Dissecting the EPC: RFID for the Commercial Sector

by Kn1ghtl0rd  (kn1ghtl0rd@hotmail.com)

There is a lot of talk about RFID and what is going to happen with it.

Walmart and the DoD are pushing the technology on all of their suppliers, and it's just a matter of time before we see RFID labels or embedded tags in our goods.

As consumers, we have a right to know what is being put onto our person or into our house.  And, as far as I know, nobody has sat down and told Joe Blow what exactly sits on these "radio tags" that everyone is talking about.

I'm here to shed a little light on the darkness of RFID, specifically the Electronic Product Code (EPC) and Gen2 standards.

For the commercial sector, there is really only one option when selecting an RFID technology for shipments and item tracking: EPC Gen2 UHF tags.

Let me break down all those annoying acronyms for you.  EPC stands for Electronic Product Code.  This is the newest version of the UPC or Universal Product Code.

I'm sure that everyone is familiar with the barcode identifiers on the labels or tags of everything we purchase.  This is UPC.

So, EPC is the logical step up from this; instead of barcodes, we have RF data.

Gen2 stands for Generation 2.

It's the newest version of the coding scheme for the EPC tags.  This defines the way that the information is put onto the tag and how it is interpreted upon read.

And lastly, UHF stands for Ultra-High Frequency, which is the RF frequency that the tags actually operate on.

Depending on where you live in the world, the precise unlicensed band set aside for UHF may differ, but it is generally between 865 MHz and 928 MHz.  In the U.S., the band is 902-928 MHz; in Europe it's 865-868 MHz.

So now, let's talk about what is actually going onto the tags.

The EPC is broken up into seven coding schemes currently.  They are as follows:

Each coding scheme is broken down into sections and the scheme defines what belongs in those sections.

Although I listed all seven schemes above, I am only going to cover two of them in this article: SGTIN and SSCC.

These are the types of tags that will most likely end up in your hometown store and in your actual home.  We will start off with the most common scheme, the SGTIN.

This is the type of tag that will end up making it on individual items when the time comes, so this is what you are most likely to actually be able to get your hands on.  The SGTIN is an electronic extension of the GTIN or Global Trade Item Number.

The GTIN is an attempt establish a unique identification number for each type of item in the world.  A GTIN might look like 00614141000012, where the first digit is a check digit, digits two through eight are the company header, and the rest is the item reference number.

So, by taking three pieces of information specific to the company and item then, we can create the GTIN.

Now, the SGTIN is just the GTIN, coded a little bit differently.

Each type of tag of EPC Gen2 RFID tag has a common element, the header.  This lets the reader know which type of tag it is seeing.

The header value for the SGTIN is 48 or, in binary, 0011 0000.

This is the first part of any tag.

The next part is the filter value, which defines whether the tagged item is a unit, case, a single-case unit (a big item like a bike or grill that only one of which fits on each pallet), or unspecified.

This field is 3-bits long and is 1, 2, 3, or 0 respectively.

The next section is called the partition, which identifies the length of the company prefix number.

This is also 3-bits and defines there to be 9-12 digits in the reference number when the partition is set to using 6 - 0 respectively.

Now, the kicker with this is that this also defines how large the item reference is as well.  The tags have a fixed length and only 44-bits, or 13-digits, total can be used for both the item and company information.

So, the next 20-40 bits are the company prefix, which is defined by the EPCglobal group.  The remaining 4-24 bits are the item reference as defined by the company selling the item.

And, finally, the last and most important number of the SGTIN is the final 38-bits, which is the tag's serial number.

This is the unique set of bits that makes every tag different.

Without the serial number, it's not a serialized GTIN.

Hopefully, that was all pretty straight forward.

Now the catch to this is that the data is encoded onto the tag, so even if you have a UHF reader to get the information, you may not be able to see what it actually says.

You have to do a little conversion first.

Here is an example:

Raw Text Entered: 12345678;9087654;64782922

Encoded Data: 3000E0DCD8D4D08000000000

The encoding scheme is under some locks at EPCglobal but I've found the key document to decoding EPC tags.

