Md Ali Ahsan Razib Id57 57

DESIGN OF A DISTRIBUTED PROTOCOL FOR A SURVIVABLE WDM WIDE AREA NETWORK ARCHITECTURE Md. Ali Ahsan Razib, Uzzal Shyam Department of Computer Science & Engineering, Shah Jalal University of Science & Technology, Bangladesh [email protected]

ABSTRACT We have proposed a survivable wide area WDM network architecture based on Multiring approach in this paper. The architecture provides implementation of high bandwidth network, use of optical components without requiring electro-optic conversion, restoration of service in case of link or node failure almost in no time and many other essential features essential features needed to establish and maintain a practical network. A novel distributed protocol for maintaining the connections of the network is also proposed. The protocol which uses pre-planning scheme for computing backup paths is ideal for maintaining survivable wide area networks as well as for accommodating the ever-increasing bandwidth requirements. Keywords: backup, node, ring, survivability, WDM.

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INTRODUCTION

WDM networks have been studied extensively over the years [1, 3]. But there has not been much work for the implementation of WDM systems over a wide area network. In this paper, we have proposed an efficient WDM architecture which is suitable for large geographic areas. A control protocol is also established for the effective use of the network. Within a local node our system uses fixed wavelength transmitters to send data only at a specific wavelength and tunable wavelength receivers to receive data at any wavelength. The system utilizes time division multiplexing (TDM) at the local nodes and wavelength division multiplexing (WDM) at the backbone network. One of the advantages of our network is the simplicity of control hardware and very low processing involved with the protocol. Ring topology for connecting smaller metropolitan areas presents a number of desirable features to the network. Hub nodes managing the transmission within the rings also lessen the protocol overhead. A data transfer operation consists of a setup phase, transmission phase and a tear down phase. Backup path is calculated along with the primary path in the setup phase. The cost of additional time for calculating backup paths while setting up connection is more than paid back when it comes to the survivability of the network 2

each division or state of a country as a single region. In a region, there may be multiple cities or districts. We define each city or district as a local node. The local nodes are connected by one or more rings. Each ring is constructed according to the required data rate of the local nodes and the distance between the local nodes. The diameter of each ring should be kept as small as possible for better quality of this network. Among the local nodes of a ring, two nodes are selected as hub nodes. They are referred as Hub-1 and Hub-2 (See Fig. 1). A backbone router node connects all the Hub-1 nodes within a region, while another router connects all the Hub-2 nodes. The reason behind simultaneously using two hub nodes and two backbone nodes is network survivability. In the local node architecture we have used Optical Add-Drop Multiplexer (OADM) to add or drop data at a particular wavelength. The proposed network has a control channel for control information and several data channels. The add-drop switch corresponded with the control channel is always in add-drop mode, not in pass mode, since every node must send and receive control information. Fixed transmitters and tunable receivers are used so that a local node can only transmit at a pre-determined wavelength, but can receive at any wavelength. The hub and router nodes contain Wavelength Selective Cross-connects (WSXC) to switch data to the desired destinations. A WSXC can switch a subset of the wavelength channels from an input fiber to an output fiber.

PROPOSED NETWORK ARCHITECTURE 3

We have proposed a novel architecture for a nationwide WDM network. The entire country is divided into a number of regions. We may consider

DESIGNED PROTOCOL

Data transmission in our network involves transfer of control frames among local nodes, hub

