Symbol Technologies AP-4131 User Manual

Spectrum24

AP-4131 Access Point

Product Reference Guide

72E-56316-01

Revision A

February 2002

www.symbol.com

Copyright

Copyright © 2002 by Symbol Technologies, Inc. All rights reserved.

No part of this publication may be modified or adapted in any way, for any purposes without permission in writing from Symbol. The material in this manual
is subject to change without notice.

Symbol reserves the right to make changes to any product to improve reliability, function, or design.

No license is granted, either expressly or by implication, estoppel, or otherwise under any Symbol Technologies, Inc., intellectual property rights. An implied
license only exists for equipment, circuits, and subsystems contained in Symbol products.

Symbol, the Symbol logo and Spectrum24 are registered trademarks of Symbol Technologies, Inc.

Other product names mentioned in this manual may be trademarks or registered trademarks of their respective companies and are hereby acknowledged.

IBM is a registered trademark of International Business Machine Corporation.

Microsoft, Windows, and Windows NT are registered trademarks of Micros oft Corporation.

Novell and LAN Workplace are registered trademarks of Novell Inc.

Toshiba is a trademark of Toshiba Corporation.

Patents

This product is covered by one or more of the following U.S. and foreign Patents:

4,496,831; 4,593,186; 4,603,262; 4,607,156; 4,652,750; 4,673,805; 4,736,095; 4,758,717; 4,760,248; 4,806,742; 4,816,660; 4,845,350;
4,896,026; 4,897,532; 4,923,281; 4,933,538; 4,992,717; 5,015,833; 5,017,765; 5,021,641; 5,029,183; 5,047,617; 5,103,461; 5,113,445;
5,130,520; 5,140,144; 5,142,550; 5,149,950; 5,157,687; 5,168,148; 5,168,149; 5,180,904; 5,216,232; 5,229,591; 5,230,088; 5,235,167;
5,243,655; 5,247,162; 5,250,791; 5,250,792; 5,260,553; 5,262,627; 5,262,628; 5,266,787; 5,278,398; 5,280,162; 5,280,163; 5,280,164;
5,280,498; 5,304,786; 5,304,788; 5,306,900; 5,321,246; 5,324,924; 5,337,361; 5,367,151; 5,373,148; 5,378,882; 5,396,053; 5,396,055;
5,399,846; 5,408,081; 5,410,139; 5,410,140; 5,412,198; 5,418,812; 5,420,411; 5,436,440; 5,444,231; 5,449,891; 5,449,893; 5,468,949;
5,471,042; 5,478,998; 5,479,000; 5,479,002; 5,479,441; 5,504,322; 5,519,577; 5,528,621; 5,532,469; 5,543,610; 5,545,889; 5,552,592;
5,557,093; 5,578,810; 5,581,070; 5,589,679; 5,589,680; 5,608,202; 5,612,531; 5,619,028; 5,627,359; 5,637,852; 5,664,229; 5,668,803;
5,675,139; 5,693,929; 5,698,835; 5,705,800; 5,714,746; 5,723,851; 5,734,152; 5,734,153; 5,742,043; 5,745,794; 5,754,587; 5,762,516;
5,763,863; 5,767,500; 5,789,728; 5,789,731; 5,808,287; 5,811,785; 5,811,787; 5,815,811; 5,821,519; 5,821,520; 5,823,812; 5,828,050;
5,850,078; 5,861,615; 5,874,720; 5,875,415; 5,900,617; 5,902,989; 5,907,146; 5,912,450; 5,914,478; 5,917,173; 5,920,059; 5,923,025;
5,929,420; 5,945,658; 5,945,659; 5,946,194; 5,959,285; 6,002,918; 6,021,947; 6,036,098; 6,047,892; 6,050,491; 6,053,413; 6,056,200;
6,065,678; 6,067,297; 6,068,190; 6,082,621; 6,084,528; 6,088,482; 6,092,725; 6,101,483; 6,102,293; 6,104,620; 6,114,712; 6,115,678;
6,119,944; 6,123,265; 6,131,814; 6,138,180; 6,142,379; 6,172,478; 6,176,428; 6,178,426; 6,186,400; 6,188,681; 6,209,788; 6,216,951;
6,220,514; 6,243 ,447; 6,244,513; 6,247,647; 6,250,551; D305,885; D34 1,584; D344,501; D359,483; D362,453; D363,700; D363,918;
D370,478; D383,124 ; D391,250; D405,077; D406,581; D414,171; D414,172; D418,500; D419,548; D423,46 8; D424,035; D430,158;
D430,159; D431,562; D436,104.

