distributions. Open source tools for wireless systems include NetStumbler and AirSnort.

Fairleigh Dickenson’s network labs run on virtual machines to limit inadvertent damage and the need for protection measures. We teach the basic network utilities available on Windows- and/or Posix-compliant systems, including ping, netstat, arp, tracert (traceroute), ipconfig (ifconfig in Linux/Unix and iwconfig in Linux wireless cards), and nslookup (dig in Linux). With the proper options, netstat displays IP addresses, protocols, and ports used by all open and listening connections, as well as by protocol statistics and routing tables.

The Wireshark packet sniffer identifies control information at different protocol layers. A TCP capture specification thus provides a tree of protocols, with fields for frame header and trailer (including MAC address), IP header (including IP address), and TCP header (including port address). Students compare the MAC and IP addresses found through Wireshark with those found through netstat and ipconfig. They then change addresses and check results by sniffing new packets, analyzing the arp packets that try to resolve the altered addresses. Capture filters in Wireshark support search through protocol and name resolution; Neville-Neil stressed the importance of narrowing one’s search but failed to mention the related mechanisms. Students are also able to make connections through ( un-encrypted) telnet and PuTTy, comparing password fields.

My favorite Wireshark assignment involves viewing TCP handshakes via statistics/flow/TCP flow, perhaps following an nmap SYN attack. The free security scanner nmap runs with Wireshark and watch probes initiated by the scan options provided. I always assign a Christmas-tree scan (nmap –sX) that sends packets with different combinations of flag bits. Capturing probe packets and a receiving station’s reactions enables identification of flag settings and the receiver’s response to them. Operating systems react differently to illegal flag combinations, as students observe via their screen captures.

Network courses and network main-
tenance are thus strongly enhanced by
sniffers and other types of tools that yield
information concerning network traffic
and potential system vulnerabilities.

What Jack Doesn’t Know about
software maintenance

I agree that the community doesn’t understand software maintenance, as covered in the article “You Don’t Know Jack about Software Maintenance” by Paul Stachour and David Collier-Brown (Nov. 2009), but much more can be done to improve the general understanding of the important challenges.

The software-maintenance projects I’ve worked on have been difficult, due to the fact that maintenance work is so different from the kind of work described in the article. The community does not fully understand that maintenance involves much more than just adding capabilities and fixing bugs. For instance, maintenance teams on large projects spend almost as much time providing facility, operations, product, and sustaining-en-gineering support as they do changing code. 1 Moreover, the work tends to be distributed differently. My colleagues and I recently found maintenance teams spending as much as 60% of their effort testing code once the related changes are implemented.

Other misconceptions include:

The primary job in maintenance is facilitating changes. We found that support consumes almost as much effort as changes and repairs;

Maintenance is aimed at addressing new requirements. Because most jobs are small, maintenance teams focus on closing high-priority trouble reports rather than making changes;

Funding maintenance is based on requirements. Most maintenance projects are funded level-of-effort; as such, maintenance managers must determine what they can do with the resources they have rather than what needs to be done;

Maintenance schedules are based on user-need dates. Maintenance schedules are written in sand, so maintenance leaders must determine what can be done within a limited time period;

Maintenance staff is junior. Average
experience for maintenance personnel
is 25 years during which they tend to
work on outdated equipment to fix soft-
ware written in aging languages; and
Maintenance involves much more
than Stachour and Collier-Brown indi-
cated. In light of the changing nature
of the work being done every day by
software maintenance teams, my col-
leagues and I urge Communications to
continue to cover the topic.

Maintenance is well tooled. We found the opposite. Maintenance tools are inferior, and development tools and regression test suites do not unfortunately support the work.

Reference

1. Reifer, D. Allen, J.-A., Fersch, b., Hitchings, b., Judy, J., and Rosa, W. Software maintenance: Debunking the myths. In Proceedings of the International Society of Parametric Analysis / Society of Cost Estimating and Analysis Annual Conference and Training Workshop (San Diego, CA, June 8-11). ISPA/SCEA, Vienna, VA, 2010.

Donald J. Reifer, Prescott, AZ

authors’ Response:

In our slightly tongue-in-cheek description of software maintenance, we were concentrating on the “add a highway” side of the overall problem, rather than “repair the railroad bridge.” We try to avoid considering software maintenance as a separate process done by a different team. That’s a genuinely difficult problem, as Reifer points out. We’ve seen it tried a number of times, with generally disappointing results.

A better question might be the one asked by Drew Sullivan, president of the Greater Toronto Area Linux User Group, at a presentation we gave on the subject: “Why aren’t you considering maintenance as continuing development?” In fact we were, describing the earlier Multics norm of continuous maintenance without stopping any running programs. We’re pleased to see the continuous process being independently reinvented by practitioners of the various agile methods. In addition, we’re impressed by their refactoring and test-directed development. These are genuinely worthwhile improvements to the continuous approach, and we hope the techniques we redescribed are valuable to that community.

Paul stachour, bloomington, Mn David collier-Brown, toronto

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