Performance evaluation of CSMA/ID MAC protocol for IP over WDM ring networks
International Journal of Communication Systems
In this paper, a packet pre-classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA/ID) scheme is investigated for supporting IP packets over all-optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the
... n of the network, the packets transmitted from a local area network are first pre-classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short-term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. exceeds 2 Tbit/s (200×10 Gbit/s), 2.4 Tbit/s (120×20 Gbit/s), 3 Tbit/s (300×11.6 Gbit/s), and 3.2 Tbit/s (80×40 Gbit/s)    . Research has demonstrated that the number of wavelengths per fiber could increase to more than 1 000  . This indicates that WDM can be a solution for the ever-growing bandwidth demand. Owing to the growing number of services and users on the Internet, IP packets dominate data networks. These packets are transferred, switched, and manipulated through complex protocol stacks, such as IP/ATM/SONET/WDM and IP/HDLC/SONET/WDM. How to merge and collapse the middle layers to reduce cost, complexity, and redundancy is an important research issue    . Additionally, since many WDM systems have been deployed in wide area networks (WANs), the bottleneck of communications will be pushed from the backbone networks to local access networks. As a result, how to apply WDM to local and metropolitan area networks has attracted a lot of research interest      . A number of papers have examined WDM ring networks. Cai et al. proposed the MTIT access protocol for supporting variable size packets over WDM ring networks based on a fixedtransmitters-and-fixed-receivers architecture  . To achieve all-optical communications, MTIT adopts the source removal policy  for dropping packets from networks to prevent packet re-circulation. Shrikhande et al. developed HORNET as a testbed for a packet-over-WDM ring metropolitan area network (MAN)  . To facilitate signal regeneration and destination removal, HORNET utilizes opto-electronic and electro-optic conversion, which may constrain the transmission rate of the network. Although the IP standard allows a packet length of between 40 and 64 kbytes, a measurement trace from one of the MCIs backbone OC-3 links shows a discrete packet-size distribution, from 40 to 1500 bytes (see Figure 1) . The smallest packet of 40 byte corresponds to TCP ACK packets and the 1500-byte packets are Ethernet's maximum transfer unit (MTU). Figure 1 shows that almost 5.34% (byte volume) of the packets are 40 bytes long, 27.58% (byte volume) of the packets are 41-552 bytes long, and 67.08% (byte volume) of the packets are 553-1500 bytes long. Hwang et al. proposed an all-optical media access control (MAC) protocol based on avoiding packet collision using a fragment packet scheme for all-optical WDM multi-rings with a tunable transmitter and fixed receiver (TT-FR)  . However, avoiding packet collisions using this fragment scheme creates a large number of fragmented packet and introduces Figure 1. Cumulative distribution function (CDF) of IP packet sizes on an Internet backbone link. PERFORMANCE EVALUATION OF CSMA/ID MAC PROTOCOL 1157 complexity. For this reason, we propose a new MAC protocol that avoids packet collision without a fragment scheme. In this paper, the WDM ring network architecture, carrier sense multiple access with idle detection (CSMA/ID) protocol, and transmission algorithms are presented in Section 2. Analytical models for evaluating the average packet delay performance are developed in Section 3. Then, Section 4 validates the accuracy of the proposed model by comparing the analytical results with those obtained using simulations. Finally, Section 5 contains the conclusion. NETWORK ARCHITECTURE AND CSMA/ID MAC PROTOCOL The network architecture The network architecture used in this paper is a single, unidirectional fiber ring network, which connects an N number of nodes. The optical fiber is composed of W data channels ( 1 , 2 , 3 , . . . , w ), as shown in Figure 2 . The network scope is assumed to cover a metropolitan area (i.e. a ring circumference of about 100 km); therefore, the system is referred to as a WDM metro ring. The access points (APs) connect local area networks (LANs) to the MAN ring network, while PoP connects the MAN to the WAN. Each data channel makes use of one specific wavelength to convey the optical signal. Therefore, using WDM technology, channels can work independently without interfering with each other. Logically, the network can be treated as a multi-ring network. The node structure of the network is shown in Figure 3 . Each node has one tunable transmitter and W fixed receivers, one for each data channel. For the optical signal sent from upstream nodes, a splitter is used to tap off a small portion of the optical power from the ring to the receivers. Every receiver detects the optical signal carried in its corresponding wavelength within the output Figure 2. Architecture of a metro WDM ring.