Invention No. 55,358; 62,539; 69,060; 69,187 (Taiwan); No. 1,601,79 6; 1,907,875; 1,9 55,269 (Japan); European Patent 367,299; 414,281;
367,300; 367,298; UK 2,072,832; France 81/03938; Italy 1,138,713

Symbol Technologies, Inc.

One Symbol Plaza

Holtsville, N.Y. 11742-1300

Telephone:(800)SCAN234, [phone], TLX:6711519

www.symbol.com

ii AP-4131 Access Point Product Reference Guide

About This Document

Reference Documents

This reference guide refers to the following documents:

Part Number Document Title

72E-51753-01 Wireless LAN Adapter 4100 Series PC Card & PCI Adapter Product

Reference Guide

72E-51754-01 Spectrum24 DS Plus Pack Users Guide

72E-51755-01 Spectrum24 Site Survey System Administrators Guide

Conventions

Keystrokes are indicated as follows:

ENTER identifies a key.

FUNC, CTRL, C identifies a key sequence. Press and release each key in turn.

Press A+B press the indicated keys simultaneously.

Hold A+B press and hold the indicated keys while performing or waiting for another

function. Used in combination with another keystroke.

Typeface conventions used include.

<angles> indicates mandatory parameters in syntax.

[brackets] for command line, indicates available parameters; in configuration files,

brackets act as separators for options.

GUI Screen text indicates the name of a control in a GUI-based application.

Italics indicates the first use of a term, book title, variable or menu title.

Screen

Terminal

URL

AP-4131 Access Point Product Reference Guide iii

indicates monitor screen dialog. Also indicates user input. A screen is
the hardware device on which data appears. A display is data arranged
on a screen.

indicates text shown on a radio terminal screen.

indicates Uniform Resource Locator.

This document uses the following for certain conditions or information:

Indicates tips or special requirements.

Indicates conditions that can cause equipment damage or data loss.

Indicates a potentially dangerous condition or procedure that only Symbol­trained personnel should attempt to correct or perform.

iv AP-4131 Access Point Product Reference Guide

Contents

Chapter 1 Introduction .......................................................................................1

1.1 Access Point (AP)...........................................................................1

1.2 Radio Basics .................................................................................3

1.2.1 S24 Network Topology........................................................3

1.2.2 Cellular Coverage ..............................................................8

1.2.3 Site Topography ...............................................................11

1.3 Access Point Functional Theory.....................................................12

1.3.1 MAC Layer Bridging..........................................................13

1.3.2 Auto Fallback to Wireless Mode .........................................14

1.3.3 DHCP Support..................................................................15

1.3.4 Media Types.....................................................................16

1.3.5 Direct-Sequence Spread Spectrum......................................18

1.3.6 MU Association Process .....................................................19

1.3.7 Mobile IP .........................................................................21

1.3.8 Supporting CAM and PSP Stations ......................................24

1.3.9 Data Encryption ................................................................25

1.3.10 Kerberos Authentication...................................................26

1.3.11 KSS Open Enrollment ......................................................31

1.3.12 KSS Databases ...............................................................32

1.3.13 Roaming and Authentication ............................................32

1.3.14 Mixed Mode Security .......................................................33

1.3.15 Web Management Support ..............................................33

1.3.16 Management Options .....................................................34

Chapter 2 Configuring the AP.........................................................................37

2.1 Gaining Access to the UI .............................................................37

2.1.1 Using Telnet .....................................................................37

2.1.2 Using a Direct Serial Connection........................................39

2.1.3 Using a Dial-Up Connection..............................................40

AP-4131 Access Point Product Reference Guide v

2.1.4 Using a Web Browser........................................................41

2.2 Navigating the UI .......................................................................48

2.2.1 Entering Admin Mode .......................................................50

2.2.2 Changing the Access to the UI ...........................................51

2.2.3 Configuring for Dial-Up to the UI .......................................53

2.2.4 Navigating the UI Using a Web Browser .............................54

2.3 Access Point Installation...............................................................54

2.4 Configuring System Parameters....................................................59

2.4.1 Encryption Administration ..................................................66

2.4.2 System Password Administration.........................................69

2.5 Configuring Radio Parameters .....................................................71

2.5.1 Wireless AP Operation Parameters .....................................80

2.5.2 Enhanced Packet Prioritization (EPP)....................................85

2.5.3 Enhanced Interference Avoidance Properties (EIAP) ..............86

2.6 Encryption Configuration and Key Maintenance.............................88

2.6.1 40-Bit WEP Encryption.......................................................90

