Zenith Cable Modem
Encyclopedia
Zenith Cable Modem is one of the first proprietary cable modem
s deployed at limited scale. There were 2 basic models, one operating at 500 kbit/s, the other at 4 Mbit/s using BPSK and about a 25% alpha.
in the mid 1980s, and used an 8 bit
full height PC/AT
type card containing an Intel 80186
dedicated CPU, connected to an external WHITE box
about 2"x12"x6". Other similar products were made by Ungermann-Bass
, and Vitalink. UB had models supporting RS-232
and Ethernet outputs, as well as a remodulating frequency translator.
In late 1993, Zenith and Prodigy provided about 12 modified 500 Kbit "white modems" to Cox Communications
in San Diego—including two with IBM Microchannel support. These modified modems were intended to support the Prodigy Cable Modem trial begun on a 1500 homes passed fiber node in El Cajon, CA. The modification allowed subsplit operation, with a fixed upstream frequency, and the downstream at 74.75 MHz, within the 4 MHz space between analog channels 4 & 5.
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 one 1500 home passed fiber node, with 6 "subscribers" including one employee of Cox who was also the Headend Manager. One card was installed in rack mount
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, and a newspaper article
appeared in the Los Angeles Times
.
Zenith updated their white modems to a matte black case, adding the Homeworx name, and marketing to cable operators in 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
version. The new design dropped the onboard CPU. The modem connected to the card using 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. Fortunately, the option to configure the card's MAC address
was dropped. Unfortunately, the card’s MAC address remained invisible once installed in the PC, and was not printed in a machine readable (barcode format). Cox added these to the CM prior to installation, and tracked the subscriber to modem MAC address in an Excel spreadsheet
, as it was too many digits to fit into the billing system.
Black Internal Modem, Homeworx
External Modem, 1 Ethernet Jack
External Modem, 2 Ethernet Jacks
HW Revision A: - First black case modem
HW Revision B: - "Volume Production" of perhaps 750-1000 units for shipment to 8-10 cable operators.
HW Revision C: - introduced a two board model and 4" tall case that would allow use with a traditional Ethernet 10BaseT
connection instead of internal PC card
. 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 would cause 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 barcode 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.
Clearly this design does 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. 3 Frequency Translators, plus 4 Channelmizers were loaded into a car and driven to El Cajon for installation Christmas Eve
. These plus 3 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
.
The 7 frequency translators + 7 Channelmizers supported 65,000 homes passed on 23 fiber nodes, and occupied a full rack.
This was no problem as two-way Impulse Pay Per View
cable box
es were being deployed like hotcakes. The Pioneer Set Top Boxes used FSK, retransmitted up to 32 times over 3 days, and worked just fine for up to 5 purchases without a return path.
, or Ethernet “like” was expanded as follows:
Data rate
reduced to 500 kbit/s for up to 50 (100?) miles plant radius
Data rate reduced to 4 Mbit/s for up to 25 miles (40.2 km) plant radius
The transmitting device would first listen for activity on the wire, 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, and appropriate backoff timers (as per Ethernet CSMA/CD standard), the CM would begin transmitting a preamble, then 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 Novel LANalyzer software on a dedicated Windows 3
.1 for Workgroups PC.
The card kept some locally accessible counters on excessive and late collisions, but there was no driver or management of any kind.
By November 20, 1996 Zenith released SNMP MIBs and management for their Channelmizer under software release 9.32, under the title “Node Data Controller SNMP”
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. There was no ability to disable a modem remotely.
Step 2: Upgrade Windows 3.1 to Windows 3.1 for Workgroups
Step 3: Open the PC, install the proprietary Zenith “Ethernet-like” card, NDIS drivers, and route the cable to the external portion of the CM.
Step 4: Pray a little that it works. Otherwise resolve interrupts, and configure frequencies.
Step 5: Update Prodigy Software to “dial in” using IPX protocol over Zenith Modem instead of 2400 baud modem on serial port
.
