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Defining GattCharacteristic as a Server

I want to fill my variable "selectedCharacteristic" with
GattCharacteristic selectedCharacteristic
selectedCharacteristic = Constants.ResultCharacteristicUuid;
Unfortunately, this doesn't work. It won't convert.
The ResultCharacteristicUuid is from the Microsoft UWP BLE Example.
https://github.com/microsoft/Windows-universal-samples/blob/main/Samples/BluetoothLE/cs/Constants.cs
My program, which has not much to do with the microsoft example (besides the constants.cs),
opens up a BLE Service on start, along with the Result-Characteristic. It acts as an BLE server, nothing more.
So when my BLE Server started, there should be a simple solution to get the device infos and everything GattCharacteristic needs, or not?
The goal is to write to the characteristic as the server, not as a client.
What do I need to get the ResultCharacteristic-Uuid into selectedCharacteristic ?

The UUID should be defined by yourself when you are creating your own service, characteristic. Based on the document- Bluetooth GATT server, you could generate your custom UUID from Visual Studio through Tools -> CreateGuid (use option 5 to get it in the "xxxxxxxx-xxxx-...xxxx" format). This uuid can now be used to declare new local services, characteristics or descriptors.

What device information can I access from the Hololens at run time? (OS Level, Serial Code etc)

What device information can I access from the Hololens at run time using MRTK?
Can MRTK determine a unique identifier for each Hololens device that runs my program? Ideally this would be a serial code, but any other unique identifier from the device would be useful.
I am trying to determine ways to track how many unique devices are running my program, as well as how often they run it.
I am aware that using a managed device might be one way to do this, but I am curious if there is any way to get such information without needing to set up ID Management.

You can use the instance of the EasClientDeviceInformation to get device information from the local device. The property Id provides the identifier of the local device. you can use the following code:
using Windows.Security.ExchangeActiveSyncProvisioning;
. . .
EasClientDeviceInformation deviceInfo = new EasClientDeviceInformation();
var deviceIdentifier = deviceInfo.Id;
In addition, you can retrieve more device information through other properties of the instance, a specific sample is provided here: Client Device Information sample.

WiFi Direct in Windows 10 says "UnsupportedHardware" althought it should be supported

I'll try to keep it short. I've been running in Windows 10 (10130) Microsoft's WiFi Direct Services example available on GitHub , the C# one in Visual Studio 2015 RC. Now, in their Build conference they said you can run in CMD a command to know if your WiFi adapter is compatible with WiFi Direct
netsh wlan show wirelesscap
Which gives me a big YES, your wireless adapter is compatible.
Wi-Fi Direct Device : Supported
Wi-Fi Direct GO : Supported
Wi-Fi Direct Client : Supported
But when I run the mentioned sample, everything goes OK until the WiFiDirectServiceWrapper.OnAdvertisementStatusChanged(. . .) is triggered, almost inmediatly after creating the advertiser. While running the sample with the profiler attached I get this:
private void OnAdvertisementStatusChanged(WiFiDrectServiceAdvertiser sender, object args)
--
sender | {Windows.Devices.WiFiDirect.Services.WiFiDirectServiceAdvertiser}
AdvertisementStatus: Aborted
AutoAcceptSession: true
CustomServiceStatusCode: 0
DeferredSessionInfo: null
PreferGroupOwnerMode: true
PreferredConfigurationMethods : _native, can't see_
ServiceError: UnsupportedHardware
ServiceInfo: null
ServiceName: "myservice"
ServiceNamePrefixes: {System.__comObject}
ServiceStatus: Available
I really don't know how I'm supposed to depurate this, as I can't find where this Event is raised (the only references to that method are
this.advertiser.AdversitementStatusChanged += OnAdvertisementStatusChanged
this.advertiser.AdversitementStatusChanged -= OnAdvertisementStatusChanged
^ those), and I can't see the WifiDirectServiceAdvertiser implementation.
My WiFi Card is a Qualcomm Atheros AR9485, and I'm using the latest drivers available through Windows Update. In the device manager I get two Wi-Fi Direct Virtual adapters:
Microsoft Wi-Fi Direct Virtual Adapter
Microsoft Wi-Fi Direct Virtual Adapter #2
The second one is disabled sometimes (the UnsupportedHardware event is the same, enabled or disabled). For all of them I've disabled the "Allow the PC to shut down this device to save energy" option.
I've tried to compile the code to x86 and x64, but I get the same result at the same point. I've tried another two generic wireless thumbs (those USB WiFi adapters) which Windows says yes, they're compatible too with no luck.
I know Windows 10 is not final, but any help is appreciated.

