This article discusses the use of policies to control calls—whether in traditional telephony or in its more modern versions such as mobile telephony or Internet telephony. Call control is as old as telephony. It allows subscribers and the network to manage calls. Trivially, users initiate calls by dialing and terminate calls by hanging up. However, modern telephony offers many more options for managing calls. For example, they may be forwarded if the user is busy or away. Conference calls may be set up. Voicemail and answering services can be used to take messages. The solutions in conventional telephony are, however, relatively limited. This article investigates the relevance to call control of the kinds of policies used to manage computerized and networked systems. As will be seen, policy-based management of call control offers a much more flexible approach.
Key Terms in this Chapter
Peer-to-Peer (P2P) Network: A communication way where each node has the same authority and communication capability. They create a virtual network, overlaid on the Internet. Its members organize themselves into a topology for data transmission.
Reliability: The improved quality of data transmission, different types of reliability exist, including data accuracy or real-time delivery.
Host-Multicast: Application-Layer multicast technology—it does not require any additional protocol in the network routers, since it uses the traditional unicast IP transmission. Its other names are: End-host multicast, Application-Layer multicast.
Host-Multicast Routing Protocol: The members of the hosts construct delivery tree using similar algorithms than the IP-multicast routing protocols do.
Client-Server Model: A communicating way, where one host has more functionality than the other. It differs from the P2P network (see below).
Multicast Transport Protocol: To improve the reliability of the multicast delivery, special transport protocols are used in addition to the unreliable User Datagram Protocol (UDP).
IP-Multicast: Network-level multicast technology, which uses the special Class-D IP-address range. It requires multicast routing protocols in the network routers.
Replication: Storing a specific piece of information at many places, to increase availability and dependability.
Ad-Hoc Network: This is a special type of the computer network, where the communication does not require any fixed computer network infrastructure (e.g., it does not need router), the nodes communicate directly with each other without access points. In the host-multicast (see below) the mobile peering hosts construct ad-hoc network.
IP-Multicast Routing Protocol: In order to forward the multicast packets, the routers have to create multicast routing tables using multicast routing protocols.