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 4-17 Channel Structure and Signaling 
4
Notes:
1. CO is any of the following  trunk types: CO, FX, and  WATS.
2. Tie is any of the following trunk typ es: ac c ess, tie, tand em, RLT, ap lt.
3. If CAS is used  on a CO trunk typ e, the c ountry p rotoc ol must b e c orrec t for 
that c ountry.
4. The TN767 c annot b e used  for ISDN PRI sig naling  on a G3rV2. It c an b e 
used  as an NFAS b oard , however, c ontaining  all B c hannels (isd n-ext).
Table 4-7. DS1/CEPT1 Port Boards Signaling Summary
Board 
CodeNo. Voice/ 
Data 
ChannelsBit Rate 
(mbps) Companding SignalingTrunk 
Ty p e
TN72223
1.544 mu-lawc omm-c han Tie
24 rob bed -b it Tie
TN722B23
1.544 mu-lawc omm-c han
24 rob bed -b it Tie
TN76723
1.544 mu-lawc omm-c han CO/DID/Tie
24 rob bed -b it CO/DID/Tie
23 isd n-p ri ISDN 
(G3iV2)
24 isd n-ext ISDN
TN464C 23 1.544 mu-law c omm-c han Tie
24 1.544 mu-law rob bed -b it CO/DID/Tie
23 1.544 A-law/mu-law isd n-p ri ISDN
24 1.544 A-law/mu-law isd n-ext ISDN
30 2.048 A-law/mu-law isd n ISDN
31 2.048 A-law/mu-law isd n-ext ISDN
30 2.048 A-law/mu-law CAS CO/DID/Tie 
						

							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 4-18 Line Coding 
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Line Coding
Line c oding  is the pattern that d ata assumes as it is prop ag ated  over a 
c ommunic ations c hannel. Dig ital trunks on DEFINITY systems use the following  
line cod ing s:
nAlternate Mark Inversion (G3 V2 only, CEPT1 interfac es only)
nAlternate Mark Inversion with Zero Cod e Sup p ression (all systems, DS1 
interfac es only)
nAlternate Mark Inversion with Bip olar 8 Zero Sub stitution (all systems, DS1 
interfac es only)
nAlternate Mark Inversion with High Density Bip olar 3-b it Substitution (G3 
V2 only, CEPT1 interfac es only)
Sinc e all of these line c od ing  sc hemes emp loy Alternate Mark Inversion (AMI) 
line c od ing , the rest of this d oc ument refers to AMI with zero c od e sup p ression 
(ZCS) as ZCS, AMI with b ip olar 8 zero sub stitution (B8ZS) as B8ZS, and  AMI with 
hig h density b ip olar 3-b it sub stitution (HDB3) as HDB3.
Governing  line c od ing  is a set of parameters that must b e defined  for all d ig ital 
transmissions. These transmission p arameters sp ec ify the voltag e levels and  
p atterns in whic h 1s and  0s c an ap p ear on the line. 
The p arameters c hosen for a given transmission stream must meet the 
req uirements set b y the hard ware throug h whic h the d ata is to b e transmitted . 
Most notab le among  these req uirements are two estab lished  b y the AT&T 
network. The first of these req uirements states that the voltag e on the line should  
b e a net DC 0. 
Alternate mark inversion (AMI) was ad op ted to fulfill this 
req uirement. The sec ond req uirement, known as the 
ones density req uirement, 
states that in every stream of 15 c onsec utive b its, a one must ap p ear. If the 
d ensity of 1s is not g reat enoug h, loss of sync hronization results. 
Zero c od e 
sup p ression
 (ZCS), b inary 8-zero substitution (B8ZS), and  high d ensity bip olar 
(HDB) line c od ing  were ad opted  to meet this req uirement. Fi g u re  4 - 3
 shows the 
rep resentation of 0s and  1s in AMI line c oding : 
						

							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 4-19 Line Coding 
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Figure 4-3. Alternating Mark Inversion
Alternating Mark Inversion Line Coding
All transmissions g enerated b y d ig ital trunk ports are enc od ed  in AMI. AMI was 
d esig ned  to fill the line rep eater’s need  for d ep end ab le and rec urring  voltag e 
c hanges on the line. With AMI, every 1 in the transmission stream c hang es the 
line state alternately to either + 3 volts or -3 volts. That is, every other 1 is 
rep resented  as + 3 volts, with the following  1 being rep resented  as -3 volts. A 
zero is always represented  as 0 volts. Note that AMI line c od ing  d oes not 
g uarantee the p roper density of 1s in the transmission. The AMI op tion is 
available on G3V2, however, by entering none
 in the Line Coding
 field  in the 
DS1 circuit pack form.
