3Com SRWL306 Users Manual

Wireless LAN Access Point

User Guide

Model WL-306

Published May 2000

3Com Corporation ■ 5400 Bayfront Plaza ■ Santa Clara, California 95052-8145

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 merchantability, satisfactory quality, and ﬁtness for a particular purpose. 3Com may make improvements or changes in the product(s) and/or the program(s) described in this documentation at any time.

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 standar d commercial license for the Softwar e. 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, the 3Com logo, and Transcend are registered trademarks of 3Com Corporation. Microsoft, MS-DOS, Windows, and Windows NT are registered trademarks of Microsoft Corporation. Novell

and NetWare are registered trademarks of Novell, Inc. All other company and product names may be trademarks of the respective companies with which they are

associated.

CONTENTS

VERVIEW OF DIGITAL WIRELESS NETWORKING

Introduction 8 Wireless LAN Network Topologies 8

Peer-To-Peer Network 8 Same-Site Separate Networks 9 Single AP Bridge 10 Multiple-AP Full Coverage Network 11

Wireless LAN Access Point 11

AP features 12 PowerBASE-T 13

Radio Basics 13

Cellular Coverage 15 Site Topography 16

Theory of Operation 16

MAC Layer Bridging 16 DHCP Support 17 Media Types 18 Bridging Support 18 Direct-Sequence Spread Spectrum 20 Wireless Client Association Process 20 Mobile IP 21 Supporting CAM and PSP Stations 22 HTTP, HTML Web Server Support 23 Management Options 23

NSTALLING ACCESS POINT HARDWARE

Introduction 26 Precautions 26 Package Contents 26 Requirements 26

Network Connection 27 10BASE-T UTP 27 Single Cell 27

Power Options 27 Mounting the AP 28

Flat Surface 28 Wall Mount 28

Ceiling Mount 29 Using the PowerBASE-T 31 LED Indicators 32 Troubleshooting 32

Wired Network 32

Setting Up Wireless Clients 34

ONITORING STATISTICS

Introduction 36 System Properties 36 Interface Statistics 36 Forwarding Counts 36 Ethernet Statistics 37 Radio Frequency Statistics 37 Miscellaneous Statistics 38

Analyzing Retries 38 Clearing Statistics 39 Known APs 39

ONFIGURING THE ACCESS POINT

Introduction 40 Gaining Access to the User Interface (UI) 40

Using a Web Browser 40

Changing UI Access 43 Installing the Access Point 44

Adding Additional Gateways 44 Conﬁguring the AP 45

Security 45

System Parameters 46

Radio Frequency Parameters 47

Conﬁguring the SNMP Agent 48

Conﬁguring PPP/Modem 49

Filtering 50 Updating AP Firmware 52 Special Functions 52

ONITORING WIRELESS CLIENTS

Introduction 54 Wireless Clients 54 Clearing Statistics 55

ONFIGURING THE

Introduction 56 Gaining Access to the User Interface (UI) 56

Using Telnet 56 Using a Direct Serial Connection 57 Using a Dial-Up Connection 57

Navigating the UI 57

Entering Admin Mode 58 Changing the Access to the UI 59

Conﬁguring for Dial-Up to the UI 59 Access Point Installation 61 Conﬁguring the AP 62

System Parameters 62

Radio Parameters 63

Conﬁguring PPP 65

Conﬁguring the SNMP Agent 67

Conﬁguring the ACL 68

Filtering 70 Clearing Wireless Clients from the AP 71 Setting Logging Options 72 Manually Updating AP Firmware 73

Update using TFTP 73

Updating using Xmodem 74 Auto Upgrade all APs Via Messaging 75 Performing Pings 76 Mobile IP Using MD5 Authentication 77 Enabling or Disabling Encryption 77

AP U

SING THE

ASCII I

NTERFACE

Encryption Conﬁguration Requirements 77

Saving, Resetting, and Restoring Conﬁgurations 77

Saving a Conﬁguration 77 Resetting an AP 78 Restoring the Default AP Conﬁguration 78

CCESS POINT SPECIFICATIONS

PGRADING

Wireless Clients 82 AP Software Upgrade Procedure 82

ECHNICAL SUPPORT

Online Technical Services 83

World Wide Web Site 83 3Com FTP Site 83 3Com Bulletin Board Service 84

3Com Facts Automated Fax Service 84 Support from Your Network Supplier 84 Support from 3Com 85 Returning Products for Repair 86

ARRANTY AND REGULATORY COMPLIANCE

3Com Corporation Limited Warranty 87 Regulatory Compliance Information 89 3Com End User Software License Agreement 90

AP F

IRMWARE

VERVIEW

IGITAL

IRELESS

Introduction

ETWORKING

The Wireless LAN from 3Com is made up of a series of products that work together to 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. Wireless LAN is based on the IEEE 802.11HR standard, and delivers 11 Mbps data transfer rates.

