55-433: A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fiber-coaxial (HFC), radio frequency over glass (RFoG) and coaxial cable infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet , taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in
110-475: A carrier signal to transmit digital information using 1 MHz of the available bandwidth in the 24 MHz frequency range. The remainder of the 294 MHz bandwidth can be used to carry other communication channels , such as off-the-air TV , FM , closed circuit TV , or a voice telephone system , or, other digital channels. The data rate of our test-bed system is 307.2 kbps . The IEEE 802 Committee defined 10BROAD36 in 802.3b-1985 as
165-491: A router and a DHCP server to provide the LAN with IP network addressing. From a data forwarding and network topology perspective, this router functionality is typically kept distinct from the cable modem functionality (at least logically) even though the two may share a single enclosure and appear as one unit, sometimes called a residential gateway . So, the cable modem function will have its own IP address and MAC address as will
220-463: A switching loop . SPB allows all paths to be active with multiple equal-cost paths. SPB also increases the number of VLANs allowed on a layer-2 network. TRILL (Transparent Interconnection of Lots of Links) is the successor to Spanning Tree Protocol, both having been created by the same person, Radia Perlman . The catalyst for TRILL was an event at Beth Israel Deaconess Medical Center which began on 13 November 2002. The concept of Rbridges [sic]
275-399: A wireless bridge . The main types of network bridging technologies are simple bridging, multiport bridging, and learning or transparent bridging. Transparent bridging uses a table called the forwarding information base to control the forwarding of frames between network segments. The table starts empty and entries are added as the bridge receives frames. If a destination address entry
330-578: A 10 Mbit/s IEEE 802.3 / Ethernet broadband system to run up to 3,600 metres (11,800 ft) over CATV coax network cabling. The word broadband as used in the original IEEE 802.3 specifications implied operation in frequency-division multiplexed ( FDM ) channel bands as opposed to digital baseband square-waveform modulations (also known as line coding ), which begin near zero Hz and theoretically consume infinite frequency bandwidth . (In real-world systems, higher-order signal components become indistinguishable from background noise .) In
385-445: A DOCSIS modem, but the company filed for bankruptcy in 2003 and closed. The DOCSIS CMTS assets of COM21 were acquired by ARRIS . CDLP was a proprietary system manufactured by Motorola . CDLP customer premises equipment (CPE) was capable of both PSTN (telephone network) and radio frequency (cable) return paths. The PSTN-based service was considered 'one-way cable' and had many of the same drawbacks as satellite Internet service; as
440-402: A bridge connected to three hosts, A, B, and C. The bridge has three ports. A is connected to bridge port 1, B is connected to bridge port 2, C is connected to bridge port 3. A sends a frame addressed to B to the bridge. The bridge examines the source address of the frame and creates an address and port number entry for host A in its forwarding table. The bridge examines the destination address of
495-408: A cable with standard television channels. 10BROAD36 was less successful than its contemporaries because of the high equipment complexity (and cost) associated with it. The individual stations are much more expensive due to the extra radio frequency circuitry involved; however the primary extra complexity comes from the fact that 10BROAD36 is unidirectional. Signals can only travel one direction along
550-421: A carrier signal to be transmitted in a radio station . In telecommunications engineering , this is a broadband signaling technique. Broadband provides several advantages over the baseband signal used, for instance in 10BASE5 . Range is greatly extended (3,600 m (11,800 ft), versus 500 m (1,600 ft) for 10BASE5), and multiple signals can be carried on the same cable. 10BROAD36 can even share
605-405: A customer LAN and the coax network. Technically, it is a modem because it must modulate data to transmit it over the cable network, and it must demodulate data from the cable network to receive it. It implements an Ethernet PHY on its LAN interface , and a DOCSIS-defined cable-specific PHY on its HFC cable interface. The term cable modem refers to this cable-specific PHY. The Network Layer
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#1732794506608660-407: A frame-by-frame basis whether or not to forward from one network to the other. A store and forward technique is typically used so, as part of forwarding, the frame integrity is verified on the source network and CSMA/CD delays are accommodated on the destination network. In contrast to repeaters which simply extend the maximum span of a segment, bridges only forward frames that are required to cross
