We mentioned last year about an iPhone app that monitored Omron PLCs called Scadamobile. The new version (1.3) that was approved on iTunes a few days ago, now supports the Ethernet/IP protocol. This app allows the user to read/write tags in the Logix family (CompactLogix and ControlLogix) of Allen Bradley controllers.
This is not new (been out since August), but I thought I would mention it as an eye opener.
Ethernet/IP, the industrial communications protocol that enables communication between machine I/O information systems, factory floor devices and enterprise systems has an open-source software stack. The stack was created and recently released by the Vienna University of Technology’s Automation and Control Institute and written in the C Programming language.
This is great from the standpoint of reducing development costs and cutting the risk of implementation. It may very well be a catalyst for vendor adoption and implementation of (the already popular) Ethernet/IP protocol. I’ll go as far as to say that it may also increase custom development from independent outfits/ system intergrators and internally within the larger industries.
Link to the license and royalty free adapter stack download @ SourceForge
NIST (National Institute of Standards & Technology) and MEL (Manufacturing Engineering Laboratory) has developed an open source test tool for Industrial Ethernet called Industrial Ethernet Network Performance Tool (IENetP).
Available through Sourceforge.net here, it allows users to test Industrial Ethernet TCP/IP systems that require deterministic operations. The current version analyzes network traffic and performance of a device on ODVA’s Ethernet/IP network only but NIST has said to be releasing additional versions for other Industrial Ethernet types (release date unavailable).
Test Tool for Industrial Ethernet Network Performance document (distributed by ISA)
NIST test tool download (Sourceforge.net)
Layer 2 switches and Layer 3 switches – you may have heard the terms before.
So what exactly are they?
Both switch types have the capability of linking network devices together from one port to another. Unlike hubs, switches distribute data more intelligently as it interprets them and sends it out to the right destination.
Layer 2 and Layer 3 terms comes from the OSI seven Layer model (a theoretical way of dividing a network architecture up with functionality, service, dependence and application). Within the model, Layer 2 represents the “Data Link Layer” while Layer 3 represents the “Network Layer”.
Layer 2 switches have the capability of moving packets around a single network. As the reference to the OSI Layer holds true, this switch facilitates data only (and) within the physical layer (also known as Layer 1 e.g. cables and connectors). It is intelligent enough to learn the MAC addresses of each device, source/ destination of each packet and routes each packet within the single domain (at wire speed). While it breaks up a collision domain, it does not have the ability to transport the data packet from one network to another nor can it prioritize packets to guarantee bandwidth. Putting devices on a Layer 2 switch makes one entire large local segment (or what some people might call a “broadcast domain”).
Layer 3 switches act like a traditional router – it enables different network segments to be linked together. With this, data can be inter-networked from one network subnet to another. Prioritization of packets can be setup and the Layer 3 switch is intelligent enough to learn which routes are the best between the networks. While the Layer 2 switch routes packets based on MAC, Layer 3 switches route data packets based on IP. Going a step further, Layer 3 switches have the capability to logically separate networks into two or more VLANs (Virtual LANs), enhancing security and unauthorized access between networks. A Layer 3 switch typically sits above Layer 2 switches and governs the routes/ access between the different networks.
An example of this would be within a water treatment facility. Being a big treatment plant, each separate department (Clorination, Aeration, Distillation, Filtration, Waste Generation etc.) is split up into smaller/mini networks. Each mini network (consisting of PLC, I/O modules, monitors, sensors, HVAC, Historian stations and more) is controlled by its own Layer 2 switch. As all departments need the ability to synchronize, coordinate and share data with each other to perform the relevant operations, there needs to be a device that allows each data to move from one department’s network to another. That is where the Layer 3 switch comes in. All Layer 2 switches essentially converges to the Layer 3 switch facilitating inter-network data transport with the ability to prioritize packets, allow/ limit access to certain networks at any given time.
The Cisco IE-3000 switch and Transition Networks’ Milan SM801PST are examples of Layer 2 switches. The Cisco Catalyst 3750 would be a good example of a Layer 3 switch.
EtherChannel is a technology used for port trunking (or “link aggregation” as Cisco calls it). It is used mostly in Cisco switches. The technology allows physical Ethernet ports to be grouped, forming one logical port/ connection. With that, only one connection is seen with the same MAC and IP address being shared, regardless of application(s) or user(s).
This is useful as a failsafe measure in the event that a link or several links are down makes it great for mission-critical applications — the technology redistributes traffic across the remaining active links with total transparency and speed. Distribution of loads across ports is based on Cisco’s proprietary algorithm which is calculated on the source/ destination IP, MAC and TCP/UDP port numbers.
EtherChannel is normally used within a network backbone rather than direct connections with end user devices/ machines. Connecting up end user devices would require the NIC / adapter of that particular device to be EtherChannel compatible. As of today, I don’t believe there is any PLC or embedded end user manufacturing/ control system device supporting EtherChannel, but that may change if the demand arises.
The maximum active number of ports that you can use with EtherChannel is eight (min. is two), regardless of the type of cable or whether it is Fast Ethernet, Gigabit Ethernet or 10 Gigabit Ethernet; with another one to eight ports acting as failover ports. The bandwidth is directly proportional to the ports and speed you use e.g. 5 ports running EtherChannel would give you 500 Mbit/s, 5 Gbit/s or 5 Gbit/s at Fast Ethernet, Gigabit Ethernet and 10 Gigabit Ethernet speeds respectively. This makes it very scalable as your traffic grows — a huge benefit.
When using EtherChannel, three things must apply:
1) All ports must be set to the same speed throughout
2) All links must comply with the IEEE 802.3 standard
3) All connected devices must support EtherChannel as well
One may argue the fact of why you would want to use EtherChannel when STP (Spanning Tree Protocol) is available. The answer would be that STP essentially limits the multiuse of links between switches and sends packets down one path at a time i.e. STP shuts down the extra redundant links. The use of EtherChannel allows the use of all available links between two devices at all times. You can use STP with EtherChannel to have a loop free topology and to prevent flooding of a network.
With all the good things being said, there is a drawback … EtherChannel is only limited to devices that support the proprietary technology. Therefore, you are bound by certain device manufacturers (mainly Cisco and Intel*). IEEE does have a similar open standard equivalent called IEEE 802.3AX (formerly IEEE 802.3ad).
*Intel has the capability to implement either the EtherChannel or IEEE 802AX within their Intel® PRO/100, PRO/1000, PRO/10GbE, Gigabit, and 10 Gigabit server adapters.
