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This is an Accep ed Manusc ip o an con e ence pape published by IEEE:
J. Muñoz-Calle, A. J. Sie a and J. M. Vozmediano, "Emula ion o ISDN mul i-
channel ci cui -mode bea e se ices in nex gene a ion ne wo ks by TDM
pseudo-wi es," 2012 Nex Gene a ion Ne wo ks and Se ices (NGNS), Fa o,
Po ugal, 2012, pp. 149-156, doi: 10.1109/NGNS.2012.6656094
“© 2012 IEEE. Pe sonal use o his ma e ial is pe mi ed. Pe mission om IEEE
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euse o any copy igh ed componen o his wo k in o he wo ks.”
Emula ion o ISDN Mul i-channel Ci cui -mode
Bea e Se ices in Nex Gene a ion Ne wo ks by
TDM Pseudo-Wi es
Ja ie Muñoz-Calle, An onio J. Sie a, Juan M. Vozmediano
Depa amen o de Ingenie ía Telemá ica
Uni e sidad de Se illa
C/ Camino de los descub imien os s/n. Se illa
{ja i,an onio,j }@ ajano.us.es
Abs ac — The speci ica ions o he Nex Gene a ion Ne wo ks
1
(NGN) ag ee on he need o mig a ion mechanisms ha enable
2
he eplacemen o adi ional ne wo ks, highligh ing he ISDN
3
ne wo ks. This equi emen has a no able impac on NGN in
4
e ms o ne wo k design. Recen solu ions p oposed by ITU-T
5
and ETSI o ISDN mig a ion only include suppo o a subse
6
o cu en ISDN se ices, no co e ing in de ail he mul i-channel
7
ci cui -mode bea e se ices. This pape examines he use o
8
TDM pseudowi es o NGN emula ion o ISDN mul i-channel
9
calls be ween ISDN e minals, p oposing new payload ypes.
10
Keywo ds-Mul i-channel se ice, ISDN bea e , NGN, Pseudo-
11
wi e
12
I. INTRODUCTION
13
The Nex Gene a ion Ne wo k P ojec aims o c ea e a
14
unique packe -swi ched ne wo k ha in eg a es any exis ing o
15
u u e se ice [1]. The p og ess o he NGN p ojec is being
16
d i en by bo h economic and s anda diza ion easons [2]. Thus,
17
ope a o s will bene i om an e icien and seamless
18
in eg a ion be ween cu en use equipmen and ne wo ks [3;
19
4], mos no ably In eg a ed Se ices Digi al Ne wo k (ISDN)
20
ne wo ks.
21
ISDN has been he las s ep in he e olu ion o he public
22
swi ched elephone ne wo k. I was o iginally designed o
23
suppo any ype o oice o da a se ice o e a ull-digi al
24
ne wo k. The b oad ange o se ices o e ed by ISDN is
25
suppo ed o e h ee ypes o bea e se ices, namely he
26
ci cui -mode, ame-mode and packe -mode. These se ices a e
27
also classi ied in o single and mul i-channel as used on each
28
call one o mo e B channels, espec i ely. The igidi y o he
29
unde lying channelized bi - a e s uc u e and he lack o
30
lexibili y in building new, complex se ices ha e inally made
31
ISDN unsui able o he as de elopmen and p o ision o ich
32
mul imedia se ices which con e sely, ha e been apidly
33
de eloped on he In e ne .
34
Fo backwa ds compa ibili y, he NGN mus suppo
35
po en ially e e y ISDN bea e se ice (ITU-T I.230 se ies)
36
wi h he same o highe QoS [5; 6]. Consequen ly, bo h he
37
ITU-T and he ETSI ha e de ined s anda dized mechanisms o
38
he anspa en in eg a ion o ISDN e minals (ISDN TEs).
39
This backwa ds compa ibili y is also equi ed wi hin he
40
Eu opean no ma i e [7]. The Eu opean di ec i e on Uni e sal
41
Se ice [8] s a es ha , a leas one ope a o Elec onic
42
Communica ion Ne wo k (ECN) mus ensu e access o Publicly
43
A ailable Telephone Se ice (PATS) a ixed loca ions such as
44
ISDN, PSTN, X.25, ... Fu he mo e, he speci ica ion [9]
45
highligh s he u gen need o a icula e he necessa y
46
speci ica ions ha would mee hose obliga ions. These
47
egula ions applied o ISDN equi e ha he ope a o 's ne wo k
48
allows access o na i e ISDN e minals.
49
The solu ions o e ed by ITU-T and ETSI o encapsula e
50
ISDN signalling and use lows ac oss he NGN ne wo k use
51
anspo o applica ion-laye p o ocols. The p oposal done by
52
ITU-T [5; 10] is limi ed o ISDN ci cui -mode bea e se ices
53
whe eas he ETSI p oposal [11] adds pa ial suppo o ame
54
and packe -mode se ices. Fo ISDN mul i-channel ci cui -
55
mode bea e se ices, he ITU-T [6] ecognizes ha he e a e
56
s ill la ge esidual amoun o ISDN use equipmen ha use
57
hese se ices, and he e o e hey mus be suppo ed. Bu ,
58
conce ning hese se ices, NGN speci ica ions made only wo
59
commen s, ela ed o hei anspo on he NGN, as desc ibed
60
below. On he one hand, he ITU-T [6] indica es ha he
61
anspo o he "N" channels o he se ice mus be pe o med
62
on a single IP low, o ensu e equal condi ions o all
63
ansmission channels. On he o he hand, pu ely acul a i e,
64
ITU-T Recommenda ions [5; 12; 13] p opose o ca y hese
65
se ices by using ITU-T TDMoIP in e wo king [13; 14],
66
equi alen o UDP/IP-based TDM pseudo-wi es (TDMPW)
67
[15], wha sa is ies indica ed by he Recommenda ion [6].
