What Is A Backplane Connector And How Can We Determine Its Capacity?

A backplane connector is a system of circuits that acts as a connector between the various modules present on a routing or switching device. Also referred to as a backplane board, or backplane, a backplane connector is a circuit that is used as a support structure to connect other PCBs. Backplanes add stability and mechanical strength to other integrated system components like daughterboards.

For instance, say you have a 24-port, Layer 2-managed switch with 3 8-port modules installed. The data bus in which the 3 modules are plugged into is the backplane connector. The backplane provides the required connectivity amongst the modules. Backplane connectors are of two types: active backplanes and passive backplanes. An active backplane board includes some form of computing power in it. Meanwhile, a passive backplane connector is just the physical connection that has no built-in intelligence.

Blocking Backplanes vs Non-blocking Backplanes

When talking about backplane connectors, it is imperative to address the key differences between blocking and non-blocking backplane boards. Non-blocking switches allow network devices to provide full bandwidth simultaneously to all the ports. A 24-port, 1 Gbps port capacity switch with 48 Gbps backplane capacity is an example of a non-blocking backplane board.

On the other hand, blocking backplanes cannot provide full bandwidth at the same time to all the ports. An example of a blocking switch is a 24 port switch that has 1 Gbps capacity for each port and only a 10 Gbps backplane.

Backplane Terminologies to Be Familiar With

To better understand how one can determine the capacity of the backplane connector of a device, it is important to understand the language of backplanes. Here are some of the most common terms associated with backplane boards:

Fabric bandwidth: This term is often used interchangeably with “backplane capacity” or “backplane bandwidth.” It can be defined as the number of ports times each port's bandwidth.
Mpps: Mpps (short for million packets per second) is a fairly common metric that is used for measuring throughput on routers and switches. Mpps is usually measured by using the 64 byte-sized Ethernet packet, in addition to some overhead.
Forwarding rate: The rate of forwarding a networking device is its maximum Mpps.
Wire speed: The wire speed is the maximum hypothetical speed of a physical link. For instance, theoretically over a given medium, a 1Gbps link can send about 1,000,000,000 bits of data per second.
Oversubscription: This is a situation in which the theoretical maximum capacity of a network device’s links is more than what can actually be provided. Oversubscription is a common phenomenon seen in the process of connecting access switches to distribution switches. However, it also occurs if all the ports on a blocking switch are used.

Capacity Determination of a Device's Backplane

Now that you are familiar with backplane language, let us understand how you can determine the capacity of a device’s backplane. A stack switch or network virtualization can easily complicate things. So, the simplest way to go about determining the capacity of a device's backplane is by checking manufacturer specifications. Usually, you can easily find specifications under the name of "backplane capacity" or "fabric bandwidth".

Most network devices today are non-blocking. You can derive the backplane device of your network devices by going backward from the number of ports and their respective capacity. So, if you have 24 ports with 1 Gbps capacity on a non-blocking switch, the capacity of your device for a full-duplex will be 48 Gbps (24*1*2).

What happens when you find out that you have blocking backplanes or an oversubscription situation? While oversubscription is a textbook design when it comes to certain spine and leaf configurations, a blocking backplane can be a serious concern and a bottleneck in other scenarios. If you're on the lookout for efficient, high-quality backplane connectors, your search ends at Purchasing Synergy.

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