This document describes the use of the Common Open Policy Service (COPS) protocol for supporting Service Level Specification (SLS) negotiation (COPS-SLS). The COPS protocol [COPS] has been defined by the IETF Resource Allocation Protocol (RAP) WG [RAP] and will be used in this memo to communicate SLS information between customer and provider. COPS-SLS can be used at different interfaces such as vertically between a service provider and a network provider or horizontally between network providers in order to decide if the network guarantees a service level for a traffic stream. This version presents COPS-SLS as a candidate protocol for the interface between the Resource Control Domain (RCD) and the Service Control Domain (SCD), according to [SESSION-AUTH] vocabulary. It enables an SCD to vertically reserve RCD resource for its customers. Once resource has been reserved in the RCD, the media session establishment, together with the horizontal resource reservation, follows the steps described in the [AUTHSESSION] framework. Moreover, the respective PDPs have to verify that all the media streams being accepted lie within the bounds of the resource reserved in the RCD by the SCD.