I E T F 6 3 , 3rd. A U G U S T 2 0 0 5

draft-frost-pwe3-timing-pw-reqs-00

IETF 63PWE3 Working Group

Paris, August 2005

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5[Page 2]

Why do we need this draft?

Purpose: To define the requirements of a protocol suitable for conveying Timing and Synchronization over Pseudo-Wires

Haven’t we done this already (e.g. TDM PWs with timing)?– there are applications for more general timing distribution, outside

the TDM context– some applications require absolute time alignment, not just phase

and frequency– separating the transport of timing and data allows improvement in

the quality of the recovered clock Aren’t there existing solutions (e.g. NTP, IEEE1588)?

– these describe how to carry timing across a LAN or the internet– they don’t explain how to distribute timing over PW services– they may be candidates for a protocol to be re-used over a timing PW

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5[Page 3]

Potential Applications

There are many applications that require distribution of accurate synchronization and timing:– Industrial applications– Real-time services

– Packet voice and video– Telecom applications

– Synchronization of IP PBXs or Voice Gateways– Synchronization of cellular base-stations

– TDM emulation– Improvement in timing quality over what can be achieved with

existing TDM PWs

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5[Page 4]

Possible Timing PW scenarioSecondary Time Server~ PRS

~ PRS

Carrier Packet

Network

PE

PEPE

PE

tunnel

tunnelPrimaryTime Server

timing pseudo-wires

timing pseudo-wires

CE

CECECE

timing attachment

circuits

timing attachment

circuits

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5[Page 5]

Main Requirements

Performance– Requirements are application-specific, and are defined in the

normative references for the applications– For example, G.pactiming is in the process of specifying the timing

performance requirements for wired TDM emulation Connectivity and compatibility Robustness

– Should be robust in the presence of common PSN error conditions Redundancy

– Should be able to monitor and switch over to alternative timing sources

– Needs an indication of the quality of timing sources Security

– Authentication of timing sources

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5[Page 6]

Comparison of draft-ietf-ntp-reqs-00 and draft-frost-timing-pw-reqs-00

NTPv4 Requirements Timing PW Reqs.

Performance Yes, TBD,(ms range)

By reference to ext. stds. (s range)

Configuration & setup Yes By reference to PWE3 architecture

Security and Authentication

Yes, defined mechanism

Yes, method not defined

Robustness Yes, covers bad implementations

Yes, covers PSN errors

Redundancy Yes Yes

Operational requirements

Yes, reference to NTP hierarchy

Yes, sync. quality messages

I E T F 6 3 , 3rd. A U G U S T 2 0 0 5

SIMPLY COMMUNICATING

c e s o p . z a r l i n k . c o m

w w w . z a r l i n k . c o m