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53-424: The ATM Forum was founded in 1991 to be the industry consortium to promote Asynchronous Transfer Mode technology used in telecommunication networks; the founding president and chairman was Fred Sammartino of Sun Microsystems . It was a non-profit international organization. The ATM Forum created over 200 implementation agreements. In 1996 ATM technology stabilized with the "Anchorage Accord", which established

106-410: A carrier wave or infrared light . The flow of data is managed with bit synchronization in synchronous serial communication or start-stop signalling and flow control in asynchronous serial communication . Sharing of the transmission medium among multiple network participants can be handled by simple circuit switching or multiplexing . More complex medium access control protocols for sharing

159-608: A 5-byte header and a 48-byte payload. ATM defines two different cell formats: user–network interface (UNI) and network–network interface (NNI). Most ATM links use UNI cell format. Diagram of a UNI ATM cell Payload and padding if necessary (48 bytes) Diagram of an NNI ATM cell Payload and padding if necessary (48 bytes) ATM uses the PT field to designate various special kinds of cells for operations, administration and management (OAM) purposes, and to delineate packet boundaries in some ATM adaptation layers (AAL). If

212-435: A cell-by-cell basis, but this is sub-optimal for encapsulated packet traffic as discarding a single cell will invalidate a packet's worth of cells. As a result, schemes such as partial packet discard (PPD) and early packet discard (EPD) have been developed to discard a whole packet's cells. This reduces the number of useless cells in the network, saving bandwidth for full packets. EPD and PPD work with AAL5 connections as they use

265-598: A dual leaky bucket controller to a PCR and CDVT and an SCR and maximum burst size (MBS). The MBS will normally be the packet ( SAR - SDU ) size for the VBR VC in cells. If the traffic on a virtual circuit exceeds its traffic contract, as determined by the GCRA, the network can either drop the cells or set the Cell Loss Priority (CLP) bit, allowing the cells to be dropped at a congestion point. Basic policing works on

318-440: A fixed length (53 octets ) called cells . This differs from approaches such as Internet Protocol (IP) (OSI layer 3) or Ethernet (also layer 2) that use variable-sized packets or frames. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the data exchange begins. These virtual circuits may be either permanent (dedicated connections that are usually preconfigured by

371-436: A low-jitter network interface. Cells were introduced to provide short queuing delays while continuing to support datagram traffic. ATM broke up all data packets and voice streams into 48-byte pieces, adding a 5-byte routing header to each one so that they could be reassembled later. Being 1/30th the size reduced cell contention jitter by the same factor of 30. The choice of 48 bytes was political rather than technical. When

424-629: A network using Open Systems Interconnection (OSI) architecture, the physical signaling sublayer is the portion of the physical layer that The Internet protocol suite , as defined in RFC 1122 and RFC 1123 , is a high-level networking description used for the Internet and similar networks. It does not define a layer that deals exclusively with hardware-level specifications and interfaces, as this model does not concern itself directly with physical interfaces. The major functions and services performed by

477-425: A proposed route through a network in order to satisfy the service requirements of a VC or VP. Another key ATM concept involves the traffic contract . When an ATM circuit is set up each switch on the circuit is informed of the traffic class of the connection. ATM traffic contracts form part of the mechanism by which quality of service (QoS) is ensured. There are four basic types (and several variants) which each have

530-452: A set of parameters describing the connection. VBR has real-time and non-real-time variants, and serves for bursty traffic. Non-real-time is sometimes abbreviated to vbr-nrt. Most traffic classes also introduce the concept of cell-delay variation tolerance (CDVT), which defines the clumping of cells in time. To maintain network performance, networks may apply traffic policing to virtual circuits to limit them to their traffic contracts at

583-606: A specific physical layer protocol, for example M-PHY . Modular transceivers for fiber-optic communication (like the SFP family) complement a PHY chip and form the PMD sublayer. The Ethernet PHY is a component that operates at the physical layer of the OSI network model . It implements the physical layer portion of the Ethernet. Its purpose is to provide analog signal physical access to

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636-412: A useful ability to carry multiple logical circuits on a single physical or virtual medium, although other techniques exist, such as Multi-link PPP , Ethernet VLANs , VxLAN , MPLS , and multi-protocol support over SONET . An ATM network must establish a connection before two parties can send cells to each other. This is called a virtual circuit (VC). It can be a permanent virtual circuit (PVC), which

689-402: Is created administratively on the end points, or a switched virtual circuit (SVC), which is created as needed by the communicating parties. SVC creation is managed by signaling , in which the requesting party indicates the address of the receiving party, the type of service requested, and whatever traffic parameters may be applicable to the selected service. Call admission is then performed by

