Quality of Service

ATM

ATM is a flexible protocol that transmits packets in 53-byte cells. ATM has emerged as a popular backbone technology because of its scalability and ability to integrate different types of network traffic. ATM-capable interfaces do not require ISSLOW because ATM already fragments packets into small cells to reduce latency and precisely schedule traffic as opposed to sending it best-effort. ATM negotiates a traffic contract between the end system and the ingress ATM switch prior to connection establishment, which includes a set of QoS parameters. Signaling includes a traffic contract that specifies an ATM service class. Table 9.7 describes the ATM-to-QoS Mappings.

Table 9.7 ATM-to-QoS Service Mappings

Intserv Service Class	ATM Service Class
Guaranteed Service	Constant Bit Rate (CBR) or Real-Time Variable Bit Rate (rtVBR).
Controlled Load	Non-Real-Time Variable Bit Rate (nrtVBR) or Available Bit Rate (ABR) with a minimum cell rate.
Best-Effort	Unspecified Bit Rate (UBR) or Available Bit Rate (ABR).