Zenith Cable Modem was one of the first proprietary

cable modem A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial (HFC), radio frequency over glass (RFoG) and coaxial cable infrastructure. Cable modems are primaril ...

s. The two basic models are one operating at 500 kilobits per second (kbit/s), and the other at four megabits per second (mbit/s) with BPSK and approximately a 25% alpha.

History

The Zenith Cable Modem was originally developed for a mid-split

cable network Networking cables are networking hardware used to connect one network device to other network devices or to connect two or more computers to share devices such as printers or scanners. Different types of network cables, such as coaxial cable, opt ...

in the mid-1980s. It was used as an

8-bit In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...

full-height PC/AT-type card containing an

Intel 80186 The Intel 80186, also known as the iAPX 186, or just 186, is a microprocessor and microcontroller introduced in 1982. It was based on the Intel 8086 and, like it, had a 16-bit external data bus multiplexed with a 20-bit address bus. The 801 ...

dedicated CPU, connected to an external white box about 2" x 12" x 6". Other similar products were made by

Ungermann-Bass Ungermann-Bass, also known as UB and UB Networks, was a computer networking company in the 1980s to 1990s. Located in Santa Clara, California, UB was the first large networking company independent of any computer manufacturer. Along with competito ...

(UB) under the

10BROAD36 10BROAD36 is an obsolete computer network standard in the Ethernet family. It was developed during the 1980s and specified in IEEE 802.3b-1985. The standard supports 10 Mbit/s Ethernet signals over standard 75 ohm cable television (CATV) ...

standard and Vitalink. UB had models supporting RS-232 and Ethernet outputs, as well as a re-modulating frequency translator. In late 1993, Zenith Electronics and Prodigy provided 12 modified 500 Kbit "white modems" to

Cox Communications Cox Communications, Inc. (also known as Cox Cable and formerly Cox Broadcasting Corporation, Dimension Cable Services and Times-Mirror Cable) is an American digital cable television provider, telecommunications and home automation services. It i ...

in San Diego, including two with IBM Microchannel support. These modified modems were intended to support the Prodigy Cable Modem trial, which began on a 1500 homes-passed fiber node in El Cajon, CA. The modification allowed sub-split operation, with a fixed

upstream Upstream may refer to: * Upstream (bioprocess) * ''Upstream'' (film), a 1927 film by John Ford * Upstream (networking) * ''Upstream'' (newspaper), a newspaper covering the oil and gas industry * Upstream (petroleum industry) * Upstream (software ...

frequency and a downstream at 74.75 MHz, within the 4 MHz space between analog channels four and five. The initial trial consisted of a Prodigy server in the El Cajon headend, connected via the Microchannel-based cable modem to an Olsen Frequency Translator. This basic network supported the 1500 home passed fiber nodes, with six "subscribers" including one employee of Cox, who was also the head-end manager. One card was installed in rackmount PC in the Federal headend, another in the El Cajon headend. 1500 high pass filters were installed to eliminate any ingress from the drops. Service was reasonably reliable''.'' Zenith updated their white modems to a matte black case, adding the Homeworx name and marketing to cable operators at the $350 price range for 250 units. The new design used the same size external case, added LEDs to indicate power/TX/RX/activity and replaced the full sized 8-bit ISA card with a smaller

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...

version. The new design dropped the onboard CPU. The modem connected to the card used a 15-pin D-shell connector—which exactly matched the PC's game connector. Both models were powered by the PC. The new modem was frequency agile, with a configuration utility that ran on the PC to set up US and DS frequencies. The option to configure the card's MAC address was soon dropped. However, the card's MAC address was not printed on the outside of the board, and thus was invisible once installed in the PC. Nor was the MAC address printed in a machine readable (bar code) format. Cox added these to the CM prior to installation, and tracked the subscriber to modem MAC address in an

Excel spreadsheet Microsoft Excel is a spreadsheet developed by Microsoft for Microsoft Windows, Windows, macOS, Android (operating system), Android and iOS. It features calculation or computation capabilities, graphing tools, pivot tables, and a macro (comp ...

