Architectural issues for robust optical access

Optical access networks are beginning to be deployed at the edge of the optical backbone network to support access by the high-end users that drive increased bandwidth demands. This development in the applications of optical networking poses new challenges in the areas of medium access, topology design, and network management. In particular, since optical access networks carry high volumes of critical traffic, the level of reliability and robustness traditionally reserved for core applications must be implemented in access networks. We survey access network architectures and outline the issues associated with providing reliability for these architectures. In the area of architecture design, two main approaches emerge. The first considers dedicated optical access networks, such as stars or folded buses, to implement optical access LANs and MANs. The second is overlay architectures, which use existing network infrastructure. Overlay architectures seek to replicate, on a smaller scale, logical topologies akin to those of backbone networks, or may instead create architectures specifically designed for access purposes     

New nodal design for high throughput data vortex optical interconnection network

This paper proposes a new three input nodal structure within the data vortex packet switched interconnection network. With additional optical switches, the modified architecture allows for two input packets in addition to a buffered packet to be processed simultaneously within a routing node. A much higher degree of parallel processing is allowed in comparison to previously proposed enhanced buffer node with two input processing or the original network node with single input processing. Unlike the previous contention prevention mechanism, the new network operates by introducing the packet blocking within the node if no exit path is available. This eliminates the traffic control signaling and the strict timing alignment associated with the routing paths which simplifies the overall network implementation. This study shows that both data throughput and the latency performance are improved significantly within the new network. The study compares the three input node with the two input node as well as the original single input data vortex node. Due to additional switch count and nodal cost, networks that support the same I/O ports and of the same cost are compared for a fair comparison. The limitation introduced by the blocking rate is also addressed. The study has shown that under reasonable traffic and network condition, the blocking rate can be kept very low without introducing complex controls and management for dropped packets. As previous architectures require operation under saturation point, the proposed architecture should also operate at reasonable level of network redundancy to avoid excessive packet drop. This study provides guidance and criteria on the proposed three input network design and operation for feasible applications. The proposed network provides an attractive alternative to the previous architectures for higher throughput and lower latency performance.     

A novel delay-aware routing algorithm (DARA) for a hybrid wireless-optical broadband access network (WOBAN)

A hybrid wireless-optical broadband access network (WOBAN) is a promising architecture for future access networks. Recently, the WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions. This architecture saves on network deployment cost because fiber need not penetrate to each end user. However, a major research opportunity exists in developing an efficient routing algorithm for the wireless front-end of the WOBAN. We propose and investigate the characteristics of the delay-aware routing algorithm (DARA) that minimizes the average packet delay in the wireless front-end of a WOBAN. In DARA we model wireless routers as queues and predict wireless link states periodically. Our performance studies show that DARA achieves less delay and congestion, and improved load balancing compared to traditional approaches such as the minimum-hop routing algorithm, shortest-path routing algorithm, and predictive throughput routing algorithm.     

Opportunistic media access control and routing for delay-tolerant mobile ad hoc networks

In delay-tolerant mobile ad hoc networks, motion of network nodes, network sparsity and sporadic density can cause a lack of guaranteed connectivity. These networks experience significant link delay and their routing protocols must take a store-and-forward approach. In this paper, an opportunistic routing protocol is proposed, along with its compatible media access control, for non-real-time services in delay-tolerant networks. The scheme is mobility-aware such that each network node needs to know its own position and velocity. The media access control employs a four-fold handshake procedure to probe the wireless channel and cooperatively prioritize candidate nodes for packet replication. It exploits the broadcast characteristic of the wireless medium to utilize long-range but unreliable links. The routing process seizes opportunities of node contacts for data delivery. It takes a multiple-copy approach that is adaptive with node movements. Numerical results in mobile ad hoc networks and vehicular ad hoc networks show superior performance of the proposed protocol compared with other routing protocols. The mobility-aware media access control and routing scheme exhibits relatively small packet delivery delay and requires a modest amount of total packet replications/transmissions.     

