OPTICAL BURST SWITCHING

OPTICAL BURST SWITCHING

1

VISHAL JANI ,

PANDYA KASHYAP N,

DIPTESH PATEL

1,2,3

Shree J.M. Sabva Institute Of Engineering And Technology, Aradhna Saikshnik

Sankul, Bhavnagar Road, Botad – 364710 Gujarat State

ABSTRACT : The current Internet is suffering as the number of users on the Internet and the varieties of applications transported are growing steadily at high rate, the available bandwidths are facing limits. Frequent congestion situations restrict the use of new time-critical applications like IP telephony, video conferencing or online games.Optical Burst Switching (OBS) is an experimental network technology that enables the construction of very high capacity routers, using optical data paths and electronic control. OBS is the transmission of the aggregation of multiple IP packets (a burst) without the need for any type of buffering at the intermediate nodes. OBS works on cut and through forwarding as against the store and forward approach in Packet switching. The bandwidth for the burst is reserved in a one-way process. One channel is reserved for control information. Other are carried the data bursts. There are several schemes for OBS signaling: Tell-and- go (TAG), in-band terminator (IBT), Just-enough-time (JET) etc

1.1 The Need For OBS:

The current Internet is suffering as the number of users on the Internet and the varieties of applications transported are growing steadily at high rate, the available bandwidths are facing limits. Frequent congestion situations restrict the use of new time-critical applications like IP telephony, video conferencing or online games. Thus, there is not only an increasing demand for bandwidth but also some sort of scalable quality of service support. One possible solution in this domain is optical burst switching (OBS), a concept combining advantages of optical circuit and packet switching. Optical Burst Switching (OBS) is one of the most important switching technologies in the future optical WDM networks and Internet.

1.2 Basic Concept:

Optical burst switching (OBS) is a technology positioned between wavelength routing (i.e., circuit switching) and optical packet switching. All-optical circuits tend to be inefficient for trace that has not been statistically multiplexed, and optical packet switching requires practical, cost-effective, and scalable implementations of optical buffering and optical header processing, which are several years away. OBS is a technical compromise that does not require optical buffering or packet-level parsing, and it is more efficient than circuit switching when the sustained trace volume does not consume a full wavelength. The transmission of each burst is preceded by the transmission of a control packet, whose purpose is to inform each intermediate node of the upcoming data burst so that it can configure its switch fabric in order to switch the burst to the appropriate output port. An OBS source node does not wait for confirmation that an end-to-end connection has been set-up;

instead it starts transmitting a data burst after a delay (referred to as offset), following the transmission of the control packet. OBS nodes have no buffers; therefore, in case of output port convict, they may drop bursts.

Optical burst switching is most promising in the sense that it utilizes both proved electronic control processing mechanism and optical transmission technology. It electronically allocates optical switching system resources ahead of optical data bursts. To avoid the discrepancy between the electronically processing speed and the speed of optical transmission, optical burst switching transports burst of large size assembled from smaller packets such as IP packets. To further support the future Internet multimedia, mission critical and real-time applications such as video on demand, telemedicine, and remote learning, optical burst switching needs to be able to support high quality of operation (e.g. low delay and loss probability). One of most important quality of service parameter in OBS is the burst loss rate (probability). It is important that high priority class of data bursts have low loss probability even under low network resource such as available wavelengths and optical switch paths in an optical burst-switching node (OBSN). One of main reason of burst loss is that after processing the request for reserving resource for incoming data burst, an OBSN is not able to schedule the output wavelength or optical switch matrix and has to drop the data burst. Each OBS node can adjust the data burst loss rates for different classes of bursts and satisfy differentiated quality of service requirement with the available resources.

2.1 Optical Circuit Switching

A Optical circuit switched network has to have a dedicated wavelength path for the duration of its connection. In order for a circuit switched network to operate, a circuit is defined from the start of the connection to the end.

This circuit is then reserved for this connection only, but becomes available once the connection is terminated.

