Designing Cisco Network Service Architectures - Free Books

Step 9 High Level VoWLAN Design• The main impact is on the wireless site survey and access point placement. Using LWAPPand controllers keeps the impact on the design minimal: controllers would probably beattached to wing or building switches, depending on how many are needed.— The Location Appliance requirement suggests placing access point s in corners andon building edges, using directional antennas. Internal access point s could then beadded as needed to achieve the appropriate cell sizes and access point densities tosupport Location triangulation and VoWLAN coverage. Since edge and corneraccess point s only cover ¼ or ½ a circle, they add to the access point count.— Using the 3000 square foot per access point figure for a first approximation to thenumber of access point s, then each wing floor would require 20,000 / 3,000 = 7access point s, or more. The 200 users would thus be divided into up to 30 per accesspoint. If they all need to use wireless simultaneously, you would need to deployadditional collocated access points on different channels.— If one knows the floor dimensions, say 100 feet by 200 feet, one can then do a littlemore careful estimation and initial access point placement. This level of detail wouldbe appropriate for a real customer, but is too time-consuming to do in this casestudy.— Each wing would then need 6 x 7 = 42 access points (or more). So one approachwould be to use a 50- access point controller per wing, with fallback to a sparesomeplace else.— Do not forget to include WCS and Location Appliance(s) to manage the WLAN Toestimate the number of Location Appliances, one needs to know what or who isbeing tracked.— Location Appliance coupled with wireless phones would permit locating staff orequipment. On the other hand, tracking staff locations might raise privacy concerns.Step 10 Network Management Design• NetFlow could be used to track traffic volumes and do cost allocation. It would be bestapplied inbound on interfaces in the traffic path. If most traffic will be data center todesktop, NetFlow might be used at the building or wing distribution layer. Note that thiswould miss some localize IP phone or desktop to desktop traffic.• IP SLA could be used to provide the desired information about the WAN. This may be oflimited value for Internet connections, since there is little that can be done to improve onpoor conditions.— IP SLA would most likely be done between the remote router and central siterouters.— As the number of remote connections increases, it might be wise to offload thecentral IP SLA responder role to dedicated routers.— IP SLA should not be needed within the campus or datacenter. However, some toolsshould be used to identify duplex or speed problems with links, and Spanning Treeor routing instability in the network, as all would cause performance problems withtraffic across the campus.60 Designing Cisco Network Service Architectures (ARCH) v2.0 © 2007 Cisco Systems, Inc.