2.6.2 128-Bit WEP Encryption .....................................................92

2.6.3 Manual Kerberos Authentication Configuration ...................94

2.6.4 Configuring EAP-TLS Support.............................................97

2.6.5 Configuring Mixed Mode Security.....................................100

2.7 Configuring the SNMP Agent .....................................................102

2.7.1 Configuring SNMPv3 Security ..........................................108

2.8 ACL and Address Filtering .........................................................111

2.8.1 Configuring the ACL .......................................................113

2.8.2 Range of MUs ................................................................113

2.8.3 Adding Allowed MUs ......................................................115

2.8.4 Removing Allowed MUs...................................................115

2.8.5 ACL Options ..................................................................116

2.8.6 Removing All Allowed MUs ..............................................116

2.8.7 Load ACL from MU List ...................................................116

2.8.8 Load ACL from File .........................................................117

vi AP-4131 Access Point Product Reference Guide

2.9 Configuring Address Filtering.....................................................118

2.9.1 Adding Disallowed MUs ..................................................119

2.9.2 Removing Disallowed MUs ..............................................119

2.10 Configuring Type Filtering .......................................................120

2.10.1 Adding Filter Types .......................................................120

2.10.2 Removing Filter Types....................................................120

2.10.3 Controlling Type Filters..................................................120

2.11 Clearing MUs from the AP .......................................................121

2.12 Manually Updating the AP Configuration ..................................121

2.12.1 Updating Using TFTP ....................................................129

2.12.2 Updating Using Xmodem ..............................................132

2.13 Setting Logging Options ..........................................................137

2.14 Updating AP Firmware ............................................................139

2.14.1 Update Using TFTP .......................................................139

2.14.2 Updating Using Xmodem ..............................................143

2.15 Auto Upgrade all APs Through Messaging ................................148

2.16 Performing Pings ....................................................................152

2.17 Mobile IP Using MD5 Authentication.........................................155

2.18 Saving the Configuration .........................................................156

2.19 Resetting the AP ......................................................................157

2.20 Restoring the Factory Configuration ..........................................157

2.21 Configuring Network Time.......................................................158

Chapter 3 Monitoring Statistics.....................................................................159

3.1 System Summary ......................................................................159

3.2 Interface Statistics......................................................................163

3.3 Forwarding Counts ...................................................................164

3.4 Mobile Units .............................................................................165

3.5 Mobile IP..................................................................................170

3.6 Known APs ...............................................................................171

3.7 Ethernet Statistics ......................................................................174

3.8 Radio Statistics..........................................................................176

AP-4131 Access Point Product Reference Guide vii

3.9 Miscellaneous Statistics ..............................................................182

3.9.1 Analyzing Channel Use ...................................................184

3.9.2 Analyzing Retries ............................................................185

3.10 Event History ..........................................................................186

3.11 Clearing Statistics....................................................................187

Chapter 4 Hardware Installation..................................................................189

4.1 Precautions ..............................................................................189

4.2 Package Contents .....................................................................189

4.3 Requirements ...........................................................................190

4.3.1 Network Connection .......................................................190

4.3.2 10/100Base-T UTP .........................................................190

4.3.3 Single Cell .....................................................................191

4.4 Placing the AP ..........................................................................191

4.5 Power Options..........................................................................192

4.6 Mounting the AP .......................................................................193

4.7 Connecting the Power Adapter...................................................193

4.8 BIAS-T Low Power Distribution System .........................................194

4.9 LED Indicators ..........................................................................198

4.9.1 WLAP mode LED display..................................................199

4.10 Troubleshooting......................................................................201

4.10.1 Ensure wired network is operating..................................201

4.11 Setting Up MUs.......................................................................202

Appendix A Specifications .............................................................................. A-1

A.1 Physical Characteristics ............................................................. A-1

