In most existing data networks, the network topology is fixed at the time the data network is created. For example an Internet Protocol (IP) data network may consist of a number of IP routers interconnected by a core transport network which may be, for example, a mesh network. The mesh network allows for various connections between the IP routers. However, in the past, the network topology of such networks has generally been static. That is, once the network is designed and implemented, and various data paths between the IP routers are provisioned, these data paths do not change because the topology of the data network does not change. The static nature of such networks results in problems when network usage changes and more or less capacity is needed among and between various network nodes. In this case, any change to the network topology is a time consuming and expensive proposition.
The introduction of new core transport network technologies is changing the static nature of data networks and is providing a basis for offering more interesting network services. For example, in a Wavelength Division Multiplexed (WDM) optical mesh network, IP routers are connected directly to a switched optical core transport network consisting of optical cross-connect (OXC) switches interconnected via high-speed Dense WDM (DWDM) line systems. The switching capability of the optical core network allows for the creation of end-to-end light paths across the optical core. Since the OXCs can be switched relatively easily, the core network is dynamically reconfigurable and as a result the overall network topology is reconfigurable.
One of the benefits of a reconfigurable core network as described above is that it allows for the efficient provisioning of data paths having a guaranteed bandwidth. Such guaranteed bandwidth paths allow for the provisioning of higher level quality of service (QoS) dependent network services. The rapid switching capabilities of OXCs allow the optical core network to be quickly reconfigured depending on bandwidth requirements.
In the reconfigurable networks as described above, there are two types of connectivity to consider. The first is the connectivity in the optical core transport layer that is defined by the physical connections created by the OXC switches. In the optical core transport layer data may be transferred between two endpoints if there exists an appropriate optical path between the endpoints. Another type of connectivity is in the IP layer that is defined by the connectivity between the IP routers. As is well known, in accordance with the IP data transmission protocol, IP routers route data between routers based on the network topology interconnecting the various IP routers. Thus, of course, the IP domain connectivity is dependent upon the optical domain connectivity. Looking at it another way, the optical domain is the physical transport layer used to set up a network topology upon which the IP layer depends for data transmission.
One typical approach to IP routing in a WDM optical network is to separate the routing at each layer so that the routing decisions are independent of each other. First the optical routing is considered in order to set up the network topology which is then used for the IP layer routing of data packets. Another approach to routing which has received attention is so-called cross-domain routing approaches which incorporate traffic and topology information from both the optical and IP layers in the data path selection process. For example, M. Kodialam and T. V. Lakshman, Integrated Dynamic IP and Wavelength Routing in IP Over WDM Networks, IEEE Infocom 2001, which is incorporated herein by reference, describes an algorithm for routing of bandwidth guaranteed paths in IP over WDM networks taking into account the combined topology and resource usage information at the IP and optical layers. The goal of such cross-domain routing is to create a more efficient end-to-end network by identifying bandwidth that would be wasted if each domain were routed independently. A cross-domain path between a source node and destination node can potentially cross the boundary between IP layer and optical transport layer multiple times.
While cross-domain routing provides benefits in data networks, we have discovered that heretofore unknown problems exist in this type of routing.