715-596: A hardware version of the modem, instead of simply allowing a supported DOCSIS version. In 2004, the Multimedia over Coax Alliance (MoCA) was established to develop industry standard for the connected home, using the existing coaxial cabling. Initially developed for in-home networking with MoCA 1.0/1.1, the MoCA standards has continued to develop with MoCA 2.0/2.1 in 2010 and MoCa 2.5 in 2016. In 2017, Multimedia over Coax Alliance introduced MoCA Access specification, based on
770-504: A result, it quickly gave way to "two-way cable." Cable modems that used the RF cable network for the return path were considered 'two-way cable', and were better able to compete with the bi-directional digital subscriber line (DSL) service. The standard is in little use now as new providers use, and existing providers having changed to, the DOCSIS standard. The Motorola CDLP proprietary CyberSURFR
825-493: A single cable modem to use concurrently more than one upstream channel and more than one downstream channel in parallel. Virtually all cable modems operating in the field today are compliant with one of the DOCSIS versions. Because of the differences in the European PAL and US's NTSC systems two main versions of DOCSIS exist, DOCSIS and EuroDOCSIS. The main differences are found in the width of RF-channels: 6 MHz for
880-451: Is an example of a device that was built to the CDLP standard, capable of a peak 10 Mbit/s downstream and 1.532 Mbit/s upstream. CDLP supported a maximum downstream bandwidth of 30 Mbit/s which could be reached by using several cable modems. The Australian ISP BigPond employed this system when it started cable modem tests in 1996. For a number of years cable Internet access
935-450: Is called network bridging . Bridging is distinct from routing . Routing allows multiple networks to communicate independently and yet remain separate, whereas bridging connects two separate networks as if they were a single network. In the OSI model , bridging is performed in the data link layer (layer 2). If one or more segments of the bridged network are wireless , the device is known as
990-537: Is called transparent when the frame format and its addressing aren't changed substantially. Non-transparent bridging is required especially when the frame addressing schemes on both sides of a bridge are not compatible with each other, e.g. between ARCNET with local addressing and Ethernet using IEEE MAC addresses , requiring translation. However, most often such incompatible networks are routed in between, not bridged. A simple bridge connects two network segments, typically by operating transparently and deciding on
1045-651: Is implemented as an IP host in that it has its own IP address used by the network operator to maintain the device. In the transport layer the cable modem supports UDP in association with its own IP address, and it supports filtering based on TCP and UDP port numbers to, for example, block forwarding of NetBIOS traffic out of the customer's LAN. In the Application Layer , the cable modem supports certain protocols that are used for management and maintenance, notably Dynamic Host Configuration Protocol (DHCP), SNMP , and TFTP . Some cable modems may incorporate
1100-518: Is known as an embedded multimedia terminal adapter (E-MTA). Many cable TV service providers also offer VoIP-based telephone service via the cable infrastructure ( PacketCable ). Some high-speed Internet customers may use VoIP telephony by subscribing to a third-party service, such as Vonage , MagicJack+ and NetTALK . In network topology, a cable modem is a network bridge that conforms to IEEE 802.1D for Ethernet networking (with some modifications). The cable modem bridges Ethernet frames between
1155-401: Is not found in the table, the frame is forwarded to all other ports of the bridge, flooding the frame to all segments except the one from which it was received. By means of these flooded frames, a host on the destination network will respond and a forwarding database entry will be created. Both source and destination addresses are used in this process: source addresses are recorded in entries in
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#17327945066081210-803: The Americas , Asia , Australia , and Europe . Internet Experiment Note (IEN) 96 (1979) describes an early RF cable modem system. From pages 2 and 3 of IEN 96: The Cable-Bus System The MITRE/Washington Cablenet system is based on a technology developed at MITRE/Bedford. Similar cable-bus systems are in operation at a number of government sites, e.g. Walter Reed Army Hospital , and the NASA Johnson Space Center , but these are all standalone, local-only networks. The system uses standard community antenna television (CATV) coaxial cable and microprocessor based Bus Interface Units (BIUs) to connect subscriber computers and terminals to
