Working Analysis of TCP/IP with Optical Burst Switching Networks (OBS)

Transcription

1 Working Analysis of TCP/IP with Optical Burst Switching Networks (OBS) Malik Salahuddin Nasir, Muabshir Ashfaq and Hafiz Sabir Hussain CS&IT Department, Superior University, 17-km off Riwind Road, Lahore Pakistan {Mubashir.ashfaq1& ABSTRACT: This paper is about the working analysis of Optical Burst Switching Network. From past few years a lot of research has been done in optical communication field, especially in optical circuit switching and optical packet switching, and combining them to form optical burst switching network. These researches were the results of increasing demand of high bandwidth for fast communication. This paper covers three aspects related to optical network. Firstly we define the complete working architecture of Burst switching network. Working of IP protocol using two nodes, 1-edge node and 2-core node is defined in second section. The third section is provided with the information of TCP as a transport layer protocol and also defined the parameters in optical burst switching network which are affecting its performance. At the end of this paper we emphasized on the issues of TCP protocol in this network and tried to give a direction to overcome these problems. I. INTRODUCTION Few years ago, there were limited number of users and demand of data was very low and is easily providable for service providers. Due to increase in number of users there was loads of data that caused mismanagement of available data rates and bandwidth to fulfill requirements. So in order to provide service according to the demand of the users, engineers and scientists started their research to find a new efficient and fast way for data communication and the way they found was optical communication. Data travels with the speed of light in optical communication providing the user with an excellent quality service and fast communication around the networks [1]. Our current core network is an optical network while access network is in electrical domain. The architecture of Present network is shown below in Fig. 1. Then concept of fiber to the home and fiber to the curb was introduced which provides a complete communication in optical domain, which is more efficiently then old technology and also very less time delay [1]. One of the big issues regarding optical communication is the compatibility of devices. Current switching devices are not applicable for optical wavelength switching although some devices have been introduced having an extra module, that converts the incoming optical signal into electrical signal in order to perform switching and then again convert that electrical signal into optical signal. Using such modules with switching devices, optical communications is affordable for those small scale communication networks, where time delay is not considered. While on the other hand using such modules, devices do not work efficiently on large scale network [2]. So the most suitable switching method for optical communication introduces is Optical burst switching OBS that provide full support to optical signals directly rather than converting these upcoming optical signals completely into electrical signal. In this network the travelling optical signal consists of two portions. First portion contains all the information about the data, source and destination, while second portion contains the data packets. This phenomenon of new type of network saves time of extra processing providing complete optical data and voice communication in efficient manner [3]. Optical bust switching is composition of optical circuit switching and optical packet switching so we can say that the purpose of optical burst switching is to provide wavelength for communication with combined properties of electronics and optics. A simple architecture of OBS network is given below in Fig. 2. For Optical Burst Switching network IP based communication is implemented with the help of two nodes implementation, which are 1- edge node and 2-core node [4]. Working of Internet Protocol (IP) is same as in our current data communication networks. TCP is also used in OBS as a transport protocol for IP based communication. TCP is providing its full support as a transport layer protocol in combination with optical layer protocols but it is affected by few parameters of Optical Burst Switching networks. These problems of TCP are tested in different environments and under different topologies. As a result of these observations a direction is given to overcome these drawbacks of Transport layer to work efficiently with Optical Burst layer [5]. Fig. 1 Present Network Architecture

2 The header processing ability of this switching method is also its draw back because processing each header separately requires move electrical equipment and each data wavelength needs to wait in queue until its header is being progressed [8]. The technical comparison between these switching techniques is in Fig. 3. Fig. 2 A Sample OBS Network II. RELATED WORK There are also few other Optical Switching techniques being used in core of different networks. These techniques are: Optical Circuit Switching O/E/O Switching (Optical to Electrical and Electrical to Optical) Optical Packet Switching The OPTICAL CIRCUIT SWITCHING technique is as like other ordinary switching in which signal is not converted from one domain to other. In this switching method a light path is setup only once and all the data on one wavelength from input fiber will be carried as it is to the output fiber on the other end. There is no Statistical Multiplexing of data coming from other networks, due to which only one wavelength is processed at a time and during processing all the bandwidth is allocated to that wavelength. By using this switching technique high bit rates for computer communication cannot be achieved [6]. O/E/O switching technique was introduced to overcome the problems faced in OCS. Statistical Multiplexing is made possible in this technique with the help of electrical processing and buffering ability. But this is not much efficient to handle bulks of wavelengths working at 30+ Gbps. In addition with high speed wavelength handling problem electrical switches have few limitations of being used at large scale. These switches consume move Power, produces move heat and require expensive Optical to electrical and electrical to optical conversion [7]. OPTICAL PACKET switching technique is a bit different from other two described above. Working of Optical packet switching is like working of router at network layer which performs routing by processing the header of each packet. In this switching data wavelengths are multiplexed statically while the header of each wavelength is converted to electrical domain for processing. Fig. 3 Comparison B/W different Optical Nodes [9] III. WORKING MODEL OF OBS In Optical Burst Switching network, different types of data from different sources are aggregated at input edge node. Here incoming data is assembled into burst form and control channel for each burst is created. Remember that this data burst is made of various data packets and control channel contains the header information for all of packets in the single burst. At the time of assembling and disassembling, the incoming data is buffered at the edges of OBS network. The control channel is much smaller in size than its data burst and it goes though O/E conversion for routing process at the nodes in OBS network. On the other hand, burst passes each node in the network by using pre-established and pre-configured circuits because the nodes do not require any information regarding the format of data bursts. When control channel of a burst is under process at any node in the network, data burst has to wait until its routing path is defined [10]. During this time data burst stays in Fiber delay lines (FDLS). FDLs consist of optical fibers that are used to store light for a specific time. It is an optical storage medium that enables compensation for a difference in time of occurrence of data in form of light wave [11].

