Link capacity

[duncandewhurst]

The supply side research surfaced that link capacity is expressed in a variety of units and notations: Mbps, Gbps, STM and E-carrier.

The standard should specify a consistent unit for link capacity so that users do not need to convert between capacities specified in different units. According to the ITU Broadband Transmission Capacity Indicators (Indicator 4), the above units can all be converted into Gbps.

Our draft description for Link.capacity is based on the description of the ITU indicator:

The transmission rate, or throughput, of this link, expressed in Gbit/sec (Gbps). The equipped capacity is the total capacity of the circuits (e.g. E1, DS3, STM-1 etc.) which have been activated in the network transmission equipment of the link.

This issue is to consider whether the standard should have a separate Link.capacityDetails field to allow publishers to provide further details in their preferred unit and whether that field should be modelled as a free-text field or as structured data.

If I understood correctly, of the measures listed above, only STM is relevant to fibre connections. It is a measure of capacity for connections that use the SDH protocol. However, it is not the only unit in which fibre network capacity is measured. In the SONET standard used in the US, the basic unit is Optical Carrier level-1(OC-1). Links can also use DWDM to create multiple SDH/SONET connections over a single fibre.

A free-text field would be fairly straightforward:

{
  "links": [
    {
      "capacity": 4.976,
      "capacityDetails": "2xSTM-16"
    },
    {
      "capacity": 2.48832,
      "capacityDetails": "1xOC-48"
    },
    {
      "capacity": 640,
      "capacityDetails": "64xSTM-64 over DWDM"
    }
  ]
}

Assuming that there can be multiple circuits of different standards active on a link, modelling as structured data starts to look like modelling details of the circuits, which becomes complex thanks to technologies like DWDM. I don't think that level of detail is necessary for the first version of the standard. However, it might be prudent to make a capacityDetails an object to allow for additional properties to be added in the future:

{
  "links": [
    {
      "capacity": 4.976,
      "capacityDetails": {
        "description": "2xSTM-16"
      }
    }
  ]
}

[duncandewhurst]

The alpha schema and codelists added in #101 reflect the latest proposal in this issue (a capacityDetails object with a .description field).

This issue will remain open against the beta milestone to gather feedback from the alpha consultation.

[duncandewhurst]

We've not heard any further feedback on this issue so I'm going to close it for now.