Deploying Technology in the Campus Infrastructure Module
Determining equipment and cabling needs

The graphic highlights the changes that will take place as the nonhierarchical network is redeployed in the new Enterprise Composite Network model strategy.

There are four objectives in the design of any high performance network: security, availability, scalability, and manageability. The Enterprise Composite Network model, when implemented properly, provides the framework to meet these objectives. In the migration from a current network infrastructure to the Enterprise Composite Network model, a number of infrastructure changes may need to occur including the replacement of current equipment and existing cable plant.

This list describes the equipment and cabling considerations that should be made when altering infrastructure:

  1. Replace hubs and legacy switches with new switches at the Building Access layer. Select equipment with the appropriate port density at the Access layer to support the current user base, and plan for growth. Some designers plan for about 30 percent growth up front. If the budget allows, use modular access switches to accommodate future growth. Consider planning for support of inline power and QoS if IP telephony may be implemented in the future.
  2. When building the cable plant from the Access layer to the Building Distribution layer devices, remember that these links will carry aggregate traffic from the end nodes at the Access layer to the Building Distribution switches. Ensure that these links have adequate bandwidth capability. EtherChannel bundles can be used here to add bandwidth as necessary.
  3. At the building distribution layer, select switches with adequate performance to handle the load of the current Building Access layer. Also plan some port density to add trunks later to support additional access layer devices. The devices at this layer should be multilayer switches that support routing between the workgroup VLANs and network resources. Depending on the size of the network, the building distribution layer devices selected may be fixed chassis or modular. Plan for redundancy in the chassis, and in the connections to the access and core layers as the business objectives dictate.
  4. The campus backbone equipment must support high-speed data communications between other submodules. Be sure to size the backbone for scalability and plan in redundancy.

Cisco has online tools for assisting designers in making the proper selection of devices and uplink ports based on business and technology needs. Cisco suggests oversubscription ratios that can be used to plan bandwidth requirements between key devices on a network with average traffic flows.

  • Access to distribution layer links – The oversubscription ratio can be 20:1. That is, the link can be 1/20 of the total bandwidth available cumulatively to all end devices using that access to distribution layer link.
  • Distribution to Core links – The ratio should be 4:1.
  • Between Core Devices – There should be little to no oversubscription planning. That is, the links between core devices should be able to carry traffic at the speed represented by the aggregate number bandwidth of all the Distribution uplinks into the core.
CAUTION:

These ratios are appropriate for estimating average traffic from access layer, end user devices. They are not accurate for planning oversubscription from the Server Farm or Edge distribution modules. They are also not accurate for planning bandwidth needed on access switches hosting atypical user applications with high bandwidth consumption. (e.g. non client -server databases or multimedia flows to unicast addresses. Using QoS end to end prioritizes the traffic which would need to be dropped in the event of congestion.


Web Links