Cabletron Systems AirConnect 3Com User Manual

AirConnect

®

11 Mbps
Wireless LAN Access Point
User Guide

Version 2.0

Part No. 09-2045-000
Published December 2000

3Com Corporation
Bayfront Plaza
Clara, California

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Santa

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95052-8145

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5400

Copyright © 2000, 3Com Corporation. All rights reserved. No part of this documentation may be
reproduced in any form or by any means or used to make any derivative work (such as translation,
transformation, or adaptation) without written permission from 3Com Corporation.

3Com Corporation reserves the right to revise this documentation and to make changes in content from
time to time without obligation on the part of 3Com Corporation to provide notification of such revision
or change.

3Com Corporation provides this documentation without warranty, term, or condition of any kind, either
implied or expressed, including, but not limited to, the implied warranties, terms or conditions of
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If there is any software on removable media described in this documentation, it is furnished under a license
agreement included with the product as a separate document, in the hard copy documentation, or on the
removable media in a directory file named LICENSE.TXT or !LICENSE.TXT. If you are unable to locate a copy,
please contact 3Com and a copy will be provided to you.

UNITED STATES GOVERNMENT LEGEND

If you are a United States government agency, then this documentation and the software described herein
are provided to you subject to the following:

All technical data and computer software are commercial in nature and developed solely at private expense.
Software is delivered as “Commercial Computer Software” as defined in DFARS 252.227-7014 (June 1995)
or as a “commercial item” as defined in FAR 2.101(a) and as such is provided with only such rights as are
provided in 3Com’s standard commercial license for the Software. Technical data is provided with limited
rights only as provided in DFAR 252.227-7015 (Nov 1995) or FAR 52.227-14 (June 1987), whichever is
applicable. You agree not to remove or deface any portion of any legend provided on any licensed program
or documentation contained in, or delivered to you in conjunction with, this User Guide.

Unless otherwise indicated, 3Com registered trademarks are registered in the United States and may or may
not be registered in other countries.

3Com and AirConnect are registered trademarks and the 3Com logo is a trademark of 3Com Corporation.

Microsoft, MS-DOS, Windows, and Windows NT are registered trademarks of Microsoft Corporation.

All other company and product names may be trademarks of the respective companies with which they are
associated.

EXPORT RESTRICTIONS: This product or software contains encryption code which may not be exported or

transferred from the U.S. or Canada without an approved US Department of Commerce export license.

C

ONTENTS

1

VERVIEW

O

Introduction 9
AirConnect Network Topologies 9

Peer-To-Peer Network 9
Same-Site Separate Networks 10
Single AP Bridge 11
Multiple-AP Full Coverage Network 12

AirConnect Access Point 12

AP Features 13
PowerBASE-T 13

Radio Basics 14

Cellular Coverage 15

Site Topography 17

Theory of Operation 17

MAC Layer Bridging 17

DHCP Support 18
Media Types 18
Bridging Support 19

Direct-Sequence Spread Spectrum 21
Wireless Client Association Process 21
Roaming 22
Extended Roaming 22
Security 23
Supporting CAM and PSP Stations 23
HTTP, HTML Web Server Support 24
Management Options 24

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IGITAL

D

Wireless LAN Service Area 16

802.1d Spanning Tree Support 16

Site Surveys 17

Filtering and Access Control 18

PPP Connection 20

Programmable SNMP Trap Support 25
Using SNMP 25
Increased MIB Support 25
Using the User Interface 26

W

IRELESS

ETWORKING

N

NSTALLING

2

I

Introduction 27
Precautions 27
Package Contents 27
Requirements 27

Network Connection 28
10BASE-T UTP 28

Single Cell 28
Power Options 28
Mounting the AP 29

Flat Surface 29

Wall Mount 29

Ceiling Mount 30
Using the PowerBASE-T 32
LED Indicators 33
Troubleshooting 34

Verify AP Operation 34

Verify Network Wiring and Topology 35

Setting Up Wireless Clients 35

3

M

ONITORING

Introduction 37
System Properties 37
Interface Statistics 37
Forwarding Counts 37
Ethernet Statistics 38
Radio Frequency Statistics 38
Miscellaneous Statistics 39

Analyzing Retries 39
Clearing Statistics 40
Known APs 40

A

CCESS

S

TATISTICS

P

OINT

HARDWARE

4

ONFIGURING

C

Introduction 41
Gaining Access to the User Interface (UI) Using a Web Browser 41

Using a Web Browser 41

Help File Access 41
Setup Network Web Server Help File Access 41
42
Accessing the Web Browser UI 42

