Coaxial cable, the type deployed by the cable companies, has long been thought to be on its way out. After all, how many channels and what Internet speeds can you possibly force through that copper wire? Turns out, it’s a LOT more than anyone might have thought. Can you believe 10 Gbps?
There’s Fiber Under the Hood
The secret that makes it possible for ordinary coax to deliver 10 Gbps, high by even fiber standards, is that you only see the cable connector on the wall and the cable jumper to your cable modem. You might think that cable runs all the way back to the cable head-end, like twisted pair telephone lines connect directly to the telco office. That’s an illusion. Once the premises connection is out of sight, the handoff is made to a metro fiber network. The copper part is just a few dozen or a few hundred feet in length. The system is referred to as a hybrid fiber-copper network or HFC.
The Magic Box
With a wire plant that can support bandwidths as high as 10 Gbps, what else is needed is an interface to transmit and receive on the HFC and provide a 10 Gbps Ethernet connection at the user’s end.That interface is the DOCSIS 3.1 Cable Modem.
DOCSIS or Data Over Cable Service Interface Specification is a set of technical standards that describe how to use the standard “TV channels” and other open capacity on cable systems to transport high bandwidth data without conflicting with the television transmissions. It was developed by CableLabs and is supported by many equipment manufacturers.
The original DOCSIS 1.0 came out in March, 1997… just in time to support the big boom in Internet growth. It was quickly upgraded to versions 1.1, 2.0 and the popular current standard, DOCSIS 3.0. It’s a new version, DOCSIS 3.1, that is causing all the excitement for fiber-like cable.
What does DOCSIS 3.1 offer? It is capable of at least 10 Gbps in the downstream direction and 1 Gbps in the upstream direction. That’s about 10x to 30x the capacity of existing cable bandwidth offerings. It is also backwards compatible with earlier DOCSIS versions so it can be seamlessly deployed on existing cable systems. What’s still needed is for cable operators to upgrade their equipment to the new standard and get DOCSIS 3.1 modems installed at customer locations.
The Bandwidth Stampede is On
It’s not a matter of if but when cable companies will embrace DOCSIS 3.1. Verizon has been deploying their FiOS Fiber to the Premises (FTTP) system for years. Google is entering market after market, albeit slowly, with their own fiber optic Internet service. Cable has a chance to protect the investment in the systems they already have by being able to offer Gigabit and 10 Gigabit Internet access with simple equipment upgrades and no need to rewire the city.
Comcast is one major cable operator that has seen the light. They have declared an intent to cover their entire service footprint with DOCSIS 3.1 capability in the next few years.
Is This the Same as SONET or Ethernet over Fiber?
In a word… NO. These are not only different technical standards, they have different performance standards and are targeted at different types of customers.
SONET is the original telephone company standard that was first deployed to transmit thousands of telephone calls on a single fiber. As bandwidth demands escalated to connect data centers and support the backbone of the Internet, SONET was made available to businesses. The lowest service level is OC3 at 155 Mbps. The highest levels are typically OC-48 at 2.5 Gbps, OC-192 at 10 Gbps and OC-768 at 40 Gbps.
A newer technology is Carrier Ethernet. This is directly compatible with the Ethernet that dominates local area networks in nearly all companies. Both copper and fiber implementations of Carrier Ethernet are available, but Ethernet over Fiber is rapidly becoming the more popular standard. Service levels range from 10 Mbps to 10 Gbps, with 100 Gbps available in some areas.
How do Cable DOCSIS, SONET and Fiber Ethernet Compare?
SONET and Ethernet over Fiber (EoF) obviously require fiber optic connections all the way to the premises. Cable only needs the standard coaxial copper cable connection. This provides cable with an advantage as to availability and speed of installation. However, that advantage is not what it once was. More and more competitive carriers are expanding their fiber optic networks and “lighting” more and more buildings for fiber service.
Cable seems to have a big cost advantage compared to the fiber technologies, but this is more a matter of the type of service offered rather than anything to do with copper versus fiber. As proof, consider Google Fiber. It’s priced like cable, but is fiber optic end to end.
SONET and EoF are considered high performance business services and are generally offered with SLAs or Service Level Agreements that define the performance and availability of the service. Cable is considered a “best effort” service and doesn’t come with the same uptime guarantees.
SONET and EoF are what are called dedicated services. That means the assigned bandwidth is dedicated to your organization. If you contract for 10 Gbps, you’ll get 10 Gbps 24/7/365. There are no usage limits. You can drive as much data down those pipes as they’ll take for the entire month. Cable is a shared service. The bandwidth is “up to”, say, 10 Gbps. At any given time, you may have all of that to yourself, or you may be sharing it with a dozen, hundred or thousand other users. Bandwidth for shared services varies, while it is solid for dedicated users.
The other big difference is symmetry. SONET and EoF are symmetrical services. That means you get the same upload and download speeds. Order 10 Gbps service and it will be 10 Gbps in both directions all the time. Cable service is asymmetrical. Download speeds are typically 10x upload speeds. DOCSIS 3.1 maxes out at 10 Gbps download and 1 Gbps upload.
How Do You Choose?
Cable is well matched to typical consumer and small business Internet access, which is download intensive. The “shared” aspect may not make that much difference and the reliability may be high enough that the cost advantage makes it an excellent choice.
However, if you are primarily transferring big files in both directions or dependent on cloud services for critical operations, or if availability of service is critical to what you are doing, you may find that only SONET or Ethernet over Fiber will be satisfactory. Costs for both types of services have dropped dramatically in recent years, with EoF especially cost effective for high performance applications.
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