Which Of The Following Describe The Channels And Data Transfer Rates

Digital telecommunications protocol for voice, video, and information

Asynchronous Transfer Fashion (ATM) is a telecommunications standard divers by ANSI and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic, including telephony (voice), data, and video signals in one network without the employ of separate overlay networks.^{[1] [two]} ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, every bit defined in the belatedly 1980s,^[3] and designed to integrate telecommunication networks. It tin can handle both traditional loftier-throughput data traffic and existent-time, low-latency content such every bit phonation and video. ATM provides functionality that uses features of circuit switching and packet switching networks. It uses asynchronous time-division multiplexing.^{[4] [v]}

In the OSI reference model data link layer (layer ii), the bones transfer units are generically chosen frames. In ATM these frames are of a fixed length (53 octets or bytes) and specifically called cells. This differs from approaches such as IP or Ethernet 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 commutation begins.^[5] These virtual circuits may be either permanent, i.e. defended connections that are usually preconfigured by the service provider, or switched, i.e. set up on a per-telephone call basis using signaling and disconnected when the telephone call is terminated.

The ATM network reference model approximately maps to the three lowest layers of the OSI model: physical layer, information link layer, and network layer.^[vi] ATM is a core protocol used in the SONET/SDH backbone of the public switched phone network (PSTN) and in the Integrated Services Digital Network (ISDN), but has largely been superseded in favor of next-generation networks based on Net Protocol (IP) technology, while wireless and mobile ATM never established a significant foothold.

IBM Turboways ATM 155 PCI network interface card

Marconi ForeRunnerLE 25 ATM PCI network interface card

Protocol architecture [edit]

If a spoken communication signal is reduced to packets, and it is forced to share a link with bursty data traffic (traffic with an abnormally large number of packets over a brief period of time, such as could occur during a large scale emergency and the cellular network has become oversubscribed) and so no matter how small the speech packets could exist made, they would always come across total-size data packets. Under normal queuing conditions the cells might experience maximum queuing delays. To avoid this issue, all ATM packets, or "cells," are the same small size. In addition, the fixed cell structure means that ATM tin can be readily switched by hardware without the inherent delays introduced by software switched and routed frames.

Thus, the designers of ATM utilized small data cells to reduce jitter (big changes in the packet circular trip fourth dimension or one-mode time, in this case) in the multiplexing of data streams. Reduction of jitter (and also end-to-terminate round-trip delays) is peculiarly of import when carrying phonation traffic, because the conversion of digitized voice into an counterpart sound indicate is an inherently real-time procedure, and to do a practiced job, the decoder that does this needs an evenly spaced (in time) stream of data items. If the next data item is not available when information technology is needed, the codec has no option but to produce silence or approximate – and if the data is late, it is useless, because the fourth dimension period when it should have been converted to a bespeak has already passed.

At the time of the design of ATM, 155 Mbit/s synchronous digital bureaucracy (SDH) with 135 Mbit/s payload was considered a fast optical network link, and many plesiochronous digital bureaucracy (PDH) links in the digital network were considerably slower, ranging from 1.544 to 45 Mbit/s in the Usa, and two to 34 Mbit/south in Europe.

At 155 Mbit/s, a typical full-length ane,500 byte (12,000-bit) data packet, sufficient to contain a maximum-sized IP packet for Ethernet, would take 77.42 µs to transmit. In a lower-speed link, such as a ane.544 Mbit/s T1 line, the same packet would take up to 7.eight milliseconds.

A queuing delay induced by several such data packets might exceed the figure of vii.viii ms several times over, in addition to whatever packet generation delay in the shorter speech packet. This was considered unacceptable for speech traffic, which needs to have low jitter in the data stream being fed into the codec if it is to produce skilful-quality sound. A packet voice arrangement tin can produce this low jitter in a number of ways:

• Using a playback buffer between the network and the codec, one big plenty to tide the codec over well-nigh all the jitter in the data. This allows smoothing out the jitter, but the delay introduced by passage through the buffer require echo cancellers even in local networks; this was considered also expensive at the time. Too, it increased the delay across the channel, and made conversation difficult over high-delay channels.
• Using a system that inherently provides low jitter (and minimal overall delay) to traffic that needs it.
• Operate on a one:1 user ground (i.e., a dedicated piping).

