Optical Networks - _J_3 Quality of Service_173

Is equal to the 48 byte atm payload and aal 5 has

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is equal to the 48-byte ATM payload, and AAL-5 has lower overhead compared to AAL-1. Also note that AAL-5 provides error detection for its payload through the use of a CRC, whereas AAL-1 does not. J.3 Quality of Service The primary motivation for use of ATM is that it is capable of providing quality- of-service (QoS) guarantees for connections. These guarantees take the form of bounds on cell loss, cell delay, and jitter. ATM provides such guarantees through a combination of traffic shaping and admission control. Roughly speaking, this works as follows: 1. Traffic Shaping: ATM requires that all user traffic adhere to a contract that has been established between the user and the network. This contract usually specifies the peak cell rate, the average cell rate, and the burst size (number of consecutive cells at the peak cell rate) that the user can transfer across the UNI. The ATM network may monitor these contracted parameters for each connection across the UNI and can drop those cells that violate this contract. Alternatively, it can admit the violating cells but mark the CLP bit for these cells so that they are preferentially dropped in the event of congestion. As a result, ATM can carefully control the traffic from each connection that enters the network. The network’s half of this bargain is the QoS guarantees that it provides to the user in terms of cell loss, delay, and jitter. 2. Admission Control: Based on knowledge of the user traffic characteristics that are enforced through traffic shaping, the ATM network can determine the set of
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  • Spring '09
  • Boussert
  • Asynchronous Transfer Mode, ATM network, segmented IP packet

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