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ORDERED TRAFFIC SELECTION DURING A MAKE BEFORE BREAK (MBB) PROCEDURE

IP.com Disclosure Number: IPCOM000249414D
Publication Date: 2017-Feb-24
Document File: 9 page(s) / 148K

Publishing Venue

The IP.com Prior Art Database

Abstract

The present disclosure relates to an ordered traffic selection during a Make Before Break (MBB) procedure. Specifically, a selector switch is dynamically triggered based on the path configuration to avoid communication loss in Optical Transport Network (OTN). Conventionally, control plane signaling messages are defined for a single function in a call flow, but the present disclosure addresses the problem where a specific call flow is disrupted by distributing the signaling message over multiple flows.

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ORDERED TRAFFIC SELECTION DURING A MAKE BEFORE BREAK (MBB) PROCEDURE

ABSTRACT

The present disclosure relates to an ordered traffic selection during a Make Before Break (MBB) procedure.  Specifically, a selector switch is dynamically triggered based on the path configuration to avoid communication loss in Optical Transport Network (OTN).  Conventionally, control plane signaling messages are defined for a single function in a call flow, but the present disclosure addresses the problem where a specific call flow is disrupted by distributing the signaling message over multiple flows.

DETAILED DESCRIPTION

Again, in various exemplary embodiments, the present disclosure relates to an ordered traffic selection during a Make Before Break (MBB) procedure. 

In a typical MBB procedure, the traffic selector switch applied on a  flexible cross-connect (FCC) between an old leg to a new leg is triggered from the terminating node towards the originating node. This is controlled by an NTFY SWITCH ACK signaling message sent from terminating node towards the Originating node.  For an OTN High Order (HO) Optical Data Unit (ODU) Subnetwork Connection (SNC), this selector switch can result in a ODU frame slip (and hence an Optical Transport Unit (OUT) frame slip since OTU framing is derived from HO ODU framing) that travels in the same direction as the signaling message leading to message loss.  Note that hardware signal processing of the frame slip event frequently results in disruptions of the OTU that may be longer than the time of the switching event itself further increasing the probability of signaling message loss.  Though the lost message is retransmitted by the signaling stack after 200ms, this results in MBB operation on an HO SNC to see multiple traffic disruptions spaced at 200ms or more.  This invariably results in larger traffic disruption in upper/ application layers. The scenario is aggravated  when paths  are longer or having numerous hops, where multiple re-transmissions could be triggered at each selector switch resulting in expiry of the MBB window of 1 sec and failure of the MBB procedure.

In FIG. 1 below consider the current path of an SNC marked in green and the protect path computed in red. When a user triggers the MBB procedure to switch to protect or any similar MBB operation, the initial MBB signaling messages sets up the FCC at various crosspoints marked as 1, 2, 3 and 4.  When NTFY SWITCH ACK is sent in response to NTFY SWITCH  from the terminating node, the selector switches occur at each node as part of the SWITCH ACK processing.  The selector switch at (1) and (3) results in timing sync or glitch to travel upstream towards the Tail end while selector switch at (2) and (4) results in timing sync or glitch to travel downstream towards the Head end. Selector switch at (2) and (4) are disruptive for HO SNC since it can catch up with the signaling message NTFY SWITCH ACK resulting in comms break leading to message loss.  A r...