283 lines
11 KiB
C#
283 lines
11 KiB
C#
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/*
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This file is part of PacketDotNet
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PacketDotNet is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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PacketDotNet is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with PacketDotNet. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* Copyright 2012 Alan Rushforth <alan.rushforth@gmail.com>
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*/
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using PacketDotNet.Utils;
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using MiscUtil.Conversion;
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using System.Net.NetworkInformation;
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namespace PacketDotNet
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{
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namespace Ieee80211
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{
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/// <summary>
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/// Format of an 802.11 management beacon frame.
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///
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/// Beacon frames are used to annouce the existance of a wireless network. If an
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/// access point has been configured to not broadcast its SSID then it may not transmit
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/// beacon frames.
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/// </summary>
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public class BeaconFrame : ManagementFrame
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{
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private class BeaconFields
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{
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public readonly static int TimestampLength = 8;
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public readonly static int BeaconIntervalLength = 2;
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public readonly static int CapabilityInformationLength = 2;
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public readonly static int TimestampPosition;
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public readonly static int BeaconIntervalPosition;
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public readonly static int CapabilityInformationPosition;
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public readonly static int InformationElement1Position;
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static BeaconFields ()
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{
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TimestampPosition = MacFields.SequenceControlPosition + MacFields.SequenceControlLength;
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BeaconIntervalPosition = TimestampPosition + TimestampLength;
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CapabilityInformationPosition = BeaconIntervalPosition + BeaconIntervalLength;
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InformationElement1Position = CapabilityInformationPosition + CapabilityInformationLength;
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}
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}
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/// <summary>
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/// The number of microseconds the networks master timekeeper has been active.
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///
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/// Used for synchronisation between stations in an IBSS. When it reaches the maximum value the timestamp will wrap (not very likely).
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/// </summary>
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public UInt64 Timestamp {get; set;}
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private UInt64 TimestampBytes
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{
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get
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{
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if(header.Length >= (BeaconFields.TimestampPosition + BeaconFields.TimestampLength))
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{
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return EndianBitConverter.Little.ToUInt64(header.Bytes, header.Offset + BeaconFields.TimestampPosition);
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}
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else
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{
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return 0;
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}
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}
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set
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{
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EndianBitConverter.Little.CopyBytes(value,
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header.Bytes,
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header.Offset + BeaconFields.TimestampPosition);
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}
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}
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/// <summary>
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/// The number of "time units" between beacon frames.
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///
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/// A time unit is 1,024 microseconds. This interval is usually set to 100 which equates to approximately 100 milliseconds or 0.1 seconds.
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/// </summary>
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public UInt16 BeaconInterval {get; set;}
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private UInt16 BeaconIntervalBytes
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{
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get
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{
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if(header.Length >= (BeaconFields.BeaconIntervalPosition + BeaconFields.BeaconIntervalLength))
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{
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return EndianBitConverter.Little.ToUInt16(header.Bytes, header.Offset + BeaconFields.BeaconIntervalPosition);
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}
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else
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{
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return 0;
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}
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}
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set
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{
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EndianBitConverter.Little.CopyBytes(value,
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header.Bytes,
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header.Offset + BeaconFields.BeaconIntervalPosition);
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}
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}
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/// <summary>
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/// Frame control bytes are the first two bytes of the frame
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/// </summary>
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private UInt16 CapabilityInformationBytes
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{
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get
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{
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if(header.Length >= (BeaconFields.CapabilityInformationPosition + BeaconFields.CapabilityInformationLength))
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{
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return EndianBitConverter.Little.ToUInt16(header.Bytes,
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header.Offset + BeaconFields.CapabilityInformationPosition);
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}
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else
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{
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return 0;
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}
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}
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set
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{
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EndianBitConverter.Little.CopyBytes(value,
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header.Bytes,
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header.Offset + BeaconFields.CapabilityInformationPosition);
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}
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}
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/// <summary>
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/// Defines the capabilities of the network.
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/// </summary>
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public CapabilityInformationField CapabilityInformation
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{
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get;
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set;
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}
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/// <summary>
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/// Gets the size of the frame.
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/// </summary>
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/// <value>
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/// The size of the frame.