1265-517: The Ungermann-Bass product noted that no installers understood both the digital and analog aspects of the system. In wide area networks it was quickly replaced by fiber-optic communication alternatives, such as 100BASE-FX (which provided ten times the data rate). Interest in cable modems was revived for residential Internet access , through later technologies such as Data Over Cable Service Interface Specification (DOCSIS) introduced in
1320-462: The DOCSIS RFI 1.0 Interim-01 document discussed quality of servce (QoS) extensions and mechanisms using IntServ , RSVP , RTP , and Synchronous Transfer Mode (STM) telephony (as opposed to ATM ). DOCSIS RFI 1.1 later added more robust and standardized QoS mechanisms to DOCSIS. DOCSIS 2.0 added support for S-CDMA PHY , while DOCSIS 3.0 added IPv6 support and channel bonding to allow
1375-644: The IETF chartered Working Groups ( WGs ) that produced various standards related to cable modem technologies (including 802.14, DOCSIS, PacketCable , and others). In particular, the IETF WGs on IP over Cable Data Network (IPCDN) and IP over Digital Video Broadcasting (DVB) produced some standards applicable to cable modem systems, primarily in the areas of Simple Network Management Protocol (SNMP) Management Information Bases ( MIBs ) for cable modems and other networking equipment that operates over CATV networks . In
1430-456: The MCNS consortium handed over control of it to CableLabs which maintained the specification, promoted it in various standards organizations (notably SCTE and ITU ), developed a certification testing program for cable modem equipment, and has since drafted multiple extensions to the original specification. While deployed DOCSIS RFI 1.0 equipment generally only supported best-effort service ,
1485-528: The MoCA 2.5 standard, suitable for addressing broadband network access in-building using coaxial cabling. MoCA Access extends MoCA 2.5 in-home networking to fit operators and ISPs that are installing fiber-to-the-basement/drop point (FTTB/FTTdp) and want to use the existing coax for connection to each apartment or house." With the development of voice over Internet Protocol (VoIP) telephony, analog telephone adapters (ATA) have been incorporated into many cable modems for providing telephone service. An embedded ATA
1540-522: The US and 8 MHz for Europe. A third variant of DOCSIS was developed in Japan and has seen limited deployment in that country. Although interoperability "was the whole point of the DOCSIS project," most cable operators only approve a very restricted list of cable modems on their network, identifying the 'allowed' modems by their brand, models, sometimes firmware version and occasionally going as far as imposing
1595-478: The basis for network switches . The forwarding information base stored in content-addressable memory (CAM) is initially empty. For each received Ethernet frame the switch learns from the frame's source MAC address and adds this together with an interface identifier to the forwarding information base. The switch then forwards the frame to the interface found in the CAM based on the frame's destination MAC address. If
1650-405: The bridge determines that the destination host is on another segment on the network, it forwards the frame to that segment. If the destination address belongs to the same segment as the source address, the bridge filters the frame, preventing it from reaching the other network where it is not needed. Transparent bridging can also operate over devices with more than two ports. As an example, consider
1705-464: The bridge. Additionally, bridges reduce collisions by creating a separate collision domain on either side of the bridge. A multiport bridge connects multiple networks and operates transparently to decide on a frame-by-frame basis whether to forward traffic. Additionally, a multiport bridge must decide where to forward traffic. Like the simple bridge, a multiport bridge typically uses store and forward operation. The multiport bridge function serves as
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1760-525: The cable. ... The cable bus consists of two parallel coaxial cables, one inbound and the other outbound. The inbound cable and outbound cable are connected at one end, the headend , and electrically terminated at their other ends. This architecture takes advantage of the well developed unidirectional CATV components . The topology is dendritic (i.e. branched like a tree ). ... The BIUs contain Radio Frequency (RF) modems which modulate
1815-455: The destination address is unknown the switch sends the frame out on all interfaces (except the ingress interface). This behavior is called unicast flooding . Once a bridge learns the addresses of its connected nodes, it forwards data link layer frames using a layer-2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth methods were performance-increasing methods when used on switch products with