Designing packet‐switched feeder networks with survivability and node compatibility constraints: Korean HiNET‐P case

In this paper we present heuristic algorithms to solve the combined problem of topology design, capacity assignment and routing for feeder transport networks that connect local access subnets to a packet‐switched backbone network. The algorithms are designed to build a two‐edge‐connected topology with the average packet delay constraint, switch throughput constraint, and two optional, additional constraints: dual homing and node compatibility requirements. Graph‐theoretic algorithms are used for topology design and the flow deviation algorithm is used for routing and capacity assignment. Computational results using Korea Telecom’s field data show that the algorithms can generate low‐cost feasible networks for 50 node problems within 20 s. This revised version was published online in August 2006 with corrections to the Cover Date.     

Topological analysis of packet networks

The author describes a unified approach for the topological analysis of nonhierarchical and hierarchical packet networks. The approach differs from previous approaches in adopting an end-to-end mean delay objective and including a variety of practical routing constraints. These include limits on the number of paths allowed in a route, limits on the number of hops allowed in a path, and constraints due to prevalent virtual circuit implementations. For a broad range of networks, quantitative analysis based on this approach provides new insights into the complex relationships between network topology and routing and delay constraints. It is shown that the sole use of a network average delay criterion often leads to network designs that exhibit poor end-to-end mean delays for some node pairs, and that it is possible to configure networks that meet an end-to-end mean delay objective for every node pair at little or no additional cost     

Mobile backbone synthesis for ad hoc wireless networks

In this paper, we present an extended mobile backbone network topology synthesis algorithm (ETSA) for constructing and maintaining a dynamic backbone structure for mobile ad hoc wireless networks. We present and analyze the mathematical features of the proposed scheme. Using these results, we prove that: (1) The ETSA scheme converges in constant time; (2) The length of each control packet is bounded by a constant value that is independent of the number of network nodes; (3) The size of the backbone network depends only on the size of the operational area and is independent of nodal density. We compare the performance features of this scheme with those characterizing other protocols that employ clustering operations and/or use selective forwarding on demand routing methods. In addition, we present an on-demand routing protocol (MBNR) that makes use of the underlying dynamically self-configuring backbone network infrastructure and demonstrate its performance advantages when compared with an on-demand routing protocol that is based on a flat architecture, as well as with other backbone-based routing protocols.     

下一代网络的核心--软交换技术

电信网络从承载单一业务的独立网络向承载多种业务的统一的下一代网络的演进正成为不争的事实，运营商必须设法改变其现有的网络的设计，以适应迅速增长的数据通信业务。这种改变的核心是利用分布式的体系结构，将语音和数据汇聚在同一个无缝网络中，通过将接入、呼叫控制和电信应用程序分离的三层结构，使运营商利用现有网络提供更灵活的适应性和更强的管理能力，这种网络结构就是下一代网络（NGN）的基本框架，而软交换是下一代网络的核心技术。本文主要介绍了软交换设备的功能特点、解决方案以及技术发展情况等。     

Mobile Network Evolution – “The Return of the Pipe”

The mobile network evolution from second generation to third generation systems has opened possibilities for inclusion of new technologies both in the network infrastructure as well as on the radio access. Within this paper, we concentrate on the evolution of the network infrastructure towards a future mobile network that balances the demand for increased flexibility with the necessity of limiting system complexity. Based on existing architectures, to lower complexity such as layered architecture for the core network and mobile packet backbone, we describe one possible evolution path for the control layer. Our approach is a step towards a control space that includes packetpipe control functions for a multitude of packetpipes. Such control function needs to be supported in the heterogeneous networks of today and the future.     

Design-dimensioning model for transparent WDM packet-switchedirregular networks

A detailed analytical traffic model for all-optical wavelength division multiplexing (WDM) photonic packet-switched networks is presented and the requirements for buffer size and link dimensions are analyzed. This paper shows that due to the topology, packets may generate traffic bottlenecks produced by a tendency of the routing scheme to send packets with different destinations through preferred paths. This effect increases the traffic load and, hence, the probability of blocking at the output links of specific routers in the network and, therefore, a large buffer depth or an increment in the number of fibers per link is required. Three router architectures are analyzed and it is shown that WDM all-optical router architectures with shared contention resolution resources are the best candidates to reduce hardware volume and cost of all-optical networks. It is shown that routers with a bank of completely shared wavelength converters (WCs) require a fraction of WCs compared to router architectures that use a WC per wavelength. This fraction depends on the location of the router, the network topology, and the traffic load in the network. However, in general terms, about 50% to 90% of WCs can be saved by architectures with shared wavelength-conversion resources. Also, it is shown that limited wavelength conversion degrees d=8 and d=10 in packet-switching routers with 16 and 32 wavelengths give the same probability of packet loss performance as full wavelength conversion     