A.2 Radio Characteristics................................................................. A-2

A.3 Network Characteristics............................................................ A-3

Appendix B Supported Modems.................................................................... B-1

Appendix C Customer Support ..................................................................... C-1

Appendix D Country Identification Codes...................................................D-1

viii AP-4131 Access Point Product Reference Guide

Appendix E Installing and Configuring Kerberos Setup Service ............. E-1

E.1 Creating a Windows 2000 Environment for the KSS ..................... E-1

E.2 Installing the KSS in a Windows 2000 Environment ...................... E-2

E.3 Preparing the KSS for Access Point Validation .............................. E-5

E.4 Manually Creating an Access Point Setup Account...................... E-12

E.5 Implementing Kerberos without the KSS .................................... E-14

Index............................................................................................................. Index-1

AP-4131 Access Point Product Reference Guide ix

x AP-4131 Access Point Product Reference Guide

Chapter 1 Introduction

Spectrum24 is a spread spectrum cellular network that operates between

2.4 and 2.5 GHz (gigahertz). This technology provides a high-capacity
network using multiple access points within any environment.

The Symbol AP-4131Access Point (AP) is a Spectrum24 direct-sequence (DS)
product. Spectrum24 DS products use direct-sequence technology to provide
a high-capacity, high-data-rate wireless network.

Spectrum24 DS infrastructure products include:

• bridging architecture to provide communication between radio and
wired multiple network segments

• a design based on the IEEE 802.11 standard

• an 11 Mbps data rate for fast operation

• seamless roaming for mobile users with devices such as laptops, wireless
PCs, scanning terminals and other computers with PCMCIA slots.

1.1 Access Point (AP)

The Access Point (AP) provides a bridge between Ethernet wired LANs and
wireless networks. It provides connectivity between Ethernet wired networks
and radio-equipped mobile units (MUs). MUs include the full line of Symbol
Spectrum24 terminals, PC Cards, bar-code scanners and other devices.

This guide provides configuration and setup information for the AP-4131
model access point. Refer to the rear of the access point for product model
information.

The AP provides an 11 Mbps data transfer rate on the radio network.
It monitors Ethernet traffic and forwards appropriate Ethernet messages to
MUs over the Spectrum24 network. It also monitors MU radio traffic and
forwards MU packets to the Ethernet LAN.

AP-4131 Access Point Product Reference Guide 1

Introduction

The AP meets the following:

• the regulatory requirements for Europe and many other areas of
the world

• FCC part 15, class A with no external shielding

• FCC part 15 class B, ETS 300-339 compliance, including CE mark.

The AP has the following features:

• built-in diagnostics including a power-up self-check

• built-in dual antenna assembly with optional diversity

• wireless MAC interface

• field upgradable Firmware

• 10/100Base-T Ethernet port interface with full-speed filtering

• power supply IEC connector and a country-specific AC power cable

• data encryption

• supports multiple MIBs

• SNMP support

• support for roaming across routers

•DHCP support

•BOOTP

•DNS support

• Web browser user interface support

•short RF preamble

• wireless AP mode.

When properly configured, an MU communicating with an AP appears on
the network as a peer to other network devices. The AP receives data from its
wired interfaces and forwards the data to the proper interface.

The AP has connections for the wired network and power supply. The AP
attaches to a wall or ceiling depending on installation-site requirements.

2 AP-4131 Access Point Product Reference Guide

1.2 Radio Basics

Spectrum24 devices use electromagnetic waves to transmit and receive
electric signals without wires. Users communicate with the network by
establishing radio links between MUs and APs.

Spectrum24 products use DSSS (direct sequence spread spectrum) to transmit
digital data from one device to another. Using FM, a radio signal begins with
a carrier signal that provides the base or center frequency. The digital data
signal is encoded onto the carriers using a DSSS “chipping algorithm”. The
radio signal propagates into the air as electromagnetic waves. A receiving
antenna in the path of the waves absorbs the waves as electrical signals. The
receiving device demodulates the signal by reapplying the direct sequence
chipping code. This demodulation results in the original digital data.

Spectrum24 uses the environment (the air and certain objects) as the
transmission medium. Spectrum24 radio devices transmit in the

2.4 to 2.5-GHz frequency range, a license-free range throughout most of
the world. The actual range is country-dependent.

