Systems Design Issues
"The technical design of mobile
computing solutions offers unique challenges to systems professionals. Mobile users have
unpredictable usage patterns, and ergonomic considerations in mobile office are
formidable. Poor technical design and/or a disregard for ergonomics may ultimately lead to
the failure of a mobile computing project." Chander Dhawan - The Editor
We suggest that mobile computing professionals should
analyze the following systems design issues:
1. Technical Design Issues
1.1 Network Design
1.1.1 Wireless LAN design issues
- How many mobile users in total will use the wireless LAN? How
many will be active during the peak period?
- Which LAN applications will they be accessing? Remember that
wireless LANs operate at much slower speeds than wired LANs. Will the slower speed be
acceptable to the intended users?
- Is a notebook with a wireless NIC going to be the primary end
user device? The use of notebooks as primary computers is being increasingly mandated even
in fixed-location offices.
- In which areas of a building or campus will users be roaming?
- How many access points will be needed?
- Where should access points be located ?
- What is the access-point range?
- What impact will construction materials like steel frames used
in walls and ceilings have on signal penetration?
- Which of the two main technologies is preferable spread
spectrum or frequency hopping?
- Will there be radio frequency interference from any other
devices in the office, factory, or campus?
1.1.2 Wide Area Radio Network Design Issues
- Should a private radio network be built, or can a public
shared radio network be used?
- Which radio network technology among those that are available
now and will be available in the future, is most appropriate for the suite of applications
that will be used?
- How are user application-usage profiles matched to a given
- Should RNA technology be integrated with a radio network
- How is good coverage and a minimum number of dead spots
- Should a distributed wireless network design with several
MCSSs like the one suggested in Chapter 11 be used?
- Which MCSS should be selected?
- Should agent-based application development tools like Oracle
Mobile Agents be used?
- How do various network design options influence the way
logical networks will be managed?
- Is network outsourcing a realistic business option to pursue?
If it is, does the proposed network service provider (NSP) have the necessary capacity and
1.2 Capacity planning and response time
A mobile computing application transaction
traverses many hardware and software components before it reaches the destination server
and has to cover the same path again in reverse to complete the trip. There are
many physical links (hops), wireless and wired line, between the end users client
application software and the information server. There are also several pieces of software
involved, many of which featuring queuing (i.e., they are asynchronous).
Thus, there are complex rules for scheduling priorities on a
network. This makes it extremely difficult to build a mathematical model to estimate
response times and therefore to plan reliable network capacities in advance.
Network providers do give some estimates, using either complex queuing models or
rule-of-thumb calculations based on the experience of other customers.
1.3 Data compression considerations
Wireless network bandwidth is scarce and expensive. Every
possible technique should be used to get the utmost service out of this bandwidth.
Compression of data is one such technique.
The most common place to compress data is in the modem.
But it is a good idea to go beyond modem hardware in reducing the amount of traffic on
wireless networks. Intelligence can be built into client application programs so that
short message codes can be used to indicate common data occurrences. Forms and screens
should be stored on the mobile computer.
1.4 System availability design
Typically, wireless networks have redundancies built into
them and network service providers guarantee an extremely high network up-time percentage.
Generally, base-station hardware and network controllers have hardware redundancy and
message switches are typically built on fault-tolerant platforms such as Tandem and
Stratus. However, nothing should be taken for granted and public shared network providers
should be asked for details of their redundancies. Similar redundancies should also be
built into private networks.
Another vital component that must have redundancy built into
it is the MCSS. Find out if the method of switch-over from failing components to standby
components is automatic or manual. If it is manual, is the station staffed, and how long
does a switch-over take?
1.5 Security issues
Securing information from unauthorized access is a major
problem for any network , especially for wireless networks, since radio signals travel
through the open atmosphere where they can be intercepted by individuals who are
constantly on the move and therefore difficult to track down.
Here are some examples common security breaches:
- networks by criminal elements.
- Interception of credit card authorizations over wireless
- Physical breach of security at unmanned base stations or other
Therefore security design must be given careful
consideration. Techniques such as on-the-air encryption (which is inherent in PCS
networks) and firewalls must be used.
2. Ergonomic and Logistics Design
The designer should evaluate the following factors:
- Form factor of end-user devices
- Battery life
- Input method - keyboard, pen, touch or voice
- Health and safety issues
- Portable or fixed