Step 6: Educate customer, and pray they do not upgrade the computer with more hardware. Each upgrade always resulted in an on site service call.
Windows 95 “modified” procedure:
Windows 95
never contained a driver for the Zenith internal Ethernet-like card, so it would ALWAYS blue screen
upon detecting this card installed. Auto-hardware detection had to be disabled, and installation typically took 4 hours – just for the computer part. Once it was working, any new hardware addition would always cause blue screen, and disable the Zenith Cable Modem.
Yes, the internal modem work with the first Intel Pentium systems. No, it was not even close to economical to maintain this network of 165 users with 2 full time
on site support people. The external version with a standard NDIS-2000 compatible Ethernet card was approximately $400/year lower in support costs, for a mere $27 Ethernet card, and $50 price difference for the external modem. The customer paid for and owned the Ethernet card as part of installation.
19 Independent causes of two errors—CT-9 and CT-16, "A communications failure has occurred"
Driver / Software:
1) IPX driver not loaded when launching windows
2) IDNX 56 kbit/s link from local Prodigy Server in El Cajon Headend to Yorktown NY was down
3) 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
4) Duplicate CM MAC address
5) Lost modem frequency configuration.
6) 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 for a few minutes, and reboot the affected systems. (Often required calling the customer on the phone and asking them to do so.)
Modem Hardware:
7) Cell phone used near the cable modem, PLL unlocked, power cycle to resolve.
8) Channelmizer lock up
, cell phone used near headend cable modem, PLL unlocked. Power Cycle to resolve.
9) 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)
10) diplex filter switch got “bumped”
11) External modem module disconnected or plugged into PC game
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:
12) LRC STS-75
end of line terminator causing Common Path Distortion (CPD)
A mechanical design defect occurred when a 22 gauge piece of stainless steel
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.
13) Return path alignment and headend combining: Independently develop the "X-point" return path alignment and amplitude compensation process. Due to the Amplitude Modulation
(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).
14) Microwave Filter Corp brick wall filter on the output path to the frequency translator was too sharp, introducing excessive group delay
15) PCS Cable Telephony
trial precision CW clock distribution tone at 73.25 MHz jamming subscriber transmitters, causing “A” light on solid, and 100% collisions
16) Poorly chosen upstream frequency for white modems, resolved for deployment of black modems
17) Too many homes passed per frequency translator. We got it working reliably with 8500 to 10,000, but it worked much better at about 6500 homes passed.
18) 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.
19) Missing return path amplifier. During the early days of the trial, few repair trucks carried return path capable amplifiers. One amplifier was replaced with a one way amplifier and improperly noted. The customer’s pregnant wife watched the service tech try for hours to resolve the fault. Their 4 month son watched the resolution after a Compaq luggable 386 based system with an Internal modem was connected to figure out why this one home was so problematic.
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 is not a technical term, but is intended to include: 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 will provide both 16QAM
and 64 QAM in 6.4 MHz at 25 dB C/noise, and in some cases negative C/I. Next-Gen CMTSs
black and white TV
(picture tube) tuned to UHF channels to see the picture. Add to that a comb generator
with 4-6 CW tones, an HP Calan 1776 ‘portable’ spectrum analyzer
, which is about the size of an igloo cooler for a weekend car camping
trip. 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
. A pad socket was also converted as well. Any signal entering an amplifier with an amplitude of above -45 dBmV was located and fixed. CLI was reduced to under 5 uV/m. 2 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.
Novel LANalyzer software w/ internal cable modem, and somebody to manually move the test connection between frequency translators. Only one frequency translator could be measured at a time.
HP Openview
(HPOV) for Windows, version 3.1, and a 24 port HP Advancestack Ethernet HUB
with AUI “uplink.” This combination allowed the Advancestack hub to send out IPX diagnostic packets to the NDIS driver in each PC. Assuming the PC was not rebooted, and 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 server / router. HPOV displayed each device in purple if active, and blue if discovered and non-responsive. The management software would generate NDIS “diagnostic pings” from the hub, and report the number of successful responses. Rebooting the PC, loading / unloading the driver, or experiencing any number of RF faults would cause each cable modem to transition from purple to blue hundreds of times per day.