ZCS Line Coding
Zero Cod e Sup p ression (ZCS) line c od ing  is AMI line c od ing  c omb ined  with a 
sc heme to ensure the prop er d ensity of 1s in the transmission. It ensures that 
eac h transmitted  AMI b yte c ontains at least one 1. DS1 p orts that are 
ad ministered  for ZCS line c od ing  examine eac h b yte, one time slot at a time, and  
arb itrarily sub stitute a 1 for the sec ond  least-sig nific ant b it of any all-zeros b yte 
they find . Note that rep lac ing a 0 with a 1 will not affec t voic e c ommunic ations 
b ut will c orrup t d ig ital d ata c ommunic ations.
B8ZS Line Coding
Like ZCS, Bipolar 8 zero substitution (B8ZS) line c od ing  is AMI line c od ing 
c omb ined  with a sc heme to ensure the p rop er d ensity of 1s in the transmission. 
B8ZS line c od ing  is used  only on DS1 interfac es in DEFINITY systems. B8ZS line 
cydfalmi RPY 060497
v(t)
t
00 0
111111 +3
-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 4-20 Line Coding 
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c od ing  sub stitutes a p red etermined  b it string  for every g roup  of eig ht 
c onsec utive zeros that it find s in the transmission stream. The p red etermined  
sub stitute string  c ontains intentional b ip olar p ulse violations so that it c an b e 
rec ognized  at the rec eiving  end . Thus, unlike with ZCS, B8ZS line c od ing  will not 
c orrup t d ig ital d ata b ec ause the far end  rec og nizes the sub stitution so that it c an 
b e restored  to its original d ata.
B8ZS works as follows:
1. The transmitting DS1 b oard  (or other B8ZS line eq uip ment) d etec ts 8 
c onsec utive 0s.
2. If the value of the last 1 transmitted  was a +  voltag e, the string  of 8 0s is 
rep lac ed  with the following  string: 000+ -0-+ . The first +  in this string  is a 
b ip olar violation b ec ause the +  of the last 1 is followed  b y another + . 
Similarly, the second - in this string is a bipolar violation because it follows 
the first -.
3. If the last 1 transmitted  was a - voltag e, the string  of 8 0s is rep lac ed  with 
the following  string : 000-+ 0+ -. Here, the first - and  the sec ond  +  are 
b ip olar violations.
4. At the rec eiving  end  (assuming  the rec eiver understand s B8ZS) this string  
is rec og nized  bec ause of the b ip olar violations and is restored  to 8 0s.
Figure 4-4. Example of B8ZS Line Coding
HDB3 Line Coding
Hig h d ensity b inary 3 sub stitution, HDB3, line c od ing, like ZCS and  B8ZS, is AMI 
line c od ing  c omb ined  with a sc heme to g uarantee 1s d ensity. HDB3 line c od ing  
rep lac es any string  of 4 c onsec utive zeros with one of the following  two 
seq uenc es:
cydfb8zs RPY 060597
Uncoded
bit stream
Pulse
stream010011 00000000 111 00000000 00000000 01
0+00-+ 000+-0-+ -+- 000-+0+- 000-+0+- 0
+
Intentional violations based on polarity
of last 1 transmitted 
						

							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 4-21 Line Coding 
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1. 100V if there has b een an even numb er of 1s sinc e the last substitution. V 
means a b ip olar violation. For examp le, if the last 1 was a + , the V would  
be a +.
2. 000V if there has b een an od d  numb er of 1s sinc e the last sub stitution.
To illustrate HDB3, c onsid er the following  string :
Input bit stream      1011   0000   01   0000   0000
HDB3-coded bit stream 1011   100V   01   000V   100V
HDB3-coded levels     -0+-   +00+   0-   000-   +00+
When the rec eiver d etec ts the 100V string  or the 000V string, it rep lac es it with 
0000.
Note that HDB3 is the line c od ing  tec hniq ue used  b y most CEPT1 c ountries with 
a 2.048 mbps primary rate. HDB3 encoding and decoding is performed by 
CEPT1 DACS, MX3 multip lexors, ASSET III, and  2.048 mb p s satellite mod ems at 
the earth stations.
