Field
Example aspects described herein relate generally to routing data on a network, and, more specifically, to add-drop multiplexing at network nodes.
Related Art
Optical networks, such as active optical networks (AON), passive optical networks (PON), and combinations thereof, contain various network elements that are capable of sending and transmitting data, thereby allowing for communications on the network (such communications are referred to herein as “network traffic”). Network elements on an optical network can include components such as, for example, switch nodes, edge nodes, transport systems, network managers, and optical network terminals. These network elements can be communicatively coupled to (and thus capable of sending network traffic to) each other, such that each network element is coupled to at least one other network element.
Network traffic can be distributed among the network elements using various topologies. One topology for provisioning network elements and network traffic is a ring network. There are known ways for arranging a ring network. Typically, a ring network includes main hubs for network traffic—referred to as “nodes”—connected by optical fiber “links” or “legs.” Each node is communicatively coupled, via one or more ports of the node that connect to links, to two other nodes, thus forming a ring of nodes.
A ring network can be provisioned such that duplicate network traffic is transmitted, one in each direction of the ring. The redundancy provided by multiple traffic paths around the ring network permits other nodes in the ring to remain connected (and thus able to continue transmitting network traffic to others node in the ring) in the event there are node or link failures.
Nodes in a ring can be configured to permit “ingress” and “egress” traffic. Ingress traffic is communications received from a source outside of the ring network that are added to the ring traffic; egress traffic is communications removed from the ring traffic that is sent to a destination outside of the ring network. Sources of ingress traffic (and destinations for egress traffic) include other networks (e.g., other rings), local intranets, and internet service providers (ISPs). Collectively, these sources are referred to herein as “clients,” and ingressing and egressing traffic at a node is referred to herein as “client traffic.”
Rings (and the network traffic transmitted thereon) can employ Synchronous Optical Networking (SONET) and/or Synchronous Digital Hierarchy (SDH) architectures and can be provisioned to incorporate one or more networking standards (e.g. IEEE standards, such as 40 Gigabit Ethernet (40 G) and 100 Gigabit Ethernet (100 G), and International Telecommunications Union Telecommunication Standardization Sector (ITU-T) Recommendation G.709, titled “Interfaces for the optical transport network”), some of which require or otherwise use multiplexed (e.g., wavelength-division multiplexed) signals. For example, a 100 G network may contain 88 channels, each supporting 100 G communications using different wavelengths. So that client traffic (which itself may or may not be multiplexed) can ingress to and egress from individual channels of multiplexed ring traffic, ring nodes can include one or more add-drop multiplexers (ADM).
For example, a ring node may have two ADM components, or “blades,” one for each ring traffic direction (e.g., one blade for each communicative coupling to another ring node). Each ADM receives ring traffic that enters a node port and opposite-direction ring traffic outgoing through that port. For example, incoming east ring traffic is demultiplexed by the ADM so that ingress traffic can be added and egress traffic removed before being multiplexed by the other ADM. Conversely, outgoing west ring traffic (which has first been demultiplexed by the other ADM and had ingress traffic added and egress traffic removed) is multiplexed by the ADM for transmission on the ring.
The ADMs at a node can be connected by a high-speed interconnection. Demultiplexed ring traffic is sent from the demultiplexing ADM via the interconnection to the other ADM, for re-multiplexing and transmission out of the port to which that other ADM is connected. Depending on the configuration of the node and its components, ingress/egress traffic can be handled at either ADM or at one or more separate components.
The bandwidth of ADMs, including the speed of the interconnection, can be a constraint that affects network speed and reliability. For example, on a 100 G ring network, a node must be able to handle the incoming and outgoing ring traffic at 100 Gb/s. Accordingly, to minimize bottlenecking, the ADMs and their interconnection(s) must support 100 G processes. Moreover, the node must further handle the client traffic, which may reach 40 G or 100 G speeds. Thus, a single 100 G interconnection between ADMs can limit the bandwidth of the node.
Upgrading a node to include additional ADM interconnections, however, may not be possible due to hardware and/or software limitations of the node and/or its components, and in any case can be expensive to implement. Moreover, even if a node is fully capable of handling all client and ring traffic without a loss of network speed, the reliability of the network still may be affected if there is not a redundant source for client traffic. For example, if client traffic is received at a node over a single fiber, any failure along that fiber can reduce or eliminate the ability of the node to handle ingress/egress traffic.