Time-to-Link Test for 1000BASE-T and 10GBASE-T


This post is composed on the basis of the physical layer (PHY) behavior assessment of 1000BASE-T and 10GBASE-T. In order to understand the test results and the meaning of this discussion, some terminologies have to be introduced first.

The Meaning of Time-to-Link

Time-to-link (TTL) is a system performance standard that characterizes and measures the PHY behavior through autonegotiation (AN) and 1G/10GBASE-T startup sequences (correspond to training). It is one of the two primary performance measures (the other is bit error rate) used to characterize BASE-T PHY link rate interoperability.

For Ethernet over twisted pair, autonegotiation is defined in clause 28 of IEEE 802.3. It is a procedure by which two connected devices choose common transmission parameters. In this process, the link partner firstly share their capabilities, such as speed, duplex mode, and flow control, and then choose the highest performance transmission mode they both support.

Since servers networking drivers must meet the third party certifications, the TTL standard used to measure link interoperability becomes rather important. Otherwise, long TTLs (>6s) can lead to device certification failures.

How to Measure the Link Interoperability?

There are several representative link interoperability metrics associated with TTL. Their meanings are explained as follows:

TTL: time to achieve link after link initiate event.

Link attempts number: number of attempts made to resolve Master/Slave status for each link. Within a link, one link partner is designated as the master timing source for transmitted signals in both directions. One partner is Master and one partner is Slave.

Link drops number: number of link drops observed after link is established.

Clock recovery: Some digital data streams, especially high-speed serial data streams, such as Ethernet, are sent without an accompanying clock signal. The receiver generates a clock from an approximate frequency reference, and then phase-aligns the clock to the transitions in the data stream with a phase-locked loop (PLL). This is one method of performing a process commonly known as clock and data recovery (CDR). Here it is also called Master/Slave resolution.

TTL distribution: percentage of links by link time.

Speed downshift/downgrade: resolved speed if other than 10Gbps.

Presentation and Analysis of the Results

Totally 1550 link tests are performed, and the results are:

  • 1,050 out of 1,550 tests, or 67% of the total number of link tests, achieved a link state in 7s or less (green slice).
  • 499 out of 1,550 tests, or 32% of the total number of link tests, achieved a link state somewhere between 7s and 15s (blue slice).
  • 1 out of 1,550 tests, or < 1 % (actually 0.15%) of the total number of link tests, achieved a link state longer than 15s (exactly 16.4s; yellow splice, actually it should be smaller than presented in the pie chart).

TTL % of total trials pie chart

Source: http://www.ieee802.org

Characterizing TTL behavior

Cumulative percentage (%) TTL is the distribution of measured link times as a percentage of total measured link time. Total link time recorded for all 1,550 tests is 10,837,835ms or about 3h 0min 38sec. The measured link time and cumulative percentage of each result is recorded in following table and chart:

Cumulative percentage TTL

Source: http://www.ieee802.org

TTL behavior

Source: http://www.ieee802.org

TTL Distribution and Master/Salve Resolution by Channel Length

In this part, the example of 10GBASE-T TTL measured from 2m to 115m channels (9790 links) will be given. The average TTL across 2m to 100m is 7.5s; the average time in autonegotiation is 5s; the average time in training is 2.6s. The following two charts illustrate the TTL distribution and clock recovery results by channel lengths from 2m to 115m.

TTL distribution by channel length

Source: http://www.ieee802.org

clock recovery distribution by channel length

Source: http://www.ieee802.org

According to the charts, we can see that there is an apparent loop timing trend towards Master preference with increasing channel length. And very long TTLs (>15s) at >100m channels are associated with downshits to 1Gb link speed.

AN & Training Times for 1000BASE-T and 10GBASE-T

Measured autonegotiation and training times from 1550 1Gb links for 10GBASE-T device to 1000BASE-T link partner, and 10GBASE-T device to 10GBASE-T link partner are respectively:

AN & traning times and TLL


From the test results on 1000BASE-T and 10GBASE-T, user TTL experience of 1000BASE-T installed over Cat5e cable or better is between 3s and 4s, and 10GBASE-T installed over Cat6a or better is about 7s, or longer in some cases. And the measured autonegotiation times for 1000BASE-T and 10GBASE-T are comparable. And for future 2.5/5GBASE-T, it is highly desirable that their autonegotiation and startup times can be improved, and that total TTL be minimized, so as to be more aligned with end-users’ expectations and requirements.