Restricted and Unrestricted Facilities and Data
A restric ted  fac ility is a DS1 or CEPT1 sp an, inc lud ing  the interfac e b oard s at 
eac h end , that p erforms zero c od e substitution at some p oint in the sp an. For 
examp le, in the U.S., many T1 fac ilities have line rep eaters that use zero c od e 
suppression. These facilities are c alled restricted because they restrict the type 
of information that c an b e transp orted  on them without b eing  c orrup ted . 
Sp ec ific ally, d ig ital d ata that c ontains an all 0s b yte c annot b e transp orted  over 
restric ted  fac ilities without b eing  c orrup ted. All other fac ilities, i.e., fac ilities 
having  line c od ing other than ZCS, are unrestric ted . Terms often c onfused  with 
restric ted /unrestric ted  fac ilities are restric ted /unrestric ted  d ata.
Unrestric ted  d ata is d ata that must b e transp orted  over unrestric ted  fac ilities to 
remain unc orrupted  b ec ause it d oes not meet the 1s density req uirements. For 
end p oints on the DEFINITY systems, mod e 0 d ata, whic h is 64 kb p s d ata with no 
p rotoc ol pac kag ing , mode 3, whic h is 64 kb p s data p ac kag ed  in non-inverted  
LAPD p rotoc ol, and  wid eb and , whic h is the same as mod e 0 but at rates that are 
multip les of 64 kb ps, are the only typ es of unrestric ted  d ata. Furthermore, 
end p oints on mod e 0 d ata mod ules c an pac kag e the d ata in an HDLC p rotoc ol 
that c an b e inverted  and  the mod e 3 b it stream c an b e inverted  with an op tion or 
a c ab le, b oth of whic h result in restric ted  d ata.
Restric ted  data is any data that meets 1s density req uirements b y never send ing  
an all zero b yte, and  thus c an b e transp orted  over either restric ted  or 
unrestric ted  fac ilities. For end points on the DEFINITY systems, mod e 1 and  
mod e 2 meet the 1s d ensity req uirements and  thus are restric ted  d ata. Mod e 1 
d ata meets 1s d ensity req uirements bec ause one c ontrol b it exists in every b yte 
and  this b it is always 1. Mod e 2 d ata meets 1s d ensity req uirements b ec ause the 
user data is p ac kag ed  in inverted  HDLC p rotoc ol. When HDLC or LAPD is 
inverted  (all 0s c hang ed to 1s and  all 1s c hang ed  to 0s), 1s d ensity is always  
						

							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 4-22 Line Coding 
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ac hieved . Mod e 3 d ata is restric ted  if it is inverted b ec ause it is p ac kag ed  in an 
un-inverted LAPD protocol.
NOTE:
The terms restric ted  d ata and  unrestric ted data are c onfusing  b ec ause 
restric ted  d ata is d ata that c an b e transp orted over any fac ility and  is thus 
less restric ted  (in an intuitive sense) than unrestric ted  d ata, whic h is 
restric ted  to b eing  transp orted  over unrestric ted  fac ilities.
The following  tab le shows the relationship  b etween restric ted /unrestric ted  
fac ilities and  d ata:
NOTE:
If you ad minister B8ZS or HDB3 at the end p oints b ut send the data over 
fac ilities that are restric ted  somewhere b etween the end p oints, the d ata will 
b e c orrup ted  b ec ause the line rep eaters will not p ass the b ip olar violations 
throug h unaltered .
Tab le 4-8
 summarizes the c ap ab ilities of various narrowb and  d ata end p oints 
sup p orted  on DEFINITY systems:Restric ted  Data (mode 2, 
mod e 1 inverted  mode 3)Restricted Facility 
(ZCS ad ministered )Unrestric ted  Fac ility 
(B8ZS, HDB3, or none 
ad ministered )
Uncorrupted Uncorrupted
Unrestric ted  Data (mod e 
0, mode 3, wideband)Corrupted Uncorrupted
Table 4-8. Data Modules Capabilities 
Data ModuleDMI 
ModeUser Data 
Rate Sync Async Bit InvertProtocol 
Packaging Handshake Comments
7400 HSL 0 64 kb p s yes no op tion none none
1 56 kbp s yes no no DDS none
7400 series 2 to 19.2 kb p s No Yes Yes HDLC Mod e 2
DTDM 2 to 19.2 kb p s Yes Yes Yes HDLC Mod e 2
AUDIX CMS 
MPDM2 to 19.2 kb p s Yes Yes Yes HDLC Mod e 2
Other 
MPDMs0 64 kb p s Yes No Yes No None Note 2
1 56 kb p s Yes No No DDS None Note 2
Continued on next page 
						

							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 4-23 Line Coding 
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Notes:
1. The mod e-2 hand shake will not work over other than 64-kb p s fac ilities (for 
example, robbed-bit facilities). 
