Dynarc to Supercharge Circuit Switching

A Swedish startup is offering a high-tech update on the concept of circuit switching that it claims creates the perfect network for real-time IP applications at the enterprise.

By: John Spofford

If you thought network time division multiplexing was dead, think again. A Swedish start-up, Dynarc AB is pushing DTM (dynamic-synchronous transfer mode)—a nonstandard dynamic circuit-oriented network architecture.

Derived from research carried out at the Swedish Royal Institute of Technology and funded by Ericsson Telecom AB of Stockholm, Sweden, DTM tries to combine the best features of circuit switching and packet switching to support real-time critical traffic as well as bursty traffic in an equally efficient manner. Due to the inherent simplicity of circuit switching, Dynarc claims DTM can cost-effectively scale up to high-speed fiber optical links.

With a new office in Mountain View, CA, the company is putting theory into practice with the introduction of access products that use DTM. The first product, announced in December, is the DS 100 (see Figure 1.) It is a LAN switch that enables network managers to integrate voice, data, and video over existing infrastructure while providing guaranteed quality of service (QoS) for IP traffic, dynamic allocation of bandwidth, and the ability to establish a secure VPN.

A second product will be introduced this week at CeBIT ‘99 (March 18–24, Hannover, Germany). The DS 300 is an edge router switch that serves as a high-performance multiservice switch for Metropolitan Area Networks (MANs) and Internet POPs.

Understanding DTM
DTM is a based on a simple circuit-switched scheme on a shared link, such as a ring or a bus. It uses a time- and space-division multiplexing as opposed to the fixed-size cell switching of asynchronous transfer mode (ATM) or the packet switching of frame relay. In the DTM scheme, data is broken down into 125-microsecond intervals that are in turn divided into 64-bit slots.

"This fast circuit switching that lets operators assign, shape and optimize the use of bandwidth is a way to give Internet protocol (IP) deterministic QoS," says Olov Schagerlund, Dynarc president and CEO. "Internet service providers are looking for a set of differentiated, value-added services such as virtual private networks (VPNs), and Internet telephony."

Time- and space-division multiplexing controls the access to a link. In order for a node to communicate with other nodes, it has to own time slots on the link segments between the nodes. A small portion of each time slot is reserved for sending the control information used to control access to the link, and for setting up and taking down DTM channels.

A DTM channel is a group of slots allocated between sender and receiver(s). The use of channels is where DMT differs from circuits in traditional circuit-switched networks in several ways:

• Multirate: channel capacity can be any multiple of 512 Kbps, up to the entire data capacity of the link. The capacity can be dynamically changed during the lifetime of the channel, allowing capacity allocation to vary with the traffic.
• Fast setup: a channel can be established and taken down within a few milliseconds, enabling dynamic capacity changes during transmission.
• Simplex data flow: allows for asymmetric communication patterns.
• Multicast: the established channels can have multiple destination points, making DTM suitable for IP multicasting applications.

Schagerlund points out that the DTM technology is able to coexist with existing technologies when deployed as a LAN backbone, or a campus-area network. "It is a cost effective way to upgrade a FDDI ring to 1 Gbps. With ATM and Gigabit Ethernet it is necessary to change topology, as neither of those topologies have a ring structure," he says.

Putting the technology to use
Dynarc is exploring two implementations for its DTM technology. First, DTM may be deployed as a data link layer technology that provides intelligent transport links between routers and hosts in an existing IP-based network. Second, DTM can serve as a highly scalable backplane architecture for a multiservice switch.

The former implementation requires the development and manufacturing of router port adapters, network interface cards, and network device drivers. Dynarc is pursuing the latter with its new products that represent the development of a high performance, multiservice switches in the backbone POP (point of presence) of an Internet network.

"It seems to be a very general purpose technology in the sense that you could adapt it for a lot of applications," says Michael Speyer, program manager at the Boston-based research firm The Yankee Group.

"While you could use it [inside a] piece of hardware as a backplane technology to build high speed multiservice backplanes, this technology lends itself to be used outside the box. I think its value rather lies more in the WAN, rather than the LAN, because of its excellent multiservice capabilities."

While DTM is an interesting new approach to building IP networks, its biggest problem is that it faces an uphill fight against a number of entrenched technologies.

"From a technical point of view it seems like a pretty good technology, the problem is, does the market need another new technology?" Speyer asks.

List price for the DS 100 starts at $17,500 depending on configuration. It is available for delivery now. The list price of the DS 300 starts at $30,000, depending on configuration, and will be available for delivery in May.