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For reliable packet delivery, the ADSP (AppleTalk Data Stream Protocol) and ATP (AppleTalk Transaction Protocol) are available. Each of these protocols is appropriate under different conditions. The NBP (Name Binding Protocol) and ZIP (Zone Information Protocol) help make addressing easier. NBP associates easy-to-remember names (used by users) with the appropriate address. ZIP is used mainly on larger networks or internetworks, which are more likely to be divided into zones. A zone is a logical grouping of nodes that together make up a subnetwork. The concept of a zone was introduced to allow for larger networks with more than 255 nodes, and also to make addressing and routing tasks easier. Applications access an AppleTalk network through the AFP (AppleTalk Filing Protocol); they access printer services by shipping PostScript files through the PAP (Printer Access Protocol). A few protocols make use of services from more than one lower-level protocol. For example, ZIP relies on ATP and DDP services.
 
For reliable packet delivery, the ADSP (AppleTalk Data Stream Protocol) and ATP (AppleTalk Transaction Protocol) are available. Each of these protocols is appropriate under different conditions. The NBP (Name Binding Protocol) and ZIP (Zone Information Protocol) help make addressing easier. NBP associates easy-to-remember names (used by users) with the appropriate address. ZIP is used mainly on larger networks or internetworks, which are more likely to be divided into zones. A zone is a logical grouping of nodes that together make up a subnetwork. The concept of a zone was introduced to allow for larger networks with more than 255 nodes, and also to make addressing and routing tasks easier. Applications access an AppleTalk network through the AFP (AppleTalk Filing Protocol); they access printer services by shipping PostScript files through the PAP (Printer Access Protocol). A few protocols make use of services from more than one lower-level protocol. For example, ZIP relies on ATP and DDP services.
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===Application Layer===
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The highest layer of the OSI model is the application layer. This layer allows for the development of application software. Software written at this layer benefits from the services of all the underlying layers. There is no AppleTalk protocol that maps directly to this layer, although some of the functions of the AppleTalk Filing Protocol (AFP) fulfill this layer.
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===Presentation Layer===
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The presentation layer assumes that an end-to-end path or connection already exists across the network between the two communicating parties, and it is concerned with
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the representation of data values for transfer, or the transfer syntax. In the OSI model, the AppleTalk Filing Protocol (AFP) spans the presentation and application layers. AFP provides an interface between an application and a file server. It uses the services of ASP, which, in turn, is a client of ATP.
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AFP allows a workstation on an AppleTalk network to access files on an AFP file server, such as an AppleShare file server. When the user opens a session with an AppleShare file server over an internet, it appears to any application running on the workstation that uses File Manager routines as if the files on the file server were located on a disk drive connected to the workstation.
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===Session Layer===
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The session layer serves as an interface into the transport layer, which is below it. The session layer allows for session establishment, which is the process of setting up a connection over which a dialog between two applications or processes can occur. Some of the functions that the session layer provides for are flow control, establishment of synchronization points for checks and recovery for file transfer, full-duplex and half-duplex dialogs between processes, and aborts and restarts.
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The AppleTalk protocols implemented at the session layer are
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* the AppleTalk Data Stream Protocol (ADSP), which provides its own stream-based transport layer services that allow for full-duplex dialogs
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* the AppleTalk Session Protocol (ASP), which uses the transaction-based services of ATP to transport workstation commands to servers
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* the Zone Information Protocol (ZIP), which provides applications and processes with access to zone names. Each node on a network belongs to a zone.
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===Transport Layer===
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The transport layer isolates some of the physical and functional aspects of a packet network from the upper three layers. It provides for end-to-end accountability, ensuring that all packets of data sent across the network are received and in the correct order. This is the process that is referred to as reliable delivery of data, and it involves providing
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a means of identifying packet loss and supplying a retransmission mechanism. The transport layer also provides connection and session management services.
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The following AppleTalk protocols are implemented at the transport layer:
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* Name-Binding Protocol (NBP)
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* AppleTalk Transaction Protocol (ATP)
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* AppleTalk Echo Protocol (AEP)
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* Routing Table Maintenance Protocol (RTMP)
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In addition to these transport layer protocols, the AppleTalk Data Stream Protocol (ADSP) includes functions that span both the transport and the session layers. ADSP provides for reliable delivery of data, and in that capacity it covers the transport layer requirements.
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===Network Layer===
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The network layer specifies the network routing of data packets between nodes and the communications between networks, which is referred to as internetworking. The Datagram Delivery Protocol (DDP) is the AppleTalk protocol implemented at the network layer. DDP is a connectionless datagram protocol providing best-effort delivery. This means that DDP transfers data as discrete packets and that DDP does not include support to ensure that all packets sent are received at the destination or that those packets that are received are in the correct order. Higher-level protocols that use the services of DDP provide for this kind of reliability.
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===Data-Link and Physical Layers===
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The data-link layer and the physical layer provide for connectivity. The communication between networked systems can be via a physical cable made of wire or fiber optic, or it can be via infrared or microwave transmission. In addition to these, the hardware can include a network interface controller (NIC), if one is used. The hardware or transport media and the device drivers for the hardware comprise the physical layer. LocalTalk, token ring, Ethernet, and Fiber Distributed Data Interface (FDDI) are examples of types of networking hardware that AppleTalk supports.
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The physical hardware provides nodes on a network with a shared data transmission medium called a link. The data-link layer includes a protocol that specifies the physical aspects of the data link and the link-access protocol, which handles the logistics of sending the data packet over the transport medium. AppleTalk is designed to be data-link independent, allowing for the use of various types of hardware and their link-access protocols.
    
