Functional Overview

The Oracle Communications Subscriber-Aware Load Balancer (SLB) is a discrete network element that processes all SIP end-point signaling traffic entering the service provider network. The SLB is not necessarily the first network device to receive signaling traffic, as, depending on network topology, additional network components (for example, routers, network address translators, and so on) can lie between the end-point and the SLB.

Upon receipt of a SIP packet from an unknown source, the SLB uses a provisioned policy to select an appropriate next-hop Oracle Communications Session Border Controller (OCSBC) for traffic originated by that end-point. Subsequent packets from the same end-point are forwarded to the same OCSBC. The first packet, the one used to make the route decision, and all subsequent packets sent through the SLB to the next-hop OCSBC are encapsulated within an IP-in-IP format as defined in RFC 2003, IP Encapsulation within IP.

SBCs that participate in the load balancing-enabled deployment are enhanced by several capabilities. First, the OCSBC supports RFC 2003 tunnel for both packet transmission and reception. Second, the OCSBC periodically transmits health and performance data to the SLB; such information is evaluated and entered into the SLB’s route determination algorithm. Lastly, the OCSBC participates in any SLB-initiated rebalance operation, as described in the Rebalancing section. A group of OCSBCs, with the above-listed capabilities, that receive signaling traffic from the SLB, is referred to as a cluster.

The IP-in-IP encapsulation technique provides SLB transparency to the terminating OCSBC. That is, when an OCSBC receives an encapsulated packet via the SLB, it can discard the outer encapsulation leaving behind an identical packet as transmitted originally by the end-point. Visibility into the actual packet transmitted by the end-point is necessary to provide certain services in the OCSBC (for example, hosted NAT traversal, session-agent matching, and so on). A secondary goal achieved by using this encapsulation technique is that it provides a disassociation function between an OCSBC’s connected network and its SIP reachability. That is, an OCSBC can be assigned any IP address it wants from a network topology standpoint, yet still process SIP packets as though it were logically situated elsewhere at Layer 5. In a larger sense, the physicality of the OCSBC is no longer important; like-configured, logically identical OCSBCs can be spread all over the globe.