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					Arcstar ATM Service Description
(subject to change) ATM (Asynchronous Transfer Mode) is an extremely high speed, low delay, multiplexing and switching technology. ATM is a multi-service technology designed to support the simultaneous transmission of all types of user traffic. ATM allows both time-sensitive traffic such as voice and video and delay-tolerant, “bursty” data traffic to be integrated within a single network. ATM works by breaking traffic into fixed length cells of 53 bytes. Each 53-byte cell contains 48 bytes of user information (voice, data, video etc) and a 5-byte header cell containing control and address information. The fixed length of each cell means that traffic is transported in a predictable manner, ensuring that time sensitive traffic such as voice is not held up by lengthy data transmissions. Incoming cells are stored in a buffer and inserted into a multiplexing slot based on priority rules using Asynchronous Time Division Multiplexing. Arcstar ATM service consists of 3 Service Categories: CBR, VBR-nrt and UBR. Each Service Category has Quality of Service (QoS) technical parameters defined by the ATM Forum. The combination of QoS technical parameters applied to each Service Category differentiates the Service Categories and specifies the QoS for the connection on an end-to-end basis. Definitions “ATM” refers to Asynchronous Transfer Mode technology as that term is commonly used in the telecommunications industry based on ITU-T and ATM Forum standards. "CBR" refers to the ATM service category called Constant Bit Rate as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards. “MBS” refers to the ATM parameter called Maximum Burst Size as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards. “PCR” refers to the ATM parameter called Peak Cell Rate as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards. “Permanent Virtual Circuit (PVC)” shall mean a virtual circuit established on a permanent logical basis between two ports “SCR” refers to the ATM parameter called Sustained Cell Rate as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards. “UBR” refers to the ATM parameter called Unspecified Bit Rate as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards. "VBR-nrt" refers to the ATM service category called Variable Bit Rate – Non-Real Time as that term is commonly understood in the telecommunications industry based on ITU-T and ATM Forum standards