Fog Computing

Fog as an Intermediate Tier

Fog computing describes a distributed computing architecture that places compute, storage, and networking resources between end devices and the centralized cloud — closer to the edge than a regional data center but more capable than a constrained IoTInternet of Things. The network of physical devices (sensors, cameras, appliances, vehicles) embedded with connectivity and software that collect and exchange data over the internet. IoT devices often use protocols like MQTT and CoAP. device. The term, coined by Cisco, evokes fog sitting between the ground and the sky. Fog nodes aggregate, filter, and pre-process data from many edge devices before forwarding relevant results upstream.

Relationship to Edge Computing

The boundary between fog and Edge ComputingA distributed computing paradigm that processes data closer to where it is generated (at the network edge) rather than in a centralized data center. Reduces latency and bandwidth usage for IoT, gaming, and real-time analytics. is debated and often used interchangeably in industry literature. In practice, fog nodes are intermediate aggregation points — a gateway appliance that collects data from dozens of IoTInternet of Things. The network of physical devices (sensors, cameras, appliances, vehicles) embedded with connectivity and software that collect and exchange data over the internet. IoT devices often use protocols like MQTT and CoAP. sensors, runs local analytics, and pushes summaries to a cloud data warehouse. The OpenFog Consortium defined fog as a system-level architecture spanning from cloud to edge, while edge computing often refers to the device-proximate tier specifically.

Network Design for Fog

Fog architectures rely on reliable low-LatencyThe time delay for a data packet to travel from source to destination, typically measured in milliseconds (ms). Lower latency is critical for real-time applications like video calls, gaming, and financial trading. links between edge devices and fog nodes, and adequate BandwidthThe maximum data transfer rate of a network link, typically measured in bits per second (Mbps, Gbps). Bandwidth represents capacity, not actual speed; real-world transfer rates depend on latency, congestion, and protocol overhead. from fog nodes to the cloud. VLANVirtual Local Area Network. A logical network segmentation technique that groups devices into separate broadcast domains regardless of physical location, using IEEE 802.1Q tagging. VLANs improve security, performance, and manageability. segmentation isolates traffic from different device classes. QoSQuality of Service. A set of technologies and techniques that prioritize certain types of network traffic (voice, video, critical applications) over others to guarantee performance levels. QoS uses mechanisms like traffic shaping, queuing, and marking. prioritizes time-sensitive control traffic. Security is a persistent challenge: fog nodes often operate in semi-trusted physical environments, making NACNetwork Access Control. A security approach that enforces policies on devices attempting to join a network, verifying identity, health (antivirus, patches), and compliance before granting access. Integrates with RADIUS and 802.1X. enforcement and encrypted Overlay NetworkA virtual network built on top of an existing physical (underlay) network using encapsulation protocols like VXLAN or GRE. Overlay networks provide logical separation and flexibility without modifying the underlying infrastructure. tunnels essential. MTUMaximum Transmission Unit. The largest packet size (in bytes) that a network interface can transmit without fragmentation. Standard Ethernet MTU is 1500 bytes; jumbo frames allow up to 9000 bytes for high-performance networks. tuning matters when fog gateways tunnel traffic across heterogeneous link types.