1870-875: The first cable modem providers. The Zenith Cable Modem technology was used by several cable television systems in the United States and other countries, including Cox Communications San Diego, Knology in the Southeast United States, Ameritech 's Americast service (later to be sold off to Wide Open West after the SBC / Ameritech merger), Cogeco in Hamilton Ontario and Cablevision du Nord de Québec in Val-d'Or. Zenith Homeworks used BPSK (Bi-Phase Shift Keyed) modulation to achieve 500 Kbit/sec in 600 kHz, or 4 Mbit/sec in 6 MHz. Com21
1925-539: The first high-speed, asymmetrical cable modem system in 1990. A key Hybrid Networks insight was that in the nascent days of the Internet, data downloading constitutes the majority of the data traffic, and this can be served adequately with a highly asymmetrical data network (i.e. a large downstream data pipe and many small upstream data pipes). This allowed CATV operators to offer high-speed data services immediately without first requiring an expensive system upgrade. Also key
1980-504: The frame and does not find it in its forwarding table so it floods (broadcasts) it to all other ports: 2 and 3. The frame is received by hosts B and C. Host C examines the destination address and ignores the frame as it does not match with its address. Host B recognizes a destination address match and generates a response to A. On the return path, the bridge adds an address and port number entry for B to its forwarding table. The bridge already has A's address in its forwarding table so it forwards
2035-637: The future). MSOs were interested in quickly deploying service to compete for broadband Internet access customers instead of waiting on the slower, iterative, and deliberative processes of standards development committees. Albert A. Azzam was Secretary of the IEEE 802.14 Working Group, and his book, High-Speed Cable Modems , describes many of the proposals submitted to 802.14. Although the Internet Engineering Task Force (IETF) generally does not generate complete cable modem standards,
2090-568: The late 1990s, a consortium of US cable operators , known as "MCNS" formed to quickly develop an open and interoperable cable modem specification. The group essentially combined technologies from the two dominant proprietary systems at the time, taking the physical layer from the Motorola CDLP system and the MAC layer from the LANcity system. When the initial specification had been drafted,
2145-498: The line, so head-end stations must be present on the line to repeat the signals (ensuring that no packets travel through the line indefinitely) on either another, backwards direction frequency on the same line, or another line entirely. This also increases latency and prevents bidirectional signal flow. The extra complexity outweighed the advantage of reusability of CATV technology for the intended campus networks and metropolitan area networks . An installer at Boston University using
2200-479: The market 10BROAD36 equipment was not developed by many vendors nor deployed in many user networks as compared to equipment for IEEE 802.3/ Ethernet baseband standards such as 10BASE5 (1983), 10BASE2 (1985), 10BASE-T (1990), etc. The IEEE 802 Committee also specified a broadband CATV digital networking standard in 1989 with 802.7-1989 . However, like 10BROAD36 , 802.7-1989 saw little commercial success. Hybrid Networks developed, demonstrated and patented
2255-516: The mid-1990s the IEEE 802 committee formed a subcommittee (802.14) to develop a standard for cable modem systems. IEEE 802.14 developed a draft standard, which was ATM-based . However, the 802.14 working group was disbanded when North American multi system operators ( MSOs ) instead backed the then-fledgling DOCSIS 1.0 specification, which generally used best-effort service and was IP-based (with extension codepoints to support ATM for QoS in
Cable modem - Misplaced Pages Continue
2310-406: The response only to port 1. Host C or any other hosts on port 3 are not burdened with the response. Two-way communication is now possible between A and B without any further flooding to the network. Now, if A sends a frame addressed to C, the same procedure will be used, but this time the bridge will not create a new forwarding-table entry for A's address/port because it has already done so. Bridging
2365-491: The router. Cable modems can have a problem known in industry jargon as "flap" or "flapping". A modem flap is when the connection by the modem to the head-end has been dropped (gone offline) and then comes back online. The time offline or rate of flap is not typically recorded, only the incidence. While this is a common occurrence and usually unnoticed, if a modem's flap is extremely high, these disconnects can cause service to be disrupted. If there are usability problems due to flap
2420-406: The same input and output port bandwidths: Shortest Path Bridging (SPB), specified in the IEEE 802.1aq standard and based on Dijkstra's algorithm , is a computer networking technology intended to simplify the creation and configuration of networks, while enabling multipath routing . It is a proposed replacement for Spanning Tree Protocol which blocks any redundant paths that could result in