The design of ATM aimed for a low-jitter network interface. However, "cells" were introduced into the design to provide short queuing delays while standing to support datagram traffic. ATM bankrupt upward all packets, information, and voice streams into 48-byte chunks, adding a v-byte routing header to each ane so that they could be reassembled later. The pick of 48 bytes was political rather than technical.^[7] When 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 adept compromise in larger payloads optimized for data transmission and shorter payloads optimized for real-time applications similar phonation; parties from Europe wanted 32-byte payloads because the small size (and therefore brusk transmission times) simplify phonation applications with respect to echo cancellation. Most of the European parties eventually came around to the arguments made by the Americans, but French republic and a few others held out for a shorter prison cell length. With 32 bytes, France would have been able to implement an ATM-based voice network with calls from ane end of France to the other requiring no echo counterfoil. 48 bytes (plus 5 header bytes = 53) was chosen as a compromise betwixt the 2 sides. 5-byte headers were chosen because it was thought that 10% of the payload was the maximum price to pay for routing information.^[three] ATM multiplexed these 53-byte cells instead of packets which reduced worst-case cell contention jitter by a factor of most thirty, reducing the need for echo cancellers.

Jail cell structure [edit]

An ATM prison cell consists of a five-byte header and a 48-byte payload. The payload size of 48 bytes was chosen equally described above.

ATM defines two different cell formats: user–network interface (UNI) and network–network interface (NNI). Virtually ATM links employ UNI jail cell format.

Diagram of a UNI ATM cell 7 4 3 0 GFC VPI VPI VCI VCI VCI PT CLP HEC Payload and padding if necessary (48 bytes)

Diagram of an NNI ATM cell 7 4 3 0 VPI VPI VCI VCI VCI PT CLP HEC Payload and padding if necessary (48 bytes)

GFC = The generic catamenia control (GFC) field is a iv-bit field that was originally added to support the connection of ATM networks to shared access networks such as a distributed queue dual bus (DQDB) ring. The GFC field was designed to give the User-Network Interface (UNI) four bits in which to negotiate multiplexing and flow control amongst the cells of various ATM connections. However, the employ and exact values of the GFC field have not been standardized, and the field is ever set to 0000.^[8]

VPI = Virtual path identifier (8 bits UNI, or 12 bits NNI)

VCI = Virtual channel identifier (16 $.25)

PT = Payload type (3 $.25)

PT bit 3 (msbit): Network direction cell. If 0, user data jail cell and the following use:

PT chip 2: Explicit forward congestion indication (EFCI); 1 = network congestion experienced

PT scrap ane (lsbit): ATM user-to-user (AAU) bit. Used by AAL5 to betoken parcel boundaries.

CLP = Cell loss priority (1-bit)

HEC = Header mistake control (8-bit CRC, polynomial = X^viii + 10^two + X + one)

ATM uses the PT field to designate diverse special kinds of cells for operations, administration and management (OAM) purposes, and to delineate packet boundaries in some ATM adaptation layers (AAL). If the most significant bit (MSB) of the PT field is 0, this is a user data prison cell, and the other ii bits are used to betoken network congestion and every bit a full general purpose header scrap available for ATM adaptation layers. If the MSB is ane, this is a direction cell, and the other two $.25 indicate the type. (Network direction segment, network management end-to-end, resource direction, and reserved for futurity apply.)

Several ATM link protocols use the HEC field to bulldoze a CRC-based framing algorithm, which allows locating the ATM cells with no overhead across what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and discover multi-bit header errors. When multi-fleck header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found.

A UNI cell reserves the GFC field for a local menstruation command/submultiplexing system between users. This was intended to let several terminals to share a single network connection, in the same manner that 2 Integrated Services Digital Network (ISDN) phones can share a single basic rate ISDN connection. All four GFC bits must exist zero past default.

The NNI jail cell format replicates the UNI format well-nigh exactly, except that the four-bit GFC field is re-allocated to the VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost two¹² VPs of up to about two^xvi VCs each (in practice some of the VP and VC numbers are reserved).