Changing UI Access 44

THE

A

CCESS

P

OINT

U

SING

A

EB

W

ROWSER

B

Installing the Access Point 45

Adding Additional Gateways 45

Configuring the AP 46

Security 46

Adding Allowed Wireless Clients 46
Adding or Deleting a Range of Allowed Wireless Clients 46
Adding or Deleting Disallowed Wireless Clients 46
Enabling or Disabling Encryption 47

Encryption Upgrade Access Codes 47

Special Configuration Considerations 47

Disable Short Preamble 47
System Parameters 48
Radio Frequency Parameters 49
Configuring the SNMP Agent 50
Configuring PPP/Modem 51

Configuring the Originating Modem 51
Configuring the Answering Modem 52

Filtering 52

Filtering to Forward Packets 52
Filtering to Discard Packets 52
Removing Filtered Packet Types (Networking Protocols) 53

Disabling Type Filtering 53
Updating AP Firmware 53
Special Functions 54

5

6

ONITORING

M

Introduction 55
Wireless Clients 55
Clearing Statistics 56

C

ONFIGURING

Introduction 57
Gaining Access to the User Interface (UI) 57

Using Telnet 57
Using a Direct Serial Connection 58
Using a Dial-up Connection 58

Navigating the UI 58

Entering Admin Mode 59
Changing the Access to the UI 60
Configuring for Dial-Up to the UI 60

Configuring The Serial Port 60

Configuring the Dial-Up System 61

Hanging Up 61

W

THE

IRELESS

AP U

LIENTS

C

SING

THE

ASCII I

NTERFACE

Access Point Installation 62
Configuring the AP 63

System Parameters 63
Radio Parameters 64
Configuring PPP 66

PPP Direct 66
Establishing a Connection 66
PPP with Modems 66
Originating AP 67

Answering AP 67
Configuring the SNMP Agent 68
Configuring the Access Control List 69

Range of Wireless Clients 69

Adding Allowed Wireless Clients 70

Removing Allowed Wireless Clients 70

Enable/Disable the ACL 70

Removing All Allowed Wireless Clients 70

Load ACL from Wireless Client List 71
Filtering 71

Address Filtering 71

Adding Disallowed Wireless Clients 71

Removing Disallowed Wireless Clients 71

Type Filtering 71

Adding Filter Types 71

Removing Filter Types 72

Controlling Type Filters 72

Clearing Wireless Clients from the AP 72
Setting Logging Options 72
Manually Updating AP Firmware 73

Update using TFTP 74
Updating using Xmodem 74

Auto Upgrade all APs Via Messaging 76
Performing Pings 77
Extended Roaming Using MD5 Authentication 77
Enabling or Disabling Encryption 78

Encryption Configuration Requirements 78
Encryption Upgrade Access Codes 78

Special Configuration Considerations 78

Disable Short Preamble 78
WLAP Mode Setting 79

Saving, Resetting, and Restoring Configurations 79

Saving a Configuration 79
Resetting an AP 79
Restoring the Default AP Configuration 80

CCESS

A

A

T

B

ECHNICAL

Online Technical Services 83

World Wide Web Site 83

3Com FTP Site 83
Support from Your Network Supplier 83
Support from 3Com 84
Returning Products for Repair 85

NDEX

I

ARRANTY

W

3Com Corporation Limited Warranty 91
Regulatory Compliance Information 93
3Com End User Software License Agreement 94

P

OINT

S

AND

PECIFICATIONS

S

UPPORT

EGULATORY

R

C

OMPLIANCE

1

Introduction

O

VERVIEW

N

ETWORKING

AirConnect
deliver high-speed digital wireless networking. This technology provides connectivity
between wireless clients and network nodes in a variety of indoor environments,
and also provides bridging architecture between wired and wireless network
segments. AirConnect is based on the IEEE 802.11B standard, and delivers 11 Mbps
data transfer rates.

The core hardware products that make up an AirConnect network include
the following:

■

A wireless network interface card (NIC) installed in a wireless client, either

a PC Card installed in a notebook computer, or a PCI card installed in a

desktop computer.

■

Access point, or AP, which serves as a wireless network node.

®

from 3Com is made up of a series of products that work together to

OF

D

IGITAL

W

IRELESS

■

PowerBASE-T (optional), which provides bus power to the access point when

connected to an Ethernet network.

