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BitTorrent 4.20 Released
June 22, 2006
Thomas Mennecke
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Allegro! Typically used to describe a quick music tempo, in the BitTorrent context it describes the latest release of the Mainline client. The primary focus of this Mainline release is to address the issue of ISP bandwidth throttling, and more importantly, BitTorrent traffic caching.

It’s no secret that bandwidth concerns have been one of the more pressing issues surrounding the BitTorrent community. CacheLogic, which provides P2P caching solutions for ISP networks, has previously calculated that approximately 60% of a networks bandwidth is consumed by the BitTorrent protocol. This average varies according to the ISP, as some ISPs report less bandwidth consumption and other reporting more.

In response to this growing bandwidth consumption, ISPs generally have three choices; throttle bandwidth, cache traffic, or do nothing. Bandwidth throttling is becoming less of an attractive option, as ISP customers in Canada have becoming increasing vocal in their opposition. In addition, new end-to-end encryption technology developed by µTorrent and Azureus has been well received by these inhibited users.

A more advantageous solution which has grown in acceptance is traffic caching. A compromise between the ISP and customer, caching allows users to participate on BitTorrent without utilizing an ISP's external bandwidth. Caching servers, which are hosted by the ISP, maintains the most popular and most queried traffic. Instead of the BitTorrent client utilizing the ISP's external bandwidth to obtain the required file(s), traffic is contained between the cache server and the end user. In other words, the traffic is maintained within the ISPs internal network, which is considerably cheaper than handling external traffic.

“We spent an extraordinary amount of time face to face with the largest ISPs in the world who now see anywhere between a third and up to 70% of all their traffic in the BT protocol,” Ashwin Narvin, president of BitTorrent, Inc., told in May. “[We’re] trying to convince them there’s a better way to manage the BitTorrent protocol then to limit it and to shape it. We’ve been strong advocates of the caching solution in the next version of the (Mainline) BitTorrent client, what we are calling the Allegro release. There’ll be a protocol which allows ISPs to cache BitTorrent content which is a great thing for users. It improves the user experience for downloading with BitTorrent no matter what client it is as long as it’s implemented the Cache Discovery Protocol and it also offers ISPs a cost effective way to allow BT to exist on their networks.”

The latest release of BitTorrent, aka the “Allegro” release contains the anticipated Cache Discovery Protocol. Like its name suggests, the new release allows ISPs that implement caching technology to recognize and store BitTorrent traffic. Although in its infancy, the protocol will be available to any developer that wishes to implement it.

"Transparent caches are sophisticated pieces of hardware," Ashwin explained to "They perform deep-packet inspection to detect the frequecy of certain files. If a file shows up on the network frequently, the cache stores that file so that its seeded in the network rather than by peers. ISPs appreciate this because their access networks are terribly congested with P2P traffic. Caches are legal and covered explicitly in the DMCA."

Specific details on Cache Discovery Protocol will be available relatively soon on

BitTorrent, Inc. has been on a continuous goodwill campaign, attempting to convince ISPs there’s an alternative to blocking or throttling BitTorrent traffic. Now that the technology is readily available, it’ll be up to the ISP to determine which direction they wish to travel.

This story is filed in these Slyck News categories
BitTorrent :: BitTorrent Inc.
BitTorrent :: BitTorrent Clients
File-Sharing/P2P Related :: New Releases

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