|Oracle® Communications Converged Application Server Administration Guide
Part Number E17647-03
This chapter describes the Oracle Communications Converged Application Server architecture.
Converged Application Server is designed to provide a highly scalable, highly available, performant server for deploying SIP applications. The Converged Application Server architecture is simple to manage and easily adaptable to make use of available hardware. The basic architecture consists of these components:
Figure 1-1 shows the components of a basic Converged Application Server installation. The sections that follow describe each component of the architecture in more detail.
Although it is not provided as part of the Converged Application Server product, a load balancer (or multiple load balancers) is an essential component of any production Converged Application Server installation. The primary goal of a load balancer is to provide a single public address that distributes incoming SIP requests to available servers in the Converged Application Server engine tier. Distribution of requests ensures that Converged Application Server engines are fully utilized.
Most load balancers have configurable policies to ensure that client requests are distributed according to the capacity and availability of individual machines, or according to any other load policies required by your installation. Some load balancers provide additional features for managing SIP network traffic, such as support for routing policies based on source IP address, port number, or other fields available in SIP message headers. Many load balancer products also provide additional fault tolerance features for telephony networks, and can be configured to consistently route SIP requests for a given call to the same engine server on which the call was initiated.
In a Converged Application Server installation, the load balancer is also essential for performing maintenance activities such as upgrading individual servers (Converged Application Server software or hardware) or upgrading applications without disrupting existing SIP clients. The Administrator modifies load balancer policies to move client traffic off of one or more servers, and then performs the required upgrades on the unused server instances. Afterwards, the Administrator modifies the load balancer policies to allow client traffic to resume on the upgraded servers.
Oracle provides detailed information for setting up load balancers with the Converged Application Server engine tier for basic load distribution. See "Configuring Load Balancer Addresses" in Chapter 21, "Managing Network Resources" to configure a load balancer used with Converged Application Server and Chapter 20, "Upgrading Converged Application Server Software" to use a load balancer to perform system and application upgrades.
The engine tier is a cluster of Converged Application Server instances that hosts the SIP Servlets and other applications that provide features to SIP clients. The engine tier is a stateless cluster of servers, and it stores no permanent or transient information about the state of SIP dialogs. Instead, all stateful information about SIP dialogs is stored and retrieved from the SIP Data Tier, which also provides replication and failover services for SIP session data. See "SIP Data tier" for more information.
Engine tier servers can optionally cache a portion of the session data managed by the SIP data tier. Caching is most useful in configurations that use a SIP-aware load balancer. See "Using the Engine Tier Cache".
The primary goal of the engine tier is to provide maximum throughput and low response time to SIP clients. As the number of calls, or the average duration of calls to your system increases, you can easily add additional server instances to the engine tier to manage the additional load.
Note that although the engine tier consists of multiple Converged Application Server instances, you manage the engine tier as a single, logical entity; SIP Servlets are deployed uniformly to all server instances (by targeting the cluster itself) and the load balancer need not maintain an affinity between SIP clients and servers in the engine tier.
Note:Converged Application Server start scripts use default values for many JVM parameters that affect performance. For example, JVM garbage collection and heap size parameters may be omitted, or may use values that are acceptable only for evaluation or development purposes. In a production system, you must rigorously profile your applications with different heap size and garbage collection settings in order to realize adequate performance. See "Tuning JVM Garbage Collection for Production Deployments" for suggestions about maximizing JVM performance in a production domain.
Because the engine tier relies on SIP data tier servers in order to retrieve call state data, Oracle recommends using dual, Gigabit Ethernet Network Interface Cards (NICs) on engine and SIP data tier machines to provide redundant network connections.
The SIP data tier is a cluster of Converged Application Server instances that provides a high-performance, highly-available, in-memory database for storing and retrieving the session state data for SIP Servlets. The goals of the SIP data tier are as follows:
To provide reliable, performant storage for session data required by SIP applications in the Converged Application Server engine tier.
To enable administrators to easily scale hardware and software resources as necessary to accommodate the session state for all concurrent calls.