Also included in your AirConnect kit are an AP mounting bracket and hardware,
a serial cable, a power adapter and associated power cables, and one CD: the

AirConnect Installation CD.

AirConnect Network Topologies

Peer-To-Peer Network The simplest AirConnect topology consists of one AP providing a single-cell

To better understand how the various AirConnect products work together to create
a wireless network, it might be helpful to depict a few of the possible AirConnect
network topologies. The topology used in a particular environment depends on many
factors, such as the functionality of the AP in the network, or desired data transfer
rates. Your AirConnect network topology will probably resemble one of the following
scenarios, or perhaps a combination of two or more.

network for wireless clients. In this scenario, as shown in the figure below, the
wireless clients (notebook and desktop computers with the AirConnect NIC
installed) communicate through the AP on a peer-to-peer network. The clients can
be moved anywhere within the coverage area of the AP, and still communicate
with each other. The AP in this instance serves the same purpose as a stand-alone
network hub, and is not connected to any other network segments.

HAPTER

C

1: O

VERVIEW

10

OF

IGITAL

D

W

IRELESS

ETWORKING

N

Same-Site Separate

Networks

In this scenario, as shown in the following figure, Multiple APs can coexist as
separate networks at the same site without interference using different network
identifiers (wireless LAN service areas). The wireless clients can move within the
coverage area of one AP and remain connected, or can roam (if configured to do
so) to the coverage area of a different AP, and communicate with the wireless
clients associated with that AP.

AirConnect Network Topologies 11

Single AP Bridge Another possible AirConnect topology is a single AP bridging an Ethernet and

wireless network. As shown in the next figure, the AP, wired to a network server
or LAN through an Ethernet cable, serves as a network node and provides the link
between the server and the wireless clients. The wireless clients can move freely
throughout the coverage area of the AP while remaining connected to the server.

HAPTER

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1: O

VERVIEW

12

OF

IGITAL

D

W

IRELESS

ETWORKING

N

Multiple-AP Full

Coverage Network

This network topology will be used in most enterprise environments: multiple APs
wired to an existing LAN to provide complete wireless network coverage. In this
scenario, as shown in the following figure, wireless clients can roam seamlessly
between different coverage areas and remain connected to the network.

AirConnect Access Point

The AirConnect access point (AP) provides either a wireless peer-to-peer network
coverage area, or a bridge between Ethernet-wired LANs and AirConnect wireless
networks. Essentially replacing the cabling of wired networks, the AP delivers
transparent connectivity between wireless clients, or between Ethernet networks
and wireless clients.

The AP provides an 11 Mbps data transfer rate, monitoring Ethernet traffic and
forwarding appropriate Ethernet messages to wireless clients over the network.
It also monitors wireless client radio traffic and forwards wireless client packets
to the Ethernet LAN.

The AP uses high data rate, direct sequence spread spectrum technology to
communicate with mobile and stationary units at distances of up to 300 feet,
providing high-capacity networking capability and the flexibility of mobility to
end users.

AirConnect Access Point 13

AP Features

A wireless client communicating with an AP appears on the network as a peer to
other network devices, rendering the wireless interface transparent. The AP receives
data from its wired interfaces and forwards the data to the proper interface.

The AP has connections for wired networks, built-in antennas, and a power supply.
It attaches to a wall or ceiling, or can be placed on a flat surface, depending on
installation-site requirements. The AP uses a diversity antenna for radio transmission
and reception, allowing the AP to automatically select the strongest of the radio
signals picked up by the antenna.

■ Built-in diagnostics (including a power-up self-check)

■ Wireless MAC interface

■ Upgradable firmware

■ 10BASE-T Ethernet port interface with full-speed filtering

■ Power supply IEC connector and a country-specific AC power cable

■ PC/AT Serial Port Interface

■ Built-in antenna diversity

■ Support for up to 63 wireless clients

■ SNMP support

■ IEEE 802.11 MIB support

■ DHCP support

■ HTTP Web server support.

PowerBASE-T This device allows the AP to be powered through the Ethernet cable connecting

the AP to a LAN. The PowerBASE-T should be used when the AP is connected to
LAN and is mounted in a location where access to a standard electric outlet is
severely limited.

14 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

For details concerning the installation of your PowerBASE-T, see “Using the
PowerBASE-T”.

Radio Basics AirConnect devices use radio signals to transmit and receive data without wires.

You can communicate with the network by establishing radio links between
wireless clients and APs.