Referring to Figure 2.1, if a connection between points A and B is required, then a circuit is set-up via S1, S3, S4 and S5. Other routes are possible allowing for resilience, and it should be noted that the links between the switches might consist of more than one circuit to allow multiple circuits to be set up.

.

Figure 2.1: Circuit Switching Network

Circuit switching has three phases: Circuit set up, Data transmission, and Circuit tear down.

During Circuit Set up, reservation of fixed wavelengths along the path is done, on each link along the path from the source to its corresponding destination.

During Data Transmission, data is sent on the dedicated line. When distributed control is used in the phase of routing, the offset time between a set up request and data transmission T, is at least as long as 2P+delta, where P is the one way propagation and the delay delta is the total processing delay encountered by the set up request along the path. There is no need for buffering on intermediate nodes since the circuit is only used for this data at that particular time.

After the whole data is sent to the destination Circuit Tear Down occurs. The destination sends an acknowledgment signal to the source. As a consequence the nodes are released to be used in another connection.

Figure 2.1. 2: Circuit Switching Signaling

2.2. Optical Packet Switching

Packet switching works by sending the packets of information along the appropriate route. The router decides the appropriate route when the packet arrives. In packet switching each packet (a piece of data) contains additional information in it (header), rather like the address on an envelope, and each switch in the network (usually called routers) looks at this information and directs it onward accordingly. As an example imagine information being sent from point C in Figure 3, and its destination is D. A packet of information leaves C and is directed by R1 onto R3, R3 then directs the packet to R4 and then onto D. However, it may not always occur like this. Perhaps during the transfer the link between R1 and R3 experiences a slow connection or is lost, R1 would then start sending the packets to R2, R2 would then send it to R5, and so on. In packet switching the length of each packet Lp, can be either fixed or variable having a minimum of S min and maximum of S max.

With a fixed packet length, a burst of size Lb will be broken into smaller packet of the same size. With a variable length the message will be broken into Lb/S max packets, and padding is used only if a packet is shorter than S min. A main feature of packet switching is store and forward. Meaning that a packet needs to be completely assembled and received by a source and each intermediate node before it can be forwarded. This will let the packet experience a delay proportional to Lp at each node and will make necessary the existence of a buffer at each intermediate node of the network with a size of at least S max.

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Passive link active link switch/router Figure2.2: Packet Switching Network 2.3. Optical Burst Switching

In Optical Burst Switching, a control packet is sent first, followed by a burst of data without waiting for an acknowledgment for the connection establishment, this is called a one-way reservation protocol. The main feature of OBS is to switch a whole burst of packet whose length can range from one to several packets to a session using one control packet, and resulting in a lower control overhead per data unit. OBS uses out of band signaling, and the control packet and the data burst are loosely coupled in time. Meaning that they are separated at the source by an offset time, which is larger than the total processing time of the control packet along the path. In consequence this eliminates the need for the data burst to be buffered at any subsequent intermediate node just to wait for the control packet to get processed.

Figure 2.3: Optical Burst Switching Nodes

Another alternative is that an OBS protocol may not use an offset time at the source, but instead requires that the data burst at each intermediate node is delayed in a fixed time that is not shorter than the maximal time needed to process a control packet at the intermediate node. To support IP over WDM in OBS, we run IP software along with other control software as part of the interface between the network layer and the WDM layer, on top of every optical (WDM) switch. In the WDM, a dedicated control wavelength is used to route the control packet. To send data, a control packet is routed from a source to a destination based on the IP address it carries to set up a connection by configuring all optical switches along the path. Next, a burst is delivered without going through intermediate IP entities, thus reducing the latency as well as the processing at the IP layer. In OBS, the wavelength of a link used by the burst will be released as soon as the burst passes through the link, either automatically according to the reservation made or by an explicit release packet. This means that bursts from different sources to different Destinations can effectively utilize the bandwidth of the same wavelength on a link in time-shared statistical multiplexed manner. In case the control packet fails to reserve the wavelength at an intermediate node, the burst is not rerouted, it is dropped. OBS protocols are not all the same; some of them support a reliable burst transmission, which has a negative acknowledgment that is sent back to the source node, which retransmits the control packet and the burst after that. Other OBS protocols are not reliable and don’t shave such negative acknowledgments.

