ITU Channel Plans¶

netbox-wdm ships with five built-in channel grids. The grid is set on each WDM profile and propagated to every WdmNode created from that profile. The grid drives both the channel labels (e.g. C32, L184.50, CWDM-1310) and the wavelength assigned to each grid position.

Grids supported¶

The constants are defined in netbox_wdm/wdm_constants.py. Wavelengths are computed from frequency for DWDM grids and held as a fixed list for CWDM.

How grid_position maps to a channel¶

The grid_position field on WdmChannelPlan and WdmChannel is a 1-based integer that indexes into the grid's channel list. The plugin uses get_channel_info(grid, position) to look up the matching (label, wavelength_nm) tuple.

grid_position also drives the rear_port_position value used in PortMappings. This is what lets multiple channels share a single COM rear port: each channel's PortMapping points at the same rear_port but carries a different rear_port_position. EXP and 1310 pass-through ports are positioned after the channel positions on the same COM rear port.

DWDM 100 GHz¶

44 channels starting from 192.10 THz, with 100 GHz spacing. Labels are C21 through C64 (the ITU C-band convention).

Wavelengths are computed as c / freq_thz and rounded to two decimal places using Decimal arithmetic so values are stable across processes.

DWDM 50 GHz¶

88 channels, 50 GHz spacing, labels alternate between C{n} and C{n}.5. Position 1 starts at 192.10 THz (label C21), position 2 is 192.15 THz (label C21.5), and so on through position 88.

DWDM L-band 100 GHz¶

72 channels spanning 184.50 THz to 191.60 THz, with 100 GHz spacing. This range is the ITU-T G.694.1 L-band (1565-1625 nm), anchored to the same 193.1 THz reference frequency as the C-band grids; 191.60 THz sits below the C-band grid's 192.10 THz start, so the two bands do not overlap. Labels are frequency-based with two decimal places and an L prefix.

DWDM L-band 50 GHz¶

143 channels over the same 184.50 THz to 191.60 THz span, at 50 GHz spacing. Labels are frequency-based with two decimal places and an L prefix, incrementing by 0.05 THz per position.

CWDM¶

18 channels with a fixed 20 nm spacing.

Picking the grid for a profile¶

The grid you set on a profile should describe what the hardware actually is. The data sheet or front-panel labelling on the device tells you which grid to pick:

• CWDM: front ports labelled by 20 nm wavelengths (typically 1270 through 1610). 18 fixed wavelengths, no temperature stabilisation.
• DWDM 100 GHz: ports labelled with ITU C-band channel numbers (C21 through C64) on a 100 GHz spacing.
• DWDM 50 GHz: 88 wavelengths on a 50 GHz spacing, with labels alternating C{n} and C{n}.5. Common on newer coherent line systems.
• DWDM L-band 100 GHz / 50 GHz: front ports labelled in the 1565-1625 nm range, or by a frequency below 192 THz -- that is the giveaway when the data sheet speaks in wavelength rather than frequency. C+L systems pair an L-band mux with a C-band mux on the same fibre pair to double usable capacity; give each mux the profile that matches its own band, not the fibre as a whole.

If the device does not fit any of these, the bundled grids cannot represent it; see Adding a new grid below.

The grid is locked once channel plans exist. Changing it later requires clearing the channel plans first or creating a new profile. In practice this only comes up when a profile was set up with the wrong grid by mistake -- the device's grid itself does not change.

Adding a new grid¶

The grid list is hard-coded in wdm_constants.py and the WdmGridChoices ChoiceSet. To add another (for example 25 GHz or 12.5 GHz spacing -- both allowed by ITU-T G.694.1, but rare on fixed-grid hardware, which is why neither is bundled), extend both.

All four DWDM grids are built by one shared generator, _dwdm_channels(start_freq_thz, spacing_thz, count, label_fn), so a new fixed grid is a start frequency, a spacing, a channel count, and a label function -- reuse _l_band_label for a frequency-labelled grid, or write a new one for a grid with its own channel numbering. Register the result in WDM_GRIDS and add the matching key to WdmGridChoices. The grid column stores the bare key string and no migration carries a CHOICES literal, so adding a grid needs no migration. There is no runtime customisation hook for grids today.