Architectures and Performance of Multichannel Multihop Packet Radio Networks

Packet radio networks that employ several parallel multiple-access channels are considered. An architecture for such a network dictates the selection of channels for packet transmission. We propose and analyze two multichannel architectures. In the first, each node employs a single radio and is assigned a channel on which it listens when it does not transmit. To transmit a packet, the node tunes its radio to the channel of the intended receiver for that transmission only. The second architecture requires each radio to use a single channel for both transmission and reception, but provides some of the nodes with more than one radio each, allowing them to serve as bridges between channels. Within these architectures, one can further select the amount of routing information held by each node and the channel-access protocol, both of which greatly affect the network performance. To ascertain the effects of the various parameters, we calculate the throughput in both architectures. The channel-access protocols we consider are slotted ALOHA and CSMA with and without capture. We also evaluate the effect of increasing the amount of routing information held by the nodes.     

Progress in millimeter-wave fiber-radio access networks

Future radio access networks operating at millimeter-wave frequencies have the capacity to offer broadband interactive services to a customer base requiring untethered access. Optical fiber-feed networks incorporating wavelength division multiplexing have been proposed as a backbone network providing full-duplex interconnectivity between multiple remote antenna basestations and a central office implementing a variety of switching and routing functions. Rapid developments in both lightwave and microwave enabling technologies have fuelled an intense effort into the research and development of these networks. In this paper, we present a review of the progress of millimeter-wave fiber-radio networks in the areas of the associated enabling technologies, sub-systems and system demonstrations.     

An approximate analysis of the performance of deflection routing inregular networks

Regular two-dimensional architectures are being considered as alternatives to the linear topology metropolitan area networks (MANs) that are popular today. Deflection routing is an adaptive routing strategy that performs well on such architectures. A general analytic model has been developed to study the performance of buffered deflection routing in regular networks. The Manhattan street network, the ShuffleNet, and the shuffle exchange network have been studied as candidate two-connected networks with different topological characteristics. The results show that deflection routing performs well on both the Manhattan street network and the ShuffleNet, even under heavy loads, while on the shuffle exchange network it does not perform as well. The introduction of just a few buffers provides significant improvement in the delay-throughput performance over unbuffered deflection routing, especially in networks with large propagation delays. The analytic results are found to match the simulations very closely in most cases     

On the stability of shuffle-exchange and bidirectionalshuffle-exchange deflection networks

In a stable packet-switched network, throughput equals offered load and packet backlogs do not build up in an unbounded manner. A network with an unstable operating region poses the problem that it may evolve eventually to a stable but saturated operating point with a low throughput. This paper considers the shuffle-exchange and bidirectional shuffle networks when operated with deflection routing. It is shown that both networks exhibit instability when packet contention is resolved in a random manner. However, instability can be avoided if contention is resolved in a manner that favors packets closest to their destinations. This obviates the need for complicated network access control to prevent instability     

SONET ring applications for survivable fiber loop networks

Synchronous optical network (SONET) self-healing rings (SHR) are studied in the loop environment. SONET SHR architectures for loop feeder networks are discussed, focusing on three possible dual central office (CO) architectures for fiber loop networks, using SONET SHRs to reduce network costs and provide network service survivability. These architectures reflect an integrated planning concept for SONET networks that eliminates the boundary between the access network and the inter-office network. It is shown that the use of SONET SHRs makes it easy to evolve to a protected dual CO access architecture. Economic and survivability studies are discussed. The economic studies show that using the ring approach yields significant advantages over the traditional diverse protection approach in terms of cost and survivability, especially for the dual CO architectures     

Layer 3 VPN Services over IPv6 Backbone Networks: Requirements, Technology, and Standardization Efforts

