Section: Information System Acquisition, Development and Implementation

Section: Protection of Information Assets
Explanation:
The application gateway is similar to a circuit gateway, but it has specific proxies for each service. To
handle web services, it has an HTTP proxy that acts as an intermediary between externals and internals,
but is specifically for HTTP. This means that it not only checks the packet IP addresses (layer 3) and the
ports it is directed to (in this case port 80, or layer 4), it also checks every HTTP command (layers 5 and 7).
Therefore, it works in a more detailed (granularity) way than the others. Screening router and packet filter
(choices A and BJ work at the protocol, service and/or port level. This means that they analyze packets
from layers 3 and 4, and not from higher levels. A circuit gateway (choice D) is based on a proxy or
program that acts as an intermediary between external and internal accesses. This means that during an
external access, instead of opening a single connection to the internal server, two connections are
established-one from the external server to the proxy (which conforms the circuit-gateway) and one from
the proxy to the internal server. Layers 3 and 4 (IP and TCP) and some general features from higher
protocols are used to perform these tasks.

Explanation/Reference:
Explanation:
A base-case system evaluation uses test data sets developed as part of comprehensive testing programs, it is used to verify correct systems operations before acceptance, as well as periodic validation. Test data/ deck simulates transactions through real programs. An ITF creates fictitious files in the database with test transactions processed simultaneously with live input. Parallel simulation is the production of data processed using computer programs that simulate application program logic.