It seems that the WiFiDirect capabilities are not the only ones you need to look at if the thing you want to do is advertise a service (which is actually the "new in Windows 10 thing" concerning Direct).
The command you must execute is exactly the same as before:
netsh wlan show wirelesscap
but if you want to advertise a service, the relevant capabilities are the following:
P2P Device Discovery : Supported
P2P Service Name Discovery : Supported
P2P Service Info Discovery : Supported
P2P Background Discovery : Supported
What WiFiDirect does in Windows since 8 and 8.1 is advertising the whole computer, but since 10, WiFiDirectServices advertises one or more services running simultaneously in your machine.
Lets say you are the developer of com.boardgames. If you want to host a board games competition somewhere without a WiFi hard AP, that could be the prefix of the name of all your services, so each client connects only to the one they want: for example, com.boardgames.solitaire or com.boardgames.chess instead of connecting to your machine.
Sadly, none of the computers nor WiFi antennas I've tried are compatible with P2P discoveries.

Bluetooth and C# PC -> Cellphone connection without paring

I'm trying to write simple app, which sends short text message to cellphones in bluetooth adapter range.
My first try is sending files: I can send file from PC to cellphone, but i must enter PIN on cellphone, and on PC.
I would rather to send text messages (something like push message) - is it possible to send it without paring devices?
If isn't possible to send push messages, maybe I can send simple file without requesting PIN ?
I use 32feet library.
Sample code (used to send files to selected device)
static int BTSendFile(string adres, string FileName)
{
Uri uri = new Uri("obex://" + adres + '/' + Path.GetFileName(FileName));
ObexWebRequest req = new ObexWebRequest(uri);
req.ReadFile(FileName);
ObexWebResponse rsp = (ObexWebResponse)req.GetResponse();
return (int)rsp.StatusCode;
}

A quick answer would be; NO, you will ALWAYS need some kind of pairing.
But if you take a look at the different kinds of pairing out there, you would see that BT 2.1 supports Secure Simple Pairing (SSP) with the Just Works-mode. This allows you to pair devices (almost) without any user interaction. From Wikipedia:
Just works: As implied by the name, this method just works. No user interaction is required; however, a device may prompt the user to confirm the pairing process. This method is typically used by headsets with very limited IO capabilities, and is more secure than the fixed PIN mechanism which is typically used for legacy pairing by this set of limited devices. This method provides no man in the middle protection.
However, since "This method is typically used by headsets with very limited IO capabilities", it would probably not apply to the cellphones you are talking about, but I thought you should know :)

According to the offical Bluetooth Message Access Profile, i.e. the specific Bluetooth profile that deals with accessing SMS/MMS systems on phones via a remote device:
'The MCE device shall use the services of the MSE device only after successfully creating a secure connection. This includes exchanging of security initialization messages, creation of link keys, and enabling encryption'
From: https://developer.bluetooth.org/TechnologyOverview/Pages/MAP.aspx
There is also a link to the full spec there if you are interested.
This certtainly suggests that secure pairing is required, which I'd assume to involve the passkey. My experience is that once a device has been paired a connection can be made without repeating the pairing as long as that pairing is remembered by the devices (i.e. I've paired a device once and not had to do it again). As to simpler, non-keyed pairing mentioned by khellang above, I've not seen anything about this - if it is purely for devices like headsets then the security requirements may be lower due to their not likely wanting write access to a device?

Get mac address from IP using DHCP?

I am trying to create scripts/services that allow for waking PCs in a windows domain via WOL. Now i want to give the user the option to select an AD container as a starting point for the waking of PCs contained within. My initial thought is using DHCP as a repository to query for MAC addresses given the hostnames (which i can easily enough pull from AD given the container).
Is there a way to programmatically query the DHCP service/server, passing hostnames and recover the associated MAC addresses?
Or, is there a better/easier way to solve my problem?

