Calculation method of Ethernet packet rate

We know that a gigabit port's wire-speed packet forwarding rate is 1.4881MPPS,

The speed packet forwarding rate of the gigabit port is 0.14881MPPS, which is the international standard, but how is it obtained?

The specific packets in the transmission process will be preceded by each package 64 (leader) preamble is a 64-byte packet, originally only 512 bit, but in the transmission process will actually have 512+64+96=672bit, That is, the length of a packet is actually a 672bit gigabit port wire-speed packet forwarding rate =1000mbps/672=1.488095mpps, approximately equal to 1.4881Mpps, hundred trillion in addition to 10

0.14881Mpps then very simple, in fact, directly with the PPS value in the device parameters multiplied by 672 then we can be more understanding of the popular BPS concept.

General sales in order to facilitate the calculation and the understanding of the integer is changed 672 to 500.

Understand this after all of a sudden found that the network equipment selection originally is so simple, I only need to anticipate the total number of nodes in the network and bandwidth requirements and traffic requirements, then need to switch performance model and router model is out of the box.

Note: Many of today's devices are three-layer switches, and the parameters we see are for three-layer modules and two-tier modules, respectively.

For example, the 6509 mentioned on the 4 floor is like this.

The data exchange capability is 720Gbps, but the routing packet forwarding capability is 400Mpps. There is no contradiction here. Because none of the two data describes one thing.

Switch backplane calculation

The backplane bandwidth of the switch is the maximum amount of data that can be throughput between the switch interface processor or interface card and the bus. The backplane bandwidth marks the total data exchange capability of the switch, in Gbps, also known as swap bandwidth, and the typical switch's backplane bandwidth ranges from a few Gbps to hundreds of Gbps. The higher the backplane bandwidth of a switch, the stronger the ability to process data, but also the higher the design cost.

In general, the calculation method is as follows:

1) wire-speed back-panel bandwidth

Investigate the total bandwidth available to all ports on the switch. Calculate the number of ports * corresponding Port rate * * (full duplex mode) if the total bandwidth ≤ the nominal backplane bandwidth, then the backplane bandwidth is wire-speed.

2) Second Layer packet forwarding line speed

Second packet forwarding rate = number of Gigabit ports x1.488mpps+ number of ports *0.1488mpps+ remaining type of port * Corresponding calculation method, if this rate can ≤ the nominal two packet forwarding rate, then the switch in the second layer of exchange can achieve line speed.

3) Third Layer packet forwarding line speed

Third-tier packet forwarding rate = number of Gigabit ports x1.488mpps+ number of ports *0.1488mpps+ remaining type of port * Corresponding calculation method, if this rate can ≤ the nominal three packet forwarding rate, then the switch in the third layer of exchange can achieve line speed.

So, how did 1.488Mpps get it?

The measure of packet forwarding line rate is the number of packets (minimum packets) that are sent 64byte per unit of time as the basis of calculation. For Gigabit Ethernet, the calculation is as follows: 1,000,000,000bps/8bit/(64+8+12) Byte=1,488,095pps Description: When the Ethernet frame is 64byte, it is necessary to consider the fixed overhead of the 8byte frame head and the 12byte frame gap. Therefore, a wire-speed Gigabit Ethernet port in the forwarding 64byte packet packet forwarding rate is 1.488Mpps. Fast Ethernet wire-speed port packet forwarding rate is just one-tenth of Gigabit Ethernet, 148.8kpps.

* For Gigabit Ethernet, the packet forwarding rate for a wire-speed port is 14.88Mpps.

* For Gigabit Ethernet, the packet forwarding rate for a wire-speed port is 1.488Mpps.

* For Fast Ethernet, the packet forwarding rate for a wire-speed port is 0.1488Mpps.

* For OC-12 POS ports, the packet forwarding rate for a wire-speed port is 1.17Mpps.

* For OC-48 POS ports, the packet forwarding rate for a wire-speed port is 468MppS.

So, if we can meet the above three conditions, then we say that the switch is really linear non-blocking

The utilization of backplane bandwidth resources is closely related to the internal structure of the switch. At present, the internal structure of the switch is mainly the following: one is the shared memory structure, which relies on the central switching engine to provide full port high-performance connection, the core engine examines each input packet to determine the route. This method requires a lot of memory bandwidth, high management costs, especially with the increase of the switch port, the central memory price will be very high, so the switch core is a performance bottleneck, and the second is the cross-bus structure, it can establish a direct point-to-point connection between the ports, which is good for single-point transmission, but not suitable for multipoint The third is the hybrid cross-bus structure, which is a hybrid cross-bus implementation method, it is the design idea is that the integrated cross-bus matrix into a small cross-matrix, in the middle through a high-performance bus connection. It has the advantage of reducing the number of cross-buses, reducing the cost and reducing bus contention, but the bus connecting the cross-matrix becomes a new performance bottleneck.

Transfer rate

1M bandwidth means 1Mbps note is bps instead of bps!

convert it, 1bps=8bps;

So 1mbps=128kbps;

So download speed up to 128KBps

1mbps=1024kbps/8=128kbps

Just say what bps is.

BPS is the abbreviation for bits per second, which indicates bits per second. So how long does it take for a customer to download a 5 trillion MP3 song? This has a direct relationship to the download rate.

Take the ordinary ADSL as an example (basically can achieve 50Kbps download rate): (5mb=5120kb÷50k=102.4 seconds, about 1.7 minutes.

Port rate and packet count PPS and BPS

Category: L2 Switch 2009-06-15 17:59 1650 people read reviews (0) Favorite reports

Byte Router interview job

Port rate and number of packets PPS and BPS

Here is a colleague's face question,

What does the switch port rate 100Mbps mean? What is the maximum number of packets that can be sent per second? ”

If you can answer please ignore below.

One, the concept of PPS and bps.

PPS = Packets Per Second

Bps = Bytes Per Second

bps = bits per Second

Two, the calculation formula,

If a packet size of 100Bytes is sent at a rate of 200 packets per second, the rate is how many byteps/bps,

(8 + +) x = 24000 Byte per seconds

Where 8 is a 8-byte forward character and 12 is a 12-byte packet interval (GAP)

(+100x8 +12x8) x = 192000 Bitps

Three, as detailed below,

100m Ethernet, full duplex is 200m, its unit is bit/s,100m conversion into byte is 100/8=12.5m byte/s, converted out is 12500000bytes. Then in the packet of Ethernet, the smallest packet size is 64byte/s, plus 8 byte leading byte and 12 byte inter-frame gap, the total is 84byte. Then use the 12500000/84=148809, get in 100m throughput one-way environment of the maximum packet forwarding per second number 148809, converted to K is 148.8k pps. Ditto, in the bidirectional 200m throughput of the Ethernet, the number of forwarding per second 297618, converted to K packet forwarding rate of 297.6k pps.

This is in the two-layer exchange above can achieve the packet forwarding rate, but if a router in the three-tier route above, even in the case of NAT, the packet forwarding rate will be greatly reduced, and this value is the real user is worth caring, so we see a lot of businesses have been emphasizing packet forwarding number of 148,810 packets, In fact, this is the theoretical limit of the two-layer exchange, not the value of the real router at the three-tier operating time.

Calculation method of Ethernet packet rate