Achieving a reliable quality of service (QoS) mechanism on the networks is a long and unfulfilled dream of network engineers. As circuit-switched networks are becoming a rarity, the concern of bandwidth starvation doesn’t go away, and QoS topic is lively as ever.
Looking at history of the subject, we can make an interesting observation: all attempts at the network QoS are some kind of a failure. It all started when IP, the Internet protocol, was in its infancy and SNA (IBM’s Systems Network Architecture) was looking as respectable business-oriented universal network protocol stack candidate. SNA introduced a concept of class of service back in nineteen-seventies. Search for TERMPRIORITY for details. For example, this one:
Transaction processing priority is equal to the sum of the terminal priority, transaction priority, and operator priority, not exceeding 255.
Amazing idea. It went nowhere.
Internet Protocol was born and raised without QoS. Every now and then people asked – Why my downloads are so slow? Can we really talk online? And (this is really one of the FAQs) – how do I make sure that the boss doesn’t notice that hundreds of other people are using same channel to the Internet?
Implementing QoS was one of the suggested answers. Early on, a byte in the IP header was allocated for TOS, the Type of Service – but its definition is ever-changing. We had a protocol with cool name RSVP. We have diffserv. Microsoft incorporates QoS features in Winsock – this actually helps to solve the boss problem… But network guys aren’ Windows guys so identity awareness is out of question, and application awareness is rather limited: protocols that use dynamic port ranges and those tunneled through HTTP (and perhaps SSL) both are not supported by router-based traffic shaping – the favourite QoS solution. Which is only manageable in point-to-point scenarios and quickly becomes a nightmare as a enterprise network grows.
Meanwhile growth of demand for bandwidth doesn’t seem to slow, and kilobyte a second tends to be cheaper every year. So the real solution to the bandwidth shortage is increasing the capacity of communication channels. Same as it always was. And those dreaming of network QoS may as well use avian carriers for data transmission.