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 4-37 Synchronization 
4
Figure 4-6. Synchronization Hierarchy
Switching nodes in digital networks are divided into synchronization layers called 
strata. There are four strata, 1 to 4, where stratum 1 has the highest ac c urac y 
and  stratum 4 the lowest. Pub lic  d igital networks use stratum 1, 2, and 3 
sync hronization. Historic ally, p rivate d ig ital networks used stratum-4 c loc ks all 
sync hronized  tog ether. However, to p rovid e hig her q uality sync hronization 
p erformanc e, stratum-3 c loc ks are now b eing  used  with c ustomer-premises 
eq uip ment in some c ases.
Bec ause of rec ent c hang es within the sync hronization hierarc hy, stratum-4 
c loc ks are now d efined as 
stratum-4 or stratum-4E. The specifications for 
stratum-4E d efine limits that minimize and  c ontrol timing  d isrup tions that oc c ur 
while switc hing  from one sync hronization sourc e to another. Stratum-4 c loc k 
sp ec ific ations, however, are not as string ent in avoid ing  timing  d isrup tions when 
switching  synchronization sources. All other stratum-4 sp ecifications remain the 
same for both c loc ks. It is rec ommend ed  that a stratum-4E c loc k b e used  as a 
sync hronization sourc e for p ub lic  network c onnec tions.
Eac h stratum, from 1 to 4, rep resents a p rog ressively less stab le and  less 
exp ensive c loc k. Within AT&T, there is a system of stratum-1 c loc ks. These 
c loc ks use the AT&T stand ard  referenc e freq uenc y, formerly the Bell System 
referenc e freq uenc y. The stratum-1 outp ut is transmitted  to various pub lic  d igital 
network nod es via either b roadb and  analog  fac ilities or the DATAPHONE
® 
cydfsych RPY 060497Digital trunk
Primary reference
Note: The dashed lines indicate which nodes supply reference
frequencies and those facilities used to transmit the reference
.
Mast er
reference
frequency
Slave
nodes
Not e 
						

							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 4-38 Synchronization 
4
Dig ital Servic e (DDS). Outsid e the United  States, AT&T p rovid es a stratum-1 
c loc k through the Private Network Customer Expert System, Synchronization and 
Timing , Servic e (PRINCE — S, T).
The p ub lic  d ig ital network nod es and  servic es that the AT&T p rivate d ig ital 
switc hes and  d igital terminal p rod uc ts c an c onnec t to are as follows:
nDDS
nDigital serving office (DSO), also called a digital toll office, such as a 4ESS
nDig ital c entral offic e (DCO) suc h as a 5ESS
nDig ital-ac c ess and  c ross-c onnec t system (DACS)
The AT&T p rivate d ig ital network nodes are the following :
nSystem 75
nSystem 85
nDEFINITY Communic ations System Generic  1
nDEFINITY Communic ations System Generic  2
nDEFINITY Communic ations System Generic  3
The AT&T d ig ital terminal p rod uc ts that interfac e with T1 c arriers inc lud e the 
following:
nD4- and  D5-c hannel b anks
nChannel-d ivision multiplexer (CDM)
nBit-c omp ression multip lexer (BCM-32000)
nDig ital d ata multip lexer (DDM-1000)
The d ig ital terminal p roduc ts that interfac e with E1 c arriers inc lud e the 
FL EXI M U X,  OPTI M U X,  SL C 1 2 0 ,  a n d  o t h e r s .
All p ub lic  and  p rivate d ig ital network nod es have internal c loc ks. Fi g u re  4 -7
 
shows the synchronization hierarchy and  the nod e’s internal clock stratum level. 
Note that the System 75 has an internal stratum-4 c loc k; the Generic  3V2 
c ommunic ations systems have an internal stratum-4E c loc k; while the internal 
c loc k on the System 85 and  Generic  2 c ommunic ations system is a stratum-4. An 
external c loc k c an provid e stratum-3 sync hronization to the System 85, Generic  
1, Generic  2, or Generic  3 c ommunic ations systems.
Eac h nod e is c ompelled  to take its timing from the following:
1. A hig her stratum level
2. A nod e eq ual to its own stratum level
3. A free-running  timing  c loc k (g enerated  internally) that meets or exc eed s 
the req uirements for its level 
						

