Switching Techniques Used In Wired Networks Computer Science Essay

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INTRODUCTION

The two principal switching techniques used in wired networks are circuit switching and packet switching. One of the main differences between them is the way resources are shared. Circuit switching provides exclusive access to the resources by means of reservation. In packet switching, on the other hand, resources are shared on demand, without prior reservation. While it is obvious that packet switching is suitable for a wired data network such as the Internet, it is not clear whether this is true in the case of ad hoc wireless networks. To the best of our knowledge, a direct study and comparison between these two switching schemes for wireless ad hoc and sensor networks has not been reported in the literature so far. In this paper, we investigate the performance of two switching paradigms:reservation-based (RB) and non-reservation-based (NRB)switching. The concepts of reservation and non-reservation are analogous to those of circuit switching and packet switching in wired networks, respectively.

In addition to posing the interesting question of whether and when RB switching makes sense in wireless ad hoc networks, in this paper, we develop novel analytical models (queuing models) for analyzing the network performance (in terms of throughput, delay, goodput, and maximum tolerable speed) under the RB and NRB switching schemes.

One of the important work is to identify under which conditions (in terms of route discovery, MAC protocol, pipelining, etc.) the delay performance of the RB scheme can be superior to the NRB scheme. While the conventional wisdom in current wireless ad hoc networking research favors NRB switching, we show, for the first time, when and under which conditions RB switching might be preferable.

Although a few analytical models which takes into account delay and physical layer characteristics exist for NRB ad hoc wireless networks [2-4], no analytical models have been reported for RB schemes. We quantify the performance tradeoff between these two schemes in terms of goodput, delay, and maximum tolerable node speed.

3.1 The Two Switching Schemes:

3.1.1 Reservation-Based (RB) Switching:

The principle of operation of an RB scheme is fairly simple. Prior to data transmission, a source node reserves a multihop route to the destination through a route discovery phase. We assume that route discovery messages are sent on a separate control channel. Once an intermediate node agrees to relay traffic for a particular source in the network, it cannot initiate a session or relay messages for any other source until the on-going session is over. The source node releases the route after the session ends. We but not to the shared common radio channel. In other words, the intermediate nodes dedicate their processing time only to the source which reserved the route; however, reservation of a multihop route does not give any node an exclusive access to the shared radio channel (in terms of frequency bands, time slots, or spreading codes).

Fig. . Reservation-based ad hoc wireless network model. (a) General scheme: Each node has its own queue, and there are disjoint multihop routes in the network. (b) Equivalent conceptual model for the multihop route between S3 and D3-observe that the queues of the relay nodes R03 and R003 and the destination node D3 are suppressed: In other words, the relay nodes and the destination nodes do not involve new queues.

3.1.2 Non-Reservation-Based (NRB) Switching

In the case of NRB switching, there is no reservation of a route prior to data transmission. As opposed to an RB scheme, in an NRB network communication scenario, multihop routes can overlap. In particular, a node can serve as a relay node for more than one route. In other words, when a node receives a message from another node (i.e., it acts as a relay), it places that message in its own queue (intermingled with its own generated messages). The messages in the queue are transmitted sequentially (i.e., the priority given to relay and new locally generated messages is the same)

Fig. Non-reservation-based ad hoc wireless network model: Each node has its own queue and the multihop routes are not necessarily disjoint. In particular, two possible multihop routes between S1 and D1 are shown (dashed and dashed-dotted links). Observe that the same source can transmit successive messages to different destination (for example, source S3 might be transmitting to destinations D3 and D03).

3.2 Module Description

Non Reservation Based Routing

In this module, here we transferring the file from source to destination through intermediate node, after transmission we are going to find route path for corresponding destination and the transfer the file to the destination, then calculate the delay .

Reservation Based Routing

In this module, we are going to transfer the same file from source to destination through intermediate node, before transmission we going give route request to all the node and find the corresponding route path for all the node and store it into database, then transfer the file from source to destination through the corresponding route path present in a table and calculate the delay

Comparison Chart

In this module, going to show performance chart for two different types of routing and this will prove reservation based is better performance than non reservation based routing

3.3 Evaluation of performance of RB and NRB switching schemes:

3.3.1 RB Switching:

To evaluate the performance of an RB switching scheme, we make the following assumptions.

• Each node in the network generates messages according to a Poisson process with average arrival rate λm (dimension: [msg/s]). While a node is acting as a relay, it still generates its own messages, which are buffered for future transmission.

• The message length Lm is exponentially distributed with average value Lm (dimension: [b/msg]). Considering a fixed transmission data rate Rb (dimension: [b/s]), the message duration is therefore exponentially distributed with mean value equal to Lm/Rb.

• Since intermediate nodes on a multi-hop route serve only one source node at a time, simultaneously active multi-hop routes are disjoint. In addition, given that each multi-hop route has a certain average length, there exists a maximum average number, denoted by Cs, of simultaneously active routes.

• If the number of nodes wishing to activate a multi-hop route is larger than Cs, then some nodes have to wait before they can activate the route. The amount of time

that a node has to wait before it can activate a route will be referred to as "access delay."

• The route activation process can be described by a conceptual "virtual request queue" which regulates requests from all sources .In this sense, one can imagine that the first message of the queue at each source node is immediately forwarded to the virtual request queue. The virtual server models the waiting time that a source experiences, after discovering a route, before being able to activate it. Each possibly active multi-hop route corresponds, in this conceptual model, to a virtual server which takes care of the messages in the virtual request queue. The number of servers corresponds

to the maximum average number Cs of disjoint multi-hop routes in the network.

• The time spent by a message in the virtual request queue corresponds to the time necessary for intermediate nodes to become available. Therefore, a message in the virtual request queue might not be served in the order in which it arrives. However, according to Little's theorem, the average delay in the system will be the same regardless of the specific queuing discipline.

• The total delay between generation and complete transmission of a message, at each source node, is obtained by adding three terms: (i) the time spent in the node's own queue (ii) the time spent in the virtual request queue and (iii) the time spent in the server.

The combination of the virtual request queue and the Cs virtual servers will be denoted as "virtual overlay system." In particular, there are N flows of information at its input, coming from the N nodes. The total arrival process at the input of the request queue can be modeled as Poisson with rate Nλm. Hence, it follows that the virtual overlay system shown in Fig.

Fig. 3. Conceptual queuing model for a reservation-based wireless

network: Real queues at each node are connected to an overall virtual

request queue. Each virtual server corresponds to a possible multihop route

3.3.2 NRB Switching:

As opposed to an RB scheme, in an NRB network communication scenario, multihop routes can overlap. In particular, a node can serve as a relay node for more than one route. In other words, when a node receives a message from another node (i.e., it acts as a relay), it places that message in its own queue(intermingled with its own generated messages). The messages in the queue are transmitted sequentially (i.e., the priority given to relay and new locally generated messages is the same

As in the case of RB switching, we assume that the message generation process is Poisson and that the message length is exponentially distributed with average value

Unlike the the case with RB switching (where the relay nodes give absolute priority to the relayed messages, stopping to serve their own messages), each multi-hop route is a tandem of queues, and the whole network can also be viewed as a tandem of queues.

Fig. 5. Conceptual queuing model for a non-reservation-based wireless

network: The queues at the nodes of a multihop route constitute a

tandem of queues.

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