68
Abou hese indica ions, we mus make he ollowing
69
assessmen s. In he i s place, ITU-T TDMoIP in e wo king is
70
only de ined o UDP/IP, while IETF de ines TDMPWs o
71
di e en unneling mechanisms apa om UDP-IP, such as
72
MPLS, L2TP 3/IP o E he ne . So, TDMPWs a e p e e ed.
73
In he second place, he ITU-T only men ions he use o
74
TDMoIP in e wo king (o TDMPWs), bu i is no de ailed
75
how o apply hem. I is necessa y o de e mine i each
76
TDMPW mus ca y one o se e al ISDN calls, o he
77
TDMPW ype and payload mo e app op ia e. A e analysis,
78
we conclude ha as hey a e s anda dized, none o he
79
TDMPWs i s he emula ion o hese mul i-channel calls. I
80
will be necessa y o p opose new ypes o TDMPW payload.
81
This pape p oposes o anspo ISDN mul i-channel
82
ci cui -mode bea e se ices [17-21] be ween wo ISDN
83
e minals by AAL2 TDMPWs (UDP/IP-based o any o he
84
packe swi ched ne wo k) wi h new payload ypes we de ine.
85
The es o his pape is o ganized as ollows. Nex sec ion
86
p o ides a shallow in oduc ion o ISDN mul i-channels calls,
87
ISDN emula ion on NGN and TDM pseudo-wi es. Sec ion III
88
add esses an analysis o he TDMPWs o anspo ISDN
89
mul i-channel se ices on he NGN. Finally, Sec ion IV
90
concludes he pape .
91
II. BACKGROUND
92
A. ISDN Mul i-channel Ci cui -mode Bea e Se ices
93
ISDN ansmission capaci y is o e ed in a combina ion o
94
se e al ypes o ixed- a e channels, one o which (B channel)
95
was specially ailo ed o ca y oll-quali y digi alized oice.
96
The ISDN also pionee ed he concep o spli ing use and
97
con ol da a lows, he la e we e enclosed in D channels. The
98
b oad ange o se ices o e ed by ISDN is suppo ed o e
99
h ee ypes o bea e se ices, namely he ci cui -mode, ame-
100
mode and packe -mode. These se ices a e also classi ied in o
101
single and mul i-channel as used on each call one o mo e B
102
channels, espec i ely.
103
Mul i-channel ISDN se ices ("N" B-channels) equi e UDI
104
(Un es ic ed Digi al In o ma ion) anspo [22] and TSSI
105
(Time Slo Sequence In eg i y) s uc u e. In pa icula , he
106
se ice 2x64 [17] also equi es RDTD (Res ic ed Di e en ial
107
Time Delay) s uc u e.
108
Wi h UDI anspo , e minals can exchange any
109
in o ma ion, nego ia ed be ween hem, anspa en ly o he
110
ne wo k. RDTD se ice s uc u e means ha i wo samples a e
111
ansmi ed a he same ime ( o any wo di e en channels o
112
se ice), hey mus each he des ina ion wi h a delay o no
113
uppe han "50 ms". TSSI s uc u e means ha in o ma ion
114
mus be deli e ed o he des ina ion in he same o de be ween
115
channels when i was sen .
116
B. ISDN emula ion in NGN
117
The ITU-T aims o de ine a wo ld-wide ne wo k
118
in as uc u e capable o suppo ing cu en and u u e
119
elecommunica ion se ices and ne wo k echnology. The Nex
120
Gene a ion Ne wo k model, as s anda dized by he ITU-T in
121
[23], is he las s ep on ha di ec ion. Bo h he ITU-T and he
122
ETSI ha e coope a ed o de elop he NGN a chi ec u e.
123
The NGN unc ional a chi ec u e exhibi s a anspo
124
s a um and a se ice s a um. The anspo s a um p o ides
125
IP connec i i y, hiding he co e and access ne wo ks’
126
echnologies. I also agg ega es use a ic o be anspo ed
127
o e he co e ne wo k, con ols, alloca es ne wo k esou ces
128
and p o ides suppo o ne wo k con ol and managemen .
129
The se ice s a um esides abo e he IP laye , con aining
130
use s’ p o iles, auxilia y applica ions and as many se ice-
131
suppo ing con ol- unc ions as needed. These con ol unc ions
132
ope a e he anspo s a um o p o ide he desi ed se ice.