Spectrum24 devices, like other Ethernet devices, have unique, hardware­encoded Media Access Control (MAC) or IEEE addresses. MAC addresses
determine the device sending or receiving data. A MAC address is a 48-bit
number written as six hexadecimal bytes separated by colons.
For example:

Introduction

00:A0:F8:24:9A:C8

1.2.1 S24 Network Topology

The variations possible in Spectrum24 network topologies depend on the
following factors:

• the AP function in the network

• the data transfer rate

• the wireless AP (WLAP) interface.

AP-4131 Access Point Product Reference Guide 3

Introduction

A WLAP communicates only with its root AP through the wireless interface.

Select from the following topologies:

• A single AP used without the wired network provides a single-cell wireless
network for peer-to-peer MUs.

• A single AP can bridge the Ethernet and radio networks.

4 AP-4131 Access Point Product Reference Guide

Introduction

• Multiple APs can coexist as separate, individual networks at the same site
without interference using different Net_IDs. The Net_ID (ESS) can be
thought of as a Wireless LAN Network Identifier. These separate Wireless
LANs may be configured to use different channel assignments to avoid
RF interference.

• Multiple APs wired together provide a network with better coverage area
and performance when using the same Net_IDs.

AP-4131 Access Point Product Reference Guide 5

Introduction

In WLAP mode, a wireless AP-to-AP connection functions:

• as a bridge to connect two Ethernet networks

Kerberos, EAP-TLS and the Mobile IP feature are not available when the
access point is operating in WLAP mode.

6 AP-4131 Access Point Product Reference Guide

Introduction

In WLAP mode, APs and MUs are required to have the same Preamble
settings to interoperate. Additionally, the root AP is required to be running
before the “leaf” or WLAP connection is established.

• as a repeater to extend coverage area without additional
network cabling.

When using a wireless AP-to-AP connection, use the optimal antenna
configuration for the site. For example, use a directional antenna when
establishing a dedicated wireless bridge or repeater.

• Each wireless AP can have connections with up to four other wireless APs.

AP-4131 Access Point Product Reference Guide 7

Introduction

Using more than two WLAPs to establish a connection slows network
performance for all topologies. To increase WLAP performance, disable

WNMP Functions and AP-AP State Xchg parameters under the Set System
Configuration screen.

To set up an AP for wireless operation automatically, select the Enabled
option for the WLAP Mode parameter. To set these values, see section 2.5:
”Configuring Radio Parameters” on page 71.

The WLAP initialization process length depends on the time specified in
the WLAP Forward Delay field. See section 2.5: ”Configuring Radio
Parameters” on page 71.

1.2.2 Cellular Coverage

The AP establishes an average communication range with MUs called a
Basic Service Set (BSS) or cell. When in a particular cell the MU associates
and communicates with the AP of that cell. Each cell has a Basic Service Set
Identifier (BSS_ID). In IEEE 802.11, the AP MAC (Media Access Control)

address represents the BSS_ID. The MU recognizes the AP it associates with
using the BSS_ID.

Spectrum24 devices, like other network devices, have unique, hardware­encoded MAC or IEEE addresses. MAC addresses determine the device
sending or receiving the data. A MAC address is a 48-bit number written as
six hexadecimal bytes separated by colons. For example:

00:A0:F8:24:9A:C8

An MU recognizes the access point it associates with using the BSS_ID.
Adding access points to a single LAN establishes more cells to extend the
range of the network. Configuring the same ESS_ID (Extended Service Set
Identifier) on all access points make them part of the same Wireless LAN.

8 AP-4131 Access Point Product Reference Guide

Introduction

APs with the same Net_ID (ESS) define a coverage area. The MU searches for
APs with a matching Net_ID (ESS) and synchronizes with an AP to establish
communications. This allows MUs within the coverage area to move
about or roam. As the MU roams from cell to cell, it switches APs. The switch
occurs when the MU analyzes the reception quality at a location and decides
which AP to communicate with based on the best signal strength and lowest
MU load distribution.

If the MU does not find an AP with a workable signal, it performs a scan to
find any AP. As MUs switch APs, the AP updates the association table.

The user can configure the Net_ID (ESS). A valid Net_ID (ESS) is an
alphanumeric, case-sensitive identifier up to 32 characters. Ensure all nodes
within one LAN use the same Net_ID (ESS) to communicate on the same
LAN. Multiple wireless LANs can coexist in a single environment by assigning
different Net_IDs (ESS) for APs.

