To keep up with department stores’ demands for quick turnaround and to reduce labour costs in its 300,000 square-foot facility in Stockton California, wholesaler Dorfman Pacific last year installed a wireless warehouse management system. The application, from HighJump Software, runs across a Symbol Technologies Wi-Fi infrastructure and Symbol bar-code scanners.
The shift away from paper-based order picking has reduced temporary warehouse labour costs by about 50 percent, says Mark Dulle, director of IT services at the company, which sells headwear and related accessories to retailers. Dulle says two capabilities of the Symbol Wi-Fi infrastructure, in particular, have proved useful:
- Symbol’s ability to map Dorfman Pacific’s wired Cisco virtual LANs to the wireless networ
- The Wi-Fi system’s support of 802.11g “protection mode” for reducing degradation of 802.11g network performance in the presence of 802.11b traffic.
By way of background, Dorfman Pacific runs Cisco power-over-Ethernet wiring closet switches and a Cisco Catalyst 6509 data center switch. A Symbol WS5000 controller plugs into the 6509 and manages a Wi-Fi infrastructure of Symbol AP300 802.11a/b/g and AP100 802.11b thin access points (AP).
Symbol supports Cisco VLANs
Precluding Dorfman Pacific from having to recreate all its Cisco VLANs for the wireless network segment, the WS5000 series supports 802.1q (VLAN) trunking. The controller pushes the existing Cisco VLAN configuration to Symbol APs while using the policies within the controller to forward traffic to the appropriate VLAN, explains Manju Mahishi, director of marketing in Symbol’s wireless infrastructure division. The latest release of the controller’s software maps VLANs to specific wireless users based on their RADIUS authentication credentials, he adds.
Protection keeps B radios in check
The “protection mode” option to the 802.11g standard facilitates the cooperation of B and G radios. The two networks each use different modulation schemes and thus cannot naturally “hear” transmission attempts on the shared RF medium. In protection mode, the G radio sends a short packet at an 802.11b rate (1, 2, 5.5 or 11Mbps) containing a field that the B client understands and indicating that it is going to transmit. So that the B client knows to back off.
Using protection mode, says Mahishi, performance will still degrade because the protection frames create additional overhead. But it will degrade “reliably,” because the overhead is predictable, he explains.
“This performance degradation is assumed to be better than a completely unpredictable….process of allowing B clients to transmit willy-nilly…causing packet loss, greater retries, and lower data rates,” he says.
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