133
Among he se ice-con ol unc ional componen s iden i ied in
134
he Se ice s a um a e: he IPTV, which p o ides IP-based
135
ele ision se ices; he IMS, which p o ides SIP-con olled
136
mul imedia se ices; and he PTSN/ISDN Emula ion
137
Subsys em (PES).
138
The e a e wo al e na i e a chi ec u es o implemen ing
139
PES, depending on Access Ga eways (AGW) be implemen ed
140
ei he monoli hically (Voice Ga eway, A-VGW) o in a
141
decomposed way (Ga eway con olle MGC and Media
142
Ga eway A-MGW) [10], as shown in Figu e 1. The i s one is
143
based on a so-called call se e (CS-PES) whe e a Media
144
Ga eway Con olle (MGC) e mina es he ISDN signaling and
145
acco dingly con ols he Access Media Ga eway ia MeGaCo
146
[24]. In he second choice, he ISDN signaling is e mina ed a
147
an Access Voice Ga eway which uses SIP signaling o
148
communica e wi h he IMS’s Call Session Con ol Func ions
149
(CSC-FE).
150
151
C. TDM Pseudo-wi es
152
IETF de ines pseudo-wi es (PWs) [16; 25] as a mechanism
153
o allow he emula ion o elecommunica ions se ices o e a
154
Packe Swi ched Ne wo k (PSN) h ough i ual connec ions
155
ha , om he use 's poin o iew, p o ides he same se ice
156
han he o iginal ci cui o link. The emula ion p ese es he
157
essen ial a ibu es o he o iginal se ices such as oice
158
quali y, delay, iming and signaling ea u es. Each pseudo-wi e
159
is es ablished be ween an ing ess and an eg ess PE (P o ide
160
Edge).
161
Depending on he unneling mechanism, di e en ypes o
162
pseudo-wi es a e de ined: UDP/IP, L2TP 3/IP, MPLS,
163
E he ne . As a ma e o ac , he UDP/IP PWs a e equi alen o
164
TDM o e IP in e wo king de ined by ITU-T [13]. This ype o
165
pseudo-wi e, albei simple, lacks o a con ol plane, able o
166
nego ia e connec ion pa ame e s a connec ion-se up ime, such
167
as he payload ype, ji e bu e 's size, he iming eco e y
168
mechanism o he a ic ype. So, o he ypes o pseudo-wi es
169
Figu e 1. Simpli ied NGN a chi ec u e
may be mo e sui able o a p ac ical implemen a ion. In
170
gene al, he choice o he ype o PWs is dependen on he
171
ope a o 's ne wo k.
172
TDM pseudo-wi es (TDMPWs) [15] can emula e he main
173
ea u es o a ime-di ision mul iplexed link: ame and mul i-
174
ame synch oniza ion (when needed), iming eco e y a he
175
ou pu end, complying wi h he pa h MTU, and simul aneous
176
anspo o se e al TDM lows. Depending on he o ma o
177
he payload, join ly de ined by IETF and ITU-T, he e a e wo
178
ypes o TDMPWs (Figu e 2).
179
180
The anspa en o s uc u e-independen TDMPWs ake he
181
TDM signal as a con inuous s eam o bi s (wi hou in e p e ing
182
any ame s uc u e ha i may ha e) anspo ing i
183
comple ely, including o e head and da a/signalling channels
184
o channelized ci cui s, so ha each TDMPW emula es a ull
185
TDM ci cui . Two TDMPWs o his ype a e de ined: SAToP
186
[13; 26] and anspa en AAL.1 TDMoIP [14; 27].
187
In he s uc u e-awa e o SDT (S uc u ed Da a T anspo )
188
TDMPWs, he ing ess PE mus unde s and and in e p e he
189
ame s uc u e o he TDM signal, and can ead/manipula e
190
TDM o e heads and signalling, which ensu es he alignmen
191
and in eg i y o he TDM ame s uc u e and p o ides mo e
192
obus ness o PSNs wi h highe packe loss a e. These
193
TDMPWs a e classi ied in wo sub ypes:
194
S a ic: hey p o ide CES (Ci cui Emula ion Se ice)
195
[28]. Two TDMPWs o his ype a e de ined:
196
CESoPSN [13; 29] and AAL1 TDMoIP wi h SDT [14;
197
27].
198
Dynamic: hey p o ide LES (Loop Emula ion Se ice)
199
[30]. IETF only de ines a TDMPW o his ype,
200
e e ed as AAL2 TDMoIP [14; 27; 31]. TDM
201
channels may belong o di e en unks, iden i ying
202
each pai "in e ace, channel" h ough a CID (Channel
203
Iden i ie ). The TDMPW payload is illed by an
204
in ege numbe o AAL2 (ATM Adap a ion Laye )
205
minicells [32]. Each AAL2 minicell is illed wi h a
206
SSCS PDU, buil i om he by es o he TDM channel
207
iden i ied by he CID assigned o ha minicell.
208
The con ol plane o he AAL1/2 TDMoIP ypes has
209
only been ully s anda dized o MPLS TDMPWs [31].
