Bummer, latency. I'm thinking that the MBP has TCP/IP set differently for initial contact than the PB? Are the two laptops running the same version of OSX? Does only the MBP have firewall on (System Preferences > internet > personal > sharing. Ascertain settings are duplicated for both laptops. I would turn off bluetooth, etc, for this testing also. In system preferences > network, click on "Show: Network Port Configurations," and have "on" only airport, both laptops, for this comparison ... just to level the playing field?
I use Sustworks NetTuner: 21 day free trial; then, like $30. The ping is I think affected by your MBP configuration, which must be different than the PB's initial, starting-point, TCP/IP
check these sites:
" ... Why is it Sometimes Necessary To Tune TCP/IP?
TCP/IP is not controlled by any manufacturer and is designed to
work on almost any kind of underlying network with widely varying
characteristics. To meet this challenge, the protocol designers made TCP adaptive. TCP is self monitoring and optimizes its own behavior to match the
network environment. Adaptation takes time and the default
settings cannot optimize for every possible kind of network. Why can't somebody just write a utility that analyzes my network and automatically selects the optimum settings? Such a tool would be both useful and popular. The answer is they already have, it's called TCP/IP, but sometimes it needs a little help. In most cases, TCP works remarkably well all by itself. Tuning is needed
in those cases where TCP doesn't quite get it right because the the
network behavior is outside the expected range. Typical problems include:
Asymmetric connections that are much faster downstream than
High performance connections with relatively long latency
(measured in bytes) such as fiber optic, satellite, or PPP via
PPPoE implementations that restrict the network MTU without
support for "Path MTU Discovery" or fragmentation.
Heavily congested links. Tuning can't solve everything. You may
need to restructure your network or use packet shaping to control
traffic flows <http://sustworks.com/site/app
The key to optimization in such cases is to measure, adjust, repeat.
Notice it's not necessary to find the perfect settings, only to get close
enough that TCP works efficiently in your environment. The tools included
with IPNetTunerX are designed to make this easy and show how well TCP
is actually working.
" ... Fluctuating Round Trip Times
Another fact of life. Pretty much caused by the same things that cause packet loss. Again, not serious cause for alarm, but don't expect optimum performance from TCP. Remember that TCP generates an internal RTT estimate that affects protocol behavior. If the actual RTT changes too much, TCP may never be able to make a satisfactory estimate. Both dropped packets and RTT fluctuations may occur in a periodic nature - a batch of slow packets every 30 seconds, for instance. If you see this symptom, check for routing updates or other periodic traffic with the same period as the problem. Poor network performance can often be traced to slow links being clogged with various kinds of automated updates. ..."
Leopard gets the best possible bandwidth from either broadband or narrowband networks by optimizing buffer sizes according to the local resources and connection type. Starting with a larger window helps TCP with ongoing dynamic optimization. This is especially valuable when connecting to high-bandwidth/high-latency networks like Verizon’s FiOS, which previously required specialized tools such as Broadband Tuner. ...
Tuning TCP for Mac OS X
Mac OS X has a single sysctl parameter, kern.ipc.maxsockbuf, to set the maximum combined buffer size for both sides of a TCP (or other) socket. ... blah blah
Beam me up already. Just work, and be fast about it already~