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Figure 1. Architecture of a region in the proposed WDM wide area network. receiving the ACK frame from Hub2 (or Hub1), the source resets the setup/transmission field of nodes and backbone router nodes. The source and connection table to ‘1’. The source then sets its destination nodes are always the local nodes. These OADM to transfer data through the calculated nodes maintain time division multiplexing and direction at a pre-determined wavelength. electrical buffering to combine and store the data If during data transmission, an ACK frame stream generated in metropolitan areas. The hub comes from Hub1 (or Hub2) informing that the path nodes control the data transfer within or outside the is not OK, the source sends a REQ frame to the other rings. It is the responsibility of the hubs to switch hub informing that backup path is about to be used. data destined for nodes outside the ring to the When the ACK is received from that hub, the source backbone router or select a free wavelength for a sends the following data of the connection to Hub2 destination to receive data within the same ring. The (or Hub1) so that data transmission continues despite backbone routers perform the switching between the primary path failure. rings in a region as well as connect the regions for After the data transmission, the source sends inter-regional transport traffic. REQ frame for tearing down the connection to Hub1 The following subsections describe the (or Hub2) and deletes the row in its connection table. distributed protocol at different nodes of the architecture. 3.2 Protocol at Hub Node The hub receives the REQ frame from the source 3.1 Protocol at Source Node or other router and checks whether the destinations The source has a Connection Management Table are within the ring. If the destinations are within this for keeping track of the ongoing connections. The ring, the hub determines a free wavelength for each columns of the table are Connection-ID, destination and sends REQ frames asking them to get primary/backup path, setup/transmission and ready to receive data at those wavelengths and waits destination list. The source extracts the destination for ACK frames for a given time. In other cases the list from the multiplexed data stored in its buffer and Hub sends REQ frames to the next backbone router. adds a row to insert the information in the table. The hub has a switching as well as a routing The source sends REQ frame containing the table. The hub adds a row in the switching table for destination list for setting up primary path to Hub1 each destination and fills some of the entries based (or Hub2) via outer fiber and sets a timer. on the REQ frame from the source or other router. If no ACK frame comes within the time limit or If any of the ACK frames does not come within ACK frame comes indicating some fault in the path the time limit; or all the ACK frames arrive, but any ahead, the source resets the primary/backup field of one indicates fault, the hub sends ACK frame to the the connection table to ‘1’ to indicate that primary source or other router indicating that the primary path can no longer be used for data transmission and path is not OK for transmitting data to the sends REQ frame to Hub2 (or Hub1) via inner fiber destinations. The hub also deletes the corresponding and sets a timer. rows of its switching table. If ACK frame from Hub1 (or Hub2) arrives The hub then multiplexes the data coming from within time limit informing that path is OK, the different local nodes destined for the same source sends REQ frame to Hub2 (or Hub1) for destination node and sends them accordingly. establishing a backup path and sets a timer. After

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Otherwise, the hub demultiplexes the data for one of its local nodes and sends at a free wavelength. During data transfer, the hub keeps checking the incoming REQ/ACK frame. If it is REQ from the source to tear down the connection, it passes this information to the next hop and deletes the corresponding rows of the switching table. If it is ACK from other router informing that path is not OK, the hub passes this information to the source and deletes the row from the switching table. If all of the ACK frames come indicating that the path is OK, the hub passes this information to the source or other router to confirm data transmission. If the hub is being used for backup path, it waits for REQ frame to come from the source or other router informing about a failure. If the REQ frame comes, the hub sends ACK frame to the sender. 3.3 Protocol at Backbone Node The router receives the REQ frame from the hub or other router and determines the next hop from its routing table. The routing table of the backbone router has all the information about the network state. The router then sends REQ frame to the next backbone router or hub. The router adds a row in the switching table for the connection and fills some of the entries based on the REQ frame from the hub or other router. If no ACK frame comes within the time limit; or the ACK frame arrives, but indicates fault, the router sends ACK frame to the previous hub or router indicating that the primary path is not OK for transmitting data to the destination. The router also deletes the corresponding row of its switching table. If the ACK frame comes indicating that the path is OK, the router passes this information to the previous hub or router to confirm data transmission. If the router is being used for backup path, it waits for REQ frame to come from the hub or other router informing about a failure. If the REQ frame comes, the router sends ACK frame to the sender. The router sets its OXC for switching. During data transfer, the router keeps checking for REQ/ACK frame. If it is REQ from the previous hub to tear down the connection, it passes this information to the next hop and deletes the corresponding row of the switching table. If it is ACK from next hop informing that path is not OK, the router sends ACK to the previous hub and deletes the row from switching table. 3.4 Protocol at Destination Node The destination node sends ACK frame to its corresponding hub whenever it receives a REQ frame and sets its OADM to receive data at the given wavelength. 3.5 Format of Control Frame The control frame contains C bits used for clock

