Lucent Technologies DEFINITY Communications System Generic 2.2 And Generic 3 V2 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 4-57 Synchronization 
4
Rule 1:
Selec t the node with the lowest stratum c loc k as the network referenc e c loc k 
master and  have the rest of the nod es d erive slave timing  from it.
If there are one or more c loc ks in the network at the lowest stratum level, the 
following  step s c an b e taken to d etermine the c loc k that should  b ec ome 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 4-58 Synchronization 
4
Figure 4-18. Nonpublic Network without Digital Switches
The d ig ital terminal p roduc ts d o not automatic ally switc h to their internal 
hig h-ac c urac y c loc k on sync hronization referenc e failure.
Figure 4-19. Proper Use of Backup Facilities
CEM CEM D4
D4 D4 D4
D4 D4
Digital transmission facilities
Primar
yfrequencyreference...

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 4-59 Synchronization 
4
Rule 2:
A nod e may use a fac ility as a b ac kup  only if the nod e at the other end  is not 
using  that same fac ility as a b ac kup .
Example For Rule 2
Fig ure 4-19 illustrates an app lic ation of rule 2 and  prop er use of a b ac kup  fac ility 
b etween nodes A and  C.
Fig ure 4-20
 shows the same network arrang ement b ut with imp...

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 4-60 Synchronization 
4
Availab ility is d efined  as the ratio of the mean time b etween failures (the averag e 
time b etween suc cessive system failures, ab breviated  
MTBFs) to the sum of the 
MTBFs and  the mean time to rep air (the total maintenanc e time d ivid ed  b y the 
total numb er of failures d uring  the same amount of time ab b reviated  
M TTR)....

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 4-61 Synchronization 
4
Figure 4-21. Optimal Diverse Routing
Fig ure 4-22
 shows nod e C d eriving  b oth p rimary and sec ond ary timing from 
nod e D, via the two sep arate T1/E1 fac ilities. If nod e D should  fail, nod e C would  
no long er rec eive timing  that is trac eab le to node A. Here, nod e C would lose 
sync hronization and  b eg in to introd uc 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 4-62 Synchronization 
4
Figure 4-22. Less Than Optimal Diverse Routing
Rule 5:
Ob taining  b oth p rimary and  sec ond ary sync hronization fac ilities from within the 
same transmission c ab le should  b e minimized .
Rule 6:
The total numb er of c asc ad e nod e c onnec tions from the referenc ed  nod e should  
be minimized.
Example For Rule 6
Fig ure 4-23...

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 4-63 Synchronization 
4
Figure 4-23. Excessive Cascading
Figure 4-24. Minimized Cascading
A
C
DB
Digital transmission facility
Primary frequency reference
Secondary (backup) frequency reference
cydfminc RPY 060397
A
E
B
DC
F
Digital transmission facility
Primary frequency reference
Secondary (backup) frequency reference
cydfx1nd 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 4-64 Synchronization 
4
Rule 7:
The numb er of nod es rec eiving  sync hronization referenc e from any g iven node 
should  b e minimized .
Example For Rule 7
Fig ure 4-25 shows an exc ess of sync hronization from one nod e. If transmission 
fac ility linking  nod es A-B fails, then nod es B, D, E, and  F will lose their 
synchronization. However, if this same...

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 4-65 Synchronization 
4
Figure 4-26. Minimized Synchronization from One Node
.PIC /ks6/lath/multiw/app b .p 22 5.0i
External-Reference Selection Rules
There are seven rules for selec ting  external sync hronization referenc es. These 
rules are d esc rib ed next.
Rule 1:
Nod es within the externally referenc ed  sub level may not use as a referenc e 
sourc e a...

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 4-66 Synchronization 
4
Availability of Synchronization Sources
Misc onc ep tion 1 The loc al exc hang e c omp any (LEC) c an always p rovid e the 
sync hronization sourc e.
Fac t 1 The LECs are not always sub sc ribers to the AT&T referenc e 
freq uenc y.
Many end  offic es still use analog  switc hes and  D4-c hannel 
b anks. In the p ast, these c hannel b anks...