ZyXEL Communications 10 - Manual (Page 94)

ZyWALL 10~100 Series Internet Security Gateway
6-10 LAN Setup
6.5 Wireless LAN
This section introduces the wireless LAN and some basic configuration. Wireless LANs can be as simple as
two computers with wireless network interface cards (NICs) communicating in a peer-to-peer network or as
complex as a number of computers with wireless NICs communicating through access points which bridge
network traffic to the wired LAN. See Chapter 7 for information on wireless LAN security features.
6.5.1 Channel
IEEE 802.11b wireless devices use ranges of radio frequencies called channels. Choose the radio channel
depending on your geographical area. Adjacent Access Points (APs) should use different channels to reduce
crosstalk. Crosstalk occurs when radio signals from access points overlap and cause interference that
degrades performance.
6.5.2 ESS ID
Extended Service Set (ESS) is defined as one or more APs acting as a bridge between a wired LAN and the
associated wireless clients. The ESS ID is a unique ID given to the APs and the wireless clients that
participate in the same wireless network. You can think of the ESS ID as being similar to a workgroup name
in a Microsoft network.
The ESS ID provides a minimum level of security for your network; see Chapter 7 for more information.
6.5.3 RTS Threshold
The RTS (Request To Send) Threshold prevents the problem of hidden nodes. The hidden node problem
occurs when two stations are within range of the same access point, but are not within range of each other.
The following figure illustrates the hidden node problem. Both stations (STA) are within range of the (AP),
however, they cannot hear each other. Therefore, they are considered hidden from each other. When a station
starts data transmission with the AP, it might not know that the other station is already using the wireless
medium. When these two stations send data at the same time, it might collide when arriving simultaneously
at the AP. The collision will almost certainly result in a loss of messages for both stations.