IEEE 1588v2 Clock Synchronization & P2MP LSP with co-routed reverse path

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IEEE 1588v2 Clock Synchronization &

P2MP LSP with co-routed reverse path

Lizhong Jin (ZTE)Frederic Jounay (France Telecom Orange)

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Requirement Analysis• According to IEEE1588v2 (BC mode), the sync p

acket and delay request should follow the same path, with same transmission quality. The details are:– The forward and backward path should be same;– The QoS should be ensured for end-to-end packet tra

nsmission.– It is preferred to do bandwidth usage optimization for

sync packet transmission.• MPLS network should provide all the above char

acteristics.

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Current Problem

• From the current deployment of IEEE 1588v2, because of the poor quality transmission provided by network, it was tested that about only 5 nodes are allowed between clock grandmaster and slave under the accepted accuracy of clock synchronization. (BC mode)

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Deployment with P2MP LSP with co-routed reverse path

IP/MPLS

R1

R2

R3

Slave_2

P2MP LSP forward path

P2MP LSP reverse path

P2MP LSP

GrandMaster

Slave_1

Sync packet

Delay Request

Before sending <delay request>, delay for some time according slave_id

Before sending <delay request>, delay for some time according slave_id

Processing clock sync between master and slave 1

Processing clock sync between master and slave 2

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Solution Description

• The P2MP LSP has co-routed reverse path, and QoS reservation for both forward path and reverse path.

• Clock synchronization process:– Grandmaster will send “IEEE1588v2 Sync” to all Slave nodes through P

2MP LSP with co-routed reverse path.– When the slave node receive “Sync packet”, it is required to send “delay

request” through P2MP LSP reverse path.– In order to avoid some packet process collision on reverse path, an opti

mized method is (optional):• When the slave node receive Sync packet, it is required to delay for sometim

e according to Slave_ID, then send delay request through P2MP LSP reverse path.

• The purpose of this method is to minimize potential packet process collision on reverse path.

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Solution Description (cont)• P2MP LSP will provide the following functions:

– Unidirectional point to multipoint connection from ingress LSR to all egress LSR;

– Reverse path from egress LSR to ingress LSR, which has the same path from ingress LSR to egress LSR.

– Unidirectional point to multipoint LSP will provide Diff-serv TE.– Reverse path LSP will provide Diff-serv TE.

• The QoS can only be guaranteed when only one of the egress LSR send packet through reverse path at one time.

• IEEE1588v2 will provide the following functions:– IEEE1588v2 will send same Sync packet to all slave node. – When Slave receive the Sync packet, it is required to delay for sometim

e according to Slave_ID, then send Delay Request through reverse path. This is necessary so as to avoid all the slave node sending “Delay Request” through reverse path at same time.

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PROS & CONS• PROS

– The BW and EF resource is optimized by using P2MP connection.

– The number of nodes that between Grandmaster and slave is increased, by virtue of MPLS high quality packet transmission.

– More scalable.• CONS

– If there is large number of nodes between Grandmaster and slave, the accuracy of clock synchronization will be poor. Hierarchy clock synchronization can be used to improve the accuracy.

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Next steps

• Add this requirements to draft-ietf-tictoc-requirements-00.

Thank you