Network Security - An overview
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Alcatel-Lucent
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
NETWORK SECURITY TERMINOLOGIES
This section explains the Network Security Terminologies.
• “Gateway”
• “Application Level Gateway (ALG)”
G
ATEWAY 
A gateway is an internetworking system used to connect two disparate network 
technologies and achieve seamless interconnectivity. Gateways typically operate 
on one or more layers of the OSI data model. Depending on the function intended 
for, they can operate from the application layer to link layer. A common type is a 
protocol gateway used to connect networks running different network or 
application protocols (e.g. TCP/IP, IPX). Because a network gateway can appear 
at the edge of the network, it is likely to implement related functions like firewalling 
on the gateway.
 
A
PPLICATION LEVEL GATEWAY (ALG)
An ALG has the capability to conduct stringent packet inspection and thereby 
augment the security infrastructure. Besides using a specialized program for each 
type of application or service that needs to pass through the firewall, ALGs look 
for altered data, potentially harmful traffic, data appropriateness, and also have 
the capability to log these.
Figure 19: Depicting ALG Scenario