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adjust the amount of bandwidth available to the user. UBR generally is used for applications that are very tolerant of delay and cell loss. UBR has enjoyed success in the
Internet LAN and WAN environments for store-and-forward traffic, such as file-transfers and e-mail. Similar to the way in which upper-layer protocols react to ABR’s traffic-control mechanisms, TCP/IP and other LAN-based traffic protocols can modify their transmission behaviour in response to latency or cell loss in the ATM network.
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a static amount of bandwidth continuously available for the life-time of the connection. The amount of bandwidth is characterized by a Peak Cell Rate (PCR). These applications include services such as video conferencing, telephony (voice services) or any type of on-demand service, such as interactive voice and audio. For telephony and native voice applications CBR provides low-latency traffic with predictable delivery characteristics, and is therefore typically used for circuit emulation.
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provides a best-effort transport service, in which flow-control mechanisms are used to adjust the amount of bandwidth available to the traffic originator. The ABR service category is designed primarily for any type of traffic that is not time sensitive and expects no guarantees of service. ABR service generally is considered preferable for TCP/IP traffic, as well as other LAN-based protocols, that can modify its transmission behaviour in response to the ABR’s rate-control mechanics.
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Sources that use rt-VBR connections are expected to transmit at a rate that varies with time (for example, traffic that can be considered bursty). Real-time VBR connections can be characterized by a Peak Cell Rate (PCR), Sustained Cell Rate (SCR), and
Maximum Burst Size (MBS). Cells delayed beyond the value specified by the maximum CTD (Cell Transfer Delay) are assumed to be of significantly reduced value to the application.
230:(PCR). The maximum allowable rate at which cells can be transported along a connection in the ATM network. The PCR is the determining factor in how often cells are sent in relation to time in an effort to minimize jitter. PCR generally is coupled with the CDVT (Cell Delay Variation Tolerance), which indicates how much jitter is allowable.
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The UBR service category also is similar to nrt-VBR, because it is used for connections that transport variable bit rate traffic for which there is no reliance on time synchronization between the traffic source and destination. However, unlike ABR, there are no flow-control mechanisms to dynamically
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The nrt-VBR service category is used for connections that transport variable bit rate traffic for which there is no inherent reliance on time synchronisation between the traffic source and destination, but there is a need for an attempt at a guaranteed bandwidth or latency. An application that might
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The CBR service category is used for connections that transport traffic at a constant bit rate, where there is an inherent reliance on time synchronisation between the traffic source and destination. CBR is tailored for any type of data for which the end-systems require predictable response time and
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A set of parameters are negotiated when a connection is set up in an ATM network. These parameters are used to measure the QoS of a connection and quantify end-to-end network performance at the ATM layer. The network should guarantee the negotiated QoS by meeting certain values of these parameters.
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ABR uses
Resource Management (RM) cells to provide feedback that controls the traffic source in response to fluctuations in available resources within the interior ATM network. The specification for ABR flow control uses these RM cells to control the flow of cell traffic on ABR connections. The ABR
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The ABR service category is similar to nrt-VBR, because it also is used for connections that transport variable bit rate traffic for which there is no reliance on time synchronisation between the traffic source and destination, and for which no required guarantees of bandwidth or latency exist. ABR
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Forum-defined service categories exist (see Table 1). The basic differences among these service categories are described in the following sub-sections. These service categories provide a method to relate traffic characteristics and QoS requirements to network behaviour. The service categories are
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The rt-VBR service category is used for connections that transport traffic at variable rates — traffic that relies on accurate timing between the traffic source and destination. An example of traffic that requires this type of service category are variable rate, compressed video streams.
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service expects the end-system to adapt its traffic rate in accordance with the feedback so that it may obtain its fair share of available network resources. The goal of ABR service is to provide fast access to available network resources at up to the specified Peak Cell Rate (PCR).
265:(CTD). The delay experienced by a cell between the time it takes for the first bit of the cell to be transmitted by the source and the last bit of the cell to be received by the destination. Maximum Cell Transfer Delay (Max CTD) and Mean Cell Transfer Delay (Mean CTD) are used.
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network in particular) to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic. The application presents this information to the network in the form of a
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require an nrt-VBR service category is Frame Relay interworking, where the Frame Relay CIR (Committed
Information Rate) is mapped to a bandwidth guarantee in the ATM network. No delay bounds are associated with nrt-VBR service.