210
III. TRANSPORT OF MULTI-CHANNEL CALLS BETWEEN ISDN
211
TERMINALS BY USING TDMPWS
212
ISDN mul i-channel se ices can be anspo ed on he
213
NGN h ough TDMoIP in e wo king lows (as p oposed by
214
ITU-T) o , p e e ably, by TDMPWs, de ined o se e al
215
unnelling mechanisms. This p oposal only applies o calls
216
be ween wo ISDN e minals, es ablishing he TDMPW among
217
hei espec i e AGWs (Figu e 3).
218
219
A. Mul iplexing o calls on each TDMPW
220
In all s anda d ISDN mul i-channel bea e se ices (ITU-T
221
I.230 se ies), a ious B channels in ol ed in one call, belong o
222
he same ISDN UNI (Use -Ne wo k In e ace). Consequen ly,
223
he "N" B-channels o a mul i-channel call mus be anspo ed
224
on he same TDMPW, sa is ying indica ed by he
225
Recommenda ion [6] (among di e en TDMPWs he e is no
226
sequencing o iming ela ionship).
227
Ins ead o using an independen TDMPW each ISDN call,
228
i is mo e e icien o concen a e se e al calls (single o mul i-
229
channel, and pe manen o swi ched) on he same TDMPW
230
(Figu e 4). Calls a e mul iplexed on he same TDMPW un il
231
comple e i s capaci y, in which case ano he TDMPW be
232
es ablished. This p o ides a lowe o e head in he da a plane
233
( he same IP and CW Con ol Wo d heade s o mul iple calls)
234
and a lowe numbe o messages in he con ol plane ( ewe
235
TDMPWs).
236
237
Al hough TDMPWs a e designed o be es ablished p io o
238
he es ablishmen o calls (managemen plane), hey can be
239
es ablished in call ime (con ol plane) i i o e s a signi ican
240
ad an age. Fo swi ched ISDN calls, he es ablishmen o
241
TDMPWs be o e calls equi es he es ablishmen o a mesh o
242
TDMPWs be ween all he AGWs o ope a o , which is no
243
easible o easons o scalabili y. Consequen ly, unless he e
244
a e pe manen calls, he es ablishmen o he TDMPW will be
245
based on he con ol signaling o swi ched calls.
246
Fo he mul iplexing o calls, i should be no ed ha :
247
Figu e 2. TDMPW axonomy
TDMPW
T anspa en
SDT S a ic
Dynamic
•CEsoPSN
•AAL1 TDMoIP wi hSDT
•AAL2 TDMoIP
•SAToP
•AAL1 TDMoIP wi hou SDT
TDMPW
T anspa en
SDT S a ic
Dynamic
•CEsoPSN
•AAL1 TDMoIP wi hSDT
•AAL2 TDMoIP
•SAToP
•AAL1 TDMoIP wi hou SDT
Figu e 3. Mul i-channel call be ween wo ISDN e minals using
TDMPWs
Figu e 4. ISDN ci cui -mode calls mul iplexed on a TDMPW
Mul i-channel o un es ic ed single-channel [33]
248
ci cui -mode se ices: hey equi e UDI anspo o e
249
he IP ne wo k, and so RTP PT (Payload Type)
250
CLEARMODE [34] wi hou Voice Ac i i y De ec ion
251
(VAD).
252
Voice single-channel ci cui -mode se ices: hey allow
253
anscoding om G.711 o any o he codec, as well as
254
inco po a ing VAD a any codec. The o me should be
255
a oided in mos cases, because o he in ol ed
256
anscoding delays [43]. Fo he la e , mo e desi able
257
because i sa es bandwid h, i is ad isable ha he
258
eg ess PE gene a es com o noise du ing silence
259
pe iods. This equi es ha he ing ess PE sends he
260
p ope com o noise pa ame e s using SID (Silence
261
Inse ion Desc ip o ) ames, iden i ied by he PT
262
Com o Noise Gene a ion (CNG) [35].
263
No e ha he di e en calls mul iplexed wi hin he
264
TDMPW may use di e en payload ypes, so he payload ype
265
indica o mus a el along he samples.
266
B. Choosing he ype o TDMPW
267
When choosing he ype o TDMPW, we ha e o disca d
268
he anspa en ones, because hey only allow o emula e
269
comple e in e aces, wi hou iden i ying hei elemen a y
270
channels.
271
The s uc u e-awa e TDMPWs can only ca y he “N” B-
272
channels o a Nx64 mul i-channel call. PEs ( hei Na i e
273
Se ice P ocesso s) will need o suppo he ISDN physical
274
ame o ma , bo h p ima y and basic UNIs V [37] in e aces,
275
acco ding o each ope a o ’s p e e ence. Since he PEs would
276
be loca ed on he AGWs esponsible o he e mina ing ISDN
277
in e aces, i seems easonable o assume his condi ion
278
sa is ied.
279
Among he di e en ypes o s uc u e-awa e TDMPWs,
280
he s a ic (CESoPSN and AAL1 TDMoIP wi h SDT) a e no
281
sui able o he ollowing easons.
282
Fi s , as hey ha e no VAD (Voice Ac i i y De ec ion)
283
suppo , hey ca y e en he idle channels, which ep esen s an
284
ine icien use o bandwid h.