2.4. Comparison:

Circuit switching is good for smooth traffic and quality of service guarantee due to a fixed bandwidth reservation. However, the bandwidth becomes inefficient for busty data traffic. This means that the bandwidth is either wasted during low traffic period or too much overhead (e.g. delay) occurs due to the frequent set up /release for every connection. The advantage of Packet switching is that a packet containing a header (e.g.

addresses) and a payload is sent without circuit set up (delay) and we have static sharing of the link wavelengths among packets with different sources and destinations. However, due to the store and forward mechanism, every node processes the header of the packet arriving to know where to route it, and this make the use of a buffer at every node necessary. OBS combines both advantages of optical circuit and packet switching. Unlike the circuit switched approach it does not need to dedicate a wavelength for each end-to-end connection due to the fast release of the wavelength on a link after the burst passes by it. Also unlike the packet switched approach, burst data does not need to be buffered or processed at the cross connect since the OBS mechanism is a cut through one.

Table 1. Comparison between the Optical Switching Techniques

3.1 Concept of OBS Network Architecture

The basic burst-switching concept is illustrated in Fig. 1. The transmission links carry data on tens or hundreds of wavelength channels and user data bursts can be dynamically assigned to any of these channels by the OBS routers. One (or possibly several) channel on each link is reserved for control information that is used to control the dynamic assignment of the remaining channels to user data bursts. When an end system has a burst of data to send, an idle channel on the access link is selected and the data burst is sent on that channel. Shortly before the burst transmission begins, a Burst Header Cell (BHC) is sent on the control channel, specifying the channel on which the burst is being transmitted and the destination of the burst. The OBS router, on receiving the BHC, assigns the incoming burst to an idle available channel at the outgoing link leading toward the desired destination and establishes a path between the specified channel on the access link and the channel selected to carry the burst. It also forwards the BHC on the control channel of the selected link, after modifying the cell to specify the channel on which the burst is being forwarded. This process is repeated at every router along the path to the destination. The BHC also includes an Offset field, which contains the time between the transmission of the first bit of the BHC and the first bit of the burst, and a Length field specifying the time duration of the burst. The offset and length fields are used to time switching operations in the OBS routers, and the offset field

is adjust by the routers to reflect variations in the processing delays encountered in the routers’ control subsystems. If a router does not have idle channels available at the output port, the burst can be stored in a buffer.

OBS router architecture consisting of a set of Input/Output Modules (IOM) that interfaces to external links and a multistage interconnection network of Burst Switch Elements (BSE). The interconnection network uses a Benes topology, which provides parallel paths between any input and output port. A three-stage configuration comprising port switch elements can support up to external links (each carrying many WDM channels). The topology can be extended to 5,7 or more stages. In general, a 2K-1 stage configuration can support up to dk ports. For example, a 5-stage network constructed from 8 port BSEs would support 512 ports. If each port carried 256 channels at 10 Gb/s each, the aggregate system capacity would be 1310 Tb/s.

Input IOMs process the arriving BHCs, performing routing lookups and inserting the number of the output IOM into BHCs before passing them on. The BSEs use the output port number to switch the burst through to the proper output. Each of the components that do electronic processing on the cell keeps track of the time spent and updates the offset field in the BHC to maintain synchronization with the burst.

3.2 OBS Fundamental

Figure 3.2.1: Burst Assembly/Disassembly at the Edge of an OBS Network

In an OBS network, various types of client data are aggregated at the ingress (an edge node) and transmitted as data bursts (Figure 3.2.1(a)) which later will be disassembled at the egress node (Figure3.2.1 (b)). During burst assembly/ disassembly, the client data is buffered at the edge where electronic RAM is cheap and abundant.