, as the MAC address contained too many digits to fit into any fields within the customer billing system.

Product versions

* White modem, from 1980s based design * Black internal modem, Homeworx * External modem, one Ethernet jack * External modem, two Ethernet jacks * HW revision A: first black case modem * HW revision B: volume production of an estimated 7501000 units for shipment to 810 cable operators * HW revision C: introduced a two board model and 4" tall case that would allow use with a traditional Ethernet 10BASE-T connection instead of an internal

PC card In computing, PC Card is a configuration for computer parallel communication peripheral interface, designed for laptop computers. Originally introduced as PCMCIA, the PC Card standard as well as its successors like CardBus were defined and devel ...

. The external models used an RJ-14 style phone jack for serial control, configuration, and management using a Zenith supplied utility application. * HW revision D: eliminated the susceptibility to RF interference from nearby cell phones. The fault caused the transmit side phased locked loop (PLL) to fail. Resolution required a power cycle, fault was non-detectable in software other than no connectivity. * HW revision E: introduced dual 10BaseT interface for University of California San Diego, and other customers. Added modem MAC address to external CM, and in a bar code readable format. All Zenith modems contained a small switch controlling the second coax port. The modem could either operate on one coax (built in diplex filter) or two (Headend use, dual plant networks, or external diplex filter.) The initial Zenith "Headend" design was to use a residential cable modem inside a server, and a frequency translator to convert the upstream transmit frequency to the downstream receive frequency. This design did not scale to more than a few networks, so the Channelmizer was introduced—a 2.5" tall rack mountable device with separate US and DS RF ports, the diplex filter switch, and an Ethernet port. The first large scale Zenith headend was constructed in Cox San Diego using Zenith's booth demonstration hardware from the 1994 Western Cable Show. Three Frequency Translators, plus four Channelmizers were installed in El Cajon. These plus three other Channelmizers were interconnected to an 8 port Cisco Catalyst 1200 Ethernet switch with single mode FDDI uplink for a 4 device, 140 km FDDI ring around San Diego county. The Prodigy server obtained a traditional

Ethernet card A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network. Ear ...

. The seven frequency translators plus seven Channelmizers supported 65,000 homes passed on 23 fiber nodes, and occupied a full rack.

Technology demonstration to initial deployment

Prodigy was deployed over cable modem to 200 users in time for the 1994 Western Cable Show. To grow the system from 16 users in three fiber nodes, to 200 required adding what became 64,000 homes passed, making the Cox San DiegoProdigy cable modem field trial the world's largest cable modem deployment (by service area) at the time. The acceptance criteria were too strict to achieve the 65% homes passed high speed internet penetration which is common today: *Prodigy Subscriber greater than nine months *Cable Subscriber *Live in 2-way activated area *Open slot in

80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistorsPay Per View cable boxes were deployed to these same places. The Pioneer Set Top Boxes used FSK, retransmitted up to 32 times over three days, and worked for up to five purchases without a return path.

The Zenith MAC layer

CSMA/CD Carrier-sense multiple access with collision detection (CSMA/CD) is a medium access control (MAC) method used most notably in early Ethernet technology for local area networking. It uses carrier-sensing to defer transmissions until no other statio ...

, or Ethernet "like" was expanded by reducing the

data rate Data rate and data transfer rate can refer to several related and overlapping concepts in communications networks: Achieved rate * Bit rate, the number of bits that are conveyed or processed per unit of time ** Data signaling rate or gross bit rate ...

to 500 kbit/s for up to 50 (100?) miles plant radius and to 4 Mbit/s for up to plant radius. The transmitting device first listened for activity. If there was activity, it would activate the "A" LED, and wait. Activity is defined as any RF energy, intelligible or not, at an absolute amplitude of -25 dBmV into the device receive port within a 1 MHz or 6 MHz passband (500kbit/s or 4 Mbit/s respectively.) Upon detection of no activity, using appropriate backoff timers (as per Ethernet CSMA/ CD standard), the CM transmitted a preamble followed by the start of the Ethernet frame. Simultaneously, the transmitting CM would begin listening for its own burst. If the CM were able to decode its own burst, and correctly compare a checksum of the first 17 bytes of the packet, it would declare no-collision, and continue. If there was a checksum error, it would declare a collision, and stop transmitting after the 19th byte. This was easily and directly measured using

Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare. Under the lead ...

