the sync network is still operating End user interface

Risk of transient In case of SDH/SYNCE reorganization due to SSM, Up to 1µs of phase error may result between frequency and time F ref T serv End user interface

Timing loops not monitored F ref T serv F ref 2 In case of timing loop, the timing will diverge fast SSM will simply indicate a G.813 source quality G.813 End user interface

phase error with same path for F & T Even with same path for F & T, phase error will be generated F ref T serv SSM:G.813 F ref T serv SSM:G.813

Conclusion Current definition of synchronization networks does not allow a proper monitoring for the OPS –Extension of SSM with source ID might help On path support is not able to maintain the accuracy required by some applications during network holdover –G.813 cannot guaranty 50ppb holdover –Transients have to be compared with application performance –Holdover performance of OPS NEs and client applications have to be compared If the client has a better holdover than the OPS, it is better to go holdover rather than staying locked on a lower quality clock

Conclusion In a large network, –there is no evidence that time and frequency are transported on the same NEs. –The SSM has not been defined for application in large networks, its use with SSUs has not been agreed. –SSM is not transported between different operators Different protection schemes for OPS frequency and time transport might impact the efficiency of the OPS There is a need to continue the work on OPS