The field of data networking is continuously evolving and part of this evolution is the emergence of new standards, protocols, and technologies. As an example, ATM technology, now widely used in many networks, was developed over the past decade to overcome specific drawbacks of the then existing networking technology. One consequence of this continuous development is the need to adapt existing technologies with the newly developed protocols and standards.
One of these newly developed technologies is the MPLS standard. In an MPLS network, incoming packets are assigned a label by a label edge router (LER). Packets are forwarded along a label switch path (LSP) where each label switch router (LSR) makes forwarding decisions based solely on the contents of a label. At each hop, the LSR strips off the existing label and applies a new label. This new label then informs the next hop how to forward the packet. This technology, among other benefits, allows routers to make forwarding decisions based on the contents of a simple label rather than by performing complex route lookup operations.
While the MPLS standard holds out much promise, ATM technology needs to be adapted to the MPLS standard so that the benefits of MPLS technology can be added to the benefits of ATM technology. ATM technology provides access to a network by multiplexing user information into fixed length units or cells. Using ATM technology, networks today can establish dedicated links between nodes. These links can be created as needed and can create high-throughput connections between nodes. Currently, there are no call control procedures for the establishment and clearing of ATM on-demand connections over MPLS.
As noted above, an MPLS network consists of MPLS switches serving as LERs and LSRS and provides connection services for the establishment of MPLS connections. To establish on-demand ATM connections, ATM connection information needs to be exchanged between its call control peers or between two communicating ATM nodes. In ATM networks, ATM signalling protocols are used to exchange ATM connection information between call control peers or nodes.
One major feature of MPLS is the unidirectional nature of its connections. Forwarding of a traffic flow is determined by the label attached to a data transfer unit. Since label assignment in one direction is not associated with the reverse direction, there is no indication as to the original source of the data transfer unit. A destination node therefore cannot be determined from where traffic flow originated. Also, since in a uni-directional system the routing is label based, a route used by one data transfer unit may be different from a route used by a second data transfer unit even if both data transfer units originated from the same source and are heading to the same destination. This feature of the MPLS standard renders it quite difficult to set up an ATM style connection between two nodes. Furthermore, this feature renders any “link” between nodes across an MPLS domain as a unidirectional link. Coordinating control signals between two nodes is, again, rendered difficult.
From the above, what is therefore required is a solution which will allow ATM connections to be established across domains implementing the MPLS standard.
It should be noted that the term data transmission unit (DTU) will be used in a generic sense throughout this document to mean units through which digital data is transmitted from one point in a network to another. Thus, such units may take the form of packets, cells, frames, or any other unit as long as digital data is encapsulated within the unit. Thus, the term DTU is applicable to any and all packets and frames that implement specific protocols, standards or transmission schemes. It should also be noted that the term digital data will be used throughout this document to encompass all manner of voice, multimedia content, video, binary data or any other form of data or information that has been digitized and that is transmitted from one point in a network to another as a payload of a data transmission unit.