Advantech Switches – What are the Uses of Switches?

The main functions of the switch include physical addressing, network topology, error checking, frame sequence, and flow control. Switches also have new features such as support for VLANs (Virtual Local Area Networks), support for link aggregation, and even firewall functionality.

Learn:

The Ethernet switch learns the MAC address of the device connected to each port and maps the address to the corresponding port in the MAC address table in the switch cache.

Forwarding/Filtering:

When the destination address of a data frame is mapped in the MAC address table, it is forwarded to the ports connected to the destination node instead of all ports (or to all ports if the data frame is a broadcast/multicast frame)

Elimination of loops:

When a switch includes a redundant loop, the Ethernet switch avoids loops through the spanning tree protocol while allowing for a fallback path.

In addition to being able to connect to the same type of network, switches can also interconnect between different types of networks, such as Ethernet and Fast Ethernet. Many of today's switches are capable of providing high-speed connectivity ports that support fast Ethernet or FDDI, etc., to connect to other switches in the network or to provide additional bandwidth for bandwidth-intensive critical servers.

Generally speaking, each port of a switch is used to connect to a separate network segment, but sometimes in order to provide faster access, we can connect some important network computers directly to the port of the switch. In this way, the network's key servers and important users have faster access speeds and support greater information traffic.

Finally, a brief overview of the basic functions of the switch:

1. Like hubs, switches provide a large number of ports for cable connection, which allows for star topology cabling.

2. Like repeaters, hubs, and bridges, when it forwards a frame, the switch regenerates an undistorted square electrical signal.

3. Like bridges, switches use the same forwarding or filtering logic on each port.

4. Like a bridge, a switch divides the LAN into multiple conflict domains, each of which has its own bandwidth, thus greatly increasing the bandwidth of the LAN.

5. In addition to the functions of bridges, hubs, and repeaters, switches offer more advanced features such as virtual local area networks (VLANs) and higher performance.

Traditional switches are developed from bridges and belong to the second layer of OSI, that is, data link layer devices. It addresses based on the MAC address, selects routes through the station table, and the establishment and maintenance of the station table is carried out automatically by the switch. Routers belong to the third layer of OSI, that is, network layer devices, which are addressed based on IP addresses and generated through routing protocols in the routing table. The biggest advantage of the switch is that it is fast, because the switch only needs to identify the MAC address in the frame, and the forwarding port selection algorithm is simple according to the MAC address, which is convenient for ASIC implementation, so the forwarding speed is extremely high. But the working mechanism of the switch also brings some problems.

1. Loop: According to the switch address learning and station table establishment algorithm, no loops are allowed between switches. Once a loop exists, the spanning tree algorithm must be started to block the port that generated the loop. The router's routing protocol does not have this problem, and there can be multiple paths between routers to balance the load and improve reliability.

2. Load concentration: There can only be one channel between switches, so that the information is concentrated on a communication link, and cannot be dynamically distributed to balance the load. The routing protocol algorithm of the router can avoid this, and the OSPF routing protocol algorithm can not only generate multiple routes, but also select different optimal routes for different network applications.

3. Broadcast control: The switch can only shrink the collision domain, but not the broadcast domain. The entire switched network is a large broadcast domain, and broadcast packets are distributed to the entire switched network. The router can isolate the broadcast domain and the broadcast packets cannot continue to be broadcast through the router.

4. Subnet division: The switch can only identify MAC addresses. MAC addresses are physical addresses and have a flat address structure, so they cannot be subnetted based on MAC addresses. The router identifies the IP address, the IP address is assigned by the network administrator, is a logical address and the IP address has a hierarchical structure, is divided into network number and host number, can be used very conveniently to divide subnets, the main function of the router is to connect different networks.

5. Confidentiality: Although the switch can also filter the frame based on the source MAC address, destination MAC address, and other content in the frame, the router filters the packet based on the source IP address, destination IP address, TCP port address, etc., which is more intuitive and convenient.

Manual exchange

The history of electrical signal exchange can be traced back to the early days of the telephone. When the telephone was invented, all it took was a long enough wire, plus two telephones at the end, to enable two people who were far apart to have a voice conversation.

As the number of telephones increases, it is impossible to have a wire between every two telephones in order for everyone who has a telephone to communicate with each other. So people set up telephone bureaus, and each telephone user connected a wire to a large circuit board of the telephone office. When A wants to talk to B, he asks the operator at the telephone office to connect to B's phone. The operator uses a wire, one end is inserted into the hole where A is connected to the circuit board, and the other end is inserted into the hole of B, which is "splicing", which is equivalent to temporarily pulling a telephone line for A and B, and then the two parties can talk. When the call is finished, the operator removes the wire, which is called "uncording". The whole process is "manual exchange", which is actually a process of "closing the switch" and "disconnecting the switch". Therefore, translating "exchange" as "switch" is technically easier to understand.

Circuit control

Manual switching is too inefficient to meet the needs of large-scale deployment of telephony. With the development of semiconductor technology and the maturity of switching circuit technology, it has been discovered that electronic technology can be used to replace manual exchange. As long as the telephone end user sends a string of electrical signals to the electronic device, the electronic device can connect the circuit of the requesting party and the requested party according to a pre-set program, and monopolize the circuit and will not share it with a third party (of course, due to design defects, there may be situations where multiple people share the circuit, which is commonly known as "serial wire"). This type of exchange is called "program-controlled switching". And this kind of equipment is also called "program-controlled switch".

Due to the long-term monopoly of program-controlled switching technology by developed countries and the high cost of equipment, China's telephone penetration rate has not been high. With the development of program-controlled switches by Huawei, ZTE and other enterprises one after another, telephones have been rapidly popularized in China.

The most commonly used communication protocol for voice-controlled switches is Signalling System No.7

Compare with hubs

1. From the perspective of OSI architecture, the hub belongs to the first layer of physical layer devices, while the switch belongs to the second layer of OSI data link layer devices. That is to say, the hub only plays the role of synchronization, amplification and shaping for data transmission, and cannot effectively process short frames and fragments in data transmission, and cannot ensure the integrity and correctness of data transmission; The switch can not only synchronize, amplify and shape the data transmission, but also filter short frames and fragments.

2. From the perspective of working mode, the hub is a broadcast mode, that is to say, when a certain port of the hub is working, all other ports can listen to the information, which is easy to produce broadcast storms, and the network performance will be greatly affected when the network is large; The switch can avoid this phenomenon when the switch is working, only the port that makes the request and the destination port respond to each other without affecting other ports, so the switch can isolate the collision domain and effectively suppress the generation of broadcast storms.

3. From the perspective of bandwidth, no matter how many ports there are in the hub, all ports share a bandwidth, only two ports can transmit data at the same time, and the other ports can only wait, and the hub can only work in half-duplex mode; For the switch, each port has an exclusive bandwidth, when the two ports work, it does not affect the work of the other ports, and the switch can not only work in half-duplex mode but also in full-duplex mode.

Advantech Switches – What are the Uses of Switches?

Advantech Switches – What are the Uses of Switches?

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