SECTION 17 The Empire Strikes Back

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SECTION 17 - The Empire Strikes Back

• Integrated Services Digital Network ISDN or
• It Still Does Nothing

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text Appendix A

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Overview

• What is it?
• Why ?
• Interfaces Services
• Why did it flop?
• Broadband ISDN the Road to ATM

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What is it?

• a proposal for a Universal Smart telco-style,
  stateful, complex HENCE unscalable Network to
  carry
• voice
• interactive data
• batch data
• fax
• video
• multimedia . . .

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Why is it?

• telcos 1980 operated
• slow circuit switching nets for voice
• PSTN analog, space division, electromechanical
• packet switching nets for interactive data X.25,
  Frame Relay
• digital, time-division, solid-state
• fast circuit switching for voice data
• video fax nets
• cellular radio for wireless voice

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proliferating networks

• each of which had to be
• designed
• built
• marketed
• maintained
• the nightmare one network per traffic class,
• the infant Internet threat
• telcos as minor players providing commodity
  bandwidth only WHICH CAME TO PASS...

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the way out?

• TDM/ time division switching offered
• all digital network, circuit or packet switched
• PCM encoding at network edges for voice
• cheap and fast
• make it the basis of a SINGLE net to carry ALL
  traffic classes

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What is ISDN?

• definitions of
• UNI User Network Interface plus
• user services
• allowing . . .

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allowing
existing PSNs existing PSTN existing fax,
video... nets
ISDN ifce
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ISDN

• followed by integration of existing networks on
  any or all of several levels
• transmission systems
• switching and MUXing
• interfaces
• protocols
• real estate
• evolving to a single network for all tfc classes
• made possible by standards defined throughout the
  network

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ISDN Pitfallover-generalization

• Other Examples
• PL/1
• scientific FORTRAN
• business edp COBOL
• string processing ... language
• the F-111
• land-based sea-based
• tactical ground support air superiority
• fighter bomber
• the SUV, the Camino
• sedan truck
• combining the handling,crudeness fuel economy
  of a truck with the cargo capacity price of a
  sedan...
• do-everything designs that do it all ... badly

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the symptom

• proliferation of features options
• poor treatment of all traffic classes
• over-fondness for generalization

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ISDN UNI

• available
• subscriber loops able to carry 105-6 b/s
  economically pre-DSL
• T-1 trunks
• needed ?
• 64 kb/s streams for voice
• then, not now -- too fast now
• 64 kb/s streams for data
• not OK even then - way too SLOW
• separation of data and control signalling
• no more Blue Box Phone Phreaks

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ISDN services

• Basic Channel B
• 64 kb/s full duplex
• Signalling Channel D
• 16 or 64 kb/s full duplex
• Primary Channel H
• 1.536 Mb/s derived easily from T1
• 1.92 Mb/s derived easily from Euro E1
• 0.384 Mb/s quarter T1

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ISDN services

• Basic channel structure
• 2B D where D16 kb/s
• derivable from 2 wirepair local loop
• Primary Channel structure
• 23B D D64 kb/s
• derivable from 1 T1
• Options
• nB D, 0 lt n lt 24

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with the advantage of hindsight

• too late, too slow, too inflexible, too
  complicated

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ISDN services

• circuit switched
• call setup on D channel
• transmission on B
• packet switched
• call setup on D or
• call setup data transmission on B
• el cheapo packet switched
• setup AND transmission on D

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WHATEVER were they thinking of?

• voice --OK
• low speed packet traffic
• 1970s telco psns
• videotex teletex
• web-like services, now defunct I think
• telemetry on the D channel
• read your home electric water meters...

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WHATEVER were they thinking of?

