By Rachel Harvey - South-East Asia correspondent, BBC News

Burma is one of the world's most closed and internationally isolated states, and yet a steady stream of people and goods make their way across the Thai-Burmese border each day.
Standing in Thailand, on the edge of the river Moei, it would be possible, with a good arm, to pick up a stone and throw it into Burma on the opposite bank.

You can hear the voices and see the faces of people on the other side.

The official crossing, the Friendship Bridge, is busy from early morning.

Trucks and cars queue up to go from Thailand into Burma and a steady trickle - sometimes a stream - of people comes in the other direction.

There are myriad reasons why people cross the border into Thailand.

One woman, very well dressed and manicured, told me she had come from the Burmese town of Myawadi, just on the other side of the river, to visit a private health clinic.

"The facilities in Thailand are much better, and much cleaner, than in Burma," she said.

Illegal entrants

When the price is right, in other words higher than back home in Burma, she also comes to Thailand to sell gold.

Another woman had come to sell dried shrimps, and a 10-year-old boy, in a smart green and white uniform was on his way back into Burma to go to school.

All cross the Friendship Bridge under the watchful eye of a young Thai immigration officer, Capt Wasuwat.

"The Burmese are only allowed to stay for one day," he told me. "The bridge crossing is open from 0600 to 1800 so they have to be back by 1800."

In theory they are also restricted to the nearby town of Mae Sot, but many stay longer and travel further.

A short distance from the bridge, in a side yard, three blue trucks were parked with their engines running.

On the ground, crouched next to the vehicles, were about 300 Burmese illegal migrants. Thai officials were loading them onto the trucks to be deported.

But they were not simply driven back across the bridge. Apparently, because they had entered Thailand illegally, they were not recognised by the Burmese government as being abroad and could not therefore be sent back the official way.

We followed the convoy through quiet, backstreet villages to a point a little further along the river.

Here the Burmese, mostly migrant workers, were transferred from the trucks to waiting boats, in what was clearly a well-established system.

'Inner-tube taxi'

One young man, a 17-year-old who had been working in a plastics factory, said it was the first time he had been deported, smiling incongruously.

"Will you try to come back again?" I asked. "Oh yes," he said, without hesitating for a second.

But there is a more precarious way of making the crossing - by inflatable rubber rings.

Large inner tubes, which look as though they were designed for competitors in a monster truck derby, are used to ferry people back and forth between Thailand and Burma.

It costs the equivalent of about $0.50 (£0.30) and, of course, it is completely illegal.

One driver, or perhaps that should be paddler, told me 200 to 300 people per day used his services.

There are several points along the river where the "inner-tube taxis" ply their trade. One is no more than three minutes' walk from the official crossing at the Friendship Bridge.

On the opposite river bank, in the shade of the bridge, there was a Burmese military checkpoint, complete with camouflage, sandbags and at least two soldiers in uniform.

They could clearly see everything that was going on - the steady traffic of people, sometimes up to eight at a time, laden with shopping, perched precariously on rubber rings making the journey across the river.

But the soldiers seemed unperturbed. Presumably they were getting a cut.

Spending time on the border puts into perspective all the talk of sanctions against the Burmese military leadership.

Burma's borders are porous. If they really want to, or really need to, people and goods will always find a way to get from one country to another.