FR Fragmentation on the interface

Evening Brains-Trust,
 
I've dug myself a nice little mental hole in relation to FR Fragmentation
that I could use some help digging myself out of.
The question I've got relates to the "FR Fragmentation at the Interface"
feature, and is based on bits of information from various sources, but 3
mains ones as described below.
Questions follow at the end. (This is an area that I've never really come to
terms with which is why I'm working to clarify all the questions I have on
this topic).
 
Info-scrap #1:
http://blog.ine.com/2008/01/25/link-efficiency-fragmentation/
By my interpretation, the above link indicates that when this feature is
enabled, there are effectively 3 queues at play:
 
[Interface Software Queue] -> [2-level Interleaving queue] -> [Interface
hardware queue]
 
Extending this to include the per-PVC queues, we get
 
[Per-PVC software queue] -> [Interface Software Queue] -> [2-level
Interleaving queue] -> [Interface hardware queue]
 
 
Info-scrap #2:
http://blog.ine.com/2008/01/24/
The above article makes a few statements that are relevant to my question:
- "Per-PVC software queue" must be CBWFQ (ok, this makes sense)
- Physical interface queue, i.e. "Interface Software Queue", can be any of
WFQ, CQ, PQ or CBWFQ
 
 
Info-scrap #3:
http://www.cisco.com/en/US/docs/ios/wan/configuration/guide/wan_frque_frag_i
f_ps6441_TSD_Products_Configuration_Guide_Chapter.html
 
-- quote
When shaping is configured and traffic exceeds the rate at which the shaper
can send frames, the traffic is queued at the shaping layer using fair
queueing. After a frame passes through the shaper, the frame is queued at
the interface using whatever queueing method is configured. If shaping
is not configured, then queueing occurs only at the interface.
-- end quote

So in my mind, this makes the queues in Info-scrap #1 different depending on
whether traffic-shaping is enabled or not.
 
With traffic-shaping disabled:
 
[Per-PVC software queue] -> [Interface Software Queue] -> [2-level
Interleaving queue] -> [Interface hardware queue]
[CBWFQ ] [WFQ,CQ,PQ or CBWFQ ] [Dual-FIFO
] [FIFO ]
 
 
With traffic-shaping enabled:
 
[Per-PVC software queue] -> [Shaper Queue ] -> [Interface Software
Queue] -> [Interface hardware queue]
[CBWFQ ] [CBTS, GTS or CAR ] [WFQ,CQ,PQ or CBWFQ
] [FIFO ]
 
 
Q1. Is my interpretation and summary of the three documents correct?
1a. are there actually 4-layers of queues involved in the non-traffic-shaped
case? If not, where have I gone wrong?
1b. does the interleaving queue disappear in the traffic-shaped case? If
not, where have I gone wrong?
 
Q2. Are GTS and CAR valid options in the traffic-shaped case?
 
Q3. How does CBWFQ on the Per-PVC software queue map into CQ or PQ on the
Interface queue? (as depicted in the non-traffic-shaped case)
 
Hopefully someone can help me work this out once and for all.
Many thanks.
 
Cheers,
Gavin

Blogs and organic groups at http://www.ccie.net
Received on Mon Apr 05 2010 - 23:39:33 ART