What is the difference between Internet and Ethernet, between LAN and WAN ?
What are the ISO layers ?
Is the Industrial Ethernet an Open standard ?
What is TCP/IP ?
What is different between an Ethernet switch and an Ethernet hub ?
What information is contained inside a message ?
What is different between unmanaged, Ring or managed solution ?
Can I connect any kind of Ethernet switches in a ring ?
How many switches can I connect together on the same LAN ?
What is Flow Control ?
What is the difference between Unicast, Broadcast and Multicast messages ?
What means Auto-MDI/MDIX-Crossover ?
MAC and IP addresses
What is the MAC address ?
What is an IP address ?
Public or private network ?
Is a switch managed with its IP address or its MAC address ?
Managed switch questions
I have a managed switch including 3 gigabit ports RJSML9MG1CAPS : Can I force the gigabit speed of ports 8 and 9 to 100 Mbps ?
What is IGMP ?
How can I access software for the managed switch ?
What is VLAN ?
What is port mirroring?
What are SNMP, RMON and MIB ?
Ring switch question
Is the Ring switch Managed or unmanaged ?
What are the advantages of a Ring switch ?
What is the difference between Internet and Ethernet, between LAN and WAN ?
Internet is a communication protocol for worldwide network (WAN = Wide Area Network).
Devices are managed through this network on the basis of IP addresses. Ethernet is a communication protocol for Local Area Network (LAN) using same media interfaces (mainly RJ45 or fiber).
LAN are independent networks but may be linked within a WAN through Internet devices such as Routers.
For many years the ISO/OSI model has described the layers of information in a network, particularly the low-level transport mechanisms.
From top to bottom, these are the layers and how these layers relate to your product design.
Ethernet is physical layers: layers 1 and 2. TCP/IP is a protocol, not a network, and uses layers 3 and 4.
7
Application
Meaning of data
HTTP
6
Presentation
Building blocks of data and encryption
5
Session
Opening and closing a specific communication path
4
Transport
Error checking
TCP, UDP
3
Network
Determination of data path within the network
IP
2
Data link
Data transmission, source destination, and checksum
Ethernet
1
Physical
Voltage level, voltage connection, wire, or fiber
RJ45, fibre optique
Layer
Name
Function
Example
A comparison with the ISO layers
Let’s compare the OSI layers with a road. A man go from office to home with a taxi on the motorway. Layer 1 (physical layer) = the roads Layer 2 (Data link) = Source is the office; destination is home.
The MAC address is the unique registration number of the car. Layer 3 (Network) = Determination of the correct road to take; the IP address is the street address. Same address may be found in several towns. Layer 4 (Transport) = Error checking: is the destination correct? Layer 5 (Session) = pay fare; handshake between source and destination Layer 6 (Presentation) = The taxi is one of many on the road – 1 message in the datastream Layer 7 (Application) = What is the purpose of travel? The passenger in the taxi is the purpose of the message, which also includes the source and destination information
Since Industrial Ethernet is derivated from office Ethernet, it is clearly an open standard.
- Main advantage for customers : there is no restriction with manufacturer’s own proprietary protocols such as with fieldbuses
Examples :
- Profibus / Profinet : Siemens
- CAN / CANOpen (/DeviceNet : Rockwell)
- FIP : Schneider
- Interbus : Phoenix contact
Thus any IEEE 802.3 device with a standard 10/100BaseT(X) Ethernet port can be easily connected to each other by just plugging them into the same Ethernet LAN. In addition, Ethernet is already commonplace in office environments, and offers many useful services, such as e-mail, FTP, and web browsing, all well known to users. Applying these services in an industrial control network gives users a head start, since they do not need to spend a lot of time learning new application programs. This also means that training costs can be lowered, and development time can be speeded up, since system developers are already familiar with the software that is readily available for Ethernet applications.
The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks.
It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard.
The TCP/IP model consists of four layers. From lowest to highest, these are the:
- Link Layer (2)
- Internet Layer (3)
- Transport Layer (4)
- Application Layer (7)
What is different between an Ethernet switch and an Ethernet hub ?
The common Ethernet hub simply broadcasts each message it receives to every one of its ports.
We may compare it to a loudspeaker.
Each Ethernet device also has to wait for its turn to 'talk' to the hub, increasing the probability of message collisions; therefore, real-time operation is jeopardized and determinism is difficult.
Alternatively, a switch automatically determines and remembers where an Ethernet device is located and routes messages only through the appropriate port.
This minimizes network loading and enables true deterministic communications over Ethernet.
See hereafter description.
Without Switch :
- All equipments receive the message, even those who do not need it.