3 There is kept a time difference between control channel and data burst due to processing and packet assembling delay. If the time difference is large, then data burst is switched optically without any delay at edge nodes. In this way Fiber Delay lines (FDLs) are not required. Working model of OBS is in Fig. 4. In OBS model working of TCP & IP with OBS is to be defined separately [12]. IV. Fig. 4 Working Model of OBS WORKING OF IP WITH OBS Internet Protocol (IP) is the basic protocol in data packet networks. It is network layer protocol and helps a lot in the routing process. Routing is highly dependent on IP of packet. Each IP packet has its header which contains the IP information for each packet. In OBS network IP work with the help of two nodes: 1. Edge node (a) Ingress node (b) Egress node 2. Core node When IP packets arrive at edge of OBS network, it is collected by input edge node called Ingress node. Here data packets and there headers are separated. Data packets are assembled and data bursts are formed. Headers of all packets in the burst are combined and assembled in control channel. These data bursts and their control channel are then sent to core node [13]. In core node control channel are processed and according to header information for each packet, these IP packets bursts are switched by switching fiber and dropped to the destination address using ADD/DROP fiber [14]. At the output edge node called Egress node, the data bursts are disassembled into IP packets again. The bursts with same FEC (forward equivalent class) are processed and assembled in single unit of burst assembly. The work of burst scheduler is to create bursts and their BHC s, adjusting offset time, scheduling of burst to egress nodes and forwarding of burst with their BHC s to OBS core network. The burst assembly algorithms are classified as timer-based, burst length based and both timer + burst length based. The characteristics of assembled burst traffic are different from the original traffic originated from other source. OBS network performance is also affected by latency, throughput and burst lost loss due to burst assembly process. The basic characteristic of OBS network is that it creates a path for specific wavelength uniformly across the core network. Like other circuit switched networks, it does not require signaling or two way reservation. Responsibility of reservation process is to separate data information from control packet. The core nodes of OBS network are responsible for initial controlling of IP packets and their routing. This routing is the combination of both control and packet forwarding. The core node consists of switch fiber and control forwarding engine. The switching fiber performs switching of bursts on specific wavelength. The forwarding tables are generated and maintained in control portion by using IGP and MPLS routing protocols. OBS network uses two types of forwarding mechanism 1. Multiprotocol Lambda Switching 2. Label Optical Burst Switching Forwarding of burst depends on forwarding table in control plane and SHIM label in control packet. Forwarding mechanism uses label swapping algorithm. The forwarding table consists of entries such as incoming label, outgoing label, incoming interface and outgoing interface. The core node uses the label of incoming packet to decide the next hope, swap the incoming label with outgoing label and sends the control packet to outgoing interface as shown in fig. 5. IP in OBS networks uses SHIM label header, which resembles the header of IP packet. SHIM label is 20 bits wide having 3 extra bits for EXP field. 1-bit of bottom stack (S) field for encapsulation. To discard MPLS looped packet in LSPs, Time to live field is also included in it. OBS core nodes store the labeling and routing information in its LIB (label information base). During forwarding each node treats each burst originated from same source as the subset of 1 st arriving burst of that source. Such subsets are referred as FECs (forwarding equivalence source) [15].

