Connection-Oriented Protocols
Connection-oriented protocols may be compared to a personal telephone call. Before you begin a conversation, you establish a connection by dialing a number and verifying that you are talking to the desired person.
Connection-oriented network protocols work in a similar manner. First, a logical connection is made between user applications. After certain parameters are negotiated and the connection has been verified by both partners, the user applications are allowed to send data. Periodically, the recipient acknowledges delivery of a group of data. The sending software examines the acknowledgement , determines if any data must be retransmitted, and re-sends it if required. Connection-oriented protocols will notify upper level software if data could not be delivered or if a connection is broken.
Connection-oriented protocols require additional network resources to set up the logical connection. In addition, they require additional processor resources to buffer data and to perform sequence validation. Connection-oriented protocols are sometimes referred to as reliable protocols because the protocol guarantees that the data will be delivered in sequence or that the sender will be notified if the protocol was unable to do so. A connection- oriented protocol would typically be used download a program to a PLC.
4.2 Common LAN Protocols
As discussed in the previous section, the Ethernet specifications cover layer 1 (physical) and layer 2 (data link) of the OSI reference model. Additional protocols are commonly used on local area networks at layer 3 (network) and layer 4 (transport) of the OSI Reference model. The more common protocols in this area are NetBIOS/NetBUEI, IPX/SPX, and TCP/IP.
NETBUEI
NETBUEI (NetBIOS Extended User Interface) is the protocol stack used by Microsoft LAN Manager and IBM LAN Server. More recently, Windows for Workgroups, a Microsoft product, uses NETBUEI.
NETBUEI uses LLC (802.2) to provide both connectionless and connection-oriented services. NETBUEI then implements an IBM/Microsoft proprietary connection-oriented NetBIOS Frames Protocol on top of 802.2. Applications interface to NETBUEI via NETBIOS calls. NETBIOS employs user defined node names to establish a logical connection with another node. The architecture of NETBUEI has the potential for excellent performance but has developed a reputation for requiring significant "tuning" to achieve this performance. Another major problem with NETBUEI is that its architecture does not allow NETBUEI to be routed among different network types.
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CTI 2572 Technical Overview Manual
