Please don't be polite, you will pick it wrong, thank you.
SNA / Appn
SNA concept and characteristics
SNA (Systems Network Architecture) system network structure, network architecture developed by IBM, is a set of large network standards and protocols, including services for configuring and managing system resources in IBM mainframe network environments, SNA defines mainframe host control The centralized architecture of the terminal is the main networking protocol of the IBM mainframe and the medium machine, which is widely used in the IBM host environment. In this architecture, including large computer systems (ES / 9000, S / 390, etc.), medium machine computer systems (AS / 400), 3270 terminals and desktop computers, and there is a system to communicate or system between these systems and host systems Strategies for mutual peer communication.
The reason why SNA is concerned is because it is still early than OSI, and its first in 1974 is the most widely available network architecture. Initially, it is designed to connect a single host to the terminal, but updated in 1976, allowing multiple host to communicate. In 1985, it was updated again, and the LAN and any topologies were added.
SNA defines the logical architecture of the data communication network, the protocol of synchronous communication between the network resources, the information format transmitted on the network; describes the network resources on the network, network configuration, transmission information, etc.
The SNA network consists of a Physical Components and Software Components. The physical part consists of a processor, a communication controller, a terminal controller, and the physical part is connected by a data link, a telephone connection, a microwave, and the like. The software part is accessed by access mode (ACF / VTAM), App Subsystem (CICS, IMS), User Applications, and Network Control Programs (ACF / NCP).
A SNA network includes a host system, a terminal, or a PC, printer, cluster controller, communication controller, and other components that run the simulation program. Terminal and printers are connected to the cluster controller, the cluster controller connects to the host or communication controller (if they stay away from the host). These hardware components and software running are called "node", which are interconnected between DataLinks. The node on the network is a connection point on the endpoint or network.
The main purpose of the SNA design is to end-to-end communications, and allow the user application to remotely depending on the complex data communication system, the user feels the transparency of the data communication system. End users are typically a terminal or an application on the host. The SNA network is a service that provides communication between users.
for example:
A bank staff submitted a request to the network, which is sent to the corresponding host application to process by the SNA network. The application gives the corresponding response and passed back to the display terminal where the bank staff is sent over the SNA network. Here, the terminals and host applications used by the staff are the end users.
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SNA physical structure
Sna Physical Components connected by data links in SNA, we call SNA nodes [1] (SNA Node). SNA divides nodes into two: subdomain nodes and peripheral nodes.
A host containing an access control method (ACF / VTAM) is called a host subdomain node. Communication processing mode (ACF / VTAM) controls all resources on all nodes. Communication controller and (ACF / NCP) are called Communication Controller Subarea Node, which controls the communication link. All other nodes we call the peripheral node.
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SNA logic part
SNA provides a host-centric communication architecture defining some logic components to implement these functions. The LU (Logical Unit) is used to handle end-to-end communication; the PU (Physical Unit) is used to manage physical resources on the SNA node; SSCP (System Services Control Point) as the center of access control in the network; DLC (Data Link Control ) The link used to manage data transmission; PC (Path Control) is used to process the route transmitted in the SNA network.
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Sublayer structure of SNA protocol
As shown in the chart 0? 1 OSI layer structure is compared with the SNA hierarchical structure, SNA has seven protocol layers [2], which is similar to the open system interconnection (OSI) reference model.
Chart 0? 1 OSI hierarchical structure compared to SNA hierarchical structures
Here, the 5th floor is introduced, including:
(1) Physical link control layer (Physical Link Control Layer)
Allow multiple different types of physical connections. Provide physical and electrical instructions. It allows various communication modes including: cable, fiber and satellite. In some cases, it also allows multiple different connections between two points, which allows the user to specify the detailed type of the transfer, similar to the type of service provided by the Internet protocol (Section 7.4). This layer can also be used to divide long string data into separate units and transmit them separately. Typical transmission uses a serial link, although a parallel transfer can be used between the host and the front-end processor (Special processor representing the host processing request). Physical layer: Allows multiple different types of physical connections. Nodes interconnected media with copper wires, fiber optic cables or microwaves.
(2) Data link control (Data Link Control Layer)
Define synchronous data link control procedures (SDLC) and LAN protocols, such as token Ring.
The data link layer is responsible for providing reliable data transmission over the physical connection within the network. Its features include defining a frame format, perform errors control and stream control (to prevent a fast transmission of the transmitter from operating for a long time).
