Dirty Little Secret (DSL) of Cable Internet for Business

When cable services boast high speeds, they are often talking about supporting a small number of users. For example, one cable company claimed 100meg/second service for business in an ad, but what they didn’t say was that it was only supporting six users! (Ask anyone in our sales department for a copy of that ad). The ad was quickly withdrawn once they realized they exposed one of the great limitations of cable.  significantly asWith Fiber Internet Center, you can handle more than 100 users on our 100 meg/sec service.  

Cable compares itself favorably to DSL, which has been around for a long time.  But cable is merely a step up from DSL.  However, if you look at how cable Internet networks function, you’ll see why cable modem customers get upset from time-to-time.  Just like DSL customers, they experience high packet drops and latency. 

The latest cable modems are DOCSIS 3.x. These modems are actually designed to drop packets when the data channels are crowded. They leverage the functionality of the TCP software stacking in your computer/TV device. TCP is designed to repeat packets after not receiving a response from the server your application or web page is connecting too. This is also true of the server packet trying to reach your computer.

Once you understand that a cable modem is a device that uses radio frequencies also called channels to communicate to and from the Internet, you begin to realize channel frequency space is limited. Limited even more in that channels upstream to the Internet and downstream from the internet cannot overlap each other. 

It's easy to understand that there are a limit to the number of frequencies or channel spaces that fit on a cable network.  These channels are shared by groups of cable modems in neighborhoods. To simplify this, imagine that all odd numbered homes and buildings are on channel 1 or frequency A for data coming from the Internet. They utilize channel 2 or frequency B for data leaving the homes going to the Internet. Channel 1's frequency is wider and uses more space in the street than Channel 2. Channel 1 might have 10x the number of lanes as Channel 2. Cable modems are asymmetrical, which contributes to this latency and packet drops. 

Why are there more channels to buildings?  The answer is that most applications are focused on delivering packets. Video streaming applications send more packets to buildings to make the video look good. Cable modems were designed for home users with the demand of packets to travel to buildings. Back to the channels...

These channels are lanes on the digital street in your neighborhood. As you can imagine, the packets from all those odd numbered buildings need to travel in correct lanes assigned to the cable modem. It's up to your cable modem to find an opening in a Channel 2 lane to transmit data up to the Internet. Data from the Internet is sent to your cable modem by a giant cable modem that uses wide Channel 1 to speak with multiple cable modems on narrow Channel 2. 

As you can see, your modem waits its turn in your neighborhood. There is an exception to this: VOIP packet handling. Special time slices are reserved for VOIP using the phone plug located on the cable modem. VOIP packets between the giant cable modem and your cable modem’s phone ports have a priority assigned to jump in and out of the channels faster in a reserved lane. However, sometimes even those lanes are full. Businesses that use VOIP services other than the cable company’s are treated to the same low priority as senders of any other packet. This is because they cannot be plugged into the cable modem phone jacks. The jack is reserved for cable phone customers.

When all the packets get to the head end (cable building) they are received by what is basically a giant cable modem.  Essentially, like a phone company DSL modem, a cable modem is not a true Ethernet switch or Internet router. Both DSL and DOCSIS use packet encapsulation. Packets are converted and then re-converted to TCP/IP packets by either giant cable modems or giant DSL modems (called DSLAM) before they can be sent to a true Internet connected router. 

On true fiber networks, there is no expectation to leverage TCP/IP software to wait and repeat packets. With a true fiber connection, you have a real Internet router right there in your building that sends and receives TCP/IP traffic directly. It's on the Internet.  A true fiber network is not a packet converted and congesting shared network adapted to the Internet. A true fiber network is Ethernet packets using Internet Protocol (IP) at the speed of light.



             Fiber Internet Center LLC          SF 650-330-0428         LA & OC 714-619-0146      SD 619-398-0268         © 2012