Service types [edit]

ATM supports unlike types of services via AALs. Standardized AALs include AAL1, AAL2, and AAL5, and the rarely used^[ix] AAL3 and AAL4. AAL1 is used for constant fleck charge per unit (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 is in employ for a given prison cell is non encoded in the cell. Instead, it is negotiated by or configured at the endpoints on a per-virtual-connection ground.

Following the initial design of ATM, networks take become much faster. A 1500 byte (12000-bit) full-size Ethernet frame takes only 1.2 µs to transmit on a x Gbit/s network, reducing the demand for small cells to reduce jitter due to contention. The increased link speeds by themselves do not alleviate jitter due to queuing. Additionally, the hardware for implementing the service accommodation for IP packets is expensive at very high speeds.

ATM provides a useful power to comport multiple logical circuits on a single physical or virtual medium, although other techniques be, such equally Multi-link PPP, Ethernet VLANs, and multi-protocol support over SONET.

Virtual circuits [edit]

A network must institute a connection before two parties can send cells to each other. In ATM this is called a virtual excursion (VC). It can be a permanent virtual circuit (PVC), which is created administratively on the end points, or a switched virtual circuit (SVC), which is created every bit needed by the communicating parties. SVC creation is managed by signaling, in which the requesting political 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 and so performed by the network to confirm that the requested resources are available and that a route exists for the connection.

Motivation [edit]

ATM operates as a aqueduct-based ship 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 xvi-bit virtual aqueduct identifier (VCI) pair defined in its header.^[10] The VCI, together with the VPI, is used to place the side by side destination of a jail 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 the user-network interface (on the edge of the network), or if it is sent on the network-network interface (within the network).

As these cells traverse an ATM network, switching takes identify by changing the VPI/VCI values (label swapping). Although the VPI/VCI values are not necessarily consequent from i end of the connection to the other, the concept of a excursion is consistent (unlike IP, where whatsoever given packet could get to its destination past a unlike route than the others).^[11] ATM switches use the VPI/VCI fields to identify the virtual channel link (VCL) of the adjacent network that a jail cell needs to transit on its way to its last destination. The part of the VCI is similar to that of the data link connexion identifier (DLCI) in frame relay and the logical channel number and logical aqueduct group number in X.25.

Another advantage of the employ of virtual circuits comes with the ability to utilise them equally a multiplexing layer, allowing different services (such equally vocalism, frame relay, due north* 64 channels, IP). The VPI is useful for reducing the switching table of some virtual circuits which take common paths.^[12]

Types [edit]

ATM tin 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 the circuit is equanimous of a series of segments, one for each pair of interfaces through which it passes.

PVPs and PVCs, though conceptually simple, require meaning effort in large networks. They also exercise 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 past specifying the characteristics of the circuit (the service "contract") and the two endpoints.

ATM networks create and remove switched virtual circuits (SVCs) on demand when requested past an stop piece of equipment. One awarding for SVCs is to carry private telephone calls when a network of telephone switches are inter-continued using ATM. SVCs were too used in attempts to supplant local area networks with ATM.

Routing [edit]

Nearly ATM networks supporting SPVPs, SPVCs, and SVCs use the Private Network Node Interface or the Private Network-to-Network Interface (PNNI) protocol to share topology information betwixt 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 access control (CAC) algorithm which determines the availability of sufficient bandwidth on a proposed route through a network in society to satisfy the service requirements of a VC or VP.

Traffic technology [edit]

Another key ATM concept involves the traffic contract. When an ATM circuit is set each switch on the circuit is informed of the traffic form of the connexion.

ATM traffic contracts form function of the machinery by which "quality of service" (QoS) is ensured. There are four basic types (and several variants) which each have a set of parameters describing the connection.

1. CBR - Constant bit rate: a Height Prison cell Rate (PCR) is specified, which is constant.
2. VBR - Variable flake rate: an average or Sustainable Cell Rate (SCR) is specified, which can height at a certain level, a PCR, for a maximum interval before beingness problematic.
3. ABR - Bachelor flake rate: a minimum guaranteed charge per unit is specified.
4. UBR - Unspecified bit rate: traffic is allocated to all remaining manual chapters.

VBR has real-fourth dimension and not-real-time variants, and serves for "bursty" traffic. Non-existent-fourth dimension 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 fourth dimension.