HPOV could export the log file to a Paradox Database for later analysis and trending. Eliminating the PC reloads / driver reloads from the RF faults, and correlating RF faults on a single frequency translator vs. the entire flat network proved beyond the capabilities of the Zenith Network. These methods became the justification and fundamental research
for what was later patented by others: Patent Numbers: 6,032,019, 5,943,604 Echo device method for locating upstream ingress noise gaps at cable television head ends. Eventually, this technique became mandatory in DOCSIS 3.0, although it was rejected and ignored for 3 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 2 @ Cisco Catalyst 1200 Ethernet to FDDI switches, and 2 @ Cabletron MMAC-3 FNB hubs (6 Ethernet + 2 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 / frequency translators.
and Apple Quicktime
Conferencing 1.0 beta worked perfectly 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
, and an Ethernet switch to join the otherwise incompatible networks.
Late in the beta, 160x120 pixel video was increased to 320x240, and the audio quality
greatly improved on the Apple PowerMacintosh 7100 AV.
Cable modem
A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high...
s deployed at limited scale. There were 2 basic models, one operating at 500 kbit/s, the other at 4 Mbit/s using BPSK and about a 25% alpha.
History
The Zenith cable modem was originally developed for a mid-split cable networkCable network
A cable channel is a television channel available via cable television. Such channels are usually also available via satellite television, including direct broadcast satellite providers such as DirecTV, Dish Network and BSkyB...
in the mid 1980s, and used an 8 bit
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
full height PC/AT
IBM Personal Computer/AT
The IBM Personal Computer AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM's second-generation PC, designed around the 6 MHz Intel 80286 microprocessor and released in 1984 as machine type 5170...
type card containing an Intel 80186
Intel 80186
The 80188 is a version with an 8-bit external data bus, instead of 16-bit. This makes it less expensive to connect to peripherals. The 80188 is otherwise very similar to the 80186. It has a throughput of 1 million instructions per second....
dedicated CPU, connected to an external WHITE box
White box
White box may refer to:*White-box testing, a specification conformance test*White box , a personal computer assembled from off-the-shelf parts*White box , a subsystem whose internals can be viewed...
about 2"x12"x6". Other similar products were made by Ungermann-Bass
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, in Silicon Valley, UB was the first large networking company independent of any computer manufacturer. UB was founded by Ralph Ungermann and Charlie Bass...
, and Vitalink. UB had models supporting RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
and Ethernet outputs, as well as a remodulating frequency translator.
In late 1993, Zenith and Prodigy provided about 12 modified 500 Kbit "white modems" to Cox Communications
Cox Communications
Cox Communications is a privately owned subsidiary of Cox Enterprises providing digital cable television, telecommunications and wireless services in the United States...
in San Diego—including two with IBM Microchannel support. These modified modems were intended to support the Prodigy Cable Modem trial begun on a 1500 homes passed fiber node in El Cajon, CA. The modification allowed subsplit operation, with a fixed upstream frequency, and the downstream at 74.75 MHz, within the 4 MHz space between analog channels 4 & 5.
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 one 1500 home passed fiber node, with 6 "subscribers" including one employee of Cox who was also the Headend Manager. One card was installed in rack mount
19-inch rack
A 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules. Each module has a front panel that is wide, including edges or ears that protrude on each side which allow the module to be fastened to the rack frame with screws.-Overview and history:Equipment designed...
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, and a newspaper article
Article (publishing)
An article is a written work published in a print or electronic medium. It may be for the purpose of propagating the news, research results, academic analysis or debate.-News articles:...
appeared in the Los Angeles Times
Los Angeles Times
The Los Angeles Times is a daily newspaper published in Los Angeles, California, since 1881. It was the second-largest metropolitan newspaper in circulation in the United States in 2008 and the fourth most widely distributed newspaper in the country....
.
