Lucent Technologies Ds1/Cept1/Isdn Pri Reference Manual

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-47 Synchronization 
4
nYellow LED is on 2.7 sec ond s and  off 0.3 sec ond s — the tone-c loc k 
sync hronizer is in “ ac tive”  mod e and an external sync hronization sourc e is 
b eing  used  as a sync hronization referenc e.
nYellow LED is on 0.3 sec ond s and  off 2.7 sec ond s — the tone-c loc k 
sync hronizer is in “ ac tive”  mod e and  the internal (on-b oard ) 
high-ac curac y c lock is being used as a synchronization reference.
nYellow LED is on c ontinuously — the tone-c loc k sync hronizer reset 
p rop erly b ut d id  not rec eive translations up d ate. It is in “ ac tive”  mod e and 
is p rovid ing  sync hronization from the internal (on-b oard ) hig h-ac c urac y 
clock.
nYellow LED is off c ontinuously — a d up lic ated  tone-c loc k sync hronizer is 
in stand b y mod e. It is neither g enerating  tones nor sup p lying  a c loc k 
referenc e. (TN768 and  TN780 only.)
nYellow LED fast flash (on 0.1 sec ond s, off 0.2 sec ond s, on 0.1 sec ond s, 
off 0.4 sec ond s, on 0.4 sec ond s, off 0.4 sec ond s, rep eated ly) — The tone 
c loc k is in the tone-generation mode. This oc c urs in d up lic ated  systems 
on the stand b y c loc k when the system status
 command is executed 
d uring  maintenanc e. The stand b y c loc k is the c loc k not c urrently 
p artic ip ating  in the sync hronization p roc ess.
Criteria for Switching to the Secondary DS1/CEPT1 or Stratum-3 
Reference
Eac h oc c urrenc e of an ab normal or error c ond ition results in inc rementing  the 
ap prop riate error c ounter. Eac h error c ounter has its own uniq ue threshold  limit. 
Exc eed ing an error c ounter’s threshold  results in a c hang e in op eration (suc h as 
switching to a different synchronization reference).
The p rinc ip al error c ond itions used  to d etermine if a c hang e to a d ifferent c loc k 
sync hronization referenc e is need ed  are, in ord er of imp ortanc e (error c ond itions 
2 throug h 6 d o not app ly when the on-p remises stratum-3 c loc k is used  as a 
referenc e):
1. The master tone-c loc k sync hronizer detec ts LOS.
2. The online reference reports a red alarm.
3. The online referenc e rep orts a b lue alarm.
4. If more than 50% of those DS1/CEPT1 sp ans that are ad ministered  for 
slip -enable are exp erienc ing slip s (with resp ec t to the p rimary), then a 
d ec ision is mad e to switc h to the sec ond ary.
5. The online referenc e rep orts that its misframe threshold  has b een 
exc eed ed .
6. The online referenc e rep orts that its slip threshold  has b een exc eed ed .
7. The online referenc e rep orts a hyp erac tive ang el alarm.
For switc hes that d o not have the sec ond ary referenc e, a switc h to the internal 
(on-b oard ) hig h-ac c urac y c loc k will only b e mad e for c ases 1, 2, and  3. 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-48 Synchronization 
4
Criteria for Switching Back to the Primary Reference
Eac h time the master tone-c loc k sync hronizer rep orts a LOS, it inc rements the 
exc essive referenc e switc h c ounter. If a total of 20 switc hes oc c ur within a 1-hour 
interval then the internal (on-b oard ) hig h-ac c urac y c loc k is p lac ed  online and 
automatic  referenc e switc hing  is d isab led . Automatic  referenc e switc hing  is only 
enab led  b y hourly maintenanc e or by the enable synchronization
 c ommand .
With automatic  referenc e switc hing  enab led, most error c ounters are 
d ec remented  b y 1 every 15 minutes and initialized  to zero on reac hing  the 
threshold  value. The following  c ond itions c ause an offline referenc e to b e 
restored to online (c ond itions 2 throug h 7 d o not ap p ly when using  the 
on-p remises stratum-3 as a referenc e):
1. The system c onfig uration maintenanc e d etec ts stratum-3 unit or 
DS1/CEPT1 c irc uit p ac k sanity (for examp le, a DS1 has b een reinitialized , 
reinserted  into the c arrier, and /or rep lac ed ). 
