James Griffiths is a Senior Producer for CNN International and author of " The Great Firewall of China: How to Build and Control an Alternative Version of the Internet ."

Jesse, an English teacher living in Xinjiang, in northwest China, had been up until the early hours reading about deadly riots which had broken out in the regional capital of Urumqi -- anxiously checking the news and emailing friends to let them know he was safe.

When he woke up the following morning, he was surprised to see he had no new emails. Then he realized that nothing was loading at all.

"Between 3am and 8 or 9am, things got cut, and then we couldn't access anything outside," Jesse said.

In response to a day or so of protests and riots in one city, the whole of Xinjiang -- a region of more than 617,700 square miles (1.6 million square kilometers) and 20 million people in 2009 -- was cut off from the internet for almost 10 months.

Businesses dependent on the web, like internet cafes or travel agencies, quickly went under, while others had to send staff on the 620-mile (1,000-kilometer) journey to the neighboring province of Gansu to get online. Some people made the 24-hour drive every week to communicate with customers, keep university applications current, or simply keep their families updated.

For Jesse, who requested to be identified by a pseudonym because he and his wife still travel to Xinjiang, the blackout was more of a personal inconvenience, but for many of their neighbors it was "extremely disruptive."

Even after the ban was eventually lifted, the Uyghur internet -- the websites aimed at the ethnic group that was the historical majority in Xinjiang -- never recovered. Website administrators were jailed and their servers seized, never to come back online.

Nearly 10 years on, 2009 is seen as a clear acceleration point, not only for China's repressive policies in Xinjiang -- where it was last year accused of putting hundreds of thousands of Uyghurs in internment camps -- but also attitudes towards the internet.

2009 was the biggest test the architects of the Great Firewall had faced at the time, and they responded with a blistering assault that shocked even their critics.

Yet 2019 could be even worse.

JUST WATCHED China exports its model of internet sovereignty Replay More Videos ... MUST WATCH China exports its model of internet sovereignty 02:31

Internet maintenance day

Every year, just as summer is really starting, sections of the Chinese internet become almost unusable.

While China has built the world's most sophisticated top-down censorship apparatus in the Great Firewall, this is mainly aimed at information originating overseas. Most of the day-to-day control is in the hands of censors working for the nominally private companies which dominate the Chinese web.

These censors are rarely given clear guidelines by the government, and must predict and second-guess what will be deemed inappropriate, lest they be punished for allowing something through that should have been forbidden.

No date is more sensitive in the Chinese calendar, and therefore more zealously over-policed, than June 4, the anniversary of the 1989 Tiananmen Square massacre , when People's Liberation Army troops -- on the orders of paramount leader Deng Xiaoping -- brutally cracked down on student and worker groups protesting in Beijing and other cities.

2019 will see not only the 10th anniversary of the Urumqi riots at a time when sensitivity over Xinjiang is at an all-time high, but also 30 years since the Tiananmen massacre. It will present perhaps the last great challenge to the censors who have managed to almost erase the incident from Chinese popular consciousness.

In the past three decades, almost all prominent figures associated with the Tiananmen movement have been driven into exile, marginalized and largely cut off from young people in the country today. Otherwise -- like reformist politician Zhao Ziyang, Nobel Peace Prize laureate Liu Xiaobo and many of the "Tiananmen Mothers" -- they have died, hounded and harassed to their graves by agents of the Chinese security state.

Even in Hong Kong, the only place on Chinese soil where a major commemoration of the Tiananmen massacre is held every year, the young generation struggles to empathize with the battles of 30 years ago. Many feel little solidarity with protesters who believed in a China that they themselves increasingly want no part of.

Activists in China will undoubtedly attempt to test the censors, and many people who were alive at the time of the massacre and remember the dashed hopes of those days will seek to force a reckoning. But they will face a Great Firewall that is even more ironclad than it was in 2009 , when multiple foreign services -- including Facebook and Twitter -- were blocked and dozens of Chinese sites went temporarily offline , leading users to coin the term "Internet Maintenance Day" for the many error messages they encountered.

As if Tiananmen and Urumqi were not sensitive enough, 2019 also marks 20 years since the crackdown on the Falun Gong spiritual movement, mention of which remains strictly forbidden on the Chinese internet, and 60 years since the Dalai Lama fled Tibet.

Spreading worldwide

According to the most recent report on internet censorship by Freedom House, a US government-funded NGO, China remains the "world's worst abuser of internet freedom."

Beijing is also increasingly exporting its model to authoritarian and even nominally democratic governments worldwide, providing training, technology and ideological support for countries to adopt their own internet systems.

For the censors overseeing that effort, 2019 could become a year-long roadshow demonstrating the effectiveness of their internet controls, showing they can stifle any criticism of the government around the key anniversaries of Urumqi and Tiananmen in time for a propaganda extravaganza in October for the 70th birthday of the People's Republic of China.

There is no doubt that activists and dissidents will try to disrupt this display of internet mastery, but the odds against them succeeding are very high. Even Google, which in 2009 was preparing to pull out of China after years of censoring its searches there, is now willing to play ball with the government, building a dedicated, self-censoring app solely for the Chinese market

If the censors cannot rein in discussion to their satisfaction they will simply cut the internet off entirely, as they did in Xinjiang a decade ago and have done in numerous other parts of the country since, reminding users once and for all that this is the censors' web -- you just post on it.