the end of haute couture design for next-generation...

Reprinted from Embedded Computing Design / Spring 2003 Reprinted from Embedded Computing Design / Spring 2003

Designers of media gateways for converged telecom networks have a daunt-ing task at hand. Their network must be flexible and scalable enough to handle new services, to add huge numbers of users, and to accommodate

very different types of information. They have to keep up with new technology to make the right decisions about how to architect a media gateway.

Researching and making these decisions in a recessed telecom market put even more pressure on designers who are already strapped for resources and time. That s̓ why industry standards, which have been widely accepted for many applications, are playing a more significant role in the simplification of next-generation platform designs. Die-hard proprietary environments are giving way to a new set of open equipment. One example is the move towards designing media gateways around a different concept: Putting the whole media gateway function on a single card.

The end ofhaute couture

design fornext-generation

telecomnetworks

By Philippe Chevallier


Figure 1

Figure 2

Figure 3

The proprietary way gives waySelecting a hardware form factor remains an important design decision. The upheaval of the telecom industry has turned the traditional approach of using proprietary chassis, back-planes, and cards on its head. This turnabout has acted as a catalyst for the acceptance of commercial-off-the-shelf products. Designers have recognized that open-standards-based platforms can be more cost effective, can deploy rapidly, and are strong long-term invest-ments. One of the most effective advantages of using standard form factors is the limited risk of changing the entire deployed platform because of higher density, higher processing power, and so on. The key to this interchangeability resides within two factors: standard formfactors and adoption of widely accepted standard protocols. However, as with personal computers, engineers originally designed VMEbus- and CompactPCI-based gateways around a traditional host-processor card, which controlled payload cards, i.e., I/O, DSP, etc., over a parallel bus. The host processor was running all the intelligence for control and operation as well as the payload information. Because of the high level of data transfer required for this bus, this form of connectivity turned out to be very inefficient for the telecommunications environment. Unpredictable latency and bandwidth were the major issues, not to mention the lack of reliability and service ability this type of bus was intro-ducing, such as hanging up the whole system when one of the cards fails to behave appro-priately over the PCI bus or, simply, when a card is being hot swapped from the backplaneduring data transfer. In a dual-host processor environment, these issues create even more complexity. Developers introduced some hot-swap and failover mechanisms and are attempting to continue to make them open standards.

Ethernet provides one solution, mesh anotherBecause of its inefficiency, other means, such as Ethernet, slowly bypassed the parallel bus. This turned out to be a much easier way to interconnect those boards. Users have proven it faster and much less complex to operate. Engineers have developed chassis with dual busses. The parallel bus controls and manages the cards, and Ethernet carries the data. However, it became obvious that the parallel bus was no longer needed except for power and ground. To provide the chassis management, a special interconnect referred to as IPMB has reduced this function to a bare minimum. Today, developers offer backplanes without any parallel buses, and the system carries all data, whether payload or control information, over these two fabrics. Developers can configure the main fabric for bearer transfer into two main categories:

Dual star, where cards interconnect to each other via two central points Full mesh, where each and every card has the ability to communicate directly to each

other without going through a central point

The dual star fabric offers simplicity, as each node is only required to connect to two well-identified central points. These points can be hubs or switches, and with an appropriate pro-tocol, it is possible for each end card to communicate with each other. This architecture is actually well suited for traffic aggregation but presents a bottleneck when all cards have to communicate with each other. The CompactPCI Serial Mesh Backplane or cSMB, ratified as PICMG 2.20, provides such capability. Although it is a bit more complicated to operate, cSMB can offer a high level of interconnect between every node.

Today, ATM and IP are predominantly the two main networking protocols that communi-cate between network equipment and that primarily operate around the concept of switches and routers. In this model, there is no host or any payload cards, network end points, gate-ways, switches, network controllers, and so on. One can apply the same concept within a chassis.

Media gateway: The next generationWithin the scope of the next-generation network, engineers now design media gateways around a different concept. A single node can host the whole media gateway function, or card, that comprises three different types of processors (see Figure 1 for a schematic of a VoATM media gateway):

Digital Signal Processor (DSP) used to digitize and packetize voice traffic into aspecific format (VoATM, VoIP)

Network Processor (NP) used to exchange bearer traffic to external nodes General Purpose Processor, or System-on-a-Chip (SOC), used to host control and

management software

To aggregate all traffic, control or bearer, each MGW node interconnects with TDM, ATM, and IP switch nodes. For instance, an IP switch node would simply use an IP switch type of network processor and an SOC as the schematic shows in Figure 2.

Such card offers IP traffic aggregation, network address translation, and QoS such as DiffServ, RSVP, etc., as well as routing protocols RIP and BGP. On the ATM side, an ATM switch card interfacing with the PICMG 2.20 standard aggregates the traf-fic (see Figure 3 for a schematic).


