aplicacion redes pon atm
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Redes PONTRANSCRIPT
AN ATM CELL BASED TRANSMISSION SYSTEM ON A PON STRUCTURE
G. DU CHAFFAUT - D. CHAPELAIN - A. MADANI - S. CARPENTIER
Centre National d'Etudes des Tblbcommunications route de Tregastel - BP 40 - 22301 Lannion cedex - FRANCE
Tel:733) 96 05 36 04
Kev words :
Fiber sharing, passive optical network, customer access
connection, ATM, local loop, broadband
communications, transmission systems.
Abstract:
An ATM cell based transmission system has been studied
and optimised for fiber sharing in the customer access
connection; it is oriented towards B ISDN @revision of
both interactive and distributive services) and take into
account last CCITT works. A passive tree star topology
with standard SM fiber is proposed allowing at least eight
customers to be connected.
A n example of application to residential customers is
presented which takes into account possible evolutionary
steps. It leads to a 622 Mbit/s downstream on one
wavelength and a 2 to 20 Mbit//s per user upstream on
another wavelentgh.
1- Introduction :
Moving from the existing copper and coaxial
distribution network to an optical one takes a long
time and costs a lot of money. So intermediate steps
(e.g. FTTC) for a smooth introduction of the optical
fiber in the local loop are to be found. Introduced after
these steps, optical distribution systems would have to
FAX: (33) 96 05 35 90
be as flexible as possible to allow system evolutions,
without removing and replacing the passive optical
link. In the following, we focuses only on the FITH
phasis, describing an ATM transmission system and
giving examples of applications to residential
customers.
2- Video service Drovision :
In the case of residential applications, two kinds of
broadband services have been identified. Others are
not broadband enough to influence the line bit rate.
Video channels :
Improvements in videocoding could likely result in
distribution codecs at the following bit rates :
- normal quality (NQ)
- HDTV (Ha)
: 34 Mbit/s --> 17 Mbit/s
: 140 Mbit/s -- > 70 Mbit/s
A PON structure with a 622.080 Mbit/s downstream
allows x NQ plus y HQ to be carried depending on the
codec bit rate (e.g. 17 NQ channels at 34 Mbit/s or 35
NQ channels at 17 Mbit/s or 4 HQ channels at 140
Mbit/s or 8 HQ channels at 70 Mbit/s). One part of
these channels could be broadcasted to every customer
whereas the other part could be switched TV channels
selected by the customers connected on the same fiber.
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To improve the efficiency of the selection, a dynamic
allocation of the broadcasted and switched parts is
handled.
Interactive video se mice :
Fast video compression technology combined with CD
ROM disk possibilities on one hand and introduction
of low cost PC computers at home on the other hand
lead to new developments of interactive video
applications. A 1.5 Mbit/s bit rate is required for both
directions.
3- A Dassive tree sta r structure :
It seems that tree structure is more suitable for
distributive services. Indeed, it looks cheaper to
broadcast only once a video service to a group of
customers rather than duplicate this service for each
customer as needed with a point to point topology. The
most part of the line bit rate is due to distributive
services, so it is of great interest to favour such a
structure at least for residential customers.
Furthermore, this leads to a reduction of costs for
ducts, optical fibers and jointing, and decreases the
number of equipments at the central side.
The counterparts with fibre sharing are achromatic
couplers added at the division point and more
constraints reported on terminal equipments.
A convenient way to introduce digital distributive
services is the OLO concept as proposed in RACE
projects. It relies on the separation between interactive
and distributive services and allows independant
upgrades of the two kinds of services.
An early step for the introduction of optical fiber in the
local loop could be to broadcast analog video channels
using SCM with AM or FM modulations on a PON
structure (figure 1).
Then using the same structure with a digital
transmission system (an ATM one is proposed in the
following), it is possible to introduce digital video
distribution (figure 2).
A next step could be to provide a more integrated
system as explained figure 3.
The three cases described before have no active point
in the access connection to avoid degradation of the
optical line reliability, decrease the number of
maintenance entities to handle, and avoid civil works
and need of remote power supply.
: Sub. Carrier - c : +
. N T 2 I N T I -. * figure 7
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: N T Z T b l N T I I U b L T
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figure 3
5- ATM transmission svstem :
ATM has been choosen for the following reasons :
- We have to cope with a large number of service bit
rates and their possible evolution in the future
including variable bit rate services.
- ATM multiplexing is very convenient for non
redondancy transmission when sharing a medium (e.g.
transmission of distributive services).
- In case of switched TV issued from a remote emitting
point and routed through cross connect nodes, ATM
offers an interesting flexibility.