2. Other MPDMs are the High Speed  Sync hronous MPDM and the Vid eo 
Teleconferenc ing  MPDM. The only difference b etween them is that the Vid eo 
Teleconferenc ing  MPDM has an RS-366 interfac e for keyb oard  dialing . Both 
MPDMs p rovid e a V.35 interfac e for information interc hang e.
3. Mod e 3/2 ad aptive means that a mode-3 hand shake is attemp ted  first. An 
algorithm is then followed  to determine the far-end’s d ata mod e and  either switc h 
to mode 2 or continue in mod e 3.
3270 A  2 to 9.6 kb p s Yes Yes Yes HDLC Mod e 3/2 
adaptNote 3
3 64 kb p s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3/2 
adaptNote 4
3270 T  3 64 kb p s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3 Note 4
PC/PB X 
Connec tion 
with ASCII 
terminal 
emulation2 to 19.2 kb p s No Yes Yes HDLC Mod e 3/2 
adapt or 
Mod e 2Note 5
3 64 kb p s No Yes Yes LAPD/X.25 d ata 
phaseMod e 3/2 
adapt
PC/PB X 
w/3270 
emulation3 64 kb p s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3 Note 5
7500 series 
BRI sets & 
ADM-T0 64 kbp s Yes No No None None
1 56 kb p s Yes No No DDS None
2 to 19.2 kb p s Yes Yes Yes HDLC Mod e 3/2 
adaptNote 6
3 64 kb p s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3/2 
adaptNotes 7, 8
3/2 64 kb p s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3/2 
adaptNotes 7, 8
PC/ISDN 
Platform with 
3270 
emulation3 64 or 56 
kbp sYes No Yes o r No  
(op tion)LAPD/X.25 d ata 
phaseMod e 3 Note 9
PC/ISDN 
Platform with 
ASCII 
terminal 
emulation2 to 19.2 kb p s No Yes Yes HDLC Mod e 3/2 
adapt or 
Mod e 2 Note 10
3 64 or 56 
kbp sYes No Yes o r No  
(op tion)LAPD/X.25 d ata 
phaseMod e 3 Note 10
Constellation 3 64 kbp s Yes No Yes LAPD/X.25 d ata 
phaseMod e 3
Table 4-8. Data Modules Capabilities  — Continued
Data ModuleDMI 
ModeUser Data 
Rate Sync Async Bit InvertProtocol 
Packaging Handshake Comments
Continued on next page 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
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July 1993
Physical Layer 
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4. Mod e-3 d ata c an only b e c irc uit-switched in Generic  2.2 and  G3V2 systems. Also, 
mod e 3 on the 3270 A and 3270 T req uires a 3270 C on the far-end .
5. Mod e 2 on the PC/PBX c onnec tion is supp orted  und er the ASCII terminal 
emulation p ac kag e. The PC/PBX c onnec tion in mode 2 uses a mod e-3/2 ad ap tive 
hand shake if the b it rate is set at 64 kb p s. If the rate is set at 19.2 kb ps or slower, a 
mod e-2 hand shake is used . 3270 emulation on the PC/PBX connection req uires a 
3270 C data mod ule on the far-end. Mod e-3 op eration is d efined  as sync hronous 
when in 3270 emulation; otherwise, it is d efined  as async hronous. 
6. Mod e 2 on the 7500 series is imp lemented  in the inc oming  (to the 7500) d irection 
only. Outg oing  c alls requiring  mod e-2 speeds use the mod e-3/2 ad aptive bearer 
c apab ility.