Zenith updated their white modems to a matte black case, adding the Homeworx name, and marketing to cable operators in 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
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
version. The new design dropped the onboard CPU. The modem connected to the card using a 15 pin D-shell
Electron shell
An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" , followed by the "2 shell" , then the "3 shell" , and so on further and further from the nucleus. The shell letters K,L,M,.....
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. Fortunately, the option to configure the card's MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
was dropped. Unfortunately, the card’s MAC address remained invisible once installed in the PC, and was not printed in a machine readable (barcode format). Cox added these to the CM prior to installation, and tracked the subscriber to modem MAC address in an Excel spreadsheet
Microsoft Excel
Microsoft Excel is a proprietary commercial spreadsheet application written and distributed by Microsoft for Microsoft Windows and Mac OS X. It features calculation, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications...
, as it was too many digits to fit into the billing system.
Product Versions
White modem, from 1980’s based designBlack Internal Modem, Homeworx
External Modem, 1 Ethernet Jack
External Modem, 2 Ethernet Jacks
HW Revision A: - First black case modem
HW Revision B: - "Volume Production" of perhaps 750-1000 units for shipment to 8-10 cable operators.
HW Revision C: - introduced a two board model and 4" tall case that would allow use with a traditional Ethernet 10BaseT
10BASE-T
Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Other Ethernet cable standards employ coaxial cable or optical fiber. Early versions developed in the 1980s included StarLAN followed by 10BASE-T. By the 1990s, fast, inexpensive...
connection instead of internal PC card
PC card
In computing, PC Card is the form factor of a peripheral interface designed for laptop computers. The PC Card standard was defined and developed by the Personal Computer Memory Card International Association which itself was created by a number of computer industry companies in the United States...
. 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
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
from nearby cell phones
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
. The fault would cause 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
University of California, San Diego
The University of California, San Diego, commonly known as UCSD or UC San Diego, is a public research university located in the La Jolla neighborhood of San Diego, California, United States...
, and other customers. Added modem MAC address to external CM, and in a barcode 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.
Clearly this design does 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. 3 Frequency Translators, plus 4 Channelmizers were loaded into a car and driven to El Cajon for installation Christmas Eve
Christmas Eve
Christmas Eve refers to the evening or entire day preceding Christmas Day, a widely celebrated festival commemorating the birth of Jesus of Nazareth that takes place on December 25...
. These plus 3 other Channelmizers were interconnected to an 8 port Cisco Catalyst 1200 Ethernet switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
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
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
.
The 7 frequency translators + 7 Channelmizers supported 65,000 homes passed on 23 fiber nodes, and occupied a full rack.
From Technology Demonstration to Initial Deployment
The commercial prospects of Prodigy over cable modem came to reality when preparing for the 1994 Western Cable Show. We needed to grow the system from 16 users in 3 fiber nodes, to 200 ASAP. Once all criteria were met—Prodigy Subscriber > 9 months, Cable Subscriber, lived in 2 way activated area, open slot in 80386 based PC or greater (we allowed a few SX machines), and willingness to participate, the population was a mere 1/4 of 1%. Thus the deployment grew to 64,000 homes passed for the acceptable 150 users.This was no problem as two-way Impulse Pay Per View
Pay-per-view
Pay-per-view provides a service by which a television audience can purchase events to view via private telecast. The broadcaster shows the event at the same time to everyone ordering it...
cable box
Cable box
The term cable box can refer to:* Cable box an electronic device that controls cable television in individual homes.* Cable box a box located outside a residence that connects cable television....
es were being deployed like hotcakes. The Pioneer Set Top Boxes used FSK, retransmitted up to 32 times over 3 days, and worked just fine for up to 5 purchases without a return path.
The Zenith MAC Layer
CSMA/CDCarrier sense multiple access with collision detection
Carrier sense multiple access with collision detection is a Media Access Control method in which:*a carrier sensing scheme is used....