synchronization, and W-1 REQ/ACK mini-frames, each pre-allocated to each wavelength except the wavelength for control channel (See Fig. 2). Each mini-frame consists of 11 fields: flag, Connection ID, Setup/ Teardown, REQ/ ACK, Sender ID, Receiver ID, Source ID, Destination ID list, VCI, Primary/ backup and Path OK. The ‘flag’ bit indicates whether a wavelength can be reserved or not. If flag is ‘1’, a node does not reserve that wavelength. The ‘connection ID’ is a unique number generated by the source node for each connection. The ‘setup/teardown’ bit is used to indicate the status of the connection. If setup/teardown is ‘0’, the connection is in setup phase. The ‘REQ/ACK’ bit indicates whether the control frame is for request or for acknowledgment. An acknowledgment frame contains ‘1’ in the REQ/ACK field. The ‘sender ID’ is a number identifying the sender of the control frame. The ‘receiver ID’ is also a unique number for the receiver of the control frame. The ‘source ID’ recognizes the original source of the connection. The ‘destination ID list’ is a list of destinations for a connection. The controlling hub of the source node uses this collection of destinations to send the data to appropriate places. The ‘VCI’ stands for Virtual Circuit Identifier. It identifies the virtual circuit through different nodes. The ‘primary/backup’ bit indicates the path to be used for data transmission. It contains ‘1’ when primary path is down for a link or node failure. The ‘path OK’ bit tells about the fault of a path. It is used to pass the information of a link or node failure to other nodes. If the network has N nodes and we use b bits for each ID fields and the VCI, the length of the control frame, L is as follows. L = C + (W - 1) [3 + (N + 5)b] 4

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PERFORMANCE ISSUES

To evaluate the performance of our proposed WDM system with respect to other networks, the following metrics may be used [2]: the processing requirements, the network throughput, the mean network delay, requirements for a network-wide synchronization. The proposed protocol has low processing requirements and provides a high throughput without requiring significant delay and a global synchronization. The network operates without wavelength converters. This greatly reduces the installation cost of the network. Data transfer between the respective hub nodes of the source and destination is accomplished entirely in optical domain without the need for electronic conversion. The protocol also ensures fairness among nodes in a ring. As each node is able to transmit only at a specific wavelength, there is no collision for sending

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Frame Format: Connection ID

Setup/ Teardown

REQ/ ACK

Sender

Receiver

Source

Destination List

Control Frame (SETUP/TEARDOWN) frame from Hub1: λ1 … sync λ0

λw-1

flag

Source

Connection Setup/ ID Teardown Figure 2. Control frame format.

REQ/ ACK

Sender

data at a wavelength. The hub determines a free wavelength for a node whenever the node is to receive data. This central control avoids any fairness problem which would have been experienced if the nodes themselves were responsible for managing the wavelengths. Due to space limitation, the detailed description of fairness control issues has been omitted and can be found in [4]. 5

CONCLUSION

A novel survivable WDM architecture with a suitable protocol for wide area networks is proposed in this paper. Multi-ring approach is used where local nodes are connected by multiple rings, which are inturn connected with arbitrary topology. Each local node is equipped with dynamic WADM. The ring consists of one control channel for the exchange of control information and W-1 data channels. The protocol implements data transfer operation in three stages: setup, transmission and tear down. The backup path is pre-calculated along with the primary path. This significantly reduces the recovery time when a link or node failure occurs in the primary path. The protocol also maintains fairness among the local nodes. The new architecture and protocol offer improved performance and fault tolerance as well as many other desirable features compared to the existing networks. Multicasting and broadcasting are also supported in this network. In a word, this architecture is a leap towards the future to provide an efficient solution to the ever-increasing bandwidth requirements of the modern computer era.

Receiver

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Wavelength

VCI

Primary/ backup

Path OK?

Guard

Destination List

VCI

Primary/ backup

Path OK?

REFERENCES

[1] D. Banerjee and B. Mukherjee: Wavelength Routed Optical Networks: Linear Formulation, Resource Budget Tradeoffs and a Reconfiguration Study, IEEE/ACM Transactions on Networking, vol. 8, no. 5, pp. 598-607 (2000). [2] P. A. Humblet, R. Ramaswami, and Kumar N. Sivarajan: An Efficient Communication Protocol for High-Speed packet-Switched Multichannel Networks, IEEE Journal on Selected Areas in Communications, Vol. 11, No. 4, pp. 568-578 (1993). [3] D. Awduche and Y. Rekhter: Multiprotocol Lambda Switching: Combining MPLS Traffic Engineering Control with Optical Crossconnects, IEEE Communications Magazine, vol. 39, no. 3, pp. 111-116 (2001). [4] I. Cidon and Y. Ofek: METARING-A fullduplex ring with fairness and spatial reuse, IEEE Trans. Commun., Vol. 41, pp-110-120 (1993).

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