Directory Services

With any type of communication system, there must be a way to find people easily. Directories are familiar and work very well, but the rapid growth and electronic environment of video conferencing require a new form of Directory Service.

THE PRIMARY QUESTIONS

• What is a Directory Service?
• Why do I need Directory Service?
• What types of Directory Services are available?

ANSWERS

What is a Directory Service? A directory service is a collection of databases that store and retrieve information in a user-friendly, accessible manner. The user-friendliness is achieved by developing front-end databases to access the information. It is a complex electronic “phonebook” that scales to accommodate rapid growth.

Why do I need Directory Service? Without a directory service, a user would have to contact the person they want to reach to obtain information about how to connect with them. After the exchange of information (gatekeeper address, IP address, E.164 address, and H.323 alias), each party can call the other. This process would have to be repeated for every desired endpoint. Eventually each person would have a large list, becoming at best unwieldy and potentially discouraging use. A directory service solves this problem by having everyone on the network register with it. The administrator enters the appropriate information for each endpoint, which then becomes accessible to all users on the network.

What types of Directory Services are available? Several directory services are available. The IPVTF focus on two leaders: Lightweight Directory Access Protocol (LDAP) and First Virtual Communications, Inc., Click to Meet™ (CTM).

Recommendation: The IPVTF recommends that First Virtual Communications, Inc., Click to Meet™ be used to provide directory services.

Lightweight Directory Access Protocol (LDAP)

LDAP augments the Directory Access Protocol (DAP, RFC 13303) to allow a more efficient search capability than DAP provides. DAP is built using the X.500 protocol, which uses the upper layers of the Open Systems Interconnection (OSI) stack.

Advantages of DAP:

• Full-featured, robust directory for recording and displaying information
• Global reach

Disadvantages of DAP:

• Overhead required in using the upper layers of the OSI stack
• Highly complex encoding for simple data elements

LDAP was created to simplify the process of creating and maintaining a directory service2, 3. LDAP can be used as a front end to DAP or as a stand-alone server. Creating links to other DAP servers maintains the “Global” function. Based on requirements for a directory, there are several applications that create user-friendliness to inputting and retrieving data. Full details of LDAP can be found in RFC 17774. Timothy Howes, author of, The Lightweight Directory Access Protocol: X.500 Lite, lists four advantages of LDAP over DAP2:

1. LDAP runs over TCP. This reduces the overhead that the OSI Session and Presentation layers require.
2. Simplifies the X.500 model in two ways:
   • Leaves out read and write operations and then emulates them through the search option.
   • Leaves out some of the less used security functions of X.500.
3. Uses string encoding for distinguished names and data elements.
4. Frees clients from chasing referrals.

There is no mention in the literature on LDAP, however, about how to integrate a directory service with multimedia applications. Such applications would have to be written specifically for LDAP.

Click to Meet™ (CTM)

FVC’s Click to Meet product can be completely integrated into a multimedia environment. While at the time of this document CTM does not integrate with LDAP, there are plans for it to be fully integrated by the end of first quarter of 2002 in version 2.3. By the end of 2001, version 2.2 of CTM should also be able to integrate with Microsoft’s Active Directory.

The front end of CTM utilizes a web interface. CTM works by integrating its database with a gatekeeper to store data and manage bandwidth on calls. The information entered can be as detailed as needed. CTM can tell when an endpoint is or is not available for a call. CTM can then make the connection by having the user select the desired endpoint. Since all the pertinent information has already been entered into CTM (Gatekeeper address, line speed to make the call, etc.), CTM can activate the call the user’s codec is on. If the codec is not on, then it will not have registered with the CTM server/gatekeeper. If the endpoint codec is not on and registered, that endpoint will show up with a “Red X” beside it instead of a “Green Check Mark” on the CTM screen. (See Figure 6.)

Figure 6

CTM can also initiate an MCU conference by having the person making the call select more than one participant from the CTM address book. CTM can interact with H.320, H.321, and H.323 endpoints.

CTM can also be used as a scheduler for prearranged, ad hoc, and point-to-point calls. (See Figure 7.) The user selects the date and time for the call, then selects the participants. At the appointed time, CTM initiates the call. If this is an MCU call (three or more participants), CTM will call the MCU, selecting a service that will fit the conference. If the MCU has the resources, the call will proceed. If the MCU does not have the resources, the call will fail.

Figure 7

CTM can also work with NAT and other firewall software by use of a proxy server. In its paper Click To Meet and NAT/Firewall Solving the Security Dilemma5, FVC outlines four call scenarios:

• A Private CTM to/from a Public Endpoint
• A Public CTM to/from a Private Endpoint
• A Private CTM to/from a Private CTM
• A Private CTM to a Private Endpoint

Other features of CTM can help with security, fault tolerance, scalability, and billing reports6.

CTM provides security in the form of authentication. Only authorized users can attach through the CTM servers. Once authenticated, users will then have access to QoS on the network. The user can still place calls without using CTM; however, quality of the call will be lower as there is no bandwidth management and no precedence for video data.

Fault tolerance is provided through load balancing by using gateway and MCU resources.

CTM can integrate with multiple MCUs, assuring scalability as a network expands.

CTM can also provide billing reports in the form of Call Detail Records (CDR), which can be integrated with third-party billing applications if desired. The CDR can be set up to run either automatically or manually by the administrator.