Traffic policing [edit]

To maintain network performance, networks may utilise traffic policing to virtual circuits to limit them to their traffic contracts at the entry points to the network, i.east. the user–network interfaces (UNIs) and network-to-network interfaces (NNIs): usage/network parameter control (UPC and NPC).^[13] The reference model given by the ITU-T and ATM Forum for UPC and NPC is the generic cell rate algorithm (GCRA),^{[14] [15]} which is a version of the leaky bucket algorithm. CBR traffic will normally exist policed to a PCR and CDVt alone, whereas VBR traffic will normally be policed using a dual leaky bucket controller to a PCR and CDVt and an SCR and Maximum Burst Size (MBS). The MBS will usually be the packet (SAR-SDU) size for the VBR VC in cells.

If the traffic on a virtual circuit is exceeding its traffic contract, as adamant by the GCRA, the network can either drop the cells or mark the Cell Loss Priority (CLP) bit (to place a cell as potentially redundant). Basic policing works on a prison cell past prison cell basis, but this is sub-optimal for encapsulated bundle traffic (every bit discarding a single prison cell will invalidate the whole packet). Equally a consequence, schemes such as fractional packet discard (PPD) and early on packet discard (EPD) have been created that will discard a whole serial of cells until the adjacent packet starts. This reduces the number of useless cells in the network, saving bandwidth for full packets. EPD and PPD piece of work with AAL5 connections equally they use the end of packet mark: the ATM user-to-ATM user (AUU) indication bit in the payload-type field of the header, which is set up in the terminal jail cell of a SAR-SDU.

Traffic shaping [edit]

Traffic shaping usually takes identify in the network interface card (NIC) in user equipment, and attempts to ensure that the cell period on a VC will meet its traffic contract, i.eastward. cells will not be dropped or reduced in priority at the UNI. Since 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.

Reference model [edit]

The ATM network reference model approximately maps to the three lowest layers of the OSI reference model. It specifies the following layers:^[16]

• At the physical network level, ATM specifies a layer that is equivalent to the OSI concrete layer.
• The ATM layer 2 roughly corresponds to the OSI data link layer.
• The OSI network layer is implemented equally the ATM accommodation layer (AAL).

Deployment [edit]

ATM became popular with telephone companies and many computer makers in the 1990s. However, even by the stop of the decade, the meliorate price/operation of Cyberspace Protocol-based products was competing with ATM technology for integrating real-time and bursty network traffic.^[17] Companies such every bit FORE Systems focused on ATM products, while other large vendors such every bit Cisco Systems provided ATM as an option.^[xviii] After the flare-up of the dot-com chimera, some all the same predicted that "ATM is going to boss".^[nineteen] Withal, in 2005 the ATM Forum, which had been the merchandise system promoting the applied science, merged with groups promoting other technologies, and somewhen became the Broadband Forum.^[20]

Wireless or mobile ATM [edit]

Wireless ATM,^[21] 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 the core network, known equally "crossover switch",^[22] which is similar to the MSC (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, Bong Labs and NEC^[23] research labs worked actively in this field. Andy Hopper from Cambridge Academy Figurer Laboratory also worked in this area.^[24] There 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.

Versions [edit]

This section needs expansion. You can assist by adding to it. (May 2021)

One version of ATM is ATM25, where data is transferred at 25 Mbit/s.^[25]

See also [edit]

• VoATM

References [edit]