• completely failed to foresee
• data rate abundance due to fiber thus
• broadband apps like HDTV, videoconference, . . .
• the InterNet
• completely ignored
• the benefits of a dumb stateless net design a
  la Internet

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ISDN present status

• telcos sell 2BD 128 Kb/s ISDN lines
• and 24B D T-1 at high prices
• switched services dead or dying except in Japan

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ISDN positive legacy

• first digital subscriber loops,predating DSL
• no mo modems!
• adequate control/data separation
• no more phone phreaks
• calling party ID

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ISDN user interface frame
4000 frames/sec B1 16 bits B2 16 bits D 4
bits L DC balance F,FA framing
F L B1 L D L FA L B2
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Design of the User Interface or UNI

• Things to do
• terminate the line
• define a telco-user boundary
• for legal revenue purposes
• nothing similar provided in the Internet
• provide loopback for testing
• isolate the user from the line design
• information hiding

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Solution

• The NT1 interface defines
• a connector large
• electrical isolation
• loopback testing

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ISDN User Interface

• NT1 structure
• user side
• 4-wire signals
• 4-wire power
• network side
• 2-wire twisted pair for Basic Rate 2B D
• 4-wire for nB D, ngt2

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Enough for

• ISDN data terminal
• supports
• NT1 ifce at L1
• HDLC variants LAP-D, LAP-B at L2
• X.25 L3 at OSI L3
• ISDN voice terminal aka telephone!
• NT1 ifce at L1
• LAP-D at L2
• I.451 Call Control at L3

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Problem of Foreign Terminals

• foreign not telco-supplied
• loss of revenue
• loss of control
• damage to the network unlikely - a pretext
• solutions . . .

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Problem of Foreign Terminals

• forbid it Albanian Solution
• carrier-supplied, expensive Terminal Adapter TA
  yes! or
• government-approved, third-party supplied,
  inexpensive TA
• leads to the following ...

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Electropolitical design

TE1
R,S,T,U interface points TE1 telco
terminal TE2 Foreign terminal TA adapter for
NT2 foreign mux, switch NT1 telco country
past here NT1,2 NT1 plus NT2
TE2
TA
NT1
NT2
R S T U
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Comments

• S T interfaces are at L1
• telcos want NT1 NT2 --gt NT12. Or . .
• T-interface not defined, so could be changed
• hourly if necessary so
• telcos do all switching and muxing
• attack on the Internet

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Comments

• times have changed, deregulation
• carriers dont dare
• T interface now defined so user-owned
• LANs
• PBXs
• workstations possible
• without defined T, each PC needs a TA!

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Comments

• Integrated voice data interface permitted ISDN
  services, e.g.
• multimedia computer
• PC with phone
• telemetry via phone
• integrated TV, PC and phone , . . .

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ISDN Protocols

• remember
• B channel for data or voice
• D channel for signalling or control

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ISDN protocols- they telcos just keep piling
on layers Louis Pouzin
management
plane
Appln Presn Session Xport Network Link Phys
E-E user protocol - user signalling
X.25 L3
I.451 X.25 who knows?
LAP-D I.441 I.430, I.431 signal packet
telemetry
LAP-B
ckt leased ckt packet
D CHANNEL B CHANNEL data plane control
plane
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Observations

• TWO protocol stacks -
• one for data
• one for control signalling in telco-speak
• and later, a THIRD - network management

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Observations

• On the control plane D
• L3
• X.25 L3 virtual ckts
• I.451 real circuits
• datagram service considered harmful
• L2 LAP-D I.441
• permits multiplexing several user terminals on
  one ISDN interface

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Observations

• 2 part address
• part 1 TEI Terminal Endpoint Identifier
• a hardware-bound address on the multidrop line
  blew it again!
• part 2 Service Access Point ID SAP
• distinguishes control from data
• similar provision in I.451 to distinguish call
  control from data
• frame structures

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frame structures
FLAG SAPI CR 0 TEI 1 CONTROL INFO FCS FLAG
SAPI-LIKE 1 CALL REF VALUE 0 MSG
TYPE PARAMETERS
LOCAL CKT ID OP CODE
LAP-D I.451
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PHYSICAL LAYER

• BIG PLUG
• full duplex transmission of
• Bchannel data
• D channel data
• timing
• circuit ON/OFF
• terminal power, id, loopback

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PHYSICAL LAYER

• manages contention for the multidrop D-line by a
  crude form of CSMA
• idle terminal sends 11...1
• interface reflects it
• collision of 0 and 1 gt 0
• terminal in state RTS awaits n consecutive 1s,
  then sends

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PHYSICAL LAYER

• bit encoding
• pseudoternary
• logic 0 gt 0V
• logic 1 gt -V and V, alternating
• 1 0 logic0V logic-V logic0V-V
  logic 0V logic 0
• dc balanced
• violations exist for framing