, or Ethernet “like” was expanded as follows:
Data rate
Data signaling rate
In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission path of a data transmission system.Notes:#The DSR is usually expressed in bits per second....
reduced to 500 kbit/s for up to 50 (100?) miles plant radius
Data rate reduced to 4 Mbit/s for up to 25 miles (40.2 km) plant radius
The transmitting device would first listen for activity on the wire, 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, and appropriate backoff timers (as per Ethernet CSMA/CD standard), the CM would begin transmitting a preamble, then 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 Novel LANalyzer software on a dedicated Windows 3
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
.1 for Workgroups PC.
The card kept some locally accessible counters on excessive and late collisions, but there was no driver or management of any kind.
By November 20, 1996 Zenith released SNMP MIBs and management for their Channelmizer under software release 9.32, under the title “Node Data Controller SNMP”
Provisioning a Zenith Cable Modem
The physical possession of a properly installed modem connected the subscriber to the network, and the use of this modem with a packet snifferPacket sniffer
A packet analyzer is a computer program or a piece of computer hardware that can intercept and log traffic passing over a digital network or part of a network...
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. There was no ability to disable a modem remotely.
Installing an internal Zenith Cable Modem
Step 1: Verify there is a free slot in the computer, and that the customer can power down the PC and reboot it without issue.Step 2: Upgrade Windows 3.1 to Windows 3.1 for Workgroups
Step 3: Open the PC, install the proprietary Zenith “Ethernet-like” card, NDIS drivers, and route the cable to the external portion of the CM.
Step 4: Pray a little that it works. Otherwise resolve interrupts, and configure frequencies.
Step 5: Update Prodigy Software to “dial in” using IPX protocol over Zenith Modem instead of 2400 baud modem on serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
.
Step 6: Educate customer, and pray they do not upgrade the computer with more hardware. Each upgrade always resulted in an on site service call.
Windows 95 “modified” procedure:
Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
never contained a driver for the Zenith internal Ethernet-like card, so it would ALWAYS blue screen
Blue screen
Blue screen may refer to:*Blue Screen of Death, a fatal system error screen in Microsoft Windows*Blue white screen is an assay useful in biotechnology*Blue screen compositing, a technique for combining two still images or video frames...
upon detecting this card installed. Auto-hardware detection had to be disabled, and installation typically took 4 hours – just for the computer part. Once it was working, any new hardware addition would always cause blue screen, and disable the Zenith Cable Modem.
Yes, the internal modem work with the first Intel Pentium systems. No, it was not even close to economical to maintain this network of 165 users with 2 full time
Full time
Full-time employment is employment in which the employee works the full number of hours defined as such by his/her employer. Full-time employment often comes with benefits that are not typically offered to part-time, temporary, or flexible workers, such as annual leave, sickleave, and health...
on site support people. The external version with a standard NDIS-2000 compatible Ethernet card was approximately $400/year lower in support costs, for a mere $27 Ethernet card, and $50 price difference for the external modem. The customer paid for and owned the Ethernet card as part of installation.
A nascent market - Quality perceptions and reality
While not directly competing against any other existing product—residential ISDN penetration was sub 0.1%, the technology had severe growing pains:19 Independent causes of two errors—CT-9 and CT-16, "A communications failure has occurred"
Driver / Software:
1) IPX driver not loaded when launching windows
2) IDNX 56 kbit/s link from local Prodigy Server in El Cajon Headend to Yorktown NY was down
3) 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
4) Duplicate CM MAC address
5) Lost modem frequency configuration.
6) 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 for a few minutes, and reboot the affected systems. (Often required calling the customer on the phone and asking them to do so.)
Modem Hardware:
7) Cell phone used near the cable modem, PLL unlocked, power cycle to resolve.
8) Channelmizer lock up
Lock up
Lock up may refer to:* Lock Up , an American rock band, featuring guitarist Tom Morello during his pre-Rage Against the Machine career* Lock Up , a UK grindcore band* Lock Up , a 1989 movie featuring Sylvester Stallone...
, cell phone used near headend cable modem, PLL unlocked. Power Cycle to resolve.
