In regulatory filing, the No. 2 Internet provider blames file-sharing, denies content blocking.
Comcast has told U.S. regulators it uses reasonable measures to manage traffic moving over its broadband service as some of its customers overwhelm the network by using file-sharing applications like BitTorrent.
In an 80-page filing with the U.S. Federal Communications Commission on Tuesday, Comcast gave its most detailed explanation of how it manages Internet traffic on its service, naming BitTorrent as prime culprit, but again denied it blocks content, applications or discriminates among providers.
Comcast, which is the second largest U.S. Internet service provider with more than 13 million subscribers, said the use of network management was essential to avoid congestion and impairment of some applications such as online video sites Joost and Veoh.
Comcast was answering claims by consumer groups that it favors or block certain types of content moving over its network. Such a move would be viewed as flouting "net neutrality".
Net neutrality is the principle of allowing all content that flows over an ISP's network to be treated equally, without any preference.
Although it is not law, it is supported by a wide range of pressure groups and businesses concerned that ISPs will start charging to prioritize the delivery of users' content.
Though Comcast reiterated it does not give preferential treatment to any content it argued that Web traffic needs to be managed to provide the best service for its customers.
"Simply stated, there is nothing "neutral" about a network that is not managed," Comcast said in the filing. "An unmanaged network simply means that users who make disproportionately resource-intensive demand on the network can crowd out fellow users," the company said.
Comcast identified BitTorrent users for blame in causing network congestion.
The file-sharing application is commonly used to share large digital media, such as TV shows and movies. Its use has caused some concern with Hollywood studio executives as some fans share such media illegally - sometimes pre-release.
Last month Vuze, a digital media platform company, asked the FCC to clarify what constitutes "reasonable network management" by broadband network operators and to establish it did not permit network operators to block, degrade or discriminate against lawful Internet applications.
Comcast said its network management practices manage traffic in a method similar to a traffic ramp control light on a freeway during rush hour.
"One would not claim that the car is "blocked" or 'prevented' from entering the freeway, rather, it is briefly delayed, then permitted onto the freeway in its turn while all other traffic is kept moving as expeditiously as possible."
ISPs are looking at different ways of managing the increasing amount of traffic moving across their networks both for cost management and for quality of service reasons.
Last month Time Warner Cable, which has more 7.5 million Internet customers, said it is planning a trial to bill high-speed Internet subscribers based on their amount of usage rather than a flat fee, the standard industry practice.