The MPLS WG Archive

["Roberto Mameli (ERI)" <Roberto.Mameli@eri.ericsson.se>]

Hi Sami,

please see my comments below.

> 
> You are correct with the statement that this
> poses a scalability issue. And forwarding
> asics have to do the translation when pushing/poping
> a label.

I am not really able to figure out why scalability is an issue in the case of dynamic EXP<->PHB mapping. It is certainly true that you have to store information about mapping for each LSP, but I think that the amount of memory used is absolutely negligible given the cost of RAM today.
As an example consider a LSR that is supporting, let's say, 10000 E-LSP at a given moment in time. This means that your ILM is composed of 10000 entries. Moreover assume that each PHB is represented by 16 bits (i.e. by its PHBID). This means that the total memory needed to store all the possible EXP<->PHB mappings for the whole set of supported E-LSP is 10000*8*16 bit = 10000*16 bytes = 160000/1024 Kbytes = 156 Kbytes that is not a huge memory requirement today.
You say that the forwarding ASIC has to do translation when pushing/popping labels. What do you exactly mean by that? When accessing the proper entry of the ILM to push/swap/pop a label, the LSR looks up the DiffServ context associated to it and, based on its content, forward the packet to the proper queue. This is exactly the same operation, both in the case of preconfigured and signaled mapping. The only difference is how the DiffServ context is populated (see par. 3.3 <draft-ietf-mpls-diff-ext-09.txt>). So no additional time is required, and again I don't see scalability issues here.

Regards
Roberto