285
Secondly, hey do no adequa ely suppo he concen a ion
286
o pe manen o swi ched calls:
287
Swi ched calls a e dynamically se up and eleased,
288
hus modi ying he agg ega ed numbe o ac i e
289
channels. Howe e , TDMPWs a e usually se up a
290
managemen ime, be o e any call is es ablished,
291
making i impossible o ollow he u u e a iyng
292
capaci y demanded by he calls.
293
Pe manen calls a e es ablished in managemen ime,
294
as TDMPW a e, howe e , when adding o dele ing a
295
new pe manen call, i would be necessa y o ea down
296
and e-es ablish he TDMPW, in e up ing he se ice
297
o he exis ing calls.
298
As opposed o s a ic TDMPWs, he dynamic s uc u e-
299
awa e TDMPWs (AAL2 TDMoIP) can emula e se ices wi h
300
channels om di e en in e aces, and can dynamically modi y
301
he numbe o ca ied channels. Mo eo e , i s con ol plane
302
may nego ia e be ween bo h PEs he oice p ocessing o apply
303
o he anspo ed channels, such as VAD.
304
F om he abo e analysis, we may conclude ha he only
305
sui able way o emula e he ISDN mul i-channel calls a e he
306
AAL2 TDMoIP TDMPWs
307
C. AAL2 TDMPW payload o ma
308
Acco ding o he de ined AAL2 TDMoIP payloads a [27;
309
30], each TDM channel is assigned a unique CID. An Nx64
310
mul i-channel call will use “N” CIDs. This payload o ma is
311
no alid o emula ing mul i-channel calls, as is discussed
312
below.
313
In a mul i-channel call, he ISDN sou ce e minal gene a es
314
a low o “Nx64 Kb/s” a e. In he ISDN in e ace, he low is
315
con eyed on "N" 1x64 kbps B-channels, so ha each TDM
316
ame o he ISDN in e ace ca ies "N" samples o ha low
317
(“N” channels i ually beha e as a single channel o a e
318
“Nx64”). The 2x64 se ice, wi h i s dis inc i e RDTD
319
s uc u e, ep esen s an excep ion o his ule: his se ice is
320
designed o suppo s e eo oice calls, so he wo channels mus
321
be anspo ed o he emo e e minal in pa allel, and samples
322
om each channel a he sou ce should always be deli e ed o
323
he same channel a he des ina ion.
324
Fo he emula ion o a mul i-channel call o be co ec , he
325
des ina ion e minal should be able o econs uc he same
326
low as sen by he sou ce e minal. Howe e :
327
To ensu e a cons an end o end delay, ega dless o he
328
bi a e o he emula ed se ice, each AAL2 TDMPW
329
packe includes he numbe o minicells ha allows
330
p ese ing his delay, depending on he channel
331
ac i i y. Consequen ly, a a mul i-channel call,
332
samples om wo o i s channels in he same TDM
333
ame can be sen in se e al TDMPW packe s.
334
AAL2 TDMPWs does no p o ide any way o indica e
335
he eg ess PE how o so he samples om di e en
336
CIDs when hey belong o he same mul i-channel call
337
( he CW o RTP sequence numbe only gua an ees he
338
sequencing o TDMPW packe s).
339
Thus, i a TDMPW packe is los , he eg ess PE can
340
miso de he samples, sending o he des ina ion TE TDM
341
ames ha di e om hose sen by he sou ce TE. No e ha
342
he eg ess PE can s ill de ec he missing TDMPW packe , by
343
inspec ing ei he he CW o RTP sequence numbe s, bu no
344
which channels (CID) we e ca ied by he minicells wi hin ha
345
packe , o how many samples we e con ained a each minicell.
346
This miso de ing o he samples could des oy TSSI (Figu e
347
5, samples “3” and “8”) and RDTD s uc u es (Figu e 5,
348
samples “3” and “4” as “4” is los and “3” does no , o be ween
349
samples “10” and “12”, since he e is no gua an ee ha TDM
350
ames TDM2 and TDM3 a e deli e ed o he des ina ion TE
351
spaced no mo e han 50 ms).
352
353
354
To summa ize, he s anda d AAL2 TDMPW payload
355
o ma , which assigns a CID o each channel, can no p ope ly
356
ca y ISDN mul i-channel calls. To suppo ha anspo ,
357
including mul iplexing se e al calls on he same TDMPW, we
358
p opose wo op ions:
359
a) AAL2 TDMPWs wi h a CID pe channel in VoIP
360
mode: VoIP mode [14] p oposes o inse a RTP
361
heade inside each AAL2 minicell AAL2 (elimina ing
362
he RTP heade o he TDMPW), which would allow
363
he eg ees PE o know he ime o play he i s sample
364
o each minicell. Thus, a e he loss o a TDMPW
365
packe , he eg ess PE can iden i y he a ec ed TDM
366
ames, p ope ly placing he samples o he ollowing
367
TDMPW packe s.
368
This anspo scheme gua an ees ha he sample
369
o de a he ing ess is kep a he eg ess PE, which
370
also ensu es TSSI and RDTD s uc u es (Figu e 6).
371
Also, he PT ield o he RTP heade o each minicell
372
allows he eg ess PE o know he codec applied o
373
each call in he IP ne wo k.
