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60-598: [REDACTED] Look up cmts in Wiktionary, the free dictionary. CMTS may refer to: U.S. Committee on the Marine Transportation System , an inter-agency committee authorized to coordinate policies affecting the U.S. Marine Transportation System Cable modem termination system , a piece of equipment which is used to provide high speed data services to cable subscribers Topics referred to by

120-588: A high-speed side (where the full line rate signal is supported), and a low-speed side , which can consist of electrical as well as optical interfaces. The low-speed side takes in low-speed signals, which are multiplexed by the network element and sent out from the high-speed side, or vice versa. Recent digital cross connect systems (DCSs or DXCs) support numerous high-speed signals, and allow for cross-connection of DS1s, DS3s and even STS-3s/12c and so on, from any input to any output. Advanced DCSs can support numerous subtending rings simultaneously. SONET and SDH have

180-483: A 'transport' in the OSI Model sense). Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDH was the choice for transporting the fixed length Asynchronous Transfer Mode (ATM) frames also known as cells. It quickly evolved mapping structures and concatenated payload containers to transport ATM connections. In other words, for ATM (and eventually other protocols such as Ethernet ),

240-631: A CMTS is to imagine a router with Ethernet interfaces (connections) on one side and coaxial cable RF interfaces on the other side. The Ethernet side is known as the Network Side Interface or NSI. A service group is a group of customers that share communication channels and thus bandwidth. A CMTS has separate RF interfaces and connectors for downlink and uplink signals. The RF/coax interfaces carry RF signals to and from coaxial "trunks" connected to subscribers' cable modems, using one pair of connectors per trunk, one for downlink and

300-508: A PDH DS1 signal. A VTG may instead be subdivided into three VT2 signals, each of which can carry a PDH E1 signal. The SDH equivalent of a VTG is a TUG-2; VT1.5 is equivalent to VC-11, and VT2 is equivalent to VC-12. Three STS-1 signals may be multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s. The signal

360-507: A QAM signal for delivery over a cable network. Edge QAMs are normally standalone devices placed at the "edge" of a network. They can also be connected to a CMTS core, to make up an M-CMTS system which is more scalable. A CMTS core is normally a conventional or I-CMTS that supports operation as a CMTS core in an M-CMTS system. A CMTS can be broken down into several different architectures, Integrated CMTS (I-CMTS), Modular (M-CMTS), Virtual CMTS (vCMTS) and remote CMTS. An I-CMTS incorporates into

420-409: A SONET/SDH signal allows it to carry many different services in its virtual container (VC), because it is bandwidth-flexible. SONET and SDH often use different terms to describe identical features or functions. This can cause confusion and exaggerate their differences. With a few exceptions, SDH can be thought of as a superset of SONET. SONET is a set of transport containers that allow for delivery of

480-585: A limited number of architectures defined. These architectures allow for efficient bandwidth usage as well as protection (i.e. the ability to transmit traffic even when part of the network has failed), and are fundamental to the worldwide deployment of SONET and SDH for moving digital traffic. Every SDH/SONET connection on the optical physical layer uses two optical fibers, regardless of the transmission speed. Linear Automatic Protection Switching (APS), also known as 1+1 , involves four fibers: two working fibers (one in each direction), and two protection fibers. Switching

540-743: A single unit all components necessary for its operation. There are both pros and cons to each type of architecture. In a M-CMTS solution the architecture of an I-CMTS is broken up into two components. The first part is the Physical Downstream component (PHY) which is known as the Edge QAM (EQAM). The second part is the IP networking and DOCSIS MAC Component which is referred to as the M-CMTS Core. There are also several new protocols and components introduced with this type of architecture. One

600-413: A subscriber's computer to obtain an IP address by forwarding DHCP requests to the relevant servers. This DHCP server returns, for the most part, what looks like a typical response including an assigned IP address for the computer, gateway/router addresses to use, DNS servers, etc. The CMTS may also implement some basic filtering to protect against unauthorized users and various attacks. Traffic shaping

660-485: A variety of protocols, including traditional telephony, ATM, Ethernet, and TCP/IP traffic. SONET therefore is not in itself a native communications protocol and should not be confused as being necessarily connection-oriented in the way that term is usually used. The protocol is a heavily multiplexed structure, with the header interleaved between the data in a complex way. This permits the encapsulated data to have its own frame rate and be able to "float around" relative to