AP-4131 Access Point Product Reference Guide 9

Introduction

The Root AP and Association Process

By default, APs with WLAP Mode enabled and within range of each other
automatically associate and configure wireless operation parameters at
power up. This association process determines the wireless connection
viability and establishes the Root AP and subsequently designated WLAPs.

APs communicating wirelessly with one another require the same: Net_ID
(ESS), Encryption mode, Data Rate and Short RF Preamble settings.

The root AP maintains the wireless connection among WLAPs by sending out
beacons, sending and receiving configuration BPDU (Bridge Protocol Data

Unit) packets between each designated WLAP. The WLAP with the lowest
WLAP ID becomes the Root AP. A concatenation of the WLAP Priority value

and the MAC address becomes the WLAP ID. All WLAPs associated with the
Root AP use the Root AP channel, DTIM (Delivery Traffic Indication Message)
and TIM (Traffic Indication Map) interval.

a

In this configuration, the WLAP Priority value is the default 8000 Hex. On
concatenating this value to the MAC addresses of the APs, AP A on Ethernet I
has the lowest WLAP ID with

800000A0F800181A, making it the Root AP.

AP C uses the AP A channel, DTIM and TIM interval.

10 AP-4131 Access Point Product Reference Guide

If AP D on Ethernet II has data for a device on Ethernet I, it requires a bridge
or a repeater. In this configuration, AP C functions as a repeater. To ensure
transmission to devices on Ethernet I, AP D has to use the AP A channel,
DTIM and TIM interval.

The AP with lowest WLAP priority value is the Root AP. To manually designate
AP B as the Root AP, assign it a WLAP Priority value less than
section 2.5: ”Configuring Radio Parameters” on page 71.

IEEE 802.1d Spanning Tree Support

This protocol creates a loop-free topography with exactly ONE path between
every device and LAN. This is the shortest path from the Root AP to each
WLAP and LAN. If the connection between a WLAP and LAN fails, a new
route is calculated and added to the tree. All packet forwarding follows the
spanning tree path determined. APs in a network have to choose one AP as
the Root AP.

1.2.3 Site Topography

For optimal performance, locate MUs and APs away from transformers,
heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and
other industrial equipment.

Introduction

8000 Hex. See

Signal loss can occur when metal, concrete, walls or floors block
transmission. Locate APs in open areas or add APs as needed to
improve coverage.

Site Surveys

A site survey analyzes the installation environment and provides users with
recommendations for equipment and its placement. The optimum placement
of 11 Mbps access points differs for 1 or 2 Mbps access points, because the
locations and number of access points required are different.

AP-4131 Access Point Product Reference Guide 11

Introduction

Symbol recommends conducting a new site survey and developing a new
coverage area floor plan when switching from 1 or 2 Mbps frequency­hopping access points to 11 Mbps direct-sequence access points.

1.3 Access Point Functional Theory

To improve AP management and performance, users need to understand
basic AP functionality and configuration options. The AP includes features
for different interface connections and network management.

The AP provides MAC layer bridging between its interfaces. The AP monitors
traffic from its interfaces and, based on frame address, forwards the frames
to the proper destination. The AP tracks the frames sources and destinations
to provide intelligent bridging as MUs roam or network topologies change.
The AP also handles broadcast and multicast messages and responds to MU
association requests.

12 AP-4131 Access Point Product Reference Guide

1.3.1 MAC Layer Bridging

The AP listens to all packets on all interfaces and builds an address database
using the unique IEEE 48-bit address (MAC address). An address in the
database includes the interface media that the device uses to associates
the AP. The AP uses the database to forward packets from one interface to
another. The bridge forwards packets addressed to unknown systems to the
Default Interface (Ethernet).

Introduction

with

The AP internal stack interface handles all messages directed to the AP.

Each AP stores information on destinations and their interfaces to facilitate
forwarding. When a user sends an ARP (Address Resolution Protocol) request
packet, the AP forwards it over all enabled interfaces (Ethernet, radio and
WLAP) except over the interface the ARP request packet was received.
On receiving the ARP response packet, the AP database keeps a record
of the destination address along with the receiving interface. With this
information, the AP forwards any directed packet to the correct destination.
The AP forwards packets for unknown destinations to the Ethernet interface.

