Posted by: Ger Rietman | September 16, 2016

The Light Weight Ethernet (LWE) implementation in NemaStudio

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Introduction

Recently Sailsoft introduced a partly implementation of LWE (Light Weight Internet) in her NMEA 0183 simulation software NemaStudio.

In the IEC standard IEC 61162-450, the term LWE is not explicitly mentioned but is described as “Part 450: Multiple talkers and multiple listeners –Ethernet interconnection”.

Protocol layers used in LWE

As the name suggests, LWE is Ethernet based, hence the Data Link layer is Ethernet. The Network layer is IP. Yet the most notable layer is the Transport layer. This is Multicast UDP, with a predefined IP address range and port destination set.

The choice of UDP over TCP/IP is rather obvious since the latter is a unicast solution and is not suitable for a “One Talker, Multiple listeners” environment, basic feature in NMEA 0183 and IEC 61162 protocols.

IP address range

IEC 61162-450 standard IP address range is 239.192.0.1 through 239.192.0.16, while the port numbers range from 60001 through 60016. each IP address is designated to a specific group, e.g.239.192.0.3 port 60003 is assigned to Satellite navigation equipment like GPS.

LWE and NMEA 2000

NMEA 2000 has been around since 2001 and with the intention to replace NMEA 0183. We are 15 years later and I cannot make another conclusion than that NMEA 2000 has failed in this respect.  Today NMEA 2000 has been commonly accepted in the pleasure yacht environment, yet I cannot find any proof that NMEA 2000 is widely used in the professional maritime industry. For some years now rumours are that the NMEA is working on an Ethernet implementation called “OneNet” to abandon the CAN bus transport layer of N2K. To me personally I wonder why NMEA does all this work since there is a good, standardized solution available since 2011 described in IEC 61162-450.

Current status of LWE support in NemaStudio

Since March 2015 (Version1.27), Multicast UDP has been available in NemaStudio. Recently (Version 3.31) the null-terminated sentence prefix string “UdPbC” was introduced to be more compliant to IEC 61162-450. From Version 3.32 NemaStudio will also (partially) support the TAG block as defined in NMEA 0183 V.4.0.

Further reading

A good article explaining LWE can be found here: https://issuu.com/mortenjc/docs/digital_ship_december_2010

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