742-551: Is going to dominate". However, in 2005 the ATM Forum , which had been the trade organization promoting the technology, merged with groups promoting other technologies, and eventually became the Broadband Forum . Wireless ATM, or mobile ATM, consists of an ATM core network with a wireless access network. ATM cells are transmitted from base stations to mobile terminals. Mobility functions are performed at an ATM switch in

795-508: Is in use for a given cell is not encoded in the cell. Instead, it is negotiated by or configured at the endpoints on a per-virtual-connection basis. Following the initial design of ATM, networks have become much faster. A 1500 byte (12000-bit) full-size Ethernet frame takes only 1.2 μs to transmit on a 10 Gbit/s network, reducing the motivation for small cells to reduce jitter due to contention. The increased link speeds by themselves do not eliminate jitter due to queuing. ATM provides

848-450: Is responsible for electromagnetic compatibility including electromagnetic spectrum frequency allocation and specification of signal strength , analog bandwidth , etc. The transmission medium may be electrical or optical over optical fiber or a wireless communication link such as free-space optical communication or radio . Line coding is used to convert data into a pattern of electrical fluctuations which may be modulated onto

901-410: Is the link layer 's job. Similarly, Wake-on-LAN and Boot ROM functionality is implemented in the network interface card (NIC), which may have PHY, MAC, and other functionality integrated into one chip or as separate chips. Common Ethernet interfaces include fiber or two to four copper pairs for data communication. However, there now exists a new interface, called Single Pair Ethernet (SPE), which

954-650: The CCITT (now ITU-T) was standardizing ATM, parties from the United States wanted a 64-byte payload because this was felt to be a good compromise between larger payloads optimized for data transmission and shorter payloads optimized for real-time applications like voice. Parties from Europe wanted 32-byte payloads because the small size (4 ms of voice data) would avoid the need for echo cancellation on domestic voice calls. The United States, due to its larger size, already had echo cancellers widely deployed. Most of

1007-420: The OSI model in a network interface controller . A PHY connects a link layer device (often called MAC as an acronym for medium access control ) to a physical medium such as an optical fiber or copper cable . A PHY device typically includes both physical coding sublayer (PCS) and physical medium dependent (PMD) layer functionality. -PHY may also be used as a suffix to form a short name referencing

1060-528: The Private Network-to-Network Interface (PNNI) protocol to share topology information between switches and select a route through a network. PNNI is a link-state routing protocol like OSPF and IS-IS . PNNI also includes a very powerful route summarization mechanism to allow construction of very large networks, as well as a call admission control (CAC) algorithm which determines the availability of sufficient bandwidth on

1113-647: The electronic circuit transmission technologies of a network. It is a fundamental layer underlying the higher level functions in a network, and can be implemented through a great number of different hardware technologies with widely varying characteristics. Within the semantics of the OSI model, the physical layer translates logical communications requests from the data link layer into hardware-specific operations to cause transmission or reception of electronic (or other) signals. The physical layer supports higher layers responsible for generation of logical data packets . In

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1166-493: The most significant bit (MSB) of the PT field is 0, this is a user data cell, and the other two bits are used to indicate network congestion and as a general-purpose header bit available for ATM adaptation layers. If the MSB is 1, this is a management cell, and the other two bits indicate the type: network management segment, network management end-to-end, resource management, and reserved for future use. Several ATM link protocols use

1219-532: The public switched telephone network and in the Integrated Services Digital Network (ISDN) but has largely been superseded in favor of next-generation networks based on IP technology. Wireless and mobile ATM never established a significant foothold. To minimize queuing delay and packet delay variation (PDV), all ATM cells are the same small size. Reduction of PDV is particularly important when carrying voice traffic, because

1272-422: The 1990s. However, even by the end of the decade, the better price–performance ratio of Internet Protocol -based products was competing with ATM technology for integrating real-time and bursty network traffic. Companies such as FORE Systems focused on ATM products, while other large vendors such as Cisco Systems provided ATM as an option. After the burst of the dot-com bubble , some still predicted that "ATM

1325-582: The European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length. 48 bytes was chosen as a compromise, despite having all the disadvantages of both proposals and the additional inconvenience of not being a power of two in size. 5-byte headers were chosen because it was thought that 10% of the payload was the maximum price to pay for routing information. An ATM cell consists of

1378-505: The GFC field for a local flow control and sub-multiplexing system between users. This was intended to allow several terminals to share a single network connection in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default. The NNI cell format replicates the UNI format almost exactly, except that the 4-bit GFC field is re-allocated to

1431-510: The HEC field to drive a CRC-based framing algorithm, which allows locating the ATM cells with no overhead beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found. A UNI cell reserves