LANalyzer software on a dedicated

Windows 3.1 Windows 3.1 is a major release of Microsoft Windows. It was released to manufacturing on April 6, 1992, as a successor to Windows 3.0. Like its predecessors, the Windows 3.1 series ran as a shell on top of MS-DOS. Codenamed Janus, Windows 3 ...

for Workgroups PC. The card kept some locally accessible counters on excessive and late collisions, but there was no driver or management. By November 20, 1996, Zenith released SNMP MIBs and management for their Channelmizer under

software release A software release life cycle is the sum of the stages of development and maturity for a piece of computer software ranging from its initial development to its eventual release, and including updated versions of the released version to help impro ...

9.32, under the title "Node Data Controller SNMP".

Provisioning

The physical possession of a properly installed modem connected the subscriber to the network, and the use of this modem with a packet sniffer would enable full viewing of all transmitted and received packets from every user sharing that frequency translator. Removing a device for non-payment required physically retrieving the device and preventing the availability of used or stolen modems. Modems could not be disabled remotely.

Quality perceptions and reality

While not directly competing against an existing product—residential ISDN penetration was sub 0.1%, the technology had severe growing pains: The team identified 19 Independent causes of two errors—CT-9 and CT-16, "A communications failure has occurred".

Driver Software

* IPX driver not loaded when launching windows * IDNX 56 kbit/s link from local Prodigy Server in El Cajon Headend to Yorktown, NY, was down * Prodigy Server in El Cajon Headend experienced driver wedge due to excessive noise in return path, and inability to transmit packets, call Prodigy and request server reset * Duplicate CM MAC address * Lost modem frequency configuration * Traffic Storm ARP Storm, excessive traffic of any kind, or an ARP storm would shut down the network. Fastest resolution was often to take the network down and reboot the affected systems. (Often required calling the customer on the phone and asking them to do so.)

Modem hardware

* Cell phone used near the cable modem, PLL unlocked, power cycle to resolve * Channelmizer lock up, cell phone used near headend cable modem, PLL unlocked. Power Cycle to resolve * Frequency translator drift, resolution: replace the Olsen unit with model made by Wavecom (now Vecima Networks, who now makes upconverters for the Cisco DOCSIS compliant CMTS platforms) * Diplex filter switch got "bumped" * Modem module disconnected or plugged into

PC game A personal computer game, also known as a PC game or computer game, is a type of video game played on a personal computer (PC) rather than a video game console or arcade machine. Its defining characteristics include: more diverse and user-deter ...

port instead of modem card. (Less of an issue with black modem as LEDs would go dark, but impossible to verify on white modem without LEDs.)

RF

* LRC STS-75

end of line End, END, Ending, or variation, may refer to: End *In mathematics: **End (category theory) **End (topology) **End (graph theory) ** End (group theory) (a subcase of the previous) **End (endomorphism) *In sports and games ** End (gridiron football ...

terminator causing Common Path Distortion (CPD) A mechanical design defect occurred when a 22-gauge piece of

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

wire was press fit into an aluminum housing and compressed to become "watertight." Unfortunately, corrosion developed anyway, and the resultant diode from dissimilar metals caused the CPD. Resolution: replace 10,000 units at $4/part + $25/labor with gold anodized model. * Return path alignment and headend combining: Independently develop the "X-point" return path alignment and amplitude compensation process. Due to the

Amplitude Modulation Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to ...

