code: public byte[] unbind(int sequenceNumber) {
          PDUByteBuffer buf = new PDUByteBuffer(SMPPConstant.CID_UNBIND, 0,
                  sequenceNumber);
          return buf.toBytes();
      }
docs: /*
  (non-Javadoc)
  
  @see org.jsmpp.util.PDUComposer#unbind(int)