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720-466: Is 10 Gigabit Ethernet (10GbE). The Gigabit Ethernet Alliance created two 10 Gigabit Ethernet variants: a local area variant ( LAN PHY ) with a line rate of 10.3125 Gbit/s, and a wide area variant ( WAN PHY ) with the same line rate as OC-192/STM-64 (9,953,280 kbit/s). The WAN PHY variant encapsulates Ethernet data using a lightweight SDH/SONET frame, so as to be compatible at a low level with equipment designed to carry SDH/SONET signals, whereas

780-491: Is added, and that SONET network element (NE) is said to be a path generator and terminator . The SONET NE is line terminating if it processes the line overhead. Note that wherever the line or path is terminated, the section is terminated also. SONET regenerators terminate the section, but not the paths or line. An STS-1 payload can also be subdivided into seven virtual tributary groups (VTGs). Each VTG can then be subdivided into four VT1.5 signals, each of which can carry

840-716: Is coming from the Internet can be routed (or bridged) through the Ethernet interface, through the CMTS and then onto the RF interfaces that are connected to the cable company's hybrid fiber coax ( HFC ). The traffic winds its way through the HFC to end up at the cable modem in the subscriber's home. Traffic from a subscriber's home system goes through the cable modem and out to the Internet in

900-516: Is composed as follows: Data transmitted from end to end is referred to as path data . It is composed of two components: For STS-1, the payload is referred to as the synchronous payload envelope (SPE), which in turn has 18 stuffing bytes, leading to the STS-1 payload capacity of 756 bytes. The STS-1 payload is designed to carry a full PDH DS3 frame. When the DS3 enters a SONET network, path overhead

960-545: Is considered a variation of SDH because of SDH's greater worldwide market penetration. SONET is subdivided into four sublayers with some factor such as the path, line, section and physical layer. The SDH standard was originally defined by the European Telecommunications Standards Institute (ETSI), and is formalised as International Telecommunication Union (ITU) standards G.707, G.783 , G.784, and G.803. The SONET standard

1020-508: Is dictated by the bandwidth requirements for PCM-encoded telephonic voice signals: at this rate, an STS-1/OC-1 circuit can carry the bandwidth equivalent of a standard DS-3 channel, which can carry 672 64-kbit/s voice channels. In SONET, the STS-3c signal is composed of three multiplexed STS-1 signals; the STS-3c may be carried on an OC-3 signal. Some manufacturers also support the SDH equivalent of

1080-467: Is different from Wikidata All article disambiguation pages All disambiguation pages Cable modem termination system A CMTS provides similar functions to a DSLAM in DSL or an OLT in a PON . In order to provide high speed data services, a cable company will connect its headend to the Internet via very high capacity data links to a network service provider . On the subscriber side of

1140-484: Is for path overhead; it is followed by the payload container, which can itself carry other containers. Administrative units can have any phase alignment within the STM frame, and this alignment is indicated by the pointer in row four. The section overhead (SOH) of a STM-1 signal is divided into two parts: the regenerator section overhead (RSOH) and the multiplex section overhead (MSOH). The overheads contain information from

1200-503: Is interleaved with it during transmission. Part of the overhead is transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted. In the case of an STS-1, the frame is 810 octets in size, while the STM-1/STS-3c frame is 2,430 octets in size. For STS-1, the frame is transmitted as three octets of overhead, followed by 87 octets of payload. This

1260-524: Is multiplexed by interleaving the bytes of the three STS-1 frames to form the STS-3 frame, containing 2,430 bytes and transmitted in 125  μs . Higher-speed circuits are formed by successively aggregating multiples of slower circuits, their speed always being immediately apparent from their designation. For example, four STS-3 or AU4 signals can be aggregated to form a 622.08 Mbit/s signal designated OC-12 or STM-4 . The highest rate commonly deployed

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1320-408: Is repeated nine times, until 810 octets have been transmitted, taking 125  μs . In the case of an STS-3c/STM-1, which operates three times faster than an STS-1, nine octets of overhead are transmitted, followed by 261 octets of payload. This is also repeated nine times until 2,430 octets have been transmitted, also taking 125  μs . For both SONET and SDH, this is often represented by displaying

1380-462: Is sometimes performed to prioritize application traffic, perhaps based upon subscribed plan or download usage and also to provide guaranteed Quality of service (QoS) for the cable operator's own PacketCable -based VOIP service. However, the function of traffic shaping is more likely done by a Cable Modem or policy traffic switch. A CMTS may also act as a bridge or router . A customer's cable modem cannot communicate directly with other modems on

