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LAN switches gear up for Web explosion.

Adding functionality layer by layer.

LAN switches have come a long way since their introduction to relieve congestion in local area networks (LANs). Because of their ability to increase the performance of overloaded networks cost-effectively, LAN switches are rapidly becoming the preferred means for connecting hubs. routers. servers and even desktops.

At the same time, LAN switches are taking on more advanced capabilities to help IT managers who have begun deploying multiservice networks that optimize bandwidth use. prioritize traffic and guarantee application performance. In addition. the explosion in Web access and e-commerce has placed further demands on LAN switches, primarily to reduce user wait times, gain better control over content and provide seamless load-balancing functionality to the Web server network.

LAN switch vendors are addressing these more advanced needs by extending their products' functionality higher into the seven-layer open system interconnection (OSI) communications model.

Most of the original switches operated at the data link layer, or Level 2 of the OSI model. This meant using the source and destination media access control (MAC) addresses to determine if a packet should be forwarded, and to which port, based on an address table lookup. By dividing the network into segments and allowing the segments to operate without interference from traffic local to the other segments, the switches were able to dramatically increase the performance of heavily trafficked LANs. Today's more intelligent switches act on information beyond the Level 2 MAC addresses.

Layer 3 switches, for example, use information from the network layer, or Level 3 of the OSI model, to route packets at wire speed, raising performance to the millions-of-packets-per-second range, compared with thousands of packets per second with software routers. At the core of these devices is a switching matrix that provides fully switched connectivity down to the port level. Custom ASICs (application-specific integrated circuits) enable the wire-speed switching on a packet-by-packet basis.

Software routers have traditionally had the advantages over LAN switches of better WAN (wide area network) connection and multiprotocol support. To compete. LAN switch vendors are introducing high-speed WAN interfaces. ranging from OC-3 to OC-12 and beyond, for both asynchronous transfer mode (ATM) and packet-over-SONET (synchronous optical network) deployments. In addition, some vendors are adding support, through software, for protocols besides Internet protocol (IP). With these new features. LAN switches can compete effectively with software-based routers for both enterprise and service provider networks.

To distinguish between different types of applications, such as file transfers, Web browsing and real-time applications, LAN switches need to use packet header information beyond the network layer. Layer 4 switches, for example, might examine the TCP Port ID in the IPheader. Layer 4 filtering and forwarding allows managers to make more sophisticated decisions in such areas as traffic prioritization, bandwidth allocation, access control and load balancing. The switches are intended for IT managers who have to focus on maintaining service levels for selected, more critical users and applications because the traffic in their campus backbones is increasing at an unpredictable rate.

Switches that operate with information in Layers 5 through 7 of the OSI model provide even more sophisticated functionality. These intelligent-content switches typically provide the Layer 3 and 4 features, and add functionality by reading into the HTTP (port 80) request header. URL or "cookie." the bit of data that identifies users.


Looking ahead over the next few years. IDC predicts that Layer 3 hardware switches will become the prevalent choice for LAN backbones. Gigabit Ethernet will be adopted in campus environments and for server consolidation, with the initial implementations in switch-to-switch implementations, just as with 100-Mbps Ethernet. LAN switches with tens of 100-Mbps connections matched to a few Gigabit Ethernet uplinks will become commonplace.

IT managers will look for scalable solutions that do not sacrifice latency or throughput as management features are activated. Security will also be a growing concern, resulting in the integration of such features as firewall and network address translation support directly into switch architectures.

IDC expects that organizations seeking to upgrade their campus infrastructures will inevitably deploy switches in a strategic role. Networks comprising high-density switches in the wiring closet/edge that cascade into Gigabit Ethernet Layer 3 or multiprotocol switches at the core are already routine. Some organizations have even begun to migrate their wiring closets to Layer 3. In the near term, however, IDC contends that Layer 2 switches with some advanced features, such as traffic filtering, are a simpler and more cost-effective approach for the edge.

Widespread availability of cost-efficient multilayer closet switches with advanced Layer 3+ packet classification will enable IT managers to extend quality-of-service (QoS) capabilities to the network edge and build policy networks, further driving demand for Layer 3+ switching. As a result, features--such as Layer 3 IP switching and Layers 2 through 7 filtering and traffic classification--will become standard on more sophisticated workgroup switches.

At the same time, router infrastructure will remain in place, providing wide area access and non-IP support to the network. IDC still views a combination of Layer 2 LAN switches and routers in the backbone as a viable alternative to Layer 3 switches.

