Premium Services over IPv6
by Dr. Lawrence G. Roberts

Today many carriers have concluded that interactive video does not work well enough over IPv4 networks to be functional. In many cases VoIP is also less than the quality we expect. As broadband access, WiFi, and 3G phone service expand, these services are needed. The reason they do not work well is that simple Class of Service (CoS) marking (DiffServ) is not capable of supporting a larger number of premium service calls than the circuit can support at the same time without discarding packets randomly from all of the calls. For example, if a DSL circuit can support 3 video calls and a fourth is requested, since they all have the same priority, they all will experience random discards of about 25% of their packets. This problem can be fixed with IPv6, using a newly approved TIA QoS signaling protocol.

The basic problem with premium services is that the user either wants good service (all packets delivered in a timely fashion) or he expects the call to be blocked. The Internet has mainly had to operate with TCP file transfer in the past, where a slowdown was acceptable if the network became overloaded. But with premium services, the call needs to be complete and operate at full rate. Slow delivery of real-time data creates a noise burst, and 25% noise is intolerable. Thus, a method is required where the network can accept or reject new calls depending on the capacity available. This is an end-to-end network function and the network must accept or reject calls or flows, not just packets, as is the practice today. The new feature of IPv6 is a flow label that tells the routers these packets are part of one flow. When this feature is combined with a signaling protocol that can request a rate, delay variance, and give precedence, then the network can look at the current load and accept or reject new flows. This is what the new TIA QoS signaling protocol accomplishes. It allows the network to control the premium service load, allowing or rejecting new real-time flows. Using the precedence field, emergency calls can still get through. For calls of the same precedence, ongoing calls are not impacted by new call requests. For more information on the protocol, an IETF RFC draft is available at http://www.packet.cc/IPv6Q-IETF-2A.htm.

Historically, signaling protocols were out-of-band and were processed in software. This resulted in very limited performance and long setup times. In the past, we started with SS-7 for the telephone network, went forward with ATM signaling, and now use RSVP and LDP for MPLS. All these protocols overload the software and are not suitable for real-time setup in IP. However, the IPv6 flow label and the TIA QoS signaling option are designed to be processed in hardware, thus there is no setup delay and no call setup overload. Calls can be processed at line rate with virtually no increase in the processing requirements. This is because the signaling option only needs to be processed for each flow, not each packet. Thus the increase in processing is typically less than 1%. This allows premium services, like video conferencing, to be set up across an IPv6 network and supported with near optimum quality, even when mixed with all other data services.