AirConnect uses Quadative Phase Shift layered modulation (QPSK) to transmit
digital data from one device to another. Using QPSK, a radio signal begins with a
carrier signal that provides the base or center frequency. The digital data signal is
superimposed on the carrier signal in process called “modulation.” The radio
signal then travels through the air as electromagnetic waves. A receiving antenna
in the path of the waves absorbs them as electrical signals. The receiving device
“demodulates” the signal by removing the carrier signal. This demodulation
results in the original digital data.

AirConnect uses its environment (the air and certain other objects) as the
transmission medium. AirConnect radio devices transmit in the 2.4-2.5 GHz
frequency range, a license-free range throughout most of the world. The actual
range your AirConnect network operates at is country-dependent.

Radio Basics 15

AirConnect devices, like other Ethernet devices, have unique, hardware-encoded
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. A typical MAC address might be:

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

The AP MAC address is printed on the bottom of the unit, as shown below.

Cellular Coverage The AP establishes an average communication range with wireless clients called a

Home Service Area (HSA), or cell. When a wireless client is in a particular cell, the

wireless client associates and communicates with the AP in that cell. Each cell has
a Home Service Area Identifier (HSA_ID). Under the 802.11 standard, the MAC
address of an AP represents its HSA_ID. The wireless client recognizes the AP it
associates with using the HSA_ID. Adding APs to a LAN establishes more cells in
an environment, creating a wireless network using the same NET_ID. This type of
network is called a Wireless LAN Service Area (WSA), as shown below.

16 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

APs with the same WLAN service area define a coverage area. The wireless client
searches for APs with a matching wireless LAN service area and synchronizes
with an AP to establish communications. This allows wireless clients within the
coverage area to roam between AP cells. As you roam from cell to cell, your
wireless client switches APs. The switch occurs when the wireless client analyzes
the reception quality at a particular location and selects an AP to communicate
with, based on such factors as signal strength and wireless client load.

When the wireless client begins to lose the signal as it moves away from an
associated AP, it performs a scan to find another AP. As wireless clients switch
APs, the AP updates the association table. Roaming is invisible to the user.

Wireless LAN Service Area

The network administrator assigns the wireless LAN service area for the APs in a
WSA. A valid wireless LAN service area is an alphanumeric, case-sensitive identifier
of up to 32 characters. All nodes within one LAN use the same wireless LAN
service area to communicate on the LAN. Multiple wireless LANs can coexist in
a single environment by assigning different wireless LAN service areas for the
corresponding APs.

802.1d Spanning Tree Support

This protocol creates a loop-free topography with exactly one path between every
LAN. This is the shortest path from the Root AP to each AP and LAN. If an AP or
LAN fails, a new route is calculated and added to the tree. All packet forwarding
follows the spanning tree. APs have to choose one AP as the Root AP. The same
holds true for WLANs associating with the root AP or another AP connected to the
Ethernet LAN to prevent forming loops.

Theory of Operation 17

Site Topography For optimal performance, place wireless clients and APs away from transformers,

heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and other
industrial equipment.

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

Site Surveys

A site survey analyzes the installation environment and provides users with
recommendations for the number and placement of APs. 3Com recommends that a
site survey be conducted at any new site prior to installing AirConnect equipment.

Theory of Operation To improve AP management and performance, you should 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 wireless clients roam or network topologies change. The AP also handles broadcast and multicast message initiations and responds to wireless client association requests.

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 with the AP. (The AP internal
stack interface handles all messages directed to 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 (either Ethernet or PPP).

Each AP stores information on destinations and their interfaces to facilitate
forwarding. When you send an Address Resolution Protocol (ARP) request packet,
the AP forwards the request over all enabled interfaces (Ethernet, PPP, or radio),
except over the interface on which the ARP request packet was received.
(Radio-received ARP request packets echo back to other APs over radio.) Upon
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.

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

18 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

Filtering and Access Control

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

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

The AP also 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 wireless clients.

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 unimportant to the wireless LAN but which utilize
bandwidth. Filtering out unnecessary frames also improve throughput.

DHCP Support The AP uses Dynamic Host Configuration Protocol (DHCP) to obtain a leased IP

address and network configuration information from a remote server. DHCP is
based on BOOTP protocol. DHCP can coexist or interoperate with BOOTP. An AP
sends out a DHCP request searching for a DHCP server to acquire the network
configuration and firmware filenames. Because BOOTP and DHCP interoperate,
the one that responds first becomes the server that allocates information. The
DHCP client automatically sends a DHCP request 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.)

