Hi Robert,
On 7/3/2018 4:07 AM, Robert Raszuk wrote:
Hello Jeff,
“What exactly do you call by "resource allocation" in WAN ?” –
anything that is not “best effort”, BW reservation, protection
type, number of hops, latency, you name it…
Somehow, between ATM and now
**
*we managed to build a technology that would work in both, control
and data planes* 😉
TE with BW reservation is a working technology, with all the bugs,
whether done as a soft state on a device and enforced in FW, aka
RSVP-TE or computed on a controller and enforced by policing
configuration out of band. We also know pretty well how to compute
a constrain path that is loop free and with the constrains. Either
way, working stuff.
It has been nearly 20 years and it seems that some marketing slides
from vendors are still in minds of many many people ...
I think this is *quite* true. There's also quiet a bit of marketing
documents on what constitutes QoS (vs CoS).
MPLS-TE does *NOT* do any data plane reservations nor any data plane
resource allocation. It is all control plane game. Let me shock you
even more today ... what we call "Guaranteed Bandwidth TE" also does
*NOT* perform any data plane reservations. This up to current days is
the most misunderstood element (or hidden secret) of one of the
technologies which has been made available during the last two decades.
This *completely* depends on which vendor and platform you choose.
From the IETF perspective, the RFCs certainly support both reservation
(i.e., book keeping) and *allocation* of resources, (i.e., configuration
of data plane queuing and even per flow shaping and policing). This is
something that continues to be included in all TE related RFCs to date.
If you signal MPLS TE LSP with 5M "reservation" to check if such a
path in your network can be established such check is *ONLY* done at
the control plane (RP/RE) pools of available bandwidth (per priority
level) registers and physical interfaces nor any data plane queues are
never aware of it.
again, this depends on the vendor and the platform. Informed users
understand this and those that care, buy equipment that satisfy their
requirements. I have worked on projects on both sides (vendors and
users/providers) and some care quite a bit about the queuing behavior
associated with TE, others are perfectly happy with TE as a path
selection/distribution/pinning tool.
Now what is a direct consequence of this is if you like to really do
control plane reservations and think of it as actual data plane you
must do it in 1:1 fashion - again all done in control plane. That
means that two fundamental conditions must be met:
A) All traffic must be sent over MPLS-LSPs - be it IPv4, IPv6,
multicast etc ... - even if I have seen 3 networks trying to do that
for IPv4 no one did it for all traffic types.
B) All traffic entering your network must be subject to very strict
admission control and excess shaped or dropped which is very hard
thing to do considering statistical multiplexing gains you count on in
any IP network (Explanation: On any single ingress node you must apply
strict CAC as you are not aware about what traffic is coming from
other ingress nodes. So you may be dropping or shaping traffic which
could flow through your network just fine end to end due to absence of
competing class from different ingress).
All RSVP-TE does is traffic steering in normal steady state or during
protection. That's all. In the WAN's data plane it is all back to
basic Diff Serve at each router's data plane.
The only technology which does provide interface data plane
reservation is RSVP IntServ - but I doubt anyone here or Linda in her
draft meant to use such tool.
While this statement may be true for certain vendors, it is not true a
*technology* or standards perspective.
Why am I jumping on this here in SPRING WG list ... Well few months
ago I have witnessed a discussion where someone was arguing that SR is
much worse then MPLS-TE as it does not provide any data plane
reservations. When I tried to nicely and politely explain how confused
the person is the look I got was comparable to those green folks
walking down from just arrived UFO.
While I certainly accept that for some vendors SR-TE is just as good as
MPLS-TE, if SR-TE is defined as only supporting path control this will
be the first instance of a TE RFC/definition (at least that I'm aware
of) that won't support resource allocation, i.e., *any* form of traffic
treatment (queue) control.
So to conclude SR just like MPLS-TE does a good job in packet steering
via your domain. (SR can do actually more via embedded
functions/apps). But the fundamental difference is that SR does that
steering without necessity of number of control plane protocols and
their required extensions - so does simplify control plane
significantly. Neither of those do any data plane reservations and all
bandwidth contentions need to be resolved via classic QoS.
There is a major difference here in what you characterize here, i.e.,
SR-TE, and how the 'TE' term is used in the existing set of RFCs. I
don't know how we (the IETF) want to denote this difference - I suspect
this will depend on which WG is asked. In this group it seems that
some (perhaps many) are perfectly happy to have SR-TE *not* include
actual resource allocation and traffic treatment (queue) control - I
personally would prefer that it be included so that the part of the
market that cares about such can be supported albeit with the need for
users to evaluate actual vendor TE implementations as is done today.
Lou
Cheers,
R.
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