The MESCAL solution for QoS delivery in the Internet adopts a hop-by-hop, cascaded model of interactions between adjacent providers. Interactions occur both at the service and IP layers. MESCAL controls the inter-domain IP layer interactions with q-BGP, an enhanced version of the BGP (Border Gateway Protocol), which is widely used today for best-effort inter-domain routing. MESCAL envisioned a suitable and enhanced BGP to convey QoS-related routing information across different domains, with the aim of enabling the discovery, the selection, the enforcement and the maintenance of QoS-aware routes at the IP layer.

MESCAL has designed q-BGP in such a way it can support any inter domain QoS delivery solutions that rely on an exchange of QoS information (either at service or control layers). Two categories of solutions groups have been identified. The first category is expected to require only a QC identifier to be carried in q-BGP messages. The second category requires, in addition to the QC identifier, that q-BGP carries also a set of QoS performance characteristics. Therefore, new attributes have been defined, mainly: QoS Service Capability and two flavours of QoS_NLRI. MESCAL has specified how a q-BGP speaker should process these attributes and proposed several new q-BGP route selection processes able to take into account received QoS information as additional inputs. Finally, MESCAL ensured that q-BGP is backward compatible and continue to gracefully interoperates with classical BGP.

As far as the provisioning of the values of the q-BGP QoS performance parameters is concerned, MESCAL distinguished two non-exclusive provisioning modes: administrative- and dynamic-set modes. Obviously, these modes differ in the time scales of their dynamic, which in turn influences the frequency of the UPDATE messages.

Simulations have shown that injecting QoS information into BGP when coupled with a QoS-aware route selection process results in the discovery of better performing routes across meta-QoS-class planes compared to using standard BGP. While the quantity of q-BGP messages is greater than for plain BGP the results indicate that when scaled to Internet-sized AS topologies there is only a three-fold increase in update messages. The injection of static, administratively-set QoS information into BGP can have a detrimental effect on QoS if pSLS capacities are not engineered appropriately or if q-BGP route selection policies are not carefully selected. Injecting dynamically measured QoS-info may alleviate this but care must be taken to dampen route fluctuations to avoid instabilities.

Further reading:

P. Levis, M. Boucadair, P. Morand, J. Spencer, D. Griffin, G. Pavlou, P. Trimintzios, A New Perspective for a Global QoS-based Internet, to appear in the Journal of Communications Software and Systems, 4th quarter 2005. [pdf document]

M. Boucadair (Ed.), "QoS-Enhanced Border Gateway Protocol", draft-boucadair-qos-bgp-spec-01.txt, Work in Progress, July 2005. [link]

MESCAL deliverable D1.3, "Final specification of protocols and algorithms for inter-domain SLS management and traffic engineering for QoS-based IP service delivery", Chapter 10, section 10.5. [link]

MESCAL deliverable D3.2, "Final experimental results: validation and performance assessment of algorithms and protocols for inter-domain QoS through service-driven traffic engineering", Chaper 4. [link]

qBGP demonstration: avi movie file of screenshots of qBGP in action in the MESCAL testbed. [qbgp-demo.avi]. Note that this is a 35 MB file and and it requires the TechSmith Screen Capture Codec.