2475-404: The standard that was ratified in 1985 as an additional section 11 to the base Ethernet standard. It was also issued as ISO/IEC 8802-3 in 1989. The standard supports 10 Mbit/s Ethernet signals over standard 75 ohm cable television (CATV) cable over a 3600-meter range. 10BROAD36 modulates its data onto a higher frequency carrier signal , much as an audio signal would modulate
2530-523: The table, while destination addresses are looked up in the table and matched to the proper segment to send the frame to. Digital Equipment Corporation (DEC) originally developed the technology in 1983 and introduced the LANBridge 100 that implemented it in 1986. In the context of a two-port bridge, the forwarding information base can be seen as a filtering database. A bridge reads a frame 's destination address and decides to either forward or filter. If
2585-640: The time had formed a joint-venture with Antec called ARRIS Interactive. Because of contractual agreements with Antec involving this joint venture, Nortel spun the LANCity group out into the ARRIS Interactive joint-venture. ARRIS continues to make cable modems and cable modem termination system (CMTS) equipment compliant with the DOCSIS standard. Zenith offered a cable modem technology using its own protocol which it introduced in 1993, being one of
2640-458: The typical cause is a defective modem or very high amounts of traffic on the service provider's network (upstream utilization too high). Types of flap include reinsertions, hits and misses, and power adjustments. In January 2020, a vulnerability affecting cable modems using Broadcom chipsets was disclosed and named Cable Haunt . Security researchers say that the vulnerability affects hundreds of millions of devices. Exploits are possible because of
2695-475: The upstream as well as the downstream path. Hybrid's system architecture is used for most cable modem systems today. LANcity was an early pioneer in cable modems, developing a proprietary system that was widely deployed in the U.S. LANcity, which was led by the Iranian-American engineer Rouzbeh Yassini , was then acquired by Bay Networks . Bay Networks was subsequently acquired by Nortel . Nortel at
2750-401: The use of default credentials in the spectrum analyzer component of the modem (mostly used for debugging purposes) accessible through a network port which is open by default in the vulnerable models. Network bridge A network bridge is a computer networking device that creates a single, aggregate network from multiple communication networks or network segments . This function
2805-658: Was another early pioneer in cable modems, and quite successful until proprietary systems were made obsolete by the DOCSIS standardization. The Com21 system used a ComController as the central bridge in CATV network head-ends, the ComPort cable modem in various models and the NMAPS management system using HP OpenView as the platform. Later they also introduced a return path multiplexer to overcome noise problems when combining return path signals from multiple areas. The proprietary protocol
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#17327945066082860-453: Was based on Asynchronous Transfer Mode (ATM). The central ComController switch was a modular system offering one downstream channel (transmitter) and one management module. The remaining slots could be used for upstream receivers (2 per card), dual Ethernet 10BaseT and later also Fast-Ethernet and ATM interfaces. The ATM interface became the most popular, as it supported the increasing bandwidth demands and also supported VLANs . Com21 developed
2915-635: Was first proposed to the Institute of Electrical and Electronics Engineers in the year 2004, whom in 2005 rejected what came to be known as TRILL, and in the years 2006 through 2012 devised an incompatible variation known as Shortest Path Bridging. 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 Institute of Electrical and Electronics Engineers standards committee IEEE 802 published
2970-673: Was only available in Sydney , Melbourne and Brisbane via CDLP. This network ran parallel to the newer DOCSIS system for several years. In 2004, the CDLP network was terminated and replaced by DOCSIS. CDLP has been also rolled out at the French cable operator Numericable before upgrading its IP broadband network using DOCSIS. Digital Video Broadcasting ( DVB ) and Digital Audio Visual Council (DAVIC) are European-formed organizations that developed some cable modem standards. However, these standards have not been as widely adopted as DOCSIS. In
3025-464: Was that it saw that the upstream and downstream communications could be on the same or different communications media using different protocols working in each direction to establish a closed-loop communications system. The speeds and protocols used in each direction would be very different. The earliest systems used the public switched telephone network (PSTN) for the return path since very few cable systems were bi-directional. Later systems used CATV for
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