Integrated Services

Integrated Services

IntServ is commonly referred to as hard QoS due to its ability to set flags related to reliability, bandwidth, and latency and also its reliance on the Resource Reservation Protocol (RSVP) to signal and reserve the desired QoS for each flow in the network. IntServ uses the first 3 bits of the ToS byte for IP Precedence (priority) and the remaining 5 bits to define the need for maximum reliability, throughput, minimum delay, and cost. The first 3 bits used by IntServ represent up to eight levels of relative priority. Table 3-1 shows the defaults for these levels, with the lower values representing lower levels of priority.

IntServ requires configuration of intermediary network devices and end nodes, and as such can be seen as a complex end-to-end system to configure in light of its capabilities. Network utilization can increase slightly due to the overhead of refreshing the end-to-end QoS policy and maintenance of state information at each network device in the path, which hinders scalability. Due to the complexity of implementing IntServ, many organizations have chosen to implement DiffServ as a less complicated alternative. However, given IntServ's robust capabilities, it is still considered the strongest solution for providing end-to-end QoS.