Research On The Half-Step Forward Switching And Furthermore Improvement

With increase of multimedia application traffic in Internet, the "best effort" service provided by Internet has been entrenched in satisfying users' QoS requirements and become one of challenges for Internet. Moreover, network nodes (routers and switches) have faced with challenges both in QoS provisioning and in switching capability when bit-rates in a single fiber has been raised to a few orders of magnitude higher. These demand simpler, more efficient network architecture and a network node capable of satisfying requirements of high-speed swiching and QoS insurance. For the very reason, SC-Netcom Lab (Sichuan Network Communication Technology Laboratory) has introduced the Single User-data transfer & switching Platfonn Architecture Network (SUPANET). The SUPANET simplifies User-data transfer & swiching platform (U-platform) into a single physical layer platform by adopting the out-band signaling concept, while keeps exist protocol stacks of Internet in the Signaling & Management platform (S&M-platform) to enable interoperation with Internet. The key technique enabling the single U-platform is called EPFTS (Ethernet-oriented Physical Frame Timeslot Switching). SUPANET provides multimedia traffic with a QoS-insured, connection-oriented physical-layer VLS (Virtual Line Service).To ensure QoS in SUPANET, a set of comprehensive mechanisms has been designed for the S&M-platform and U-platform respectively. They are QoS Negotiation Protocol (QoSNP), QoS-based lambda Routing Information Protocol (λQoS RIP), Traffic Monitoring & Exchange Protocol (TMEP), Call Admission Control (CAC) in the S&M-platform, and User-data Admission Control (UAC), Multimidia Quota-assignment Algorithm (MQA), together with switch fabric and switching mechanism in U-platform. The work presented in this dissertation is QoS ensurance techniques pertainent to switch fabric and switching mechanisms of U-platform and an emphsis has been given to the innovative Half-step Forward Switching (HFS) technique.The basic idea of Half-step Forward Switching (HFS) is to carry output port numbers of individual network nodes in an output frame/packet from theupstream nodes, which are available during connection establishment phase for connection-oriente service;consequently, an input unit can directly use this information to request for switching without the need for looking up switching tables.The background for instruction of HFS is the fact that the processing tasks and cost of input units in a swich are around 70% of a switch;therefore, it is beneficial to release an input unit from looking-ups to obtain the output port so as to reduce transit delay and jitters (looking-up times in routers are variable). It is called "Half-step forward" because it has to update new switching field in the output although request for arbitration and switching can be done as soon as a frame arrives.When researching on HFS, the author discovered that two VLJs for HFS in the frame can be merged, should updating of output ports, output lambdas, and VLI be combined with looking-ups in input unit. This can be done through one access to the Connection Control Block for a VL and further improve the processing efficiency. The new approach is termed as the "One-step Forward Switching" (OFS) since a frame always carries switching fields needed for one node ahead downstream. The author's main contributions can be summarized as:A. The author has systematically studied HFS and implementation techniques, and shown through simulation results that transit delay and jitter can be shorter with HFS compared with traditional approaches.B. Based on analysis of inadequacy of HFS, author has further explored potential improvement to HFS with a new approach called OFS (One-step Forward Switching). Inplementation issues relevant to OFS in the background of multi-cast, backed with NISO-MEFS (N-Input-Single-Output Multiplexed Express Forwarding Structure) are discussed in some detail.