Contents. Network Topology. Common Network Topology. Chain Network. Protection Mode. Ring with Chain Network, страница 6

If the working fiber between NE A and NE B is broken, while the protection fiber is normal, the E1 service between A and C only needs to be switched to the protection fiber in the span between NEA and NEB. That is 1:1 linear multiplex section switching. Figure 2-14 illustrates the service flow from A to C in this case: NE A tributary unit → NE A east 2:6-SL16-1 → NE B west 2:13-SL16-1 → NE B east 1:7-SL16-1 → NE C west 1:12-SL16-1→NE C tributary unit. The service from C to A is carried on another fiber in the same way.

Figure 2-14 Service flow between NE A and NE C upon fiber cut (span switching)

Span switching requires less network resources and features high efficiency.

n  Typical NE configuration

Take NE A as an example.

The line of the working ring uses two SL16 boards, inserted in slot 7 and slot 12. The line of the protection ring uses two SL16 boards, inserted in slot 6 and slot 13. The tributary uses a PQ1 to add/drop E1 services. Figure 2-15 shows the typical NE configuration.

Figure 2-15 Typical configuration of NE A

3.  Sub-Network Connection Protection (SNCP)

Sub-Network connection protection (SNCP) means that when the working subnet connection fails or its performance is below due level, the working subnet connection will be substituted by the protection subnet connection.

SNCP is frequently used in the ring network. Its working principle is similar to path protection and does not need the support of APS. It features fast switching and flexible networking.

Besides the ring network, SNCP also can be applied in ring with chain, tangent rings, intersecting rings and DNI to protect services from ring to chain or from ring to ring.

For the example of SNCP, refer to section 2.4 “Ring with Chain Network”.

2.4  Ring with Chain Network

Usually, the optical transport networks adopt complex networks composed of rings and chains. Here introduces the ring with chain network.

2.4.1  Application

The ring with chain network is a complex network consisting of rings and chains. The most frequent applications are:

n  Single ring with single chain

n  Single ring with multiple chains meeting at a point

n  Two rings with one chain

2.4.2  Protection Mode

In the ring with chain network, select the protection mode according to the networking topology.

n  The service on a single ring can adopt the protection mode applicable to the ring network.

n  The service from chain to ring can adopt the protection mode applicable to the chain network, or SNCP.

n  The service between nodes on ring and chain can adopt MSP or SNCP. The SNCP is recommended.

Refer to section 2.2 “Chain Network” and section 2.3 “Ring Network” for the protection of the first two cases. This section focuses on the third case, and the configuration of the interconnecting node of ring and chain.

1.  MSP Ring with Non-Protection Chain

n  Configuration plan

In Figure 2-16, NEs A, B, C and D form an STM-16 ring. NEs D and E form an STM-4 chain.

Figure 2-16 MSP ring with chain network

Table 2-6 shows the service allocation among nodes in the network.

Table 2-6 Service allocation among nodes

Node	A	B	C	D	E
A	-	32 x E1		32 x E1	32 x E1
B	32 x E1	-	32 x E1	-	-
C	-	32 x E1	-	32 x E1	-
D	32 x E1	-	32 x E1	-	3 x E3
E	32 x E1	-	-	3 x E3	-

n  Configuration description