343 Too many hops

Originator sent Max-Forwards: 0 in the Invite packet.

According to the RFC3261 call should not be forwarded any further and must be dropped.

RFC 3261            SIP: Session Initiation Protocol           June 2002

8.1.1.6 Max-Forwards

  The Max-Forwards header field serves to limit the number of hops a
  request can transit on the way to its destination.  It consists of an
  integer that is decremented by one at each hop.  If the Max-Forwards
  value reaches 0 before the request reaches its destination, it will
  be rejected with a 483(Too Many Hops) error response.

  A UAC MUST insert a Max-Forwards header field into each request it
  originates with a value that SHOULD be 70.  This number was chosen to
  be sufficiently large to guarantee that a request would not be
  dropped in any SIP network when there were no loops, but not so large
  as to consume proxy resources when a loop does occur.  Lower values
  should be used with caution and only in networks where topologies are
  known by the UA.