1440-596: Is the OC-768 or STM-256 circuit, which operates at rate of just under 38.5 Gbit/s. Where fiber exhaustion is a concern, multiple SONET signals can be transported over multiple wavelengths on a single fiber pair by means of wavelength-division multiplexing , including dense wavelength-division multiplexing (DWDM) and coarse wavelength-division multiplexing (CWDM). DWDM circuits are the basis for all modern submarine communications cable systems and other long-haul circuits. Another type of high-speed data networking circuit

1500-650: Is the DOCSIS Timing Interface, which provides a reference frequency between the EQAM and M-CMTS Core via a DTI Server. The second is the Downstream External PHY Interface (DEPI). The DEPI protocol controls the delivery of DOCSIS frames from the M-CMTS Core to the EQAM devices Some of the challenges that entail an M-CMTS platform are increased complexity in RF combining and an increase in the number of failure points. One of

1560-407: Is the lowest SONET layer and it is responsible for transmitting the bits to the physical medium. The section layer is responsible for generating the proper STS-N frames which are to be transmitted across the physical medium. It deals with issues such as proper framing, error monitoring, section maintenance, and orderwire. The line layer ensures reliable transport of the payload and overhead generated by

1620-444: Is transmitted in exactly 125  μs , therefore, there are 8,000 frames per second on a 155.52 Mbit/s OC-3 fiber-optic circuit. The STM-1 frame consists of overhead and pointers plus information payload. The first nine columns of each frame make up the section overhead and administrative unit pointers, and the last 261 columns make up the information payload. The pointers (H1, H2, H3 bytes) identify administrative units (AU) within

1680-436: The CMTS. For example, if the cable modems on every service group use 24 channels for downstream, and 2 channels for upstream, then 3 downstream connectors can service the cable modems on two service groups, and be serviced by 1 upstream connector. A service group may serve up to 500 households. A service group has channels, whose bandwidth is shared among all members of the service group. The channels are later regrouped at

1740-559: The LAN PHY variant encapsulates Ethernet data using 64B/66B line coding. However, 10 Gigabit Ethernet does not explicitly provide any interoperability at the bitstream level with other SDH/SONET systems. This differs from WDM system transponders, including both coarse and dense wavelength-division multiplexing systems (CWDM and DWDM) that currently support OC-192 SONET signals, which can normally support thin-SONET–framed 10 Gigabit Ethernet. User throughput must not deduct path overhead from

1800-505: The Q3 interface protocol suite defined in ITU recommendations Q.811 and Q.812. With the convergence of SONET and SDH on switching matrix and network elements architecture, newer implementations have also offered TL1. Most SONET NEs have a limited number of management interfaces defined: To handle all of the possible management channels and signals, most modern network elements contain a router for

1860-701: The RF signals into light pulses for delivery over fiber optics through an HFC network. Examples of optics platforms are the Arris CH3000 and Cisco Prisma II. At the other end of the network, an optical node converts the light pulses into RF signals again and sends them through a coaxial cable "trunk". The trunk has one or more amplifiers along its length, and on the trunk there are distribution "taps" to which customers' modems are connected via coaxial cable. In fact, most CMTSs have both Ethernet interfaces (or other more traditional high-speed data interfaces like SONET ) as well as RF interfaces. In this way, traffic that

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1920-484: The SDH/SONET frame structure and rate. This interleaving permits a very low latency for the encapsulated data. Data passing through equipment can be delayed by at most 32  microseconds  (μs), compared to a frame rate of 125 μs; many competing protocols buffer the data during such transits for at least one frame or packet before sending it on. Extra padding is allowed for the multiplexed data to move within

1980-467: The STS-1/OC-1, known as STM-0. In packet-oriented data transmission, such as Ethernet , a packet frame usually consists of a header and a payload . The header is transmitted first, followed by the payload (and possibly a trailer , such as a CRC ). In synchronous optical networking, this is modified slightly. The header is termed the overhead , and instead of being transmitted before the payload,

2040-458: The STS-3c is carried over OC-3, it is often colloquially referred to as OC-3c , but this is not an official designation within the SONET standard as there is no physical layer (i.e. optical) difference between an STS-3c and 3 STS-1s carried within an OC-3. SONET offers an additional basic unit of transmission, the STS-1 (Synchronous Transport Signal 1) or OC-1 , operating at 51.84 Mbit/s—exactly one third of an STM-1/STS-3c/OC-3c carrier. This speed

2100-569: The amount of buffering required between elements in the network. Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or they can be used to directly support either Asynchronous Transfer Mode (ATM) or so-called packet over SONET/SDH (POS) networking. Therefore, it is inaccurate to think of SDH or SONET as communications protocols in and of themselves; they are generic, all-purpose transport containers for moving both voice and data. The basic format of

