mptcp in ns-3-dev, m_txBuffer->m_firstByteSeq or m_txBuffer->HeadSequence () returns zero in MpTcpSocketBase class

[cutesmi...@gmail.com]

I am trying to implement mptcp in ns-3-dev. When I access m_txBuffer->m_firstByteSeq or m_txBuffer->HeadSequence () in MpTcpSocketBase class it returns me always zero. m_firstByteSeq  is a private member of TcpTxBuffer class, I declared MpTcpSocketBase class a friend class in TcpTxBuffer to access it. But it always returns me zero. In TcpSocketBase class both m_txBuffer->HeadSequence () or m_txBuffer->m_firstByteSeq returns actual value.

Please give some suggestions to solve this problem.