Salamun Alaikum,
A mutawwatir transmission is one which is passed on by so many narrators directly from source that it is inconceivable that they could have come to be agreed upon a falsehood with regards the information they collected from the primary source. Therefore, the veracity of what is being narrated by them is unquestionable. The Quran calls itself a
'Hasan Hadith' (The best hadith) and its oral transmission remained 'mutawwatir'.
The Quran has reached us
both by a rigorous oral transmission and a written form of transmission in tandem. So there was not only a written codex (book) from the time of the Prophet but also a powerful mutawwatir transmission in oral form. This is possibly why no major sect in Islam disagrees with the contents of the Quran whereas there is huge disagreement with the veracity of Hadith between the sects.
Some related articles:
THE BEST HADITHhttp://quransmessage.com/articles/best%20hadith%20FM3.htmTHE DIFFERENCE BETWEEN HADITH AND SUNNAhttp://quransmessage.com/articles/hadith%20and%20sunna%20FM3.htmI hope that helps, God willing.
Your brother,
Joseph.