AP-4131 Access Point Product Reference Guide 13

Introduction

Transmitted ARP request packets echo back to other MUs.

The AP removes from its database the destination or interface information
that is not used for a specified time. The AP refreshes its database when it
transmits or receives data from these destinations and interfaces.

Filtering and Access Control

The AP provides facilities to limit the MUs that associate with it and the data
packets that can forward through it. Filters provide network security and
improve performance by eliminating broadcast/multicast packets from the
radio network.

The ACL (Access Control List) contains MAC addresses for MUs
allowed to associate with the AP. This provides security by preventing
unauthorized access.

The AP uses a disallowed address list of destinations. This feature prevents
the AP from communicating with specified destinations. This can include
network devices that do not require communication with the AP or its MUs.

Depending on the setting, the AP can keep a list of frame types that it
forwards or discards. The Type Filtering option prevents specific frames
(indicated by the 16-bit DIX Ethernet Type field) from being processed by
the AP. These include certain broadcast frames from devices that consume
bandwidth but are unnecessary to the wireless LAN. Filtering out
frames can also improve performance.

1.3.2 Auto Fallback to Wireless Mode

The AP supports an Auto Fallback to wireless mode when the hardware
Ethernet connection fails or becomes broken. The Auto Fallback function
operates only with an AP in WLAP mode and connected to the Ethernet
network. The AP resets itself and during initialization attempts to associate
with any other WLAP in the network.

14 AP-4131 Access Point Product Reference Guide

See section 2.4 “Configuring System Parameters” on page 59 and section

2.5.1: ”Wireless AP Operation Parameters” on page 80.

To enable this feature, set the WLAP Mode to Link Required.

1.3.3 DHCP Support

The AP can use Dynamic Host Configuration Protocol (DHCP) to obtain a
leased IP address and configuration information from a remote server. DHCP
is based on BOOTP protocol and can coexist or interoperate with BOOTP.
Configure the AP to send out a DHCP request searching for a DHCP/BOOTP
server to acquire Kerberos security information, HTML, firmware or network
configuration files when a boot (an AP boot) takes place. Because BOOTP
and DHCP interoperate, whichever responds first becomes the server that
allocates information.

The AP can be set to only accept replies from DHCP or BOOTP servers or
both (this is the default setting). Setting DHCP to
and DHCP (configure network settings manually). If running both DHCP and
BOOTP, do not select BOOTP Only. BOOTP should only be used when the
server is running BOOTP exclusively. See section 2.3 “Access Point
Installation” on page 54.

Introduction

disabled disables BOOTP

The DHCP client automatically sends a DHCP request at an interval specified
by the DHCP server to renew the IP address lease as long as the AP is
running (This parameter is programmed at the DHCP server). For example:
Windows NT servers typically are set for 3 days.

AP-4131 Access Point Product Reference Guide 15

Introduction

Program the DHCP or BOOTP server to transfer these files (Kerberos security
information, HTML, firmware or network configuration files) with these DHCP
options for the specific file or information to download:

DHCP Option Value

Firmware and HTML file 67 (filenames are separated by a space)

ESSID 128

Configuration filename 129

ACL filename 130

Kerberos enable/disable flag 131(set to 0 for disable or 1 for enable on

KDC name 132

KSS name 133

KSS port number 134

When the AP receives a network configuration change or is not able to renew
the IP address lease the AP sends out an SNMP trap if SNMP is configured.

1.3.4 Media Types

the DHCP server)

The AP supports bridging between Ethernet and radio media.

The Ethernet interface fully complies with Ethernet Rev. 2 and IEEE 802.3
specifications. The 4131 AP supports a 10/100Base-T wired connection. The
data transfer rate is 11 Mbps.

The radio interface conforms to IEEE 802.11 specifications. The interface
operates at 11 Mbps using direct-sequence radio technology. The AP
supports multiple-cell operations with fast roaming between cells. With the
direct-sequence system, each cell operates independently. Each cell provides
an 11 Mbps bandwidth. Adding cells to the network provides increased
coverage area and total system capacity. The AP supports MUs operating in
Power Save Polling (PSP) mode or Continuously Aware Mode (CAM) without
user intervention.