The core hardware products that make up a Wireless LAN network include the following:

■

Network Interface Card (NIC) installed in a wireless client, either a PC card installed in a notebook or laptop computer, or a PCI card installed in a desktop computer.

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

■

PowerBASE-T (optional), which provides bus power to the access point when connected to an Ethernet network.

Also included in your Wireless LAN kit are an AP mounting bracket and hardware, a serial cable, a power adapter and associated power cables, and two CDs: the Wireless LAN Administrator CD, and the Wireless LAN User CD.

Wireless LAN Network Topologies

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

To better understand how the various Wireless LAN products work together to create a wireless network, it might be helpful to depict a few of the possible Wireless LAN 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 Wireless LAN 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 (laptop and desktop computers with the Wireless LAN 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.

Wireless LAN Network Topologies 9

Same-Site Separate

Networks

In this scenario, as shown in the followng 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.

HAPTER

1: O

VERVIEW

IGITAL

IRELESS

ETWORKING

Single AP Bridge Another possible Wireless LAN 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.

Wireless LAN Access Point 11

Multiple-AP Full

Coverage Network

Wireless LAN Access Point

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.

The Wireless LAN access point (AP) provides either a wireless peer -to-peer network coverage area, or a bridge between Ethernet-wired LANs and Wireless LAN 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.

HAPTER

1: O

VERVIEW

IGITAL

IRELESS

ETWORKING

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.

■

Radio Basics 13

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.

Radio Basics

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

Wireless LAN 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.

Wireless LAN uses 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 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.

Wireless LAN uses its environment (the air and certain other objects) as the transmission medium. Wireless LAN 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 Wireless LAN network operates at is country-dependent.

Quadative Phase Shift layered modulation (QPSK) to transmit

in process called “modulation.” The radio

HAPTER

1: O

VERVIEW

IGITAL

IRELESS

ETWORKING

Wireless LAN 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.

Radio Basics 15

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

Home Service Area

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

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

Wireless LAN Service Area (WSA), as shown below.

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

Wireless LAN System Area

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

association table . Roaming is invisible to the user.

HAPTER

1: O

VERVIEW

Site Topography

IGITAL

IRELESS

ETWORKING

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.

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 Wireless LAN equipment.

Theory of Operation

MAC Layer Bridging

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, forwar ds 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.

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

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).

Theory of Operation

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.

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.

18 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

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 802.11 HR 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.

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.)

Theory of Operation 19

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.

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.

20 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

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 Wireless LAN 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 recr eate 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)

Theory of Operation 21

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 r esponse 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.

Mobile IP 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, 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.

Mobile IP 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.

Mobile IP 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 Mobile IP operation and functionality, it does not represent the implementation of Mobile IP used.

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.

22 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

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.

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 wir eless 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.

The Wireless LAN Mobile IP (roaming across routers) feature enables a wireless client on the Internet to move from one subnet to another while keeping its IP address unchanged. To conﬁgure this feature, see “System Parameters” on page 46.

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.

Supporting CAM and

PSP Stations

Set the wireless client for Mobile IP as speciﬁed in the Wireless LAN Network Interface User Guide.

Security

Security involves two distinct areas: authentication and privacy. Authentication 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 addr ess, the Broadcast destination addresses, a time stamp, Delivery T rafﬁc 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 Interval where

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

Beacon

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

Theory of Operation 23

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 Wireless LAN 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 Wireless LAN 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.

24 CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

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.

Theory of Operation 25

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 following

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. See “Using Telnet” in Appendix C.

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. See “Using a Direct Serial Connection” in Appendix C 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. See “Using a Dial-up Connection” in Appendix C.

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

including remote Ethernet connections.

INSTALLING ACCESS POINT HARDWARE

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 the 3Com Support Center 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.

Power Options 27

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.

+ 63 hidden pages