2160-511: The benefits of an M-CMTS architecture is that it is extremely scalable to larger numbers of downstream channels. Virtual CCAPs (vCCAPs) or virtual CMTSs (vCMTSs) are implemented on commercial off the shelf x86-based servers with specialized software, and can be used to increase service capacity without purchasing new CMTS/CCAP chassis, or add features to the CMTS/CCAP more quickly. Remote CMTS/Remote CCAP moves all CMTS/CCAP functionality to

2220-428: The cable headend or distribution hub and serviced by CMTSs and other equipment such as Edge QAMs. The RF signals from a CMTS, are connected via coaxial cable to headend RF management modules for RF splitting and combining, with other equipment such as other CMTSs so that several CMTS can service one service group, and then to an "optics platform" or headend platform, which has transmitter and receiver modules that turn

2280-448: The first layer in the OSI networking model. The ATM and SDH layers are the regenerator section level, digital line level, transmission path level, virtual path level, and virtual channel level. The physical layer is modeled on three major entities: transmission path, digital line and the regenerator section. The regenerator section refers to the section and photonic layers. The photonic layer

2340-575: The frame graphically: as a block of 90 columns and nine rows for STS-1, and 270 columns and nine rows for STM1/STS-3c. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload. The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. Their standards are extremely similar in implementation, making it easy to interoperate between SDH and SONET at any given bandwidth. In practice,

2400-515: The functionality of regenerators has been absorbed by the transponders of wavelength-division multiplexing systems. STS multiplexer and demultiplexer provide the interface between an electrical tributary network and the optical network. Add-drop multiplexers (ADMs) are the most common type of network elements. Traditional ADMs were designed to support one of the network architectures, though new generation systems can often support several architectures, sometimes simultaneously. ADMs traditionally have

2460-605: The headend or Internet) is carried in Ethernet frames encapsulated inside DOCSIS frames modulated with QPSK , 16-QAM, 32-QAM, 64-QAM or 128-QAM using TDMA , ATDMA or S- CDMA frequency sharing mechanisms. This is usually done at the "subband" or "return" portion of the cable TV spectrum (also known as the "T" channels), a much lower part of the frequency spectrum than the downstream signal, usually 5–42 MHz in DOCSIS 2.0 or 5–65 MHz in EuroDOCSIS. A typical CMTS allows

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2520-480: The headend, the CMTS enables communication with subscribers' cable modems . Different CMTSs are capable of serving different cable modem population sizes—ranging from 4,000 cable modems to 150,000 or more, depending in part on traffic, although it is recommended for an I-CMTS to service, for example, 30,000 subscribers (cable modems). A given headend may have between 1–12 CMTSs to service the cable modem population served by that headend or HFC hub . One way to think of

2580-416: The information payload. Thus, an OC-3 circuit can carry 150.336 Mbit/s of payload, after accounting for the overhead. Carried within the information payload, which has its own frame structure of nine rows and 261 columns, are administrative units identified by pointers. Also within the administrative unit are one or more virtual containers (VCs). VCs contain path overhead and VC payload. The first column

2640-473: The internal complex structure previously used to transport circuit-oriented connections was removed and replaced with a large and concatenated frame (such as STS-3c) into which ATM cells, IP packets, or Ethernet frames are placed. Both SDH and SONET are widely used today: SONET in the United States and Canada , and SDH in the rest of the world. Although the SONET standards were developed before SDH, it

2700-554: The line. In general, cable modem traffic is routed to other cable modems or to the Internet through a series of CMTSs and traditional routers. However, a route could conceivably pass through a single CMTS. A CCAP (Converged Cable Access Platform) combines CMTS and Edge QAM functionality in a single device so that it can provide both data (internet) with CMTS functionality, and video (TV channels) with Edge QAM functionality. Edge QAM (Quadrature Amplitude Modulator/Modulation) converts video sent via IP (internet protocol) or otherwise, into

2760-461: The network commands and underlying (data) protocols. With advances in SONET and SDH chipsets, the traditional categories of network elements are no longer distinct. Nevertheless, as network architectures have remained relatively constant, even newer equipment (including multi-service provisioning platforms ) can be examined in light of the architectures they will support. Thus, there is value in viewing new, as well as traditional, equipment in terms of

2820-439: The older categories. Traditional regenerators terminate the section overhead, but not the line or path. Regenerators extend long-haul routes in a way similar to most regenerators, by converting an optical signal that has already traveled a long distance into electrical format and then retransmitting a regenerated high-power signal. Since the late 1990s, regenerators have been largely replaced by optical amplifiers . Also, some of

