northernTelecom :: meridian :: Northern Telecom Meridian 1 Design Guidebook Version 1.0 1998

260 Pages·1998·132.7 MB·English

Meridian 1 Design Guidebook
Information, admonitions & gUidelines for Ml designers
Version 1.0
Issued July, 1998
Proprietary
NtJ-RTEL
NORTHERN TElECOM
Copyright © 1998 Northern Telecom Limited
/dl rights reserved.
() Printed in the USA on recycled paper.
Information subject to change without notice.
The information disclosed herein is proprietary to Northern Telecom or others and is not to be
used by or disclosed to tmauthorized persons without the written consent of Northern Telecom
Limited. The recipient of this document shall respect the security status of the information.

Version 1.0 Meridian 1 Design Guidebook
Why does this book exist?
Meridian 1 software is a big, scary continent of code: millions of lines of source,
multiple languages, decades of evolutionary change. New designers struggle to
navigate software that's older than they are. Even old hands worry that the plate
tectonics of recent projects have altered once-familiar territories beyond
recognition. The most common travel advice today, from both managers and
designers, seems to be "don't go there".
For a while, many folks hoped that we could simply seal off the SL-llibrary
frontiers and at least stay out of that jungle. Alas, fundamental changes, such as
porting to a new CPU and operating system, adding wireless communications, or
moving to an ATM switching fabric, mean that someone has to go explore how
those changes will affect the system, and so expeditions continue to be mounted.
This book is an attempt to take some of the scariness out of such Ml
exploration. Think of it as a travel guide: where to go, what to do when you get
there, and what to watch out for. It maps out each of the broad areas of concern
for an Ml designer. It tries to convey the essential patterns that recur in the
system, so that when designers look at unfamiliar code (which is inevitable) they
will understand what they see more easily. It points out the occasional minefield.
It also explains some design rules and why they exist, which should mean that
people find it easier to create better software. By understanding the issues, they'll
even be able to make informed decisions not to follow the rules sometilT'(,s
Hyper-extending the metaphor, they can learn to be good Ml ecotourists, tv
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avoid offending the natives, and to improve the chances that future visitors will
have a good experience.
What wisdom this book contains has been distilled from the best advice we could
elicit from various seasoned Ml travelers. Despite our best efforts to get our
facts straight, it presumably still has some errors or omissions, and even the
correct information will become out-of-date eventually. So, like all good travel
guide publishers, we urge you to write back to us to tell us what
recommendations were useful, what services have gone out of business, and what
new things we need to include to cover the changing Ml geography. Tradition
dictates that the best suggestions will be rewarded with a free copy of the next
edition.
Our dream is that someday, if everyone learns and follows these rules, we may all
be able to travel safely throughout the Ml world without one of these ...
+- the Ml Tank
(no relation)
Happy trails,
~#--
Geoff Huenemann
(on behalf of the Ml System Architecture team)
July, 1998
BOGOSITY ALERT: The "Ml.Rules" presented in this book are at best heuristics- they
guide the process of discovering good designs by describing things that often work, but
you still have to think through whethet they're really right in any given circumstance.