(AM) format of the return path FP lasers, a +25 dBmV CW tone injected at the fiber node status monitoring module would not arrive at the headend with constant amplitude. Pad inputs to frequency translator to ensure +5 dBmV input on this tone for each fiber node (individually). * Filter Corp brick wall filter on the output path to the frequency translator was too sharp, introducing excessive

group delay In signal processing, group delay and phase delay are delay times experienced by a signal's various frequency components when the signal passes through a system that is linear time-invariant (LTI), such as a microphone, coaxial cable, amplifier, l ...

. * PCS Cable Telephony trial precision CW clock distribution tone at 73.25 MHz jamming subscriber transmitters, causing "A" light on solid, and 100% collisions * Poorly chosen upstream frequency for white modems, resolved for deployment of black modems. * Too many homes passed per frequency translator. Worked reliably with 8500 to 10,000, but much better at about 6500 homes passed. * Speaker modulation. When the coax connector on a nearby television set is loose, and the audio is really loud, the mechanical vibration of the television set alters the physical connection of the coax, allowing ingress and other interference. * Missing return-path amplifier. During the early days of the trial, few repair trucks carried return-path capableamplifiers. One amplifier was replaced with a one-way amplifier and improperly noted.

RF requirements

Carrier/anything of at least 25 dB at the receive port of all modems. To support the time varying nature of an HFC network, 35 dB C/anything was required at the input to the frequency translator in the headend. "Carrier/anything" includes: C/Noise, C/Interference and distortion products. Downstream input to each cable modem of +5 dBmV ± 2 dB. Due to the non-existence of any real input AGC, the lack of a re-modulating frequency translator and lack of upstream transmit power control, the tight receive level range accommodated upstream path variation. In comparison, a 2003 DOCSIS 2.0 compliant CMTS operating at 0.5 to 1 dB from theory dprovide both

16QAM Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signal ...

and 64 QAM in 6.4 MHz at 25 dB C/noise, and in some cases negative C/I
Next-Gen CMTSs

RF plant maintenance in 19941995

An HP 8590L (low cost version of 8591c), video out connected to a Cadco channel modulator operating above 550 MHz, with a Radio Shack

black and white TV Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, e ...

(picture tube) tuned to

UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...

channels to see the picture. Add to that a

comb generator A comb generator is a signal generator that produces multiple harmonics of its input signal. The appearance of the output at the spectrum analyzer screen, resembling teeth of a comb, gave the device its name. Comb generators find wide range of u ...

with 46 CW tones, an HP Calan 1776 "portable" spectrum analyzer. Not all amplifiers contained a good return-path test point, so the repair lab was asked to modify some line extender diplex filters to pass the forward, and divert the return path to an

F connector The F connector (also F-type connector) is a coaxial RF connector commonly used for "over the air" terrestrial television, cable television and universally for satellite television and cable modems, usually with RG-6/U cable or with RG-59/U c ...

. A pad socket was also converted. Any signal entering an amplifier with an amplitude above -45 dBmV was located and fixed. CLI was reduced to under 5 uV/m. Two years later, Milo Medin, CTO of @Home was reported to have said, "Please show me the fiber receivers that are connected to the outside plant, these don't have enough noise, so they are certainly not connected or properly aligned." Later, he was quoted as saying "Cox San Diego return plant is so clean you could eat off it." San Diego never had serious RF issues when it came to return path after 1995.

Network Operations Center (NOC)

Modeled after the University of California, San Diego Telecommunications NOC at the Central Utilities Building, Novell LANalyzer software w/ internal cable modem, and a technician to manually move the test connection between frequency translators. Only one frequency translator could be measured at a time.

HP OpenView HP OpenView is the former name for a Hewlett-Packard product family that consisted of network and systems management products. In 2007, HP OpenView was rebranded as HP BTO (''Business Technology Optimization'') Software when it became part of the ...

