5 Replies Latest reply: Jun 23, 2008 10:32 PM by Shridhar Nagarhalli RSS

Difference between Simple, EPC Gen 1 & EPC Gen 2 tags?

Shridhar Nagarhalli
Currently Being Moderated

Hi All,

 

1. Can some one explain me the difference between Simple, EPC Gen 1 & EPC Gen 2 tags?

2. When are they used?

3. Which is the one, widely used?

 

Thanks,

Shridhar..

  • Re: Difference between Simple, EPC Gen 1 & EPC Gen 2 tags?
    Pawan Khilari
    Currently Being Moderated

    Hi Shridhar,

     

    Your 3-point query would be probably solved by this.

     

    <b>Some  information about Gen-1 and Gen-2 tags.</b>

         EPC Gen-1 and Gen-2 uses Use Aloha-based random anti-collision protocol called Q protocol(Q algorithm) Q Protocol (Anti-Collision Protocol) . Select phase - Single out particular tag population with one or more bits like query tree protocol .

    Inventory phase - identify individual tag using Q protocol (slotted-aloha based) - Reader sends Query with parameter Q and Session number (Q=4 is suggested default) - Reader creates slotted time - Tags pick random 16-bit number for handle - Tags in requested session pick a random number in the range [0,2^Q-1] for slot_number - If slot_number = 0, backscatter handle - If slot_number != 0, wait that number of slots to backscatter handle - Reader ACKs individual tag with handle and goes to access phase. All other tags wait. - If more that one tag answers, reader can send same Q again or send modified Q . Access phase - Reader interacts with tags requesting EPC number and any other information Description of the the Q-protocol in detail One issue with the Gen 1 protocols is that they require rfid readers to use the tags' unique serial numbers to singulate tags (to identify them uniquely). If two tags have the same epc, they confuse the reader.

     

       Some retailers are considering using tags with the same epc-that is, information similar to what they have on bar codes today-as an interim measure as they move from bar codes to rfid and prepare their software systems to handle unique ids. Those retailers asked EPCglobal's Hardware Action Group to make it possible to singulate the tags even if two or more tags have the exact same epc. Alien Technology's Steve Smith came up with a solution that enables a Gen 2 reader to count Gen 2 tags-for the purpose of taking inventory, for instance-even when they have the same epc or no serial number.

     

       The reader can do this without broadcasting the tags' epcs, which makes the system more secure. (Since the reader doesn't transmit a message "Tag 12345, are you out there?" it prevents someone from eavesdropping on the reader-to-tag communication to gather information.) Smith's innovation was dubbed "the Q algorithm" for "Query with a parameter Q." Gen 2 tags have the ability to generate random numbers. The reader will tell the tags the range in which it should generate a random number by issuing a query comm and with a Q value ranging from 0 to 15. If it often gets back no response to its queries, it will automatically decrease the Q value. If it gets more than one tag responding, it will increase the Q value, thereby increasing the range of numbers that can be generated by the tags.

       The reader might issue a query with a parameter of Q=4. The tags generate two random numbers, the first one ranging from zero and 65,535, and the second ranging from zero and 2 to the power of Q, minus 1. If Q is four, then 2 to the fourth power is 16, minus 1 equals 15. So all tags choose a second random number ranging from zero and 15. The reader asks any tag that chose zero for their second random number to respond. If one tag has zero, then it responds with the first random number, between zero and 65,535, and the reader acknowledges it. Since the tag has now been singulated,the reader could simply count the tag as present ("I know a tag with a random number of 45,101 is in the field"). It could write an epc to the tag, if it doesn't have one, or it could ask tag 45,101 for its epc if it does have one. It then asks the remaining tags to subtract one from their second random number and singulates the next tag that has a zero, and it keeps doing that until all the tags are singulated. If no tags choose zero for their first random number, then the reader asks all the tags to decrement their random number by one, and it keeps doing that until a tag with zero responds. If two tags respond, the reader can't read either tag, so it issues a negative acknowledge, which tells the tags to wait for another query until they respond again. "This protocol makes it extremely unlikely that a reader will singulate two tags when it meant to only talk to one" .

     

    <b>Also go through these links.....

    1.http://www.rfidjournal.com/article/articleprint/2404/-1/358/

     

    2.http://www.rfidbuzz.com/news/2005/epc_class_1_generation_2_rfid_tag_specification_available_online.html

     

    3.http://www.epcglobalinc.com/standards_technology/EPCglobalClass-1Generation-2UHFRFIDProtocolV109.pdf

     

    4.http://www.ferret.com.au/articles/6e/0c03d56e.asp- Info on GEN2 TAGS

     

    5.http://www.rfidalliancelab.org/publications/FY2006-TR-40980-01.pdf.</b>

     

    Regards,

    Pawan .

