Special Report: Next Generation Internet Applications
Advantages of implementing deflection routing in an optical network are a simpler and less expensive infrastructure implementation, network congestion reduction, and adaptability to mesh topologies. Disadvantages of deflection routing consist of network synchronization issues that yield out-of-order packet arrival, no control over maximum number of hops through the network, difficult quality of service (QoS) implementations, and possible localized bandwidth inefficiency.
In the event that the network becomes somewhat asynchronous due to varying switch transmission rates or dramatic changes in switch utilization, congestion may increase and create a packet roaming condition. This condition would cause an increase in the number of hops for each packet in the network. An overall reduction in network throughput and possible network collapse would result. In an optical network, where signal degradation is an issue, this condition could lead to data compromise or the necessity for expensive signal regeneration. Also, if packets are prevented from entering the network because the ingress node is congested, they will be dropped since there is no facility for storing the optical signal.
Packets already in the network are given priority over entering packets. Quality of service is difficult to implement because predetermined paths are not allocated and routing is determined at each node. Research is underway to advance deflection routing algorithms to address the issues of packet life and deflection strategies.
Understanding the advantages and disadvantages of deflection routing, researchers are investigating the implementation of a hybrid deflection routing and optical buffering scheme. The hope is that this would provide optical networks with a stable time/interface contention resolution solution. For optical networks to proliferate, the balance between infrastructure cost and network speed must be maintained. Deflection routing offers a method to reduce these costs while used in conjunction with optical buffering.
2.2.6 Digital Wrapper Technology Administration and maintenance functions for optical networks have historically been achieved by means of SONET/SDH encoding. In order to continue to utilize these capabilities, each signal must be formatted for SONET/SDH.[16] This violates the transparency goal of all-optical networks due to the inherent OEO conversion necessary to append the required SONET/SDH maintenance overhead. Digital wrapper technology, introduced by Lucent in 1999, currently exploits the necessity for the conversion process at the optical signal regeneration nodes by appending overhead bytes to support network management and maintenance.[17] Digital wrapper technology removes the legacy of SONET/SDH from optical networks by treating each wavelength as its own independent optical channel. Each optical channel maintains the structure of packetized information data within its payload, adding the benefit of protocol independence. Header information is used to provide overhead bytes for monitoring and analysis information and wavelength based restoration.[16] The trailer contains forward error correction (FEC) data for the encapsulated payload. Figure 12 illustrates the protocol structure of the digital wrapper. A benefit of digital wrapper technology is that it provides the optical network convenient access to information necessary for determining bit error rate (BER). This, in turn, yields longer distances and reduces the quantity of OEO conversion repeaters on the network. Hence, the effective network speed increases. Another benefit of digital wrapper technology is that it is FEC method independent. Each segment of the network could perform different implementations of FEC, depending upon the characteristics of the link. Digital wrapper technology also provides for a separate optical channel called the Optical Supervisory Channel (OSC). The OSC allows for end-to-end management of the different wavelengths within the optical network.
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