1999 Cabletron Systems

Wireless Networking RoamAbout Roaming Between AccessPoints Multi-channel roaming Associating multiple AccessPoints within the same wireless network

1999 Cabletron Systems Wireless Networking RoamAbout Multi-channel Roaming Multiple AccessPoints can be in the same wireless network as long as they do not overlap frequencies (Channels) –Overlapping cells should be at least 5 channels apart to provide protection from interference. Advantage here is the ability to have a wireless network larger than a single cell

1999 Cabletron Systems Wireless Networking RoamAbout Multiple Cells on One Wireless Network Wired LAN (Ethernet) Channel 1 Channel 11 Channel 6

1999 Cabletron Systems Wireless Networking RoamAbout Multi-channel roaming AccessPoints are set to a fixed frequency Stations switch frequency when roaming between AccessPoints to associate with a particular AccessPoint Stations “associate” dynamically to the AccessPoint which offers the best service This implies –Easier configuration!! –Faster installation!!

1999 Cabletron Systems Wireless Networking RoamAbout Communications Quality (CQ) Parameter used assess link between Station and AccessPoint Determined by Signal to Noise Ratio (SNR) on path between station and current AccessPoint

1999 Cabletron Systems Wireless Networking RoamAbout Using Communications Quality Station monitors the CQ to the AccessPoint When station moves away from AccessPoint the CQ decreases –In the example below the station has a good strong CQ to the AccessPoint Highest Quality Lowest Quality Cell Search Threshold Out Of Range Threshold Not Searching (NS) zone Cell Search (CS) zone Out of Range CQ

1999 Cabletron Systems Wireless Networking RoamAbout Using Communications Quality As the station moves away from the AccessPoint the CQ will decrease This is normal and there is nothing to be alarmed about Highest Quality Lowest Quality Cell Search Threshold Out Of Range Threshold Not Searching (NS) zone Cell Search (CS) zone Out of Range CQ

1999 Cabletron Systems Wireless Networking RoamAbout Highest Quality Lowest Quality Cell Search Threshold Out Of Range Threshold Not Searching (NS) zone Cell Search (CS) zone Out of Range CQ Using Communications Quality If the CQ falls below a set threshold, the station will enter the Cell Search (CS) zone In the Cell Search Zone the station is actively looking for another AccessPoint that is better able to service that station At this point the station is said to be roaming!!

1999 Cabletron Systems Wireless Networking RoamAbout In the Cell Search State In the cell search state, the station will enter a sweep mode –Sweep mode is when a station will actively scan all channels to determine if there is an AccessPoint on the network that is better able to service the Station –The station also blocks its own transmissions during sweep

1999 Cabletron Systems Wireless Networking RoamAbout Determining Which AccessPoint to Associate With Once a station discovers an AccessPoint (on the network) that can better service it, it will make an association to that AccessPoint. To be considered for association, an AccessPoint must: –Have a CQ that is better than any other applicable AccessPoint and Have a matching Network Name of that station or Have the Network Name set to ANY and not be operating in the “closed” mode

1999 Cabletron Systems Wireless Networking RoamAbout Creating an Association Station sends an “Association Request” AccessPoint enters the station in its Association Table (and assigns an “Association Code” to it) AccessPoint then sends an “Association Response” to the station

1999 Cabletron Systems Wireless Networking RoamAbout Roaming As Station A is associated with AccessPoint 1 and decides to move away from away from AccessPoint 1. AccessPoint 1 AccessPoint 2 Wired LAN (Ethernet) Channel 5 Channel 1 Station A

1999 Cabletron Systems Wireless Networking RoamAbout Roaming At some point the Cell search Threshold will be passed. Station A maintains its association to AccessPoint 1 since no other AccessPoint offers a better CQ (following a sweep) AccessPoint 1 AccessPoint 2 Wired LAN (Ethernet) Channel 5 Channel 1 Station A

1999 Cabletron Systems Wireless Networking RoamAbout Roaming Station A now sees AccessPoint 2 offers the best CQ Station A now creates an association with AccessPoint 2 AccessPoint 1 AccessPoint 2 Wired LAN (Ethernet) Channel 5 Channel 1 Station A

1999 Cabletron Systems Wireless Networking RoamAbout Determining AccessPoint to Associate with Cell Search Threshold exceeded Sweep for new AccessPoint New Acces s Point found Same network name (SSID)? Security check (if required) Associated with new AccessPoint YES NO granted denied

1999 Cabletron Systems Wireless Networking RoamAbout Roaming Summary For a station to begin to seek out another AccessPoint, the CQ must fall below the set threshold Once in the sweep mode, only other AccessPoints with the same Network Name will be considered Once a better AccessPoint is found then an association will be made