C++: Best way to use vector in send bytes over tcp/ip

I have a proplem for transfering big data over tcp/ip. The size of vector of byte to transfer is always about 500000. I have 2 solution to deal with this, but I dont know what is the better or having another solution.

For 2 solution, I have 2 class to store data. Each class have 2 methods is:

1. push(std::vector) ;


2. vectorpop();

define BYTE_T unsigned char

Way 1:Use vector

    class buffDdata1 {
      vector<BYTE_T> listData;
      vector<BYTE_T> listDataTmp;
public:      
     buffDdata1 () {
        listData.reserver(500000);
        listDataTmp.reserver(500000);
     }
void push(vector<BYTE_T>& data) {
     lock();
     listData.insert(listData.end(), data.begin(), data.end());
     unlock();
}

vector<BYTE_T>& pop() {
          lock();
          listDataTmp.clear();
          listDataTmp.swap(listData);
          unlock();
          return listDataTmp;
}
};

Way 2: Use vector of vector

class buffData2 {

      vector<vector <BYTE_T> > listData;
      int nCount;
public:
      buffData2() {
           listData.reserver(200000);
      }
      void push(vector <BYTE_T>& data) {
           lock();
           listData.push_back(data);nCount++;
           unlock();
      }
      vector <BYTE_T> pop() {
           vector <BYTE_T> listRet;
           lock();
           for(int i=0; i< nCount; ++i) {
                listRet.insert(listRet.end(), listData[i].begin(), listData[i].end());
           }
           unlock();
           return listRet;
      }
};