Fiber Optic Wiki

Visual Fault Location

December 19, 2011

A higher power version of the fiber tracer called a visual fault locator (VFL) uses a visible laser that can also find faults. The red laser light is powerful enough for continuity checking or to trace fibers for several kilometers, identify splices in splice trays and show breaks in fibers or high loss connectors. You can actually see the loss of light at a fiber break by the bright red light from the VFL through the jacket of many yellow or orange simplex cables (excepting black or gray jackets, of course.) It's most important use is finding faults in short cables or near the connector where OTDRs cannot find them.

Myths regarding Pure Ethernet:

December 17, 2011

The biggest myth being propagated regarding pure metro-ethernet or carrier ethernet is that there are 4094 VLANs available network wide for a provider network. This is simply not true. There are 4094 VLANs available on each switched path. So the VID(vlan id) cannot be reused along the path from point a to point z, but can be reused anywhere else in the network as long as the paths are separated.

RSTP convergence takes many seconds

December 17, 2011

Another myth is that RSTP convergence takes many seconds. In certain situations and with some equipment this may be true. However, some vendors are offering devices that will converge RSTP in sub-50ms with little to no planning or effort.

L2 metro-ethernet connections remove the need

December 17, 2011

Another myth is that L2 metro-ethernet connections remove the need for using L3 routers or L3 switches. This is also not true. While equipment will operate just fine over your new metro-ethernet gear on L2 without a router.

SONET/SDH-based Ethernet MANs

December 17, 2011

A SONET/SDH based Ethernet MAN is usually used as an intermediate step in the transition from a traditional, time-division based network, to a modern statistical network (such as Ethernet). In this model, the existing SDH infrastructure is used to transport high-speed Ethernet connections.

MPLS-based Ethernet MANs

December 17, 2011

An MPLS based Metro Ethernet network uses MPLS in the Service Provider's Network. The subscriber will get an Ethernet interface on Copper (ex:-100BASE-TX) or fiber (ex:-100BASE-FX). The customer's Ethernet packet is transported over MPLS and the service provider network uses Ethernet again as the underlying technology to transport MPLS. So, it is Ethernet over MPLS over Ethernet.

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