Lecture Note on Dense Wave Division
Multiplexing (DWDM)
Typical Deployment of UPSR and BLSR
Regional Ring (BLSR)
BB DACs
Intra-Regional Ring (BLSR)
Intra-Regional Ring (BLSR)
WB DACs
Access Rings (UPSR)
WB DACS = Wideband DACS - DS1 Grooming
BB DACS = Broadband DACS - DS3/STS-1 Grooming
Optical Cross Connect = OXC = STS-48 Grooming
DACS=DCS=DXC
WDM NE
Fiber Pairs
WDM NE
Dense Wave Division Multiplexing (DWDM)
in Long Distance Networks
• Limited Rights of Way
• Multiple Fiber Rings Homing to a Few Rights of Way
• Fiber Exhaustion
Fiber Pairs
DWDM versus SONET
40km
40km
40km
40km
40km
40km
40km
40km
40km
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
SONET Transport - 20 Gb/s
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
120 km
120 km
OLS
TERM
OLS
RPTR
120 km
OLS
RPTR
OLS
TERM
DWDM Transport - 20 Gb/s
Increased Fiber Network Capacity
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
Public/Private
Internet Peering
Example
Core
Core
Router
Router
RAS
RAS
EtherSwitch
Core
Access
Router
Router
RAS
RAS
RAS
Access
ATM
Switch
Core
ATM
Switch
RAS
Router
EtherSwitch
Router
RAS
RAS
RAS
ATM
Switch
Core
ATM
Switch
Router
RAS
ATM Access
Access
Router
RAS
RAS
Core
RAS
Router
Access
RAS
Router
ATM Access
RAS
RAS
Backbone
SONET/WDM
T1/T3/OC3
ATM
Access
Switch
Router
T1/T3 IP
Leased-Line
Connections
ATM
ATM
ATM
ATM
Access
Access
Access
Access
T1/T3 FR
and ATM IP
Leased-Line
Connections
Remote Access Systems
High Capacity Path Networking
IP router
IP router
STS-12c/48c/...
IP router
STS-3c
Existing SDH-SONET Network
• Existing SONET/SDH networks are a bottleneck for Broadband Transport.
Most Access Rings are OC-3 and OC-12 UPSRs while most Backbone
Rings are OC-48. Transport of rates higher than OC-48 using the existing
SONET/SDH network will require significant and costly changes. Clearly
upgrading the SONET/SDH network everywhere is not an appropriate
solution.
IP/SONET/WDM Network Architecture
OC-3/12
[STS-3c/12c]
OC-48
EMS
Access
Routers/
Enterprise
Servers
.
.
.
SONET
DCS
SONET
NMS
SONET
ADM
OC-3/12
[STS-3c/12c/48c]
SONET
ADM
EMS
OC-12/48
SONET Transport Network
Core IP
Node
Core IP
Node
.
.
.
OTN
NMS
OC-3/12/48
[STS-3c/12c/48c]
WDM
LT
l1, l2, ...
WDM
LT
Pt-to-Pt WDM Transport Network
IP = Internet Protocol
OTN = Optical Transport Network
ADM = Add Drop Multiplex
OC-3/12/48
[STS-3c/12c/48c]
LT = Line Terminal
EMS = Element Management System
NMS = Network Management System
Evolution of Optical Networks
Point-to-Point WDM
Line System
Multipoint Network
WDM Add/Drop
Optical Cross-Connect
WDM Networking
l1
l2
lN
l1
l2
lN
WDM
ADM
WDM
ADM
li
lk
Optical
Cross
Connect
IP over OTN Architecture
EMS
Core Data
Node
.
.
.
OTN
NMS
OXC
EMS
OXC
OXC
Access Routers
Enterprise Servers
.
.
.
Core Data
Node
IP = Internet Protocol
OTN = Optical Transport Network
OXC = Optical Cross Connect
Optical Transport Network
EMS
Core Data
Node
.
.
.
EMS = Element Management System
NMS = Network Management System
Architectural Alternatives
Quadruple Redundant Configuration
of IP Routers at PoPs
• Currently deployed by carriers to increase router reliability and perform
load balancing.
• Two routers are service routers adding/dropping traffic from the network
side and passing through transit traffic.
• Other two routers are drop routers connected to client devices.
• Two connections from the network port at the ingress service router to two
drop ports, one in each of the drop routers. Client device sends 50% of the
traffic on one of these drop interfaces and 50% on the other (it is attached
to both of the drop routers).
Network Deployment Cost Analysis
•
Analysis of the two architectures from an economic standpoint.
•
Contrary to common wisdom, a reconfigurable optical layer can lead to substantial
reduction in capital expenditure for networks of even moderate size.
•
Amount of transit traffic at a PoP is much higher than the amount of add-drop traffic.
•
Hence, a reconfigurable optical layer that uses OXC ports (instead of router ports) to
route transit traffic will drive total network cost down so long as an OXC interface is
marginally cheaper than a router interface.
•
Savings increases rapidly with the number of nodes in the network and traffic demand
between nodes.
Assumptions: Network Model
•
Transit traffic uses router ports in IP-overWDM and OXC ports (only) in IP-overOTN.
•
Quadruple redundant configuration of IP
routers at a PoP to improve reliability and
perform load-balancing.
•
Typical PoP has two, in some cases three, and in
rare occasions four conduits connecting it to
neighboring PoPs. Average degree = 2.5.
•
Routing uniform traffic (equal traffic demand
between every pair of PoPs) on networks of
increasing size.
•
Two traffic demand scenarios: uniform demand of
2.5 Gbps (OC-48) and 5 Gbps between every pair •
of PoPs.
•
•
Multiple routers or OXCs can be placed at each
PoP to meet port requirements for routing traffic.
•
Core OXC network provides full grooming of
OC-192 ports into OC-48 tributaries.
•
Shortest-hop routing of lightpaths.
IP routers have upto 64 ports and OXCs
have upto 512 ports (in keeping with port
counts of currently shipped products).
With or without traffic restoration (diverse
backup paths).
Pricing Assumptions
•
IP routers and OXCs have fixed costs and per-port costs for OC-48 and OC-192
interfaces.
•
IP router:
– fixed cost of $200K and
– per-port cost of $100K and $250K for OC-48 and OC-192 interfaces respectively.
•
OXC:
– fixed cost of $1M and
– per-post cost of $25K and $100K for OC-48 and OC-192 interfaces respectively.
2.5 Gbps of Traffic between PoP Pairs
Total $-Cost (M)
2.5 Gbps uniform traffic
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
IP-over-WDM
IP-over-OTN
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of about 18 nodes.
50
60
5 Gbps of Traffic between PoP Pairs
5 Gbps uniform traffic
Total $-Cost (M)
8000
7000
IP-over-WDM
IP-over-OTN
6000
5000
4000
3000
2000
1000
0
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of about 15 nodes.
50
60