What
is the default user name, password and IP
address for Ethernet Direct managed switches
?
User name is root, the password
is root, the default IP address
is 192.168.16.1
What is ethernet ?
Ethernet is a network that is a very efficient method of transmitting vast amounts of data. Ethernet is an open standars that is, any device can communicate over ethernet if it adheres to an OSI model that defines how ethernet operates. Multiple protocols can be used over the same network like Modbus and Ethernet I/P can work simultaneously over an ethernet network. The defined ethernet packet is the key to ethernet's flexibility. It is simply a method of transmission and is scalable and speeds have increased as technology has improved. Ethernet can work over copper cables, fiber optics and can also use wireless technology. It is simply the best way to communicate in an industrial environment.
What types of devices are used in an ethernet network ?
Hubs, switches, routers, media converters and the various user devices that can connect to them. Switches are used to manage traffic in an efficient manner and are available in managed and unmanaged versions. Hubs are older technology devices that repeat the transmission that is received on one port to all ports in a very inefficient operation. Media converters allow two different forms of media: copper and fiber - to connect. A router is a device that manages traffic between network segments. It connects networks at Layer 3 of the OSI model.
Can I use managed and unmanaged switches on the same network ?
Yes, however, in an application where managed switches are required, such as I/O over ethernet, it is advisable to use all managed switches. Large networks, more than 10 devices ( PLCs, HMIs, drives, etc. ) should use only managed switches for multicast control and diagnostics. IntraVUE™ software can effectively show the status of the network and quickly diagnose potential problems.
Can I use different brands of switches in a Redundant Ring ?
No, different manufacturers use proprietary firmware to manage ring redundancy. Use the same manufacturer for all switches on the ring for the guaranteed recovery time, usually 300ms for up to 50 switches on a fiber ring.
Is SNMP important?
Extremely! It is a well known tool that defines a structure and set of rules for managing network devices. With SNMP software and managed switches, it allows the user to see' the network and analyze the traffic and perform diagnostics. Unmanaged switches are blind on the network and can not be accessed by the user to diagnose traffic and problems. Some manufacturers advertise that they have mananaged switches, but they are not true SNMP enabled. They use proprietary software to look at a limited number of switch parameters. Use only switches that are SNMP compliant.
What is the purpose of IGMP?
IGMP is a method of limiting multicasts and broadcasts. PLCs create multicast traffic that can severely limit the bandwidth of a network. Managed switches allow the user to set up the network to limit the amount of multicast traffic. If using I/O over ethernet, IGMP is required for fast updates of the I/O.
What is required for I/O over ethernet?
Managed switches with IGMP snooping, port mirroring and, in some cases, VLAN capability. It is important to have fast response times and the ability to diagnose the network when problems arise. Port mirroring allows the user to forward copies of incoming and outgoing packets from one port of a switch to another. The mirrored port can then be used to send packets to a diagnostic tool for analysis without interrupting the client on the original port. Always use managed switches when implementing I/O over ethernet.
What is a VLAN ? What is its purpose ?
A technique that allows switches to create a single collision domain logically even though the nodes are on separate network segments physically. The benefit is that instead of installing physical hardware to segment a network, which can be difficult on a factory floor or water treatment plant, VLANs can do it logically. It allows fast response over several network segments by connecting to remote devices through a software implementation. Managed switches are required.
How do I set up IP addresses for my network ?
An IP address is a logical address assigned by the user of a managed switch and allows the switch to be recognized by SNMP software. The address allows the switch to be part of a collision domain. It is similar to a phone number. A typical private collision domain is usually 192.168.xxx.xxx.
What is a subnet mask ?
A method of determining what network devices are local is if all the devices have the same subnet mask, usually 255.255.255.0 , then they are in the same collision domain.
What is a multicast ? Unicast ? Broadcast ?
Multicast - data packet intended for a group of devices such as i.e., PLC to its I/O nodes
Unicast - data packets that are addressed to only a single device
Broadcast - data packet that will be sent to all nodes of a network. Cannot cross a router
How do I reset a switch ?
Most switches have a RESET' button that must be pressed for 5 seconds. All programmed data will be lost, including the IP address. The switch defaults to an IP address, i.e., 192.168.1.10. It can hen be re-programmed by the user. Most manufacturers have a similar feature so it is important to know the default IP address.
