Question

What is an overlay network? Does it include routers? What are the edges in the overlay network?

Short answer

An overlay network is virtual and uses existing networks but does not rely on traditional physical routers. Its edges are logical connections between nodes.

Step-by-step solution

Define an Overlay Network

An overlay network is a computer network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network.

Relationship with Routers

Overlay networks do not necessarily include the physical routers found in traditional network architectures. Instead, they use existing networks' infrastructure, like the internet, to connect nodes while forming their own network topology on these underlying networks.

Identify Edges in Overlay Networks

In an overlay network, the edges are the virtual or logical connections between nodes. These can be implemented as a set of rules or software that allows for different network structures, without relying on direct physical pathways.

Key concepts

Virtual Links

In the world of networking, virtual links are key elements of an overlay network. Imagine you have two computers that need to communicate with each other over the internet. In a regular network, these computers would connect using physical cables or hardware. However, in an overlay network, the connection is established using virtual links.

These virtual links are not physical connections. They are more like agreements that data will flow between these two computers.

• They use existing physical paths but represent a higher-level connection.
• They rely on software or protocols to manage the data flow, rather than physical hardware.
• Virtual links can traverse multiple physical networks to create a direct logical connection between nodes.

This abstraction allows overlay networks to be flexible and efficient, adapting quickly to changes or requirements without altering physical infrastructure.

Network Topology

Network topology refers to how nodes in a network are structured and connected. In overlay networks, the topology is determined by the virtual links we previously discussed.

For example, one might arrange nodes in a star, mesh, or ring topology, no matter how the physical network looks beneath it.

• Overlay networks can dynamically change their topology to optimize performance, ensuring data is efficiently routed between nodes.
• This flexibility offers robustness, as it can easily adapt to failures or traffic demand changes.
• Overlay topology exists independently of the physical network structure, meaning the same physical nodes can participate in different overlay topologies.

Understanding overlay network topology helps in designing efficient networks that can provide desired services without needing new physical infrastructure.

Underlying Network

The underlying network serves as the foundation upon which an overlay network is built. Think of it as the real-world physical infrastructure that handles the actual data transmission.

It consists of components like routers, switches, and physical connections such as cables and fibers.

• Overlay networks utilize these underlying networks to provide a transport medium for virtual links.
• They do so without altering the hardware, relying instead on software to create new paths.
• The underlying network supports multiple overlay networks coexisting without interference.

This separation from the physical infrastructure allows overlay networks to be flexible and scalable, able to extend or adapt quickly to new conditions without requiring new hardware investments.

Logical Connections

Logical connections are the non-physical links established in an overlay network to enable communication between nodes. Unlike traditional connections that rely on physical components, logical connections use existing infrastructure.

• These connections are defined by software that determines how data flows through various network paths.
• Logical connections can span multiple physical paths, creating efficient routes between nodes.
• They are crucial for overlay networks, allowing nodes to communicate as if they were directly connected, irrespective of the physical distances in the underlying network.

By relying on logical connections, overlay networks can function independently of physical network changes, continuing to provide reliable communication even as the real-world components change.