7. On outg oing  mode-3 and mod e-3/2 ad aptive calls, the 7500 series always inverts 
b its. On incoming mod e-3 and  mod e-3/2 ad ap tive c alls, the 7500 series c hec ks 
the restric tion bit in the low-layer c ompatibility information element (IE) and  either 
inverts or does not invert, d ep end ing  on the c ontents of the IE. This is not done for 
incoming mod e-0 c alls, however.
8. The alg orithm for the mod e-3/2 hand shake is d ifferent for DCP data mod ules and 
the 7500. When called , the 7500 d ata mod ule starts a mod e-3 handshake. If it 
receives a mod e-3 or mode-2 hand shake from the c alling  end within a sp ecified  
numb er of second s, it switc hes to that mod e. Otherwise, it switc hes to mod e 2. If it 
d oes not receive a mod e-2 hand shake within 15 more sec ond s, it times out and  
d rop s the c all.
9. Options exist on the PC/ISDN Platform with 3270 emulation to allow the user to 
c hoose either 56 kbp s or 64 kbp s and  to choose to invert or not invert bits. The PC 
ISDN Platform with 3270 emulation req uires a 3270 C d ata mod ule on the far-end .
10. Options exist on the PC/ISDN Platform with ASCII terminal emulation to allow the 
user to choose either 56 kb ps or 64 kbp s and  to c hoose to invert or not invert b its. 
Either mode-3/2 adap tive or mode-2 hand shakes are used d epending on the 
b aud -rate op tion setting . If the setting  is 19.2 kb p s or slower, a mod e-2 handshake 
is used . Mod e-3 op eration is d efined  as synchronous when in 3270 emulation; 
otherwise it is async hronous. 
For c omp lete d efinitions of the DMI mod es 0, 1, 2, and 3, refer to 
Dig ital 
Multip lexed Interfac e (DMI) Tec hnical Sp ec ific ation
, selec t cod e 500-029. Ask for 
the most recent issue. 
Bit Inversion on ISDN PRI D Channels
ISDN PRI D c hannels are c omp osed  of d ig ital d ata that must not b e c orrup ted . 
When transp orting  the D c hannel over restric ted  fac ilities, however, ZCS must b e 
ad ministered , whic h will c orrup t the d ata. To guarantee 1s d ensity on the D 
c hannel without c orrup ting  the d ata, all DEFINITY systems automatic ally invert 
the outg oing  and  inc oming  b it stream on the D c hannel when ZCS is 
ad ministered . This works b ec ause the D c hannel uses the LAPD p rotoc ol, whic h 
g uarantees 1s d ensity when inverted . Exc ept for G2.2, the D c hannel is left 
uninverted  for all line c od ing s other than ZCS. In G2.2, if B8ZS is ad ministered  
you have the op tion in p roc ed ure 260, word  1, field  15, to invert or not invert the 
D c hannel. 
						

							DEFINITY Communications System Generic 2.2 and Generic 3 V2 
DS1/CEPT1/ISDN PRI Reference  
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July 1993
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NOTE:
It is rec ommend ed  that the D c hannel not b e inverted  if B8ZS is 
ad ministered .
G2.2 Line Coding Implementation
G2.2 imp lements line c od ing  in p roc ed ure 260, word1, field 9. This 
ad ministration is req uired for all DS1-b ased  trunk b oard s, inc luding  those in the 
universal mod ule. You c an c hoose either B8ZS or ZCS in this field . If unrestric ted  
d ata (d ata not meeting  the 1s density requirement) is to b e transported  over any 
c hannels on the b oard , you must administer B8ZS and also ensure that the 
fac ility is unrestric ted  end -to-end . If the end -to-end fac ilities are restric ted , ZCS 
must b e ad ministered , in whic h c ase you will not be ab le to send  unrestric ted  
d ata without it b eing  c orrup ted . You c an send  restric ted  d ata over either 
restric ted  or unrestric ted  fac ilities.
G3V2 Line Coding Implementation
In G3V2 systems, if the CEPT1 (2.048) b it rate is ad ministered , you c an also 
c hoose none
 to have AMI-only line c od ing , whic h d oes nothing  to g uarantee 1s 
d ensity requirements, or you c an c hoose hdb3
 for HDB3 line c od ing . If the DS1 
(1.544) b it rate is ad ministered, you c an administer either b8zs
 or zcs
. As with 
B8ZS, if HDB3 line c od ing  is used , the fac ilities must b e HDB3-c omp atib le 
end -to-end , whic h means unrestric ted  fac ilities.
