Optical Network Design and Implementation

SONET Ring Architectures

This section examines SONET unidirectional and bidirectional ring architectures and examines the differences between two-fiber and four-fiber SONET rings. A comparison is also made between line (ring) switching versus path (span) switching. SONET provides for three attributes with two choices each, as shown in the Table 5-10.

Table 5-10. SONET Ring Types

SONET Attribute	Value
Fibers per link	Two-fiber
	Four-fiber
Signal direction	Unidirectional
	Bidirectional
Protection switching	Line switching
	Path switching

Table 5-10 shows various SONET ring configurations that differ in at least one major attribute. The commonly used ring types and topologies are as follows:

• Two-fiber unidirectional path-switched rings (two-fiber UPSRs)

• Two-fiber ...