16 AP-4131 Access Point Product Reference Guide

Introduction

The DB-9, 9-pin, RS-232 serial port provides a UI (User Interface)
connection. The UI provides basic management tools for the AP. The serial
link supports short haul (direct serial) or long haul (telephone-line)
connections. The AP is a DTE (Data Terminal Equipment) device with male
pin connectors for the RS-232 port. Connecting the AP to a PC requires a
null modem cable.

AP-4131 Access Point Product Reference Guide 17

Introduction

1.3.5 Direct-Sequence Spread Spectrum

Spread spectrum (broadband) uses a narrowband signal to spread the
transmission over a segment of the radio frequency band or spectrum.
Direct-sequence is a spread spectrum technique where the transmitted signal
is spread over a particular frequency range. The Spectrum24 AP-4131access
point uses Direct-Sequence Spread Spectrum (DSSS) for radio
communication.

Direct-sequence systems communicate by continuously transmitting a
redundant pattern of bits called a chipping sequence. Each bit of transmitted
data is mapped into chips by the access point and rearranged into a
pseudorandom spreading code to form the chipping sequence. The chipping
sequence is combined with a transmitted data stream to produce the AP
output signal.

18 AP-4131 Access Point Product Reference Guide

Mobile Units receiving a direct-sequence transmission use the spreading
code to map the chips within the chipping sequence back into bits to recreate
the original data transmitted by the access point. Intercepting and decoding
a direct-sequence transmission requires a predefined algorithm to associate
the spreading code used by the transmitting access point to the receiving MU.
This algorithm is established by IEEE 802.11b specifications. The bit
redundancy within the chipping sequence enables the receiving MU to
recreate the original data pattern, even if bits in the chipping sequence are
corrupted by interference.

The ratio of chips per bit is called the spreading ratio. A high spreading ratio
increases the resistance of the signal to interference. A low spreading ratio
increases the bandwidth available to the user. The access point uses a
constant chip rate of 11Mchips/s for all data rates, but uses different
modulation schemes to encode more bits per chip at the higher data rates.
The access point is capable of an 11 Mbps data transmission rate, but the
coverage area is less than a 1 or 2 Mbps access point since coverage area
decreases as bandwidth increases.

1.3.6 MU Association Process

Introduction

APs recognize MUs as they associate with the AP. The AP keeps a list of the
MUs it services. MUs associate with an AP based on the following conditions:

• the signal strength between the AP and MU

• MUs currently associated with the AP

• the MUs encryption and authentication capabilities and the type enabled

• the MUs supported data rates (1 Mbps, 2 Mbps, 5.5 Mbps or 11 Mbps).

MUs perform preemptive roaming by intermittently scanning for APs and
associating with the best available AP. Before roaming and associating with
APs, MUs perform full or partial scans to collect AP statistics and determine
the direct-sequence channel used by the AP.

AP-4131 Access Point Product Reference Guide 19

Introduction

Scanning is a periodic process where the MU sends out probe messages on
all channels defined by the country code. The statistics enable an MU to
reassociate by synchronizing its channel to the AP. The MU continues
communicating with that AP until it needs to switch cells or roam.

MUs perform full scans at start-up. In a full scan, an MU uses a sequential
set of channels as the scan range. For each channel in range, the MU tests
for CCA (Clear Channel Assessment). When a transmission-free channel
becomes available, the MU broadcasts a probe with the Net_ID (ESS) and
the broadcast BSS_ID. An AP-directed probe response generates an
MU ACK (Mobile Unit Acknowledgment) and the addition of the AP to the AP
table with a proximity classification. An unsuccessful AP packet transmission
generates another MU probe on the same channel. If the MU fails to receive
a response within the time limit, it repeats the probe on the next channel in
the sequence. This process continues through all channels in the range.

MUs perform partial scans at programmed intervals, when missing expected
beacons or after excessive transmission retries. In a partial scan, the MU
scans APs classified as proximate on the AP table. For each channel,
the MU tests for CCA. The MU broadcasts a probe with the Net_ID (ESS)
and broadcast BSS_ID when the channel is transmission-free. It sends an
ACK to a directed probe response from the AP and updates the AP table.
An unsuccessful AP packet transmission causes the MU to broadcast another
probe on the same channel. The MU classifies an AP as out-of-range in the
AP table if it fails to receive a probe response within the time limits. This
process continues through all APs classified as proximate on the AP table.

20 AP-4131 Access Point Product Reference Guide