Calculation of the bandwidth and port rate of the Resolution switch board

Source: Internet
Author: User

Resolve the calculation of the bandwidth and port rate of the vswitch backboard. When using the bandwidth of the vswitch backboard, problems such as the bandwidth of the vswitch backboard frequently occur, as well as the bandwidth of the vswitch with line speed and related knowledge, here we will introduce the solutions to many problems related to the vswitch backboard bandwidth.

We all know that the unit of the total data exchange capability of the vswitch's backboard bandwidth is Gbps, which is also known as "switching bandwidth". The bandwidth of A vswitch generally ranges from several Gbps to hundreds of Gbps. The higher the bandwidth of A vswitch board, the stronger the ability to process data. Of course, the design cost will also increase. Generally, the vswitch backboard bandwidth is calculated as follows:

◆ Wire speed vswitch board bandwidth

The bandwidth of the vswitch backboard. The formula is as follows: number of ports * corresponding port rate * 2 (full duplex mode) if the total bandwidth is less than or equal to the bandwidth of the backboard of the Standard switch, the bandwidth of the backboard is linear.

◆ Second-layer packet forwarding speed

Layer 2 packet forwarding rate = number of Gigabit ports x 1. 488 Mpps + 0.1488 MB port count * Mpps + number of other types of ports * Calculation Method. If this rate can be less than or equal to the forwarding rate of a nominal L2 packet, then, the bandwidth of the vswitch backboard can achieve the line speed during Layer 2 switching.

◆ Layer 3 packet forwarding speed

Layer 3 packet forwarding rate = number of Gigabit ports x 1. 488 Mpps + 0.1488 MB port count * Mpps + number of other types of ports * Calculation Method. If this rate can be less than or equal to the forwarding rate of a nominal three-tier packet, then, the bandwidth of the vswitch backboard can achieve the line speed during layer-3 switching.

So how does 1.488Mpps get it?

The packet forwarding speed is measured by the number of 64 bytes of data packets (minimum packet) sent per unit time. For Gigabit Ethernet, the bandwidth of the vswitch is calculated as follows: 1,000,000,000 bps/8bit/(64 + 8 + 12) byte = 1,488,095 pps vswitch bandwidth description:

When the Ethernet frame is 64 bytes, the fixed overhead of the 8 byte frame header and the 12 byte frame gap must be considered. Therefore, the packet forwarding rate of A 1-gigabit Ethernet port when forwarding a 64-byte packet is 1.488 Mpps. The 10-in-10 Gigabit Ethernet packet forwarding rate is 148.8 kpps.
◆ For 10-Gigabit Ethernet, the packet forwarding rate of a wire speed port is 14.88 Mpps.
◆ For Gigabit Ethernet, the packet forwarding rate of a wire speed port is 1.488 Mpps.
◆ For fast Ethernet, the packet forwarding rate of a wire speed port is 0.1488 Mpps.
◆ For the POS port of the OC-12, the packet forwarding rate of a wire speed port is 1.17 Mpps.
◆ For the POS port of the OC-48, the packet forwarding rate of a wire speed port is 4.68 MppS.

Therefore, if the above three conditions can be met, we will say that this switch is truly linear and non-blocking, and the utilization rate of the backboard Bandwidth Resources is closely related to the internal structure of the switch. Currently, the internal structure of a vswitch mainly includes the following types: first, the shared memory structure, which relies on the central switching engine to provide high-performance connections across all ports, the core engine checks each input packet to determine the route.

This method requires a lot of memory bandwidth and high management costs. Especially with the increase of switch ports, the price of the central memory will be very high, so the switch kernel becomes a bottleneck for performance implementation; the second is the cross-bus structure, which can establish direct point-to-point connections between ports, which is good for single-point transmission performance, but not suitable for multi-point transmission;

The third is the hybrid cross-bus structure. This is a hybrid cross-bus implementation method. Its design idea is to divide the integrated cross-Bus Matrix into small cross matrices, it is connected through a high-performance bus. The advantage is that the number of Cross buses is reduced, the cost is reduced, and the bus contention is reduced. However, the bus connected to the cross matrix becomes a new performance bottleneck.

How to check whether the vswitch backboard bandwidth is sufficient

The backboard bandwidth is the maximum amount of data that can be transferred between the vswitch interface processor or interface card and the data bus. The higher the bandwidth of A vswitch's backboard, the stronger the ability to process data, but the higher the design cost. However, how can we check whether the bandwidth of A vswitch backboard is sufficient? Obviously, the estimation method is useless. I think we should consider the following two aspects:

The sum of the total port capacity X ports should be 2 times smaller than the backboard bandwidth, enabling full-duplex non-blocking switching, proving that the switch has the conditions to maximize the data exchange performance. Full configuration throughput (Mbps) = number of fully configured GE ports × 1. 488Mpps the theoretical throughput of One gigabit port when the packet length is 64 bytes is 1.488 Mpps.

For example, A vswitch that can provide up to 64 Gigabit ports must have a full configuration throughput of 64 × 1.488 Mpps = 95.2 Mpps to ensure that all ports are working at the same speed, provides non-blocking packet switching. If a vswitch can provide a maximum of 176 Gigabit ports and the declared throughput is less than 261.8 Mpps (176x1.488 Mpps = 261.8 ), the user has reason to think that the switch adopts a blocking structure design.

Generally, the switches that both meet the requirements are qualified switches. For vswitches with relatively large backboards and low throughput, the software efficiency/dedicated chip circuit design is not a problem, but the backboard is relatively small. The overall performance of vswitches with relatively high throughput is relatively high.

However, the Board bandwidth can be believed by the manufacturer, but the throughput cannot be believed by the manufacturer. because the latter is a design value, the test is very difficult and the significance is not great. The back-end speed of a vswitch is generally Mbps, which refers to the second layer. Mpps is used for switching between three or more layers.

Port Rate Calculation

The minimum packet length for Ethernet transmission is 64 bytes, And the POS port is 40 bytes. The packet forwarding speed is measured by the number of 64 bytes of data packets (minimum packet) sent per unit time. For Gigabit Ethernet, the calculation method is as follows: 1,000,000,000 bps/8bit/(64 + 8 + 12) byte = 1,488,095 pps Description: When the Ethernet frame is 64 byte, the fixed overhead of the frame gap between 8-byte frames and 12-byte frames must be considered.

Therefore, the packet forwarding rate of A 1-gigabit Ethernet port when forwarding a 64-byte packet is 1.488 Mpps. The line-rate port forwarding rate of Fast Ethernet is exactly 148.8 of that of Gigabit Ethernet, which is kpps. 488 Mpps. The line-rate port forwarding rate of Fast Ethernet is exactly 148.8 of that of Gigabit Ethernet, which is kpps.

Total port Rate

In Ethernet, each frame header must contain an 8-byte leading character, which is used to tell the listener that data is coming. Then, there must be a frame gap between each frame in the Ethernet, that is, after each frame is sent, wait for a while before another frame is sent. In the Ethernet standard, the minimum value is 12 bytes, however, the frame gap may be larger than 12 bytes in practice. Here I use the minimum value.

Each frame requires a fixed overhead of 20 bytes. Now let's calculate the actual throughput of a single port of the switch: 148,809 × (64 + 8 + 12) × 8 ≈ 100 Mbps, this formula makes it easy to see that the actual data exchange volume accounts for 64/84 = 76%. The "line rate" data throughput of the switch port link is actually only 76 Mbps, and the other part is used to handle additional overhead, both of them are standard Mbit/s or Gbit/s.

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