ISDN History

• Telephone network used to be entirely analog
• During the 1960s, internal connections were converted to packet-based, digilat switching system
• ISDN implementation was slow because 2 major switch manufacturers developed different digital switching systems
  • Northern Telecom
  • AT&T
• In the 1990s, National ISDN 1 (NI-1) was created to establish a standard implementation for digital switching

ISDN in Theory

Basics

• Digital Communication end-to-end
• Runs on regular copper phone wire; also on fiber optic media
• 2 Channel Types:
  • B (bearer)
    • Carries user information: voice, data, etc.
    • 64 Kbps
  • D (delta)
    • Carries call set-up, signaling, etc.
    • 64/16 Kbps
    • Packet-Switched
• 2 Service Types:
  • BRI (Basic Rate Interface)
    • 2 B channels
    • 1 D channel
    • Total of 128 Kbps transfer rate
  • PRI (Primary Rate Interface)
    • 23 B channels
    • 1 D channel
    • Total of ~ 1.5 Mbps transfer rate
• Hardware:
  • Interface Equipment
    • U
      • between customer location and phone company central office
      • single pair of wires
      • easier to install
    • S/T (Subscriber/Termination)
      • between terminal adapter and wall jack
      • two pairs of wires
      • requires an additional Network Termination 1 (NT-1) device
  • ISDN modem
    • device to connect computer to ISDN line
    • normally includes a TA (terminal adapter)
    • usually, used to connect a single machine to a network
  • ISDN router
    • connects ISDN line (with ISDN digital protocol) to network media (networking protocol)

Advanced

• Bonding
  • Combining channels to make larger data pipes
  • e.g. bonding 2 BRI B channels = 128 Kbps data pipe
  • aka inverse multiplexing
• Dynamic Allocation
  • manage traffic through multiple paths to relieve traffic back-ups or damaged lines
• Error checking is rarely used

Advantages

• Speed
  • 5+ times faster than a 28.8 Kbps analog modem
• Flexibility and multi-tasking
  • use multiple devices on same phone line
  • voice, fax, network, videoconference, etc.
• Intelligence
  • drop from 2 B channels to 1 when incoming call is detected
  • dynamic allocation
  • ISDN channels are dialed only as needed for overflow or out-of-service conditions.

Disadvantages

• Proximity
  • physical location must be close to telephone company's central office
  • general rule: within a 5 mile radius
• Installation
  • difficult set up, especially with internal ISDN modems
  • external modems are easier to install but have lower performance levels
• Interference
  • ISDN is extremely sensitive to unusual or anomalous wiring

  ISDN
  BRI Functional Groups:
  TE1	Terminal equipment 1; devices which are ISDN compatible; provides a 4-wire subscriber connection
  TE2	Terminal equipment 2; devices which are ISDN compatible; example: rs-232 or V.35
  TA	Terminal adapter; connects TE2 equipment to an ISDN network
  NT1	Network Termination Type 1;  connects 4-wire subscriber wiring to a 2-wire local loop; in the US it is CPE, in Europe it is Telco owned
  NT2	Network Termination Type 2 ; directs traffic from various subscriber devices to the NT1 (usually integrated w/NT1)
  LT	Line Termination; located on the Telco side, functions are identical to NT1
  BRI Reference Points:
  U	Between NT1 and LE;  2-wire-loop
  T	Between NT2 and NT1; usually virtual
  S	Between TE1 and NT2; 4-wire subscriber connection
  R	Between TE2 and TA; any non-ISDN DTE connection
  ISDN Layer 1:
  BRI bit rate	192 Kbps
  Per channel	B^1 = 64Kbps
  	B^2 = 64Kbps
  	D = 16Kbps
  	Framing and sync = 48Kbps
  What line-coding does BRI use?	2 binary bits to 1 quaternary (2B1Q)
  TE Pinout:
  1	Power source +3V
  2	Power source –3V
  3	Tx+
  4	Rx+
  5	Rx-
  6	Tx-
  7	Power sink –2V
  8	Power sink –3V
  ISDN Layer 2:
  SAPI	Service Access Point Identifier; identifies different processes on the same TE; 0=call control 63=layer 2 management
  TEI	Terminal Endpoint Identifier;  identifies the TE; 0-63: statically assignment 64-126: dynamically assigned 127: broadcast
  ISDN Layer 3:
  Call setup (calling party) -	Setup - out
  	Setup ACK - in
  	Call proceeding - in
  	Alerting - in
  	Connect - in
  	Connect ACK - out
  Call setup (called party)	Setup - in
  	Call proceeding - out
  	Alerting - out
  	Connect - out
  	Connect ACK - out
  Call teardown (initiating party)	Disconnect - out
  	Release – out
  	Released - in
  	Release complete – out
  Call teardown (disconnected party)	Disconnect – in
  	Released – out
  	Release complete - in

   

Copyright (c) 2001 Boson Software, Inc.  All Rights Reserved.