374
375
b) AAL2 TDMPWs wi h a CID pe call using basic
376
s uc u es: al hough he IETF speci ica ion [27] only
377
p o ides o he alloca ion o a CID o each channel,
378
he de ini ion o AAL2 in e wo king lows by ITU-T
379
Recommenda ions [14; 40] is much mo e gene al,
380
allowing eedom o he na u e o he lows iden i ied
381
by each CID (i.e., mul iplexed lows o any kind and,
382
e en, RTP lows om any TDM in e ace). Taking
383
ad an age o his lexibili y, we p opose o associa e a
384
CID o each call ca ied by he TDMPW, ei he single
385
o mul i-channel (same CID o all i s channels).
386
387
Samples will be anspo ed by “basic s uc u es”
388
simila o hose de ined o he CESoPSN TDMPWs
389
unde basic Nx64 se ice [29]. Each basic s uc u e
390
consis s o he sample o "N" channels o he call
391
con ained in a single TDM ame. The payload o
392
each AAL2 minicell con ains an in ege numbe o
393
basic s uc u es (Figu e 7).
394
395
This scheme ensu es ha he low egene a ed a
396
he ou pu o he TDMPW ma ches he o igin, which
397
also ensu es he TSSI s uc u e. The RDTD s uc u e
398
is also gua an eed, since he “N = 2” samples om he
399
same TDM ame will sha e he same minicell,
400
shaping a “basic s uc u e”.
401
Figu e 5. 4x64 mul i-channel ISDN call on s anda dized AAL2 TDMoIP
PW wi h a CID pe channel
Figu e 6. 4x64 mul i-channel ISDN call on AAL2 TDMoIP PW wi h a
CID pe channel and VoIP mode
Figu e 7. AAL2 TDMoIP payload wi h a CID pe call based on basic
s uc u es
PayloadCPS-PDU (0, 1, … ALL2 minicells)PayloadCPS-PDU (0, 1, … ALL2 minicells)
CPS-PDU (wi hou
S a FieldSTF)
8 bi s
CID=x
PDU SSCS
IT 1
8 bi s
IT 2 IT K
8 bi s
8xN bi s
Oc e 2 Oc e NOc e 1 Basic s uc u e o he
Nx64 call wi hCID=x
…
TDM ame
IT N
…
CID=x LI UUICRCBasic s uc u e 1, Basic s uc u e2, …
AAL2 minicell heade
In ege numbe o
basic s uc u es
CID=z LIUUICRCPDU
Va iable leng h
…
AAL2 minicells
Heade
L2
PHY
IP/MPLS
PW label
L2 speci ic
sublaye /CW
RTP
TDMPW Payload
L2
PHY
IP/MPLS
PW label
L2 speci ic
sublaye /CW
RTP
TDMPW Payload
…
In ege numbe
A he des ina ion, he eg ess PE needs o know
402
he ype o codec o each call, be i o anscode o
403
he p ope ou pu codec o o inse com o noise
404
should VAD is used. To in o m he PE, we p opose
405
wo al e na i es:
406
VoIP mode, wi h an RTP heade in each AAL2
407
minicell (Figu e 8): he PT would be included in
408
he RTP heade .
409
410
PT in he Use - o-Use Indica ion (UUI) o e e y
411
AAL2 minicell (Figu e 9): Annex A o he
412
speci ica ion [30] ou lines a possible use o UUI
413
ield o indica e he encoding o he media. This
414
op ion has he same heade s ha AAL2
415
TDMPWs de ined by [27], hus keeping he same
416
TDMPW's RTP heade .
417
Fo single- channel oice calls, wi h CNG PT, he ing ess
418
PE would sends wo di e en AAL2 minicell ypes: one ype
419
o oice samples, and ano he ype o he SID ames wi h
420
CNG PT. In bo h cases he payload- ype will be indica ed in
421
he PT RTP o UUI AAL2 ield. The wo king-ou o he noise-
422
gene a ion in e al depends on he al e na i e:
423
Fo he VoIP mode, wi h a CID pe channel o call, he
424
eg ess PE shall use he imes amps om he RTP
425
heade .
426
Fo he PT in he UUI AAL2 ield mode he e a e no
427
imes amps, so he eg ess PE gene a es com o noise
428
un il he nex oice minicell is ecei ed.
429
430
D. Compa ison o he p oposed TDMPW payload o ma s
431
The 3 ypes o p oposed AAL2 TDMPW payloads can be
432
compa ed in e ms o bandwid h e iciency, a ainable
433
g anula i y and delay (Table I):
434
a) In he VoIP mode, he inclusion o an RTP heade in
435
e e y minicell was es bandwid h. Gi en he g ea
436
simila i y ha hese heade s may show, he p oblem
437
could alle ia ed by applying RTP heade comp ession
438
mechanisms [41]. Fo he wo op ions p oposed unde
439
his mode, we can conside he ollowing commen s:
440
When using one CID pe channel samples o a call
441
placed in he same TDM ame a he ing ess PE
442
can be sen in se e al TDMPW packe s. The
443
eg ess PE will ha e o wai o he a i al o all
444
hose packe s o success ully build up he TDM
445
ame, which may inc ease he delay.