1484-868: The MFA to form the MFA Forum, which was renamed to be the IP/MPLS Forum. In May 2009 the IP/MPLS Forum merged with the Broadband Forum . A widely adopted specification to emerge from the ATM Forum was the Circuit Emulation Service (CES) specification. This specification defined a method of creating a service out of mapping TDM DS0 and DS1 /E1 Plesiochronous Digital Hierarchy (PDH) signals into Asynchronous Transfer Mode (ATM) cells. It also supported J2 and DS-3 signals. The service

1537-449: The OSI abstraction can be brought to bear on all forms of device interconnection in data communications and computational electronics. The physical layer defines the means of transmitting a stream of raw bits over a physical data link connecting network nodes . The bitstream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a transmission medium . The physical layer consists of

1590-547: The US, and 2 to 34 Mbit/s in Europe. At 155 Mbit/s, a typical full-length 1,500 byte Ethernet frame would take 77.42  μs to transmit. On a lower-speed 1.544 Mbit/s T1 line , the same packet would take up to 7.8 milliseconds. A queuing delay induced by several such data packets might exceed the figure of 7.8 ms several times over. This was considered unacceptable for speech traffic. The design of ATM aimed for

1643-743: The VCI is similar to that of the data link connection identifier (DLCI) in Frame Relay and the logical channel number and logical channel group number in X.25 . Another advantage of the use of virtual circuits comes with the ability to use them as a multiplexing layer, allowing different services (such as voice, Frame Relay, IP). The VPI is useful for reducing the switching table of some virtual circuits which have common paths. ATM can build virtual circuits and virtual paths either statically or dynamically. Static circuits (permanent virtual circuits or PVCs) or paths (permanent virtual paths or PVPs) require that

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1696-550: The VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 2 VPs of up to almost 2 VCs each. ATM supports different types of services via AALs. Standardized AALs include AAL1, AAL2, and AAL5, and the rarely used AAL3 and AAL4. AAL1 is used for constant bit rate (CBR) services and circuit emulation. Synchronization is also maintained at AAL1. AAL2 through AAL4 are used for variable bitrate (VBR) services, and AAL5 for data. Which AAL

1749-407: The VPI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. The length of the VPI varies according to whether the cell is sent on a user-network interface (at the edge of the network), or if it is sent on a network-network interface (inside the network). As these cells traverse an ATM network, switching takes place by changing

1802-521: The VPI/VCI values (label swapping). Although the VPI/VCI values are not necessarily consistent from one end of the connection to the other, the concept of a circuit is consistent (unlike IP, where any given packet could get to its destination by a different route than the others). ATM switches use the VPI/VCI fields to identify the virtual channel link (VCL) of the next network that a cell needs to transit on its way to its final destination. The function of

1855-458: The baseline of ATM implementations. While ATM did not live up to every expectation, it remained an important core network technology. The Frame Relay Forum (promoting Frame Relay ) also started in 1991. The MPLS Forum (which supported Multiprotocol Label Switching had begun in 2000. Those two merged in 2003 to become the MPLS and Frame Relay Alliance (MFA). In 2005, the ATM Forum joined forces with

1908-435: The circuit (the service contract ) and the two endpoints. ATM networks create and remove switched virtual circuits (SVCs) on demand when requested by an end station . One application for SVCs is to carry individual telephone calls when a network of telephone switches are interconnected using ATM. SVCs were also used in attempts to replace local area networks with ATM. Most ATM networks supporting SPVPs, SPVCs, and SVCs use

1961-409: The circuit is composed of a series of segments, one for each pair of interfaces through which it passes. PVPs and PVCs, though conceptually simple, require significant effort in large networks. They also do not support the re-routing of service in the event of a failure. Dynamically built PVPs (soft PVPs or SPVPs) and PVCs (soft PVCs or SPVCs), in contrast, are built by specifying the characteristics of

2014-454: The conversion of digitized voice into an analog audio signal is an inherently real-time process. The decoder needs an evenly spaced stream of data items. At the time of the design of ATM, 155 Mbit/s synchronous digital hierarchy with 135 Mbit/s payload was considered a fast optical network link, and many plesiochronous digital hierarchy links in the digital network were considerably slower, ranging from 1.544 to 45 Mbit/s in

2067-459: The core network, known as a crossover switch , which is similar to the mobile switching center of GSM networks. The advantage of wireless ATM is its high bandwidth and high-speed handoffs done at layer 2. In the early 1990s, Bell Labs and NEC research labs worked actively in this field. Andy Hopper from the University of Cambridge Computer Laboratory also worked in this area. There

