Essential Ring Nomenclature And Rules - Alcatel-Lucent 9500 MXC User Manual

Ring Operation

Essential Ring Nomenclature and Rules

Vol. VI-A-2
Ring protection is provided by auto-routing traffic in a reverse direction around a
ring to bypass a break in the ring. For NxE1 or NxDS1 (Super PDH) rings the
failure detection and circuit re-routing is managed by the 9500 MXC Node, no
external switching device is required. Refer to Essential Ring Nomenclature and
Rules.
9500 MXC PDH rings, support capacities to 75xE1 or 84xDS1.
Auxiliary Data circuits will be interrupted beyond a break-point, and will not be
restored until the ring unwraps. Alarm I/O actions are not affected.
A ring comprises a closed network of nodes where the protection partner RACs
at each node are assigned in an East and West direction, within the CT Protection
screen.
Within a ring there are two traffic rings:
• One is designated primary, where at each node traffic is received by the West
RAC and transmitted by the East RAC (clockwise direction). Under normal
no-fault conditions, all traffic flows only on this primary ring.
• The other is designated secondary, where traffic at each node is received by the
East RAC and transmitted by the West RAC (anti-clockwise direction). This
secondary ring is only used in the event of a fault; traffic is switched from the
primary ring onto the secondary ring just prior to a break point, then travels on
the secondary ring (East to West, anti-clockwise direction) to connect back to
the primary ring at the other side of the break.
This process of switching traffic from primary to secondary at one side of the
break, and from secondary to primary at the other side, is termed 'circuit
wrapping', or just 'wrapping'.
Each E1 or DS1 ring-protected circuit is unique on the ring; it cannot be reused
within the ring.
At each node, traffic may be passed-through, or dropped-and-inserted:
• Pass-through circuits are directly analogous to a repeater circuit; they are
carried through a node.
• Drop-insert circuits are local traffic circuits. On the primary ring, Rx traffic is
routed from the West RAC to a DAC (or RAC) where it will be available on the
trib as DAC-out to a user connection. Data from the user is provided on the
DAC-in trib, which is routed to the East RAC for transmission around the ring
to its destination node/DAC.
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