ISDN

1
ISDN

• Integrated Services Digital Network
• 2BD Basic Rate Interface (BRI) to the desktop
• Two 64-kbps B channels
• Can be bonded for 128 kbps service
• One 16-kbps D channel, usually for supervisory
  signals

64 kbps
BRI 2BD
64 kbps
ISDN Modem
2
ISDN

• Primary Rate Interface (PRI)
• Connection between firm and ISDN carrier
• 23BD (on a T1 line)
• 30BD (on an E1 line)
• One 64 kbps D channel for supervision

2BD
23BD
BRI
PRI
3
ISDN

• Circuit-Switched
• Dedicated capacity
• Expensive for data
• Dial-Up Connection
• Must connect each time you wish to communicate
• Other PSDNs are dedicated (always on)
• Unreliable
• Only Popular PSDN that is either circuit-switched
  or dial-up

4
ISDN

• Never achieved strong market use
• Being overtaken by PSDNs that are both faster and
  less expensive
• Often, ISDN is spelled out as It still does
  nothing
• However, there is enough ISDN in use that you
  must know it
• Also, if connectivity is only needed a short time
  each day, ISDN is still a good choice for
  low-speed transmission

5
X.25

• First Packet-Switched PSDN Standard
• Developed in the 1970s
• Now obsolete
• But still used, especially in third-world
  countries and Europe
• Slow Usually 64 kbps or slower
• Some faster X.25 services are available
• Reliable, so costs of switches are high
• So cost of service is high
• But works even if transmission lines are poor