TIA TIA-1039 PDF

This document provides a Quality of Service (QoS) signaling standard for use within IPv4 and IPv6 network-layer protocols. This mechanism will allow the necessary resources to be allocated to a flow (or group of flows) as they traverse the network. This signaling scheme is designed to work "in-band", and requires hardware or microcode support in the participating network elements (i.e. routers). Thus, the QoS is setup in real time across the network without a separate, out-of-band, software signaling structure like Reservation Protocol (RSVP). The resource "request" and (when needed) the "response" messages are incorporated into the user data packets themselves, allowing the QoS requirements to be setup during the initial network traversal from sender to receiver (and back if needed). This signaling scheme can be used to set the rate, burst tolerance, preemption priority, delay priority and charging direction for a flow.

The signaling strategy for IPv4 and IPv6 uses the same QoS Structure but due to the protocol differences, is transported in slightly different ways. For IPv4, the document specifies a QoS Structure to be added to the first data packet or "Start Packet" of a flow, requiring a unique Diffserv code-point. An additional QoS Structure can also be sent in this manner, whenever the rate needs to be changed. For IPv6, the same QoS information is added as a hop-by-hop option so that it is not encrypted. Each network router in the path examines the QoS Structure and agrees to or adjusts the rates requested to the rates it can support. If any of the rate parameters have been changed, by the network elements in the flow path, this is communicated back to the sender by the receiver.

The QoS defined within this signaling structure can support four general types of service. The first is a fully guaranteed rate flow, which implies no oversubscription of network resources. The second is a maximum rate flow, which allows some oversubscription but virtually no packet loss. The third is a variable rate flow, where available rate is combined with a minimum rate guarantee. The fourth is an available rate flow, one that can jumpstart the Transmission Control Protocol (TCP) to the highest rate the network can support, eliminating slow-start problems. In the available rate case the capacity available based on network congestion is fed back to the sender very rapidly at all times. This will help to differentiate congestion problems from channel errors (measured in bit error rates), permitting the sender to then optimize his packet error control without confusing it with congestion. For premium services like voice and video maximum rate service sets up a low delay, low loss path with a minimal of effort.