getDataChannelId (type, filter) {
    return Object
      .keys(this._channelMap)
      .find(cid => {
        const c = this._channelMap[cid]
        const fv = _pick(c, Object.keys(filter))
        return c.channel === type && _isEqual(fv, filter)
      })
  }
Fetch the ID of a channel matched by type and channel data filter

@param {string} type - channel type
@param {object} filter - to be matched against channel data
@returns {number} channelID