							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 4-39 Synchronization 
4
Figure 4-7. Stratum Levels for the Synchronization Hierarchy
The minimum c loc k ac c urac y for eac h stratum level is as follows:
nStratum 1 (\(+ - 0.00001 pp m, most ac c urate)
nStratum 2 (\(+ - 0.016 p p m, more ac c urate than stratum 3)
nStratum 3 (\(+ - 4.6 p p m, more ac c urate than stratum 4)
nStratum 4 (\(+ - 32 ppm, least acc urate)
NOTE:
When a hierarc hic al p ub lic  dig ital network is imp lemented (and  when full 
network sync hronization is ob tained ), eac h nod e c loc k, reg ard less of its 
stratum level, will have an averag e freq uenc y id entic al to its master and  to 
the AT&T stand ard  referenc e freq uenc y.
cydfsync RPY 060597
Lucent standard reference frequency
DSO
DEFINITY
G1, G2, G3System 85
System 85 System 75 System 85 DEFI NI TY
G1, G2, G3DSO
DACS DSO
DCO
D4 CEMDCO
Digital transmission facility
Primary frequency reference
Secondary frequency reference
Note
Note: For the System 75, System 85, Generic 1, Generic 2, and Generic 3, the internal clock
provides stratum-4 or stratum-4E synchronization. However, a statum-3 exter nal clock may
be used instead of the inter nal clock.
Stratum 1
Stratum 2
Stratum 3
Stratum 4 
						

							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 4-40 Synchronization 
4
Synchronization Architecture and Operations
The timing  ac c urac y availab le to a c ommunic ations system d epend s on 
c ommunic ations system version and  the typ e of sync hronization c irc uit b oard it 
uses. Tab le 4-11
 lists the sync hronization b oard s that are availab le, the versions 
of the switc h in which they are delivered, and the level of timing ac curac y that the 
b oard s p rovid e. Note that all b oard s are b ac kward  c omp atib le, so that even 
thoug h a board  is d elivered  with a p artic ular switc h version, it c an b e installed  on 
earlier versions of the same switc h.
Generic 2.2
Generic  2.2 c ommunic ations systems use either the TN463 or the TN2131 as 
their internal sync hronization b oard . The TN463 p rovid es stratum-4 
sync hronization to the system in the ab senc e of an external p ub lic -network 
sync hronization sourc e. The TN2131 p rovid es sync hronization from an 
on-p remises stratum-3 c loc k in the ab senc e of external pub lic -network 
sync hronization. The pub lic -network sync hronization sourc e arrives at the 
c ommunic ations system over the same DS1 links that c arry voic e and  d ata to 
and  from the system. The DS1 links func tion as p rimary and  sec ondary 
sync hronization sourc es. When servic e from the b oth of the DS1 links is 
d isrup ted , the external p ub lic -network sync hronization sourc e is also 
d isc ontinued . When p ub lic -network sync hronization is d isc ontinued , switc hes 
with TN463 c irc uit board s use an on-board , stratum-4, hig h-ac c urac y c loc k for 
sync hronization; those with a TN2131 use on-p remises external stratum-3 c loc k. 
This sec tion d esc rib es sync hronization through the TN463. See ‘‘The External 
(ST3) Sync hronization Cloc k’’ later in this sec tion for TN2131 op eration.
1. External only
Table 4-11. Available Synchronization Circuit Boards
SwitchSynchronization 
Board Accuracy
Generic  1.1 TN768 stratum-4E
Generic  2 TN463 stratum-4
TN2131 stratum-3*
Generic  3i TN768 stratum-4E
TN780 stratum-4E and  stratum-3
1
Generic  3r TN768 stratum-4E
TN780 stratum-4E and  stratum-3
1 
						

							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 4-41 Synchronization 
4
TN463 Synchronization Architecture
When the TN463 c irc uit b oard  is installed , Generic  2.2 c ommunic ations systems 
c an func tion as either timing  slaves or timing  masters. As a slave, the switc h 
rec eives d ig ital d ata from one or two DS1s. One interfac e sup p lies the p rimary 
sync hronization referenc e and the other interfac e sup p lies the sec ond ary 
referenc e. The timing  sourc e selec ted  is d etermined  b y the system c loc k 
sync hronizer (SCS) TN463 c irc uit p ac k and  sync hronization software. The SCS 
sync hronizes (p hase loc ks) to either the p rimary referenc e, sec ond ary referenc e, 
or the internal hig h-ac c urac y c loc k. Fi g u re  4 - 8
 shows the SCS c irc uit p ac k.
Figure 4-8. SCS (Generic 2.2 Internal Stratum-4 Clock)
Typ ic ally, the switc h will b e eq uip p ed  with several DS1 c irc uit p ac ks. The DS1 
that is selec ted  as the p rimary or sec ond ary referenc e is d ep end ent on the 
internal c ab le c onfig uration and  ad ministration d etails. Here, eac h Generic  2.2 
that is c onfig ured  with at least one DS1 req uires a SCS, inc lud ing  the master 
nod e. Unless sync hronized  to the p ub lic  network the master nod e will not have 
the p rimary and  sec ond ary sync hronization c ab les. A Generic  2.2 may b e 
c onfig ured  as either a single-mod ule or multimod ule system. Typ ic ally, the switc h 
arc hitec ture is und up lic ated , b ut it may also b e d up lic ated  for c ritic al reliab ility 
cydfscs4 RPY 060597
Stratum 4
high accuracy
clock
Main
phase locked
loop Pr i mar y
reference
Secondary
reference
Backplane
cable to
primary DS1
interface (note)
Backplane
cable to
secondary DS1
interface (note)
TN463 circuit pack
Module
control or
TMS cloc
k
oscillator
Optional cross-coupled cable from duplicated SCS
Note: These cables should not be installed if the switch
is the master timin
gsource for the network. 
						

