ECE442 Communications Lecture 4. Optical Networks Husheng Li Dept. of Electrical Engineering and Computer Science Spring, 2014
Network Elements 1 WDM networks provide circuit switched end-to-end optical channels, or light paths. 2 A light path consists of an optical channel or wavelength between two network nodes. 3 These networks may be thought of as wavelength-routing networks.
Network Elements 1 A wavelength-routing mesh netwrok consists of OLTs, OADMs and OXCs.
Features of the Structure 1 Wavelength reuse. 2 Wavelength conversion 3 Transparency 4 Circuit switching 5 Survivability 6 Lightpath topology
Optical Line Terminals 1 OLTs are used at either end of a point-to-point link to multiplex and demultiplex wavelengths.
Optical Line Amplifiers 1 Optical line amplifiers are deployed in the middle of the optical fiber link at periodic intervals, typically 80-120 km.
Optical Add/Drop Multiplexers 1 OADMs provide a cost-effective means for handling passthrough traffic in both metro and long-hual networks.
Structures of OADMs 1 There could be various types of OADMs.
Optical Crossconnects 1 OXCs are used to handle more complex mesh topologies.
Key Functions of OXC 1 Service provisioning. 2 Protection 3 Bit rate transparency 4 Performance monitoring, test access and fault localization 5 Wavelength conversion 6 Multiplexing and grooming
A Realistic Example of All Optical Network
Survivability 1 A common requirement is that the connection be available 99.999% (5 9s). 2 The only practical way of obtaining the availability is to make the network survivable (i.e., able to continue providing service in the presence of failures). 3 Protection switching is the key technique used to ensure survivability.
1 The protection switching could be unidirectional or bidirectional. Protection Switching
Classifications of Switchings 1 The protection switching could be classified into path, span and ring switchings.
Point-to-point Protection in SONET/SDH 1 There are different types of protection techniques for point-to-point links.
Self-healing Rings: UPSR 1 Much of the carrier infrastructure today uses SONET/SDH rings. These rings are called self-healing. Above is a unidirectional path-switched ring.
Self-healing Rings: BLSR/4 1 A four-fiber bidirectional line-switched ring.
BLSR/4: Span and Ring Switchings
BLSR: Spacial Reuse Multiple working connections can share protection bandwidth around the ring as long as they do not overlap on any link.
Ring Connections A simple interconnection is vulnerable to the failure of one of the two nodes that form the interconnection.
Protection in Client Layer: In Resilient Packet Ring 1 Resilient packet rings (RPRs) have two mechanisms for survivability.
Protection in Client Layer: In Ethernet 1 Spanning trees are used for the protection in Ethernets.
Protection in Client Layer: In IP 1 If there is a failure in the network, the intradomain routing protocol (OSPF or IS-IS) operates in a distributed manner.
Protection in Client Layer: In MPLS 1 MPLS can be protected by fast reroute protection switching (in the order of 60ms).
Why Optical Layer Protection? 1 SONET/SDH networks incorporate extensive protection functions. However, other networks such as IP networks do not provide the same level of protection. 2 Significant cost savings can be realized by making use of optical layer protection, instead of the client layer. 3 Optical layer protection can be used to provide an additional degree of resilience.
Goal of Design 1 Our goal is to study who to design a wavelength-routing network.
Cost Tradeoff 1 Network topologies are usually designed to be 2-connected. Fiber ring topologies are more widely deployed.
Example: PWDM Ring 1 The number of wavelengths needed to support this traffic is W =. N+1+ 1 N 1 8 t
Elements Determining the Cost 1 Router ports: we would like to use the minimum possible number of IP router ports to support the given traffic. 2 Wavelengths: we would like to use the minimum possible number of wavelengths. 3 Hops: it refers to the maximum number of hops taken by a light-path.
LTD and RWA 1 We divide the wavelength-routing network design problem into that of an LTD problem and an RWA problem. 2 This separation is a good heuristic approach for practical designs since solving the two problems in a combined fashion is very difficult.
Lightpath Topology Design The LTD problem can be formulated as an optimization problem: 1 Cost function to be minimized. 2 Constraints: Flow conservation Total flow on a link Degree constraints Bidirectional lightpath constraint Nonnegativity and integer constraint
Wavelength Conversion 1 The wavelength conversion could be either full, fixed or limited.
Statistical Dimensional Models 1 First-passage model: In this model, the network is assumed to start with no lightpaths at all. Lightpaths arrive randomly. 2 Blocking model: In this model, the light path requests are treated in the same way that a telephone network treats phone calls.
Maximum Load Dimensioning Models 1 The results are classified into two categories: offline requests and online requests. 2 The offline problem corresponds to a static network design problem. 3 The online one corresponds to the dynamic network design case where light paths arise one at a time and have to be assigned routes and wavelengths when the request arrives, without waiting for future requests to be known.
SONET/SDH Core Network 1 Given today s capacity demands, many of the rings actually consist of multiple rings connecting the same set of nodes.