1. An end-to-end usage of the IPv6 flow label jochen.metzler@icn.siemens.de

2. 2 Today's definition of the flow label [1] The usage of the flow label is not completely specified within RFC2460: "The 20-bit Flow Label field in the IPv6 header may be used by a source to label sequences of packets for which it requests special handling by the IPv6 routers, such as non-default quality of service or "real-time" service." "Hosts or routers that do not support the functions of the Flow Label field are required to set the field to zero when originating a packet, pass the field on unchanged when forwarding a packet, and ignore the field when receiving a packet."

3. 3 jochen.metzler@icn.siemens.de Today's definition of the flow label [2] Understanding of the term “flow”: "A flow is a sequence of packets sent from a particular source to a particular (unicast or multicast) destination for which the source desires special handling by the intervening routers." The flow is uniquely identified within the network by the flow label and its source address. All packets belonging to one flow should be treated within the network in the same way.

4. 4 jochen.metzler@icn.siemens.de End-to-end usage of the flow label [1] Reasons from an application point of view common understanding of flows from an application point of view as well as from a network point of view. make use of QoS enhancements for flows (e.g. traffic engineering) request a special handling by the network for every single stream (e.g. wanting all packets belonging to one single stream to take the same way through the network)

5. 5 jochen.metzler@icn.siemens.de End-to-end usage of the flow label [2] Usage from the Application End-to-end semantics of the flow label required flow label does not change, or network ensures that receivers receive packets with the same flow label as it has been sent by the data source Application must be able to select the label that should be used this does not mean, that the application can choose the label free Global Management of label Space unique (pseudo-randomly) assignment per IP source address

6. 6 jochen.metzler@icn.siemens.de Treatment of the flow label within the network Network elements that do not support the function of the flow label field MUST set the field to zero when originating a packet, pass the field on unchanged when forwarding a packet and ignore the field when receiving a packet. Network elements that do support the function of the flow label field but do not know the specific flow MUST set the field to zero when originating a packet, ignore the field when receiving a packet, pass the field on unchanged when forwarding a packet. The whole packet should be passed on in a standard way. Network elements that do support the function of the flow label and know the specific flow label MUST process that packet in the agreed way. Network elements MUST NOT change the flow label or MUST ensure that the original flow label would be re-set before the packet reaches its destination.

7. 7 jochen.metzler@icn.siemens.de Conclusion The flow label should have end-to-end characteristic. Minimize the restrictions to the network layer A fully standardized flow label would help both: application and network design.

8. Would You like to completely standardize the flow label soon ? End-to-end usage of the label ? Access from the application ?