9) Frequency translator drift, resolution: replace the Olsen unit with model made by Wavecom (now Vecima Networks, who now makes upconverters for the Cisco DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
compliant CMTS platforms)
10) diplex filter switch got “bumped”
11) External modem module disconnected or plugged into PC game
Personal computer game
A PC game, also known as a computer game, is a video game played on a personal computer, rather than on a video game console or arcade machine...
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:
12) LRC STS-75
STS-75
STS-75 was a United States Space Shuttle mission, the 19th mission of the Columbia orbiter.-Crew:-Mission parameters:*Mass: payload*Perigee: *Apogee: *Inclination: 28.5°*Period: 90.5 min-Mission objective:...
end of line terminator causing Common Path Distortion (CPD)
A mechanical design defect occurred when a 22 gauge piece of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
wire was press fit
Interference fit
An interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening...
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.
13) 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
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
(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).
14) Microwave Filter Corp brick wall filter on the output path to the frequency translator was too sharp, introducing excessive group delay
Group delay
Group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component...
15) PCS Cable Telephony
Cable telephony
Cable telephony is a form of digital telephony over cable TV networks. A telephone interface installed at the customer's premises converts analog signals from the customer's in-home wiring to a digital signal, which is then sent over the cable connection to the company's switching center. The...
trial precision CW clock distribution tone at 73.25 MHz jamming subscriber transmitters, causing “A” light on solid, and 100% collisions
16) Poorly chosen upstream frequency for white modems, resolved for deployment of black modems
17) Too many homes passed per frequency translator. We got it working reliably with 8500 to 10,000, but it worked much better at about 6500 homes passed.
18) Speaker modulation. When the coax connector on a nearby television set
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
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.
19) Missing return path amplifier. During the early days of the trial, few repair trucks carried return path capable amplifiers. One amplifier was replaced with a one way amplifier and improperly noted. The customer’s pregnant wife watched the service tech try for hours to resolve the fault. Their 4 month son watched the resolution after a Compaq luggable 386 based system with an Internal modem was connected to figure out why this one home was so problematic.
RF Requirements for a reliable and predictable Zenith Network
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 is not a technical term, but is intended to include: 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 will provide both 16QAM
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
and 64 QAM in 6.4 MHz at 25 dB C/noise, and in some cases negative C/I. Next-Gen CMTSs
“State of the art” RF plant maintenance in 1994/1995
An HP 8590L (low cost version of 8591c), video out connected to a Cadco channel modulator operating above 550 MHz, with a Radio ShackRadioShack
RadioShack Corporation is an American franchise of electronics retail stores in the United States, as well as parts of Europe, South America and Africa. As of 2008, RadioShack reported net sales and operating revenues of $4.81 billion. The headquarters of RadioShack is located in Downtown...
black and white TV
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
(picture tube) tuned to UHF channels to see the picture. Add to that a comb generator
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....
with 4-6 CW tones, an HP Calan 1776 ‘portable’ spectrum analyzer
Spectrum analyzer
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals...
, which is about the size of an igloo cooler for a weekend car camping
Camping
Camping is an outdoor recreational activity. The participants leave urban areas, their home region, or civilization and enjoy nature while spending one or several nights outdoors, usually at a campsite. Camping may involve the use of a tent, caravan, motorhome, cabin, a primitive structure, or no...
trip. 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
F connector
The F connector is a type of 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, in older installations, with RG-59/U cable. It was invented by Eric E...
. A pad socket was also converted as well. Any signal entering an amplifier with an amplitude of above -45 dBmV was located and fixed. CLI was reduced to under 5 uV/m. 2 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
Outside plant
In telecommunication, the term outside plant has the following meanings:*In civilian telecommunications, outside plant refers to all of the physical cabling and supporting infrastructure , and any associated hardware located between a demarcation point in a switching facility and a demarcation...
, 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.
