Media gateway a bridge on the way to the convergent network

Transcription

1 Media gateway a bridge on the way to the convergent network By Tomaz Vidonja and Gregor Polansek A little less than a year ago, a representative of one of our major customers came to Iskratel with an idea for a new product a universal media gateway. Universal, in this case, was meant in the sense of simultaneous VoIP/FoIP support and modem traffic. This idea not only provided us with a technical solution, but even more importantly, we also solved the problem of having only a short time to develop the product. The next step was to achieve the required quality and reliability for the product as well as the necessary openness and connectivity of the interfaces. Our final decision was to use CompactPCI, as it offered solutions to almost all of our problems. The rest, is history Requirements It was clear from the requirements that the customer wanted next-generation network (NGN) equipment. However, they wanted a product that could be integrated into their existing telecommunications network, where they provide data-transfer services to existing users in the form of modem traffic. At the same time the customer wanted to provide other, mostly new services, such as VoIP and FoIP, which are characteristic of NGNs. The customer raised a second, and possibly more important point. Due to the problems with providing investment funds for new equipment, the following questions are becoming increasingly important for both operators and users: Which services to quote? How to configure and what to include in the NGNs? What equipment to buy to satisfy the current needs, while at the same time allowing the simple integration of new interfaces and new services? The specifications of the new product were designed to provide answers to these questions. One of the principle objectives was to achieve the highest possible level of channel density at the unit level, in order to cover the market segment where end-equipment users are entering the market for an NGN. In the case of the Calidia CompactPCI card, all the functionalities needed to build the basic universal media gateway application (248 channels) are integrated on the same CompactPCI card. Simultaneously, due to its high level of density, the size of the product s basic configuration package is also suitable for existing racks (enclosures), or for set up in companies where shortage of space is a consideration. The user also has the option to expand the system easily to be able to match market requirements. There are several Iskratel Media Gateway (I-MeGa) products that can be interconnected (interchassis connection) or, the CompactPCI unit and other additional units can be included in a larger subrack. Challenges Because of the short time available to develop the product, an architecture based on a standard CompactPCI construction was investigated in the company s R&D department. Earlier architectures were, to a large extent, based on non-standard proprietary interfaces and formats. In the past this was more a rule than an exception for the telecommunications equipment market. The reasons for this were mainly that the products lifetimes, and consequently the products depreciation periods, were relatively long, the times from idea to planning to sale were long, and the markets were much less competitive. In addition, there were not many standards upon which it could have been efficiently constructed. With the increasingly rapid developments in technology, the capacity of embedded systems approaching that of personal computers, and the tendency for larger amounts of data being transmitted between individual points in networks, the conditions in telecommunications have drastically changed, too. Mainly it was the Internet and a wish to transfer various types of information speech, picture, video, etc. through optional interfaces that were the forerunners of the new network. Whether it is called a NGN, a new public network (NPN), or a convergent network, the old telecommunications bus, VME, and a variety of proprietary solutions no longer represent the right technological basis for the development of future products. Furthermore, market globalization, the continuous and rapid technological development, and the pressure on development departments for a short timeto-market have called for new standard solutions that provide the proper environment for telecommunications equipment manufacturers. The increasingly widespread use of CompactPCI in various fields has also resulted in a wider variety of sub-units, units, enclosures, etc., which has in turn led to price cuts. One of the most significant events that finally made the CompactPCI application a basis for products in the communications market was the appearance of new specifications within PICMG, especially the introduction of dedicated serial links to transfer ever-larger quantities of data. Among these recently approved specifications, PICMG 2.16 Compact Packet- Switched Backplane (CPSB) and the coming PICMG 2.17 StarFabric specifications are the most well known. The PICMG 2.16 specification approved in the middle of 2001 brings 10/100/1000 Mbit Ethernet links to the back panel. PICMG 2.17 specifications are currently being defined, and should be approved within a few months. They add 2.5 Gbits/sec serial links to the back panel, within which a special StarFabric protocol to transfer an optional type of information (ATM, IP/Ethernet, TDM, PCI, etc.) is applied. Architecture The product is designed on a single CompactPCI unit (Calidia). Thus, it is very