2880-431: The opposite direction. CMTSs typically carry only IP traffic. Traffic destined for the cable modem from the Internet, known as downstream traffic, is carried in IP packets encapsulated according to DOCSIS standard. These packets are carried on data streams that are typically modulated onto a TV channel using either 64-QAM or 256-QAM versions of quadrature amplitude modulation . Upstream data (data from cable modems to

2940-482: The other for uplink. In other words, there can be a pair of RF connectors for every service group, although it is possible to configure a network with different numbers of connectors that service a set of service groups, based on the number of downstream and upstream channels the cable modems in every service group use. Every connector has a finite number of channels it can carry, such as 16 channels per downstream connector, and 4 channels per upstream connector, depending on

3000-540: The outside plant, in stark contrast to conventional CMTSs or CCAPs which are installed at a service provider location. Synchronous optical networking Synchronous Optical Networking ( SONET ) and Synchronous Digital Hierarchy ( SDH ) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. The method

3060-488: The overall framing, as the data is clocked at a different rate than the frame rate. The protocol is made more complex by the decision to permit this padding at most levels of the multiplexing structure, but it improves all-around performance. The basic unit of framing in SDH is a STM-1 (Synchronous Transport Module, level 1), which operates at 155.520 megabits per second (Mbit/s). SONET refers to this basic unit as an STS-3c (Synchronous Transport Signal 3, concatenated). When

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3120-638: The path layer. It provides synchronization and multiplexing for multiple paths. It modifies overhead bits relating to quality control. The path layer is SONET's highest level layer. It takes data to be transmitted and transforms them into signals required by the line layer, and adds or modifies the path overhead bits for performance monitoring and protection switching. Network management systems are used to configure and monitor SDH and SONET equipment either locally or remotely. The systems consist of three essential parts, covered later in more detail: The main functions of network management thereby include: Consider

3180-622: The payload bandwidth, but path-overhead bandwidth is variable based on the types of cross-connects built across the optical system. Note that the data-rate progression starts at 155 Mbit/s and increases by multiples of four. The only exception is OC-24, which is standardized in ANSI T1.105, but not a SDH standard rate in ITU-T G.707. Other rates, such as OC-9, OC-18, OC-36, OC-96, and OC-1536, are defined but not commonly deployed; most are considered orphaned rates. The physical layer refers to

3240-405: The same term [REDACTED] This disambiguation page lists articles associated with the title CMTS . 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=CMTS&oldid=1027698421 " Category : Disambiguation pages Hidden categories: Short description

3300-450: The terms STS-1 and OC-1 are sometimes used interchangeably, though the OC designation refers to the signal in its optical form. It is therefore incorrect to say that an OC-3 contains 3 OC-1s: an OC-3 can be said to contain 3 STS-1s. The Synchronous Transport Module, level 1 (STM-1) frame is the basic transmission format for SDH—the first level of the synchronous digital hierarchy. The STM-1 frame

3360-515: The three parts defined above: This will often consist of software running on a Workstation covering a number of SDH/SONET network elements SONET equipment is often managed with the TL1 protocol. TL1 is a telecom language for managing and reconfiguring SONET network elements. The command language used by a SONET network element, such as TL1, must be carried by other management protocols, such as SNMP , CORBA , or XML . SDH has been mainly managed using

3420-406: The transmission system itself, which is used for a wide range of management functions, such as monitoring transmission quality, detecting failures, managing alarms, data communication channels, service channels, etc. The STM frame is continuous and is transmitted in a serial fashion: byte-by-byte, row-by-row. The transport overhead is used for signaling and measuring transmission error rates , and

3480-524: Was defined by Telcordia and American National Standards Institute (ANSI) standard T1.105. which define the set of transmission formats and transmission rates in the range above 51.840 Mbit/s. SDH differs from Plesiochronous Digital Hierarchy (PDH) in that the exact rates that are used to transport the data on SONET/SDH are tightly synchronized across the entire network, using atomic clocks . This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing

3540-605: Was developed to replace the plesiochronous digital hierarchy (PDH) system for transporting large amounts of telephone calls and data traffic over the same fiber without the problems of synchronization. SONET and SDH, which are essentially the same, were originally designed to transport circuit mode communications (e.g., DS1 , DS3 ) from a variety of different sources, but they were primarily designed to support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primary difficulty in doing this prior to SONET/SDH

3600-408: Was that the synchronization sources of these various circuits were different. This meant that each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within a single framing protocol. SONET/SDH is not a complete communications protocol in itself, but a transport protocol (not

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