Figure3.2.2: Separated Transmission of Data and Control Signals

Figure 3.2.2 depicts the separation of data and control signals within the core of an OBS network. For each data burst, a control packet containing the usual ”header” information of a packet including the burst length information is transmitted on a dedicated control channel. Since a control packet is significantly smaller than a burst, one control channel is sufficient to carry control packets associated with multiple (e.g., hundreds of) data channels. A control packet goes through O/E/O conversion at each intermediate OBS node and is processed electronically to configure the underlying switching fabric. There is an offset time between a control packet and the corresponding data burst to compensate for the processing/configuration delay. If the offset time is large enough, the data burst will be switched all-optically and in a “cut-through” manner, i.e., without being delayed at any intermediate node (core). In this way, no optical RAM or fiber delay lines (FDLs) is necessary at any intermediate node.

3.3 Assembly algorithms

Usually, assembly algorithms can be classified as

1) Timer-based

2) Burst length-based

In the timer-based scheme, a timer starts at the beginning of each new assembly cycle. After a fixed time T, all the packets that arrived in this period are assembled into a burst.

In the burst length-based scheme, there is a threshold on the (minimum) burst length. A burst is assembled when a new packet arrives making the total length of current buffered

Packets exceed the threshold. The time out value for timer-based schemes should be set carefully. If the value is too large, the packet delay at the edge might be intolerable. If the value is too small, too many small bursts will be generated resulting in a higher control overhead. While timer-based schemes might result in undesirable burst lengths, burst length-based assembly algorithms do not provide any guarantee on the assembly delay that packets will experience.

After a burst is generated using the algorithms mentioned above, the burst is buffered in the queue for an offset time before being transmitted to give its corresponding control packet enough time to make reservations at the downstream nodes as shown in Figure 3.2.2. During this offset period, packets may continue to arrive.

3.4 Node Architecture

An intrinsic feature of OBS is the physical separation of transmission and control. A data burst (DB) and its control signal (CS) are transmitted separately on different channels with the CS slightly ahead in time. The CS is used to reserve resource for DB. In our OBS network, one link (or fiber) carries 5 WDM channels, 4 dedicated data channels and one shared control channel. We employ variable length optical burst running in an asynchronous manner. This matches the natural form of packets and simplifies implementation by avoiding synchronization and burst alignment. The bit rate of control channel is substantially lower than that of data channel, thereby allowing electronic processing of CS. In addition, the sharing of control channel leads to a better link utilization.

3.4.1 Core Node

The main function of CN is to realize burst switching. As shown in Fig. 1, CN is composed of an electronic control block and an optical channel block. It supports 4 links. The electronic control block consists of two parts: control signal processing part performs route searching with contention resolution [2], CS updating and forwarding, channel scheduling and switching control; while system management part performs supervision and control of optical devices. The optical channel block consists of splitters, MUX/DEMUXs, optical switch matrix, power equalizers and optical amplifiers (AMP). More specially, (1) Splitter separates control channel operating at 100Mb/s with 1510nm wavelength from data channels operating at 1Gb/s

Fig 3.4.1 Core Node Architecture

With 200GHz channel interval on C band. (2) MUX/DEMUX are used to multiplex and de-multiplex 4 data channels. (3) Optical switch matrix is composed of four non-blocking same

Wavelength 4×4 thermo-optic switches with the switching speed of less than 3ms. Burst cut through switches, thereby its format and bit rate can be arbitrary. (4) Power equalizer and AMP are used to equalize and amplify the power of data channels respectively. We construct a software-based electronic control block and a general- purpose optical channel block within CN. They can be flexibly reconfigured to realize wavelength/burst/label

switching. Various routing and signaling protocols can be adopted and extended so that we can make field trial and evaluate performance more flexibly.