2 Functions and uses of I-MeGa I-MeGa applications Some typical product applications are shown in Figures 1a and 2a. Basically, the product enables the synchronous termination of modem traffic, as well as voice and fax transmission over IP (VoIP and FoIP). The product s smallest configuration allows it to be connected to eight E1 standard links, i.e. eight times by 32 DS0 (64 Kbits/sec) channels. Connection to a PSTN can be extended, on request, to 32 E1 links. A link to an IP network or the Internet can be provided via an Ethernet port. I-MeGa has the Media Gateway Controller Protocol (MGCP) client setup, and it currently has no Media Gateway Controller (MGC). Therefore, it is controlled and managed through the MGCP with an external MGC. I-MeGa as remote access server (RAS) The Media Gateway I-MeGa supports all conventional features that are needed for residential users to connect via standard protocols to the Internet or a corporate network. See Figure 1a. This includes support for bonding channels from/to residential/corporate users via the Multilink Point-to-Point Protocol (MPPP) and Multichassis MPPP. For corporate networking support for LANto-LAN dial-in/dial-out and routing, protocols like the Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) are included. There is also special consideration for multi Internet Service Provider (ISP) support. Virtual private networking based on a widely accepted protocol such as the Layer 2 Tunneling Protocol, traffic filters, or America Online (AOL)-specific issues are all taken into consideration. For authentication, authorization, and accounting a Remote Access Dial-In User Service (RADIUS) client is included. I-MeGa as a voice trunking solution I-MeGa also provides the facility to use an IP network as a transport medium for telephony, rather than using the PSTN, by providing packet-based telephony. See Figure 2a. In such a situation, a telephone call from the PSTN (analog or ISDN) subscriber between the media gateways is converted to a digital audio stream in the form of packets. Besides voice trunking applications, Iskratel s media gateway also supports phone-to-ip phone scenarios. In this case a PSTN subscriber calls an IP phone subscriber and the media gateway converts the PSTN call to H.323 messages. In addition to packet-based telephony, the transmission of facsimile documents is supported. See Figure 3a. The product also includes a limited signaling gateway functionality. A statically defined channel inside the bearer trunk that includes signaling can be enabled for packetization of signaling and sending to the special destination (e.g. MGC) via data network. Support for transport of PSTN signaling (e.g. SS7) over data networks (SS7/IP) is also provided. Figure 1a Figure 2a Figure 3a

3 easy and cheap to construct an initial or basic configuration that starts with 248 ports (corresponding to eight E1 links). Unlike other I-MeGa systems, all the functionalities required for the final product implementation are combined on a single unit. However, some supplementary options are added to extend the unit applicability. These supplementary functionalities are as follows: Two free PMC add-on slots The add-on slots are universal and are not used in a standard RAS/media gateway application. In addition to the PCI bus on Jn1 and Jn2, there are TDM and ATM Utopia L2 buses available on other PMC slots. By equipping powerful processor PMC units, the unit processing power required to carry out specific, more demanding applications, can very simply be increased. Adding various interface PMC units, for example STM-1 (OC-3) for a link to the ATM network, is available as an option. Naturally, many other units, either the L2/L3 Ethernet switch, a unit with a DSP, or any other can be equipped on free PMC slots. Local ATM bus On the CompactPCI unit there is a Utopia Level 2 bus available; it connects the main processor with PMC add-on slots. It also enables ATM traffic. VoATM on DSP Besides speech packetization for IP, DSP can also packetize speech to ATM cells, namely for AAL2. Together with the ATM bus on the unit, it offers the possibility to carry out traffic conversion between IP and ATM interfaces and vice versa. CompactFlash disk with IDE interface The IDE interface with a FlashDisk connector represents a handy and robust solution for applications that typically require a disk with the capacity of several tens or hundreds of Mbytes for saving data. An external disk is not required. Naturally, for very large capacities the price of a standard HDD is much more favorable, but the current price-breaking point between FlashDisks and HDD is already at 256 Mbytes and is constantly increasing. Besides, certain applications do not need any disk. Digital PLL A built-in digital phase-locked loop that can be locked to any E1/T1 interface, to an 8 KHz clock of the ATM optical link, or to an accurate external oscillator, is intended for special requirements. On one hand, Calidia is planned as a highly integrated CompactPCI singleboard system. On the other hand, the unit can easily be applied in major systems as a DSP resource unit at an affordable price, with or without E1/T1 framers. As a product, I-MeGa is currently available in the two smallest CompactPCI enclosures 1U and 2U packaging. In the first case, configurations with eight or 16 E1 links are possible and in the second case, configurations up to 32 E1 links are supported. Unit description Calidia is intended for the construction of universal gateways between conventional TDM-oriented telephone traffic and IP- or ATM-oriented data transmission. It is outlined as a standard CompactPCI unit that supports standard interfaces according to CompactPCI specifications like the 64-bit CompactPCI bus, the H.110 bus, and PICMG 2.16 Ethernet links. Together with the rear transition unit (RTM), it forms an entity known as a single-board RAS server or the media gateway. The classical approach to gateway construction is by means of CompactPCI systems wherein several different CompactPCI units are located, each of which performs its defined function. Such a typical system, presented in Figure 1, consists of the following: A Line Interface Unit (LIU), usually of the E1 or T1 type A unit with DSPs for the signal processing, the conversion of speech to data and vice versa, and the termination of modem traffic A central processing unit (CPU) to control and manage the system with an interface towards the IP network The approach taken by Iskratel combines all of the above-described functions on a single unit. This ensures a higher costeffectiveness, considerably better use of space (it only occupies one slot), lower power consumption, and higher scalability. In just one unit there are already eight framers that can operate in the E1 or the T1 mode (the T1 mode enables only 186 channels). On the unit, there are digital signaling processors (Texas Instruments TMS320VC5441) capable of processing 248 channels of modem (e.g. V.90) or speech connections (e.g. G.729). With modem traffic, RISC processors on the unit enable data compression and decompression of 248 modem channels. An efficient PowerPC communication microcontroller (processor) that runs at 266 MHz or more enables the packet processing of all 248 universal channels. This processor also acts as a control processor on which the main application runs, and as a processor that can process HDLC telephone signaling like SS7 and DSS1 using a built-in communication part. The processor also includes Ethernet and Utopia II interfaces with which it is connected to the world of data. The high-density unit, which merges all gateway functions, is presented in Figure 2. Designing the unit represented a challenge for the R&D department. Despite expertise with the PCI bus and broad experience in designing PMC units, there was some initial concern about the success of the project. The concern was in connection with the unit s high density and its technical and technological implementation. But it soon became clear that well-defined Compact- PCI specifications enabled engineers to focus on the unit implementation, and thus save a lot of time that would otherwise be required to define system interfaces, and the size of the units and enclosure. Carrier class gateway Calidia, together with the RTM, represents the smallest I-MeGa configuration of the product and can perform the role of both the RAS server and the media gateway for 248 universal channels. Due to standard interfaces in the unit and because it can be plugged into a system or non-system CompactPCI bus slot, the unit is also appropriate for the construction of larger gateways made up of several Calidia units and one or two Ethernet switch units in a single CompactPCI enclosure. By applying the 19-inch CompactPCI enclosure with 21 slots it is possible to construct a more efficient and highlyavailable, modular, and cost-effective system. Two power supplies, each of which occupies one slot, and two Ethernet switch units, which occupy one slot each, are plugged into the system. Two CompactPCI Ethernet switch units enable sys-

