Misplaced Pages

#883116

59-684: EMTA may refer to: Embedded Multimedia Terminal Adapter , a combination cable modem and telephone adapter Endless Mountains Transportation Authority (now BeST Transit, serving Bradford , Sullivan , and Tioga counties in Pennsylvania) Erie Metropolitan Transit Authority European Metropolitan Transport Authorities Estonian Academy of Music and Theatre Emergency Medical Technician Ambulance Topics referred to by

118-491: 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

177-578: 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

236-445: 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

295-427: A call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channels between them. In a half-duplex or semiduplex system, both parties can communicate with each other, but not simultaneously;

354-510: A communications system or integrated into the communication system's central processing unit . Where channel access methods are used in point-to-multipoint networks (such as cellular networks ) for dividing forward and reverse communication channels on the same physical communications medium, they are known as duplexing methods. Time-division duplexing ( TDD ) is the application of time-division multiplexing to separate outward and return signals. It emulates full-duplex communication over

413-405: 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

472-426: A half-duplex communication link. Time-division duplexing is flexible in the case where there is asymmetry of the uplink and downlink data rates or utilization. As the amount of uplink data increases, more communication capacity can be dynamically allocated, and as the traffic load becomes lighter, capacity can be taken away. The same applies in the downlink direction. The transmit/receive transition gap (TTG)

531-669: A half-duplex system. For example, station A on one end of the data link could be allowed to transmit for exactly one second, then station B on the other end could be allowed to transmit for exactly one second, and then the cycle repeats. In this scheme, the channel is never left idle. In half-duplex systems, if more than one party transmits at the same time, a collision occurs, resulting in lost or distorted messages. A full-duplex ( FDX ) system allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex since they allow both callers to speak and be heard at

590-596: 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

649-505: 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 the cable. ... The cable bus consists of two parallel coaxial cables, one inbound and

SECTION 10

#1732786959884

708-504: 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

767-493: 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

826-432: Is a signal-processing operation that subtracts the far-end signal from the microphone signal before it is sent back over the network. Echo cancellation is important technology allowing modems to achieve good full-duplex performance. The V.32 , V.34 , V.56 , and V.90 modem standards require echo cancellation. Echo cancelers are available as both software and hardware implementations. They can be independent components in

885-451: 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

944-453: Is different from Wikidata All article disambiguation pages All disambiguation pages Embedded Multimedia Terminal Adapter 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

1003-443: Is for sending packets. Other Ethernet variants, such as 1000BASE-T use the same channels in each direction simultaneously. In any case, with full-duplex operation, the cable itself becomes a collision-free environment and doubles the maximum total transmission capacity supported by each Ethernet connection. Full-duplex has also several benefits over the use of half-duplex. Since there is only one transmitter on each twisted pair there

1062-402: Is frequently used in ham radio operation, where an operator is attempting to use a repeater station. The repeater station must be able to send and receive a transmission at the same time and does so by slightly altering the frequency at which it sends and receives. This mode of operation is referred to as duplex mode or offset mode . Uplink and downlink sub-bands are said to be separated by

1121-651: 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

1180-518: 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

1239-414: Is no contention and no collisions so time is not wasted by having to wait or retransmit frames. Full transmission capacity is available in both directions because the send and receive functions are separate. Some computer-based systems of the 1960s and 1970s required full-duplex facilities, even for half-duplex operation, since their poll-and-response schemes could not tolerate the slight delays in reversing

SECTION 20

#1732786959884

1298-447: Is not completely standardized between defining organizations, and in radio communication some sources classify this mode as simplex . Typically, once one party begins a transmission, the other party on the channel must wait for the transmission to complete, before replying. An example of a half-duplex system is a two-party system such as a walkie-talkie , wherein one must say "over" or another previously designated keyword to indicate

1357-525: Is shared alternately between the two directions. For example, a walkie-talkie or a DECT phone or so-called TDD 4G or 5G phones requires only a single frequency for bidirectional communication, while a cell phone in the so-called FDD mode is a full-duplex device, and generally requires two frequencies to carry the two simultaneous voice channels, one in each direction. In automatic communications systems such as two-way data-links, time-division multiplexing can be used for time allocations for communications in

1416-453: Is that it makes radio planning easier and more efficient since base stations do not hear each other (as they transmit and receive in different sub-bands) and therefore will normally not interfere with each other. Conversely, with time-division duplexing systems, care must be taken to keep guard times between neighboring base stations (which decreases spectral efficiency ) or to synchronize base stations, so that they will transmit and receive at