							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 4-42 Synchronization 
4
ap plic ations. The switc h arc hitec ture d etermines the equip ment c arriers that will 
c ontain the SCS c irc uit p ac ks.
For sing le-mod ule ap p lic ations, the SCS is loc ated  in the mod ule c ontrol c arrier. 
In ad d ition to the SCS, a mod ule c loc k is also req uired . The SCS c ontrols the 
mod ule c loc k. For multimodule ap p lic ations, the SCS is loc ated  in the 
time-multip lexed  switc h (TMS) c arrier and  c ontrols the TMS c loc k osc illator.
When the switc h arc hitec ture is d up lic ated , the sync hronization c omp onents and  
cables will also be duplicated. For duplicated systems, functioning modules are 
called 
online, while backup modules are called offline. The offline SCS p hase 
loc ks to the c ross-c oup led  c loc k sig nal from the online SCS. In a d uplic ated 
sync hronization system, the same DS1 fac ility p rovid es the p rimary and  
sec ond ary referenc e for b oth d up lic ated  halves. Fi g u re  4 -9
 shows a System 85 
or Generic  2.2 with a d up lic ated  arc hitec ture and  c ross-c oup led c ab les.
Figure 4-9. System 85/G2.2 Duplicated Synchronization Architecture and Cross 
Coupling
The TN767 is a DS1 c irc uit p ac k for a universal mod ule; the ANN11 is a DS1 
c irc uit p ac k for a trad itional mod ule. 
The sync hronization software c onsists of a series of tasks that monitor several 
system status p arameters and  thus maintain the b est sync hronization sourc e 
online. (The online sourc e is the sync hronization referenc e c urrently in c ontrol. 
This referenc e c an b e either the p rimary or sec ond ary referenc e, or an on-b oard , 
hig h-ac c urac y c loc k, sometimes c alled the loc al osc illator.) Several levels of 
c ontrol are maintained . One level is c ontrolled  b y a 1-sec ond  software task that 
cydf85g2 RPY 060497
DS1
interfacePr imar y
Pr imar y
Seconar ySeconar y
DS1
interfaceSCS (0)
SCS (1)Modul e
clock
or TMS
clock (0)
Modul e
clock
or TMS
clock (1)Switching
network
(0)
Po r t
carriers
Switching
network
(1) 
						

