Is pinging site's backlinks is essential or it is a Black Hat technique? If it is OK how can I ping all of my backlinks?

There is really no need to ping all of your links... You can use social bookmarking, Twitter, Digg, etc. if you want the links crawled quickly.  If the links are on high quality sites with good backlinks they will be discovered before too long regardless.  If you want to ping you can use a service like pingoat, pingomatic, etc.

The main purpose of pinging yoru backlinks is to get them indexed faster by the search engines you target, so they can pass link equity faster than they would anyway. The better way to go for this is without doubt by using social bookmarks, like Jason Wilson mentioned in his answer. The main difference between Black Hat and White Hat is how you do things. If you review the most popular black hat SEO techniques, you will find out that they are actually used by White Hat SEOs, but this time with regards to the users and the search engines, not juts to gain traffic and rankings. More about black hat techniques: http://www.seopalbg.com/blog/the-nature-of-black-hat-seo/

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