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characterised as being real-time or non-real-time. CBR and rt-VBR are the real-time service categories. The remaining three service categories (nrt-VBR, UBR and ABR) are considered non-real-time service categories.
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Each ATM connection contains a set of parameters that describes the traffic characteristics of the source. These parameters are called source traffic parameters. They are
396:
Congestion
Control and Traffic Management in ATM Networks, Invited submission to Computer Networks and ISDN Systems, Vol 28 (1996), 1723-1738, Raj Jain,
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271:(CDV). The difference between the maximum and minimum CTD experienced during the connection. Peak-to-peak CDV and Instantaneous CDV are used.
398:
353:
Ferguson P., Huston G., Quality of
Service: Delivering QoS on the Internet and in Corporate Networks, John Wiley & Sons, Inc., 1998.
277:(CLR). The percentage of cells that are lost in the network due to error or congestion and are not received by the destination.
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242:(MBS). The maximum allowable burst size of cells that can be transmitted contiguously on a particular connection.
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236:(SCR). A calculation of the average allowable, long-term cell transfer rate on a specific connection.
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248:(MCR). The minimum allowable rate at which cells can be transported along an ATM connection.
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When a connection is requested by an application, the application indicates to the network:
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8:
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24:
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20:
428:
440:
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Hiroshi Saito, Teletraffic
Technologies in ATM Networks, Artech House, 1993.
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http://broadband-forum.org/ftp/pub/approved-specs/af-tm-0121.000.pdf
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ATM Service
Categories: The benefit to the user, Livio Lambarelli,
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http://www.atmforum.com/atmforum/library/service_categories.html
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The
Traffic Parameters of each data flow in both directions.
399:"Congestion Control and Traffic Management in ATM Networks"
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88:
ATM Forum
Traffic Management 4.0 ATM Service Category
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418:
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370:Traffic Management Specification Version 4.1,
304:Teletraffic engineering in broadband networks
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58:(QoS) Parameters requested in each direction.
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429:http://www.byte.com/art/9412/sec10/art5.htm
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185:Non-Real-Time Variable Bit Rate (nrt-VBR)
138:Resource exploitations, feedback control
121:Non-Real-Time Variable Bit Rate (nrt-VBR)
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364:
439:
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83:Table 1: ATM Forum Traffic Services
176:Real-Time Variable Bit Rate (rt-VBR)
110:Real-Time Variable Bit Rate (rt-VBR)
427:ATM Traffic Control, Mark Juliano,
91:ITU-T I.371 ATM Transfer Capability
13:
69:
14:
468:
387:, last accessed 20 February 2005.
269:Peak-to-peak Cell Delay Variation
23:(or application) wishes to use a
1:
431:, Last accessed 3 March 2005.
415:, Last accessed 7 March 2005.
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253:Quality of service parameters
160:Burst level feedback control
48:The Type of Service required.
102:Deterministic Bit Rate (DBR)
7:
374:, Last accessed 7 May 2010.
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149:Best effort, no guarantees
116:Statistical mux, real time
10:
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457:Asynchronous Transfer Mode
298:Asynchronous Transfer Mode
207:Unspecified Bit Rate (UBR)
143:Unspecified Bit Rate (UBR)
124:Statistical Bit Rate (SBR)
105:Real-time, QoS guarantees
62:These parameters form the
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194:Available Bit Rate (ABR)
157:ATM Block Transfer (ABT)
135:Available Bit Rate (ABR)
132:Available Bit Rate (ABR)
16:Network service contract
293:Teletraffic engineering
167:Constant Bit Rate (CBR)
99:Constant Bit Rate (CBR)
40:The Traffic descriptor
234:Sustainable Cell Rate
66:for the connection.
263:Cell Transfer Delay
113:(for further study)
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288:Broadband Networks
240:Maximum Burst Size
216:Traffic parameters
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64:traffic descriptor
56:quality of service
246:Minimum Cell Rate
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25:broadband network
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127:Statistical mux
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74:Currently, five
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275:Cell Loss Ratio
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154:(No equivalent)
146:(No equivalent)
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70:Type of Service
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21:network service
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407:. Retrieved
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94:Typical Use
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452:Teletraffic
441:Categories
310:References
447:Broadband
282:See also
409:7 March
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300:(ATM)
19:If a
411:2005
355:ISBN
323:ISBN
54:The
27:(an
76:ATM
29:ATM
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420:^
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.