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Shared Subscriber Information
One thing that may be evident from the above text is that the subscriber information on the telephone network is spread over multiple locations and stored in different formats. As stated earlier about the hodgepodge of network protocols and control messages, this is the case since the systems have been acquired from different vendors and deployed over a wide time frame.
In this access gateway application scenario, the access gateway again is used to connect the telephone network to the Internet. However, in this scenario the access gateway will be used to enable the networks to share subscriber information. The ultimate goal of subscriber information access of this type is a common, centralized location for the information. For example, presently subscriber information is duplicated over both the telephone network and the Internet provider's network. A better configuration would be to locate the information in a common data store where it can be more easily accessed, updated, and administered. However, this ultimate configuration may not be possible. As a result, this scenario shows how an access gateway would most practically allow for subscriber information access and updating across the two networks.
As shown in Figure 9, the access gateway again acts as the connection point between the two networks. In this scenario, the access gateway is the translation point between the information access protocols used in the two networks. On the telephony network side, these protocols are often vendor- or application-specific. In addition, some utilize the SS7 signaling network. On the Internet provider side, many of the protocols can also be vendor- or application-specific. However, many Internet provider networks are fortunately moving toward the use of a common protocol, such as the lightweight directory access protocol (LDAP). In addition, in many networks a common information access point is deployed. As an example, the common access point might be the Active Directory capability from Microsoft. As shown in Figure 9, if a common access point such as Active Directory has been deployed in the Internet provider's network, the access gateway connects to it for information access from the Internet side. In a similar manner, the access gateway acts as a node on the Active Directory system, enabling access to the information maintained on the telephony network.
Figure 9. Shared Subscriber Information
Call/Connection Control Across Networks
A final access gateway application scenario addresses the control of calls or connections across the two networks. On the telephony side, call control capabilities such as computer telephony integration (CTI) are available on smaller telephone switching systems. Integrated services digital network user part (ISUP) signaling for call setup is available on medium to large switches. On the highest end of switch bandwidth, standardized capabilities such as third-party call control (TPCC) are available to create switched virtual circuit connections on asynchronous transfer mode (ATM) switches. On the Internet side, the trend for similar connection control capabilities is growing. For example, Cisco is promoting its Internetwork Operating System™ (IOS), which tells routers, hubs, and other network devices what to do.
The purpose of the access gateway in this scenario is to translate the signaling differences between the networks. An application on the Internet side could set up a voice call on the telephony network using CTI or possibly ISUP. A similar application could establish a high-bandwidth, multimedia connection on a series of ATM switches using TPCC. In either case, the access gateway provides the necessary protocol conversion. Figure 10 shows a network diagram representing this application scenario.
Figure 10
