||Addendum to TM 4.1: Differentiated UBR
||The UBR service category is often utilized by elastic data networking applications, primarily because it imposes few
requirements on the end equipment and enables a higher degree of connectivity (i.e., more connections can be
configured on a given access interface) than do services which explicitly reserve capacity per connection.
Such a configuration offers no means by which the service quality of individual flows (virtual channel or virtual
path connections) may be differentiated. This may not be an issue if the higher layer intends to offer only best effort
service. It has, however, become increasingly common for technologies which traditionally offered only best effort
service (e.g., Ethernet, IP) to incorporate service differentiation mechanisms. In order to optimize their support over
ATM, it is desirable that the UBR service category be extended with similar capabilities.
This specification defines a mechanism by which a UBR connection may be associated with one of a set of network-specific
Behavior Classes (see section 2.5). Using this mechanism, the adaptation function may assign traffic to a
UBR connection, based in part on a mapping of the higher-layer service classification to the Behavior Class with
which that UBR connection is associated. The ATM network may differentiate the treatment of UBR connections
based on the Behavior Class with which each such connection is associated, for example by governing access to
queuing and scheduling resources. By coordinating the adaptation function at the edge of the ATM network with
the behaviors implemented within the network, an operator can enable consistent service differentiation end to end.
UBR connections which do not indicate a Behavior Class are associated with a network-specific default behavior.
Networks which do not support the specification of Behavior Class ignore this attribute and handle the connection as
if it had not been specified. The enhancements defined herein are optional and interoperable with TM4.1 compliant
This specification uses the term Differentiated UBR to refer to the UBR service, augmented by the specification of a