51-20-08 Creating Network Expressways Using Previous screen Ethernet Switching Engines Andres Llana, Jr. Payoff Today, high-powered Ethernet switching engines with support for full-duplex technology and advanced multiprotocol filtering functions provide an inexpensive route to high-speed expressways. These devices, when properly deployed, can reduce network contention and greatly improve network throughput. Introduction The new, high-powered Ethernet switches provide the network administrator with many more options to more efficiently manage LAN traffic. Low-cost Ethernet switches can be used to create virtual LANs at the protocol or broadcast group level. For example, Internetwork Packet eXchange traffic could be filtered at the port level, restricting it from entering another network segment while Internet Protocol (IP) traffic might be allowed to pass. Broadcast traffic might be limited on a port-by-port basis to further control traffic on each network segment. High-bandwidth traffic can be selectively isolated from the rest of the network. Properly deployed, Ethernet switches can consolidate traffic in multiprotocol LANs (e.g., IP, Internetwork Packet Exchange (IPX), DECnet, AppleTalk) while effectively improving overall network throughput. Competitive switches selling for less than $4,000 (for as many as eight Ethernet ports with routing and filtering options) provide a cost- effective method for consolidating LAN segments, greatly improving network throughput. Conserving Bandwidth Network congestion has greatly increased in recent years as more nodes are added and applications become more complex. LAN segmentation was originally deployed as one means of organizing groups of users into separate but interconnected LAN segments. This technique improved network performance by reducing contention, however, it is not as effective as LAN switching. The advent of the LAN switch represented a major leap forward for LANs. The first Ethernet switch was introduced by Kalpana in 1990, with LAN switching taking on many more refinements since that time. A LAN switch can provide a dedicated bandwidth segment for the connection of high-traffic workstations or servers. These switching engines, when combined with the more advanced network management systems, extend the ability of the network administrator to fine-tune and tailor a network to optimum performance levels. The issue now—and the basis for discussion in this article—is how best to deploy this technology, particularly as Ethernet networks continue to expand and grow. Going Beyond Segmentation When properly integrated into the architecture of a LAN, intelligent hubs can greatly enhance the process for network optimization. For example, a network planner can easily reduce network traffic by aggregating users with common needs on separate LAN segments. Through this process, any requirements for large amounts of bandwidth between Previous screen common users can be restricted to their common segment environment. This process of establishing high-bandwidth users on common segments, however, can be further improved through the application of Ethernet switches. A switched LAN has several advantages over segmentation, including: · Ease of migration. The introduction of a switch into a LAN does not create a problem for the network staff because the LAN technology remains the same. · Capital conservation. Introduction of a switch does not affect the overall structure of the LAN because no new cabling, hardware, or network infrastructure changes are required. · Evolutionary migration. Switches enable the network planner to migrate toward the development of a virtual LAN and eventually integration with Asynchronous Transfer Mode backbone facilities. About Ethernet Switches Original Ethernet was a shared LAN technology that allowed only one data conversation at a time. In this situation, the 10M bps of available bandwidth may end up being shared by multiple users. Consequently, when more than one user wants to access the network, collisions may result that cause delays limiting user productivity. Because of the half-duplex nature of the Ethernet network and its distributed arbitration methodology, only 40% to 50% of the network's throughput potential is ever realized. For this reason, an Ethernet switch might be viewed as a throughput enhancer that allows multiple conversations to occur at the same time on the network. An Ethernet switch essentially creates parallel data conversations by establishing a dedicated point-to- point connection between two workstations (see Exhibit 1). This type of capability can increase normal Ethernet 10M bps throughput to 20 or 40M bps. Full-Duplex Point-to-Point Ethernet Connection Earlier switches were separate modules designed to fit into the backplane of an intelligent hub. The newer LAN switches, however, are robust standalone units that can be used to support desktop-to-desktop switching, workgroup switching, or serve as larger enterprise backbone switches. Desktop Switches These are used to link users with a common interest in applications that may be bandwidth intensive (e.g., imaging, high-speed modeling, or multimedia applications). An example of a desktop switch might be Fore System's ANTswitch or Cisco's Catalyst Switch series. Workgroup Switches These switches are deployed to add capacity to a congested LAN, allowing the connection of individual workstations or LAN segments. These switches can be connected to backbone networks or high-speed links connecting them to other servers. Examples of workgroup switches are LinkSwitch, Cabletron's TSX-1620, and Performance Technologies' Nebula 2000. Backbone Switches Larger switches provide very high speed backbone switching. These may use store-and- Previous screen forward or other advanced networking techniques to support large numbers of connections and high traffic volumes. These switches are likely to integrate a high degree of redundancy and support some form of interface to a high-speed public network facility (e.g., T1, frame relay, or Asynchronous Transfer Mode backbone). They also support multiple protocols. An example of an Enterprise Switch would be the IBM 8250/60 series multiprotocol switches, Alantec's Power Hub 7000,3Com's LANplex 6000, or XYLAN's OmniSwitch. Originally, Ethernet switching engines were deployed in conjunction with intelligent hubs to enhance and extend LAN segments. In this setting, an Ethernet switch— when deployed in a segmentation infrastructure—could clear up network bottlenecks that would under other circumstances create significant response time delays. They also provided the ability to establish high-speed multiport internetworking solutions to allow the LAN administrator to segregate those high-speed workstations that had high bandwidth requirements. LAN switches support 100M-bps LAN speeds to include 100Base-T, 100VG-AnyLAN, and FDDI networks. Not All Switches Perform the Same Not all Ethernet switching engines are designed the same and therefore their characteristics are a performance factor that must be considered in the configuration of an extended LAN. Switching modules are designed to interconnect LAN segments in much the same way that a telephone conversation is linked using a PBX. The LAN switching engine itself provides for the full wire speed interconnection of a LAN's segments. Although the terminology has changed in the past few years, two prevalent switching designs may be found in Ethernet switches: cut-through switching and store-and-forward switching. Cut-Through Switching Under this switching architecture, the switch has been designed to forward packets to their destination before a packet is fully received and before the collision window passes. This type of architecture does not limit the end-to-end throughput as do store-and-forward bridges, for example. Cisco and IBM switches use this design characteristic. Store-and-Forward Architecture Under this switching architecture, the whole packet is fully received before the forwarding process begins. Each packet is buffered in memory and the switch examines the entire packet. Because the packets can be inspected, more advanced management capabilities are available. The forwarding method used by Ethernet switches varies and is based on whether there is bridging or routing software. Some vendors (e.g., 3Com, Cisco, and Performance Technologies, Inc.) have methods that combine techniques from cut-through and store and forward. Depending on error thresholds, these switches may switch from store and forward to a form of adaptive cut-through. Using proprietary software, a vendor will incorporate one of these designs into a proprietary switching matrix. This software switching matrix is integrated into specially designed hardware that will support back-to-back packets in a Full-DupleX mode. Most switch designs offer multiple ports (four to eight) to support simultaneous Ethernet connections between connected switches. Through this design, some Ethernet switches can offer as high as 40M-bps throughput with a transit delay as low as 70 microseconds. In some switches, filters are incorporated into the design of the switch to filter out packet fragments or runts generated as the result of the Ethernet collision process. Some Ethernet switches support both broadcast and multicast frames at as many as 59,520 packets per second. Although port designs vary among manufacturers, most use an RJ-45 Previous screen interface and provide support for several 10Base-T ports as well as multimedia (i.e., 10Base-2, 10Base-5).