- Risk for jam on the network => Low bandwidth utilisation => High probability of messages collisions => No real-time application possible
With Switch :
- Only the involved equipments receive the message
- No risk for jam
=> High bandwidth utilisation => No probability for messages collisions => Real-time is possible
An IP frame contains several information such as:
- The destination IP and MAC address
- The source IP and MAC address
- The type of protocol used (TCP, UDP and others)
- The length of the message
- Encryption data
- VLAN tags
- and much more
What is different between unmanaged, Ring or managed solution ?
Basically, an unmanaged switch is a device that forwards packets within a LAN. It is a truly plug and play device which does not require any configuration. Just plug in it, connect the Ethernet cables from users such as personal computers or I/O devices, and it will immediately communicate data between users.
The Ring switch has extended capabilities. It allow to connect devices in a Ring topology. When a link is broken, the Ring switch instantly transfers data to new path. This provide fast network and avoid fault on the network. A managed switch is a device that forwards packets between LANs. This device also has to capability to support loop configurations using Spanning Tree Protocol. Loop configurations are used to prevent a single point of hardware failure in a network. Management Information about the network is also obtained through the switch by querying the MIB can be configurated to improve the network performance and control the traffic. They may be configurated via a Telnet console or even a web browser. Different management features are available.
Can I connect any kind of Ethernet switches in a ring ?
Not any.
Be careful ! Unmanaged switches cannot form a ring. In an unmanaged Ethernet network there can be only one path between any two ports on the network. If there is more than one path from one switch to another a broadcast message (and in some cases other messages) sent by the network will be forwarded until it completes a loop by returning on the second path. Since the switches forward all broadcasts and do not keep track of the messages they have sent, the returning message will be sent around the loop again and again. A single message circulating forever around a loop at high speed is clearly not a good thing, so no loops are allowed. Ring switches allow to form rings based on unique propretary protocol. This protocol is based on MAC address. Managed switches allow you to form a ring through the RSTP feature. The Rapid Spanning Tree Protocol (RSTP) allows you to have an Ethernet network with extra connections, so if one path between two points on the network fails, another path can be used to deliver messages. If one link or switch fails, another link or switch can take over transparently to prevent unnecessary down time.
How many switches can I connect together on the same LAN ?
Switches can be cascaded almost without limit because unlike a passive hub that has retransmission limitations, an active switch regenerates Ethernet messages as if it were an original transmission.
There really is no limit as long as the total latency is acceptable to your application. For example, the total latency of 10 Ring Switches cascaded (connected in series) is typically less than 50 us.
Devices use Flow Control to ensure that the receiving device takes in all the data without error. If the transmitting device sends at a faster rate than the receiving device, then the receiving device will eventually have its buffer full. No further information can be taken when the buffer is full, so a flow control signal is sent to the transmitting device to temporarily stop the flow of incoming data.
For each port, Flow Control can be enabled or disabled.
What is the difference between Unicast, Broadcast and Multicast messages ?
Broadcast messages are sent to all stations in the network.
Whereas an unicast message is only sent to one station on the network. Multicast messages are sent to a group of stations, for example video cameras type.
Using multicast allows the building of distribution networks, which are suitable for video monitoring or television transmissions over the Internet, i.e. information with one sender and many receivers.
IPv4 addresses as 255.255.255.255 or 192.168.0.255 are BROADCAST IP addresses.
IPv4 addresses from 224.0.0.0 to 239.255.255.255 are MULTICAST IP addresses.
MDI = Media Device Interface
The RJ45 (copper) ports on the switch will automatically detect the cable type (straight-thru vs. cross-wired) and re-configure themselves accordingly.
MAC = Media Access Control
Each Ethernet device has a unique assigned MAC address. This MAC address corresponds to the hardware unique name of the product. It may be compared with the DNA of a human.
This address is fixed during production by the manufacturer and can’t be changed.
Each Ethernet device inserts its unique “MAC” address into each message it sends out. The port on the switch used for a given MAC address is automatically learned when a frame is received from that address. Once an address is learned, the switch will route messages to only the appropriate port, instead of broadcasting messages out all ports like a hub. A time stamp is also placed in memory when a new address is learned. This time stamp is used with the aging feature, which will remove unused MAC addresses from the table after 300 seconds. If a device moves, the associated port on the switch will be changed (migrated) as needed. In most switches, up to 2,048 MAC addresses can be stored and monitored at any time.
The IP address (Internet Protocol) is the unique identifier of each device inside a network.
The IP Address of both source and destination device is included in each IP message. They indicate the source and the destination where IP packets shall go.
An IP address consists of four bytes (for example 192.10.0.5). IP addresses are divided into two parts :
- a network part
- a computer part.
It may be manualy or automaticaly (DHCP) assigned by a server device such as a server, or even a managed Ethernet switch.
There may be cases where you can not use or do not want to use public IP addresses on your internal network, instead you can use private IP addresses. These IP addresses will not work on an Internet connection, the solution is then to use NAT (Network Address Translation).
