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How to parse KLV formatted byte array using C#

I am working on a PC hosted application which communicates to an embedded device. The application and the embedded device communicates with an UART interface. The communication protocol states that the data payload is formatted in KLV format. The host PC is written in C# and it can receive the hex data from device and put them into a byte array now. But I am not sure how to parse data. Also I am wondering how to compose the KLV data if I need to send some data to device.

If you are using an UART interface between the devices I doubt you receive 'hex'. Hex is just the representation often used for bytes itself. However as you have written it is already converted to bytes (e.g. by BitConverter class - strongly recommend taking a look in it).
Regarding the KLV format - i hope this is referring to the key-length-value protocol. Somewhere should be a document exactly descriping what data you get, because this protocol is often dimplemented different in following terms.
In the basics it is like: [KEY][LENGTH of VALUE][VALUE]. If you convert (Encoding.GetString, e. g. Encoding.ASCII.GetString()) everything to string you should already see some readable data (also I found that some folks used numbers for keys).
So you need the documentation about:
What KEYs are sent (mostly all have got the same length)
What data types you receive in VALUE for each Key
Without this information, you have to listen to the device for some time and afterwards analyse the data.

Convert IByteBuffer to String in C#

I am working on existing project which is built using DotNetty library, mostly networking framework. I am not that much aware with this framework but as a quick fix, I want to convert IByteBuffer value to the String.

IByteBuffer represents a stream of binary data of various data types, not a string.
If you want a dump of all the bytes in the buffer, you can use ByteBufferUtil.HexDump. This gives you a string of the individual bytes in hexadecimal. This is useful for troubleshooting, if the buffer doesn't contain quite the data you are expecting - you can go tracing the data byte by byte, and find where it goes wrong.
If you want to interpret the bytes differently, you really need to know the types in the buffer. There's no generic method, because the buffer isn't self-descriptive (unlike e.g. XML). If you're trying to get a quick look at the string data in the buffer, and the data happens to be encoded in ASCII, you can try something like this:
Encoding.ASCII.GetString(byteBuffer.Array)
Needless to say, unless the whole buffer contains an ASCII string, this will produce lots of garbage. Whether this is useful or not depends entirely on the data you're working with; if the buffer has something like an HTTP request, you'll probably see the data just fine. Needless to say, this should only be used for debugging purposes - for any production use, you should really know the layout of the buffer explicitly, rather than guessing at it.

Redis messages contain unicode?

I am currently reading in from a Redis server and from the Redis-Cli monitor I am receiving messages that are publishes that have data in-between unicode that looks like this:
\x93\xa6Xz05FH\x83\xa4type\x02\xa4data\x92\xad
Is this generated from some redis related thing or is this because of the original publisher ?
If I publish messages there is no unicode attached so I find it hard to believe this is Redis' doing but I want to be sure.

Redis doesn't care about the format of things unless you are using numeric operators such as incr, hincrby, etc; other than that, strings, hash fields, pub/sub payloads etc are all binary-safe opaque values defined purely by what the client specified. Since you mention StackExchange.Redis, if you use a .NET string to populate a RedisValue, then that string will be encoded with UTF-8. However, there are other ways of populating a RedisValue for specifying an arbitrary binary payload - the most common of which would be a byte[].
It is possible that redis-cli - since it is a text-based tool - is switching to this representation by a simple heuristic of "does something look non-ASCII / non-printable" - that \x02 is looking particularly suspicious (is that a STX?). But the actual data flowing through redis on a publish is raw binary.

How can i evaluate a stream (string)

First of all, what I do at the moment:
I sniff a asyncron serial bus with 9 bit protocol and send the data to the PC. At the PC side I receive the data as an endless string, that looks like that: .12_80E886.02_80E894.13. The Software of the PC-side is written with winforms with C#. Now I have the problem that I haven´t a clearly start you can see it in the stream example. The reason for that is, that I start the sniff somewhere in the protocol.
What I want to do:
I think I can use startindex = IndexOf("_"), and set them now as new start. I have to evaluate sign´s in the stream the stream is build: _(timestamp in milliseconds).(addressbyte databyte). The only what I want to display in my RichTextBox is the databyte, also I need a data management method for the timestamp. Because I have in the GUI the function that I can see the time beetween two or more databyte´s, for that I think I make a sql database. The addressbyte need I to collor the byte with an one as address in a special collor.
Question:
How can I evaluate the stream so that i have alternately timestamp,
addressbyte and than databyte as single substring?
The reason why I want them so, is that, I think I can make an easy if elseif else block to realize all what I want to do.
When someone has an better suggestion for my project pls write it as comment.
With friendly wishes sniffi

