fix: use ref power on transceiver to Roadm (or transceivers) links

The recent refactor removed a default pref in case of transceivers-OMS
(amplified links starting with a transceiver).
This resulted in a mismatch between input power during design
(default 0 forced in the function) and the design ref power using SI
power_dbm.

This change ensures that the same power is used for the input power
and for the design ref power, and avoid inconsistent gain computatiion.

The code has been using the same power input (SI power_dbm) to define the
power target out of a transceiver and the target out of amplifiers
(at the input of fibers). This will be changed in a future patch.

Signed-off-by: EstherLerouzic <esther.lerouzic@orange.com>
Change-Id: I610c8df19039bcf156a8ba77c79114b22913a538

gnpy/core/network.py

@@ -295,7 +295,9 @@ def set_egress_amplifier(network, this_node, equipment, pref_ch_db, pref_total_d
         prev_node = this_node
         node = oms
         if isinstance(this_node, elements.Transceiver):
-            this_node_out_power = 0.0     # default value if this_node is a transceiver
+            # for the time being use the same power for the target of roadms and for transceivers
+            # TODO: This should be changed when introducing a power parameter dedicated to transceivers
+            this_node_out_power = pref_ch_db
         if isinstance(this_node, elements.Roadm):
             # get target power out from ROADM for the reference carrier based on equalization settings
             this_node_out_power = this_node.get_per_degree_ref_power(degree=node.uid)

tests/test_network_functions.py

@@ -10,7 +10,7 @@ from gnpy.core.exceptions import NetworkTopologyError
 from gnpy.core.network import span_loss, build_network
 from gnpy.tools.json_io import load_equipment, load_network, network_from_json
 from gnpy.core.utils import lin2db, automatic_nch
-from gnpy.core.elements import Fiber
+from gnpy.core.elements import Fiber, Edfa
 
 
 TEST_DIR = Path(__file__).parent
@@ -170,3 +170,73 @@ def test_eol(typ, expected_loss):
     fibers = [f for f in network.nodes() if isinstance(f, Fiber)]
     for i in range(2):
         assert fibers[i].loss == expected_loss[i]
+
+
+@pytest.mark.parametrize('p_db, power_mode, elem1, elem2, expected_gain, expected_delta_p, expected_voa', [
+    (-17, True, 'edfa', 'fiber', 15.0, 15, 15.0),
+    (-17, True, 'fiber', 'edfa', 15.0, 5.0, 5.0),
+    (-17, False, 'edfa', 'fiber', 0.0, None, 0.0),
+    (-17, False, 'fiber', 'edfa', 10.0, None, 0.0),
+    (10, True, 'edfa', 'fiber', -9.0, -9.0, 0.0),
+    (10, True, 'fiber', 'edfa', 1.0, -9.0, 0.0),
+    (10, False, 'edfa', 'fiber', -9.0, None, 0.0),
+    (10, False, 'fiber', 'edfa', 1.0, None, 0.0)])
+def test_design_non_amplified_link(elem1, elem2, expected_gain, expected_delta_p, expected_voa, power_mode, p_db):
+    """Check that the delta_p, gain computed on an amplified link that starts from a transceiver are correct
+    """
+    json_data = {
+        "elements": [
+            {
+                "uid": "trx SITE1",
+                "type": "Transceiver"
+            },
+            {
+                "uid": "trx SITE2",
+                "type": "Transceiver"
+            },
+            {
+                "uid": "edfa",
+                "type": "Edfa",
+                "type_variety": "std_low_gain"
+            },
+            {
+                "uid": "fiber",
+                "type": "Fiber",
+                "type_variety": "SSMF",
+                "params": {
+                    "length": 50.0,
+                    "loss_coef": 0.2,
+                    "length_units": "km"
+                }
+            }
+        ],
+        "connections": [
+            {
+                "from_node": "trx SITE1",
+                "to_node": elem1
+            },
+            {
+                "from_node": elem1,
+                "to_node": elem2
+            },
+            {
+                "from_node": elem2,
+                "to_node": "trx SITE2"
+            }
+        ]
+    }
+    equipment = load_equipment(EQPT_FILENAME)
+    equipment['Span']['default'].power_mode = power_mode
+    equipment['SI']['default'].power_dbm = p_db
+    network = network_from_json(json_data, equipment)
+    edfa = next(a for a in network.nodes() if a.uid == 'edfa')
+    edfa.params.out_voa_auto = True
+    p_total_db = p_db + 20.0
+
+    build_network(network, equipment, p_db, p_total_db)
+    amps = [a for a in network.nodes() if isinstance(a, Edfa)]
+    for amp in amps:
+        assert amp.out_voa == expected_voa
+        assert amp.delta_p == expected_delta_p
+        # max power of std_low_gain is 21 dBm
+        assert amp.effective_gain == expected_gain