Distributed Network Control for Optical Networks Presented by, Sree Rama Nomula

Introduction What are Optical Networks? Optical network is a network with transmission links that are optical fibers, and with an architecture that is designed to exploit the unique features of the fibers.

WDM Networks Technique used in optical communications networks by which two or more optical signal having different wavelengths may be simultaneously transmitted in the same direction over one fiber and separated by wavelength at the end.

Controller Communication Network The Network E BA C D Controller Switching Node

Controllers Switches in a node are controlled by a controller. Controllers communicate with each other over communication network, either in- band or out-of-band. Assumption: – The transport protocol for message passing between controllers is reliable.

Controllers Keeps track of the connections in its associated node. – Connection Switch table(CST) – Connection update procedure – Topology update protocol

Connection Switch Table Every connection has a unique id. – – Sequence numbers can be same if two connections have different originators or destinations. A connection can be in the up or reserved state.

CST at Node A Connection-idPort State E,D,12 B, 3D, 1 up B,C,10 B, 1C, 3 up E,C,8 B, 2C, 2 reserved C,A,8 D, 3 I/Oup

Status bits For every port in a switch a status bit is attached, which can be modified by the controller. Status bit is 0 if the port is being used else it is set to 1. If a port recovers from failure, the status bit is set to 1.

CST recovery CST is lost if the controller goes down. Revival process. – Current switch settings in the node are read. – Ports with status bit = 1 are disregarded. – For ports with status bit = 0 an entry is made in the CST. – The connection-id is set to null. CST is updated by using a CST update protocol.

CST recovery(contd.) Status bit = 1 on (C, 3) and (B, 1). Status bit = 0 on (B, 3),(D, 1) and (D, 3) Connection-idPort State B, 3D, 1 up D, 3 I/Oup

Connection Update Procedure Periodically or whenever CST changes, messages are passed to the neighboring controller. The message contains a list of wavelength, id and state of all connections that go over the link connecting the two nodes. Ex: From node A to C – { [ 3, (B,C,10), up], [ 2, (E,C,8), reserved]}

Topology Update Procedure Each node periodically broadcasts pertinent topology information to other nodes. Also, event driven updates can be generated. A topological update message contains the list of up links adjacent to the nodes and their wavelength usage. Ex: Node A generates the message … – { (B, 1, 2, 3), (C, 2, 3 ), (D, 1, 3) }

Connection Setup Wavelength and Route Determination – Using the data in the topology and wavelength usage database, the route and wavelengths can be determined. Reservation – The originator node requests all the controllers on the connection to reserve wavelengths on all links on the path. This step makes sure that there are no loops of committed resources. Connection Setup/Release – If reservation is successful at all nodes in the path, switches are setup by the corresponding controllers. Otherwise all the reservations are released.

Takedown and Update For dropping a connection two procedures are employed. – Explicit TAKEDOWM messages. – CST Update. A TAKEDOWM message is sent to each controller on the connection. The controllers delete the entry corresponding to the connection in their CST. If some controllers are down it takes connection down at all working controllers.

Takedown and update(Contd.) Periodically or if there is a change in the CST, each controller sends update messages to its neighboring controllers. The Update message contains a list of wavelength, id and state of all connections that go over the link. On receiving the update, the controller matches it with the local CST. If no entry is found in the update message, corresponding to an entry in the local CST, the entry in the local CST is deleted.

CST Update If a controller deletes an entry, then related entries will be deleted at all controllers along the path. This will continue till the end of connection or failed controller is met. Similar is the case when a link or wavelength is failed. If the other end wants to takedown when the originator controller fails, then it will simply delete the appropriate entry. The switch setting remain the same till a new connection is requested.

Finite State Machine unused reserve d up confirme d up(no id) entry delete d RESERVE(id) SETUP(id) Controller recovery (status = 0) TAKEDOWN (id) RESERVE-TIMER(id) expires LST(related in confirmed) CONFIRM(id) LST(related no entry) TAKEDOWN(id) LST (no related entry)

Summary Proposed distributed protocols for setting up, taking down and maintaining the state of connections in a WDM optical network. These protocols can be used in networks – With different kinds of node architectures. – Different route computation algorithms and underlying constraints of the physical layer. – Different kinds of underlying mechanisms for the controllers communication.

Thank You !