446
When using a CID pe call all he samples om a
447
call placed in he same TDM ame a he ing ess
448
PE a e con eyed in he same TDMPW packe . I s
449
disad an age is a coa se packing g anula i y,
450
because he payload o he minicells is o ced o
451
be a mul iple o ela i ely la ge basic s uc u es.
452
This educes he ma gin o ensu e a cons an end
453
o end delay be ween bo h PEs.
454
b) A CID pe call wi h he PT in he UUI ield: When
455
compa ed o he VoIP mode, i is mo e bandwid h-
456
e icien , as i does no equi e addi ional RTP
457
heade s. This solu ion also shows he coa se
458
g anula i y ea u e desc ibed abo e.
459
460
Figu e 8. 2x64 mul i-channel ISDN call on AAL2 TDMoIP PW wi h a
CID pe call and VoIP mode
Figu e 9. 4x64 mul i-channel ISDN call on AAL2 TDMoIP PW wi h a
CID pe call and PT in UUI ield
461
TABLE I. COMPARISON OF THE PROPOSED AAL2 TDMOIP TDMPW PAYLOAD FORMATS TO SUPPORT ISDN MULTICHANNEL CALLS
Gua an ees
TSSI and
RDTD
s uc u es
Suppo
ISDN mul i-
channel calls
AAL2
minicells'
g anula i y
T anspo
o he PT
o each
call
Suppo call
mul iplexing
De e mina ion o he
noise-gene a ion pe iod
o VAD-enabled single
-channel calls
O e head
E ec o delayed
TDMPW packe s
AAL2
TDMPW
payload o ma
s anda dized
by [27]
No
No
Oc ec s
No (i
assumes
he same
codec o
all calls)
No (i
assumes he
same codec
o all calls)
VAD no suppo ed
Lowe
Eg ess PE should wai
o las TDMPW wi h
samples o he same
ame TDM
VoIP
mode
CID pe
channel
Yes
Yes
Oc ec s
PT RTP
ield in
AAL2
minicells
Yes
By using RTP imes amp
High (RTP
heade s in
AAL2
minicells)
Eg ess PE should wai
o las TDMPW wi h
samples o he same
ame TDM
CID pe
call
Yes
Yes
Basic
s uc u es
PT RTP
ield in
AAL2
minicells
Yes
By using RTP imes amp
High (RTP
heade s in
AAL2
minicells)
None (samples a el
oge he in basic
s uc u es)
CID pe call
and PT in he
UIUI ield
Yes
Yes
Basic
s uc u es
UUI ield
o AAL2
minicell'
heade
Yes
Un il he nex oice
minicell a i es
Lowe
None (samples a el
oge he in basic
s uc u es)
IV. CONCLUSIONS
This pape add esses he anspo o ISDN mul i-channel
ci cui -mode bea e se ices o i s NGN emula ion.
Fi s , we ha e e alua ed he di e en TDMPWs,
concluding ha he AAL2 TDMPWs a e he bes choice,
al hough i s s anda d payload o ma does no gua an ee he
TSSI s uc u e. To sol e his, we ha e de ined h ee new ypes
o he TDMPW’s payload o ma . Two o hem a e based on
he inclusion o a heade a he beginning o he RTP payload
o each AAL2 minicell (VoIP mode), assigning a CID o
e e y channel o call (in he la e , by o ganizing he samples
om he channels o a call in basic s uc u es.) The hi d ype,
which also assigns a CID o each call, uses he minicells’ UUI
ield o indica e he ype o p ocessing applied o he samples,
sa ing bandwid h.
REFERENCES
[1] ETSI TR 180 001 1.1.1. "Telecommunica ions and In e ne con e ged
Se ices and P o ocols o Ad anced Ne wo king (TISPAN); NGN
Release 1; Release de ini ion". (03/06).
[2] ITU-T Y.2201. "NGN elease 1 equi emen s". (04/07).
[3] ITU-T Y.2000 Suplemen 1. "Supplemen on NGN elease 1 scope".
(07/06).
[4] ITU-T Y.2006. "Desc ip ion o capabili y se 1 o NGN elease 1".
(02/08).
[5] ITU-T Y.2262. "PSTN/ISDN emula ion and simula ion". (12/06).
[6] ETSI ES 282 002. "Telecommunica ions and In e ne con e ged
Se ices and P o ocols o Ad anced Ne wo king (TISPAN);
PSTN/ISDN Emula ion Sub-sys em (PES); Func ional a chi ec u e".
(1/06).
[7] ETSI SR 002 211. "Lis o s anda ds and/o speci ica ions o elec onic
communica ions ne wo ks, se ices and associa ed acili ies and
se ices; in acco dance wi h A icle 17 o Di ec i e 2002/21/EC".
(2/04).
[8] The Eu opean Pa liamen and he council o he Eu opean Union.
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Di ec i e 2002/22/EC. (03/02).
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Telephone Ne wo k; Suppo o legacy e minals by B oadband IP
ne wo ks and equipmen ; Pa 2: Analogue PSTN e minals". (3/05).
[10] ITU-T Y.2031. "PSTN/ISDN emula ion a chi ec u e". (09/06).