							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 4-43 Synchronization 
4
uses the system status to keep the best inc oming  DS1 referenc e c loc k online. 
The other is c ontrolled  b oth b y hard ware and  the 1-sec ond software task to 
maintain a healthy SCS on line. If a SCS c an rec eive a suitab le referenc e c loc k 
from a DS1, then the b est c omb ination is c hosen. 
Criteria for Switching Reference Sources
With the TN463 c irc uit b oard , any of three sourc es c an b e used as c loc k 
referenc es for sync hronization — an external p rimary DS1 sourc e, an external 
sec ond ary DS1 sourc e, or the on-b oard , stratum-4, hig h-ac c urac y c loc k. The 
p rinc ipal error c ond itions used to d etermine if a switc h to a d ifferent c loc k 
referenc e is need ed  are, in ord er of imp ortanc e:
nLoss of sig nal (LOS) at the SCS c irc uit for more than 200 ms.
A switc h is mad e to the hig h-ac c urac y c loc k (HAC) on the SCS b y the 
SCS. A further analysis is then mad e to d etermine if the LOS is network 
related  or switc h related . A switc h to a healthy referenc e is d one if 
ap prop riate.
nRec ep tion of a b lue alarm, whic h means that the fac ility c annot b e used  as 
a referenc e
nAn out-of-loc k (OOL) c ond ition, whic h means that the HAC is unab le to 
loc k onto the inc oming  c loc k from the c urrent DS1 referenc e
A switc h to a healthy referenc e is d one if one is availab le. Otherwise, a 
switc h to the HAC is p erformed .
nRec ep tion of a red  alarm, whic h means that two out of four (or worse) 
framing patterns were received
nSlip  rate of selec ted  DS1 fac ilities (with resp ec t to the p rimary referenc e) 
exc eed s a g iven threshold
nMisframes at the p rimary referenc e exc eed  a g iven threshold
nRec ep tion of a yellow alarm 
nPoor SCS c irc uit p ac k health
nInsane c ond ition of the b oard p roc essor on a DS1 c irc uit
Tab le 4-12
 summarizes these c ond itions. In the tab le, the PRI is the DS1 sourc e 
that is used  as a p rimary c loc k referenc e, while the 
SEC is the DS1 sourc e that is 
used  as the sec ond ary referenc e. Eac h tab le entry g ives the timing  sourc e that is 
used when the primary and secondary DS1 references are in the states shown in 
the intersec ting columns and rows. For example, when the primary reference 
indicates a 
Ye llow alarm c ond ition, and  the sec ond ary referenc e is GOOD, then 
the sec ond ary referenc e is used ; d uring  all other sec ond ary referenc e states, the 
p rimary DS1 referenc e is used  althoug h it d isp lays a 
Ye llow alarm.
The SCS c irc uit p ac k’s health is examined when the system c loc k’s health is 
evaluated . Error c onditions of varying severity c an exist on the SCS. If the fault is 
minor and  the SCS c an still loc k on the c urrent DS1 referenc e, a low-p riority 
req uest for a soft switc h to the offline sid e is mad e after an unsuc c essful attemp t 
to c lear up the error c ond ition on the SCS. If the SCS c annot loc k onto the c urrent  
						

							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 4-44 Synchronization 
4
DS1 referenc e c loc k, a hig h-p riority req uest for a soft switc h is mad e. The offline 
SCS is also monitored  to make sure that a switc h is not attemp ted  to an unhealthy 
SCS. If the SCS is not d up lic ated  and  the HAC is healthy, serious failures c ause a 
switc h to the HAC to ensure switc h reliab ility. When the SCS c an onc e more loc k 
onto a DS1 referenc e, a switc h to that referenc e is p erformed .
Notes:
PRI Primary c loc k referenc e
SEC Sec ond ary c loc k referenc e
BLUE Blue alarm
RED Red  alarm
YEL Yellow alarm
LOS Loss of signal
HAC System 85/G2.2 internal hig h-ac c urac y c loc k
BO Maintenanc e b usied  out
MISF Misframe
GOOD No alarms
Synchronization Software Operation
Sync hronization oc c urs at several priority levels; rec ord s are kep t for p erusal at 
the d emand  test level with proc ed ure 625. In ad d ition, several yellow LEDs on 
the SCS c an b e ob served  to g et a c urrent p ic ture of how the system is 
c onfig ured  from a referenc e c loc k p oint of view.
nThe LED in p osition #4 refers to the primary DS1 referenc e. The LED is 
OFF if a sync hronization sig nal is p resent and  the SCS is c ap able of 
loc king . The #4 LED is ON if an error c ond ition exists and  the 
sync hronization c ab le is p resent.
Table 4-12. SCS References Switches
Primary 
Reference 
IndicatorsSecondary Reference Indicators
RED BLUE YEL GOOD LOS MISF BO
RED H A C H A C SEC SEC H A C SEC H AC
B L U E H A C H A C SEC SEC H A C SEC H AC
YEL PRI PRI PRI SEC PRI PRI PRI
GOOD PRI PRI PRI PRI PRI PRI PRI
L OS H A C H A C SEC SEC H A C SEC H AC
M I SF PRI PRI SEC SEC PRI PRI PRI
B O H A C H A C SEC SEC H A C SEC H AC 
						