The AP can optionally download two files when a boot takes place, the firmware
file and an HTML file, because firmware versions 4.00-31 and above support Web
servers. Users can program the DHCP or BOOTP server to transfer these two files
when a DHCP request is made.

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.

Media Types The AP supports bridging between Ethernet, radio, and serial media.

The Ethernet interface fully complies with Ethernet Rev. 2 and IEEE 802.3
specifications. The AP supports 10BASE-T wired connections and full-speed
filtering. The data transfer rate over radio waves is 11 Mbps. The Ethernet
interface is optional for single-cell or PPP-connected networks.

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

Theory of Operation 19

The DB-9, 9-pin, RS-232 serial port provides a User Interface (UI) or a
Point-to-Point Protocol (PPP) connection. The UI provides basic management

tools for the AP. The PPP provides a link between APs using a serial connection.
The serial link supports short haul (direct serial) or long haul (telephone line)
connections. The AP is a Data Terminal Equipment (DTE) device with male pin
connectors for the RS-232 port. Connecting the AP to a PC requires a null-modem
cable; connecting the AP to a modem requires a straight-through cable.

Bridging Support The AP PPP interface, accessible from the serial port at the rear of the AP, provides

two types of bridging operations: Internet Protocol (IP) bridging between an AP
and a computer, and between two APs (with one AP connected to a LAN). To
establish an Internet Protocol bridge with an AP, ensure that the computer
includes the appropriate Telnet software with PPP and TCP/IP protocols. Using
Telnet, a remote computer can connect to any AP on an Ethernet network, as
long as data transfers through IP packets.

A PPP link provides the option of using a direct serial link or modem to extend
wired Ethernet topologies. Once in PPP mode, the AP automatically attempts to
communicate with the other device using the Data-Link Bridging (DLB) protocol.
An AP using DLB communicates on the MAC level, and receives and transmits
Ethernet frames.

If the other device does not support DLB, the AP attempts to communicate using
Internet Protocol Control Protocol (IPCP). An AP using IPCP communicates on the
IP level, and receives and transmits IP packets.

The PPP implementation in the AP uses the Link Control Protocol (LCP) and
Network Control Protocol (NCP) as described in:

■ RFC 1171: the Point-to-Point Protocol, July 1990.

■ RFC 1220: PPP Extensions for Bridging, April 1991.

■ RFC 1332: The PPP Internet Protocol Control Protocol, May 1992.

■ RFC 1661: The Point-to-Point Protocol, July 1994.

(RFCs are Requests For Comments used in Internet Communities.)

The AP database dynamically tracks wireless clients and APs on the PPP interface.
Packets forward to the PPP link after the AP determines their destination.

The PPP implementation in the AP uses the NCP as described in RFC 1220: PPP
Extensions for Bridging to encapsulate packets at the Ethernet level. The PPP provides
IP bridging control as defined by RFC 1172 and MAC-level bridging. The protocol
provides support for PPP negotiations conforming to RFC 1661. Users cannot plug a
non-AP node directly into the AP serial port, only AP-to-AP PPP links.

For detailed information, refer to RFC 1171: The Point to Point Protocol and RFC

1220: PPP Extensions for Bridging.

20 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

PPP Connection

Connecting an AP and a computer with a direct serial link requires the use of a
null-modem serial cable.

Connecting an AP and computer with modem devices requires the use of
straight-through cables between the APs and modems. Using modems requires
a telephone line for as long as the link remains active.

When using a modem connection, one AP represents the originating AP and the
other represents the answering AP. When using a PPP link, do not use the serial
port to access the UI. Access to the UI requires establishing a Telnet session with
the AP.

Theory of Operation 21

Direct-Sequence Spread

Spectrum

Wireless Client

Association Process

Direct Sequence Spread Spectrum (DSSS) uses a high-speed, non-information
bearing signal to spread the transmitted information over a segment of the
radio frequency band or spectrum. The AirConnect access point uses 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 to find the chipping sequence corresponding to the
output signal.

Wireless clients receiving a direct-sequence transmission use the same chipping
sequence to recreate the original data transmitted by the access point. Intercepting
and decoding a direct-sequence transmission requires a predefined algorithm to
associate the chipping sequence used by the transmitting access point to the
receiving wireless client. This algorithm is established when the access point and
wireless client are configured. The bit redundancy within the chipping sequence
enables the receiving wireless client to recreate the original data pattern, even if bits
in the chipping sequence are corrupted by interference.

