href="#fb3_img_img_8e918635-4d1f-537b-9187-cff7fca854a4.gif" alt="Schematic illustration of fronthaul, backhaul, and midhaul networks."/>
Figure 3.4 Fronthaul, backhaul, and midhaul networks.
3.10 Last Mile or Access Networks
When defining infrastructure edge computing in a previous chapter, the term last mile networks was used to denote the dividing line between the locations of the device edge and infrastructure edge to allow us to separate these two very different domains from one another. Last mile networks are key because they represent, for the majority of users and endpoints, the way that they connect to any of the network‐accessible resources that they seek to use. That is why these networks are also referred to as the access layer, when we consider the internet as a network of networks; there must be a first layer of network infrastructure which the endpoint connects to. The connectivity between that first layer then shapes much of the performance and cost that will be achievable in the network overall.
Recalling our discussion in a previous section on network interconnection, we can see that last mile network interconnection is especially critical to fulfil the promises of infrastructure edge computing. Where one endpoint is connected to one network and the endpoint or resource they want to access is connected to another, even if that endpoint is located in a nearby infrastructure edge data centre, if interconnection between these networks must take place a significant distance away in an IX, then the lower latency and cost of data transportation offered by the infrastructure edge data centre will not provide any benefit, as all traffic will move through the IX before it reaches the edge data centre.
The diagram in Figure 3.5 illustrates this challenge. Where access networks are not interconnected at the infrastructure edge, the benefits of the infrastructure edge data centre then cannot be achieved:
A last mile network does not necessarily have to be a publicly accessible LTE network, cable network, or a similar entity; it may be a dedicated fibre connection for a single large entity such as a hospital to provide that entity with direct connectivity to resources which are of significant interest on the infrastructure edge. This network connectivity could be referred to, playing on the terminology used for the cloud on‐ramp services briefly described in a previous section, as an edge on‐ramp of sorts.
Figure 3.5 Last mile or access network interconnection failure.
Infrastructure edge computing does not prescribe a specific type or scale of access network, and the ideal infrastructure edge computing deployment will be able to support multiple concurrent access networks of scales varying from a single intended user through to hundreds of thousands. How each type of access network can interconnect at the infrastructure edge data centre will be explored in a later chapter, but for the purposes of this section, just remember that the more networks the better.
3.11 Network Transport and Transit
Ideally, an infrastructure edge computing network, which we will define here as the combination of infrastructure edge computing data centres combined with their supporting network infrastructure within a specific area such as a city, will serve as much of the traffic entering it from interconnected access networks as possible. Serving the traffic in this context refers to the ability of these resources to respond satisfactorily to the needs of the traffic and not have to send that traffic to a destination that is off of the infrastructure edge computing network, such as a regional data centre via backhaul.
Network transport is the ability of a network to move data from one endpoint to another, such as from its source to its destination. This is the core functionality of all communications networks. It does not matter what scale the network is operating at in terms of geographical coverage or the number of endpoints; ultimately it is required to provide transport from one endpoint to another using however many endpoints or links between endpoints are required to achieve this single goal.
Network transit is the ability of a network to function as a bridge between two other networks. In the context of infrastructure edge computing, consider the diagram in Figure 3.6, which shows how the infrastructure edge computing network can provide transit services between an access network on the left and a backhaul network on the right. In this example, the infrastructure edge computing network is not serving any of the traffic which comes in from the access network and is instead simply passing it through to another destination, which is accessible via its own backhaul network.
Figure 3.6 Infrastructure edge computing network providing transit services.
A typical infrastructure edge computing network will aim to minimise the amount of network transit it provides; although it is essential that the infrastructure edge computing network is able to provide transit for traffic that the network itself is unable to serve, this capability should not be seen as the main use of the infrastructure edge computing network. Although it is beneficial to the operator of the network if as great a proportion of the access layer traffic flows through the infrastructure edge computing network as possible, because this provides the greatest opportunity to serve traffic using resources at the infrastructure edge, if the bulk of this traffic cannot be served by the infrastructure edge due to the tenants present or other factors, the network is just joining access back to backhaul. This does not utilise the full capability of the infrastructure edge computing network for applications.
Of course, the physical data centre and network infrastructure of the infrastructure edge computing network is not enough alone to satisfy traffic; first, the right networks must be interconnected at the infrastructure edge to enable traffic to be exchanged efficiently without transporting it all the way to the IX and back, and second, the resources that an endpoint is trying to access must also be located at the infrastructure edge. These resources may include streaming video services, cloud instances, or any other network accessible resources, including new use cases such as IoT command and control.
Data Centre Interconnect (DCI) typically refers to the physical network infrastructure that is used to connect one data centre to another, regardless of the scale of the two facilities, combined with a protocol set used to facilitate inter‐data centre communication. This connectivity between facilities may be used to provide both transport and transit services; for example, in the context of several infrastructure edge data centres deployed within a single area such as a city, where a resource is not available in one data centre, it may be in another where that data centre is connected to directly or indirectly. In this case, the traffic can be sent to that serving data centre and can be served while still remaining on the same infrastructure edge computing network, providing some latency advantages.
Although in the ideal case traffic is served by the first infrastructure edge data centre that it enters, as long as the connectivity between infrastructure edge data centres is sufficient to provide a lower latency and cost of data transportation than sending the traffic back to another destination over a backhaul network, this process can still provide a better user experience than is otherwise possible.
Physically, the network connectivity between
