The Internet is based on an X-Domain topology: interconnected domains are managed by independent actors (Fig.1). Deploying critical services (e.g. VPN, video-conference etc.) over such a topology requires to be able to guarantee end-to-end QoS. For this, and to guarantee privacy, Service Level Agreements (SLAs), also called QoS contracts, are committed pairwise between domains. While local QoS control issues inside on each participating domain can be considered solved [4], open problems persist in the field of end-to-end QoS provisioning and monitoring for multi-domain services. The key factors to be taken into account are the heterogeneity, independence and privacy requirements of the individual domains.