First Zenith Network Network Operations Center (NOC), built by Mark Millet April 1994
Modeled after the University of California San Diego Telecommunications NOC at the Central Utilities Building:Novel LANalyzer software w/ internal cable modem, and somebody to manually move the test connection between frequency translators. Only one frequency translator could be measured at a time.
HP Openview
OpenView
HP OpenView was the former name for a Hewlett Packard product family that consists of network and systems management products. In 2007, HP OpenView was rebranded when it became part of the HP Software Division. HP OpenView software provided large-scale system and network management of an...
(HPOV) for Windows, version 3.1, and a 24 port HP Advancestack Ethernet HUB
Ethernet hub
An Ethernet hub, active hub, network hub, repeater hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. A hub works at the physical layer of the OSI model. The device is a form of multiport repeater...
with AUI “uplink.” This combination allowed the Advancestack hub to send out IPX diagnostic packets to the NDIS driver in each PC. Assuming the PC was not rebooted, and 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 server / router. HPOV displayed each device in purple if active, and blue if discovered and non-responsive. The management software would generate NDIS “diagnostic pings” from the hub, and report the number of successful responses. Rebooting the PC, loading / unloading the driver, or experiencing any number of RF faults would cause each cable modem to transition from purple to blue hundreds of times per day.
HPOV could export the log file to a Paradox Database for later analysis and trending. Eliminating the PC reloads / driver reloads from the RF faults, and correlating RF faults on a single frequency translator vs. the entire flat network proved beyond the capabilities of the Zenith Network. These methods became the justification and fundamental research
Research
Research can be defined as the scientific search for knowledge, or as any systematic investigation, to establish novel facts, solve new or existing problems, prove new ideas, or develop new theories, usually using a scientific method...
for what was later patented by others: Patent Numbers: 6,032,019, 5,943,604 Echo device method for locating upstream ingress noise gaps at cable television head ends. Eventually, this technique became mandatory in DOCSIS 3.0, although it was rejected and ignored for 3 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 2 @ Cisco Catalyst 1200 Ethernet to FDDI switches, and 2 @ Cabletron MMAC-3 FNB hubs (6 Ethernet + 2 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 / frequency translators.
Videoconferencing over Cable Modems in 1994/1995
CUseeMECU-SeeMe
CU-SeeMe is an Internet videoconferencing client. CU-SeeMe can make point to point video calls without a server or make multi-point calls through server software first called a "reflector" and later called a "conference server" or Multipoint Control Unit...
and Apple Quicktime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
Conferencing 1.0 beta worked perfectly 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
Frequency-division multiplexing
Frequency-division multiplexing is a form of signal multiplexing which involves assigning non-overlapping frequency ranges to different signals or to each "user" of a medium.- Telephone :...
, and an Ethernet switch to join the otherwise incompatible networks.
Late in the beta, 160x120 pixel video was increased to 320x240, and the audio quality
Sound quality
Sound quality is the quality of the audio output from various electronic devices. Sound quality can be defined as the degree of accuracy with which a device records or emits the original sound waves...
greatly improved on the Apple PowerMacintosh 7100 AV.
Zenith at Cogeco in Canada
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 was failing for 3 reasons:- The Zenith network is a pure bridged CSMA/CD Ethernet. It has no understanding of the Layer 3Network layerThe network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
ARP protocol. Thus ARP storms through the layer 2Data link layerThe data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
switches used in the first headend designs would clog the network. - The layer 2 switches and layer 3 routers of the time did perform any QOS or rate limitingRate limitingIn computer networks, rate limiting is used to control the rate of traffic sent or received on a network interface. Traffic that is less than or equal to the specified rate is sent, whereas traffic that exceeds the rate is dropped or delayed...
, 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 particular amplifier contained a design defect whereby the pad and equalizer plug in modules would literally fall off the circuit boardPrinted circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
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.”
External links
- David Waks recalls 1993-1994 launch Article
- Modern CMTS performance measurements Article
- Patent Search Patent Numbers: 6,032,019, 5,943,604 Echo device method for locating upstream ingress noise gaps at cable television head ends