Sierra Wireless / Semtech

Sierra Wireless — field brand hub (AirLink modem)

Sierra Wireless AirLink (and similar cellular gateways) carry the OCPP websocket for many cabinets. Tickets present as soft-offline chargers: Cloud red, local Ready. RSSI OK ≠ stable websocket. Fix antenna placement, connectors, SIM/APN, and MTU/keepalive before condemning the EVSE power stage—or the modem—blindly.

When this OEM shows up / ownership

EVSE tech owns: Correlate Heartbeat gaps with ALEOS signal history; inspect SMA/antenna location; temporary external antenna prove; document metal-cabinet attenuation.

Network / carrier owns: APN provisioning, SIM status, private APN firewalls, MTU.

OEM modem owns: Bricked FW recovery, RF hardware after path proven.

Guide: /guides/ocpp-faulted-triage · /learn/reading-ocpp-statusnotification.

How faults typically present

EVSE / CSMS

• Heartbeat timeout, BootNotification storms, Unavailable while local Available (/entries/protocol-ocpp-f02-heartbeat-timeout-to-csms).
• DNS/TLS failures to CSMS (/entries/protocol-net-c01-dns-resolution-failure-to-csms).

ALEOS / modem

• Weak signal LEDs, no service, SIM not provisioned, wrong APN after swap, FW brick after update.

Physical cues

• Antenna inside shielded door, loose SMA, water in connector, recent SIM change, metal cabinet, landscaping that moved the antenna whip.

Ranked common failure patterns

1. RSSI too low in cabinet — Placement/attenuation. Free sample: /entries/sierra-wireless-mdm-rssi-rssi-too-low-in-cabinet.

2. Antenna connector loose — SMA torque / water intrusion. /entries/sierra-wireless-mdm-ant-antenna-connector-loose.

3. SIM not provisioned / APN — Carrier side. /entries/sierra-wireless-mdm-sim-sim-not-provisioned-apn.

4. Wrong APN after SIM swap — Config drift. /entries/sierra-wireless-mdm-apn-wrong-apn-after-sim-swap.

5. Modem FW bricks OCPP path — Recovery image on stable power; don’t leave half-bricked. /entries/sierra-wireless-mdm-fw-modem-fw-bricks-ocpp-path.

Log sources / tools

Source	What you pull
ALEOS	RSSI/RSRP history, APN, FW version, LED pattern
CSMS	Heartbeat gaps, disconnect storms, BootNotification
Known-good external antenna	Placement prove
Carrier portal	SIM active, APN profile

Field checklist (first 15 minutes)

1. Local Ready + Cloud red? → modem/backhaul branch first.
2. Pull ALEOS RSSI vs OCPP disconnect timestamps.
3. Inspect antenna location and SMA.
4. Temporary external antenna test.
5. Confirm SIM/APN only after RF path looks sane.
6. FW recovery only with stable supply and OEM image.
7. Do not RMA power modules for Heartbeat-only failures.

When to escalate

Carrier / network — Provisioning, private APN, firewall to CSMS.

Modem OEM — RF fail after external antenna prove; bricked FW after recovery fails.

EVSE OEM — Protective Faulted with healthy Heartbeat (different branch).

Worked examples

A — Soft-offline evenings only; antenna inside door. External antenna restores link → relocate permanent antenna.

B — After SIM swap, ALEOS up, OCPP dead. Wrong APN.

C — RSSI “fine” snapshot; websocket drops every 90s. Keepalive/MTU/NAT—not a new modem first.

False friends

Looks like	Often actually
Dead charger	Soft-offline modem path
Bad power supply	Antenna in shield / loose SMA
Needs new EVSE board	Wrong APN after SIM swap
Random Faulted	BootNotification storm after reconnect

Ticket hygiene

Export ALEOS signal history with CSMS Heartbeat gaps on the same clock. Scrub site credentials. Note cabinet metal and antenna photos.

Related learning

/help · /brands/delta (backend unreachable cousins) · /entries/protocol-net-c01-dns-resolution-failure-to-csms

RF vs OCPP (drill)

Heartbeat dead + local Ready → backhaul first. Isolation Faulted + Heartbeat alive → not a modem ticket. RSSI snapshot “OK” with 90-second drops → keepalive/MTU/NAT or multipath fade—not “buy a new modem” as step one. Antenna inside the door is the most common self-inflicted soft-offline on metal cabinets. After SIM swaps, verify APN before reseating EVSE control boards. FW recovery needs stable DC and the OEM image—random files brick units.

Placement checklist

1. Is the antenna outside the Faraday cage of the door/cabinet?
2. Is the SMA finger-tight then wrenched per OEM (not loose, not crushed)?
3. Does a temporary external antenna restore Heartbeat for 15 minutes?
4. Do disconnects still track weather or only shift changes (SIM/APN work)?
5. Is FW current and known-good, or was there a mid-update brownout?

If 1–3 fail, stop blaming OCPP URL first. If 1–3 pass and APN is wrong, stop blaming antennas. If FW is bricked, recover once on stable power—then board. Pair every modem ticket with CSMS Heartbeat CSV so “RSSI fine” arguments die against timestamps. Browse Sierra Wireless entries below or database. For cellular failover flapping on Tritium and similar, see also /brands/tritium. Soft-offline without RF evidence is still an OCPP URL/cert problem until proven otherwise.

Closeout template

“Local Ready: [y/n]. Heartbeat gaps: [times]. ALEOS RSSI/RSRP: [range]. Antenna: [inside door/external/prove result]. SIM/APN: [verified]. FW: [version/recovery]. Next owner: [carrier/network/modem OEM/EVSE if protective]. Power stage opened: no.” Attach the CSMS Heartbeat CSV whenever possible. Prefer RF placement prove before modem RMA, and modem/APN prove before EVSE control-board RMA. Keep the order honest.

When in doubt, restore Heartbeat with an external antenna prove before you touch EVSE HV covers.