							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 4-45 Synchronization 
4
nThe LED in p osition #5 refers to the sec ond ary DS1 referenc e. The LED is 
OFF if a sync hronization sig nal is p resent and  the SCS is c ap able of 
loc king . The #5 LED is ON if an error c ond ition exists and  the 
sync hronization c ab le is p resent.
nThe following  four yellow LEDs ind ic ate the selec ted  timing  referenc e: #14 
(HAC), #15 (p rimary referenc e), #16 (sec ond ary referenc e), and  #17 
(c ross-c oup ling ). When the system is first b roug ht up  and  no referenc es 
are ad ministered , the HAC LED should b e lit for the online SCS and  the 
c ross-c oup ling  LED should  b e lit for the offline SCS. Shortly after the DS1 
referenc es are ad ministered , the p rimary referenc e LED should  turn on 
and  the HAC LED should  turn off for the online SCS. The c ross-c oup ling  
LED is the only one lit for the offline SCS.
The sync hronization sub system d esc ribed  ab ove also func tions as a p eriod ic  
maintenanc e monitor. Status d etec ted  d uring  the sync hronization p roc ess is 
p assed  along  to other levels of maintenanc e software for p roc essing. This 
p roc essing inc lud es error log g ing  for p roc ed ure 600 and  alarming .
Generic 3V2
The sync hronization b oard s used  on the Generic  3V2 c ommunic ations systems 
d iffer from those used  on the Generic  2.2. The TN768 is available on the Generic  
3V2 to p rovid e stratum-4E sync hronization in the ab senc e of a pub lic -network 
sync hronization sourc e. The TN780 p rovid es either stratum-4E or stratum-3 
sync hronization to the Generic  3V2 and earlier c ommunic ations systems in the 
ab senc e of a p ub lic -network sync hronization sourc e. Stratum-3 sync hronization 
is p rovid ed  throug h an on-p remises unit that interfac es with the TN780 (see ‘‘The 
External (ST3) Sync hronization Cloc k’’ later in this c hapter). Stratum-4E 
sync hronization is provid ed  throug h an internal (on-b oard ) hig h-ac c urac y c loc k.
Synchronization Architecture
Generic  3V2 systems c an func tion as either timing  slaves or timing  masters. As a 
slave, the switc h rec eives dig ital d ata from one or two DS1s/CEPT1s, or timing  
p ulses from the one or two interfac es p rovid ed  on the external on-p remises 
stratum-3 sync hronization unit. One interfac e sup p lies the p rimary 
sync hronization referenc e; the other sup p lies the sec ond ary referenc e. The 
timing  sourc e selec ted  is d etermined  b y the tone-c loc k c irc uit p ac k and  
maintenanc e software. The tone c loc k sync hronizes (phase loc ks) to an external 
(off-b oard ) p rimary referenc e, an external sec ond ary referenc e, or the internal 
(on-b oard ) hig h-ac c urac y c loc k. Fig ure 4-1 0
 shows the tone c loc k c irc uit.
Whic h DS1 or stratum-3 interfac e should  b e used  as the p rimary or sec ond ary 
referenc e is totally d ep end ent on ad ministration d etails. The referenc es should  
b e loc ated in the first c ab inet (proc essor p ort network) to maximize reliability; 
and  b oth referenc es must resid e in the same c ab inet for Generic  3V2 
imp lementations. The tone c loc k g enerates the c all-p roc essing  system tones and  
also p rovid es the switc h with the stratum-4 or stratum-4E c loc k in the ab senc e of 
a reliab le DS1/CEPT1 or stratum-3 referenc e. 
						

							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 4-46 Synchronization 
4
Figure 4-10. Internal Tone-Clock Synchronizer (G3V2)
Software Operation
G3V2 sync hronization software d iffers slig htly from Generic  2.2 b ec ause of 
arc hitec tural d ifferenc es; however, b oth switc hes p rovid e the same overall 
func tions. Primarily, these func tions inc lud e monitoring  the sync hronization 
referenc es and  keeping  the p rimary or other referenc e that has the b est health 
online and  thus p roviding  hig h q uality d ig ital c ommunic ations via DS1/CEPT1 
facilities.
A sub p art of the maintenanc e software monitors the sync hronization c irc uit p ac k 
and  sync hronization referenc es. Dep end ing  on the state-of-health of the 
referenc es, the maintenanc e software p rovid es automatic  switc hing  b etween the 
referenc es. Switc hing  from one referenc e to another c an b e done by any of the 
following  c ond itions:
nOn-line sync hronization referenc e failure
nPrimary or sec ond ary referenc e restoration
nAd ministration referenc e c hang es, either from Initialization and  
Ad ministration System (INADS) or the loc al terminal.
nSystem Tec hnic ian c ommand  from a system ad ministration terminal
The TN768 and TN780 c irc uit p ac ks display ed g e-mounted  LEDs. These LEDs 
ind ic ate the following  status seq uenc es:
cydfitcs RPY 060597
Stratum 4 or 4E
accuracy
clock
Mai n
phase-locked
loop Tone
generator
Pr imar y
reference
Secondary
reference
Exter nal
sync
source
Exter nal
sync
source
Miscellaneous
tones TN741, TN768, or TN780 circuit pack
Main system
bus