    • Re: Difference between Simple, EPC Gen 1 & EPC Gen 2 tags?
      Shridhar Nagarhalli
      Currently Being Moderated

      Hello Pawan,

       

      Thanks for your quick reply.

       

      This is what i have understood, please correct me if i am wrong,

       

      <u>Gen 1:</u>

      Reader sends out requests to the Tags [Group]. The request will be a binary number. If the Tags first bit of the query match with the Tags ID, The tag will respond with the Tags ID, and after that the Reader can get more info about that particular tag.

       

      <u>Q's:</u>

      1. What if the Tag ID is alpha-numeric?

       

       

      <u>Gen 2:</u>

      These type of Tags have the ability to generate random numbers. The reader asks the tag to generate random numbers.

       

      <u>Q's:</u>

      1. What is the match/criteria upon which Tag/s respond to the reader with the EPC, after which the reader can continue the flow.

       

      Thanks,

      Shridhar..

      • Re: Difference between Simple, EPC Gen 1 & EPC Gen 2 tags?
        Pawan Khilari
        Currently Being Moderated

        Hi Shridhar,

        Actually earlier I only mentioned the main difference between the two that was the Q Algorithm and mentioned some links which would help you to get some more differences.

        From your reply I thought should make more easier for you.I have segregated some differences for you from those Links .

         

        <b>Difference between GEN1 and GEN2 tags.</b>

         

        <b>New features that were incorporated in the Gen 2 protocol.</b>

         

        <b>1.The biggest difference between Gen 1 and Gen 2 is that there is now a single global protocol.</b> The first-generation epc had two protocols, Class 0 and Class 1, and the same reader could not read both unless it was a multiprotocol reader. The International Organization for Standardization (iso) also approved two uhf air-interface protocols, 18000-6A and 18000-6B, as international standards, so there have been four uhf standards.

         

        <b>

        2. Another important aspect of the UHF Gen 2 protocol is it was designed to optimize performance in different regulatory environments around the world.</b>  

            Europe’s communications authoritiesrecently adopted reader regulations that are more relaxed, but the new rules are still quite stringent compared with those in the North America. Because the Gen 2 protocol uses the available radio spectrum more efficiently, it will provide better performance in Europe than any other uhf protocol. “Gen2 creates a good foundation for higher-function products, such as Class 2 and Class 3 tags and readers”.

         

        <b>3. Dense-reader mode</b>

        The Gen 2 standard allows readers to operate in three different modes: Single-reader mode, multi-reader mode and dense-reader mode. To function optimally, readers will need to operate in

        dense-reader mode when more than 50 readers are present within a building, such as within a distribution center. Dense reader mode is designed to prevent readers from interfering with

        one another, which could be a problem if many readers are used in a confined space, particularly in Europe and other regions where only a small band of the uhf spectrum has been allotted

        for rfid systems.

         

        <b>4. Dual methods of backscatter encoding</b>

        The Gen 2 protocol also supports another method of encoding the backscatter signal called FMO. The purpose of allowing the reader to use either FMO or Miller subcarrier was to improve

        performance not just when there are many readers in a facility but also when there is a lot of noise in the area.

        FMO, a format used effectively in the current ISO standards, is fast but susceptible to interference. Miller subcarrier is slower but works better in noisy environments.

         

        <b>5. Secure read-write memory</b>

        First-generation EPC Class 0 tags are programmed at the factory, when the chips are made. First-generation Class 1 tags are user programmable, meaning that an end user company can write EPC’s to the tag after taking delivery. In most applications today, Class 1 tags are programmed one by one as they come off a spool.

        Gen 2 tags are field programmable, meaning that readers can write information to tags even if they are attached to cases on a pallet or a conveyer belt. Gen 2 tags will feature three required memory banks—one bank for storing the epc, one for passwords, one for tag identification (the tag stores information about itself)—and an optional bank for memory that end users can use for whatever purpose they wish (one of the few optional features tags can have). User memory could be to store codes to indicate where products are being shipped to, for instance.

        The memory banks can be locked temporarily or permanently.So a product supplier might write an epc to a tag and lock it permanently. It might then write the identification number of a store that the product is being shipped to in the optional user memory. The supplier might lock that memory with a password to avoid having it overwritten, but a manager in the store’s distribution center might have the option of unlocking the memory (if the manufacturer supplies the password), changing the store id to indicate the destination has changed, and then locking the memory again.