2. The DS1/CEPT1 referenc e d etermines that the LOS error no longer exists.
3. The remote loop -around test is c omp leted .
4. The red  alarm has b een c leared .
5. The b lue alarm has b een c leared .
6. The slip  error c ounter has c leared.
7. The misframe error c ounter has c leared .
8. The hyp erac tive ang el alarm has b een c leared .
The External (ST3) Synchronization Clock
It is rec ommended  that all c ustomer p remises switc hes that c onnec t to the AT&T 
p ublic  network and  transfer timing  use a stratum-4E c loc k or b etter. Althoug h a 
stratum-4 or 4E c loc k alread y exists in the DEFINITY c ommunic ations systems, 
they c an also ob tain their timing from an external stratum-3 c loc k. One 
ad vantag e of the stratum-3 c loc k is that it offers 24-hour hold over ac c urac y. 
Using  an external stratum-3 c loc k, therefore, c an avoid  many slip s when a 
network is severed . 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-49 Synchronization 
4
Figure 4-11. Public-Network and External Stratum-3 Clock Connection to G2.2
By rep lac ing  the TN463 with a TN2131 in the same slot, the G2.2 may also use 
the external stratum-3 c loc k.
Most Generic  2.2 and  Generic  3V2 c ommunic ations systems will use the external 
c loc k. This c loc k is p hysic ally mounted  external to the switc h c ab inets. The 
external stratum-3 c loc k req uires d up lic ated  -48VDC p ower. This p ower sourc e 
may b e an existing  -48VDC p ower p lant (whic h is loc ated  on c ustomer 
premises), or a duplicated, cabinet-mounted power supply with battery backup. 
The inp ut voltag e toleranc e is -45V to -52V with a worst-c ase c urrent d rain of 3A. 
The c ab inet mounted  p ower sup ply p rovid es up  to 10 minutes of holdover. In 
cydfx3g2 RPY 060597
NCTEYellow
cross-connect
field
External
clock
(Note 3)
Switch Note 2
Note 1
Notes:
1. The external clock cabinet has one 50-pin connector. It is labeled EXT CLOCK OUTPUT.
One B25A cable is required for connecting the cabinet to the cross-connect field.
2. Refer to the appropriate installation manual or wiring guide for details on how to
configure the cross-connections.
3. When the external clock is used, the SCS must not be administered. Those SCS softwar
efunctions are done bythe hardware and firmware within the external clock.TN492C or
external alarm
interface
TN2131
external clock
interface
DS1
DS1 Public
network
NCTE
Y
Y
B25A
cable
B25A
cable
B25A cablesRef. 1
Ref. 2
Cl ock A
Cl ock B
Alar ms
Alar ms
C6F or
GR-380
cables 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-50 Synchronization 
4
terms of ap p lic ation, the external c loc k c onnec ts b etween the NCTEs and  the 
switc h. Cab ling  for the I/O and alarm c onnec tions is via 25-p air c ab les with 
50-p in telep hone c onnec tors. The NCTE-to-external c loc k c onnec tion has the 
same d istanc e limitations as the NCTE-to-DS1 c onnec tion (655 feet maximum).
For Generic  2.2, the c ab le-run from the external c loc k to the TN2131 c irc uit p ac k 
c annot exc eed  3000 feet; the c ab le run from the external stratum-3 c loc k to the 
TN780 c irc uit p ac k c annot exc eed  3000 feet. Cab le c onnec tions to and  from the 
external c loc k will route via the yellow cross-connec t field. Figure 4-11
 shows a 
p ublic -network c onnec tion to the external c loc k and  the external c loc k 
c onnec tion to the Generic  2.2 c ommunic ations system. Next, Fig ure 4-12
 shows 
how the external c loc k is c onnec ted  to the Generic  3V2 c ommunic ations system.
The external c loc k rec eives two timing referenc e inp uts and  may c onnec t to two 
NCTEs. These timing reference inputs are c alled 
Referenc e 1 and  Refe ren c e 2. 
For the external c loc k, these referenc es perform the same func tion as the p rimary 
and  sec ond ary referenc es d o for the internal sync hronization b oards. That is, 
they are the p rimary and  sec ond ary c loc k referenc es, and  only when these 
referenc es fail is sync hronization d erived  from the c loc k in the external stratum-3 
unit. The same b asic  c onsid erations that ap p ly to the selec tion of p rimary and 
sec ond ary referenc es also ap p ly to these referenc es.
For Generic  2.2, all func tions p reviously p erformed  b y SCS sync hronization 
software c an b e p rovid ed  external to the switc h — b y the external c loc k. 
Furthermore, the switc h d oes not know whic h referenc e (1 or 2) is online nor c an 
the switc h c hang e from one referenc e to the other.
