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Cisco's Move To Eliminate Up-Front Channel Licenses

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At CES, held January 9-12 in Las Vegas, Cisco Systems Inc. announced a new licensing model for its Converged Broadband Router (cBR-8) converged cable access platform, or CCAP, product, allowing its customers to purchase capacity based on expected bandwidth consumption by their subscribers, as opposed to individual quadrature amplitude modulation, or QAM, channels. The new licensing model, called Infinite Broadband Unlocked, or IBU, is enabled by the transition to DOCSIS 3.1 technology, which introduces orthogonal frequency division multiplexing, or OFDM, as a completely new physical layer scheme.

The primary benefit to moving to IBU is to eliminate the need for Cisco's customers to purchase up-front channel licenses, which has been the standard licensing model across CCAP and cable modem termination system, or CMTS, vendors for years. IBU instead introduces a perpetual license for total bandwidth consumption per individual service group. In other words, if a cable operator has a service group of 100 homes, instead of being forced to pay for future bandwidth consumption through the up-front purchase of DOCSIS downstream and upstream channels, the operator can make a one-time purchase of total capacity based on the current capacity requirements of those 100 homes.

Cisco is first out of the gate with a public announcement of its new licensing model. But every CCAP vendor, from ARRIS International plc to Casa Systems, Inc., Harmonic Inc. to Nokia Corp., will be moving in this direction as well. The transition to DOCSIS 3.1 and its focus on OFDM subcarriers and total capacity, as opposed to individual QAM channels, makes this model a reality.

Many years ago, cable operators purchased new bandwidth for their service groups in the form of a fixed ratio of downstream to upstream channels per individual CMTS line card. Early on, those channel ratios were 4:1 and 8:1, designed to match the traffic patterns seen in their networks. With the introduction of DOCSIS 3.0 came the need to eliminate these fixed ratios and instead move to a total number of QAM channels per service group, which could be mixed and matched in the downstream and upstream direction based on observed and expected traffic patterns.

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Now, with cable operators looking to reduce the amount of rack space devoted to monolithic CMTS and CCAP platforms in their headend and hub sites, while also pushing DOCSIS physical, or PHY, and media access control, or MAC layer intelligence closer to subscribers, there are multiple architectures requiring support, which add more complexity to decisions about bandwidth consumption per service group.

Here are just a few of the technological and architectural shifts in cable broadband access networks that make the need for more flexible bandwidth models necessary:

  • DOCSIS 3.0 to DOCSIS 3.1
  • Optical node logical and physical node segmentation
  • Centralized to distributed architectures
  • Remote PHY and Remote MACPHY architectures

Being locked into traditional 6 MHz QAM channels no longer makes sense and is also quite inefficient. Each QAM channel includes a guard band, designed to prevent channels from overlapping and the resulting signal becoming too garbled for a set-top box or modem to demodulate. To cable operators, those guard bands are lost revenue. They are signals carrying no data, however, they are a necessary evil.

DOCSIS 3.1 eliminates those guard bands by using OFDM to change the QAM channel from 6 MHz to 25 or 50 KHz subcarriers. These subcarriers can be bonded to adjacent subcarriers without the need for any guard bands. The result is a single block of RF spectrum because there is no separation of individual channels in the frequency domain. It is this block of spectrum that is generated by the CCAP platform, the license to which is what is covered under Cisco's new model. The increased spectrum availability is what has led to the rapid increase in total DOCSIS channel (or equivalent channel) shipments over the past year. In fact, total combined DOCSIS upstream and downstream channel shipments are estimated to have surpassed 10 million for the first time ever in 2017.

Many cable operators still prefer to purchase new broadband capacity in the form of DOCSIS equivalent channels, as that is how they have purchased for years. The addition of DOCSIS 3.1 and OFDM has once again resulted in a significant drop in price-per-downstream channel, as spectral efficiency gains have increased the amount of capacity available per CCAP line card.

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