Layer 3 virtual private networks (L3VFN) enable organizations to connect geographically dispersed sites to one another across the packet switched network of a service provider. The most popular form of L3VPN is based on BGP/MPLS (border gateway protocol/multiprotocol label switching) technology in which the service provider offers a network-based IP VPN routing and forwarding service to its customers across its own IPv4-based MPLS backbone network. With the deployment of IPv6-based backbone networks underway, there is an emerging requirement to support these same L3VPN services across a native IPv6 backbone network. This introduces a requirement to provide routing and tunneling of IPv6 VPN (and IPv4 VPN) packets across an IPv6 backbone network. Softwires is an Internet Engineering Task Force (IETF) Working Group chartered to address the requirement of providing a generalized, network-based, multi-address family, IP routing and tunneling capability across native IP backbone networks pursuant to IPv6 transitions. Elements of the softwires work can form the basis of an L3VPN over IPv6 solution. After providing a brief overview of how L3VPN works in various topologies, this article presents the requirements for L3VPN services over an IPv6 backbone network and discusses a possible solution set that builds over the softwire technology and related IETF standards. Finally, we outline future directions and how the softwire technology can support new services and improved scalability     

Performance of Double-Tier Access-Control Schemes Using a Polling Backbone for Metropolitan and Interconnected Communication Networks

We consider a double-tier communication network architecture for metropolitan area and packet radio networks for controlling the access of network terminals into a single shared broadcast channel. Terminals are organized into local groups in accordance with their geographical proximity or other criteria. Each local group can be associated with a primary station. The latter can serve as an unbuffered repeater for terminal transmissions unto the multiple-access channel. A polling policy is used by the primary stations to gain access into the shared communications backbone. Once a primary station is provided access into the channel, it initiates a local access control procedure. Message delay performance results and bounds are obtained for general reservation local-access procedures. In particular, we analyze and present performance results for a polling/tree-random-access procedure which can be effectively used for many packet radio and cellular digital radio networks, as well as for a polling/positionalpriority scheme for CATV and fiber-optic based networks.     

An IP transport and routing architecture for next-generationsatellite networks

Over the past several years, a number of new satellite systems have been proposed to provide high-speed Internet and multimedia services to businesses and home users. These proposals have been driven by the desire of network operators to reach end users that do not have cost effective access to other alternatives such as fiber, DSL, and cable, and by the availability of new spectrum (Ka-band) for use by new satellite services. The proposed systems generally employ multiple high-power spot beams, an onboard fast packet switch, and a demand-assigned multiple access scheme to provision IP-based services. In this article we concentrate on a geosynchronous satellite system where packet transport and switching within the satellite system are based on ATM. We describe an IP/ATM interworking and IP routing architecture that is driven by three main requirements: (1) the ability to support ATM SVCs between hundreds of thousands of satellite terminals by a single ATM switch located onboard; (2) a scalable IP routing architecture that does not result in large volumes of routing traffic to be transported over the satellite; and (3) the ability to segment the satellite terminals for routing and administrative control by ISPs and enterprise networks     

Photonic slot routing: a cost effective approach to designingall-optical access and metro networks

In the backbone network, the high level of traffic aggregation achieved by numerous users is efficiently served by means of optical circuit switched solutions-the so-called wavelength routing approach. In the access and metro networks, on the contrary, the reduced level of traffic aggregation makes wavelength routing solutions inadequate. The finer and more dynamic bandwidth allocation provided by packet-interleaved optical time-division multiplexing is thus advocated in these network areas. This article presents a survey of an OTDM approach, known as photonic slot routing, or PSR. It is illustrated how this approach may provide a cost-effective solution to deploying all-optical access and metro networks with today's technology     

The scalable lightwave network

In principle, an optical network employing wavelength routing, wavelength reuse, and multihop packet switching is modularly scalable to very large configurations in both the hardware and software sense. As such, it is a viable architecture for a new ATM-based telecommunications infrastructure The network architecture considered for a new, scalable, broadband telecommunications infrastructure is based on (1) the use of wavelength division multiplexing (WDM) and wavelength routing; (2) the translation of signals from one wavelength to another at the access stations; and (3) the use of multihop ATM packet switching. These principles permit networks to be built whose size is essentially unlimited