2120-413: The end of packet marker: the ATM user-to-ATM user (AUU) indication bit in the payload-type field of the header, which is set in the last cell of a SAR-SDU. Traffic shaping usually takes place in the network interface controller (NIC) in user equipment, and attempts to ensure that the cell flow on a VC will meet its traffic contract, i.e. cells will not be dropped or reduced in priority at the UNI. Since

2173-506: The entry points to the network, i.e. the user–network interfaces (UNIs) and network-to-network interfaces (NNIs) using usage/network parameter control (UPC and NPC). The reference model given by the ITU-T and ATM Forum for UPC and NPC is the generic cell rate algorithm (GCRA), which is a version of the leaky bucket algorithm . CBR traffic will normally be policed to a PCR and CDVT alone, whereas VBR traffic will normally be policed using

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2226-554: The link. It is usually interfaced with a media-independent interface (MII) to a MAC chip in a microcontroller or another system that takes care of the higher layer functions. More specifically, the Ethernet PHY is a chip that implements the hardware send and receive function of Ethernet frames ; it interfaces between the analog domain of Ethernet's line modulation and the digital domain of link-layer packet signaling . The PHY usually does not handle MAC addressing, as that

2279-415: The network to confirm that the requested resources are available and that a route exists for the connection. ATM operates as a channel-based transport layer, using VCs. This is encompassed in the concept of the virtual paths (VP) and virtual channels. Every ATM cell has an 8- or 12-bit virtual path identifier (VPI) and 16-bit virtual channel identifier (VCI) pair defined in its header. The VCI, together with

2332-419: The physical layer are: The physical layer performs bit-by-bit or symbol-by-symbol data delivery over a physical transmission medium . It provides a standardized interface to the transmission medium, including a mechanical specification of electrical connectors and cables , for example maximum cable length, an electrical specification of transmission line signal level and impedance . The physical layer

2385-492: The physical layer include: bit rate ; point-to-point , multipoint or point-to-multipoint line configuration; physical network topology , for example bus , ring , mesh or star network ; serial or parallel communication; simplex , half duplex or full duplex transmission mode; and autonegotiation A PHY , an abbreviation for physical layer , is an electronic circuit , usually implemented as an integrated circuit , required to implement physical layer functions of

2438-607: The physical layer is commonly implemented by dedicated PHY chip or, in electronic design automation (EDA), by a design block . In mobile computing , the MIPI Alliance *-PHY family of interconnect protocols are widely used. Historically, the OSI model is closely associated with internetworking, such as the Internet protocol suite and Ethernet , which were developed in the same era, along similar lines, though with somewhat different abstractions. Beyond internetworking,

2491-426: The reference model given for traffic policing in the network is the GCRA, this algorithm is normally used for shaping as well, and single and dual leaky bucket implementations may be used as appropriate. The ATM network reference model approximately maps to the three lowest layers of the OSI reference model . It specifies the following layers: ATM became popular with telephone companies and many computer makers in

2544-408: The service provider), or switched (set up on a per-call basis using signaling and disconnected when the call is terminated). The ATM network reference model approximately maps to the three lowest layers of the OSI model: physical layer , data link layer, and network layer . ATM is a core protocol used in the synchronous optical networking and synchronous digital hierarchy (SONET/SDH) backbone of

2597-468: The transmission medium may use carrier sense and collision detection such as in Ethernet's Carrier-sense multiple access with collision detection (CSMA/CD). To optimize reliability and efficiency, signal processing techniques such as equalization , training sequences and pulse shaping may be used. Error correction codes and techniques including forward error correction may be applied to further improve reliability. Other topics associated with

2650-408: Was a wireless ATM forum formed to standardize the technology behind wireless ATM networks. The forum was supported by several telecommunication companies, including NEC, Fujitsu and AT&T . Mobile ATM aimed to provide high-speed multimedia communications technology, capable of delivering broadband mobile communications beyond that of GSM and WLANs. Physical layer At the electrical layer,

2703-762: Was built around the ATM Adaption Layer 1 specification from the ITU . The 1.0 version was approved about 1995 and the 2.0 version was approved in January 1997. Asynchronous Transfer Mode Asynchronous Transfer Mode ( ATM ) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital transmission of multiple types of traffic. ATM

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2756-576: Was developed to meet the needs of the Broadband Integrated Services Digital Network as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time , low-latency content such as telephony (voice) and video. ATM provides functionality that uses features of circuit switching and packet switching networks by using asynchronous time-division multiplexing . ATM

2809-494: Was seen in the 1990s as a competitor to Ethernet and networks carrying IP traffic as, unlike Ethernet, it was faster and designed with quality-of-service in mind, but it fell out of favor once Ethernet reached speeds of 1 gigabits per second. In the Open Systems Interconnection (OSI) reference model data link layer (layer 2), the basic transfer units are called frames . In ATM these frames are of

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