Beyond the enterprise, LAN switches are finding use in such applications as the transparent LAN services provided by incumbent and competitive local exchange carriers, as well as DSL (digital subscriber line) access concentration, and Web hosting and collocation facility management. To capitalize on this growing market, vendors are touting the benefits of delivering new services as a key selling point of next-generation switches. In IDC's opinion, though, these services are not the primary driver for the deployment of LAN switching equipment. First and foremost, organizations are interested in solving near-term network bottlenecks.

The first step in freeing a network bottleneck is to increase bandwidth. Most enterprises are moving, or have moved, to 100-Mbps Ethernet speeds. Gigabit Ethernet is also coming onstream, but it will have to wait for a couple of years to become a ubiquitous standard, since organizations will first need to get over the infrastructure cost of upgrading to 100-Mbps Ethernet.

The next step will be 10-Gbps Ethernet Layer 3 switches, which will provide a significant alternative to ATM switches for IP-centric applications. Typically, network managers will combine Layers 2, 3 and 4 switches with ATM cell switches.

Wiring closet switches that have traditionally supported only Layer 2 switching will need to also support Layers 3 and 4 services, such as traffic classification, protocol filtering and multicast, to handle and prioritize different types of traffic. Layer 3 wiring closet switches will become commonplace as IT managers purchase the devices to future-proof their networks.


Layer 4 switches were an important first step in allowing IT managers to exert more control over the network by using higher levels of information contained in network-traversing packets. These switches look at the TCP destination or source-port number assigned to certain applications and use that information to set up a policy to prioritize one type of traffic over another in the event of congestion. Besides distinguishing among different types of traffic, the switches provide one of the most straightforward and common ways to implement QoS within a network, by utilizing IP port numbers, source and destination addresses, and network priority policies to process packets.

In addition to managing the flow of traffic across the network, Layer 4 switches enable the better use of connected, shared resources, such as overloaded Web servers. Increasingly, e-business demands are challenging the best-effort approaches of traditional traffic-management solutions. Guaranteeing website availability and performance is absolutely critical to organizations relying on Web sales to sustain their business models. Furthermore. Web-hosting companies, especially service providers, need to make certain they can support application performance with stable network access, latency and security. Previous-generation devices do not meet these new challenges.

A small number of vendors have introduced switches that examine and act on packet information beyond Layer 4. Why is this higher layer awareness important? Because switches that use only Layer 4 information to make QoS decisions are proving insufficient for network managers who want to control and manage traffic within e-commerce, and at Web hosting and Web content sites. HTTP has even become the dominant platform at enterprise sites as they attempt to "Webify" applications.

To a Layer 4 load-balancing device, for instance, Web applications are indistinguishable from HTTP traffic because the applications appear to be using TCP port 80, the typical TCP port for HTTP traffic. Simply recognizing HTTP traffic does not provide enough information about the content of the packets. Optimizing traffic management in a Web-server environment requires additional packet processing and decision making.

The intelligent-content switch looks into an HTTP payload and recognizes URLs and cookies. In this way, it determines what content is being requested and routes TCP or user datagram protocol (UDP) flows to targeted servers based on the requested content. Switches that use URL or Layer 7 information can control which applications receive priority by distinguishing and prioritizing HTTP applications. Through URL and cookies, intelligent-content switches learn where specific content resides, either locally or remotely, and dynamically select the best reverse proxy cache or Web server for client requests at that moment, avoiding busy or overloaded sites.

Because of these features, Internet service providers and Web-hosting companies, in particular, will make increasing use of intelligent switches during the next few years to deliver new tiered services and provision bandwidth for a demanding corporate customer base. At the same time, the switches will have a greater presence in the enterprise for handling intranet and other IP applications.

IT managers will demand scalable platforms that allow them to support a true multi service network, with special features and functions for each part of the network. As a result, buying decisions will increasingly be based less on box comparisons than on how a vendor positions a total networking solution.

Edwards manages communications and network consulting for IDC, a global IT market research and consulting firm headquartered in Framingham, MA.
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Comment:Vendors of LAN switches are working to address the needs of E-business and Internet-enabled systems by extending product functionality to higher OSI layers.
Author:Edwards, Morris
Publication:Communications News
Geographic Code:1USA
Date:Dec 1, 2000
Previous Article:NEW PRODUCTS.
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