How can I look at the network ? At the bridge devices ?
By using SNMP enabled managed switches and SNMP software, such as IntraVUE. IntraVUE™ is especially adept at looking at devices on the network and bridge devices in a graphical format.
How can I determine when I have a node or switch dropout?
Many switches have a fault relay that can be enabled when a port, set by a DIP switch, drops out. The fault relay closes a circuit that can indicate to a PLC, light, horn, etc. that a node has dropped out. Managed switches can do all of the above and can also send a warning email to a client or server. A switch has port indicating LEDs that indicate that there is a physical connection and that there is a data connection. These are located wherever the switch is installed and may not be able to be viewed easily. Use the fault relay option to an indicator of some type.
How can I gain access to the network from an outside computer ?
Access by an outside computer can be handled in different ways depending upon the level of security required. Outside access to a factory floor network can be a dangerous situation if some type of security appliance is required. VPN tunneling is one method and a security appliance is necessary.
What does UTP, STP cabling mean?
Twisted pair cables. UTP is for Unshielded, twisted pair, while STP is for SHIELDED, twisted pair. UTP is what's typically installed by phone companies (though this is often not of high enough quality for high- speed network use) and is what 10BaseT Ethernet runs over. UTP is graded according to its data carrying ability (e.g., Level 3, Level 4, Level 5). 10BaseT Ethernet requires at least Level 3 cable. Many sites now install only Level-5 UTP, even though level 4 is more than sufficient for 10BaseT, because of the greater likelihood that emerging high-speed standards will require cable with better bandwidth capabilities. STP is typically used for applications that have devices that can create noise (such as AC drives) attaching the shield at one switch grounds the noise.
Should I invest in gigabit switches now ?
Yes, you can build in excess bandwidth with gigabit switches for future needs at a small cost today. Managed gigabit switches will ensure that your future needs are accommodated in your current infrastructure.
What is a "segment"?
A piece of the network wire bounded by bridges, routers, repeaters or terminators. Segments reside in the same collision domain and have the same subnet mask.
What is a "subnet"?
A segment of a network, such as a set of machines grouped together by a specific protocol feature
What is a switch?
The common ethernet hub simply broadcasts each message it receives to every one of its ports. Each ethernet device also has to wait for its turn to talk to the hub, increasing the likelihood of message collisions; therefore, real-time operation is jeopardized and determinism is difficult. Alternatively, the industrial ethernet switch automatically determines and remembers where an Ethernet device is located and routes messages only through the appropriate port. Internal to as industrial switch is a memory for Ethernet MAC addresses so it remembers the routing for even the largest industrial network. In addition, it contains message buffers to store incoming messages until it is safe to transmit them over the appropriate network segment. This buffering not only avoids collisions, but it can further speed up the system by transmitting message packets over multiple network segments simultaneously.
Industrial ethernet switches further enhance the performance of your network by performing automatic speed changes on the appropriate port. Some user devices communicate at 10 Mbits per second (which is more than adequate for the small lightly loaded messages that some devices need). These devices, when connected to an industrial ethernet switch can be uplinked to a controller or computer at 100 Mbits per second. In effect, the computer can talk to ten times as many stations at the higher speed. The industrial switch routes the messages to multiple devices at the reduced speed in parallel (at the same time).
By avoiding collisions and directing network traffic efficiently, the Industrial Ethernet Switch promotes real-time performance in your deterministic industrial system.
There are two types of switches: managed and unmanaged. The unmanaged switch requires no setup and does not have an IP address. It regulates traffic according to preset parameters in its firmware. It is a Plug & Play device.
A managed switch, allows the user to change the parameters of operation. An IP address can be given, as well as a name and location, so that the switch can be identified by an SNMP software package such as IntraVUE. A managed switch stores port data and traffic data to memory locations that can be viewed with SNMP software. Security features, such as, who can access the switch, turning unused ports off, and Alarm emails can be programmed by the user to indicate fault conditions. VLANs, Redundancy, ring or RSTP, are set up by the user in a managed switch. IGMP snooping is a feature to control PLC multicasting. It is extremely important to use managed switches when I/O over ethernet is implemented.
What is a Transceiver?
A transceiver allows a station to transmit and receive to/from the common medium. In addition, Ethernet transceivers detect collisions on the medium and provide electrical isolation between stations.
