Fiberhome Network Based On OLT
The following figure shows the typical networking topology of EPON access. EPON carrying integrated services, the upward convergence of two cases:
The first case: EPON OLT larger business, directly on the BRAS and SR, single uplink, traffic diversion mode. As OLT to BRAS and SR are single uplink, will inevitably bring the hidden dangers of reliability.
The second case: EPON OLT traffic smaller, first through the aggregation switch convergence again, then BRAS and SR. As the aggregation switch to the SR and BRAS, respectively, is also a single uplink, so there are also risks of reliability.
In order to solve the problem of reliability, in general, there are two ways of traditional dual-star networking and Ethernet ring network (as shown in the figure)
In the traditional way, the general consideration is the way of direct drive of binary star type fiber. However, this approach has several drawbacks:
1) The dual-star network occupies a large amount of optical fiber resources, and the optical fiber distance is far;
Especially with the increase in the number of EPON OLTs (more than 100 medium-sized metropolitan area networks are normal), so many OLTs must each use two different routed fibers to converge to the backbone nodes, which occupy a lot of cables.
2) Expansion is not convenient
Every time a new OLT is deployed, it is necessary to directly connect the long-distance optical fibers to the backbone nodes, which is not convenient for capacity expansion.
3) take up more backbone equipment optical port
With dual-star networking, each additional OLT means that the backbone equipment above must be configured with two GE optical ports. With 100 OLTs, it means that each backbone device is configured with 100 GE ports. The GE optical ports of BRAS and SR are relatively expensive.
The use of Ethernet ring convergence, the following benefits:
1) Save fiber resources, add new OLT more convenient.
The new OLT only needs to access the nodes of the Ethernet ring nearby and does not need to directly connect long-distance optical fibers to backbone devices. Especially in rural areas, the townships are more scattered and far away. In particular, the ring network saves optical fiber resources in particular.
2) The existing ring fiber resources (for mobile operators) in the transport network can be utilized.
According to statistics, in general, there is some surplus of the optical cable resources in the transmission network, so that the existing ring optical cable resources can be utilized to form an Ethernet ring network.
3) Reduce the occupancy of GE optical ports on the backbone device.
After Ethernet ring aggregation, only 1-4 GE ports or several 10G ports are connected to the backbone device, which obviously reduces the optical port usage on the backbone device.
4) provides a reliable OLT connected.
50ms Ethernet ring switching protection capabilities, providing a reliable OLT even. Of course, dual-star networking can also provide 50ms active-standby switching mechanism.