Transcript ppt - Adaptive Systems Lab - University of California, San Diego

Real-Time Performance Monitoring and
Evaluation of an 802.11 Wireless LAN
– Wireless Research API (WRAPI)
Anand Balachandran
Charles Hudak
Geoffrey M. Voelker
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Motivation
1. Users in a wireless LAN benefit from
an understanding of the RF network
weather – recd. signal strengths,
operating power, RF channel, SSID etc.
A
P
Interne
t
Access Points
A
P
A
P
2. Network administrators and
applications need to monitor the
wireless LAN for site survey, nature
of RF environment, load balancing
decisions, etc.
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Outline
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Motivation
Existing Mechanisms
WRAPI – purpose
Features
Methodology
Demo of WRAPI
Future Work
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Existing Mechanisms

WLAN monitors (e.g. OriNoCo Client Manager)
» Vendor Specific
» Expose different interfaces
» Not all vendors support the same OIDs (object identifiers)

Firmware Implementations
» Proprietary – written by the hardware vendors
» Code is not made available
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So, What is WRAPI?

Wireless Research API (WRAPI)
» A software library that allows applications running in userspace on mobiles hosts (and APs) to query/set information in
the network they are attached to.

WRAPI:
» Is hardware-agnostic WLAN monitoring tool (supports all
802.11b compliant hardware)
» Is Programmable!!
» Exposes all IEEE 802.11 WLAN objects
» Currently runs on Windows XP
» Can be ported to WinCE (Pocket PC 2002)
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WRAPI – Features

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WRAPI provides an interface
to applications to monitor the
WLAN in real time
Supports 25 WLAN OIDs
(see table for a sample)
OIDs are either read-only,
read-write, or write-only
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IEEE 802.11 OID
Query
Set
Service Set Identifier
(SSID)
Yes
Yes
Base Service Set Identifier
– BSSId (AP MAC Addr.)
Yes
No
BSSId List Scan (scan
channels
No
Yes
Received Signal Strength
Yes
No
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IEEE 802.11 Network Objects
typedef struct OID_802_11_BSSID {
ULONG
NDIS_802_11_MAC_ADDRESS
UCHAR
NDIS_802_11_SSID
ULONG
NDIS_802_11_RSSI
NDIS_802_11_NETWORK_TYPE
NDIS_802_11_CONFIGURATION
NDIS_802_11_NETWORK_INFRASTRUCTURE
NDIS_802_11_RATES
Length;
MacAddress;
Reserved[2];
Ssid;
Privacy;
Rssi;
NetworkTypeInUse;
Configuration;
InfrastructureMode;
SupportedRates;
} NDIS_WLAN_BSSID, *PNDIS_WLAN_BSSID;
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Methodology

The NDIS Stack
WRAPI DLL
DeviceIoControl()ioctl
WINSOCK API
NDISUIO
NDISUIO
User
TCP/IP
Intermediate Driver
Network Driver Interface Specification (NDIS)
NDIS Miniport(s)
Kernel
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Methodology (2)
Flow of Logic in the WRAPI DLL:
 Gets a handle to the NDISUIO Protocol Driver
 Enumerate Devices
 Bind NDISUIO to the device
 Query/Set the parameter using WIN32
DeviceIoControl() API
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WRAPI – Demo
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Future Work
We are using WRAPI
 To build the signal map of a location-determination
system
 To implement inter-AP load balancing algorithms that
take into account individual user workloads
Traces and scripts available at:
http://ramp.ucsd.edu/pawn/wrapi/
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