A Protocol Architecture for a Flexible High Performance Communication Subsystem

نویسندگان

  • Torsten Braun
  • Claudia Schmidt
  • Burkhard Stiller
  • Martina Zitterbart
چکیده

PATROCLOS (parallel transport subsystem for cell-based high-speed networks) is a transport subsystem to support modern applications, such as multi-media applications, in high-speed network environments. PATROCLOS increases the throughput performance by the integration of protocol and implementation issues. It provides the required functionalities between the media access layer interface of cell-based networks and the transport service interface (functionality of the OSI layers 2b-4) in a single protocol component. The key feature of PATROCLOS is its parallel and modular protocol architecture [1]. The approach combines a very fine granularity with a function-oriented decomposition into basic modular building blocks. The parallel protocol architecture allows efficient implementations on multiprocessor platforms. PATROCLOS provides a number of protocol mechanisms to support different application and network requirements. They can be selected dependent on application requirements. This paper concentrates on both issues: the protocol architecture and the implementation of the transport subsystem on a transputer based multiprocessor architecture. Because of its modularity, PATROCLOS can be used to populate a protocol function pool for the function-based communication subsystem (F-CSS). F-CSS [2] is a framework for flexible communication subsystems, in which PATROCLOS may be integrated. F-CSS allows applications to request individually tailored services from the communication subsystem. Based on the service requirements and available resources, suitable protocol functions are selected from a protocol function pool and configured to protocol machines dependent on the service required by the application. 1 PATROCLOS Protocol Architecture Based on the analysis of the XTP specification (version 3.4) and the performance results of the corresponding multiprocessor implementation, several design guidelines for protocol architectures appropriate for concurrent processing have been derived. PATROCLOS follows these guidelines and uses a modular design to achieve a high degree of parallelism. Redundant placement of protocol functions in several layers can be avoided, e.g., segmentation and reassembly functions in layer 3 and 4 of the OSI Reference Model. Parallel extended finite state machines (FSMs) are the building blocks of the protocol architecture. The set of all FSMs forms a FSM system. FSMs belonging to the same PATROCLOS entity exchange messages for co-operation. All FSMs are designed as autonomous as possible to minimize interactions with other FSMs of the same entity. Communication among FSMs is uni-directional to allow a high degree of parallelism. If possible, the necessary information exchange is performed periodically to reduce the communication overhead. PATROCLOS consists of two types of FSMs: interface and protocol FSMs (Figure 1). Interface FSMs are located at the interfaces of the transport subsystem to the application and the network. They support interactions of PATROCLOS with the transport service user or with the underlying network unit. They are only involved in local communications within one entity. The network interface FSM (send control FSM) controls and schedules transmission of all protocol data units (PDUs) to the underlying network unit. The transport service interface FSM maps service primitives to signals for the protocol FSMs. high speed network application component (layers 5-7) network component (layers 1-2a) transport subsystem (layers2b-4) protocol FSMs FSM protocols interface FSMs application component (layers 5-7) network component (layers 1-2a) Figure 1: Protocol Architecture The key feature of protocol FSMs is their use of separate partial protocols to communicate directly with the corresponding FSMs at the peer entity. They are designed to allow parallelism between send and receive part and to decouple the connection state information exchange from user data exchange (Figure 2). All partial protocols have special PDUs, individual error recovery mechanisms, and timers. Each partial protocol is performed by communicating peer FSMs, using PDUs containing only the necessary information for their protocol function. Multiplexing of PDUs by different FSMs is avoided to support concurrency. Together, the autonomous partial protocols build the PATROCLOS protocol. The decomposition into independent FSMs permits parallel execution and has the benefit of a highly modular system. Currently, the following protocol FSMs are defined: The connection management FSM is responsible for establishment, management, and correct release of a full duplex connection. Therefore, it has to activate and initialize the other FSMs of the same entity for each new connection and has also to deactivate these FSMs after connection termination. The peer FSMs exchange connection establishment PDUs, initialize the connection, and forward quality-ofservice requirements to other FSMs. The connection management FSMs also guarantee the unique use of connection identifiers. The transport service FSM selects handshake-based or implicit establishment procedures dependent on the required service. Additionally, explicit/timer-based and graceful/normal connection release can be selected. User data transfer can be divided into a send path and a receive path. Data transfer FSMs send and receive user data. The main tasks of both FSMs are formatting and analyzing PDUs with user data. Additional functions are segmentation and reassembly. On sending side, transport service data units (TSDUs) are segmented by the segmentation FSM into PDUs. The user data send FSM formats the header fields of the PDUs to describe the user data (e.g., sequence numbers). On receive side, the user data receive FSM operates on these informations to detect duplicates or errors. Furthermore, it checks the packet lifetime. The reassembly FSM reassembles PDUs to TSDUs. send FSMs receive FSMs connection establishment and termination messages

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تاریخ انتشار 2007