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Version 1.0 Meridian 1 Design Guidebook
Table of Contents
WHY DOES THIS BOOK EXIST? ................................................................. i
TABLE OF CONTENTS ............................................................................... iii
Part I: Understanding the Context
1. A BRIEF OVERVIEW OF M1 ................................................................. 3
1.1 MARKI.:TNIC[-[liS .............................................................................................................. 3
1. 1.1 Ga.rsic Private Branch Exchanges ................................................................................ 4
1.1.2 Call centers ................................................................................................................... 6
1. 1.3 ucalp oints ofp resence ................................................................................................. 8
1.1.4 Virtual Private Networking (VPN) ......................................................................... 12
1. 1.5 Power networks .......................................................................................................... 15
1.2 CUSTOMER VALUES ....................................................................................................... 15
1.2. 1 Size matten· ................................................................................................................ 16
1.2.2 How do we stack up against the mmpetition? .............................................................. 17
1.3 DISTRIBUnON CHANNELS ........................................................................................... 18
1.4 Ml GENEALOGy ............................................................................................................ 20
1.5 TI-IE lIARDWARE ............................................................................................................ 23
1.5.1 Pl?Jsical packaging ...................................................................................................... 23
1.5.2 ugical demmposition ................................................................................................. 23
1.5.3 Bells and whistles ........................................................................................................ 39
1.5.4 Putting it all together .................................................................................................. 50
Part II: Implications for Design
2. PERVASIVE DESIGN ASPECTS ........................................................... 55
2.1 IT'SNOTOURI .. r\Ul.T ..................................................................................................... 55
2.2 HIGII PERFORMANCE. ................................................................................................... 56
2.2.1 No stopping (ever ever ever) ......................................................................................... 58
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2.2.2 Getting it wrong: Using the wrong algorithm ............................................................... 58
2.2.3 Getting it wrong: No seatbelts ..................................................................................... 59
2.2.4 Getting it wrong: Trying too hard. ............................................................................... 60
2.2.5 Getting it wrong: Not trying hard enough .................................................................... 60
2.3 ZERO DOWNTIMI~ .......................................................................................................... 60
2.3.1 Hotswap .................................................................................................................... 61
2.3.2 No single points 0/f ailure ........................................................................................... 62
2.3.3 No losing stuff ........................................................................................................... 63
2.4 NOBODY'S MANNING TI IE SWITCH ............................................................................ 64
2.4.1 An ounce o/prevention: Protected memory ................................................................... 64
2.4.2 Watchdogs .................................................................................................................. 66
2.4.3 5 uper-ultra-mega-reliab!e restart code .......................................................................... 66
2.4.4 The backup plan ........................................................................................................ 67
2.5 CUSTOMERS' BUDGET WOIUUES ................................................................................. 68
2.5.1 scalabili!J ................................................................................................................... 69
2.5.2 srifiware packaging ..................................................................................................... 69
2.5.3 Configurabili!J ............................................................................................................ 70
2.5.4 Modular design ........................................................................................................... 70
2.5.5 Reuse .......................................................................................................................... 71
2.6 BIGNESS ........................................................................................................................... 72
2.6.1 Vestigial code ............................................................................................................. 72
2.6.2 Data hiding ................................................................................................................ 73
2.6.3 More about reliabili!J ................................................................................................. 74
2.6.4 Paranoid code ............................................................................................................. 74
2.7 NETWORKING COMPI.IC\TIONS ................................................................................. 75
2. 7.1 Standards compliana: .................................................................................................. 75
2.7.2 Version contro!. .......................................................................................................... 75
2.7.3 Glare .......................................................................................................................... 75
2.8 CONCLUSION: PBX SOFlWARE IS ROCKET SCIENCE ............................................. 76
~ .............................................................................................
