Common use of Path Computation Element Clause in Contracts

Path Computation Element. In order to configure the forwarding of HTTP or IP-level packets from one SR to another (see above), the PCE SF is being utilized. This PCE works closely with the underlying infrastructure, through suitable management interfaces, specifically the I1 and I3 infrastructure interfaces, to configure the forwarding actions of the SDN-enabled switching fabric and to obtain the topology information from the infrastructure to do so. For this, the PCE assigns every link of the underlying network topology to a unique bit in a pre-defined bitarray (with the size of the bitarray large enough to store all such unique bit positions, i.e. the size of the array equals the number of network links). A forwarding action from point A in the network to another point B can now be represented a unique bitarray in which all bitpositions of those links belonging to the path from A to B. Figure 15 shows this simple forwarding operation. In this example, the path from S (originating in a peering network) to A is represented as a simple binary OR of the three links from the border GW to the SR to which media component A connects, i.e. 10010010 is the binary representation of this path. On the other hand, the path from S to B is represented as 10100010 as one link is different here compared to the previous. With that in mind, the transfer of a packet from S to A and B is now easily achieved by a binary OR of the individual path. We refer to this capability as coincidental multicast, which is utilized to send a single HTTP-level response to more than one client at the same time (for cases in which the arrival of the client requests is aligned in the right arrival window). It is the role of the PCE to receive path computation requests in the form of either an IP or FQDN destination as well as a source node identifier (which is assigned to each SR by the PCE during the bootstrapping process). The result of this operation is the bitarray, as shown in Figure 15, and is returned to the requesting, i.e. originating SR. In order to improve HTTP (request/response) operations, the PCE will also return the return path from the destination SR to the requesting SR in the same operation. This supports requests and responses being sent over different paths in the network.