At work, we recently subscribed to "Comcast Workplace" cable
Internet service, to supplement our existing feed. Since Internet
feeds seem to be a popular topic on this list, and there is a lack of
good information out there, I thought I'd post a write-up of my own
experiences.
Basically, the intent here was to get some cheap, disposable
bandwidth for web browsing. This is intended to complement the SLA
feed we get from a local ISP, not replace it.
Service location is Amesbury, MA. This is an old Adelphia town, FWIW.
COST
We're paying $64/month. $59/month base, plus $5/month for a static
IP address. (I was told a block of 5 addresses would cost $10/month.)
This is an introductory offer. After a year, the price is supposed
to go up. Supposedly to $105/month if it happened today. We'll see.
There were some one-time costs related to getting a line run on the
poles to our facility. These will not generalize to anyone else's
experiences, so I'm not going to post them.
SLA
SLA = Service Level Agreement. This is what spells out exactly what
you're getting for your money, and what the provider promises.
Basically, this feed comes without one. If we're happy with it,
great. If not, we're free to cancel the service.
Comcast did offer a 1.5 meg symmetric feed with what they called an
"SLA". However, the "SLA" only gave a refund schedule which kicked on
on unavailability. They never defined "available". Specifics about
things like committed rate, packet loss, and round trip time were
nowhere to be found. Sales rep couldn't provide more detail.
In short, if you need or want an SLA, Comcast is not the right choice.
SPEED
Advertised speed: Varies. The sales rep told me it would burst to
12 megabit down, 2 megabit up. The work order the installer brought
just says 6 megabit down, 768 kilobit up. Given that none of it is
guaranteed, that Comcast explicitly states it will vary and burst and
clamp, and that this is all just speeds to the nearest concentration
point, these numbers are pretty worthless anyway.
Further: Comcast employs a bursting algorithm that lets you get much
higher speeds at the start of a "download" (which I guess means TCP
connection). It clamps that down after a few seconds. I see that as
pretty reasonable behavior, since it makes web browsing *really* fast
without letting bandwidth hogs capsize the boat, and Comcast loudly
advertises they do this. ("SpeedBoost" is their trademark for it.)
But if your life consists of downloading disc images or other large
files, Your Mileage *Will* Vary.
At http://www.speedtest.net: To NYC, I get around 15 megabits down
and 2 up. To San Jose, around 10 down and 2 up. Those numbers are
also fairly artificial, since the providers make sure they're well
connected to the test sites, but at least they have *some* connection
to reality.
Downloading a 16 megabyte Symantec AV update package took 11 seconds
(roughly 12 megabit throughput). However, watching the numbers,
throughput started to take a real nose dive a few seconds in. See
above about bursting/clamping.
Downloading the CentOS 5 CD BitTorrent two weeks ago saw speeds
bounce all over the place. The swarm may have been unstable, or it
might have been general irregularities in the feed, or an artifact of
the burst/clamp algorithm. Dunno.
Interactive SSH performance seems pretty darn snappy.
Spot checking average RTT with ping: Geographically nearby hosts
seems to hover around 20 ms. Ditto for unicast East Coast root DNS
servers which respond to ping. anycast and West Coast servers vary
from 20 to 90 ms. (Keep in mind that the roots may not give ICMP a
high priority.) I see around 10 ms for UNH hosts. www at Google
and Yahoo around 20 ms.
FEED DELIVERY
The static IP is delivered via plain old Ethernet. Just configure
address, netmask, and default gateway, and go.
Comcast installed a small box that is a combination of cable modem,
IP router/firewall, and four port Ethernet switch. It says "Comcast"
and "SMC" on it. It appears to be a re-badged SMC SMC8014-BIZ, with
firmware modified for Comcast. They gave me a username/password to
manage my side of the box. Fairly typical SOHO firewall/router web
UI.
The box has multiple IP networks on the local side. One is the
static IP subnet. It's a CIDR /30 -- our own firewall gets an IP
address, plus the Comcast box has one. The other is an RFC-1918
network, a /24 subnet of the 10/8 net. The box does NAT for that.
There's also a DHCP server for the NAT net (web UI says you can turn
the DHCP off).
The web UI has options for firewall/NAT, including port forwarding
and triggering. According to the Comcast docs, I can actually use the
CPE's local side public IP address to forward ports to my equipment.
So I guess it's kind of like having one-and-a-half static IP
addresses.
SERVICE BLOCKING
Outbound SMTP, web, SSH, BitTorrent, etc., all appeared to work right away.
Inbound attempts failed at first. Comcast apparently firewalls the
public IP net by default. I guess that's reasonable in today's
climate. There was an option to turn that off. Once the firewall was
off, I was able to connect inbound and run things like SSH and SMTP.
I haven't tried putting up an MX record pointing at the Comcast feed
yet.
So while I haven't run a comprehensive analysis, it looks like
they're not blocking anything.
RELIABILITY
Insufficient data. We just put the Comcast feed into production for
web surfing a few days ago.
CUSTOMER EXPERIENCE
Insufficient data to draw solid conclusions, but so far, it's about
what I expected: Adequate, but barely. People who are well
intentioned, but don't really seem to know what they're doing.
It took the Comcast sales force a few tries to figure out which
local sales rep I should be dealing with. The sales rep paid a site
visit, and eventually two more technicians did site surveys. Plus I
gather they did an engineering survey of their outside plant (wires on
the poles).
I had to request corrections in our customer info (phone #, that
kind of thing) multiple times before our sales rep found the right
system at Comcast to enter the corrections in so they stuck.
The coax drop from the pole was installed by a contractor who was
well seasoned, had good practical knowledge, and got the job done
quickly. I thought his attitude towards jostling our inter-building
fiber line (which came in through the same service conduit) was a
little cavalier, though.
The modem was "installed" separately. This consisted of a different
Comcast tech/contractor showing up with a box, plugging it in, and
making sure the right lights lit up. He did make an adjustment on the
pole first. Still, given that he didn't even have a laptop of his own
to test the feed with, this strikes me as something that could be done
better as a self-install. Oh well.
CONCLUSION
Like I said: Cheap, disposable bandwidth. The speed really is quite
impressive for the price. Getting an SLA feed with a committed rate
of 12 megabit/sec from a "real" ISP would easily cost us over $1000
per month. I wouldn't rely on it for critical operations, but to
complement our SLA feed, it seems like a good solution so far.
Hope somebody finds this info useful.
-- Ben
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