  Cloud computing has provided economies of scale, savings, and efficiency for
both individual consumers and enterprises. Its key advantage is its ability to
handle increasing amounts of data and provide functionality that gives users
the ability to scale their computing resources, including processing, data
storage, and networking capabilities. Virtual Machines (VM), enabled via
virtualization technology, allow cloud service providers to deliver their
services to users. This, however, results in increasing carbon dioxide
emissions from increased energy use. This paper introduces a Mixed-Integer
Linear Programming (MILP) model that investigates the VM placement, focusing on
the British Telecom (BT) network topology, in a cloud-fog network architecture
when renewable energy sources are introduced in the fog layer located near
traffic-producing sources. VMs can be placed on nodes hosted on the core,
metro, and access (fog) layers. We first investigate the effect of varying
traffic on IP over WDM power consumption in the backbone network and the number
of optical carrier signals to serve the traffic over a period of time. We later
extend the model to consider the CO2-minimized optimal virtual machine
placement given the sporadic traffic quantity, and the consideration of solar
renewable energy sources placed in data centers located in the access (fog)
layer throughout the day, imposed on the VM and the minimum workload
requirement of the VM to maintain a service level agreement (SLA).