3.4.2 Edge Node

As shown in Fig.3.4.2, besides the same functions as CN, another main function of EN is to connect legacy client networks, which is realized by a burst transceiver (BT) unit with Gigabit Ethernet (GbE) interfaces. An EN supports 4 links, 2 remote links connected to other OBS nodes and 2 local links (or 8 channels) connected to client networks through BT. Both bursts come from other OBS nodes and bursts generated within BT are routed and scheduled by BT with contention resolution.

The main functions of BT include generating, receiving, forwarding and scheduling of DB and CS. At ingress EN, BT transmitter assembles multiple GbE frames into bursts according to their egress EN addresses and generates the corresponding control signal simultaneously. At egress EN, BT receiver disassembles the received bursts back into GbE frames. The detail of BT refers to [3]. We construct a programmable burst transceiver unit within EN, which allows design flexibility and fast design cycles. Various assemble and scheduling algorithm can be adopted, and the related parameters can also be modified flexibly.

Fig 3.4.2 Edge Node Architecture 3.5 Comparison OBS Layers with other IP Layers

There are at least four reasons why a transport layer architecture for OBS networks will likely differ from transport layer architectures for other networks, especially networks that use IP or a comparable layer 3 datagrams service:

1) The network architectures are fundamentally different (Figure 3.5). OBS architectures typically do not buffer bursts in the all-optical core, and intermediate burst switches provide no IP-like network layer services.

OBS architectures typically do not require a link layer protocol in the optical domain. Traditional link layer services are either not provided, or are provided by an end-to-end protocol, or are severely constrained. Service differentiation in IP/datagram networks typically requires resource reservations and/or packet queuing and active queue management at intermediate nodes. In contrast, service differentiation in OBS networks is performed at OBS edge nodes (except for burst-level priority-based preemption, and experimental mechanisms like burst aging and burst segmentation with head drop6,7). The OBS transport layer architecture will have to take on some traditional network layer, link layer, and service quality functions.

2) OBS networks inherently support a range of circuit- and packet-like services. OBS is technologically positioned between all-optical circuit switching and all-optical packet switching.

Figure3.5: Generic a)IP and (b) OBS layered architecture.

Most OBS variants can support circuit-like and packet-like services by varying burst lengths, and/or by establishing long-lived ‘light paths’. Light paths are analogous to provisioned circuits, and support pseudo wire and circuit emulation services. Some OBS variants support ‘persistent paths’ (pinned routes), which are analogous to burst-multiplexed fixed route tunnels. Single bursts, and burst streams that are individually and dynamically routed are roughly analogous to a bufferless optical packet-switched service (with burst overhead).

OBS ‘circuits’ and ‘tunnels’ can be provisioned in tens of microseconds (depending on switch configuration times), and have lifetimes from a few milliseconds to many hours. The OBS transport layer architecture will greatly benefit from OBS’ triform (circuit-, tunnel-, packet-like) character.

(1) Some transport layer services can be provided by OBS services.

There is little value in requiring the transport layer to provide redundant services. E.g., OBS pinned routes guarantee sequenced delivery without transport-layer sequence numbering and reassembly mechanisms.

End-to-end flow control may not be required over circuit-like OBS light paths. Sources receive nearly instantaneous indications of channel blocking over the OBS signaling channel, so there is no need for TCP-like timeouts or other congestion avoidance mechanisms. The OBS transport layer architecture will likely map some transport layer services directly onto OBS layer services.

(2) Many transport protocols have performance limitations when used in optical WANs,

Especially lossy protocols optimized for noisy, low-bandwidth links. These limitations have spawned a great deal of research on high-performance transport protocols for IP networks†. Feature sets include support for time-critical and scheduled transfers, high-performance network interfaces, OS bypass, network-aware OSs, service differentiation across administrative domains, etc. The OBS transport layer architecture must support a number of new features. We discuss functions, services, features, issues, and requirements for transport layer architecture for OBS networks. We focus on the OBS transport layer and on ancillary functions above and below the transport layer that may be required to implement both traditional and novel transport layer services within the architecture. These collectively comprise a reference model, a suite of transport services, and a conceptual transport protocol.

