Using VT6526 to build low-cost Gbit Ethernet switch

1 Introduction With the development of network technology and the popularization of informatization applications, Ethernet switches have become more and more widely used as the core equipment of local area networks. In the local area network, the switch can filter data packets or regenerate and forward new packets, divide a large network into several independent conflict domains, and different conflict domains can communicate with each other, effectively reducing or even eliminating signal collisions in the network , Avoid broadcast storm, reduce the occurrence of error packets and error packets, support longer transmission distance and more network nodes. Currently, after the emergence of broadband networks, network applications are becoming more advanced, such as multimedia applications such as video on demand and MP3. In the constantly developing environment, various applications have more requirements for Ethernet switches. In addition to higher speeds, it also requires a complete network management and a higher degree of intelligence, which can achieve virtual subnet division (Virtual LANs), VLAN Tagging, link aggregation, flow control and other functions. However, with the improvement of functions, the price of equipment has also risen. The following introduces an Ethernet switch with extremely high cost performance.
2 Introduction to VT6526 chip VT6526 is a low-power, non-blocking shared memory layer 2 single-chip switching integrated circuit produced by VIA Technology Inc. of Taiwan, which provides 24 10M / 100Mbps at line speed Port and two 10M / 100M / 1000Mbps ports. Figure 1 is its principle block diagram. In Figure 1, BSF is the reference frequency, MAC is the medium access control, MIB is the management information base, and the rest, for example, LEDC, LEDIO, BS__ALERT, SMII, SSMIIx24, GMII, TBI, MIIX2, etc. are all interface protocols.

As can be seen from Figure 1, VT6526 is a low-cost, non-blocking layer 2 Ethernet switching chip. It has a total of 26 MACs, including 24 10M / 100Mbps ports and 2 10M / 100M / 1000Mbps ports. Each port can be set in the initial configuration through the EEPROM or the CPU online to be manual or adaptive at full speed or half-double It operates at 10Mbps and 100Mbps, and can choose whether to enable flow control.
Perform a CRC check on each data packet at the input port. The input and output control module forwards the received data packet with the assistance of the queue controller and the buffer controller according to the forward table. The forward table controller according to the received The data updates the forward table under the spanning tree algorithm. In VLAN mode, the input and output modules add, remove, and change VLAN tags according to the corresponding VLAN rules.
Initial configuration data is stored in EEPROM, and key data and global information during switch operation are stored in the global configuration module; CPU-I / O control provides an interface between the chip and the CPU, which can be connected to a 16-bit CPU (such as 80186) through DMA , ARM, etc.) interface, can also interface with 8-bit CPU (such as 8051) through the IDE interface; LED controller will send the status of the switch to the LED display by sending serial data; BSF control module stores the broadcast package; SRAM controller Stores all access requests for control data and packet data.
3 Network-managed intelligent Ethernet switch application solution?
A variety of Ethernet switches can be developed using VT6526. The following introduces a network-managed intelligent Ethernet switch system developed with VT6526 as the core and a 24 10M / 100M ports plus two 1G ports.
3.1 Hardware The hardware of a network-managed Ethernet switch is mainly composed of the following parts:
(1) Layer 2 switching chip: It stores and forwards data packets of the data link layer (Layer 2) according to the MAC address, and completes various applications based on the layer 2 protocol such as VLAN under the support of the CPU. Layer 2 switching chip;
(2) Embedded CPU subsystem: The embedded CPU subsystem mainly manages the switch through network management software such as configuration and monitoring, so that the switch can manage its network under the support of the layer 2 protocol and communicate with other switches or Routers exchange information to form a larger network. Choose Samsung's S3C4510B CPU, which is an integrated 16 / 32-bit ARM7TDMI RISC processor, which is relatively inexpensive and suitable for embedded Ethernet applications (such as HUB / Switch, etc.). The CPU is connected to the VT6526 by DMA, and is connected to 88E3081 and 88E1000 with a serial port that complies with the IEEE 802.3u protocol part 22.
(3) Physical layer (PHY) chip: The physical layer chip realizes the function of the physical layer in the 802.3 protocol. Three MARVELL 88E3081 10M / 100Mbps Fast Ethernet transceivers are selected as the physical layer chips of port 0 to port 24. The chip It is an 8-port 10M / 100Mbps fast Ethernet transceiver; ports 25 and 26 are 10M / 100M / 1000Mbps ports, so 88E1000 Gbit Ethernet transceiver is selected, which conforms to IEEE802.3 1000BASE? 10BASE-T. If you choose 88E1000S chip, you can provide Gbit optical interface.
(4) Transceiver Module: This module modulates the output data of the physical layer chip into a signal suitable for line transmission, and demodulates the received line signal into data that can be recognized by the physical layer chip. Choose three H1140 modules of Pulse Company from port 0 to port 24. The module is an 8-port 10M / 100Mbps Fast Ethernet transceiver modulation module. Ports 25 and 26 use the H5012 module, which is a 2-port module that supports Ethernet 10/100 / 1000BASE? T applications and supports UTP Category 5 cables.
(5) There are several types of power supply for this switch: 3.3V, 2.5V, 1.8V and 1.5V.
Figure 2 is a block diagram of the hardware principle of the switch. ?