This is a little bit wacky it seems that there's no way to query the DHCP server programmatically. Thanks cottsak for asking the question. I understand that the DHCP protocol doesn't have such a query, but I thought mayb the executable from Microsoft might have some way you can address it from the command line. I haven't heard anybody anywhere say that there is no such case, but it must be so.
WHOA, wait a minute... I think I found what we're looking for: NETSH. cf:
http://social.technet.microsoft.com/Forums/en/ITCG/thread/afb4be16-09bd-4260-b515-8323d85d4ccb
Where it says if you open a command prompt on the DHCP server you can run this command:
netsh dhcp server scope 192.168.1.0 show clients
and get a report such as this:
10.10.98.53 - 255.255.255.0 -00-0c-29-02-a4-09 - NEVER EXPIRES -D
10.10.98.54 - 255.255.255.0 - 00-22-19-10-29-75 -1/21/2012 8:39:25 AM -D
Yippeee! Thanks for the thread!! If it wasn't for this one, I enver would have narrowed my search to technet adn found that one.

Try dhcpexim.exe from microsoft.
or, if you prefer using pure C. DhcpEnumSubnetClientsV4

No problem; because all of the machines are in your domain you can put together a VBScript that will get the MACAddress(es) from the local machine and store it as an attribute of the computer object in Active Directory.
Here's a quick hack on how to do that (save this as a .vbs-file):
Option Explicit
Const ADS_PROPERTY_UPDATE = 2
Const COMPUTERLOCATION = "ou=Member Servers,dc=yourdomain,dc=com"
Const ATTRIBUTETOUSE = "otherTelephone"
Dim wshNetwork, strComputerName
Set wshNetwork = WScript.CreateObject("WScript.Network")
strComputerName = wshNetwork.ComputerName
Dim objWMIService, colNetCards, objComputer, objNetCard
Set objWMIService = GetObject("winmgmts:\\" & strComputerName & "\root\cimv2")
Set colNetCards = objWMIService.ExecQuery("Select * From Win32_NetworkAdapterConfiguration Where IPEnabled = True")
Set objComputer = GetObject("LDAP://cn=" & strComputerName & "," & COMPUTERLOCATION)
For Each objNetCard in colNetCards
objComputer.PutEx ADS_PROPERTY_APPEND, ATTRIBUTETOUSE, Array(objNetCard.MACAddress)
objComputer.SetInfo
Next
Because your clients aren't all in the "Member Servers" OU above you'll need to modify the above script to include a directory search for the strComputerName do get the COMPUTERLOCATION.
When you have a working script, ask your domain administrator to put the script as a start-up script targetting the computers you need to monitor; that way it'll execute whenever a computer boots up. You can also run the script as a scheduled task to get your data from any clients that haven't rebooted or use psexec or some other way you can think of to get the data immediately. Or you can rewrite the script entirely to remote connect to all of your machines and get the data that way (which might not be possible due to local firewalls). Or you could write a small .NET console application which does the same thing, it's up to you...
Also, although there is a networkAddress-attribute defined for computer objects; by default the computer object itself does not have access to write to this property. Because start up-scripts run in the context of the SYSTEM account on the particular machine the easiest thing is to use an attribute that the computer object (SELF) has write access to. The otherTelephone-attribute is multivalued and part of the Personal-Information Property Set which all computer objects has write access to by default. If you want to use the networkAddress-attribute you need to set explicit write access to that attribute for all of your computers.
Also you need to bear in mind that storing the the MAC address in Active Directory means that all of the users in your domain will have read access to it which in turn might possibly (depending on your environment) pose a small security risk.

To do it the way the network does.
Grab SharpPcap (Pcap wrapper for C#) and WinPcap (Windows) or libpcap (*nix). Write an application that creates SNMP packets to query the ARP table on the router.
Note: The ARP (Address Resolution Protocol) table is the table containing the mapping of IP address to MAC address.
I've been thinking about implementing an example that does this lately but I don't have one to show yet. Once I do, I'll make sure it gets added to the SharpPcap examples found in the project's source tree.

You can't do that with DHCP. DHCP attributes IP from MAC, not the other way around.
ARP is what converts IP into MAC but it's the machine itself that answers ARP requests so if it's off it's obviously not gonna answer ...
I suggest you store the MAC in your AD directly (I guess AD supports custom attributes ?)

you need to use arp to get a mac adress and doing so In C is a long process.
Mac adresses are hard coded, so if you have X computers go and get X mac addresses and tie them to the AD.
Note that the computer will have to be on to request its mac address.
Finding MAC address from IP address

Yeah dun worry about it, you can pull this info directly from DHCP if the PC has a lease.
Know how you right click and add a reservation in DHCP?
Look in DHCP for the 'unique ID'. It's the MAC address, sans the colons.