1. Lecture Note on Dense Wave Division Multiplexing (DWDM)

2. 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

3. Dense Wave Division Multiplexing (DWDM) in Long Distance Networks
WDM NE
Fiber Pairs
Fiber Pairs
WDM NE
Limited Rights of Way
Multiple Fiber Rings Homing to a Few Rights of Way
Fiber Exhaustion

4. Increased Fiber Network Capacity
DWDM versus SONET
120 km
OC-48
OLS
TERM
RPTR
DWDM Transport - 20 Gb/s
SONET Transport - 20 Gb/s
1310
40km
Increased Fiber Network Capacity 9
120

5. Example Public/Private Internet Peering Backbone SONET/WDM T1/T3 IP
Core
Router
Core
Router
RAS
RAS
Core
Router
EtherSwitch
Access
Router
RAS
RAS
RAS
Access
Router
ATM
Switch
ATM
Switch
Core
Router
RAS
EtherSwitch
RAS
RAS
RAS
ATM
Switch
RAS
ATM Access
Access
Router
RAS
Core
Router
RAS
RAS
Access
Router
RAS
ATM Access
RAS
Backbone
SONET/WDM
RAS
Access
Router
T1/T3 IP
Leased-Line
Connections
Remote Access Systems
ATM
Switch
ATM
Access
ATM
Access
ATM
Access
ATM
Access
T1/T3 FR
and ATM IP
Leased-Line
Connections
T1/T3/OC3

6. 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.

7. IP/SONET/WDM Network Architecture
OC-3/12
[STS-3c/12c]
SONET
NMS
OC-3/12
[STS-3c/12c/48c]
SONET
DCS
OC-48
EMS
SONET
ADM
SONET
ADM
EMS
Access .
OC-12/48
Routers/
Core IP
Node . .
Enterprise
SONET Transport Network
Core IP
Node .
Servers . .
OTN
NMS
WDM LT
WDM LT
OC-3/12/48
[STS-3c/12c/48c]
OC-3/12/48
[STS-3c/12c/48c]
l1, l2, ...
Pt-to-Pt WDM Transport Network
LT = Line Terminal
EMS = Element Management System
NMS = Network Management System
IP = Internet Protocol
OTN = Optical Transport Network
ADM = Add Drop Multiplex

8. Evolution of Optical Networks
Point-to-Point WDM Line System l1 l2 lN
Multipoint Network WDM Add/Drop
WDM ADM
WDM ADM li lk
Optical Cross-Connect WDM Networking
Optical
Cross
Connect

9. IP over OTN Architecture
EMS .
Core Data
Node . .
OTN
NMS
OXC
EMS
EMS
OXC
OXC .
Access Routers .
Core Data
Node .
Enterprise Servers
Optical Transport Network
Core Data
Node . . .
IP = Internet Protocol
OTN = Optical Transport Network
OXC = Optical Cross Connect
EMS = Element Management System
NMS = Network Management System

10. Architectural Alternatives

11. 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).

12. 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.

13. Assumptions: Network Model
Transit traffic uses router ports in IP-over-WDM and OXC ports (only) in IP-over-OTN.
Quadruple redundant configuration of IP routers at a PoP to improve reliability and perform load-balancing.
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).
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.

14. 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.

15. 2.5 Gbps of Traffic between PoP Pairs
Cross-over point at network size of about 18 nodes.

16. 5 Gbps of Traffic between PoP Pairs
Cross-over point at network size of about 15 nodes.