ONU consists of active Optical Network Unit and passive Optical Network Unit.It has two functions: selective reception of the broadcast sent by OLT, and receiving response to OLT if the data is needed;The Ethernet data that the user needs to send is collected and cached, and the cached data is sent to the OLT side according to the assigned send window.

Switches, routers are almost all network devices used in modern local area networks. Among them, switches are responsible for connecting network devices (such as switches, routers, firewalls, wireless APs, etc.) and terminal devices (such as computers, servers, cameras, network printers, etc.) ); The router realizes the interconnection between the local area network and the local area network, and the interconnection between the local area network and the Internet; In general, the switch is responsible for connecting devices, the router is responsible for connecting to the network.

Switches：

The function of the switch is to connect terminal devices such as computers, servers, network printers, network cameras, IP phones, and realize the interconnection with other network devices such as switches, wireless access points, routers, network firewalls, etc., so as to build a local area network and realize all devices Communication between.

The switch is located in the second layer (data link layer) of the OSI reference model. The work of the switch relies on the identification of the MAC address (all network devices have a unique MAC address, which is usually directly burned into the network card by the manufacturer) ).

Routers：

Routers are also called gateways, which connect local area networks to form a larger wide area network. When connecting heterogeneous networks (heterogeneous networks refer to different network types, such as ATM networks, FDDI networks, Ethernet networks, etc.). Heterogeneous networks use different data encapsulation methods and cannot communicate directly, and routers can “translate” these different encapsulated data to achieve communication in heterogeneous networks. In addition, for the local area network, the wide area network is undoubtedly a heterogeneous network.

In general, the main differences between routers and switches are reflected in the following aspects:

(1) Different levels of work

The original switch worked at the data link layer of the OSI/RM open architecture, which is the second layer, and the router was designed to work at the network layer of the OSI model from the beginning. Since the switch works on the second layer of OSI (data link layer), its working principle is relatively simple, while the router works on the third layer of OSI (network layer), it can get more protocol information, and the router can make Smarter forwarding decisions.

(2) The data forwarding is based on different objects

The switch uses the physical address or MAC address to determine the destination address of the forwarded data. The router uses the ID numbers (ie IP addresses) of different networks to determine the address for data forwarding.
(3) Traditional switches can only divide conflict domains, not broadcast domains; routers can divide broadcast domains

The network segment connected by the switch still belongs to the same broadcast domain. Broadcast data packets will spread to all network segments connected to the switch, and in some cases will cause communication congestion and security vulnerabilities. Although the switches above the third layer have the VLAN function, they can also be divided into broadcast domains, but the sub-broadcast domains cannot communicate, and the communication between them still requires a router.
(4) The router provides firewall services

The router only forwards data packets with specific addresses, and does not transmit data packets that do not support routing protocols and network data packets whose purpose is unknown, which can prevent broadcast storms. Switches are usually used for LAN-WAN connections. Switches are classified as bridges, which are devices at the data link layer. Some switches can also achieve Layer 3 switching. In contrast, routers are more powerful than switches, but they are relatively slow and expensive. The three-layer switch combines the wire-speed packet forwarding capability of the switch and the good control function of the router, so it is widely used.

Summarize：

Whether it is a switch, a router , the realization of the functions of these network devices requires the network engineer to configure the device in advance (such as VLAN virtual network port division, firewall security policy configuration, router default gateway setting, etc.). At a different level, these network devices are computers with cpu and memory, and all implement hardware functions through the “translation” of the cpu to the machine language.

Switches are the common equipment for data forwarding in local area networks(LAN), and their performance and functions determine the manageability and data forwarding performance of the LAN. The following aspects should be considered when choosing a switch:

Number of ports
The number of physical ports supported by the switch determines the number of terminals or secondary devices connected to the switch, which need to be selected according to actual needs. Of course, subsequent network expansion needs to be considered. The access port of the switch is used to connect the internal network terminal, and the uplink port is used to connect to the upper-level equipment.

2.Port Speeds and Types

Switches come in Fast Ethernet and Gigabit Ethernet. Fast Ethernet allows up to 100 Mb/s of traffic per switch port while Gigabit Ethernet allows up to 1000 Mb/s of traffic per switch port. These ports may be a combination of SFP/SFP+ slots for fiber connectivity, but more commonly they are copper ports with RJ-45 connectors on the front, allowing for distances up to 100 meters. With Fiber SFP modules, you can go distances up to 40 kilometers. Currently, Gigabit Ethernet is the most popular interface speed though Fast Ethernet is still widely used, especially in price-sensitive environments.

3.Switch access capacity
The amount of equipment attached to the switch is mainly reflected in the depth of the MAC address table of the switch. At the same time, it is also necessary to pay attention to the number of host routing entries for the three-layer switch. For example, when selecting a Layer 3 switch, the number of all access terminals of the Layer 3 switch is required to be less than the number of host routing entries of the Layer 3 switch.

4.Network scale and switch network structure
Considering the scale and level of switch application networks, which are mainly divided into small and medium-sized networks and large and medium-sized networks, the recommendations are as below:
5.Functional support
Divide VLANs to realize that ports belonging to different VLANs can’t communicate with each other; Set static routes to realize that VLANs of different network segments can communicate with each other; DHCP snooping prevents the access of other DHCP servers from affecting the LAN. The above functions are commonly used in large and medium LANs.

6.Safety function
Specifically, such as: Access Control List, 802.1X authentication(Radius,Tacacs+), loopback detection, IGMP Snooping, etc.

7.Power requirements

At any layer, a modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies, the connected device can continue operating even when regular office power fails. Another characteristic you consider when choosing a switch is PoE. This is the ability of the switch to deliver power to a device over the existing Ethernet cabling. To find the switch that is right for you, all you need to do is choose a switch according to your power needs. When connecting to desktops which do not require PoE switches, the non-PoE switches are a more cost-effective option.