What is a Repeater?
A repeater acts on a purely electrical level to connect to segments. It amplifies and reshapes (and, depending on the type, possibly retime) the analog waveform to extend network segment distances. It does not know about addresses or forwarding, thus it cannot be used to reduce traffic as a bridge can in the example above. Switches can be repeaters. A hub cannot.
What is a Hub?
A hub is a common wiring point for star-topology networks, and is inefficient in today's networks because every port sees the traffic of any port. What comes into port 1 of a 5 port hub is duplicated to all the ports and switches allow point to point traffic for efficient use of the bandwidth.
How does a Router work?
Routers work much like bridges, but they listen to the upper network layer protocols (OSI layer 3) rather than physical layer (OSI layer 1) protocols. A router will decide whether to forward a packet by looking at the protocol level addresses (for instance, TCP/IP addresses) rather than the MAC address. Because routers work at layer 3 of the OSI stack, it is possible for them to transfer packets between different media types (i.e., leased lines, Ethernet, token ring, X.25, Frame Relay and FDDI). Many routers can also function as bridges.
What is a Driver ?
The software that allows an Ethernet card in a computer to decode packets and send them to the operating system and encode data from the operating system for transmission by the Ethernet card through the network. By handling the nitty-gritty hardware interface chores, it provides a device-independent interface to the upper layer protocols, thereby making them more universal and [allegedly] easier to develop and use.
What is a Broadcast Storm?
It describes a condition where devices on the network are generating traffic that by its nature causes the generation of even more traffic. The result is a degradation of performance or complete loss of the network as the devices continue to generate more and more traffic. This can be related to the physical transmission or to very high level protocols.
What is a MAC address ?
It is the unique hexadecimal serial number assigned to each Ethernet network device to identify it on the network. With Ethernet devices (as with most other network types), this address is permanently set at the time of manufacturer, though it can usually be changed through software.
Why must the MAC address to be unique?
Each card has a unique MAC address, so that it will be able to exclusively grab packets off the wire meant for it. If MAC addresses are not unique, there is no way to distinguish between two stations. Devices on the network watch network traffic and look for their own MAC address in each packet to determine whether they should decode it or not. Special circumstances exist for broadcasting to every device. Layer 2 works off MAC addresses.
Are there any restrictions on how Ethernet is cabled?
Yes, there are many, and they vary according to the media used. First of all, there are distance limitations: 10Base2 limited to 185 meters (607 ft) per unrepeated cable segment. 10Base5 limited to 500 meters (1,640 ft) per unrepeated cable segment. 10BaseF depends on the signaling technology and medium used but can go up to 2KM. 10BaseT generally accepted to have a maximum run of 100-150M, but is really based on signal loss in Db's (11.5db maximum loss source to destination). 10Broad36 limited to 3,600 meters (almost 2.25 miles). Then there are limitations on the number of repeaters and cable segments allowed between any two stations on the network. There are two different ways of looking at the same rules:
The Ethernet way: A remote repeater pair (with an intermediate point-to-point link) is counted as a single repeater (IEEE calls it two repeaters). You cannot put any stations on the point to point link (by definition!), and there can be two repeaters in the path between any pair of stations. This seems simpler to me than the IEEE terminology, and is equivalent.
The IEEE way: There may be no more than five (5) repeated segments, nor more than four (4) repeaters between any two Ethernet stations; and of the five cable segments, only three (3) may be populated. This is referred to as the "5-4-3" rule (5 segments, 4 repeaters, 3 populated segments). It can get difficult when you start cascading through 10BaseT hubs, which are repeaters unto themselves. Just try to remember, that any possible path between two network devices on an unbridged/unrouted network cannot pass through more than 4 repeaters or hubs, or more than 3 populated cable segments. Finally, 10Base2 is limited to a maximum of 30 network devices per unrepeated network segment with a minimum distance of 0.5m (1.5ft) between T-connectors. 10Base5 is limited to a maximum of 100 network devices per unrepeated segment, with a minimum distance of 2.5m (8.2ft) between taps/T's (usually indicated by a marker stamped on the cable itself every 2.5m). 10Base T and 10BaseF are star-wired, so there is no minimum distance requirement between devices, since devices cannot be connected serially. You can install up to the Ethernet maximum of 1024 stations per network with both 10BaseT and 10BaseF.