Line Compensation
Line c omp ensation is the method  used  to ensure that the shap e of eac h p ulse in 
the DS1/CEPT1 b it stream at the terminating end  of the c ab le is within the 
sp ec ific ations of PUB 62411, 
ACCUNET T1.5 Servic e Desc rip tion and  Interfac e 
Sp ec ific ation
. Elec tric al c harac teristic s of a c ab le p lus the c ab le’s leng th d istort 
the p ulse. A c hip  on the DS1 or CEPT1 c irc uit p ac k mod ifies the p ulse, 
d epend ing  on the leng th of the c ab le, so that the p ulse is the c orrec t shap e by 
the time it reac hes the end  of the c ab le.
G2.2 trad itional modules, whic h use either the ANN11C or ANN35, imp lement 
line c omp ensation as hard ware switc hes on the b oards. See the ‘‘ANN11C and  
ANN35 Line Compensation Jumper Settings’’ sec tion in Chapter 3, ‘‘Eq uip ment 
and  Software Requirements’’ for these settings. On G2.2 universal mod ules that 
use the TN722 or TN767, line c omp ensation is ad ministered in proc ed ure 260, 
word  1, field  18. The value entered  in this field  should  b e set to the leng th of the 
c ab le from the DS1 c irc uit p ac k to the CSU. If the c ab le is c onnec ted  to another 
DS1 interfac e that also performs line c omp ensation, the value should  b e set to 
one half the leng th of the c able.
In G3V2 systems, line c omp ensation ap p lies only to DS1 (1.544 mb ps) 
interfac es. G3V2 systems imp lement this c ap ab ility in the DS1 c irc uit p ac k form.  
						

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The value entered  into the Line Compensation
 field  of this form should  b e set 
to the leng th of the c ab le from the DS1/CEPT1 c irc uit p ac k to the CSU. If the 
c ab le is c onnec ted  to another DS1/CEPT1 interfac e that also p erforms line 
c omp ensation, the value should  b e set to one half the leng th of the c ab le.
Idle Code
Idle c od e is the eig ht-b it seq uenc e that oc c up ies the time slot on a DS1/CEPT1 
trunk c hannel when it is not b eing  used . In G2.2 this idle c od e is always 
11111111. In G3V2 systems, however, this item c an b e ad ministered  to b e any 
p attern of 0s and  1s. The DS1 Circ uit Pac k form has a field  c alled  Idle Code
 
that allows you to enter the d esired  c od e. The following  list shows a few 
examp les of the idle c od e for sp ec ific  c ountries; for c ountries that do not d efine 
the id le c od e, the user must d ec id e whic h one to administer.
United States  11111111
Australia      11111111
Italy          01010100
Japan          at least 3 1’s must be administered
NOTE:
On DS1 b oard s ad ministered for rob b ed  b it sig naling , the A or B b it, whic h 
oc c urs every sixth frame, will always b e 0 when id le. In G2.2, you c an forc e 
this b it to 1 b y d isab ling  sig naling  in p roc ed ure 116, word  1, field  8 (enter 
1
). In G3V2 systems, the only way to forc e this b it to 1 is to maintenanc e 
b usy out the c hannel. When the switc h is reinitialized, however, the c hannel 
will b e released  from its b usyout state.
The Digital Loss Plan
Transmission loss is the total of all losses and  g ains (measured  in d ec ib els) from 
one end  of a c onnec tion to the other. Distrib uted  transmission losses as well as 
any connec tion loss inserted  b y the switch are inc luded . Transmission loss is 
req uired  so that talker ec ho is minimized . Furthermore, transmission loss must b e 
kep t low enoug h so that sp eec h volume is p erc eived  as ad eq uately loud . Two 
d ifferent loss p lans are availab le. They are known as:
nVia-net loss (VNL), whic h has trad itionally b een used  to assig n losses for 
analog  c irc uits terminating  on an analog  switc h
nDig ital loss, whic h is used  to assig n losses for d ig ital c irc uits terminating  
on a digital switch
The introd uc tion of dig ital switc hing  systems and  dig ital trunk fac ilities 
p ermit more flexib le c ontrol of the switc h c onnec tion loss (insertion loss) 
and  thereb y transmission p erformanc e. From the network p ersp ec tive, 
transmission performance becomes entirely a function of the port-to-port 
losses (total loss) from all switc hes in the transmission link.