Design Considerations for Outdoor Wireless Networks

Traditional outdoor wireless deployment options include point-to-point or point-to-multipoint bridging between buildings. Outdoor wireless mesh is a relatively new option in which the APs are connected in a mesh with many redundant connections between nodes. Figure 9-33 illustrates these options.

Figure 9-33 Outdoor Wireless Options

Figure 9-33 Outdoor Wireless Options

Outdoor Mesh Network
Wireless Mesh Networking

Mesh APs discover each other automatically and select the best path through the mesh for maximizing system capacity and minimizing latency. APs continuously communicate with other nodes in the mesh, evaluating the potential of each link to improve performance. If a link degrades, the AP determines whether a better path exists and routes traffic through a more optimal node. A mesh network eliminates the need to wire every AP in the network, making it easier and more cost-effective to extend the network's reach. It is easy to connect an existing indoor wired or wireless network with the outdoor mesh network so that users can roam from one area to another without reconnecting. Perhaps more importantly, administrators can set up one access policy that works across all environments, increasing security and making the systemwide network infrastructure more manageable.

Wireless Mesh Components

A mesh network consists of two or more indoor or outdoor Cisco LWAPP-enabled mesh APs, communicating with each other over one or more wireless hops (using 802.11a) to join multiple LANs or to extend IEEE 802.11b/g wireless coverage. Cisco LWAPP-enabled mesh APs are configured, monitored, and operated from and through any Cisco WLC deployed in the network. The wireless mesh solution consists of several components, as illustrated in Figure 9-34:

■ Cisco WCS: WCS includes easy-to-use and intuitive software for wireless mesh management and enables networkwide policy configuration and device management. WCS provides the overall view of the wireless mesh and supports Simple Network Management Protocol and Syslog.

■ Cisco WLC: The WLC connects the wireless mesh APs to the wired network.

■ Rooftop APs (RAP): A RAP is connected to the wired network and serves as the root or gateway to the wired network. As its name implies, a RAP is typically located on a rooftop or tower. A RAP uses wireless 802.11a to communicate with up to 32 neighboring poletop mesh APs (MAP).

■ Poletop MAPs: The poletop MAPs are the remote APs that provide 802.11b/g wireless client access. MAPs are typically located on top of a pole such as a lamppost and connect through a separate 802.11a wireless interface to a RAP as the gateway to the wired network. MAPs require AC or DC power and might support PoE. MAPs typically also have an Ethernet port for connecting peripheral devices, such as a camera.

Figure 9-34 Outdoor Wireless Mesh Components

Figure 9-34 Outdoor Wireless Mesh Components

Cisco Wireless Control System

Cisco Wireless LAN Controller

Rooftop Access Point

Mesh Access Points

Cisco Wireless Control System

Cisco Wireless LAN Controller

Rooftop Access Point

Mesh Access Points

MAP-to-RAP Connectivity

The outdoor component of the Cisco wireless mesh networking solution is based on the Cisco Aironet 1500 Series, an outdoor Wi-Fi (802.11/a/b/g) mesh AP using Cisco's patent-pending Adaptive Wireless Path Protocol. The 1500 series uses a two-radio design where the radios have dedicated roles. One radio provides local access for client devices, and the second radio provides the wireless backhaul for network connectivity. The network's overall throughput is controlled by topology and path considerations in the mesh network.

During bootup, an AP tries to become a RAP if it is connected to the wired network. If a RAP loses its wired network connection, it attempts to become a MAP and searches for an appropriate RAP. By default, the backhaul interface (to the MAPs) on the RAP uses the 802.11a 5 GHz radio and is set to a speed of 18 Mbps. A RAP is the parent node to any bridging or mesh network and connects a bridge or mesh network to the wired network. By default, only one RAP can exist for any bridged or mesh network. A mesh algorithm enables APs to find the least-cost path back to the controller or RAP to minimize latency and maximize usable bandwidth. The algorithm takes into account total hop count and throughput at each hop to determine the best path back to a RAP.

KEY POINT

MAPs do not have any wired connectivity to a WLC. MAPs can be completely wireless, supporting clients that are communicating with other MAPs or RAPs, or they can be wired and serve as a bridge to a remote wired network.

MAPs are typically installed in places where a wired connection cannot be provided, but power can be made available. The MAP provides IEEE 802.11b/g client access via the 2.4 GHz radio and connects wirelessly to the RAP via the 802.11a backhaul radio. MAPs can connect back to a RAP using one or multiple hops, thereby providing a broader coverage area than a typical wireless bridge device. Figure 9-35 illustrates a sample deployment.

634 Chapter 9: Wireless Network Design Considerations Figure 9-35 Sample MAP-to-RAP Connectivity

634 Chapter 9: Wireless Network Design Considerations Figure 9-35 Sample MAP-to-RAP Connectivity

Mesh Design Recommendations

Figure 9-36 illustrates the throughput in a mesh network. Notice that each hop reduces the throughput by half because the data has to be re-sent across the same half-duplex network. The MAP connection back to the RAP can support eight hops on a 1500 Series AP, although Cisco recommends four or fewer hops for best performance because each hop can add 1 to 3 ms of latency.

Figure 9-36 Wireless Mesh Throughput

Figure 9-36 Wireless Mesh Throughput

HOPS

One

Two

Three

Four

Throughput

~10 Mbps

~5 Mbps

~3 Mbps

up to 1 Mbps

RAPs can connect up to 32 MAPs. Cisco recommends connecting only 20 to 25 MAPs to a RAP; a maximum of 20 MAPs provides the best performance.

Was this article helpful?

+1 0
Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

Get My Free Ebook


Post a comment