Figure 4

The fourth element pertinent to designing a full media gateway platform is the shelf manager. The shelf manager essentially provides operation and management of the chassis, and does so via IPMI and Ethernet. Mainly, an SOC, plenty of memory, and some local storage for data preservation purposes constitute this ele-ment. Figure 4 shows a schematic of the shelf manager card.

These four main elements within a single CompactPCI chassis combine with an N+M (N active, and M standby) redun-dancy architecture to constitute a fully scalable and serviceable MGW solution as shown in Figure 5, a schematic of a media gateway.

PICMG 2.16 is useful for IP communica-tion over the backplane for bearer and/or control traffic, while PICMG 2.20 is use-ful for ATM bearer traffic, and PICMG 2.9 is useful for shelf management. Besides configuration of the media gateway cards in an N+M environment, every other ele-ment, such as an IP switch, ATM switch, and shelf manager double in configuration in a 2N environment (active/standby) for redundancy purposes.

Developers can apply the same concept to other platforms such as signaling gate-ways, softswitches, and media servers. The only differentiator between these different platforms resides on the type of payload card and its software. All the other cards such as the switch cards and shelf manager remain the same. See Figure 6 for a sche-matic of a softswitch + SS7 gateway.

Standards have played a major role in the simplification of next-generation platform designs. The long lasting proprietary environment has given way to a new set of equip-ment. This equipment offers better compromises within all the given constraints: time to market, cost, availability, service ability, reliability, and probably most importantly, long-term investment protection.

Philippe Chevallier is a system architect and member of the technical staff at Motorola Computer Group. He has 15 years experience in telecommunications related to both hardware and software development and has been with Motorola for the past 12 years. Chevallier has a master s̓ degree in computer science from the University of Science and Technologies at Lille, France.

Motorola Computer Group provides innovative intelligent building blocks for standards-based embedded computing. Motorola Computer Group is a business unit of the Motorola Integrated Electronic Systems Sector (IESS).

For further information contact Motorola at:

Motorola Computer Group2900 South Diablo Way • Tempe, AZ 85282

Tel: 800-759-1107 • Fax: 602-438-5627 • E-mail: [email protected] site: http://www.motorola.com/computer

Figure 5

“Standards have playeda major role in

the simplification ofnext-generation

platform designs.”

Figure 6


Between the softswitch and the signaling gateway, the protocol is based around the SIGTRAN protocol under the IETF directives. There are many variants to implement-ing SIGTRAN, but the basic requirement is to communicate SS7 information over anIP network. Due to the level of reliability the SS7 network required, the IETF defined a new variant of the TCP also known as Stream Control Transmission Protocol – RFC2960 (SCTP).

At the upper layers, the designer has the choice between different bridging configurations as follows:

MTP2 – User Peer-to-Peer Adaptation Layer (MTP2) MTP3 – User Adaptation layer (MTP3) Signaling Connection Control Part User Adaptation Layer (SUA) V5.2 – User Adaptation Layer (V5UA) ISDN Q.921 – User Adaptation Layer RFC3057 (IUA)

To communicate call information between softswitches, engineers have devel-oped two main protocols: H.323 and Session Initiation Protocol – RFC3261 (SIP). H.323 and SIP have both been deployed, but lately SIP has gained significant momentum due to its design. SIP is a text-based protocol that is based on HTTP and MIME. The SIP design supports voice transmission, uses fewer resources, and is considerably less complex than H.323. Its addressing scheme is URL-like and humanly readable, for example, sip:[email protected]. SIP relies on the session description protocol (RFC2327) for session initiation. Besides the point-to-point con-nection between two SIP elements, media gateway, IP phone, etc., it also offers mobilityand unified messaging functionality. It allows call conferencing capabilities, voice mail, voice portal, and more.

The third generation wireless infrastructure is currently embracing this standard, which will provide the same level of feature sets that landlines will be offering.

Next-generation telecom networksO

ne of the key aspects to deal with when designing any converged network element is to make sure it is standard-based and fully

interoperable with all types of off-the-shelf components that support those standards.

For instance, between the call control-ler and the media gateway, the Internet Engineering Task Force (IETF) and the International Telecommunication Union (ITU) have developed standard proto-cols such as H.323, the Simple Gateway Control Protocol (SGCP), Network Cable Signaling (NCS), and the Media Gateway Control Protocol (MGCP).

Now, the first ITU/IETF full cooperation has resulted in a unique protocol, H.248/Megaco (RFC3015). It is important to point out that all of these protocolsare IP-based and, therefore, able to be carried over any IP-based network.

To communicate subscriber, billing, and other information with the traditional telecommunication network, a signaling gateway interfaces between the SS7 network and the softswitch.

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the end of haute couture design for next-generation...

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