4 tem redundancy (switch-over to another Ethernet switch unit in the event of the Ethernet switch unit or individual Ethernet interface failure). In the same way, if one or both power supplies fail, the system continues to operate without disturbance. All the remaining slots in the enclosure are intended for Calidia universal slots. Thus, in one CompactPCI system we can construct a universal gateway for 17 x 248 = 4216 subscribers, which is very cost-effective. A higher-capacity gateway constructed with several CMA units is presented in Figure 3. Integrated gateway A lot of installed telecommunications equipment designed on the basis of CompactPCI is now available. Most of this equipment has a built-in back panel with the H.110 system bus described in the PICMG 2.5 specifications and developed for the needs of computer telephony (CT). To be able to incorporate it into such systems and to be able to construct simple CT applications, Calidia has the H.110 bus available. Thus, 64 Kbits/sec (DS0) TDM channels are directed to the unit and passed through H.110 buses on the back panel, and not through E1 framers connected outwards. Further development At least a doubling of current system capacities is expected this year, which naturally means the development of a new CompactPCI unit that is the successor to the existing Calidia. Quite a few questions arise: Is the CompactPCI bus still required, because new serial broadband links defined in PICMG 2.16, and soon in PICMG 2.17, practically annul the need for a dedicated control (CPU) bus such as CompactPCI? This also eliminates other limitations connected with the CompactPCI bus application in the system and enables the construction of open and more universal products. A partial answer to these questions is coming with new specifications within PICMG, where the preparation of the PICMG 3.x specifications with the meaningful subtitle A new platform for telecommunications equipment is being developed. Summary CompactPCI represents a well-defined and robust platform and has shown many advantages over proprietary solutions. Its widespread use and additional specifications have conditioned its penetration into the telecommunications equipment market. This product, which was developed at Iskratel and launched in record time, is additional proof and guarantee of the Figure 1 Figure 2 Figure 3

5 future success of the CompactPCI architecture. It is the power of broadband serial buses that produce a basis for the efficient implementation of various applications in telecommunications. Tomaz Vidonja is a System Design Manager at Iskratel where he is responsible for systems architectures. In addition, he leads a team responsible for next-generation and converged network platforms. Tomaz coordinates activities between product marketing and R&D and helps in strategic orientations. He has more than seven years of experience in technology and communications, having worked as system developer and project manager. He is currently involved in PICMG activities including representing PICMG Europe in the PICMG 2.17 StarFabric subcommittee and PICMG 3.1 and 3.3 working groups. He received his BS in Electrical Engineering and this year he expects to receive an MS in Business Management from the University in Ljubljana. Gregor Polansek is a senior design engineer at Iskratel working on embedded system solutions. He has more than five years experience in processor board design, HW/SW codesign and co-verification, and he specializes in network processors and DSP. Gregor is responsible for CompactPCI design and system integration. He has a Masters in Electrical Engineering and a Bachelors of Science, Electrical Engineering from the University of Ljubljana. For more information, the authors can be contacted at: Iskratel, Wireline BU, Ljubljanska 24a, 4000 Kranj, Slovenia, Web site: Tomaz Vidonja Tel: Fax: vidonja@iskratel.si Gregor Polansek Tel: Fax: polansek@iskratel.si