A message handling system for B-ISDN user-network interface signaling test software

Hewlett-Packard Journal, April, 1997 by Satoshi Naganawa, Richard Z. Zuo

B-ISDN user-network interface signaling has many different protocol variants and each of them has tens of different types of messages. The message handling system provides a powerful tool for the developer to easily support these variants and messages in the HP Broadband Series Test System (BSTS).

Over the past several years, as the "information superhighway" has gained the attention of many countries and communication network service providers, the focus of the Broadband Integrated Services Digital Network (B-ISDN) industry has shifted from providing transmission capabilities via Asynchronous Transfer Mode (ATM) to providing a variety of B-ISDN network services such as private and public B-ISDN, switched virtual connections, and LAN emulation over ATM. Signaling plays a key role in realizing these services. The key functions of signaling are:

* Call setup and disconnection

* Negotiating and agreeing on quality of service (QoS)

* Providing accounting and charging information

* Resolving internetwork and intranetwork routing

* Facilitating basic services and supplementary services

* Identifying the occurrence and cause of any network or service failure.

Signaling consists of user-network interface (UNI) signaling, network-node interface (NNI) signaling for public networks, and private network-node interface (PNNI) signaling for private networks. The UNI is the boundary between a private or public network and the user equipment. User equipment can be a telephone, a computer, or video conference equipment as illustrated in Fig. 1.

[Figure 1 ILLUSTRATION OMITTED]

The Broadband ISDN UNI signaling test software, HP E4214A, is a new addition to the HP Broadband Series Test System (BSTS). It is designed for R&D engineers and network engineers to develop, troubleshoot, and verify the features and functionality of UNI signaling. Fundamental features of the UNI signaling test software are protocol message decoding and encoding. With decoding, the user can monitor the message transaction between the user equipment and an ATM switch. With encoding, the user can execute a condition test such as constructing a correct or incorrect message and sending it to a switch to analyze the response.

UNI Signaling Standards

As ATM emerges as the mainstream technology in the telecommunication network market, the standardization of UNI signaling has been progressing at a very rapid pace during the last several years. Two major standardization organizations--the International Telecommunications Union Telecommunications Standardization Sector (ITU-T) and the ATM Forum--created their UNI signaling standards in an interlocked way. In May 1993, ITU-T published its first draft recommendation Q.93B[1] to support point-to-point ATM switched virtual connections. The ATM Forum adapted Q.93B to support point-to-multipoint connection control, variable-bit-rate connections, and the ability to signal quality of service (QoS) on a per-call or per-connection basis. These enhancements were published in the ATM Forum UNI 3.0 specification[2] in September 1993. Later, the ITU-T updated Q.93B as Q.2931[3] with some important changes. Following those changes the ATM Forum also updated UNI 3.0 into UNI 3.1[4] in September 1994. In the meantime, the ITU-T defined point-to-multipoint switched virtual connection features and published its standard as Q.2971[5] in June 1995. About half a year later, the ATM Forum published UNI 4.0[6] to incorporate the leaf-initiated join capability and the available bit rate (ABR) service in Q.2931 and Q.2971. In addition to the protocols promoted by the ITU-T and the ATM Forum, some countries and network service providers also created their own UNI signaling protocol variants. From this brief history, it can be understood why there are many UNI signaling protocol variants. Undoubtedly, more variants will come soon to support more new features.

In addition to having many different UNI signaling protocol variants, each variant has many different types of messages. A message is a protocol data unit (PDU) used in a signaling protocol. Each message can contain multiple information elements, called IEs. Some IEs must be contained in a particular message and are referred to as mandatory IEs. Some IEs are optional for a particular message, and therefore will not always appear in that message type. For example, the UNI 3.0 standard[2] has 16 different types of messages and 21 different types of IEs. SETUP, CALL PROCEEDING, CONNECT, and CONNECT ACKNOWLEDGE are the messages for call establishment, as shown in Fig. 2. The other categories of messages are designed for call clearing, point-to-multipoint communication, and other purposes.

[Figure 2 ILLUSTRATION OMITTED]

The situation described above created a challenge for HP's BSTS UNI signaling test software developers. The software needed to support many protocol variants, with many different types of messages and IEs in each variant. Simultaneously, the R&D cycle time was much reduced. We realized that hard-coding each message and IE for each protocol variant in the decoding and encoding engines would make software maintenance a nightmare, would require the programmer to change the decoding and encoding engines whenever adding a new protocol variant, and would be of little help to us in developing NNI and PNNI signaling test software in the future.