[11] ETSI ES 283 002 2.1.0. "Telecommunica ions and In e ne con e ged
Se ices and P o ocols o Ad anced Ne wo king (TISPAN);
PSTN/ISDN Emula ion Subsys em (PES); NGN Release 2 H.248 P o ile
Ve sion 2 o con olling Access and Residen ial Ga eways". (03/08).
[12] ITU-T Y.2012. "Func ional equi emen s and a chi ec u e o nex
gene a ion ne wo ks". (9/06).
[13] ITU-T Y.1453. "TDM-IP in e wo king - Use plane in e wo king".
(03/06).
[14] ITU-T Y.1452. "Voice unking o e IP ne wo ks". (3/06).
[15] IETF RFC 4197. "Requi emen s o Edge- o-Edge Emula ion o Time
Di ision Mul iplexed (TDM) Ci cui s o e Packe Swi ching Ne wo ks".
(10/05).
[16] IETF RFC 3985. "PseudoWi e Emula ion Edge- o-Edge (PWE3)
A chi ec u e". (03/05).
[17] ITU-T I.231.5. “Ci cui -mode 2 x 64 kbi /s un es ic ed, 8 kHz
s uc u ed bea e se ice". (11/88).
[18] ITU-T I.231.6. “Ci cui -mode 384 kbi /s un es ic ed, 8 kHz s uc u ed
bea e se ice". (7/96).
[19] ITU-T I.231.7. “Ci cui -mode 1536 kbi /s un es ic ed, 8 kHz s uc u ed
bea e se ice". (7/96).
[20] ITU-T I.231.8. “Ci cui -mode 1920 kbi /s un es ic ed, 8 kHz s uc u ed
bea e se ice". (7/96).
[21] ITU-T I.231.10. “Ci cui -mode mul iple- a e un es ic ed 8 kHz
s uc u ed bea e se ice". (8/92).
[22] ITU-T I.140. “A ibu e echnique o he cha ac e iza ion o
elecommunica ion se ices suppo ed by an ISDN and ne wo k
capabili ies o an ISDN". (3/93).
[23] ITU-T Y.2011. "Gene al p inciples and gene al e e ence model o
Nex Gene a ion Ne wo ks". (10/04).
[24] ITU-T H.248.1. “Ga eway con ol p o ocol: Ve sion 3". (9/05).
[25] IETF RFC 3916. "Requi emen s o Pseudo-Wi e Emula ion Edge- o-
Edge (PWE 3)". (09/04).
[26] IETF RFC 4553. "S uc u e-Agnos ic Time Di ision Mul iplexing
(TDM) o e Packe (SAToP)". (6/06).
[27] IETF RFC 5087. "Time Di ision Mul iplexing o e IP (TDMoIP)".
(12/07).
[28] B oadband Fo um a - oa-0078.000. "Ci cui Emula ion Se ice (CES)
In e ope abili y. Speci ica ion Ve sion 2.0". (1/97).
[29] IETF RFC 5086. "S uc u e-Awa e Time Di ision Mul iplexed (TDM)
Ci cui Emula ion Se ice o e Packe Swi ched Ne wo k (CESoPSN)".
(12/07).
[30] B oadband Fo um a - moa-145.001. "Voice and Mul imedia O e ATM
- Loop Emula ion Se ice (LES) Using AAL2 (Re 1)". (2/03).
[31] IETF RFC 5287. "Con ol P o ocol Ex ensions o he Se up o Time-
Di ision Mul iplexing (TDM) Pseudowi es in MPLS Ne wo ks". (8/08).
[32] ITU-T I.363.2. "B-ISDN ATM Adap a ion Laye speci ica ion : Type 2
AAL". (11/00).
[33] ITU-T I.231.1. “Ci cui -mode 64 kbi /s un es ic ed, 8 kHz s uc u ed
bea e se ice". (11/88).
[34] IETF RFC 4040. "RTP Payload Fo ma o a 64 kbi /s T anspa en
Call". (4/05).
[35] IETF RFC 3389. "Real- ime T anspo P o ocol (RTP) Payload o
Com o Noise (CN)". (9/02).
[36] ITU-T G.961. "Digi al ansmission sys em on me allic local lines o
ISDN basic a e access". (3/93).
[37] ITU-T Q.512. "Digi al exchange in e aces o subsc ibe access".
(2/95).
[38] ITU-T I.430. "Basic use -ne wo k in e ace – Laye 1 speci ica ion".
(11/95).
[39] ITU-T I.431. "P ima y a e use -ne wo k in e ace – Laye 1
speci ica ion". (3/93).
[40] ITU-T Y.1414. “Voice se ices – MPLS ne wo k in e wo king". (7/04).
[41] IETF RFC 2508. "Comp essing IP/UDP/RTP Heade s o Low-Speed
Se ial Links". (2/99).
[42] IETF RFC 3550. "RTP: A T anspo P o ocol o Real-Time
Applica ions". (7/03).
[43] ETSI TS 183 002 3.3.1. "Telecommunica ions and In e ne con e ged
Se ices and P o ocols o Ad anced Ne wo king (TISPAN);
PSTN/ISDN Emula ion Subsys em (PES); H.248 P o ile Ve sion 3 o
con olling Access and Residen ial Ga eways". (8/09).