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

■ Signal strength between the AP and wireless client

■ Wireless clients currently associated with the AP

■ Wireless client Supported Rate (see table below).

■ Positive match between the wireless client and encryption keys (optional)

■ Positive wireless client authorization by the Access Control List (optional)

Data Rate Requirement

11 Mbps Optional

5.5 Mbps Optional

2 Mbps Required

1 Mbps Required

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

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

Wireless clients perform scans at start-up. In a scan, a wireless client uses a
sequential set of channels as the scan range. For each channel in range, the
wireless client tests for Clear Channel Assessment (CCA). When a
transmission-free channel becomes available, the wireless client broadcasts a
probe with the wireless LAN service area and the broadcast HSA_ID. An
AP-directed probe response generates a wireless client Acknowledgment (ACK)

22 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

and the addition of the AP to the AP table with a proximity classification. An
unsuccessful AP packet transmission generates another wireless client probe on
the same channel. If the wireless client fails to receive a probe response within the
time limits, it repeats the probe process on the next channel in the sequence. This
process continues through all channels in the range.

A wireless client can roam within the coverage area by switching APs. Roaming
is transparent and virtually instantaneous in high-level applications. Roaming
occurs when:

■ An unassociated wireless client attempts to associate or reassociate with an

available AP.

■ The supported rate changes or the wireless client finds a better transmit rate

with another AP.

■ The signal quality of a potential AP exceeds that of the current AP.

■ The ratio of good-transmitted packets to attempted-transmitted packets falls

below a threshold.

■ The wireless client detects an imbalance in the number of wireless clients

associated with available APs and roams to a less loaded AP.

A wireless client selects the best available AP and adjusts itself to the AP
direct-sequence channel to begin association. Once associated, the AP begins
forwarding any frames it receives addressed to the wireless client. Each frame
contains fields for the current direct-sequence channel. The wireless client uses
these fields to resynchronize to the AP.

Roaming The AirConnect Roaming feature enables a wireless client on the Internet to move

from one AP to another within a single subnet. The scanning and associating
process continues for active wireless clients. This allows the wireless clients to find
new APs and discard out-of-range or deactivated APs. By testing the airwaves, the
wireless clients can choose the best network connection available.

Extended Roaming The AirConnect extended roaming (roaming across routers) feature enables a

wireless client on the Internet to move from one subnet to another while keeping
its IP address unchanged. extended roaming enables a wireless client to
communicate with other hosts using only its home IP address after changing its
point-of-attachment to the Internet/Intranet.

For extended roaming to work, you must use a static IP address.

The Internet Protocol identifies the wireless client point of attachment to a
network through its IP address. The AP routes packets according to the location
information contained in the IP header. If the wireless client roams across routers
to another subnet with extended roaming disabled, the following situations occur:

■ The wireless client changes its point of attachment without changing its IP

address, causing forthcoming packets to become undeliverable.

■ The wireless client changes its IP address when it moves to a new network,

causing it to lose connection.

Theory of Operation 23

Enabling the extended roaming feature is like giving an individual a local post
office forwarding address when leaving home for an extended period. When mail
arrives for the individual home address, it is forwarded by the local post office to
the current care-of-address. Using this method, only the local post office requires
notification of the individual current address. While this example represents the
general concept of extended roaming operation and functionality, it does not
represent the implementation of extended roaming used.

If you wish to use extended roaming, set your wireless clients for extended
roaming as specified in the AirConnect Wireless PC Card User Guide.

The following terms describe elements of the extended roaming feature:

■ A tunnel is the path taken by the original packet encapsulated within the

payload portion of a second packet to some destination on the network.

■ A Home Agent is an AP acting as a router on the wireless client home network.

The home agent intercepts packets sent to the wireless client home address

and tunnels the message to the wireless client at its current location. This

happens as long as the wireless client keeps its home agent informed of its

current location on some foreign link.

Security Security involves two distinct areas: authentication and privacy. Authentication

Supporting CAM and

PSP Stations

■ A Foreign Agent is an AP acting as a router at the wireless client location on a

foreign link. The foreign agent serves as the default router for packets sent out

by the wireless client connected on the same foreign link.

