Lecture Note on Dense Wave Division Multiplexing (DWDM)

Typical Deployment of UPSR and BLSR

Regional Ring (BLSR)

Intra-Regional Ring (BLSR) Intra-Regional Ring (BLSR)

Access Rings (UPSR)

WB DACs

BB DACs

WB DACS = Wideband DACS - DS1 GroomingBB DACS = Broadband DACS - DS3/STS-1 GroomingOptical Cross Connect = OXC = STS-48 Grooming

DACS=DCS=DXC

Dense Wave Division Multiplexing (DWDM)in Long Distance Networks

WD

M N

EW

DM

NE W

DM

NE

WD

M N

E

• Limited Rights of Way• Multiple Fiber Rings Homing to a Few Rights of Way• Fiber Exhaustion

Fiber PairsFiber Pairs

DWDM versus SONET

120 km

OC-48

OLSTERM

OLSRPTR

OLSRPTR

OLSTERM

120 km 120 km

DWDM Transport - 20 Gb/s

OC-48OC-48

OC-48

OC-48OC-48

OC-48OC-48

SONET Transport - 20 Gb/s

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM

40km 40km 40km 40km 40km 40km 40km 40km 40km

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM1310

RPTR1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

1310RPTR

TERMTERM

OC-48OC-48

OC-48OC-48

OC-48OC-48

OC-48OC-48

Increased Fiber Network Capacity

T1/T3/OC3

ATM

Access

ATM

Access

ATM

Switch

Public/PrivateInternet Peering

ATM

Access

ATM

Access

Access

Router

T1/T3 IPLeased-LineConnections

Core

Router

Core

Router

Access

Router

Access

Router

ATM Access

ATM Access

RAS

RAS

RAS

RAS

RAS

RAS

RAS

RAS

Access

Router

Access

Router

EtherSwitch

EtherSwitch

RAS

RAS

RAS

RAS

RAS

RAS

RAS

RAS

Core

Router

Core

Router

BackboneSONET/WDM Remote Access Systems

T1/T3 FRand ATM IPLeased-LineConnections

ATM Switch

ATMSwitch

ATMSwitch

ATMSwitch

Core

Router

Core

Router

Example

High Capacity Path NetworkingHigh 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.

• 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.

Existing SDH-SONET Network

IP router

IP router IP router

STS-3c

STS-12c/48c/...

IP/SONET/WDM Network ArchitectureIP/SONET/WDM Network Architecture

Core IPNode

EMS

.

.

.

SONET ADM

OC-3/12[STS-3c/12c]

OC-12/48

OC-3/12[STS-3c/12c/48c]

SONET Transport Network

SONETNMS

Core IPNode

EMS

.

.

.

Access Routers/EnterpriseServers

OC-48

SONET ADM

SONETDCS

WDMLT

WDMLT1, 2, ...

OC-3/12/48[STS-3c/12c/48c]

Pt-to-Pt WDM Transport Network

OC-3/12/48[STS-3c/12c/48c]

OTNNMS

IP = Internet ProtocolIP = Internet ProtocolOTN = Optical Transport NetworkOTN = Optical Transport NetworkADM = Add Drop MultiplexADM = Add Drop Multiplex

LT = Line TerminalLT = Line TerminalEMS = Element Management SystemEMS = Element Management SystemNMS = Network Management SystemNMS = Network Management System

Evolution of Optical NetworksEvolution of Optical Networks

Multipoint NetworkWDM Add/Drop

Point-to-Point WDM Line System

Optical Cross-ConnectWDM Networking

OpticalCross

Connect

i

WDMADM

WDMADM

k

IP over OTN ArchitectureIP over OTN Architecture

Core DataNode

EMS

.

.

.

OXC

Optical Transport Network

OTNNMS

Core Data Node

EMS

.

.

.

Access RoutersEnterprise Servers

OXC

OXC

Core Data Node

EMS

.

.

.

IP = Internet ProtocolIP = Internet ProtocolOTN = Optical Transport NetworkOTN = Optical Transport NetworkOXC = Optical Cross ConnectOXC = Optical Cross Connect

EMS = Element Management SystemEMS = Element Management SystemNMS = Network Management SystemNMS = 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

• 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).

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

Cross-over point at network size of about 18 nodes.

2.5 Gbps uniform traffic

0500100015002000250030003500400045005000

0 10 20 30 40 50 60Network size (nodes)

To

tal

$-C

ost

(M

)

IP-over-WDM

IP-over-OTN

Cross-over point at network size of about 15 nodes.

5 Gbps uniform traffic

0

1000

2000

3000

4000

5000

6000

7000

8000

0 10 20 30 40 50 60Network size (nodes)

To

tal

$-C

ost

(M

)

IP-over-WDM

IP-over-OTN

5 Gbps of Traffic between PoP Pairs5 Gbps of Traffic between PoP Pairs