Do I have to be a holder of a college degree to convince employers of getting a high salary, although I have a practical experience of 20 years?

Often the degree is a way for employers to filter out a high volume of applicants.
In this case, not having it will definitely hold you back.
However, most employers will value good experience, coupled with matching references and a portfolio to match, far higher than a degree.
Your work experience provides them with a track record to view your skills and accomplishments and shows them that you are definitely able to do the job.
I have employed many graduates who were hopeless at their positions and people who had no degrees but good experience ran circles around them all the time.
Ultimately, without a degree it will be harder, as you will have to prove yourself and convince the potential employer that you have the skills that they will assume the degree holder already has, but your work history can provide a tangible and convincing argument to show your real value.

it will always be a surface limit ...a hard roof for possiblities actualy but limits forever puted tobe cracked agian

Good question? I have the two opinion to discuss: 1.just like to drive a vehicle you need a driving licence to operate the vehicle .
2.But it is not always possible when one have a driving licence it does not state that he has to mandatarly drive the vehicle ...even his or her know how practical judgements can effictintly insrtuct the driver for effienct drive.
But as a mandatary requiremetns few employers prefer as a qualifying criteria ,as in my case you see i had completed UG degree only but iam handling the entire pan india training operations and delivering tranings and training models to Management .
Its all depend how you choose and how the employer choose as a policy of hiring....
Simply to tell person make the difference not the place ..........
like wise we have many examples who suceeded .
Today scenerio shows importance of practical implication of what learnt inside the class rooms and more effienctiently addresing the corporate industry to bridge the gap by syncronise the Class room learning and apply in the practical way to prodeuce industry relevant peoples.
simple formula : Knowledge * skill = Ability Ability * situation = opportunity Ability + opportunity = sucess Hope you understand how to convice the employer .

employers using college degrees as screening devices.

Degree part of competancy, & also its a way to upgrade knowlege of yourself.

When there is so much experience, degree doesn't matter