The external c loc k is d esig ned  to p rovid e stratum-3 reliab ility and  exists in a 
d uplex version only. This version provid es 
hot stand b y cap ab ility (the ab ility to 
p ull out c irc uit p ac ks with p ower on) to the alternate c loc k and  may b e used  in a 
p roc essor p ort network with either simp lex or d uplex TN780 tone-c loc k c irc uit 
packs. Fig ure 4-1 3
 shows a func tional d iag ram of the external c loc k. 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-51 Synchronization 
4
Figure 4-12. G3V2 Connections to the External Stratum 3 Synchronization Clock
cydfg3v2 RPY 060597
Stratum 3
external
synchronization
clockYe l l o w f i e l d
cross-connect
Designator
cableCabl e
typeAA
A
C
CY
Y Y
Y Y
Y B
BTN780 A Carrier
B Carrier
Primary
Secondary
A
B
C
YB25A
C60
C6E
H-600-274TN780
DS1
DEFINITY generic 1 or 3
System end
System endClock end
Clock end
Plug
SimplexprocessorincludesTN780Acarrier
Duplex processor includes TN780 A and B carrier Note:
ReceptacleDS1
CSU
CSUSecondary
Pr i mar y 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-52 Synchronization 
4
Figure 4-13. External Clock Connection to G3V2 or G2.2
Private network ap p lic ations that d o not have d ig ital c onnec tions to stratum-3 or 
b etter referenc e sourc es will not p rovid e the 
Re f e re n c e  1 and  Refe ren c e 2 inp uts 
or the c loc k-inp ut #1 and  c loc k-inp ut #2 c irc uit p ac ks. These typ es of network 
ap plic ations are allowed  only when they are timing  masters for a p rivate network 
that is not c onnec ted  to the pub lic  network. 
For p ub lic -network ap p lic ations, the c loc k-inp ut c irc uit p ac k rec eives a 
1.544-mb p s or 2.048 mbp s c loc k signal from the referenc e. The c loc k inp ut #1 
and  #2 c irc uit p ac ks g enerate a 4-kb p s stratum-3 c loc k sig nal and  sup p ly it to 
the c loc k and  outp ut b oard s. The 
c omp osite c loc k outp ut c irc uit p ac k monitors 
the 4-kb p s sig nals from the referenc es and c loc ks and , on d etec ting  a failure or 
other error, automatic ally c hang es from the online referenc e c loc k to an 
alternate. Furthermore, an alarm sig nal alerting  you of the p rob lem is g enerated. 
Ad d itionally, the c omp osite c loc k outp ut c irc uit p ac k g enerates a 64-kb p s 
c omp osite c loc k sig nal. This sig nal is a sp ec ial b ip olar (return-to-zero) sig nal that 
c ontains a bipolar violation every eighth bit and is c abled to the switch through 
the TN2131 c irc uit pac k for G2.2 and throug h the TN780 c irc uit p ac k for the 
Generic  3V2.
Cl ock
input
#1
Stratum 3
clock ATiming
output,
composite
clock A
Timing
output,
composite
clock B Stratum 3
clock B
Cl ock
input
#2
Switch
alarm
interface
St ratum 3
Reference #1
St ratum 3
Reference #2Phase
build
out
-48VDC A
-48VDC B
Retur n-48VDC
ReturnPowe r bu s
System alar m bus
System alarms
cydfxclk RPY 060597
To TN2131(0)(S85/G2)
To TN2131(1
)(S85/G2) To T N 7 8 0
(G1/G3)
To T N 7 8 0
(G1/G3)
To TN492C
external alar m
(S85/G2 only) 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-53 Synchronization 
4
Figure 4-14. G2.2 External Stratum-3 Clock Interface
Figure 4-15. G3V2 External Stratum-3 Clock Interface
cydfg22x RPY 060497
Composite
clock
converterLOS
detectionAlar ms
Sync
output
Composite
clock
output A
Composite
clock
output B
Note 1
Note 2Backplane signal
to TMS or modul
econtrol clock TN2131 circuit pack
Notes:
1. Alarm signals are cabled to the cross-field. For System 85 and Generic 2, they are then
cross-connected and cabled back to the TN492C or external alarm interface. They use
the same cable the composite clock signals come in on.
2. System 85 and Generic 2 applications require that the composite clock synchronization
signal be connected from the skin of the cabinet to the module control or TMS carrier via
an intercarrier cable. TMS and module control carriers (for both System 85 and Generic 2)
use the H-600-260 group 1 cable, while Generic 2 universal module control carriers use the
H-600-271
group 1 cable.
cydfg3vx RPY 060597
Composite
clock
converterLOS
detection Alar m
detection
Out put
clocks
Composite
clock
output AExternal
clock
alarms
Composite
clock
output B
Note 1Backplane
TDM bus Backplane signal
sto system
maintenance TN780 circuit pack
Note 1: All signals use the same cable between the cabinet skin and the cross-connect
field and between the cross-connect field and the control (and/or port) carrier. 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-54 Synchronization 
4
Figure 4-16. External Stratum-3 Clock Duplicated Synchronization for G3V2 or G2.2
Network Synchronization and Engineering
The p rimary g oals of network sync hronization are:
nTo keep each digital network node reliable
nTo make sure that eac h d ig ital termination c an meet the network 
ob jec tives
With the g rowth in the number of d ig ital fac ilities and  the d emand s that tod ay’s 
ap plic ations p lac e on these fac ilities, d esig ning  a p rop er sync hronization p lan 
has become a complex and cruc ial process. Designing a synchronization plan 
c an b e ac c omp lished by using  the AT&T ACCUNET Sync hronization Desig n 
Servic e availab le from BC Servic es or b y following  the g uid elines d esc rib ed  on 
the preceding pages.
