Marconi OMS 1200
Technical Product Description
221 02-ZAP 701 25/1 Rev C 2006-08-04
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Similarly, in bi-directional mode when using the ITU-T/ETSI standard protocol, when a
bridging request is transmitted to the remote multiplexer in byte K1, a 50 ms time-out
is applied. If the received K2 byte (bits 1-4) does not indicate the same channel
number as that in the transmitted K1 byte (bits 5-8) within this time-out period, the
multiplexer reverts to unidirectional operation and raises a Tx K1, Rx K2 mismatch
alarm.
Note:
This timing is a constraint on the K1,K2 byte protocol only. It is derived from
the need for 1:N systems to bridge a channel at the head-end before a
tail-end multiplexer switches its selector. Although not strictly required in a
1+1 architecture, the application of this time-out is nevertheless retained in
ITU-T/ETSI to maintain compatibility.
Since operation of the MSP mechanism may corrupt switch-unit diagnostic messages
(internal to the SMA), the maximum duration of disrupted diagnostic messages
received at the destination ports due to operation of this mechanism is 3.0ms for TU-1
or TU-2 traffic, or 0.75ms for TU-3 signals.
7.5 VC-Trail
SNCP
7.5.1
Introduction to SNCP
Sub-Network Connection Protection (SNCP) is supported. SNC protection operates on
an individual VC- basis at all VC-n path layers (i.e. VC-4, VC-3, VC-2, and VC-12).
In an SDH network, traffic is mapped into a VC- container and is transported across
the network on a VC-trail.
A VC-trail exists from the NE at which the VC- termination is sourced, across to the
NE at which that VC- termination is sinked. Any VC-trail may only be connected
through these two NEs or, more commonly, it may be cross-connected through
various NEs on-route between the source and sink NEs. The end-to-end VC-trail is
known as a network connection.
Each segment of the VC-trail, as it is transported between one NE and the next, is
known as a Sub-Network Connection (SNC).
1+1 SNC protection provides a means of protecting against failure of the components
of a SNC in a network, including functions of the involved NEs, optical components,
interconnecting fibres and intermediate regenerator equipments.
If we consider a segment (or successive segments) of a VC-trail then this SNC has a
source NE and a sink NE, just as the end-to-end VC-trail has. Protection is achieved
by setting up a worker SNC through certain NEs in the network, and then a separate
protection SNC through a different NE route.
At the source NE, the same VC- has two connections (worker/protection) for
broadcast to two separate SDH interface unit ports. In this way, two diverse routes can
transport the same VC- traffic across the network.
At the sink NE, those connections are received by two SDH interface units and
connected into the core unit as a protection pair.
Protection switch selection is then made between worker and protection connections,
based on the detected failure/degrade status of each, or on operator command.
