It is the intent of this Supplement to discuss guidelines that are applicable to the interconnection of VPNs spanning multiple service providers. Because QoS deployment is much better established in private networks than in public networks, VPN provider interconnection is the primary focus, but the intent is to outline solutions that may also be applicable to public network service interconnection as well. Specific guidelines for public network service interconnection are for further study. This Supplement is primarily concerned with the network support for two service classes across multiple providers' networks. These two classes being: A service class suitable for latency and loss insensitive data (Class 5). An additional service class, considered more suitable for the transport of conversational voice over IP (VoIP) and other latency and loss-sensitive applications (Class 0). A key distinguishing characteristic of private network services, compared to public network services, for services guaranteeing low packet loss and delay, is that the service provider(s) may not need to implement any means of avoiding congestion occurring for traffic in this class. This is discussed further in clause 3.10. Within the VPN context, it is likely that many VPN providers will deliver a service based on [IETF RFC 4364] (BGP/MPLS VPNs, formerly known as 2547 VPNs1). This Supplement will not restrict itself to BGP/MPLS VPNs – any IP VPN service should be supported – but the specific QoS issues of interconnecting providers of BGP/MPLS VPNs are addressed, including the MPLS-based interconnection styles (referred to as options B and C in [IETF RFC 4364]).