A ???+??™ or ?????’??™ is adjacent to the head of an arrow and should be interpreted as described
in the following example. Consider an arrow originating from the variable ???(Improved
Service Provider) Economics??? and terminating at ???(Carrier Ethernet) Demand.??? The +
sign with this arrow indicates that an increase (or decrease) in improvement in Service
Provider economics will have a correspondingly positive (or negative) impact on the
demand; a negative sign instead indicates an inverse relationship, i.e., a negative impact
(demand will decrease) if economics improve or a positive impact (demand will
increase) if economics decreases.
The arrow pointed in the other direction (i.e., from ???...Demand??? to ???...Economics???
indicates that an increase in demand would mean improvement in economics (perhaps
due to the effects of scale). These arrows, in both directions, form a loop; if they
both have the same sign they are called reinforcing loops and result in exponential
growth/reduction.
Figure 16.6 Factors influencing the demand for Carrier Ethernet
Carrier Ethernet Demand
Applications Standardization
Fiber deployment
(improved)
Economics
Technology
improvements
Technology
improvement
+ (positive) ??’ (Negative/inverse)
Substitutes
Regulation
Competition (Amongst
Service Providers)
Direct influence
Indirect influence
Competition
(amongst Service
Providers)
Substitutes
Fiber deployment
Technology
Improvements
Standardization
(Improved
Service Provider)
Economics
Applications
Regulation
Carrier Ethernet
demand
+
+ ?
+
+
+
+
+
+ +
+
+
+
+
+
??’
??’
??’
??’
??’
??’
+
Evolution of Carrier Ethernet Solutions 521
Figure 16.
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