I think you're trying to solve two problems at the same time. It would be better to separate them and solve them individually.
There is the issue of transporting the data, for this you are using streams. That is a valid solution. There is sending and receiving the data (bits) over the stream.
You have the problem of transforming these bits (after receiving them) into actual objects (dates, strings, etc..). For that you an use a simple parser, tokenizer, a local script that can get the correct parts from the data and convert it, or you can use a serialization framework (like DataContracts).
If you have simple data, I would opt for using a single method that can parse the data. For more complex scenarios I would look into serialization.
Also be ware that you will need to validate your inputs, since you cannot assume that there is always a trusted (non compromised) piece of software that is sending the bits to you.

I think string is bad choice. Propably data is send as bytes. Sniff rather bytes than string. And you need protocol description to understand data.
You need to read bytes form bus and interpret it.

FileHelpers-like data import/export utility for binary data?

I use the excellent FileHelpers library when I work with text data. It allows me to very easily dump text fields from a file or in-memory string into a class that represents the data.
In working with a big endian microcontroller-based system I need to read a serial data stream. In order to save space on the very limited microcontroller platform I need to write raw binary data which contains field of various multi-byte types (essentially just dumping a struct variable out the serial port).
I like the architecture of FileHelpers. I create a class that represents the data and tag it with attributes that tell the engine how to put data into the class. I can feed the engine a string representing a single record and get an deserialized representation of the data. However, this is different from object serialization in that the raw data is not delimited in any way, it's a simple binary fixed record format.
FileHelpers is probably not suitable for reading such binary data as it cannot handle the nulls that show up and* I suspect that there might be unicode issues (the engine takes input as a string, so I have to read bytes from the serial port and translate them into a unicode string before they go to my data converter classes). As an experiment I have set it up to read the binary stream and as long as I'm careful to not send nulls it works quite well so far. It is easy to set up new converters that read the raw data and account for endian foratting issues and such. It currently fails on nulls and cannot process multiple records (it expect a CRLF between records).
What I want to know is if anyone knows of an open-source library that works similarly to FileHelpers but that is designed to handle binary data.
I'm considering deriving something from FileHelpers to handle this task, but it seems like there ought to be something already available to do this.
*It turns out that it does not complain about nulls in the input stream. I had an unrelated bug in my test program that came up where I expected a problem with the nulls. Should have investigated a little deeper first!

I haven't used filehelpers, so I can't do a direct comparison; however, if you have an object-model that represents your objects, you could try protobuf-net; it is a binary serialization engine for .NET using Google's compact "protocol buffers" wire format. Much more efficient than things like xml, but without the need to write all your own serialization code.
Note that "protocol buffers" does include some very terse markers between fields (typically one byte); this adds a little padding, but greatly improves version tolerance. For "packed" data (i.e. blocks of ints, say, from an array) this can be omitted if desired.
So: if you just want a compact output, it might be good. If you need a specific output, probably less so.
Disclosure: I'm the author, so I'm biased; but it is free.

When I am fiddling with GPS data in the SIRFstarIII binary mode, I use the Python interactive prompt with the serial module to fetch the stream from the USB/serial port and the struct module to convert the bytes as needed (per some format defined by SIRF). Using the interactive prompt is very flexible because I can read the string to a variable, process it, view the results and try again if needed. After the prototyping stage is finished, I have the data format strings that I need to put into the final program.
Your question doesn't mention anything about why you have a C# tag. I understand FileHelpers is a C# library, but I that doesn't tell me what environment you are working in. There is an implementation of Python for .NET called IronPython.
I realize this answer might mean you have to learn a new language, but having an interactive prompt is a very powerful tool for any programmer.