Transport interoperability using a virtual transport layer

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1990
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Ahuja, Ratinder
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Douglas W. Jacobson
James A. Davis
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Electrical and Computer Engineering

The Department of Electrical and Computer Engineering (ECpE) contains two focuses. The focus on Electrical Engineering teaches students in the fields of control systems, electromagnetics and non-destructive evaluation, microelectronics, electric power & energy systems, and the like. The Computer Engineering focus teaches in the fields of software systems, embedded systems, networking, information security, computer architecture, etc.

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The Department of Electrical Engineering was formed in 1909 from the division of the Department of Physics and Electrical Engineering. In 1985 its name changed to Department of Electrical Engineering and Computer Engineering. In 1995 it became the Department of Electrical and Computer Engineering.

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1909-present

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  • Department of Electrical Engineering (1909-1985)
  • Department of Electrical Engineering and Computer Engineering (1985-1995)

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Currently transport layer interoperability techniques are based on protocol converters and transport service bridges. Protocol converters translate the Transport Protocol Data Units (TPDUs) between the two transport entities. In doing so they preserve the end-to-end meaning of the transport service. The major drawback is that a unique protocol converter needs to be designed for each transport architecture for which interoperability is desired. Transport service bridges provide interoperability by copying the Transport Service Data Units (TSDUs) of one architecture to another. They are simple to implement, and are an attractive migration strategy to using applications from other architectures. The disadvantage is loss of the end-to-end meaning of the transport service. Each end transport entity has a separate connection with the service bridge. As a result, critical transport mechanisms such as flow control, error control, and credit allocation have a per segment rather than an end-to-end significance;This dissertation describes an approach to provide interoperability between heterogeneous transports based on translating the TPDUs of individual transport protocols into a common intermediate format and transferring them between gateways using a connection less transport service (CLTS). The intermediate format is identified as that belonging to a Virtual Transport Layer (VTL), and the messages are accordingly called Virtual Transport Data Units (VTPDUs). Components in the gateways called Transport Convergence Functions (TCFs) translate to and from VTPDUs to the local TPDUs. The conversion rules for TCFs are specified such that the design of the TCF depends only on the nature of the local transport Architecture; No assumption is made about the nature of the peer (same or different) transport entity. Thus an end system sees its peer due to a compounding of the VTL and the actual end transport entity;The Virtual Transport Layer approach provides an open ended solution to the problem of interoperability at the transport layer. Interoperability can be offered to any transport architecture by designing a TCF component in a single gateway according to a set of predefined rules. Since there is no connection between the gateways and the end systems, the end-to-end significance of the transport service is preserved. An attempt has thus been made to overcome the limitations of both protocol converters and service bridges;Proof of concept is offered by demonstrating interoperability, using the VTL, between DoD TCP and ISO TP4. TCFs for TCP gateways and TP4 gateways are formally specified using the ESTELL FDT. A set of rules are specified to aid in the definition of TCFs from other transport architectures. The issue of transparent addressing is also discussed.

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Mon Jan 01 00:00:00 UTC 1990