Comparing Cable And Fiber Networks - bbcmag.com

1 TECHNOLOGY. Comparing Cable And Fiber Networks Fiber Networks are capable of sustained, symmetrical 100 Mbps service that Cable Networks cannot match. By Andrew Afflerbach, Matthew DeHaven, Marc Schulhof and Eric Wirth / CTC Technology & Energy C. able broadband technology is currently the primary means of providing broadband data service to homes and businesses in most of the United States. Hybrid Fiber -coaxial (HFC) Cable Networks will be the main pathway for broadband communications for most homes and businesses for the Learn more about the foreseeable future because of their ubiquity in advantages of FTTH technology populated areas and their inherently greater at the Broadband Communities capacity than commercial wireless solutions and Summit in Austin, April 14 16.

2 Copper telephone lines (the medium underlying DSL service). However, Cable Networks face significant and costly challenges to achieve the performance, capability and scalability afforded by Fiber -to- HOW DO Cable SYSTEMS. DELIVER DATA? the-premises (FTTP) Networks . The delivery of Internet data services over Though Cable operators widely offer traditional HFC Cable television systems was download speeds of up to 150 Mbps over standardized by a nonprofit research and their HFC Networks , they are unable to support development consortium, Cable Television these speeds on a sustained basis for a large Laboratories (CableLabs), and ratified by the percentage of customers simultaneously without International Telecommunication Union (ITU).

3 Significant upgrades to their Networks . On the under the name Data Over Cable Service other hand, most current FTTP deployments Interface Specification (DOCSIS). can provide sustained speeds ranging from DOCSIS is the technical standard by which 100 Mbps to 1,000 Mbps at one time, to all data communications can occur bidirectionally customers, with the ability to scale network over a Cable TV system. Like Cable television capacity exponentially with relatively minor services, DOCSIS uses separate channels upgrades. Depending on the technology used, within the radio frequency (RF) spectrum of FTTP can provide sustained symmetrical the network Cable plant. Traditionally, Cable services at these speeds; most Cable operators television channels each use 6 MHz of spectrum.

4 Limit their residential service offerings to 20 The latest deployed version of the Mbps or less in the upstream direction. standard, DOCSIS , enables combining, 62 | BROADBAND COMMUNITIES | | JANUARY/FEBRUARY 2015. Figure 1: Sample DOCSIS network or bonding, multiple channels, neighborhood separately to the system to IP transmission over the both downstream (from a provider and the Internet, effectively segmenting DOCSIS Cable modem network , to a customer) and upstream (from a the network . In a four-channel or eliminating channels). Cable customer to a provider). The DOCSIS configuration, each segment has modems capable of supporting standard requires that Cable approximately 170 Mbps downstream 32 downstream channels and modems bond at least four channels and 120 Mbps upstream.

5 Eight upstream channels are to achieve maximum connection Figure 2 illustrates how this now available, and the DOCSIS. speeds of approximately 170 Mbps architecture quickly runs into Modular CMTS (M-CMTS). downstream and 120 Mbps upstream. limitations. In a peak usage period, a architecture more readily allows for (Actual usable throughput is reduced customer may, conservatively speaking, the use of additional channels. by approximately 10 percent due to use 10 Mbps downstream and 2 Mbps 2 Reduce the size of the segment by physical layer overhead related to upstream a load that can be generated constructing additional Fiber in error correction and coding.) A Cable by two Netflix HDTV streams and the neighborhood or, if possible, operator can carry more capacity by uploads of photos, videos, iCloud segmenting the node (this is possible bonding more channels.)

6 Synchronization and gaming. if the node sits at the juncture of Ultimately, the maximum speed Typical Cable systems in our two or more coaxial trunk cables). delivered over an HFC network is experience have 250 customers limited by the physics of the Cable per segment, so the hypothetical One strategy might be to expand plant; although an HFC network has demand per segment at peak time in to 32 channels downstream, which some Fiber , the final connection to the this scenario is effectively Gbps would increase Cable modem capacity customer uses coaxial Cable . The coaxial downstream and 500 Mbps upstream. to Gbps downstream and 120. portions of the network generally are Cable operators manage the capacity Mbps upstream per segment, and cut limited to less than 1 GHz of usable by monitoring segment utilization the segment size to 100 customers, spectrum in total (generally 860 and identifying areas where utilization which would reduce the hypothetical MHz or 1 GHz in the most advanced exceeds certain thresholds.

7 When an peak demand in the segment to 1 Gbps Networks ). By comparison, the available operator hits the threshold in a segment, downstream and 200 Mbps upstream. capacity of Fiber optic Cable is in excess it has two short-term options: This approach will temporarily fill of 10,000 GHz 10,000 times greater 1 Add channel capacity to the the gap. As more applications and which allows for virtually limitless DOCSIS Cable modem network , devices are introduced, however, Cable scalability into the future by simply potentially requiring the operator operators will need to build Fiber deeper upgrading the network electronics. to modify video compression or into neighborhoods and closer to end Figure 1 illustrates DOCSIS reallocate video channels (this is users, free up more spectrum from network architecture in a four-channel possible by migrating channels television channels and introduce configuration.

8 In a DOCSIS to more efficient MPEG-4 new technologies, such as DOCSIS. network , Fiber optic connections enable compression, moving on-demand , which can increase spectrum the Cable operator to connect each and less-frequently used channels efficiency further. JANUARY/FEBRUARY 2015 | | BROADBAND COMMUNITIES | 63. TECHNOLOGY. Figure 2: Illustration of DOCSIS peak usage scenario These upgrades will obviously entail equipment replacement. However, Mbps as a peak speed at the top end costs, though how much they will DOCSIS is not completely of their service offering. It is not require above normal life cycle expenses backward-compatible with DOCSIS guaranteed as a minimum speed is difficult to judge and will vary by and earlier versions, meaning that available at all times (or at any one provider.)

9 Gigabit speed will push the DOCSIS Cable modems cannot time). Few customers will reach 150. limits of the RF capacity of most Cable use DOCSIS channels. Thus, a Mbps other than as part of a speed test systems (750 MHz, 860 MHz) and Cable operator may need to allocate or possibly when transferring large files therefore require replacing the Fiber from online storage services. In offering non-overlapping channel space for both node equipment, the RF amplifiers up to 150 Mbps, Cable operators bet technologies for at least some migration and, depending on the level of upgrade, that only a small fraction of users will period if it intends to fully leverage the possibly the active taps and subscriber capacity advantages of DOCSIS ; use this speed at the same time and that drop cables.

10 Some of these upgrades this would further drive the need for they will not really have to deliver the would occur as a matter of course, expensive field upgrades of active and advertised speed to most customers or but some will represent extra costs for operators. passive RF components to increase the on a sustained basis. Similarly, upgrading to DOCSIS bandwidth of the coaxial portions of Further, these Cable operators face would require replacing customers' the HFC network . no penalty if a user tries for 150 Mbps modems and making some upgrades in during a busy peak time and can attain the headend/hubs. Depending on how DON'T Cable OPERATORS only 60 or 80 Mbps, because 150. this is done, an operator would incur OFFER 150 MBPS SERVICE Mbps is offered only as a maximum, expenses ranging from $50 to $150 ALREADY?