1475-402: Is the gap (time) between a downlink burst and the subsequent uplink burst. Similarly, the receive/transmit transition gap (RTG) is the gap between an uplink burst and the subsequent downlink burst. Examples of time-division duplexing systems include: Frequency-division duplexing ( FDD ) means that the transmitter and receiver operate using different carrier frequencies . The method

1534-551: The frequency offset . Frequency-division duplex systems can extend their range by using sets of simple repeater stations because the communications transmitted on any single frequency always travel in the same direction. Frequency-division duplexing can be efficient in the case of symmetric traffic. In this case, time-division duplexing tends to waste bandwidth during the switch-over from transmitting to receiving, has greater inherent latency , and may require more complex circuitry . Another advantage of frequency-division duplexing

1593-464: 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

1652-646: 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

1711-456: 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 ,

1770-529: 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

1829-527: 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

EMTA - Misplaced Pages Continue

1888-404: 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

1947-474: The button, which turns on the receiver and turns off the transmitter. This terminology is not completely standardized, and some sources define this mode as simplex . Systems that do not need duplex capability may instead use simplex communication , in which one device transmits and the others can only listen. Examples are broadcast radio and television, garage door openers , baby monitors , wireless microphones , and surveillance cameras . In these devices,

2006-400: The communication is one direction at a time. An example of a half-duplex device is a walkie-talkie , a two-way radio that has a push-to-talk button. When the local user wants to speak to the remote person, they push this button, which turns on the transmitter and turns off the receiver, preventing them from hearing the remote person while talking. To listen to the remote person, they release

2065-474: The communication is only in one direction. Simplex communication is a communication channel that sends information in one direction only. The International Telecommunication Union definition is a communications channel that operates in one direction at a time, but that may be reversible; this is termed half duplex in other contexts. For example, in TV and radio broadcasting , information flows only from

2124-441: The direction of transmission in a half-duplex line. Full-duplex audio systems like telephones can create echo, which is distracting to users and impedes the performance of modems. Echo occurs when the sound originating from the far end comes out of the speaker at the near end and re-enters the microphone there and is then sent back to the far end. The sound then reappears at the original source end but delayed. Echo cancellation

2183-405: The end of transmission, to ensure that only one party transmits at a time. A good analogy for a half-duplex system would be a one-lane road that allows two-way traffic, traffic can only flow in one direction at a time. Half-duplex systems are usually used to conserve bandwidth , at the cost of reducing the overall bidirectional throughput, since only a single communication channel is needed and

2242-877: 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

2301-539: 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

2360-514: The form of cable Internet , taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in 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

2419-639: 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,

EMTA - Misplaced Pages Continue

2478-565: The half-duplex and simplex capacity of their new transatlantic telegraph cable completed between Newfoundland and the Azores in 1928. The same definition for a simplex radio channel was used by the National Fire Protection Association in 2002. A half-duplex ( HDX ) system provides communication in both directions, but only one direction at a time, not simultaneously in both directions. This terminology

2537-568: 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,

2596-480: 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

2655-518: 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

2714-511: 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 a carrier signal to transmit digital information using 1 MHz of

2773-492: 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

2832-404: The same term [REDACTED] This disambiguation page lists articles associated with the title EMTA . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=EMTA&oldid=800669833 " Category : Disambiguation pages Hidden categories: Short description

2891-427: The same time. Full-duplex operation is achieved on a two-wire circuit through the use of a hybrid coil in a telephone hybrid . Modern cell phones are also full-duplex. There is a technical distinction between full-duplex communication, which uses a single physical communication channel for both directions simultaneously, and dual-simplex communication which uses two distinct channels, one for each direction. From

2950-641: 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

3009-456: The transmitter site to multiple receivers. A pair of walkie-talkie two-way radios provide a simplex circuit in the ITU sense; only one party at a time can talk, while the other listens until it can hear an opportunity to transmit. The transmission medium (the radio signal over the air) can carry information in only one direction. The Western Union company used the term simplex when describing

SECTION 50

#1732786959884

3068-460: 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

3127-477: 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

3186-425: 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. Simplex communication In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service ; the parties at both ends of

3245-403: The user perspective, the technical difference does not matter and both variants are commonly referred to as full duplex . Many Ethernet connections achieve full-duplex operation by making simultaneous use of two physical twisted pairs inside the same jacket, or two optical fibers which are directly connected to each networked device: one pair or fiber is for receiving packets, while the other

3304-658: 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

3363-453: 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

3422-673: 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

3481-464: 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

#883116