Why download file through browser fail?

Though both ultimately transfer files over a network, a BitTorrent download differs from a classic full-file HTTP request in several fundamental ways. First, BitTorrent makes many small P2P requests over different TCP sockets, while web-browsers typically make a single HTTP GET request over a single TCP socket. Second, the BitTorrent protocol limits a client's download speed to roughly its upload speed, while HTTP gives no preferential treatment to cooperative nodes. And third, BitTorrent downloads in a random or "rarest-first" approach that ensures high availability, while HTTP downloads in a contiguous manner. Taken together, BitTorrent achieves much lower cost, much higher redundancy, and much greater resistance to abuse or "flash crowds" than a regular HTTP server. However, this protection comes at a cost: downloads take time to ramp up to full speed because these many peer connections take time to establish, and it takes time for a node to get sufficient data to become an effective uploader. As such, a typical BitTorrent download will gradually ramp up to very high speeds, and then slowly ramp back down toward the end of the download. This contrasts with an HTTP server that, while more vulnerable to overload and abuse, ramps up to full speed very quickly and maintains this speed throughout. Furthermore, BitTorrent's non-contiguous download methods prevent it from supporting "progressive downloads" or "streaming playback", as is possible with HTTP.