■ A care-of-address is the IP address used by the wireless client visiting a foreign

link. This address changes each time the wireless client moves to another

foreign link. It can also be viewed as an exit point of a tunnel between the

wireless client home agent and the wireless client itself.

ensures that only authorized users access the wireless network. Privacy ensures
that communication between authenticated users and the network cannot be
intercepted or overheard. The Access Control List provides authentication using
the wireless LAN service area and a system administrator-supplied list of all the
wireless client MAC addresses authorized to access the Home Service Area. Privacy
is ensured by enabling the 40-bit WEP encryption option.

Continuously Aware Mode (CAM) stations leave their radios on continuously to
hear every beacon and message transmitted. These systems operate without any
adjustments by the AP.

A beacon is a uniframe system packet broadcast by the AP to keep the network
synchronized. A beacon includes the wireless LAN service area, the AP address, the
Broadcast destination addresses, a time stamp, Delivery Traffic Indicator Maps, and
the Traffic Indicator Message (TIM).

Power Save Polling (PSP) stations power off their radios for long periods. When a
wireless client in PSP mode associates with an AP, it notifies the AP of its activity
status. The AP responds by buffering packets received for the wireless client. The
PSP-mode wireless client wakes up to listen to the AP beacon every n

th

Beacon

Interval where n is a PSP-mode value from the 1 to 5-range; the Beacon Interval is

set on the wireless client. When the wireless client wakes up and sees its bit set in
the TIM, it issues a poll request to the AP for packets stored for it. The AP sends

24 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

them to the wireless client and the wireless client goes back to sleep. A DTIM field,
also called a countdown field, informs wireless clients of the next window for
listening to broadcast and multicast messages. The AP sends the messages
following the

nth beacon where n is the DTIM interval defined in the AP. When the

AP has buffered broadcast or multicast messages for associated wireless clients, it
sends the next DTIM with a DTIM Interval value. This value decreases by '1' with
each successive beacon. The AP sends broadcast and multicast messages
immediately following the beacon where the DTIM value is '0.' To prevent a
PSP-mode wireless client from sleeping through a DTIM notification, select a PSP
mode value less than or equal to the DTIM value. PSP-mode wireless clients hear
the beacons and awaken to receive the broadcast and multicast messages.

A TIM is a compressed virtual bitmap identifying the AP associated wireless clients
in PSP mode that have buffered directed messages. wireless clients issue a poll
request when APs issue a TIM. A beacon with the broadcast-indicator bit set
causes the wireless client to note DTIM Count field value. The value informs the
wireless client of the beacons remaining before next DTIM. This ensures the
wireless client turns on the receiver for the DTIM and the following BC/MC packet
transmissions.

HTTP, HTML Web Server

Support

Hypertext Transfer Protocol (HTTP) is the native language of the World Wide Web.
The HTTP protocol makes requests from browsers to servers and responses from
servers to browsers. This function provides the user with a Web-based format for
configuration and firmware download.

Web pages are written in Hypertext Markup Language (HTML). HTML allows the
user to create Web pages containing text, graphics, and pointers or links to other
Web pages or elsewhere on the page or document. Pointers are known as
Uniform Resource Locators (URLs). A URL is essentially the name of the Web page.
The URL consists of three parts:

1 Protocol (or Scheme)

2 Fully Qualified Domain Name (FQDN), the machine where the page is located

3 Local name that identifies the page (usually the HTML file name).

The HTML language describes how to format the document, indication which
fonts to use, much like a copy editor describes which fonts to use, such as the
location, color, header size and text.

Management Options Managing AirConnect includes viewing network statistics and setting

configuration options. Statistics track the network activity of associated wireless
clients and data transfers on the AP interfaces. Configuration involves, among
other things, setting system operating parameters and filters used in bridging.

The AP requires one of the following to perform a custom installation or maintain
the AirConnect network:

■ Simple Network Management Protocol (SNMP).

■ Wired or wireless LAN workstation with a telnet client.

■ Terminal or PC with RS-232 connection and access to ANSI emulation.

Theory of Operation 25

Changing one AP does not affect the configuration of other APs on the network.
Make configuration changes to APs individually. Each AP requires an individual
IP address.

Programmable SNMP Trap Support

The SNMP protocol defines the method for obtaining information about networks
operating characteristics and changing router and gateway parameters. The SNMP
protocol consists of three elements:

■ Management stations

■ Management information

■ Management protocol (MIB)

Nodes can perform as hosts, routers, bridges or other devices that can
communicate status information. An SNMP Agent is a node that runs the SNMP
management process to systematically monitor and manage the network. The
management station performs network management by running application
management software.