3. PATTERNS m~ 77
3.1 GOOD I'ATfERNS ~ ...................................................................................................... 79
3. 1. 1 T ransattion engine ...................................................................................................... 79
3.1.2 LAyers ........................................................................................................................ 82
3.1.3 Master-slave ............................................................................................................... 84
3.1.4 Publisher-subscriber .................................................................................................... 84
3. 1.5 Corredive Audit. ........................................................................................................ 85
3.1.6 Memory manager ........................................................................................................ 87
3.1.7 Safe interpreter ........................................................................................................... 88
3.2 NOl'-SO-GOOD PATTERNS ~ ...................................................................................... 89
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3.2.1 Bury wait ................................................................................................................... 89
3.2.2 Global variables ......................................................................................................... 89
3.2.3 Replicated data ........................................................................................................... 90
3.2.4 Overlaid data ............................................................................................................. 91
3.3 THE USUAL SUSPECTS: PATTERNS OF PROBLEMS :!: ................................................ 91
3.3.1 Race conditions ........................................................................................................... 91
3.3.2 DeadlY embraces ......................................................................................................... 92
3.3.3 Constipation ............................................................................................................... 93
3.3.4 Software version mismatches ........................................................................................ 93
3.3.5 Partial failures ............................................................................................................ 94
3.3.6 Too maf!J tasks .......................................................................................................... 94
3.3.7 Power and groundingproblems .................................................................................... 94
Part III: Software Architecture
4. CORE SOFTWARE ARCHITECTURE ................................................ 97
4.1 TilE LOGICAL VIEW ....................................................................................................... 98
4.2 TIlE PROCESS vmw ..................................................................................................... 100
4.2.1 How processes talk to eath other ............................................................................... 101
4.3 TIIE PIIYSICAL VIEW. ................................................................................................... 102
4.3.1 Mappingjobs to processors ........................................................................................ 102
4.3.2 Mapping data !ype to store !Ype ................................................................................. 103
4.4 TIlE DIWELOPMENTVIEW ......................................................................................... 104
4.5 SCENARIOS .................................................................................................................... 105
4.5.1 Cold restart .............................................................................................................. 105
4.5.2 Service lhange ........................................................................................................... 1 06
4.5.3 Telephone call ........................................................................................................... 107
5. THE COMPUTING PLATFORM ....................................................... 109
5.1 WHAT'S IN A PLATFORM? ........................................................................................... 109
5.2 VANILLA VXWORKS .................................................................................................... 111
5.2.1 Tasks ....................................................................................................................... 112
5.2.2 Interrupts ................................................................................................................. 118
5.2.3 Tjpes of memory ....................................................................................................... 119
5.2.4 Poszx ........................................................................................................................ 120
5.2.5 Assorted VxTools ................................................................................................... 120
5.2.6 Compiled caveator ...................................................................................................... 121
5.3 HIGH AVAILABILITY: OUR MODIFICArIONS TO VXWORKS ............................... 123
5.3.1 Robust memory ......................................................................................................... 123
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5.3.2 Robust mass storage .................................................................................................. 128
5.3.3 Watthdogs ................................................................................................................ 129
5.3.4 Restarts .................................................................................................................... 130
5.3.5 Dual CPUs ............................................................................................................. 132
5.3.6 Packaging ................................................................................................................. 134
5.3.7 Tools ........................................................................................................................ 134
5.4 MAINTI':Ni\NCI': FRAMEWORKS .................................................................................. 136
5.5 IN·l"RINSICS .................................................................................................................... 136
5.5.1 Hardware intrinsics .................................................................................................. 136
5.5.2 S rifiware intrinsics ..................................................................................................... 136
5.6 TI IIRD-PAWIY EXTENSIONS TO TIlE PLATFORM .................................................... 137
5.7 DISTRIBUTED PROCESSING ........................................................................................ 137
5.8 EVOlVTNG TIlE PLATFORM ....................................................................................... 138
6. THE PHONES (SL-l ) .......................................................................... 139
6.1 TIIESL-1 LANGUAGE ................................................................................................. 142
6.1.1 ''Stupid wde tricks': ................................................................................................. 146
6.1.2 SL-l wde strudure ................................................................................................... 149
