The source of server-to-server traffic might be virtual machine migrations, web index computation, extensive data replication between clusters or mailbox moving. Maltz, it often amounts to 80% of all DC traffic. According to the Microsoft researcher, David A. Traffic is called east-west or server-to-server traffic. Other type of applications generates traffic that mostly stays within the DC. It is called north-south or server-to-user traffic. Traffic is sent as a query from users to servers and then back, as a response from servers to the users. Applications serving web pages, generating onward network traffic that leaves the DC. Generally, every DC runs two kinds of applications. Therefore, there is no need for a bulky and expensive infrastructure of copper cabling running between racks and throughout the data center.Large-scale data centers (DCs) connect hundreds of thousands or even more servers, having millions of users. Fiber cables to each rack provide much better flexibility and investment protection than copper cables because of the unique ability of carrying higher bandwidth signals with longer distances. However, there are a few fiber cables used in the rack as well in order to link the rack to the data center network. The key characteristic is that all the copper cabling is inside the rack and most of the cables connecting servers to the rack switch are short RJ45 patch cables. Normally, the top-of-rack switch is fixed low-profile (1RU/2U) configuration.

However, ToR switch can be placed anywhere inside a rack and connected to aggregation switches via fiber optic cables. The top-of-rack switch is usually placed at the top of the server rack for easier accessibility and cleaner cable management, which is the coming of its name. In the top-of-rack design, servers connect to one Ethernet switch or two (for example, gigabit Ethernet switch or 10GbE switch) installed inside the rack. But actually, top-of-rack switch is one kind of various switches located or installed inside a rack.

There is no precise saying about top-of-rack switch definition on wiki and other sites. However, what is top-of-rack switch and how to buy it when needing? Let’s find out the answers together with the illustration below. You may heard about it that top-of-rack switch is very popular to support power required for large installations and the ToR design is very convenient for servers to connect. When it comes to server connecting in data center, network switch is a vital part.

Tor switches to distribution switches