Pervasive computing environments require ubiquitous interfaces for customers. The emerging wireless technology-Ultra Wide Band (UWB) is expected to be a promising candidate in these environments thanks to the efficiency of impulse radio (IR). Former MAC protocols for narrow band became unfit for the novel UWB PHY and numbers of protocols emerge. In this paper, the primary MAC protocols classified into two categories are reviewed and compared. The analyses are focus on MAC organization, media sharing and superframe framework. Based on these analyses, the UWB issue and innovation in MAC design are proposed.