View Full Version : Comcast Internet throttling is up and running

01-17-09, 11:55 PM
Comcast Internet throttling is up and running

Cunning plan replaces P2P blocking
By Egan Orion
Tuesday, 6 January 2009, 11:08
COMCAST, the second-largest US cable television and Internet
communications service provider, has a new broadband traffic
throttling scheme installed and operating in all of its markets.
The ISP's new regime for restricting its customers' bandwidth
utilisation replaces its former stealthy practice of arbitrarily
blocking subscribers' peer-to-peer (P2P) upload traffic, which was
criticised by the FCC last year after it was exposed by the Associated
Press and others.
Comcast's filing with FCC (PDF) says it has put in new hardware and
software technology at its Regional Network Routers locations to
effect this cunning traffic management plan.
Its network throttling implements a two-tier packet queueing system at
the routers, driven by two trigger conditions.
Comcast's first traffic throttling trigger is tripped by using more
than 70 per cent of your maximum downstream or upstream bandwidth for
more than 15 minutes.
Its second traffic throttling trigger is tripped when the Cable Modem
Termination System you're hooked-up to along with up to 15,000 other
Comcast subscribers gets congested, and your traffic is somehow
identified as being responsible.
Tripping either of Comcast's high bandwidth usage rate triggers
results in throttling for at least 15 minutes, or until your average
bandwidth utilisation rate drops below 50 per cent for 15 minutes.
The Comcast two-tier traffic throttling system enforces different
quality-of-service levels. Internet packets to and from a specific
subscriber are assigned 'Priority Best Effort' (PBE) queueing by
default, and the traffic rate is throttled by switching packets to
lower priority 'Best Effort' (BE) queueing.
Comcast uses a bus analogy to explain how its two-tier traffic
throttling system works:
"If there is no congestion, packets from a user in a BE state should
have little trouble getting on the bus when they arrive at the bus
stop. If, on the other hand, there is congestion in a particular
instance, the bus may become filled by packets in a PBE state before
any BE packets can get on. In that situation, the BE packets would
have to wait for the next bus that is not filled by PBE packets."
According to the company, upstream and downstream traffic is managed
separately, and its router packet queueing increments - the waiting
time between each 'bus' in its analogy - are two milliseconds, or
1/500th of a second.
Comcast says that a throttled subscriber's connection that is forced
into the lower BE quality of service queue "may or may not result in
the user's traffic being delayed or, in extreme cases, dropped before
PBE traffic is dropped."
Thus, Comcast's latest traffic throttling method can lead to transfers
being blocked, too. But only in 'extreme cases' it says, so that's
alright then.
Comcast has also imposed a monthly 250GB bandwidth usage cap on all of
its customers, and it will, after one warning, terminate service for
one year to those who exceed that cap twice within a six-month period.
So you punters who signed up with Comcast as your ISP can be assured
that the company will deliver only about half of the maximum bandwidth
it advertises, on a consistent basis.
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