Understanding “Switching Bandwidth” and “Forwarding Rate” of a Switch

Unlike modular matrix switcher that uses HDMI/DVI with FPGA switching technology, IP-based videowall system depend on switch’s switching bandwidth and forwarding rate. Let’s grasp a good understanding of what these two factors when selecting a switch for your IP-based KVM Videowall in order to get the best user experience. This is especially critical when you have many inputs from various sources and display outputs. This will avoid any obvious video lagging, pixelated pictures, delayed response time or poor picture in your videowall implementation.

Switching Bandwidth

Switching bandwidth is the aggregate input and output bandwidth of all ports. So a 48 port gigabit switch would have 48Gbp/s and 48Gbp/s out, that leaves us with only 96Gbps and apparently, 80GBps would likely be the stacking port rate.

Forwarding Rate

That’s a measure of how many packets per second the switch can process for certain sized packets.  When packet’s size isn’t described, today it’s usually denoted for minimum size Ethernet packets, i.e. each 64 bytes. Minimum size Ethernet, to run at gig rate, is 1.488 Mpps.  Unlike fabric, you don’t need to account for duplex as one port’s in is another port’s out. So for 24 gig ports, and for the optional dual 10g ports, we need (24 + 20) * 1.488 = 65.472 Mpps to support full rate.

“Laymens” explanation

Think of many traffic lanes (for network links) leading up to (river) bridge (for network switch [or multi-port bridge]). How many vehicles (packets) you can move across the bridge depends on how fast each vehicle can pass through the toll process (a device’s packets per second, PPS, rate) and how many lanes (bandwidth) the bridge has.  So a “forwarding rate”, is the count of how many packets you can examine, per second, as they transit your switch (toll gate analogy).

Let’s look at another example, using the previously mentioned 24 port 3750-X. It’s bandwidth is 160 Gbps, the forwarding rate is 65.5 Mpps. It means that the smallest packet size can be ~320 B (160 Gbps / 65.5 Mpps) to utilize the maximum available bandwidth. If the forwarding rate is only 20 Mpps, the smallest packet size would be ~1 KB (160 Gbps / 20 Mpps). If you send smaller packets, you cannot utilize the 160 Gbps bandwidth. With 512 B packets, the bandwidth would be 80 Gbps, even if the switching bandwidth in 160 Gbps.

For Ethernet switches, full “speed” requires 1,488 Kpps, for minimum (64 byte) packets, or 81.3 Kpps, for maximum (1500) packets, and 2 gig of internal bandwidth per duplex gig port. 160 Gbps is more than the 24 port versions need to support all their gig ports, but not by as much as you might think at first glance.  Don’t forget these models support optional uplink modules, which supports up to two 10g ports.  Lastly, in the 3750-X, they have stack ring ports, two 16 Gbps.  So we have 24 + 20 + 32 = 76 then we double for duplex giving 152 Gbps.

For 24 gig and 2 10g, worst case (minimum size packets – if vehicles were motorcycles) Ethernet requires 24 + 20 = 44 * 1.488 = 65.472 Mpps.  If you want a bridge to allow vehicles to cross it without delay, it must have enough lanes to support all the lanes leading up to it (bandwidth) and a tolling system (forwarding rate, PPS) to deal with the number of vehicles (packets) crossing it as they arrive.  Many times actual switches (or real bridges) can’t sustain full capacity but that’s fine when there’s less loading (like crossing a bridge at 2 AM vs. 5 PM).

Our recommendation

We recommend a good switcher for your IP-based KVM Videowall with Cat6e cabling and Forwarding performance over 150 Mpps and Switching capacity over 500 Gbit/s. Gigabit switch with POE feature is useful as our KVM node support KVM.  Huawei S5720-56C-PWR-HI-AC is advanced Gigabit Ethernet switch that provides rich agile features, based on Huawei Versatile Routing Platform (VRP). It has a Forwarding performance of 192 Mpps and Switching capacity 598 Gbit/s.

With forty-eight Ethernet 10/100/1,000 ports, and four 10 Gig SFP+, the switch provides the ubiquitous service function to ensure consistent user experience, what’s more, the special PoE function guarantees constant power supply to meet customers’ electricity demand. The Super Virtual Fabric (SVF) function virtualizes the entire network into one device. In addition, the switch supports flexible Ethernet networking, comprehensive VPN tunnel solutions, various security control methods, intelligent deployment, and simple operation and maintenance. The S5720-56C-PWR-HI-AC switch is the best choice for the branches of high-quality large- and middle-sized campus networks.