Re: [Status] 答复: 答复: 答复: fwd: New Version Notification for draft-xu-rtgwg-global-label-adv-00.txt

[Hannes Gredler <[e-mail]>]

On Jul 25, 2013, at 11:15 AM, Xuxiaohu wrote:

[ … ]

>>>> What does the SPT label mean?
>>> 
>>> an SPT label  is a label inside a label block. the actual label
>>> is determined by an index advertised by egress routers.
>>> the path to the egress router gets determined using an SPT
>>> calculation.
>> 
>> It uses the trick which has been used by BGP-based VPLS solution. Interesting.
> 
> In this way, the labels would be locally significant. Then how to achieve source routing by using stacked MPLS tunnels ?

SPT labels are used complimentary to 1-hop strict labels
(which are used for explicit routing)

in fact SPT labels can be seen as a way of compressing the
label-stack. lets say you have a given path with <N> segments
to a destination. what you can then do is to replace some of the <N>
segments with corresponding SPT labels.

furthermore the draft allows to have <M> algos infrastructure labels.
i.e. SPT(IGP metric), SPT(latency), SPT(TE-metric), MRT(red), MRT(blue) etc.
that way you increase the likelihood of finding a corresponding shared
path segment to replace an explicit segment.

the idea for multiple algos is that there aren't many dimensions to
optimize a network for (latency, utilization, bandwidth).

pre-computing all those topologies will give you
an "instruction set" for guiding your traffic with the most
minimal instructions possible.

/hannes