6.1.3 The SL-l memory model. ......................................................................................... 150
6.1.4 Major SL-l data structures ...................................................................................... 155
6. 1.5 Some wmmon hooks ................................................................................................. 163
6.2 TI IE PBX Pl.ATFORM .................................................................................................. 165
6.2.1 Sysload ..................................................................................................................... 165
6.2.2 InitialiZe ................................................................................................................... 166
6.2.3 Switchover ................................................................................................................ 167
6.2.4 Workshed. ................................................................................................................ 167
6.2.5 II 0 .......................................................................................................................... 170
6.3 CAI,L PROCI~SSING ....................................................................................................... 170
6.3.1 Messaging ................................................................................................................. 171
6.4 OPERATTONS ................................................................................................................. 173
6.4.1 Traffic ...................................................................................................................... 173
6.4.2 Billing ...................................................................................................................... 173
6.5 ADMINIS·mATION ........................................................................................................ 174
6.5. 1 Overlqys ................................................................................................................... 174
6.5.2 Set-based administration ........................................................................................... 17 6
6.5.3 The overlqy supervisor ............................................................................................... 17 6
6.5.4 Securiry ..................................................................................................................... 177
6.6 MAlNTI':Nt\NCII ............................................................................................................ 177
6.6.1 System Event and Error Reports (SEER) ............................................................... 177
6.6.2 Alarms. .................................................................................................................... 178
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6.6.3 Overload contro!.f ...................................................................................................... 178
6.6.4 "/}udit.f ...................................................................................................................... 179
7. MANAGEMENT ~£': ................................................................................... 181
7.1 WI [,\'j"S IN '1'1I I ': 1()11 I)I':S(:R II)'I'I( )N? """",." .. , .... ,', .. ,.,""" """, .... ,.".,", ..................... 181
7.1.1 [<ault managemenl .................................................................................................... 181
7.1.2 Conflguralion managemenl ........................................................................................ 182
7.1.3 _,Iccounling ............................................................................................................... 182
7. 1.4 Pe!i017nan,'e .............................................................................................................. 182
7.1.5 S ecurz!y ..................................................................................................................... 182
7.2 LI'J;,\(:Y OA&M ........................................................................................................... 183
7.2.1 The data architecture problem ................................................................................... 183
7.2.2 Overlq;'J ................................................................................................................... 183
7.2.3 /-lardJvare },,/h'J/ructllre (/-I}) .................................................................................. 18-1-
7.3 TRI':NDS IN ;\I.\N,\(;I·:;\!I·:N·I' ........................................................................................ 186
7.3.1 _'lutomalioll .............................................................................................................. 186
7.3.2 NehvorkJ ................................................................................................................. 186
7.3.3 Management In/o17nalion BaJeJ (MIBJ) ................................................................... 187
7.3.4 Graphiml UJer InteduceJ (GUJ.I) ............................................................................ 188
7.4 MI-:J\II)L\N AmlINISTR,\TI\'I': T<)( )IS (1v1AT) .............................................. ,. ......... 188
7.4.1 M,lT H Meridian I commlll1im!ionJ. ................................................................... 189
7.4.2 The M ,IT platjo17n ................................................................................................. 190
7.4.3 Meridian I .I)'Jtem JlieJv ............................................................................................. l91
7.4.4 5,y.r!em admil7iJlraliotl ............................................................................................... 191
7.4.5 _'l!arm mallagemenl .................................................................................................. 191
,·eM
8. MERIDIAN EVOLUTION , .................................................................. 193
8.1 ISN"I'ME I'::-':'I'IN<:'I? .................................................................................................... 193
8.2 Ev( ll,\'IN(; Till': PBX 11.\luW:,\lu·: ............................................................................ 195
8.2.1 Tbe bigpic!ltre .......................................................................................................... 197
8.2.2 Call Sen1er (eS) ...................................................................................................... 198
8.2.3 Inter Node SJvikb (I1':S) ......................................................................................... 199
8.2.4 Node Controller (NC) ............................................................................................. 199
8.2.5 Peripheral Al odllle (ml) ............................................................................... ,. ......... 200
8.2.6 _'lauJ A10dllie (,1M) ............................................................................................... 200
8.2.7 The embedded control L ,lN (I~L,1N) .................................................................... 201
8.2.8 ., Ivai/able (ol?/lgllrationJ. ........................................................................................... 202
8.2.9 Il:7ha! abollttbe Option 11 C? .................................................................................. 202
8.3 E\'ol.\, INC; Till,: PBX s< WI'W,\RI': .................................................................. ,. ......... 203
8.3.1 ME J~fhvare OllervieJv ............................................................................................... 203
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