Lecture Note on Dense Wave Division Multiplexing (DWDM)

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

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

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

6. High Capacity Path Networking • 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 router IP router IP router STS-12c/48c/... STS-3c Existing SDH-SONET Network

7. SONET NMS SONET DCS SONET SONET ADM ADM WDM WDM LT LT IP/SONET/WDM Network Architecture OC-3/12 [STS-3c/12c] OC-3/12 [STS-3c/12c/48c] OC-48 EMS EMS Access OC-12/48 . . Routers/ Core IP Node . Core IP Node SONET Transport Network . Enterprise . Servers . OTN NMS 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. l1 l1 l2 l2 lN lN Evolution of Optical Networks Point-to-Point WDM Line System Multipoint NetworkWDM Add/Drop WDMADM WDMADM li lk Optical Cross-ConnectWDM 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 Core Data Node . Optical Transport Network . Enterprise Servers . . 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 • 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. • 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).

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.