- Fiber sharing implies packet oriented transmission
for upstream.
- Confidency between users connected to the same
fiber requires to filter information flow. This is simply
done by reading cell headers.
- To move towards an ISDN network switching all
kinds of services, ATM is considered as a good
candidate.
A transmission system has been studied at the U
reference point which is described below :
Maintenance ceZZ : the PL OAM cell (figure 4) is
inserted every 134 cells. It carries F1 (regeneration
section OAM flow) and F2 (digital section OAM flow)
as defined in I610 draft recommendation and use a
specific pattern in the header. This cell is not passed to
the ATM layer. The phasing and access control fields
following the cell header are protected against line
errors.
Scrambling : a 15 stages self synchronized phased
scrambler is used with the following advantages :
- no error vultiplication or propagation
- reasonable hardware complexity
- high immunity against malicious user (no relation
between cell boundaries and scrambler length)
- good efficiency for transmission aspects
Synchronisation criterias : synchronisation process is
based on the recognition of a four bytes pattern and
confirmed using the CRC code from cell headers as
shown on the figure 5.
non scrumbled par/
01 22
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figura 4
303.2.3
Timing characteristics :
Propagation time : the maximum length retained to
connect subscribers to a local exchange (figure 6) is
6 km (hax). This covers about 93% of subscribers in
France (quite similar for other countries in Europe).
The maximum distance between the division point and
each subscriber does not exceed 500 meters (lma).
This gives the following maximum propagation times:
.
DisDersion time dtt for the DP-NT-DP delay is due to :
- dispersion time dtp from length differences between
DP and NTs :
dtp = 2.lmmtpd
tpd is the optical propagation time
dtp= 5 I . ~ S
- dispersion time dtd from optical and electronic
devices
dtd< = 1 ps
Upstream access control :
CMI code is prefered for the upstream specially
because of the easy and fast clock recovery associated
which is very suitable with transmission of non phased
blocks.
For low bit rate upstream (2 Mbit/s per user), there is
no need to take into account dtt. Access control to the
medium is obtained by decoding the MAC field
(Medium Access Control) carried by the PL OAh4 cell
(every 92.0 ps). Each NT is activated during a fixed
time slot (figure 7); if there is no information cell to
transmit, the block is completed with empty cells. A 4
cells fifo is needed in the NT to buffer the upstream
information flow (downstream at 622.080 Mbit/s).
I 1 usern 1-
Upgrading the system for higher bit rates (10 to 20
Mbit/s per user), leads to take into account dtt (figure
8). This is done when connecting a new NT. The LT
equipment sends a RFI message (Request For
Identification) to the concerned NT. The new NT
answers by sending a message including its UID (User
Identification) and PHS (Phasis Status). Then the LT
processes the correct delay to send to the NT. A PHL
(phasis to load) message is sent and decoded by the
new NT. As previously, a 4 cells fifo buffer is needed.
303.2.4 01 23
n r l pj!, mer f \ UDI, PHS I mer2 I
I user n I Rh
1
figure 8
7- User eauipment :
Considering the overcost on user equipment as soon as
the distance between NT1 and NT2 requires signal
regeneration and maintenance process, it is clearly
prefered on a technical and economic point of view to
set NT1 close to NT2, at least for residential
customers. Obviously, this implies to face and cope
with constraints due to national regulations.
A convenient implementation to reduce the user
equipment cost is to use a parallel interface between
NT1 and NT2. It is based on primitives exchanged
between ATM and TC layers (I321 CCIIT draft
recommendation ):
- the TC layer provides to the ATM layer: data
indication
- the ATM layer provides to the TC layer: data request
In case of no cell available (empty cells or cells issued
for other users in case of fiber sharing), no data is
passed through the parallel interface.
8- BiblioeraDhy :
CCITT SGXVIII draft recommendations Geneva May 1990
MOLENE system.
J. Abiven. ECHO DES RECHERCHES NO138 4th term
1989
Fiber optic point to multipoint interface. Configuration for
Broadband ISDN
Hiroshi Uno and Naoya Aragaki. J. LIGHTWAVE
TECHNOLOGY vol. 7 NO11 Nov. 1989
Experimental data link using SM fiber and ping pong
transmission
A. Jaillard, H. Prigent, Y. Guillauseau. EFOC LAN 1989
Broadband Upgrade Options for Passive Optical Networks
J.R. Stern, A.R. Beaumont, D.W. Faulkner, D.B. Payne,
J.W. Ballance IEEE Workshop on PON May 1990.
A Study of Optical Passive Bus Network K. IGUCHI
IEEE Workshop on PON May 1990.
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