4. OPTICAL BURST SWITCHING TECHNIQUES There are three variations of burst switching:

1) Tell-and-go (TAG)

2) In-band-terminator (IBT) 3) Reserve-a-fixed-duration (RFD).

In all three variations, bandwidth is reserved at the burst level using one a way process, and the most important point is that bursts are cut through intermediate nodes, instead of being stored and forwarded.

4.1 Tell-and-go (TAG)

In TAG, the source sends the control packet on a separate control channel to reserve Bandwidth (and set switches) and set the switches along the path for a data burst that can be sent on the data Channel without receiving an acknowledgment first. This means that the offset time T Between the control and the burst packet is much smaller than the circuit set up time. After The burst is sent, another control signal is sent to release the bandwidth.

4.2 In-band-Terminator (IBT)

In IBT, every burst has a header like in packet switching and also a special delimiter or terminator indicating the end of the burst. IBT is not exactly like packet switching that has a store and forward mechanism, instead, IBT uses virtual cut through. Specifically, a source And the intermediate node can send the head of a burst even before the tail of the burst is received, this means that the burst will encounter less delay and a smaller buffer size is Needed at a node, except for one case when the entire burst has to wait at a node because the

Wavelength at the link is not available.

4.3 Reserve-a-fixed-duration (RFD)

RFD is somehow similar to TAG, in the sense that the control packet is sent first to reserve Bandwidth and set the switches, followed by the data burst after a time offset T. However, in RFD, the bandwidth is reserved for duration specified by the control packet, which, like a Header of variable length packet contains the burst length.

However, this means that the burst will have a limited maximum size.

4.4 Just Enough Time Protocol (JET)

JET is a RFD scheme proposed by Qiao and You. The source node having a burst of data to transmit sends at the beginning a control packet on a signaling channel which has a dedicated wavelength other than for the data to the destination node. At each node on the way, the control packet is processed in order to establish an all- optical path for the data burst. Each node of the path chooses a convenient wavelength on the outgoing link, reserves bandwidth on that link and sets up the optical switch, this is all based on the information carried by the control packet. During that time, the data burst wait for a time offset T, at the source node in the electronic domain. In JET the intermediate network nodes work as follows. The incoming data from end-stations is buffered according to its destination. After some time the data is ready for dispatch as an optical burst. A control signal (the burst header) is then sent to the next downstream node and some time later ‘T offset (launch)’ the burst is transmitted on the wavelength specified in the header. T offset is the time delay between a header and its respective data. T is sufficient for the intermediate nodes to fulfill the arrival of a burst header on the control channel of a link which signals a node to attempt to reserve a wavelength/time-slot for the soon-to-arrive data to be switched to an output link closer to the destination. Full wavelength translation capability at each link is needed so that any burst can be routed to any free wavelength on the output link; therefore the wavelength of a burst has local significance only. The downstream node then sends a new header to the next downstream node.

At each hop T offset is reduced by the processing time (per-hop-offset or Tpro) at each node; therefore for a burst to travel n hops, Toffset(launch) >.n * Tpro. The advance notice provided by the header suffices that when the data-burst arrives at an intermediate node, that node is already set to route the signal from input to output channel.

One advantageous feature of the JET protocol is the fact that the resources are reserved only for the time they actually are used. The control packet allocates a channel from the arrival time of the burst to the departure time of the burst. This additional information gives benefits over the traditional system, where the only information in the node is whether the channel is free or in use.

fig 4.4.1 Decrease in Offset as burst is processed

5. CONTENTION AND BURST LOSS IN OBS 5.1 What is Contention?

Contention occurs when more than one burst attempts to go out of same output port at the same time as shown in fig 5.1.

Contention is serious problem with Optical burst switching.

Fig.5.1 Contention Problem

Using one-way reservation protocols such as JET, the ingress node sends out bursts without having reservation acknowledgements or global coordination. This however, requires an intermediate OBS node to resolve possible contention among bursts.

