IP has emerged as the internetworking protocol of choice. IP is a best-effort protocol which provides no guarantee of delivery or ordering of packets at their destination. IP is designed to be transparent to the topology of the underlying transport network. This transparency is provided by a framing protocol operating over the data link or MAC layer. Due to the popularity of IP, attempts are underway to transport IP traffic over transport networks such as ADSL, HFC, ATM, SONET/SDH, and WDM. This paper examines the dynamics of IP traffic over SONET/SDH using PPP in HDLC-like framing. Although IP in ATM framing (IP/ATM/SONET) is also presented, the main focus of this paper is on IP/PPP/SONET and its extensions, such as PPP multilink, and PPP tunneling protocol. A discussion on the applicability of these PPP extensions to wavelength division multiplexing (WDM) networks is also presented in the conclusion.

A method is proposed to support confidentiality in broadcast fiber-optic LAN/MAN (local/metropolitan area network) systems. This approach, which is different from the conventional approach, is based on a fundamental property of fiber optics, viz., optical bidirectionality. That is, two distinct transmissions in opposite directions can occur simultaneously on the same channel. This property can be used to arrive at network structures to support privacy in a broadcast environment. The basic idea is that when two stations are engaged in a private conversation, they can effectively jam (or blank out) the reception at all other stations. In this sense, security close to that of point to point links is achieved in a broadcast environment. It is shown that this concept can be successfully applied to LAN/MAN systems, specifically, in the context of DQDB, to the proposed IEEE 802.6 MAN standard. Performance issues in terms of throughput are also discussed.>

Mesh and mesh-of-pyramids implementations of iterative image restoration algorithms are proposed. These implementations are based on a single-step algorithm as well as on a multistep iterative algorithm derived from the single step regularized iterative restoration algorithm. One processor is assigned to each picture element, with local memory depending on the support of the restoration filter. The implementations consist of interprocessor communication and intraprocessor computations. The efficiency of the proposed VLSI algorithms is judged by establishing lower bounds on AT/sup 2/, where A is the area of the VLSI and T is its computation time.>

A method to design resilient protocols for spanning tree problems is proposed. The method consists of a generic resilient protocol that can be used for any spanning tree problem. A resilient protocol for a particular spanning tree problem can be obtained by adjusting various run-time parameters of the generic protocol. The generic protocol is designed by using the concepts of replacement sets that contain the links that can be used to replace a link that fails and replacement values that measure the change in the spanning tree when a link in a replacement set is used to recreate a spanning tree. The approach is as general as the common approach (for the case of spanning trees) because the generic protocol can solve a new spanning tree problem without an individual design. The protocols obtained with this method are efficient and easy to implement and verify because they are all derived from the generic protocol.>

Distributed algorithms for shortest-path problems are important in the context of routing in computer communication networks. We present a protocol that maintains the shortest-path routes in a dynamic topology, that is, in an environment where links and nodes can fail and recover at arbitrary times. The novelty of this protocol is that it avoids the bouncing effect and the looping problem that occur in the previous approaches of the distributed implementation of Bellman-Ford algorithm. The bouncing effect refers to the very long duration for convergence when failures happen or weights increase, and the nonterminating exchanges of messages, or counting-to-infinity behavior, in disconnected components of the network resulting from failures. The looping problems cause data packets to circulate and, thus, waste bandwidth. These undesirable effects are avoided without any increase in the overall message complexity of previous approaches required in the connected part of the network. The time complexity is better than the distributed Bellman-Ford algorithm encountering failures. The key idea in the implementation is to maintain only loop-free paths, and search for the shortest path only from this set.

We present a distributed protocol for updating and maintaining a minimum-weight spanning tree (MST) in a network with changing topology. The protocol can respond to multiple link/node failures and recoveries that can occur at arbitrary times. Given that an arbitrary finite number of topological changes occur during a period, the protocol finds the MST corresponding to the latest network, within finite time after the last change. The message complexity of the protocol is O(m|E|+k|V|) when k link recoveries and m link failures occur, where |V| and |E| are the total number of nodes and links, respectively.

We present a resilient distributed protocol that enables a synchronous algorithm to run on an asynchronous network. The protocol is resilient in the sense that it can continue providing network synchronization in the presence of topological changes in the underlying communication network of a distributed system. These changes are caused by link/node failures and recoveries that occur while running the protocol. In general, the protocol is a useful tool in the design of resilient distributed algorithms as it isolates the algorithm from the characteristics of the communication network.