Wireless LANs Describing WLAN Topologies

WLAN Topologies Wireless client access –Mobile user connectivity Wireless bridging –LAN-to-LAN connectivity Wireless mesh networking –Combination of bridging and user connectivity

WLAN and LAN

WLAN 组成 1Ssid （ service set id ）：服务集 id ，一组无线设备标 示，必须相同，包含在帧中发送。 2Bss （ basic service set ）：基本服务集，包含一个 ap ，所有客户必须向 ap 申请资格。 3Ibss （ independent basic service set ）：独立基本 服务集，只有客户，没有无线设备。 4Ess ：扩展服务集，包含多个 ap ，连接到以太网中。

Service Set Identifier (SSID) SSID is used to logically separate WLANs.( 使用 ssid 逻辑区分无线网 ) The SSID must match on client and access point. （必须匹配） Access point broadcasts one SSID in beacon. Client can be configured without SSID. Client association steps: 1.Client sends probe request. （发 送请求探针） 2.A point sends probe response. （ ap 回复请求） 3.Client initiates association. （开始 请求关联） 4.A point accepts association. （同 意关联） 5.A point adds client MAC address to association table.

Ap 工作原理 Ap 就像一个集线器，将无线终端设备关联起来，连入到无 线网络，以太网络中。 可以使用不同的 ssid 来关联 vlan ，使用 ssid 把无线客户关 联到相应的 vlan 中。

WLAN Access Topology

Wireless Repeater Topology

Workgroup Bridge Topology

Alternative Peer-to-Peer Topology

Service Sets and Modes Ad hoc mode Independent Basic Service Set (IBSS) （独立基本服务集） –Mobile clients connect directly without an intermediate access point. Infrastructure mode Basic Service Set （ bss ）（基本服务集 ） –Mobile clients use a single access point for connecting to each other or to wired network resources. Extended Services Set （ ess ）（扩展服 务集） –Two or more Basic Service Sets are connected by a common distribution system.

Roaming Through Wireless Cells （无线漫游）

Roaming Through Wireless Cells Roaming

Client Roaming （漫游） Roaming without interruption requires the same SSID on all access points.( 有相同的 ssid) Maximum data retry count exceeded Too many beacons missed Data rate shifted Periodic intervals

Layer 2 vs. Layer 3 Roaming

Wireless VLAN Support Multiple SSIDs Multiple security types Support for multiple VLANs from switches 802.1Q trunking protocol

Wireless VLAN Support (Cont.) VLANs propagate across access points. VLAN numbers are unique. Access points handle up to 16 VLANs.( 可处理 16 个 vlan)

Enterprise Voice Architecture

Wireless Mesh Networking In a mesh network topology, devices are connected with redundant connections between nodes. （在节点之间冗余 连接）

Wireless Mesh Networking （无线网状网） Mesh access points automatically establish connection to controller. –Rooftop access points (RAP) connect via wired connection. – 根接入点连接到有线网络 –Mesh access points (MAP) connect via self-configuring backhaul connection. Cisco uses mesh access points. Adaptive Wireless Path (AWP) protocol establishes best path to root. （自适应无线路径协议建立最 佳路径） Access point authenticates to controller and downloads configuration and radio parameters. （ ap 下载配置与参数）

Adaptive Wireless Path Protocol (AWP) AWP protocol establishes an optimal path to root. （ awp 建立最佳路径） Each access point carries a feasible successor or successors if topology or link health changes. AWP uses a “parent sticky” value to mitigate route flaps. 在拓扑或环境的改变导致链路或强或弱的情况下，能够通过 AWPP 建立起回到 RAP 的替换路由 。

Key Market Segments for Outdoor Wireless Enterprise outdoor （室外） Indoor and outdoor wireless solutions for education customers. Rugged mesh solutions for enterprise customers. Public sector （公共场合） Connecting peripheral devices across the mesh. Establishing hot zones for public safety or municipal departments. Service provider （服务提供商） Hot spots become hot zones with Wi-Fi access.

Summary Types of WLAN topologies are client access, bridging, and mesh networking. Wireless networks are built with multiple wireless cells. WLAN roaming occurs seamlessly between wireless cells. WLANs support VLANs and QoS. WLAN mesh networks extend the wireless network beyond the boundaries of wired LANs.