1. ^ Telcordia Technologies, Telcordia Notes on the Network, Publication SR-2275 (October 2000)
2. ^ ATM Forum, The User Network Interface (UNI), v. 3.one, ISBN 0-13-393828-X, Prentice Hall PTR, 1995, page 2.
3. ^ ^{a b} Ayanoglu, Ender; Akar, Nail (25 May 2002). "B-ISDN (Broadband Integrated Services Digital Network)". Center for Pervasive Communications and Computing, UC Irvine. Retrieved 3 June 2011.
4. ^ "Recommendation I.150, B-ISDN Asynchronous Transfer Mode functional characteristics". ITU.
5. ^ ^{a b} McDysan (1999), p. 287.
6. ^ McDysan, David E. and Spohn, Darrel L., ATM : Theory and Application, ISBN 0-07-060362-6, McGraw-Hill series on computer communications, 1995, page 563.
7. ^ D. Stevenson, "Electropolitical Correctness and High-Speed Networking, or, Why ATM is similar a Nose", Proceedings of TriCom '93, Apr 1993.
8. ^ "ATM Jail cell Structure". Retrieved 13 June 2017.
9. ^ "A Brief Overview of ATM: Protocol Layers, LAN Emulation, and Traffic Direction". www.cse.wustl.edu . Retrieved 21 July 2021.
10. ^ Cisco Systems Guide to ATM Technology (2000). Section "Performance of an ATM Switch". Retrieved ii June 2011.
11. ^ Cisco Systems Guide to ATM Technology (2000). Section "ATM Prison cell Header Formats". Retrieved 2 June 2011.
12. ^ "What is VPI and VCI settings of broadband connections?". Tech Line Info. Sujith. Retrieved one July 2010.
13. ^ ITU-T, Traffic control and congestion command in B ISDN, Recommendation I.371, International Telecommunication Wedlock, 2004, page 17
14. ^ ITU-T, Traffic control and congestion control in B ISDN, Recommendation I.371, International Telecommunication Union, 2004, Annex A, folio 87.
15. ^ ATM Forum, The User Network Interface (UNI), 5. 3.ane, ISBN 0-thirteen-393828-X, Prentice Hall PTR, 1995.
16. ^ "Guide to ATM Technology for the Catalyst 8540 MSR, Goad 8510 MSR, and LightStream 1010 ATM Switch Routers" (PDF). Customer Gild Number: Doc-786275. Cisco Systems. 2000. Retrieved 19 July 2011.
17. ^ Steve Steinberg (October 1996). "Netheads vs Bellheads". Wired. Vol. 4, no. 10. Retrieved 24 September 2011.
18. ^ "What'south in store for FORE?". Network World. xvi September 1996. p. 12. Retrieved 24 September 2011.
19. ^ "Optical Ethernet firms dauntless stormy industry seas". Network World. 7 May 2001. p. fourteen. Retrieved 24 September 2011.
20. ^ "About the Broadband Forum: Forum History". Archived from the original on 9 October 2011. Retrieved 24 September 2011.
21. ^ Wireless ATM
22. ^ Book on Wireless ATM Networks - Chai Keong Toh, Kluwer Academic Press 1997
23. ^ WATMnet: a prototype wireless ATM system for multimedia personal communication, D. Raychaudhuri,at.al
24. ^ "Cambridge Mobile ATM work". Archived from the original on 25 June 2015. Retrieved 10 June 2013.
25. ^ Inc, IDG Network Globe (26 March 2001). Network Globe. IDG Network World Inc.

• Black, Uyless D. (1998). ATM—Volume Three: Internetworking with ATM . Toronto: Prentice Hall. ISBN0-xiii-784182-5.
• De Prycker, Martin (1993). Asynchronous Transfer Manner. Solutions for Broadband ISDN. Prentice Hall.
• Joel, Amos East., Jr. (1993). Asynchronous Transfer Way. IEEE Press.
• Golway, Tom (1997). Planning and Managing ATM Network . New York: Manning. ISBN978-0-13-262189-2.
• McDysan, David East.; Darren 50. Spohn (1999). ATM Theory and Applications. Montreal: McGraw-Hill. ISBN0-07-045346-2.
• Neelakanta, P. S. (2000). A Textbook on ATM Telecommunications, Principles and implementation. CRC Press. ISBN0-8493-1805-X.
• ATM Jail cell formats- Cisco Systems
• "Asynchronous Transfer Mode (ATM)". Cisco Systems. Archived from the original on 29 October 2007.

External links [edit]

• "ATM forum". Archived from the original on ane July 2005.
• ATM Info and resources
• ATM ChipWeb - Chip and NIC database
• A tutorial from Juniper web site
• ATM Tutorial
• "Asynchronous Transfer Mode Switching". DocuWiki. Cisco Systems. Archived from the original on 31 Jan 2018.

Which Of The Following Describe The Channels And Data Transfer Rates,

Source: https://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode

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