According to the Jerusalem Post Brahimi is visiting the Arab capitals and Iran in order to get support for an armistice. According to the article Brahimi thinks the opposition is prepared to that and it is the Syrian government that is resisting: We heard from everyone we met in the opposition, and everyone (else) we met that, if the government stops using violence 'We will respond to this directly'," he told reporters.
It seems hard to me to believe that an opposition that is attacking peaceful areas like Aleppo and Raqqa province where a majority of the population prefers to be ruled by Assad is interested in peace.
What the opposition really is interested in is having its own color revolution. One can expect that as soon as there are serious talks about an armistice they will demand the right to demonstrate. Never mind that the level of intimidation that emanates from those demonstrations is such that they might be forbidden in many Western countries. Never mind too that they will aim for a big final demonstration in the center of Damascus - that will end with an attempt to overrun parliament and government buildings.
Syria's opposition has yet to show any interest in real peace - that should come from negotiations and compromise. It is a pity that Brahimi is not stressing that point more.
We know how Annan's armistice went: some rebel groups openly refused to participate - while many others confessed to journalists that they committed themselves only because they feared refusing to so so might make bad propaganda in the West - but that they didn't expect anything from it. Brahimi has done nothing to diminish this lack of faith in a negotiated solution.