Within the SIP data tier, session data is managed in one or more "partitions" where each partition manages a fixed portion of the concurrent call state. For example, in a system that uses two partitions, the first partition manages one half of the concurrent call state (sessions A through M) while the second partition manages another half of the concurrent call states (sessions N through Z). With three partitions, each partition manages a third of the call state, and so on. Additional partitions can be added as necessary to manage a large number of concurrent calls. A simple hashing algorithm is used to ensure that each call state is uniquely assigned to only one SIP data tier partition.
Within each partition, multiple servers can be added to provide redundancy and failover should other servers in the partition fail. When multiple servers participate in the same partition, the servers are referred to as "replicas" because each server maintains a duplicate copy of the partition's call state. For example, if a two-partition system has two servers in the first partition, each server manages a replica of call states A through M. If one or more servers in a partition fails or is disconnected from the network, any available replica can automatically provide call state data to the engine tier. The SIP data tier can have a maximum of three replicas, providing two levels of redundancy.
See "Configuring SIP Data Tier Partitions and Replicas" for more information about configuring the SIP data tier for high availability.
Note:Because the engine tier relies on SIP data tier servers in order to retrieve call state data, Oracle recommends using dual Network Interface Cards (NICs) on engine and SIP data tier machines to provide redundant network connections.
When an initial SIP message is received, Converged Application Server uses Servlet mapping rules to direct the message to the appropriate SIP Servlet deployed in the engine tier. The engine tier maintains no stateful information about SIP dialogs, but instead persists the call state to the engine tier at SIP transaction boundaries. A hashing algorithm is applied to the call state to select a single SIP data tier partition in which to store the call state data. The engine tier server then "writes" the call state to each replica within that partition and locks the call state. For example, if the SIP data tier is configured to use two servers within each partition, the engine tier opens a connection to both replicas in the partition, and writes and locks the call state on each replica.
In a default configuration, the replicas maintain the call state information only in memory (available RAM). Call state data can also be configured for longer-term storage in an RDBMS, and it may also be persisted to an off-site Converged Application Server installation for geographic redundancy.
When subsequent SIP messages are generated for the SIP dialog, the engine tier must first retrieve the call state data from the SIP data tier. The hashing algorithm is again applied to determine the partition that stores the call state data. The engine tier then asks each replica in the partition to unlock and retrieve the call state data, after which a Servlet on the engine tier can update the call state data.
Converged Application Server enables you to store long-lived call state data in an Oracle RDBMS in order to conserve RAM. The SIP data tier persists a call state's data to the RDBMS after the call dialog has been established, and retrieves or deletes the persisted call state data as necessary to modify or remove the call state. See "Storing Long-Lived Call State Data in an RDBMS".
Converged Application Server can be installed in a geographically-redundant configuration for customers who have multiple, regional data centers, and require continuing operation even after a catastrophic site failure. The geographically-redundant configuration enables multiple Converged Application Server installations (complete with engine and SIP data tier clusters) to replicate call state transactions between one another. If the a particular site's installation were to suffer a critical failure, the administrator could choose to redirect all network traffic to the secondary, replicated site to minimize lost calls. See "Configuring Geographically-Redundant Installations".
Converged Application Server's flexible architecture enables you to configure engine and SIP data tier servers in a variety of ways to support high throughput and/or provide high availability.
Not all Converged Application Server requirements require the performance and reliability provided by multiple servers in the engine and SIP data tier. On a development machine, for example, it is generally more convenient to deploy and test applications on a single server, rather than a cluster of servers.
Converged Application Server enables you to combine engine and SIP data tier services on a single server instance when replicating call states is unnecessary. In a combined-tier configuration, the same Converged Application Server instance provides SIP Servlet container functionality and also manages the call state for applications hosted on the server. Although the combined-tier configuration is most commonly used for development and testing purposes, it may also be used in a production environment if replication is not required for call state data. Figure 1-2 shows an example deployment of multiple combined-tier servers in a production environment.
Because each server in a combined-tier server deployment manages only the call state for the applications it hosts, the load balancer must be fully "SIP aware." This means that the load balancer actively routes multiple requests for the same call to the same Converged Application Server instance. If requests in the same call are not pinned to the same server, the call state cannot be retrieved. Also, be aware that if a Converged Application Server instance fails in the configuration shown in Figure 1-2, all calls handled by that server are lost.