The first thing we need to do is to decode the hex into binary.  For this example, I will use the following data:

EPC Code: 30140029B689BA8000898682

Actual data entered into application: 48, 0, 5, 0021357, 009962, 10000002

So when we convert the 30140029B689BA8000898682 hex to binary, we get:

00110000000101000000000001010011011011010001001101110101000000000000000100110001001011010000010

So, let's break this apart:

        Header: 00110000 = 48
        Filter: 000 = 0
     Partition: 101 = 5
Company Prefix: (00000000000)0101001101101101(0) = 0021357
Item Reference: 0010011011101010(0000) = 009962
 Serial Number: (0000000000)100110001001011010000010 = 10000002

There you go; that's how you decode a SGTIN tag.

Note that this is actually a practical demonstration, as this tag data was encoded using a Zebra R110Xi RFID label printer.

Let's go ahead and move on to the next coding scheme, the SSCC.

The SSCC is already a standard practice for many companies, as it was originally a barcode technology standard.

This has obviously been migrated to the RFID realm and hasn't seen any change.

Now, as mentioned above, the header defines what type of tag we are looking at, and the SSCC has a header value of 49 or 0011 0001.

The SSCC is laid out similarly to the SGTIN, but it does not have to be item-specific; instead, it's pallet-specific.

So, each pallet has an SSCC to identify the pallet uniquely.  If you have multiple SGTINs on one pallet, you can't put an SGTIN pallet tag on it as the SGTIN is specific to a single item, so the SSCC allows you to group items together for shipment.

You must, however, send an ASN or Advanced Shipment Notice to the recipient in order for them to be able to decipher the SSCC and allocate the correct SGTIN items to the correct places.

So the SSCC also has a filter and partition value.  The filter will always be 0 because the tag will always be on a single pallet.

The partition will also always be 5, because each tag has the same number length with no fluctuation.

The next bits are the company prefix and the serial reference.

So far, this is very similar to the SGTIN, except without the item reference number.

Then the last 24-bits must be unallocated in order to conform to the current version of the specification.

As with the SGTIN, the SSCC data is also encoded.  You should expect to see:

Raw Text Entered: Text1;Text2;Text3;Text4

Encoded Data: 31215195E1D0C87433787434

Each of these tag types comes in a 64-bit or 96-bit version.

I have showed you the coding scheme for the 96 bit version because that is the RFID mandate in place by Walmart, and we can guess that any smaller company wishing to implement RFID will probably stick with the same standard.

Now, the next logical question for all of you is probably where can I find these?  Are there any stores in my area that have RFID implemented?  How long until it's everywhere?  I have some answers for you, but for the sake of brevity, I suggest you take a look at the spreadsheet at infonomicon.org/rfid/Live%20Stores.xls.

This spreadsheet shows all Walmart stores and distribution centers throughout the U.S. where RFID is currently being used.

Note, however, that there are no stores currently requiring tagging at the item level and that only cases or pallets are being tagged.  There is a good chance that you may see a case or pallet on the floor, however, and you can find the RFID tag simply by looking for the EPC logo on the label.

It is required for any distributor that is using the EPC standard to be EPC-compliant, and that includes putting the EPC logo on every RFID tag.

For more EPC and Walmart mandates and guidelines, please refer to infonomicon.org/rfid/RFID%20Guidelines%20and%20Requirements.pdf.

If you are curious about the other coding schemes that I have mentioned, you can also check out the document at www.technoriversoft.com/doc/smartrfid.pdf.

Use the examples I have given and the examples listed in the Walmart guidelines to decipher what each one means.

And, for more information on how to decode EPC information, you can check out infonomicon.org/rfid/epc-standards.pdf.

Hopefully you now feel a little more enlightened about the EPC standard and what is actually being put on the tags on those jars of mayonnaise.

Shoutz: droops, morgellon, dosman, zach, goatse, cs_weasel, mirovengi, coldsteal, operat0r, phizone, slick0, and the rest of the Infonomicon crew.  Also thanks to the DDP for keeping it real.
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