Tuesday, November 8, 2011

ISDN

ISDN: Integrated Services Digital Network


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
  • 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

    Sumber : SinauOnline

0 comments:

Post a Comment