DLC supports a variety of different network protocol implementations, such as Tong Dataset Control (SDLC) protocol, IEEE802.5 token ring network (IEEE802.5 token ring network (IEEE802.5 token ring network (IEEE802.5 token ring network, x. 25 and IEEE802.2 Logical Link Control Protocol, Frame Relay, and Fiber Distributed Data Interface (FD-DI). The DLC layer provides a unified implementation method for PC or CS LU.
SDLC is controlled on the flow of the frame in the SNA network. Additionally, a channel link is a direct connection between the host or between the host and the front-end processor thereof. These links can be a slow copper or a high speed cable (expandable to many kilometers). DLC provides a unified interface for the path control layer.
(3) Path Control Layer: (Path Control Layer) Controls the route selection, and can subdivision and reload the datagram to accommodate the transmission facilities, responsible for the sorting services related to correct data decomposition. The path control layer is also responsible for routing.
Network Control Program (NCP): Used for routing, segmentation, and frame functions. NCP is typically run on a communication controller (host) or front-end processor. It mitigates the host's communication processing, such as routing, session management, buffer, and error correction and other tasks in communication.
(4) Transmission control layer (Transmission Control Layer)
Provides a connection-oriented service, establish a monitoring data stream and ensuring the link between the two end points.
System Services Control Point, SSCP This software runs and manages all resources in the host domain.
Virtual Communication Access (VTAM): Used for queue, traffic control, error recovery, and session management. VTAM can be used to implement network accessible units (NAUs), which is used to control data from the SNA network. The VTAM includes SSCP.
(5) Data stream control layer (Data Flow Control Layer)
Monitor the data stream and process sessions between two endpoints to prevent data overflow.
(6) Represents the presentation service layer
Perform data conversion and provide an application interface.
(7) Transaction Services Layer
Provide the application to the interface of the network service.
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SNA extension ---- Appn
In order to provide program communication, IBM introduces a session established between program communication (Appc), APPN processing peer nodes, dynamic transparent routing calculations, and give business priority for the APPC service.
Advanced Pertopeer Networking, Appn: Allows establishing a SNA connection between the two hosts, which is IBM to link SNA and TCP / IP network in 1985 as a popular client in 1985 in order to fight TCP / IP threats. / Server computing techniques are proposed. The Appn is a peer-to-peer route selection protocol, supports point-to-point communication and distributed client / servers.
For example, a PC host is accessible to an application that runs on a large machine using the Advanced Program Inter-Duty Communication (AppN) session. The physical unit (PU) and logic unit (LU) can be implemented using the APPN, both of which are used to control the host and terminal communication process. The LU represents a SNA end node, such as a user or application: PU is a hardware device or terminal, and two LUs communicate through associated PUs. Many types of LU and PU are used in the SNA network environment.
The APPN provides a variety of non-centralized network computing in an enterprise while maintaining the diversity of the host system. On the APPN, the size system is pertiler. IBM's strategy is to continue to support Appn while inclusive industrial standard protocols such as TCP / IP and OSI protocols. This idea has been expressed in the networked scheme, a multi-protocol transmission network (MPTN, Multi Protocol Transmission Network) is an example, which allows the application to solve the application from the baseline network protocol, allowing applications that work with a specific protocol Use other protocols. The multi-protocol transport network (MPTN) using IBM can connect AS / 400 to the token ring or Ethernet or Ethernet that supports common PC protocols such as TCP / IP and IPX. ?
Development of APPN ---- HPR
High Performance Routing (HPR, HIGH Performance Routing) is a network interconnect protocol made by IBM, which is used for the second-generation route selection algorithm (also named APPN ), which is used for advanced peer network technology (APPN). APPN HPR, referred to as HPR. IBM Design This protocol acts as an alternative to TCP / IP. The HPR Source Routing Select Alteration Requirements Switching Routing Algorithm, routing by bypassing the fault node and avoiding the processing of data packet assistance by the network node, improves the performance of the network.
The HPR is a case where the link fails, specifies a non-interrupted routing to select a non-connection session layer; it also specifies an end-to-end stream control, error control, and sorting facing-oriented layer.
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[1] See http://www-306.ibm.com/software/neetwork/commserver/library/publications/csaix_60/DYVL
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[2] But note that someone refers to the current SNA as a 6-layer or even 5-layer protocol. ISO uses IBM's SNA protocol stack as its OSI's original model. The IBM website is defined at 5 layers. http://www-306.ibm.com/software/neetwork/commserver/windows/library/clsvr15.htm#ptoc_142