(HPOV) and a 24 port HP AdvanceStack Ethernet HUB with AUI "uplink" was available. This combination allowed the AdvanceStack hub to send out IPX diagnostic packets to the NDIS driver in each PC. Assuming the PC was running the driver at all times, the HP OpenView application would display the NetWare device ID – 00000, mac-address as there was no real

NetWare NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol. The original NetWare product in 19 ...

server router. The management software would generate NDIS "diagnostic pings" from the hub, and report the number of successful responses. Rebooting the PC, loading and unloading the driver, or experiencing RF faults would cause each cable modem to transition from active to inactive hundreds of times per day. HPOV could export the

log file In computing, logging is the act of keeping a log of events that occur in a computer system, such as problems, errors or just information on current operations. These events may occur in the operating system or in other software. A message or lo ...

to a Paradox database for later analysis and trending. Eliminating the PC reloads and driver reloads from the RF faults, and correlating RF faults on a single frequency translator vs. the entire flat network was not available. These methods became the justification and

fundamental research Basic research, also called pure research or fundamental research, is a type of scientific research with the aim of improving scientific theories for better understanding and prediction of natural or other phenomena. In contrast, applied resear ...

for what was later patented by others: and . Eventually, this technique became mandatory in DOCSIS 3.0, although it was rejected and ignored for three years as a "proprietary extension to DOCSIS" by @Home and copied by every DOCSIS CMTS vendor. By September 1994, the NOC was expanded with the introduction of two @ Cisco Catalyst 1200 Ethernet to FDDI switches, and two @ Cabletron MMAC-three FNB hubs (six Ethernet plus two FDDI), constructing a reliable path from the Federal Headend to the El Cajon headend, and eliminating one unreliable path between the AdvanceStack hub and the various Channelmizers and frequency translators.

Videoconferencing over cable modems in 19941995

CUs-SeeMe and

Apple QuickTime QuickTime is an extensible multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. Created in 1991, the latest Mac version, QuickTime X, is avail ...

Conferencing 1.0 betaQuickTime Conferencing Press Release
/ref> ran over the Zenith and Lancity proprietary cable modems when the RF path was sufficiently clean. These modems were able to interoperate on the same RF fiber nodes using Frequency Division Multiplexing, using an Ethernet switch to join the otherwise incompatible networks. Late in the beta, 160 x 120 pixel video was increased to 320 x 240, and the audio quality greatly improved on the Apple Power Macintosh 7100 AV.

Cogeco

Cogeco in Canada launched with the 4 Mbit/s, external Rev D cable modem in roughly 1996, and by August 1997 had 2500 subscribers. The network experienced failures for three reasons: * The Zenith network is a pure bridged CSMA/CD Ethernet. It has no understanding of the

Layer-3 In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transf ...

ARP protocol. Thus ARP storms through the

layer-2 The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

switches used in the first headend designs would clog the network. * The Layer-2 switches and Layer-3 routers of the time did not perform any QOS or

rate limiting In computer networks, rate limiting is used to control the rate of requests sent or received by a network interface controller. It can be used to prevent DoS attacks and limit web scraping. Research indicates flooding rates for one zombie machine ...

, thus a 4 Mbit/s input port on the Channelmizer could be flooded with up to 10 Mbit/s of traffic bursts. * The Cogeco network contained an unusual reverse path amplifier as part of the retrofit to accommodate return path. This amplifier contained a design defect whereby the pad and equalizer plug-in modules would literally fall off the circuit board when the device was opened. A thermal incompatibility existed causing the holes for the parts to increase in diameter, while the pins would elongate and become smaller. This fault was documented and proven as a result of Cogeco's first DOCSIS deployment with the Cisco uBR7246, MC11-FPGA linecard, and IOS 11.3(4)NA, which contained the "flap list."

References

External links

* {{cite web , url=https://www.nytimes.com/1993/11/24/business/prodigy-to-test-use-of-cable.html , title=Prodigy to Test Use of Cable , date=1993-11-24 , access-date=2014-11-11 , work=New York Times * David Waks recalls 1993-1994 launc
Article
* Modern CMTS performance measurement

Patent Numbers

[https://archive.today/20121214094008/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/PTO/srchnum.htm&r=1&f=G&l=50&s1=5943604.PN.&OS=PN/5943604&RS=PN/5943604 5,943,604 Echo device method for locating upstream ingress noise gaps at cable television head ends] Modems