5.1.1 Contention Resolution Techniques

In a buffer less OBS network, contention among the bursts can be resolved in three ways:

1) Dropping

2) Wavelength Conversion

3) Optical Buffering (Fiber Delay Lines)

I In Burst Dropping all the burst are processed in the same way as mentioned above ,but when a contention is occurs that time the second burst is dropped and process is begin.

So the main problem with the burst dropping is we cannot give grantee for delivering of burst. So the burst loss in increasing in buffer dropping.

Wavelength Conversion In this when a contention is occur that time contending burst can be sent on another wavelength through wavelength conversion as shown in fig. 5.2.1.

Fig 5.1.1 Wavelength Conversion

So main advantages is no additional hardware is required and it also balance the load over the wavelength. But the problem with approach is this technique is very expensive and not mature.

Optical Buffering (Fiber Delay Loop): in this approach when contention is occurs that time we can use a fiber delay loop(FDL) to delay the conflectinf loop. So a conducting burst is by passing through an FDL, a

contending burst can be delayed for a fixed time . shown in fig.

Fig 5.1.2 Optical Buffering(Fiber Delay Loop)

The problem with this approach is the complexity is increased and the cost of maintaining is increasing.

5.2 Burst Loss

There are mainly two reasons when the burst loss occurs:

1) At the time of processing of control packet the error occurs and channel is not properly allocated that time

2) At the time of contention problem.

To remove the burst loss there are two approach:

1) NAK

2) Burst retransmission approach

In NAK approach if the control packet is unable to allocate a channel, it sends a NAK packet back to the source node. The NAK packet frees the allocated channels along the path. If the offset time is long enough compared to the propagation delay, the NAK packet might catch the burst before it is sent. If the burst has already been sent before the NAK packet arrives at the source node, the NAK packet meets it at some node along the path, and the burst is removed there. The NAK packet then continues to the sending node and informs it that the burst was lost.

In RETRANSMISSION approach the source node sends a burst, keeps a copy and sets a timer. If the source receives a negative acknowledgement it retransmits the burst and repeats the same process. If no acknowledgement is received during the timer life, the node assumes that the burst has reached its destination and removes the local copy.

6. FEATURES AND APPLICATION OF OBS Features:

1) Decoupling of header processing and data forwarding 2) Allows sophisticated processing of control information, 3) data can stay in optical domain resulting in high throughput, 4) Out-of-band signaling.

5) No buffer required at intermediate node.

6) Bandwidth is consumed only when data is transferred 7) One-pass reservation saves time and bandwidth 8) Scalability and flexibility by sharing of wavelengths 9) QoS support in the optical layer

Application:

1) The main application is in the Feature 3G Optical Internet

2) Where the high bandwidth required such as IP Telephony, online gaming, videoconference, etc 7. Conclusion

In this paper we have discussed a novel paradigm called the optical burst switching (OBS) as an efficient way to resolve the problem of congestion that the Internet is suffering from. Bursty traffic, also OBS is a very promising switching technique that will most likely be adopted in the future Optical network. We say that Optical burst switching (OBS) is a technology positioned between wavelength routing (i.e., circuit switching) and optical packet switching. Also we compare it with the other optical switching and resolve that optical burst switching is best among them.

8.Bibliography Websites:

[1]. Www.ec ucl.ac.uk/lcs papers 2002/LCS 075.pdf

[2]. Www.csc.ncsu.edu/faculty/fouskas/arora/conference/ITC-XU-2003.pdf [3]. Www.csc.buffalo.edu/-9190/ON-OBS. PDF

[4]. Www.ieee.infocom.org/2003/papers/49_02. PDF

[5]. Www.cc.geatech.edu/people/home/younger/obs_network.pdf [6]. Www.utdallas.edu-vinod/obs.htm

BOOKS:

[1]. BEHROUZ A. FOROUZAN,(Second Edition) “Data Communication and Networking”,TMH.

[2]. UYLESS BLACK,(Second Edition) “Optical Networks”, Pearson Education.