Re: [SUA]About hop Counter

fan.dongming,

[email protected] wrote:                                (Tue, 07 Aug 2007 08:54:56)
> 
>    Sua RFC3868£º
>    3.10.1.  SS7 Hop counter
>       SS7 Hop Counter (3.18/Q.713)
>        The  value  of the SS7 Hop Counter is decremented with each global
>    title translation and is in the range 15 to 1.
>    I  find Q714 only metions the hop counter decremented  when receipt of
>    SCCP messages transfered by the MTP:
>     Receipt of SCCP messages transferred by the MTP
>     The SCCP Hop Counter (if present) is decremented and if a Hop Counter
>    violation is   encountered (i.e. the value zero is reached), then....
>    So My Questions are:
>    1)Hop  Counter will be only decremented when GT transfering,and in the
>    initial signal point,SCCP recieve message from user and translates the
>    GT  and  send  message  to  next  signal  point,hop  Counter  will not
>    decremented and set 15.Is this right?

Yes and no.  The count is not decremented by the originating node, it is _set_
by the originating node.  (Note that this is true also for the relay node
where there is coupling of connection sections, the relay node _sets_ the hop
counter for the next connection section.)  The count is also not decremented
when the node performs successive global title translations within the same
node.  The node is responsible for detecting loops in its own tables and does
not need the hop counter to do so.  Hop counter is for loops between nodes,
not for loops within a node's own tables.

>    2)At   one  signal  point,after  GT  translating,the  hop  counter  is
>    decremented  to 0 and translating result is DPC+SSN,should the message
>    be  sent  to  next  signal point with hop counter valued 0? and if the
>    result  is local signal point and the  hop counter is decremented to 0
>    after the GT translating,should violation happen?

Check the SDLs in Q.714: the count is decremented _before_ GTT is performed
and action taken if the count decrements to zero.  So, there is no GTT result
at this point.  A message is never sent with a hop count of zero: it is a
protocol violation.  The hop count must be in the range from 1 to 15
inclusive.  Zero appearing in the parameter within a message is an immediate
hop counter violation.

>    Thanks alot for your answer.

But all this is SS7.  SUA does not differ in this regard with the exception
that routing on IP Hostname is treated the same as "Route on GT" for the
purpose of decrementing the hop counter.

-- brian

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/