framing and line coding

Could you please clear how frame is actually
structured and sent on wire...



how is framing ESF and BSF different from each other ?

what is line coding like
HDB3 etc?

what are channelised time slots ? how it works


i did a lot of google search.. but not able to understand the clear
picture.



--
Taqdir Singh
+91 -9911709496
+91 -8010415988

"do today what others wont so you can live tomorrow as others cant"

Comments

  • Taqdir,

    I don't know the "cisco" answers to your questions. But I think I can help you figure out what you are looking for or put you on the right track to find it.

    So please excuse me if I run on.  The topics you are asking about best lend themselves to statistical analysis, and hands on observation.

    But here goes:

    SUPERFRAME:

    In the 1980's AT&T identified a way to include an in-band magagement channel for T1's. The primary reason for this was so that they could be used to instruct end devices to initiate loopbacks so that T1's could be tested.  This tests would result in the discovery of the number of framing errors and other information associated with the circuit. This formating change of the "T1" allowed CRC (Block Checking) to be added to the circuit in order to identify, but not correct framing errors.  This was called SF (or BSF today), where a superframe is defined as a set of 192 digit time-slots for information payload preceded by a one digit time-slot containing the framing (F) bit, for a total of 193 digit time-slots.  Traditional SuperFrame used 12 consecutive frames.

    Extended (ESF) superframe utilizes 24 consecutive frames. Of the these 24 frames, 12 carry management information, 6 frames provide CRC information and the remaing 6 frames carry synchronization bits. Extended Superframe (ESF) provides more information regarding the the data, better synchronization and is easier to troubleshoot (presumably).

    The key thing to keep in mind is that these framing types are not compatible given that they each use there "in-band management channel" differently.

    LINE CODING:

    Many people confuse line coding and framing (thinking that they are one and the same). This is not true. Line coding involves the manner in which bits are sent and provides synchronization.  You specifically asked about HDB3 (which is an encoding for E1 circuits - European), HDB3 follows the Standard AMI (Alternative Mark Inversion) convention but adds a special violation bit. In a nut shell these Line Coding solutions are designed to help provide synchronization by elimitating long lines of consecutive "1's or 0's" in a data stream.  This way can we create "logical divisions" by imposing rules on how the traffic is "encoded" as it is feed into the wire. Please keep in mind that all this translates to a square wave from.  In the end we need to alter the wave form to ensure that it is "modulated" periodically so we can isolate errors or line problems, without disrupting the flow of data.  This allows us to impose a series of "fixed" transitions, on an otherwise "dynamic" pulse train.

    Example:

    Data flow with out Line Coding:      1111111111111111111111111111111111111111111111111111111111000000000000000000000000000000000000

    To over simplify we use line coding to invert a bit in the stream at regular intervals:

    Same Data flow with Line Coding:  1111111111110111111111101111111111011111111110111111111101111111111000000000001000000000010000

    The receiver will know that every Nth bit is inverted and will change it back, but since it is inverted we know there are no issues in transit.

    Again an over simplification.

     

    CHANNELIZATION:

    Channelization governs how the circuit is divided up into timeslots.  Each timeslot will is a window during which information can be send along with it its associated management, CRC and synchronization information.  Again an over simplification but you should get the idea.


    There are as many forms of channelization as there are framing and inversion technologies. If you want to learn more about this topic I would suggest you look at "Channel Associated Signalling" for the most part this technology lends its self best to studying the "rules" of signalling.

    --The TechEdit Team

     

  • <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">





    The best thing I can tell you is to check out Newton's Telecom
    Dictionary for the different pieces!  The detailed information, while
    good to know and could be helpful at some point, is really not covered
    in detail of Cisco exams. 



    At least not that I've ever come across!



    HTH,






     



    Scott Morris, CCIEx4
    (R&S/ISP-Dial/Security/Service Provider) #4713,

    CCDE #2009::D, JNCIE-M #153, JNCIS-ER, CISSP, et al.

    JNCI-M, JNCI-ER

    [email protected]



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