3.2 Network management software?
Since this is a network-managed switch, in addition to the driver control of the chip such as VT6526, the software of the switch also needs to support the relevant layer 2 protocol and some layer 3 protocols to provide perfect network management functions. The network management software is The important part of the switch is also more complicated. The function hierarchy diagram and basic flow chart of the network management software are shown in Figure 3 and Figure 4. In Figure 3, CLI is the calling line identification, SNMP is a simple network management protocol, and IGMP is a snoop on the Internet group management protocol. In Figure 4, UDP is the user datagram protocol and STP is signaling forwarding.

The main functional requirements are as follows:
Use Vxworks embedded real-time operating system (RTOS) to develop the following network management software unit:
· Drive control of VT6526 and other chips;
· Support for Layer 2 related protocols: spanning tree, GVRP, GMRP, IGMP SNOOPING;
· Management mode: SNMP, web mode, CLI (command line), where CLI is also based on telnet or serial port (console port);
· IP related protocol requirements: TCP / IP, SNMP, RMON, Telnet, tftp, http;
· File system (based on flash). ?

3.3 What are the main functions of the switch?
In addition to the basic functions of storing and forwarding traditional wire-speed data packets, this network-managed intelligent switch also provides the following powerful functions under the support of comprehensive network management software:
(1) VLAN?
According to the configured VLAN tag rules, the switch adds, removes and changes VLAN tags on the corresponding data packets of the IO port, and performs corresponding forwarding processing. The switch can provide multiple ways of VLAN:
· Port-based VLAN: In this mode, all the data packets are associated with the PVID of the relevant port, and the PVID is used as a tag to forward between the relevant ports forming the VLAN. You can use no label;
· Tag-based VLAN: In this mode, with the support of the software, a VLAN bridge that conforms to the 802.1Q protocol is established in the switch. It analyzes each packet received, based on the VLAN tag header of the received packet. The packet is assigned to one and only one VLAN, and forwarded in the corresponding VLAN. In this [LL] process, the switch supports cross-VLAN packet filtering and VLAN-based spanning tree;
· Protocol-based VLAN: In this mode, the switch establishes the VLAN ID of the packet based on the protocol used by the data packet and forwards it based on the packet. This mode supports IP, ARP, Novell IPX, Apple Talk, DECnet More than ten kinds of agreements such as MOP.
(2) Support 802.3ad connection aggregation: The switch supports up to 8 aggregation groups, and users can choose up to 4 ports from 0 to 25 ports (10M / 100M / 1000 Mbps ports) to establish an aggregation group.
(3) Provide data flow monitoring function: the switch can monitor the bidirectional data flow of inlet, outlet and port.
(4) Support STP and VLAN-based STP. ?
(5) Under the premise of IGMP request, the switch provides IP multicast. ?
(6) It can be quickly reconfigured when the network topology changes. ?
(7) Support input and output rate control: The switch supports rate control based on port input and output. For example, if port 0 is configured to 10Mbps, the user can control its effective rate to 1Mbps through programming.
4 Conclusion?
This switch provides 24 10M / 100M ports and 2 10M / 100M / 1000M ports, which is very suitable for broadband access of medium-sized LAN core switching, metropolitan area networks and local area networks. The switch uses a cheap VT6526 switching chip, combined with S3C4510B CPU and perfect network management software, making the switch has a very strong level of intelligence and network management capabilities, therefore, the cost is low, with a high cost performance.

Metal Pole

Metal Pole, Metal Light Pole, Metal Power Pole, Metal Utility Pole

YIXING FUTAO METAL STRUCTURAL UNIT CO.,LTD( YIXING HONGSHENGYUAN ELECTRIC POWER FACILITIES CO.,LTD.) , http://www.chinasteelpole.com