14.1 Evaluation of Protocol Stacks for DSL

The DSL Forum in TR-43 [1] discusses several ATM-based architectures that are currently deployed by carriers for DSL services. This document lists criteria that can be used for evaluating the appropriateness of a particular protocol stack for use in supporting a DSL service. Although TR-43 describes protocols that are currently deployed, these same criteria are also appropriate for the discussion of any protocol stack that might be used over a DSL system.

Payload efficiency : How much overhead is required to support a particular protocol stack? What is the size of the protocol headers required, and what is the ratio of data required for these headers, compared with that available for carrying payload data?
Error detection : Is the protocol stack capable of detecting errors introduced, as the data are transported end to end over the network? Is it capable of correcting these errors?
Session multiplexing : Can the stack support multiple sessions from the customer's premises across the network? These separate sessions might support multiple users from the premises, or multiple services to the same premises (e.g., voice and data). Also separate sessions might exist to separate end points at the far end of the network (e.g., simultaneous sessions from the same premises to different providers, such as an ISP and a corporate network).
Multiprotocol support : What protocols can be supported over the stack? Given the same lower layers , what higher layer protocols can be supported on the stack?
Autoconfiguration and management : From the viewpoint of equipment and software on the customer's premises, what information is required to configure this equipment to communicate over the network using a particular protocol stack? How much of this information is inherently carried in the information flows of the protocol? What information can be provided to the CPE over special management protocols? What are these management protocols? How much "bonding" (information exchange and network management cooperation) between the carrier and a service provider is required to allow the service to be configured? Is there any information that the end- user must configure manually to allow them to connect their equipment to the network?
Service selection : Does the protocol stack allow the end-user to select the services that they use over the network? How does the protocol stack provide this function?
Security : How secure are the communications? What features are inherent in the protocol to provide security to the user and to the network provider? What are the particular protocol stacks weaknesses?
Authentication, authorization, and accounting (AAA) : How does the stack provide support for these functions? How does it interact with existing tools to support these functions?
Standards status : What parts of the stack are standardized? What is the status of the standardization for those that are not yet standards?

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