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AN INCREMENTAL APPROACH

Reserved Bandwidth

Several vendors sell video-enabled application solutions today that are designed to run over existing LAN technology with no modification. However, the number of video streams that can be sent simultaneously from a multimedia server are limited. Some vendors claim that five video streams can be sent simultaneously on a 10M bps LAN, based on MPEG quality video at 1.5M bps. This claim seems a bit optimistic considering the fact that few network managers allow their LANs to run at full capacity, as a precautionary measure for avoiding crashes.

Realistically, LAN managers should expect that no more than a few video streams can be sent simultaneously over a 10M-bps LAN.

Organizations using the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol over Ethernet can only stream one or two video segments at a time because the TCP/IP protocol does not currently support reserved bandwidth. Reserved bandwidth is especially important for transmitting video and eliminating interruptions. Work is being done by the Internet Activities Board to enhance TCP/IP to support reserved bandwidth.

Structured Wiring Schemes

Network technology can be optimized while preserving existing investments. Changes can be made to add bandwidth and capacity, which in turn increases the efficiency and reliability of the network infrastructure for accommodating networked high-bandwidth applications such as multimedia.

Many organizations have already installed structured wiring schemes, such as star topology networks for their 10M-bps Ethernet or 16M-bps Token Ring LANs. A structured wiring system gives organizations the flexibility to accommodate multiple media—for example, shielded and unshielded twisted-pair, twin axial, copper and fiber-optic wire, and multiple devices. Over time, organizations with structured wiring systems can add to them modularly to grow the system. The advantage of this approach is that the organization can make the necessary moves and changes cost-effective.

Star Topology

Star topology networks have grown increasingly popular and may be favored over bus or ring networks, whereby a wire snakes from one computer to the next. The star topology offer network managers the most flexibility because each client has its own wire.

Although 10M-bps to 16M-bps network configurations may provide sufficient bandwidth for today’s applications, multimedia-based applications, particularly those that include video, will demand more bandwidth. The fact of the matter is that even though star topologies connect individual clients with a hub, Ethernet and Token Ring networks operate like a bus or ring, which means that a limited amount of bandwidth gets shared.

Switched Hubs

Switched hub technology can be implemented to give users their own dedicated bandwidth for multimedia applications. What this means is that instead of, say, five clients sharing a single 10M-bps LAN, each client gets its own equivalent of a 10M-bps LAN. This solution requires additional cost at the hub but does not require any wiring changes or changes in the client hardware.

The network manager can decide who requires dedicated bandwidth, each user or only those users with file-intensive applications. The objective is to reduce contention on the network, performance degradation, or jeopardizing mission-critical applications in any way. Vendors provide switched technology for both Ethernet, Token Ring, and fiber distributed data interface (FDDI) networks.

Different applications require different switches. For example, turbo-charging the pipeline to individual users for data-intensive applications focuses on the individual desktop. Switching at the departmental level usually arises because issues such as traffic control and security, also called firewalling, come into play.

For example, a group of users within a department works with image-based applications that include information-sensitive data. This group of users not only needs additional bandwidth but requires segmentation from other LAN users as well.

Configuration and LAN Switches

There are two types of LAN switches: configuration switches that are software-based, and LAN switches, which represent a hardware solution. Configuration switching defines logical links whereas LAN switches define physical links.

Configuration switching requires a port-switching device, but it is through software that the network manager creates virtual, personalized LANs to those users or groups of users with high-bandwidth requirements.

LAN Switches

LAN switches actually switch data packets from one physical LAN segment or user to another. LAN switches are scalable in that they can be grown in various ways: by increasing the number of switch ports, or combining switch technology with faster LAN technologies.

Switched LAN solutions boost network performance. Because existing twisted-pair copper cable can be used, there is no need to change the cable infrastructure. Switched LAN technology solutions makes sense as a desktop application, especially for large data applications, like multimedia.

There are several types of switches that span a range of applications from workgroup to departmental to campuswide. Enhancing a LAN with a switch to support multimedia applications requires either a port-switching device, a desktop switch, or a workgroup or floor switch.

The workgroup switch is optimized for a wiring closet or small LAN application, when the high-speed port connects to servers located either physically with the workgroup or through a fiber backbone to a server farm.


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