Level 3 concurs: Comcast appears to be prioritizing traffic

Comcast (s cmcsa) may have given users a break on Thursday by raising its monthly data cap to 300GB, but Level 3 (s lvlt), the backbone Internet provider and content delivery network, wants people to know that Comcast is still likely prioritizing its traffic over others’. The issue is an important one even with the new cap, because if Comcast is prioritizing its own traffic, it is violating the terms of its merger with NBC-Universal (s ge).

In a blog post Thursday afternoon, Andrew Dugan, SVP of Network Engineering & Architecture, and Nasser El-Aawar, principal network architect, use a service called Wireshark to test out claims that Comcast is prioritizing its Xfinity on demand traffic that users access via the Xbox. Much like Bryan Berg, who kicked off this kerfuffle with a post on Comcast labeling packets and then accusing it of prioritizing packets, the Level 3 engineers detailed their tests and provided graphs showing that Netflix traffic was degraded on the network when it was congested while the Xfinity traffic going over the Xbox was unaffected.

From the Level 3 post:

While there are a number of factors that can influence download performance for Internet traffic, it appears to us that Xfinity consistently gets good performance in both the congested and uncongested tests, while Netflix traffic is significantly impaired when the home connection is congested. These results seem to be consistent with the practice of prioritization.

Comcast has denied that it prioritizing traffic and instead claims it is marking packets so it can exempt them from the cap and create a “logical” separation. The argument seems to depend on Comcast saying it is creating a logical, but not a physical separation of its traffic by labeling it, with the other side pointing out that this logical separation has physical effects that look an awful lot like physical prioritization.

Comcast has depended on technicalities before when it argued that it did not block peer-to-peer traffic back in 2007, but merely delayed the traffic. But as a result of those delays, the packets were dropped, thus blocking the P2P flows for users.

However, Level 3 is not exactly a neutral party. It is a content delivery network for Netflix, (s nflx) and in 2010 was in a very public spat with Comcast over peering, after Comcast demanded Level 3 pay it for the additional traffic it was sending over its network. The issue faded away and its resolution wasn’t publicized.

Despite Comcast’s efforts to raise its cap and render questions about how it handles its Xfinity traffic via Xbox moot, it appears that those questions are still as relevant as they were before Comcast tossed users 50 extra gigabytes per month.

Comcast van image courtesy of Flickr user Titanas.