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/// </value>
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public override int FrameSize
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{
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get
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{
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return (MacFields.FrameControlLength +
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MacFields.DurationIDLength +
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(MacFields.AddressLength * 3) +
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MacFields.SequenceControlLength +
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BeaconFields.TimestampLength +
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BeaconFields.BeaconIntervalLength +
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BeaconFields.CapabilityInformationLength +
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InformationElements.Length);
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}
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}
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/// <summary>
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/// The information elements included in the frame
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///
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/// Most (but not all) beacons frames will contain an Information element that contains the SSID.
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/// </summary>
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public InformationElementList InformationElements { get; private set; }
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/// <summary>
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/// Constructor
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/// </summary>
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/// <param name="bas">
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/// A <see cref="ByteArraySegment"/>
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/// </param>
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public BeaconFrame (ByteArraySegment bas)
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{
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header = new ByteArraySegment (bas);
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FrameControl = new FrameControlField (FrameControlBytes);
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Duration = new DurationField (DurationBytes);
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DestinationAddress = GetAddress (0);
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SourceAddress = GetAddress (1);
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BssId = GetAddress (2);
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SequenceControl = new SequenceControlField (SequenceControlBytes);
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Timestamp = TimestampBytes;
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BeaconInterval = BeaconIntervalBytes;
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CapabilityInformation = new CapabilityInformationField (CapabilityInformationBytes);
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if(bas.Length > BeaconFields.InformationElement1Position)
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{
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//create a segment that just refers to the info element section
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ByteArraySegment infoElementsSegment = new ByteArraySegment (bas.Bytes,
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(bas.Offset + BeaconFields.InformationElement1Position),
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(bas.Length - BeaconFields.InformationElement1Position ));
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InformationElements = new InformationElementList (infoElementsSegment);
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}
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else
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{
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InformationElements = new InformationElementList ();
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}
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//cant set length until after we have handled the information elements
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//as they vary in length
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header.Length = FrameSize;
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="PacketDotNet.Ieee80211.BeaconFrame"/> class.
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/// </summary>
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/// <param name='SourceAddress'>
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/// Source address.
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/// </param>
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/// <param name='BssId'>
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/// Bss identifier (MAC Address of the Access Point).
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/// </param>
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/// <param name='InformationElements'>
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/// Information elements.
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/// </param>
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public BeaconFrame (PhysicalAddress SourceAddress,
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PhysicalAddress BssId,
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InformationElementList InformationElements)
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{
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this.FrameControl = new FrameControlField ();
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this.Duration = new DurationField ();
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this.SequenceControl = new SequenceControlField ();
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this.CapabilityInformation = new CapabilityInformationField ();
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this.InformationElements = new InformationElementList (InformationElements);
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this.FrameControl.SubType = FrameControlField.FrameSubTypes.ManagementBeacon;
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this.SourceAddress = SourceAddress;
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this.DestinationAddress = PhysicalAddress.Parse ("FF-FF-FF-FF-FF-FF");
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this.BssId = BssId;
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this.BeaconInterval = 100;
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}
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/// <summary>
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/// Writes the current packet properties to the backing ByteArraySegment.
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/// </summary>
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public override void UpdateCalculatedValues ()
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{
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if ((header == null) || (header.Length > (header.BytesLength - header.Offset)) || (header.Length < FrameSize))
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{
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//the backing buffer isnt big enough to accommodate the info elements so we need to resize it
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header = new ByteArraySegment (new Byte[FrameSize]);
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}
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this.FrameControlBytes = this.FrameControl.Field;
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this.DurationBytes = this.Duration.Field;
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SetAddress (0, DestinationAddress);
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SetAddress (1, SourceAddress);
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SetAddress (2, BssId);
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this.SequenceControlBytes = this.SequenceControl.Field;
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this.TimestampBytes = Timestamp;
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this.BeaconIntervalBytes = BeaconInterval;
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this.CapabilityInformationBytes = this.CapabilityInformation.Field;
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//we now know the backing buffer is big enough to contain the info elements so we can safely copy them in
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this.InformationElements.CopyTo (header, header.Offset + BeaconFields.InformationElement1Position);
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header.Length = FrameSize;
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}
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}
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}
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}
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