Appendix: AN & Training Times for 1000BASE-T and 10GBASE-T

1G AN time ditribution

1G traning time ditribution

10G AN time ditribution

10G traning time ditribution

Source: http://www.ieee802.org

CAT5 – Copper Network Solutions Choice

Defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA), CAT5 (Category 5) cable is the copper wiring using twisted pair technology, designed for Ethernet networks. The term “Category” refers to the classifications of UTP (unshielded twisted pair) cables. Since its inception in the 1990s, CAT5 has become one of the most popular types of of all twisted pair cable types which include CAT3, CAT4, CAT5, CAT6, etc. This article details CAT5 used in copper networks from its working principles, its standard, as well as its installation considerations.

How CAT5 Cable Technology Works

CAT5 is widely used in 100BASE-TX and 1000BASE-T Ethernet networks. CAT5 typically contains four pairs of copper wire. In 100BASE-TX standard, the signals are transmitted across only two of the CAT5 pairs. One pair is used to transmit signals, and the second pair receives the signals, leaving the other two unused in signal transmission. What’s more, the 100BASE-TX signals only run in one direction across the pairs. As technology advanced, the 1000BASE-T Gigabit Ethernet (GbE) standard was developed. 1000BASE-T standard utilizes all four copper pairs to transmit up to 250 megabits of data per second (Mbps) in full duplex transmission across each pair. That is to say, each pair is able to transmit and receive signals simultaneously. 1000BASE-T modules (eg. GLC-T) functioning over CAT 5 with RJ-45 connector achieve full duplex transmission with link length up to 100m (328ft).

GLC-T, functions over CAT 5 with RJ-45 connector

There are two standards for CAT5 wiring, EIA/TIA-568A and EIA/TIA-568B. The following passages mainly discuss EIA/TIA-568A.


The TIA-EIA-568-A standard defined the following three main parameters for testing Category 5 cabling installations: wiremap, attenuation, and Near End Crosstalk (NEXT).

Wiremap is a continuity test. It assures that the conductors that make up the four twisted pairs in the cable are continuous from the termination point of one end of the link to the other. This test assures that the conductors are terminated correctly at each end and that none of the conductor pairs are crossed or short-circuited.

Attenuation is the loss of signal, as it is transmitted from the end of the cable to the opposite end at which it is received. Attenuation, also referred to as Insertion Loss, is measured in decibels (dB). For attenuation, the lower the dB value is, the better the performance is, and of course less signal is lost. This attenuation is typically caused by absorption, reflection, diffusion, scattering, deflection.

Near End Crosstalk (NEXT) measures the amount of signal coupled from one pair to another within the cable caused by radiation emission at the transmitting end.If the crosstalk is great enough, it will interfere with signals received across the circuit. Crosstalk is measured in dB. The higher the dB value, the better the performance, more of the signal is transmitted and less is lost due to coupling.

NEXT: the amount of signal coupled from one pair to another

CAT5 Installation Considerations

After testing parameters are mentioned above, here goes the notes of CAT 5 installation.

  • Never pull CAT5 copper wire with excessive force. The CAT5 tension limitation is 25 lbs, much lower than standard audio/video cable.
  • Never step on, crush, or crimp CAT5.
  • Avoid periodic sags; vary the intervals if the cable must sag.
  • Do not bend CAT5 wire tightly around a corner; ensure that it bends gradually, so that a whole circle would be at least two inches in diameter.
  • Do not allow knots or kinks, even temporarily.
  • Never run CAT5 parallel to power wiring closer than six inches.
  • Avoid splices. Every splice degrades the line.

Although CAT5 is superseded by CAT5e in many applications, most CAT5 cable meets Cat5e standards and it’s still a commonplace in Local Area Networks (LANs). Many copper networks choose CAT5 as their transmission media because of its low price and high performance. Fiberstore supplies many CAT5 RJ45 pluggable modules, like 100BASE-TX, and 1000BASE-T transceivers (eg. SFP-GE-T). For more information about copper network solutions, you can visit Fiberstore.