User's Manual

10/10/03 Client Roaming
90-100584-004 Airespace Product Guide 15
About Client RoamingClient Roaming
The Airespace System supports seamless client roaming across APs managed by the same Airespace
Wireless Switch or WLAN Appliance, between Airespace Switches and Appliances on the same subnet,
and across Airespace Switches and Appliances on different subnets. The following chapters describes
the three modes of roaming supported by the Airespace System.
Same-Airespace Switch or Appliance (Layer 2) RoamingSame-Airespace Switch or Appliance (L ayer 2) Roaming
Each Airespace Switch and Appliance supports same-Airespace Switch or Appliance client roaming
across Airespace APs and third-party APs managed by the same Airespace Switch or Appliance, whether
in Direct Connect Mode
, Appliance Mode or Hybrid Mode. This roaming is transparent to the client, as
the session is sustained and the client continues using the same DHCP-assigned or client-assigned IP
address. Same-Airespace Switch or Appliance roaming is supported in Single-Airespace Switch or
Appliance Deployments and Multiple-Airespace Switch and Appliance Deployments.
Inter-Airespace Switch and Appliance (Layer 2) RoamingInter-Airespace Switch and Appliance (Layer 2) Roaming
Similarly, in Multiple-Airespace Switch and Appliance Deployments, the Airespace System supports
client roaming across Airespace APs and third-party APs managed by Airespace Switches and Appli-
ances on the same subnet. This roaming is also transparent to the client, as the session is sustained
and a tunnel between Airespace Switches and Appliances allows the client to continue using the same
DHCP-assigned or client-assigned IP address as long as the session remains active. Note that the
tunnel is torn down when the client sends a DHCP Discover with a 0.0.0.0 client IP address or a
169.254.*.* client auto-IP address, or when the operator-set session timeout is exceeded.
Inter-Subnet (Layer 3) RoamingInter-Subnet (Layer 3) Roaming
Similarly, in Multiple-Airespace Switch and Appliance Deployments, the Airespace System supports
client roaming across Airespace APs and third-party APs managed by Airespace Switch and Appliance
on different subnets. This roaming is transparent to the client, because the session is sustained and a
tunnel between the Airespace Switches and Appliances allows the client to continue using the same
DHCP-assigned or client-assigned IP address as long as the session remains active. Note that the
tunnel is torn down when the client sends a DHCP Discover with a 0.0.0.0 client IP address or a
169.254.*.* client auto-IP address, or when the operator-set session timeout is exceeded.
Special Case: Voice Over IP Telephone RoamingSpecial Case: Voice Over IP Telephone Roam ing
802.11 VoIP telephones actively seek out associations with the strongest RF signal to ensure best
Quality of Service (QoS) and maximum throughput. The minimum VoIP telephone requirement of
20 millisecond or shorter latency time for the roaming handover is easily met by the Airespace System,
which has an average handover latency of nine or fewer milliseconds.
This short latency period is controlled by Airespace Switches and Appliances, rather than allowing inde-
pendent APs to negotiate roaming handovers.
The Airespace System supports 802.11 VoIP telephone roaming across Airespace APs and third-party
APs managed by Airespace Switches and Appliances on different subnets. This roaming is transparent
to the VoIP telephone, because the session is sustained and a tunnel between Airespace Switches and
Appliances allows the VoIP telephone to continue using the same DHCP-assigned IP address as long as
the session remains active. Note that the tunnel is torn down when the VoIP telephone sends a DHCP
Discover with a 0.0.0.0 VoIP telephone IP address or a 169.254.*.* VoIP telephone auto-IP address, or
when the operator-set session timeout is exceeded.