Quarterly Technical Report, October 2001
- Cost benefit decision making: We have rewritten our global flow
control in the ns2 simulation. The new implementation scales much better
with the number of sites. We are now able to simulate our cost-benefit
flow control in network scenarios with up to 1600 sites,
800 different senders sending to several groups each,
out of 800 different groups in the system. This gives us the ability
to simulate very large overlay networks.
- New replication protocol: We have started to experiment with the
replication server we developed. We are now benchmarking the replication
server with and without the Postgres database on local area network and on
the CAIRN wide area network. We are experiencing a lot of problems in terms
of the CAIRN nodes' performance (e.g. disk sync performance) and hope
to be able to get a better network in place. We could use any
external help that can be provided here...
- Wackamole: We have developed and released Wackamole, a software
tool that allows N-Way Fail Over for IP Addresses in a cluster.
Wackamole is a tool that helps with making a cluster highly available.
It manages a bunch of virtual IPs that should be available to the outside
world at all times. Wackamole ensures that exactly one machine within the
cluster is listening on each virtual IP address that Wackamole manages.
If it discovers that particular machines within the cluster are not alive,
it will almost immediately ensure that other machines acquire the
virtual IP addresses the down machines were managing. At no time will more
than one connected machine be responsible for any virtual IP.
Wackamole also works toward achieving a balanced distribution of the
public IPs within the cluster it manages.
How it works:
Wackamole runs as root on each of the cluster's machines.
It uses the membership notifications provided by the
, also developed in our lab,
to generate a consistent state that is agreed upon among
all of the connected Wackamole instances.
Wackamole uses this knowledge to ensure that all of the public IP addresses
served by the
cluster will be covered by exactly one Wackamole instance.
- Archipelago: We have developed an initial version of the Archipelago
system. The system allows us to
investigate efficient ways to form an extended ad-hoc network of laptops,
handhelds, and other wireless capable devices, and bridge it to the Internet.
Archipelago constructs a multi-hop dynamic network using the wireless devices of participating users. The current system is fully operational, capable of
supporting up to about fifty participants using handhelds (Windows CE) and
laptops (Windows and Linux), and up to 10 hops in network diameter.
Global Flow Control for Wide Area Overlay Networks: A Cost-Benefit Approach
Technical Report CNDS-2001-3.
This paper presents a flow control for multi-sender multi-group
multicast and unicast in wide area overlay networks.
The protocol is analytically grounded and achieves real world goals,
such as simplicity, fairness and minimal resource usage.
Flows are regulated based on the "opportunity" costs of
network resources used and the benefit provided by the flow.
In contrast to existing window-based flow
control schemes, we avoid end-to-end per sender or per group
feedback by looking only at
the state of the virtual links between participating nodes. This produces
control traffic proportional only to the number of overlay network
links and independent of the number of groups, senders or receivers.
We show the effectiveness of the resulting protocol
through simulations and validate the simulations with live Internet experiments.
We have released version 1.0.0 of Wackamole, an NxWay fail-over for
IP addresses in a cluster. Version 1.0.0 supports the Linux operating
system. Wackmole is available at www.backhand.org/wackamole.
Plans for Next Quarter:
Questions or comments to:
webmaster (at) dsn.jhu.edu
TEL: (410) 516-5562
FAX: (410) 516-6134
Distributed Systems and Networks Lab|
Computer Science Department
Johns Hopkins University
3400 N. Charles Street
Baltimore, MD 21218-2686