[c-nsp] to shape or not to shape

[Roger Wiklund]

I have a question I have been thinking about.

Let's say we purchased a 5Mbit Ethernet Link. The physical speed of
the link is 10Mbit, so we shape outbound traffic to 5Mbit, like such:

class-map ef
match ip dscp ef
class-map af4
match ip dscp af41, af42, af43
class-map af3
match ip dscp af31, af32, af33
class-map af2
match ip dscp af21, af22, af23
class-map af1
match ip dscp af11, af12, af13
class-map be
match ip dscp be

policy-map qos
class ef
priority 1024
class af4
bandwidth remaining percent 40
random detect dscp-based
class af3
bandwith remaining percent 30
random detect dscp-based
class af2
bandwith remaining percent 20
random detect dscp-based
class af1
bandwith remaining percent 9
randon detect dscp-based
class be
bandwith remanining percent 1


service-policy shape
class class-default
shape avarage 5000000
policy-map qos

interface wan
service-policy output shape

So, as we shape, as long as we have buffers, we will never see any
tail drops, as we will just delay the packets until we send it,
correct?

Now imagine we have a framed e1.

interface wan
bandwith 1984

As we have the full bandwith, no need to shape, so I will just apply
the qos service policy for outbound traffic.

If this e1 is 100% utilized, we will get tail drops when the buffers are full.

So my question now, what if the shape the e1 to 1984, we will still
have the full speed, but we shape, and thus avoid tail drop, and just
delay the packets instead. I'm thinking we avoid TCP restarts etc etc.
pros/cons, or am I wrong about the whole thing? :)

Appreache any comments,

Thanks!

/Roger