Switching routers answer the call for more bandwidth

The widespread adoption of high-performance switching, increased centralisation of servers and the rapid acceptance of Internet- and intranet-based communications are taxing today's router-based networks.

A next-generation communications product, known as a multilayer switch or a switching router, solves the connectivity and performance problems of today's routers and provides a foundation for growing bandwidth and quality-of-service (QoS) requirements.

The switching router melds Layer 2 and Layer 3 functionality using hardware integration and advanced silicon. Using hardware-based technologies that provide multigigabits of capacity, the products provide scalable bandwidth and capacity to the growing number of enterprises moving to Fast and Gigabit Ethernet speeds.

Switching routers perform Layer 2 switching and multiprotocol routing at wire speed. Such high levels of performance are achieved by integrating routing functionality into an Application Specific Integrated Circuit (ASIC). This "router on a chip" architecture enables switching routers to provide many times the performance of traditional routers.

Traditional routers use a processor to perform Layer 3 forwarding. In existing routed architectures, each packet is sent to a forwarding processor that performs next hop lookup and packet modification functions.

When these tasks are complete, the packet is sent to the destination queue for delivery.

Switching routers streamline this process in two ways. First, they remove the processor from the normal data forwarding path. All Layer 3 forwarding functions are performed when a packet is received, enabling the packet to be queued directly to the transmit path. Second, the router on a chip handles Layer 3 forwarding on the fly.

Another key performance-enhancing feature of switching routers is hardware-based Layer 2 and Layer 3 address resolution. In traditional processor-based routers, the most time-consuming activity is address lookup and resolution. Switching routers include Integrated Layer 2/ Layer 3 Address Resolution Logic that performs the high-speed address lookup and resolution needed to deliver wire-speed performance.

Cost savings

In addition to dramatic performance improvements, this hardware-based design approach produces significant cost savings. In contrast to traditional routers that include multiple processors, a switching router may be composed of only one processor, which handles topology protocols such as Routing Information Protocol (RIP) and Open Shortest Path First (OSPF).

The cost savings realised through the use of ASIC technology rather than higher priced processors are passed on to users.

Finally, the integration of Layer 2 and Layer 3 functions into a single piece of silicon reduces system costs even further.

The benefits of this approach are clear when comparing switching router prices with those of traditional routers.

When a switching router is deployed in a network, end-stations can communicate by means of Layer 2 or Layer 3 forwarding.

The type of forwarding used depends on the subnet membership of the end-stations.

Subnets are portions of a network that share resources and are typically defined by their own net address.

Traffic from end-stations that belong to the same subnet is automatically forwarded at Layer 2, while traffic from stations belonging to different subnets is transported via Layer 3 forwarding.

Switching routers handle a full suite of protocols, including IP, RIP, OSPF, IPX and multicast.

However, many networks include non-routable protocols, such as NetBIOS or DEC LAT, that do not recognise Layer 3 forwarding.

When used in such environments, switching routers will automatically switch or route between ports depending on whether a protocol is routable.

The hardware integration of a multiport Layer 2 switch and multiprotocol router into one package lets users greatly simplify their network infrastructure.

For example, replacing one or two switches and a traditional router with a switching router enables multiple ports to perform as a switched subnet yet link to the router as a single entity.

Switching routers can also be used to increase network efficiency and decrease equipment costs by supporting virtual LANs.

VLANs are a grouping of users on a net regardless of their location. With switching routers, VLANs can be interconnected at Layer 2 or Layer 3.

This allows the physical network infrastructure to be shared by multiple subnets. For instance, multiple broadcast domains or VLANs can be connected to a single gigabit port on a switching router.

QoS features

Multimedia applications are a driver for next-generation products such as the switching router. These applications require advanced network QoS services such as QoS and multicast. Switching routers include inherent QoS capabilities, such as priority queuing and flow control, that provide delay-sensitive applications with adequate bandwidth and consistent latency.

Switching routers are the next step in the evolution of the router and switch. Before the advent of these products, Layer 2 and Layer 3 technologies were often force-fitted into existing environments at the expense of network performance and end-user satisfaction.

Faced with increasing loads, unpredictable traffic patterns and new applications, users and vendors clearly saw the need for a better mousetrap.

Drusie Demopoulos is vice president of marketing at Gigabit Ethernet start-up Foundry Networks