ISDN

• Integrated Services Digital Network (ISDN): is a useful service. for voice calls, but it's not that useful for data.
• You will probably never use it for data services, and if you run into it, you will probably be migrating away from it.
• It is a popular connectivity technology for phone systems, like private branch exchanges (PBXs).
• You may have to interface with a PBX for integrated voice services someday.
• ISDN is still used today by phone service providers.
• ISDN is deployed in two different modes: Basic Rate Interface (BRI) and Primary Rate Interface (PRI).

  • PRI is the most common implementation