An SNMP trap is an alert to all configured management stations of some
significant event that occurred on the network. The management station queries
all stations for details of each specific event, including what, when and where the
event took place and the current status of the node or network. The format or
structure is defined in the SNMP protocol. The MIB defines what and who
monitors the variables.

Using SNMP

The AP includes SNMP agent versions accessible through an SNMP manager
application (HP Open View or Cabletron Spectrum MIB browser). The SNMP agent
supports SNMP versions 1 and 2, MIB II, 802.11 MIB and one proprietary 3Com
Management Information Base (MIB). The SNMP agent supports read-write,
read-only or disabled modes. The AP supports traps that return to the SNMP
manager when certain events occur. The Wireless LAN Installation and Utilities disk
packaged with wireless clients contains the MIB.

Increased MIB Support

The MIB defines what the management station needs to understand and which
objects the station manages. The MIB has ten categories defined with
approximately 175 variables.

26 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

Using the User Interface

The User Interface (UI) is a text-based maintenance tool integrated into the AP. It
provides statistical displays, AP configuration options, and firmware upgrades.
Access to the UI requires one of the methods listed in the following table:

Method Description

Telnet Client Gain access to the AP built-in Telnet server from any AP interface

Direct Serial
Connection

Dial Up Access The dial-up access method requires a communication program

SNMP Via a MIB
Browser

Web Browser Gain access to the AP built-in Web server from any AP interface

including remote Ethernet connections. Refer to “Using Telnet”
on page 57.

Acts as a DTE device to connect directly to a DTE device with a
null-modem serial cable. The direct serial access method requires a
communication program with ANSI emulation. Refer to “Using a
Direct Serial Connection” on page 58 for more information.

with ANSI emulation on the remote terminal or PC. The terminal
or PC dials to an AP with a modem connection. The AP supports
connection to a Hayes-compatible 28,800-baud or faster modem.
Refer to “Using a Dial-up Connection” on page 58.

Gain access to the AP SNMP function via a MIB Browser.

including remote Ethernet connections.

INSTALLING ACCESS POINT HARDWARE

2

Introduction To install an AP, you will have to connect the AP to your network, mount the AP in

a location best suited for reception, and provide power to the AP.

Precautions Before installing the AP, review the following guidelines and precautions.

■ Ensure that you have performed the preinstallation procedure outlined in the

Access Point Quick Start Guide.

■ Do not install the AP in wet or dusty areas without additional protection.

Contact a 3Com representative for more information.

■ Verify the environment has a temperature range between

-20˚ C to 55˚ C.

■ If you attach the AP to a wired Ethernet, make sure that the AP is on the

same subnet.

Package Contents The AP package contains the following items.

■ 1 access point (Check the AP model number on the bottom of the unit against

the model listed on the packaging.)

■ 1 power adapter

■ 1 mounting bracket and hardware

■ 1 PowerBASE-T module

■ 1 null-modem serial cable

■ 2 power cords

Contact 3Com Customer Support (see Appendix B) to report missing or improperly
functioning items.

Requirements The minimum installation requirements for a single-cell, peer-to-peer network

is a power outlet. The AP supports a 10BASE-T unshielded twisted pair (UTP)
Ethernet cable.

28 CHAPTER 2: INSTALLING ACCESS POINT HARDWARE

Network Connection Locate the Ethernet port and power plug on the back of the AP, as shown by items

2 (power plug) and 3 (Ethernet port) in the figure below. Item 1 is the serial port.

Ethernet configurations vary according to the environment. Determine the
Ethernet wiring to connect the AP, 10BASE-T UTP, or single cell.

10BASE-T UTP Use a 10BASE-T connection for multiple APs or an AP attached to a wired UTP

Ethernet hub. Normal 10BASE-T limitations apply.

1 Plug the data cable with an RJ-45 connector into the AP Ethernet port.

2 Plug the other end of the data cable into the LAN access port (possibly a hub or

wall connection).

3 Add additional APs as needed.

Single Cell The single-cell connection option allows a single AP to connect wireless clients

without a wired network. Wireless clients appear as peers, as in any Ethernet
environment.

Power Options ■ Standard power supply: 115/230VAC, 50/60Hz, 24V/14.

■ US line cord Part Number: 23844-00-00

■ Remote power distribution system, Part Number: AP-PS-11

■ Refer to application note AP-PS-01 located on the 3Com Technologies

web page.