Switched on, baby

Cisco Systems' Catalyst 3550-12T provides Layer 2 and 3 switching with 10 10/100 ports and two GBIC uplinks. It's priced at $9,995.

SMC Networks' 6924VF, priced at $3,550, has 24 ports and two fiber Gigabit uplinks in a stackable configuration.

Enterasys Networks' $1,550 VH-2402S2 is a stackable, 24-port, Layer 2 switch with two Gigabit uplinks.

Layer 2 and 3 switches pave the road to Gigabit Ethernet

Gigabit Ethernet eventually will come directly to desktops, but for now, most workgroups will get by on 10/100-Mbps Fast Ethernet with a couple of Gigabit ports for connecting to high-speed network backbones.

Before Gigabit Ethernet takes over entirely, there needs to be a sizeable increase in sales of client-based Gigabit network interface cards (NICs) and a smaller price difference between Gigabit and Fast Ethernet switch ports, according to the Dell'Oro Group, a market research firm in Portola Valley, Calif.

'We expect both of these conditions to be met by 2004. At this time, we anticipate strong growth in Gigabit desktop connectivity and a peak in growth for certain Fast Ethernet segments,' said Seamus Crehan, senior analyst at the Dell'Oro Group.

So for the time being, Layer 2 or Layer 3 Fast Ethernet switches with 10 or more 10/100 auto-sensing copper Ethernet/Fast Ethernet ports and two fiber or copper Gigabit uplinks that connect to network backbones should be considered 'best buys' for workgroups.

Workgroup switches come in standalone, rackmount or stackable versions, with stackable configuration being the choice if you want to be able to instantly add modules.

Fixed-port units are fine for cost-conscious users, but you can't reconfigure the number and types of ports built into them. If you want to do this, look for a higher-end switch, such as Cisco Systems Inc.'s Catalyst 3550-12T and 3Com Corp.'s SuperStack 3 Switch 4900. These include an autonegotiation feature that lets you adjust speeds and levels of management.

Ethernet switches working at Layer 2 of the Open Systems Interconnection (OSI) model can deliver data at wire speeds to stations around the network because they don't actually handle individual data packets.

Roundabout and straight ahead

Layer 3 switches, sometimes called multilayer switches or switch routers, use OSI address information to decide where to forward data. They are built around application-specific integrated circuits and use fast RISC processors to enable them to route data at or near wire speed.

In effect, Layer 3 switches combine Layer 2 processing with high-speed routing in a single device that actually costs less than traditional switch-router combinations.

Do you need a Layer 3 switch? Maybe. Inexpensive Layer 2 switches like EtherWan Systems Inc.'s $999 Xpresso 3224A, Hawking Technology Inc.'s $799 GS224S and Hewlett-Packard Co.'s $899 Procurve Switch 2524 will often meet most of your requirements at lower prices than Layer 3 switches. But you'll see huge performance gains from a Layer 3 switch if traditional routers are used to link IP subnets, according to an Anritsu Co. white paper. Anritsu makes the MultiFlow 5024, a standalone Layer 3 switch with 24 copper 10/100 ports and two fiber Gigabit uplink slots.
Layer 3 switches can also help deal with 'chatty' protocols'those using lots of traffic overhead'such as IPX and AppleTalk, especially when connecting to Gigabit Ethernet backbones. Using Layer 3 switches at network edges with VLANs will help protect against network device faults and help the VLANs prevent broadcast storms, according to Anritsu.

Whether you opt for a Layer 2 or Layer 3 switch, a managed switch is probably a good idea.
Even at the LAN level, advanced networks must enable voice, video and data over IP while facilitating such applications as voice over IP, streaming video, distance learning, teleconferencing and video conferencing. Managed switches will meet all these requirements best. Look for plug-and-play installation, easy maintenance and enough features to meet your immediate needs as you plan for your network's Gigabit and 10-Gigabit network future.

In a white paper on managed switches, Netgear Inc. provides a useful shopping list of seven basic features of managed switches. They are: Gigabit Ethernet support, port monitoring, central/remote monitoring, detecting packet errors, fault isolation, capacity planning and port control.

Gigabit Ethernet support. Workgroup switches with one or more Gigabit Ethernet uplinks are the first step to making Gigabit Ethernet the common office connection.

Port monitoring. An Ethernet switch should monitor the number of data packets sent or received by every switch port. This feature lets network administrators identify traffic patterns, monitor network trends and determine appropriate bandwidth needs. Port monitoring also makes it possible to identify port congestion and failures, minimizing their potential impact, according to Netgear.

Central and remote port monitoring. A managed switch usually contains embedded software that lets you monitor ports centrally or remotely.

Central port monitoring usually is accomplished via client software that lets you monitor performance without being at the switch's location.

Remote port monitoring is done via a Web browser or a Simple Network Management Protocol remote monitoring tool. Monitoring software assigns an IP address to the switch, so managers can access it via browser. SNMP is built into most switch manufacturers' proprietary management software and can include RMON. Together, they let you manage a switch from any network management application or Telnet.

Detecting packet errors. Managed switches not only detect data packets, they also can detect and record errors in the packet send/receive process. Minimally, bundled switch software should provide baseline packet error information; more advanced software can alert administrators to problems via e-mail or telephone.
Fault isolation. Basically a network fault is anything that impedes or blocks the flow of traffic. A managed switch that supports fault isolation can locate a fault and isolate it before it causes a serious problem. Factors that contribute to network faults include traffic patterns, traffic congestion and port status, according to Netgear.

Capacity planning. Understaffed government departments should look for a switch that supports capacity planning. This feature lets administrators analyze their current network requirements so they can plan for future growth and development. The objective is to analyze current network workloads to provide solid information about the resources that will be required in coming months or years.

Switch capacity typically is measured in the following ways:
Speed. The ports on a managed switch should support both autosensing and manual configuration. Autosensing is the switch's ability to determine the speed of attached devices and adjust the speed of the port accordingly. If a legacy device doesn't support autosensing, a port can be set manually for the optimum speed.

Half- and full-duplex. Half-duplex enables packets to be sent and received, but only full-duplex let you send and receive packets simultaneously. This effectively doubles the port's bandwidth'from 10 Mbps to 20 Mbps or from 100 Mbps to 200 Mbps. The autonegotiation feature enables the switch to negotiate between half-duplex and full-duplex operations on its ports, depending on the capabilities of attached devices.

Flow control. If a port is already saturated with data packets and new ones arrive, its buffer might overflow, resulting in dropped packets and lost data. A switch's flow control feature manages port congestion by controlling data flow from transmitting devices, thereby enabling receiving devices to handle the data.

J.B. Miles of Pahoa, Hawaii, writes about communications and computers. E-mail him at [email protected]


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