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Latency and power consumption of 10GBASE-T

Latency and power consumption of 10GBASE-T

10GBASE-SR

10GBASE-T

10GBASE CX(DAC)

Power

0.7W

3.5-5.0W

1.0W

Length

300m

100m

7m

Cable

LC-LC MMF

Cat6A

COAX

Latency (µs)

0.1

2.6

0.3

Reference: IDF2010

Latency

Since 10GBASE-T uses a low-density parity check (LDPC) code with a long block length (25.6Kbit), this block will cause latency accumulation. It will be 2.56 µs, and some more for processing time may be added to this. When you use a TCP-based application, this latency doesn’t affect its performance so much. However, when you use multistage relay, it’s better to use 10GBASE-T only at the edge for avoiding latency accumulation. UDP-based applications are sensitive to latency. Therefore, you may see some performance issues with 10GBASE-T.

Cable latency is about 5ns/m, so 2.6 µs is equivalent to latency of a 520m cable. This latency might become a big issue for the HPC-based applications.

Power consumption

Using a LDPC circuit shall result in a higher of power consumption. A large cooling fan was attached to a10GBASE-T NIC that Teranetics demonstrated in 2007. It is possible for devices with a high port density to cause a shortage of power supply and/or lack of cooling.

In addition, the power consumption of 10GBASE-T will vary depending on the transmission distance. While 10GBASE-T over a 100m cable, which is the longest length of CAT6A, will consume maximum power, when using a less-than-30m cable, it will switch to short reach operation.

According to IEEE Tutorial of 10GBASE-T in November 2003, a 10GBASE-T product with 65nm process was estimated to consume about 6.2W.

Power consumption comparison of 10GBASE-T NIC

vender

type

port

process

power

launched

Intel

X710-DA2

SFP+ x 2

28nm

3.3W(DAC)

4.0W(SR)

Q4 2014

Intel

X540-T1

RJ45 x 1

40nm

10.8W

Q1 2012

Intel

X550-T1

RJ45 x 1

28nm

7.4W

Q1 2016

Intel

X550-T2

RJ45 x 2

28nm

11.2W

Q1 2016

Power consumption of WST-SFP+Cu-C

Parameter & Cabling type

Power consumption

 

10G 2m Cat7

615mA

 

10G 100m Cat7

880mA

2.9W at 3.3V

1Gbps 100m Cat6a

375mA

 

Compared to 1.5W of BX40 models that have the longest distance over optical fiber, WST-SFP+Cu-C models consume much more power.

25G/40G-T

25G/40G-T task force documents were completed with the approval of IEEE Std 802.3bq. The modulation rates were increased 2.5 and 4 times from 10GBASE-T, but there was no progress about reducing its power consumption; no such products have been announced as of April 2018.

LDPC (Low Density Parity Check)

LDPC codes are widely used for strong error correction in such as WIMAX, satellite communications, and so on. When a LDPC length code is defined by n, its computation amount is proportional to 2^n.

For example, 1,723/2,048bit LDPC code will recover signals to 10-12 BER from the communication channel quality of 10-2 .

10GBASE-PHY

Throughput is 4 lanes x 833Mbaud x 3 bit/baud = 10Gbps. The raw bit rate is  11.2Gbps (4x200Mx7x2). After applying FEC, the throughput becomes 9.32Gbps.

The frequency of 833M baud is 450MHz. Since the frequency of 128Mbaud required for 1G is 80MHz, it is 5 times more than that of 1G. Error correction is required.

iMac Pro uses Aquantia AQC107 chip.