A router or “firewall” with support for NAT translates private addresses to public addresses:
When the computer with address 10.0.1.2 needs to access the Internet, 10.0.1.4 is
addressed which is the “Default Gateway” or “way out”. When data from address
10.0.1.2 passes through the router NAT translates the internal IP address 10.0.1.2 to
60.20.10.10 i.e. the IP address on the “outside”. In this way an internal IP address can
communicate with other computers on the Internet.
IANA (Internet Assigned Numbers Authority) has reserved the following three
address blocks for IP addresses in private networks:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
Is a switch managed with its IP address or its MAC address ?
The MAC address is the unique hardware signature of each device. When the IP address is the identifier of each device inside a local network.
A managed switch is differenciated in a network using its IP address.
An unmanaged switch will be recognised only based on its MAC address.
Our Ring switches are intermediate models, partially managed. Like unmanaged switches, they use MAC addresses to handle the network.
Moreover, due to a proprietary network, they also offer some of the interesting management features, normally available with managed switches.
I have a managed switch including 3 gigabit ports RJSML9MG1CAPS : Can I force the gigabit speed of ports 8 and 9 to 100 Mbps ?
Yes, on this model the ports 6, 7 and 9 are 10/100/1000 BaseT(X) compliant. Each port can be set up for an automatic negotiation of the speed and full or half duplex operation.
But their speed can also be forced to 100 or 1000 mpbs. This may be useful when host devices do not manage auto negotiation.
IGMP (Internet Group Management Protocol) allows hosts and routers to work together to optimize forwarding of multicast traffic on a network. Without IGMP, all multicast packets must be forwarded to all network segments. With IGMP, multicast traffic is only forwarded to network segments, which connect interested hosts.
An IGMP snooping switch performs many of the functions of an IGMP router.
Periodically, routers and IGMP snooping switches in active mode send an IGMP Query on each attached network. (The query interval is generally around 1-2 minutes.)
How can I access software for the managed switch ?
The recommanded method for accessing the switch is using a Web User Interface such as Internet Explorer.
This method is very simple. Just be careful by configuring the network parameters.
Refer to the Managed Software user manual for details.
Some models may also be accessed with a serial connection or also with a Telnet connection.
VLAN can segregate traffic flowing through a switch to improve bandwidth utilization or security. Segregation is done based on membership in a group of ports (port-based VLANs) or on IEEE 802.1Q tags which include a VLAN ID (tag-based VLANs).
A port-based VLAN limits traffic coming in a port to the group of ports to which that port belongs. For example, if ports 1, 3, 5, 7, and 9 were placed in a port-based VLAN, broadcast frames coming in port 3 would be sent to ports 1, 5, 7, and 9 (which are members of port 3's VLAN) but not to ports 2, 4, 6, and 8 (which are not members).
A tag-based VLAN limits traffic based on the VLAN ID in a 'tag' associated with the frame. VLAN tags may be explicitly placed in frames by applications or switching equipment, or implicitly assigned to frames based on the switch port where they arrive.
The VLAN feature is available on our managed switches.
The mirroring feature is ideal for performing diagnostics by allowing traffic that is being sent to and received from one or more source ports to be replicated out a monitoring/target port. Port mirroring is available both with managed switches and Ring switches. Data is monitoring with a network monitor software.
SNMP (Simple Network Management Protocol) and RMON (Remote Monitoring) provide a means to monitor and manage your network. Each SNMP device maintains Management Information Bases (MIBs) containing information about the operation and configuration of the device.
Each MIB contains a variety of information such as:
- Information about the switch as a system: name, description, physical location;
- VLAN
- IGMP
- statistics
- and much more
The Ring models are "half-managed". They combines the plug-and-play simplicity of an umanaged switch with some high performance features of managed switches. Ring Switch can be pre-configurated to just run. But it is also possible to fine tune the performance of the ring by using a simple Windows wizard.
Other advanced capabilities include :
- priority queuing for prioritizing your traffic
- message rate filtering for broadcast storm protection
- port mirroring for diagnostics.
A Ring switch bases its switching process on MAC address instead of IP address.
Thus, the Ring switch is a layer 2 device.
The fault tolerance provided by Ring switches is not possible with conventional Ethernet hubs or unmanaged switches.
The RSTP (Rapid Spanning Tree Protocol) algorithm in Managed Switches can be used to create rings. However, Spanning Trees were designed for the office environment and do not guarantee deterministic performance. Ring switches, on the other hand, are deterministic by design and use their knowledge of the well-known alternative paths to ensure real-time recovery of network failures. Ring switches are also simpler to install, with no configuration necessary in most situations.
Ring Advantages Over Spanning Trees and Other Schemes
· Deterministic performance – 5 mS per hop
· No IP address or complex set up required
· Expandable to 50+ nodes (RSTP limited to 6 hops max.)
· Can increase reliability by establishing multiple rings
· No ring master is required – no one switch is critical
· Ring switches are ultra stable
· Ring switches cost less than Managed Switches
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