IEC 61162-450 (Maritime Bridge / Multicast)
IEC 61162-450 is the standard that defines how bridge equipment shares NMEA 0183 sentences over Ethernet UDP multicast. It is commonly referred to as "Lightweight Ethernet" (LWE).
The key point is that this is a transport method, not a new data format. The sentences themselves are exactly the same as in NMEA 0183; they are simply broadcast to a multicast group instead of over serial or TCP. This allows multiple devices (talkers) to transmit to the same group while multiple listeners receive simultaneously.
The gateway driver joins the specified multicast group, receives the datagrams, strips off the standard prefix and TAG block, and then parses the sentences with the same parser used by the NMEA 0183 driver. It is read-only.
Registration Form Inputs
| Field | What to enter | Example |
|---|---|---|
| IP address | (Not used) The group is specified in the options below | — |
| Port | (Not used) | — |
The default value of the IP address field is 127.0.0.1. The driver only accepts values in the multicast range (224–239) as a group, so if you leave the IP field as is, the option value or the standard's default is used. This is by design, to prevent accidentally listening on a unicast address.
Advanced Options
| Option key | Default | Description |
|---|---|---|
mcast-group | 239.192.0.4 | Multicast group to receive from |
mcast-port | 60004 | Port |
mcast-nic | (automatic) | Name of the network interface used for reception (e.g. eth0) |
strict-prefix | false | Whether to discard datagrams that lack the standard prefix (UdPbC) |
Shipboard networks usually have multiple NICs (separate navigation and office networks). If mcast-nic is not specified, the driver joins via the OS default route, which may leave it listening on the wrong interface and receiving nothing.
Transmission Groups
These are the eight groups defined by the standard. Register one connection per group (to receive multiple groups simultaneously, create separate connections).
| Group | Purpose | Address | Port |
|---|---|---|---|
| MISC | Miscellaneous | 239.192.0.1 | 60001 |
| TGTD | Target data (radar/ARPA) | 239.192.0.2 | 60002 |
| SATD | Satellite | 239.192.0.3 | 60003 |
| NAVD | Navigation data (default) | 239.192.0.4 | 60004 |
| VDRD | Voyage Data Recorder (VDR) | 239.192.0.5 | 60005 |
| RCOM | Remote communication | 239.192.0.6 | 60006 |
| TIME | Time | 239.192.0.7 | 60007 |
| PROP | Manufacturer-specific | 239.192.0.8 | 60008 |
Most navigation sensors (GPS/gyro/speed log) transmit on NAVD.
PLC Address Notation for Tags
Identical to NMEA 0183. Since the same parser is shared, the supported sentence range and aliases are also the same.
| Notation | Meaning |
|---|---|
RMC.7 | Field 7 of RMC (speed over ground, kn) |
GGA.lat | alias — latitude |
RMC.speed | alias — speed |
RMC | (field omitted) the entire last received raw sentence |
For the full list of supported sentences and aliases, refer directly to the alias table in the NMEA 0183 document.
Datagram Structure (Reference)
UdPbC\0 ← 6바이트 규격 프리픽스
\s:GP0001,n:0042*5A\ ← 선택적 TAG 블록 (송신자 식별)
$GPRMC,123519,A,...,W*6A ← NMEA 0183 문장
- Some field equipment implementations send only the sentence without a prefix, so the default behavior is lenient acceptance.
- To enforce standard compliance, set
strict-prefixtotrue.
Limitations
This driver is receive-only. The gateway does not transmit sentences to bridge equipment (talker role).
- AIS encapsulated sentences (
!AIVDM, etc.) are not supported — they are extracted from the datagram, but the sentence parser only handles sentences beginning with$. - IEC 61162-460 (the security-hardened edition) is not supported.
- IPv6 multicast is not supported.
Troubleshooting
| Symptom | Possible cause | What to check |
|---|---|---|
| No values arrive at all | NIC not specified, so listening on the wrong interface | Set mcast-nic to the navigation network NIC |
| No values arrive at all | Group/port mismatch | Check the transmission group in the equipment manual (table above) |
| Only some sentences arrive | Those sentences are transmitted on a different group | Register an additional connection for each group |
| Connection succeeds but values are empty | The sentence type in the tag address differs from the sentences actually received | Register the type only (RMC) and check the raw sentence first |