0 . 0 0 2
0 . 0 0 4
0 . 0 0 6
0 . 0 0 8
0 . 0 1 0
0 . 0 1 2
0 . 0 1 4
0 . 0 1 6
0 . 0 1 8
0 . 0 2 0
350
300
Energy consumption
(μJ)
250
200
150
100
50
Network
Router
Link
0
Offered load (packets/cycle/IP)
88
Network-on-Chip
4.4.4 energy Consumption at Different Locality Factors
Total energy consumption in NoC is the summation of energy consumed by
the routers and communication links. Both the factors are network topology
dependent. The total energy consumption of a MoT-based network for uniformly distributed self-similar traffic is shown in Figure 4.10 (simulation for
200,000 clock cycles with a 666-ps clock period taken as evaluation parameter).
It can be observed that the network energy consumption increases linearly
with the offered load but saturates as the offered load increases to the throughput limit. Beyond saturation, no additional packets can be injected successfully
into the network and, consequently, no additional energy is consumed.
Figure  4.11 depicts the component-wise energy consumption of the network at saturation. It can be observed that the energy consumption of all
the FIFOs is 60% of the total network energy consumption, whereas all the
links consume only 30% of it. The combined energy consumption of all the
routing logic, arbiters, and control logics is about 10% of the same. Thus, from
Figure  4.11, this can be concluded that FIFOs are the most energy hungry
component in NoC.
The average energy consumption per cycle of a MoT-based NoC at saturation with uniformly distributed and localized traffic is shown in Figure 4.12.
With increasing locality factor, packets traverse lesser hops to reach their
destinations. Although the energy consumption of the local link increases
with increasing locality factor, the stem and root routers and the inter-router
links consume lesser energy due to lesser switching. From Figure  4.12, it
can be noticed that the average energy consumption of the overall network
decreases as the locality factor increases.
To get an idea about the energy spent per packet, the average packet
energy is computed. This is another important attribute for characterizing
NoC structures. Figure 4.13 shows the average packet energy consumed at
different locality factors at saturation. As the energy consumption decreases
Figure 4.10
Energy consumption in MoT network with uniformly distributed load.