=AppleTalk Protocol Suite=
 
=AppleTalk Protocol Suite=
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===AEP (AppleTalk Echo Protocol)===
 
===AEP (AppleTalk Echo Protocol)===
 
A transport-layer protocol used to determine whether two nodes are connected and both available.
 
A transport-layer protocol used to determine whether two nodes are connected and both available.
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The AppleTalk Echo Protocol (AEP) exists on every node as a DDP client process called the AEP Echoer. The AEP Echoer uses a special socket to listen for packets sent to it from socket clients on other nodes. When it receives such a packet, the AEP Echoer returns it directly to the sender. A socket client can send a packet to the AEP Echoer on another node to determine if that node can be accessed over the internet and to determine how long it takes a packet to reach that node. There is no application programming interface to AEP. A socket client can send packets to an AEP Echoer socket on another node from a DDP socket, but it cannot access the AEP implementation directly.
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===AFP (AppleTalk Filing Protocol)===
 
===AFP (AppleTalk Filing Protocol)===
 
A presentation/application-layer protocol used by applications to communicate with the network.
 
A presentation/application-layer protocol used by applications to communicate with the network.
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AFP is a remote filing system protocol that provides a workstation on an AppleTalk network with access to a server that is implemented according to the AFP file system structure. AFP also includes user authentication support and an access control mechanism that supports volume-level and folder-level access rights. AppleShare is the AFP file server that is implemented on Macintosh computers.
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Through the native file system and AFP, your application running on one node can manipulate files on another node using the same file system commands on the remote node that it uses to manipulate files on its own node. You can use AFP commands to
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* obtain and modify information about the file server and other parts of the file
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* system structure
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* create and delete files and directories
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* read files or write to them
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* retrieve and store information within individual files
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AFP is implemented by the .XPP driver. The .XPP driver maps an AFP function call from the client workstation into one or more ASP function calls.
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===ASDSP (AppleTalk Safe Data Stream Protocol)===
 
===ASDSP (AppleTalk Safe Data Stream Protocol)===
 
A session-layer protocol that is similar to ADSP but that provides additional security against unauthorized use.
 
A session-layer protocol that is similar to ADSP but that provides additional security against unauthorized use.
 
===ASP (AppleTalk Session Protocol)===
 
===ASP (AppleTalk Session Protocol)===
 
A session-layer protocol used to begin and end sessions, send commands from client to server, and send replies from server to client.
 
A session-layer protocol used to begin and end sessions, send commands from client to server, and send replies from server to client.
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The AppleTalk Session Protocol (ASP) allows one or more ASP workstation applications or processes to establish a session with the same server at the same time. To track communication from various sessions, ASP assigns a unique session identifier that is referred to as a session reference number to each session. ASP is an asymmetrical protocol that provides one set of services to the workstation and a different set of services to the server. The ASP workstation application always initiates the process of setting up a session and the communication across a session, and the ASP server replies to commands that it receives. (ASP is built on top of ATP, and it follows the transaction model of ATP while adding session-connection services.) The only case in which an ASP server can initiate communication is through the ASP attention mechanism.
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===ATP (AppleTalk Transaction Protocol)===
 
===ATP (AppleTalk Transaction Protocol)===
 
A transport-layer protocol that can provide reliable packet transport. Packets are transported within the framework of a transaction (an interaction between a requesting and a responding entity program or node).
 
A transport-layer protocol that can provide reliable packet transport. Packets are transported within the framework of a transaction (an interaction between a requesting and a responding entity program or node).
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===RTMP (Routing Table Maintenance Protocol)===
 
===RTMP (Routing Table Maintenance Protocol)===
 
A transport-layer routing protocol for moving packets between networks.
 
A transport-layer routing protocol for moving packets between networks.
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The Routing Table Maintenance Protocol (RTMP) provides AppleTalk internet routers with a means of managing routing tables used to determine how to forward a datagram from one socket to another across an internet based on the datagram's destination network number. The RTMP implementation on a router maintains a table called a routing table that specifies the shortest path to each possible destination network number. The AppleTalk protocol software in a workstation (that is, a node other than a router) contains only a small part of RTMP, called the RTMP stub, that DDP uses to determine the network number (or range of network numbers) of the network cable to which the node is connected and to determine the network number and node ID of one router on that network cable.
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===ZIP (Zone Information Protocol)===
 
===ZIP (Zone Information Protocol)===
 
A session-layer protocol used to help find a node; for example, in a large internetwork.
 
A session-layer protocol used to help find a node; for example, in a large internetwork.
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* Allows a network to be assigned more than one network number
 
* Allows a network to be assigned more than one network number
 
* Introduced the AppleTalk Internet Router, which allows up to eight AppleTalk networks to be connected
 
* Introduced the AppleTalk Internet Router, which allows up to eight AppleTalk networks to be connected
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The Phase 2 versions of the AppleTalk drivers are included as part of system software version 7.0 and later. They can be installed on any Macintosh computer other than the Macintosh 128K, Macintosh 512K, Macintosh 512K enhanced, and Macintosh XL computers.
    
=Related Articles=
 
=Related Articles=

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