4 Time of each packet transmission delay. TCP fast is the evolution of TCP Vegas with better throughput. These are the basic approaches adopt by TCP sender to check the intensity of traffic congestion in network and to adjust the rate of transmission [17]. VI. Issues of TCP in OBS network TCP reacts on the Packets drop, End to End delays and Throughput changes in the network. As a result of these reactions, TCP faces some problems in OBS network like: a) Effect of Burst drops Fig. 5 Forwarding Mechanism V. TCP in OBS TCP is the transport layer protocol of communication networks, which handles the issues of reliability, flow, and congestion control in an efficient way. It was originally made for military communication by ARPANET. In modern network it works as a basic transmission protocol with traffic share between 83-90%. In OBS networks multiple TCP packets are aggregated in single burst. One core node corresponds to thousands of TCP segments. Due to multiple number of TCP flows and the process of burst assembly, behave of TCP with OBS networks is much different from other networks [16]. Congestion control mechanisms of TCP are classified as: a) Explicit notification-based TCP with Explicit Loss Notification (ELN) and TCP with Explicit Congestion Notification (ECN) are two basic approaches in this mechanism. These are developed in order identify packet losses which cause retransmissions. TCP ECN and ELN can differentiate loss of packets due to contention, link failure and congestion. Retransmission of lost packets starts when one of ELN or ECN is received. b) Loss-based TCP Reno is the basic approach in Lost-based TCP mechanism. It is based on AIMD (Additive Increase Multiplicative Decrease) window-based congestion control mechanism to maintain network bandwidth and data transmission regulation. AIMD has four states for each TCP sender e.g. congestion avoidance, fast recovery, slow start and fast transmission. c) Delay-based In this mechanism of TCP two implementations are Fast TCP and TCP Vegas. It estimates the congestion and bandwidth status of network by measuring Round Trip The burst drop probability depends on network load and contentional level of burst in network. b) Effect of burst-assembly delay Packets experience some delay during the process of burst assembly at edge nodes. This affects the performance of TCP. c) Effect of fiber-delay-lines In OBS networks when data is stored in FDLs also produces some delays and effect TCP. On the basis of these issues TCP performance is tested under three types of environment a) A Single TCP source with three node topology b) Multiple TCP sources with a three node topology c) Multiple TCP sources with an eight node topology As a result of TCP working analysis we come to know that, higher drop probabilities resulted in poorer performance and the performance degradation was severe for drop probability as low as While for low drop probabilities, increasing burst sizes resulted in higher throughput and increased delay [18]. VII. Suggested Solution for TCP Issues Issues of TCP in OBS network can be resolved using these approaches. A. Link-Layer Solutions a) Solutions based on Burstification Processes b) Burst Contention Loss Recovery c) TCP with Burst Acknowledgement

5 d) TCP Decoupling e) Retransmission-Count Based Dropping Policy B. Solutions with Explicit Notifications a) Burst TCP b) TCP with Burst Contention Loss Notifications C. Solutions without Explicit Notifications a) Burst TCP with Burst Length Estimation b) Burst AIMD c) Statistical AIMD d) Threshold based TCP Vegas [19] [20] Conclusion In this paper we have described the requirement of Optical networks for high data rates. Compared different types of optical nodes and proved the best one among all. OBS is the new and effective optical node for the implementation of OBS network. Provided full detail of OBS architecture explained its features with its complete working. Working of IP with OBS is explained in detail and the usage of two protocols MPLS and IGP which are helpful in routing and forwarding process. After that TCP is defined in IP and OBS network along with the factors affecting the TCP performance in OBS network. At the end we tried to give an affective direction to solve the problems of TCP by using different approaches. REFERENCES [1] (2014) [Online]. HYPERLINK " [2] Biswanath Mukherjee. (2011, september) [Online]. HYPERLINK " Program/Tutorials/Issues-and-Challenges-in-Optical- Network-Design.aspx" [3] (2006) [Online]. HYPERLINK " [4] EVan Breusegem, "An OBS architecture for pervasive grid computing". [5] Sunil Gowda, "Performance Evaluation of TCP over Optical," p. 25, [6] (2005) techopedia. [Online]. HYPERLINK " [7] wikipedia. [Online]. HYPERLINK " [8] Politechnika Cz estochowska, "Overview of optical packet switching," p. 14, August [9] S. J. Ben Yoo, "Optical Packet and Burst Switching Technologies," p. 25, [10] Sunil Gowda, "Performance Evaluation of TCP over Optical," p. 25, [11] wikipedia. [Online]. HYPERLINK " [12] Krishna M Sivalingam, "Performance Evaluation of TCP over Optical," p. 5, [13] S. J. Ben Yoo, "Optical Packet and Burst Switching Technologies," p. 25, [14] globalspec. [Online]. HYPERLINK " Optical Components and Optics Fiber Optics" [15] Ioannis P. Karamitsos, "Routing Mechanisms for IP over OBS-WDM Optical Networks," p. 4. [16] Basem Shihada, Transport Control Protocol (TCP) over. Canada, [17] AND PIN-HAN HO BASEM SHIHADA, "TRANSPORT CONTROL PROTOCOL (TCP) IN OPTICAL BURST SWITCHED NETWORKS: ISSUES, SOLUTIONS, AND," p. 25. [18] Basem Shihada, Transport Control Protocol (TCP) over Optical Burst Switched Networks. Canada. [19] PIN-HAN HO, "TRANSPORT CONTROL PROTOCOL (TCP) IN OPTICAL BURST SWITCHED NETWORKS: ISSUES, SOLUTIONS,

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