Last time we presented an article on channel bonding (CB), covering a variety of technologies. Today we’ll look more into depth at DOCSIS 3.0 or D3 channel bonding—CB for data delivered via coax to a cable modem (CM). If you’re a customer of a cable provider (known as a multiple services operator or MSO) delivering data/video/voice services, you’re undoubtedly using technology known as DOCSIS—Data Over Cable Service Interface Specification—and likely you’re using D3, the latest version of DOCSIS widely available. Rather than revisit yesterday’s D1/D2 technology or salivate about what might be available in a few years with D3.1, we’ll discuss the benefits of D3 CB.
D3 is a wondrous improvement over earlier DOCSIS versions as it allows for a much higher maximum throughput. Simply put, a higher throughput means greater bandwidth and faster speeds. To illustrate, D3 spectrum spans 108 MHz – 1.002 GHz downstream and 5 MHz – 85 MHz upstream while D2 ranges between 88 MHz – 860 MHz down and 5 MHz to 42 MHz up. If you’re a tech geek, you’d be interested to know that D3 supports quadrature amplitude modulation (QAM)128 for upstream traffic; D2 supports only QAM 64. QAM is important because it doubles the effective available bandwidth into a single channel. Ergo, D3 carries twice as much data as D2.
Take a look at this intro to D3 CB from Netgear:
Why Your MSO Won’t Want You to Use Your Own Cable Modem
First, let’s mention that leasing CMs to subscribers is a big source of revenue for MSOs. But you, the customer, should realize that buying your own CM will pay for itself in mere months. Plus, you may be able to upgrade your CM to provide more features than the one you’re leasing from your service provider. For instance, your MSO may be leasing you a CM that serves as a IEEE 802.11n Wi-Fi access point when you could purchase a newer CM with greater 802.11ac capabilities. We would be remiss if we were to omit that should you buy a CM to replace the one provided by a MSO, you’re required to register and activate it through your cable provider.
Realize that upgrading to a D3 capable modem won’t ramp up the connection speeds you receive from your MSO; for that, you’ll have to subscribe to a higher performance service tier. However, D3 can use multiple down or up channels simultaneously—channel bonding—to maintain maximum possible speed. This is an important consideration since your cable service is not a dedicated connection, i.e., you share signal with other subscribers from a cable modem termination system (CMTS) housed in a nearby hub (or the cable headend if you’re close to the MSO office). Thus, during peak usage hours, a D3 using CB should be less susceptible to drops in connection speeds. Speed drops are contingent upon the number of channels made available by the MSO but since D3 has up to eight times the bandwidth of D2, the subscriber should see a more commensurable connection.
You may have heard that in the past year or so, MSOs now serve more data subscribers than video subscribers. In other words, people are ditching cable TV packages for Over-the-Top (OTT) video streamed over Internet, e.g., Hulu, Netflix and Sling TV. With the bigger data pipes available from D3, made possible by CB, tech savvy consumers keep only the Internet connection and subscribe to OTT providers. Not only do subscribers cherrypick the shows they want, in effect creating their own cable tier of programming, they substantially lower the price of their cable bill.
Let’s look at one D3 CM model in particular, the TP-Link TC-7610. It’s certified by CableLabs for use on the DOCSIS networks of Comcast, TWC, Cablevision and Brighthouse and is backward compatible with D1 and D2. For the cost of leasing a modem from your MSO for six months or less, you could buy this CM from Amazon and take advantage of 343 Mbps down and 143 Mbps up, if such speeds are available from your cable provider. The TC-7610 employs CB for use on as many as eight channels, assuring the subscriber of more constant and consistent speeds, particularly in areas congested with other users. Moreover it supports both legacy IPv4 and cutting edge IPv6 dual stack to identify devices and route data to the proper destination. The main difference between IPv4 and IPv6 is the number of bits in the address: IPv4 has a 32 bit IP numeric address scheme while IPv6 are 128 bit IP hexadecimal addresses— vital for the upcoming onslaught of computing devices in the Internet of Things (IoT) where tens of billions of devices are forecast to need their own unique IP address.
One caveat: some CMs, including the TC-7610, are not voice modems and thus are not for use with VoIP. Another caveat: the use of virtual private networks (VPNs) can affect download and upload speeds. As Lawrence Neves of bhphotovideo.com explains, “VPNs reroute your service through a proxy (of sorts) and bounce your signal through several different channels.”
Want even faster speeds? Consider the TC-7620, which bonds 16×4 channels to achieve a downstream data rate of up to 680 Mbps.
D3 CB QED
So just how fast is D3? That depends on the number of channels bonded. See the chart below. Note that EuroDOSCIS has different specifications. Numbers in parenthesis denote maximum payload throughput after overhead.
|Number of Downstream Channels||Number of Upstream Channels||Downstream Throughput||Upstream Throughput|
|4||4||171.52 (152) Mbps||122.88 (108) Mbps|
|8||4||343.04 (304) Mbps||122.88 (108) Mbps|
|16||4||686.08 (608) Mbps||122.88 (108) Mbps|
|24||8||1029.12 (912) Mbps||245.76 (216) Mbps|
|32||8||1372.16 (1216) Mbps||245.76 (216) Mbps|
Here let’s revisit our two favorite tech geeks Brady Volpe of the Volpe Group and his colleague, Cisco Consulting Network Engineer John Downey, as they delve deeper into DOCSIS CB. You may remember their earlier dialogue from our previous article on CB:
How can you check your modem to see if CB is being performed? Log in to the device’s IP address, typically 192.168.x.x, and access the internal status page. Bonding info is typically found under the “signal status” page or something similar and the data displayed should look akin to this:
Downstream Bonded Channels
|1||Locked||QAM256||235||123 M Hz||5.2 dBmV||43.2 dB||271||496|
|2||Locked||QAM256||233||111 M Hz||6.2 dBmV||44.6 dB||180||588|
|3||Locked||QAM256||234||117 M Hz||5.9 dBmV||43.9 dB||235||525|
|4||Locked||QAM256||236||129 M Hz||4.7 dBmV||43.9 dB||248||515|
|5||Locked||QAM256||237||147 MHz||5.2 dBmV||43.9 dB||354||432|
|6||Locked||QAM256||238||153 MHz||4.6 dBmV||42.5 dB||292||467|
|7||Locked||QAM256||239||159 Mhz||3.8 dBmV||43.0 dB||270||494|
|8||Locked||QAM256||240||165 MHz||3.4 dBmV||43.0 dB||314||456|
Upstream Bonded Channels
|Channel||Lock Status||US Channel Type||Channel ID||Symbol Rate||Frequency||Power|
|1||Locked||ATDMA||4||2560 Ksym/sec||25 MHz||46.9 dBmV|
|2||Not Locked||Unknown||4||0 Ksym/sec||0 MHz||0,0 dBmV|
|3||Not Locked||Unknown||4||0 Ksym/sec||0 MHz||0,0 dBmV|
|4||Not Locked||Unknown||4||0 Ksym/sec||0 MHz||0,0 dBmV|
Here, 8 channels are bonded for downstream and 1 channel is used for upstream.