         

        <b>6. The Q algorithm</b>

        One issue with the Gen 1 protocols is that they require rfid readers to use the tags’ unique serial numbers to singulate tags (to identify them uniquely). If two tags have the same epc, they confuse the reader. Some retailers are considering using tags with the same epc—that is, information similar to what they have on bar codes today—as an interim measure as they move from bar codes to rfid and prepare their software systems to handle unique ids. Those retailers asked EPCglobal's Hardware Action Group to make it possible to singulate the tags even if two or

        more tags have the exact same epc.

        This Algorithm is mentioned in my first reply above.

         

        <b>7. Sessions</b>

        One weakness of the Gen1 protocols was the possibility that one reader would interfere with another reader's ongoing counting of a group of tags. So let's say a fixed reader is counting all the tagged items on a shelf. It reads a tag and commands it to go to sleep so it can read the next tag.When it is halfway through 100 items, someone comes along with a handheld reader, looking for a specific item on that shelf. The handheld commands all the tags to wake up and respond. Now the fixed reader has to start the counting all over again. To avoid this problem, the Gen 2 protocol introduces something called sessions. Each tag will be able to operate within four

        separate sessions. A retailer or manufacturer could set up their system so that all fixed readers read tags in session 1, and all handhelds use session 2. So if the fixed reader puts the tags to

        sleep in session 1, the handheld reader could communicate with the tags in session 2 and not interfere with the ongoing count by the fixed reader in session 1.

         

        <b>Enhancements made to the Gen 1 protocols.</b>

        <b>

        1.Faster read rates:</b>

        The Gen 2 protocol is designed to enable readers to read data from and write data to rfid tags much faster than the Gen 1 protocols. Gen 2 supports a tag-to-reader data transfer rate of up

        to 640 kilobits per second, versus up to 80 kilobits per second for Gen 1 Class 0 and 140 kilobits per second for Gen 1 Class 1.

         

        <b>2. Fewer ghost reads</b>

        One problem early adopters have encountered with the Gen 1 Class 0 protocol is ghost reads. Sometimes the reader thinks it has read a tag with a particular Id when no tag with that id is present.

         

        <b>3. Longer passwords</b>.

         

        Now to talk about your queries.

        >>Q's:1. What if the Tag ID is alpha-numeric?

        let me know from which link you  read this so that I can comment on it.(If i missed it).

         

        >>Gen 2:These type of Tags have the ability to generate random numbers. The reader asks the tag to generate random numbers.

        Q's:1. What is the match/criteria upon which Tag/s respond to the reader with the EPC, after which the reader can continue the flow.

         

        Now if you again go through the Q Algorithm mentioned in my above reply.This query is answered.

         

        Well I again mention the part of the Algorithm

                " Gen 2 tags have the ability to generate random numbers. The reader will tell the tags the range in which it should generate a random number by issuing a query command with a Q value ranging from 0 to 15. If it often gets back no response to its queries, it will automatically decrease the Q value. If it gets more than one tag responding, it will increase the Q value, thereby increasing the range of numbers that can be generated by the tags. The reader might issue a query with a parameter of Q=4. The tags generate two random numbers, the first one ranging from zero and 65,535, and the second ranging from zero and 2 to the power of Q, minus 1. If Q is four, then 2 to the fourth power is 16, minus 1 equals 15.  So all tags choose a second random number ranging from zero and 15. The reader asks any tag that chose zero for their second random number to respond. If one tag has zero, then it responds with the first random number, between zero and 65,535, and the reader acknowledges it. Since the tag has now been singulated,the reader could simply count the tag as present ("I know a tag with a random number of 45,101 is in the field"). It could write an epc to the tag, if it doesn't have one, or it could ask tag 45,101 for its epc if it does have one. It then asks the remaining tags to subtract one from their second random number and singulates the next tag that has a zero, and it keeps doing that until all the tags are singulated. If no tags choose zero for their first random number, then the reader asks all the tags to decrement their random number by one, and it keeps doing that until a tag with zero responds. If two tags respond, the reader can't read either tag, so it issues a negative acknowledge, which tells the tags to wait for another query until they respond again. "This protocol makes it extremely unlikely that a reader will singulate two tags when it meant to only talk to one" . "

         

        The above mentioned is the match/criteria upon which Tag/s respond to the reader with the EPC, after which the reader can continue the flow.

         

         

        I suppose this should clear all your doubts.Let me know if still there are any.

        Thanks,

        Pawan

Actions