On Cooperative Inter-Domain Path Computation

Abstract

Inter-domain path computation, or the ability to compute end-to-end paths across multiple domains, is the next step toward wide deployment of a distributed control plane with support for traffic engineering. A key enabler to achieve this goal is the introduction of a Path Computation Element (PCE) in each domain. There are various ways these elements can collaborate to compute an end-to-end path; of particular interest to us in this paper is cooperative path computation, a scheme where PCEs exchange path information in the context of a specific end-to-end path computation instance, often prior to signaling the path. We show that depending on the information available to each PCE, cooperation can take one of two forms, which we call model-based and ad hoc. We demonstrate that model-based cooperation is essentially a multistage decision problem, and offer a probabilistic analysis which we believe is the key to understanding the problem and developing efficient inter-domain path computation heuristics. In particular, we argue that having an estimate of the blocking probability in each domain can be helpful in determining the path computation effort needed to find an end-to-end path.

Enhanced crankback signaling for multi-domain IP/MPLS networks

“…Consider a source node fielding a request for x units of bandwidth to a destination node in another domain. This source queries its PCE to determine an egress link to the next-hop domain, e.g., using the PCE-to-PCE protocol [3,5]. The PCE then determines the nexthop domain to the destination domain (detailed in Section 3.2) and returns a domain egress border node/link to this domain.…”

“…To address these challenges, a diverse set of provisions have emerged to help improve multi-domain TE support, both at the IP/MPLS and underlying optical GMPLS layers [1][2][3][4][5]. On the standards side, many ubiquitous routing protocols already provide varying levels of inter-domain visibility, e.g., next-hop/path-vector dissemination in exterior gateway protocol (EGP) and hierarchical link-state dissemination in two-level open-shortest-path-first (OSPF-TE).…”

“…This state is then flooded to other domains using hierarchical link-state routing between border gateways to build a ''global" aggregated graph. As such, these types of schemes can best be classified as PCE-based strategies as per [5]. For example, earlier work in peer group summarization for asynchronous transfer mode (ATM) networks has shown very high levels of state reduction [1].…”

“…Hence the adoption of this approach may be limited in real-world settings where more scalable distance/path-vector protocols are already well-entrenched. Along these lines, a handful of studies have proposed signalingbased crankback strategies for ''per-domain" path computation (akin to PCE classification [5]). The goal here is to have individual domains compute their own traversing segments to build a concatenated end-to-end path.…”

A Virtual Node-based Shared Restoration scheme in multi-domain networks

“…Many research studies have explored routing schemes in multi-domain networks. One example of these studies is found in [2]. We noticed that the scope of all of these studies is limited to the "routing" of transport connections in multi-domain networks, rather than the restoration (survivability) of these connections.…”