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Passive Optical Broadband Communications in Local Access
Network
Kae-hsiang Kwong
21 January 2004
What is an Access Network?
Access Networks provide necessary interfaces to end-users accessing telecommunication services.
Accessunit
Access Network
Feeder +
Distribution
Backbone Network
InternetPSTNCATV
Backbone Network
InternetPSTNCATV
Evolution of Access Networks
Telephony Cable TV Internet
Telephony+
Internet
Cable TV+
Internet
Telephony + Cable TV + Internet
Passive Optical Access NetworksPON: network architecture constructed solely using passive optical devices; no signal regeneration in the transmission path.
ONU
ONU
ONU
users
Combiner
Copper network Optical fibre network
Backbone network
PSTNCATV
Internet
Backbone network
PSTNCATV
Internet
OLT
Backbone network
Medium Access ControlInterleaved Polling with Adaptive Cycle Time (IPACT)
• Provides Dynamic bandwidth allocation.
• OLT assigns each ONU for transmission based on the information exchanged between OLT and ONUs.
• Buffer status and traffic load of ONU sent to OLT.
• OLT utilises incoming information to schedule ONU transmissions.
• OLT issues Grants to inform individual ONUs start time and duration of transmission.
Medium Access Control
ONU 1
ONU 2
ONU x
users
Combiner OLT
ONU 1 ONU 2 ONU 3
G G G
• Grant is broadcast to every ONU.
• Information is carried to OLT at the end of each ONU transmission.
IPACT Results
0.00001
0.0001
0.001
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
Traffic load
De
lay
(se
co
nd
s)
16 ONUs IPACT
24 ONUs IPACT
32 ONUs IPACT
16 ONUs TDMA
WDM IPACT + DiffServ
Classifier
Packets from users
Class 1
Class 2
Class 3
scheduler
ONUOLT
DS Network
ONU:
• Incoming packets are classified and marked.
• Traffic flows are grouped into traffic classes according to the similarity of QoS requirements.
• Different level of reservation treatments applied to each traffic class.
OLT:
• Bandwidth are allocated to ONUs according to the buffer status and traffic load.
• Associates traffic classes to bandwidth allocation schemes.
Conclusion• WDM PON systems
1. WDM-IPACT with fixed transceivers.
2. WDM-IPACT with tuneable transmitters, fixed receivers.
• Highly cost efficient solution in upgrading access network.
• Single network architecture, supporting Telephony, CATV broadcast, Internet, etc.
• DS domain extended to local access networks.
• Achieves end-to-end QoS provisioning.
• Eliminates the need for per-flow resource reservation.
