Designing our way out of a rats nest!

A few (5) words on the process of designing new access networks, aka regional aggregation networks (health warning: written by not-a-network-designer).

  1. It
  2. Takes
  3. A
  4. Long
  5. Time

I could leave it there, but for the sake of clarity I’ll delve into some of the more interesting and relevant details.

So, we have a contractual requirement to replace a Janet regional network, and we have a list of member and customer services we need to deliver…3…2…1…GO!

First thing we do is open up our copy of the Openreach Exchange spreadsheet. I’m told that this information is a national secret, but it appears to be one of those secrets that everyone knows (well, service providers know), so we use it. We start by mapping each customer site in a region to its logically closest Exchange, this uncovers the spread of Exchanges we ideally need to build into, but more importantly the important ones where multiple customers will connect. These will form the basis of the regional aggregation network. We also factor into that the locations of the current RNEPs and other key PoPs within the region, and build that into the design. The common outcome of this (so far) is that we’ll end up with a core set of PoPs and Exchanges where the majority of customers will connect, then some outlying Exchanges where few customers will connect, and over longer distances, but that represents the best value solution. We then connect the dots with Openreach optical services to give us a complete core topology of rings and arcs that deliver diverse connectivity into each location. This is what we call our reference design.

The next phase is to engage our fibre suppliers. We have a Dynamic Purchasing System with a number of fibre providers registered, so we issue an invitation to all of them, to bid fibre spans to replace Openreach optical services on our reference design (on the basis fibre that we can light ourselves is better, etc). We’ll then evaluate the bids that come back and re-design the network on a ‘pick & mix’ basis, where we’ll use individual spans from separate suppliers if that represents best value. The main rule of thumb here is that any individual ring or arc needs to be either 100% dark fibre or 100% Openreach optical services, not a combination of both. As you can imagine, this takes a lot of time, especially when 4 or 5 fibre bids containing multiple fibre spans and resilience options are on the table, but it’s a key step to get right to ensure that we’re getting best value from the market whilst also building a resilient, scalable and future-proofed network. Once complete, we have a final topology, and experience to date tells us that the most likely outcome is a fibre core in the centre of a region (where the big towns and cities are, and where the majority of our customers are), then Openreach optical services out to the more remote parts of the region, where we have less customers and the aggregated capacity requirements are lower. We’re happy with this.

We then move to more detailed mapping of individual customer connections to their serving Openreach Exchange, checking fibre routing, adding resilience where required, investigating fibre vs Openreach services. All of the same steps as above but this time with an eye on services to Members and Customers rather than the regional aggregation network. Again a time consuming exercise, but another one that it’s important to get right.

Once all of the above has been completed, we mash it all together into a list of optical and Ethernet equipment that is needed, at Exchanges and at customer sites, that goes out to our equipment suppliers to quite against. It’s only at this point that we have a genuine view of the total cost of the network (we estimate up front, but as we all know, all estimates are wrong), so we cross fingers (and toes) and hope that it’s within budget – thankfully it usually is.

And when we’ve done all of that and have a final design, we proceed to ordering the required rack space at Openreach Exchanges, one outcome of which could be that the space we want isn’t actually available, and we have to start the whole process again 🙂

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