The AT&T Sync hronization Desig n Servic e is an eng ineering  c onsulting servic e 
d esig ned  for c ustomers with p rivate d ig ital networks. This servic e p rovid es a 
sync hronization d esig n that c an b e ec onomic ally imp lemented  along  with an 
estimate of the slip  p erformanc e. This servic e also inc lud es an op timal 
sync hronization d esig n that improves the sync hronization p erformanc e with c ost 
effec tive network ad d itions. Furthermore, this servic e reevaluates the entire 
p rivate network sync hronization p lan eac h time there is a c hang e in the 
c ustomer’s network.
NCTE
NCTECl ock
A1
Cl ock
A2S85/
G2
S85/
G2G1 or G3
G1 or G3S85/
G2
S85/
G2 Cl ock
B1
Cl ock
B2 Stratum
3
external
clockTN780
or
TN2131(0)
TN780
or
TN2131(1)S85/G2
module
or
TMS clock
(0)
S85/G2
module
or
TMS clock
(1)Switching
network
(0)
Switching
network
(1)DS1
interfacePo r t
carriers
DS1
interface
Reference
1
Reference
2
cydf3clk RPY 060597 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-55 Synchronization 
4
A sync hronization p lan c an also b e desig ned  b y using  the following guid elines 
and  rules.
nEnsure that all nod es and  fac ilities are sync hronized to a sing le sourc e of 
timing ; or at the worst, to two or more stratum-2 timing  sourc es
nSelec t the most reliab le d ig ital fac ilities to serve as sync hronization 
referenc es at eac h nod e
nChoose fac ilities with the g reatest availab ility and  least outage. For 
examp le, fac ilities that are loc ated  in hostile environments or that have a 
history of servic e disruptions should  not be used .
nEnsure that no timing  loop s c an b e c reated  even und er failure c ond itions, 
that is, timing  from one nod e c an never serve as a sourc e of timing  b ac k to 
that nod e, even if it is loop ed throug h several other nod es.
Selecting a Timing Source for the Switch
Before selec ting  a timing  sourc e, you should  d raw or ob tain a c op y of the 
network topology (whic h indic ates eac h nod e and  the interc onnec ting  d ig ital 
trunk fac ilities). The nod es in the p rivate network should  b e stratified (d ivid ed ) 
into two levels known as 
externally referenc ed  and  internally referenc ed  
(sometimes c alled  
unreferenc ed). Externally referenc ed  nod es are those within 
the p rivate network that c onnec t d irec tly to p ub lic  network timing  sourc es. 
Internally referenc ed  nod es have d ig ital fac ilities that d o not c onnec t d irec tly to 
p ublic  network timing  sourc es. Fig ure 4-17
 shows a typ ic al network top olog y with 
externally and  internally referenc ed  nod es. 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
555-025-107  Issue 1
July 1993
Physical Layer 
Page 4-56 Synchronization 
4
Figure 4-17. External and Internal Reference Levels
For externally referenc ed  nod es, the op erating  c omp any p ersonnel will sp ec ify 
what the sourc e of timing  is on those links. If the network d oes not rec eive timing  
from the pub lic  network at any of its nodes, the master-slave relationships in the 
network will then b e d etermined  b y those p ersons resp onsib le for eng ineering  
the sync hronization of the network.
This internal and  external referenc ing c onc ep t p ermits c onstraints in 
synchronization network layout to b e exp ressed  in terms of network layout rules. 
The rules c onstitute a p roc ed ure to selec t the nod es used  as p rimary and  
sec ond ary referenc es. Two sets of referenc e selec tion rules are availab le: one 
set for internally referenc ed  networks and  the other for externally referenc ed  
networks.
Internal Reference Selection Rules
The seven rules used  to selec t internal sync hronization referenc es are d esc rib ed 
next.
Digital serving office
System 85/G2 or
System 75/G1/G3
System 85/G2 or
System 75/G1/G3 Externally
referenced
nodes
Internally
referenced
nodes
Digital transmission facility
Primary frequency reference
cydfeirl RPY 060397