A SEMINAR REPORT ON1 Content 1. Introduction 2. Design 3. Addressing 4. AppleTalk Network Components 5. AppleTalk protocol and OSI Model 6. Physical Implementation 7. Advantage Introduction: 2 AppleTalk is a network with a bus topology that uses a trunk cable between connection modules. Any device (computer. peripheral. while the devices that make use of these resources (such as a user's Macintosh computer) are referred to as clients. Nodes can be separated by a maximum cable length of 1000 feet. AppleTalk is one of the early implementations of a distributed client/server networking system. This type of network is known as a multidrop line or a multipoint link. The devices that supply these resources are called servers. Fig. Interfacing with the network is handled by the Serial Communications Control chip found in every Mac. was developed in conjunction with the Macintosh computer. as shown in figure 1. 1 The Physical Connection Design 3 . such as files and printers. AppleTalk is capable of supporting up to 32 nodes (devices) per network and can transmit data at a rate of 230. AppleTalk's purpose was to allow multiple users to share resources. etc. a protocol suite developed by Apple Computer in the early 1980s.400 bits per second.AppleTalk.) attaches to a connection box via a short cable (called a drop cable). Hence. Each node dynamically chose its own node number. all services had names which. Of these. which is the second enhanced AppleTalk implementation. which is the first AppleTalk specification. the actual operations of the AppleTalk protocols are invisible to end users. Addressing An AppleTalk address was a 4-byte quantity. Phase 2 addresses the key limitations of AppleTalk Phase 1 and features a number of improvements over Phase 1. being obtained from a router. Phase 2 allows any combination of 253 hosts or servers on a single AppleTalk network segment and supports both nonextended and extended networks. and a one-byte socket number. was developed in the early 1980s strictly for use in local workgroups. Two versions of AppleTalk exist: AppleTalk Phase 1 and AppleTalk Phase 2. according to a protocol which handled contention between different nodes accidentally choosing the same number. and also could be sufficiently long enough to minimize the chance of conflicts. AppleTalk Phase 2. Because of this dynamism. a few well-known numbers were reserved for special purposes specific to the AppleTalk protocol itself. all application-level protocols were expected to use dynamically-assigned socket numbers at both the client and server end. In particular. users could not be expected to access services by specifying their address. In addition. only the network number required any configuration. and it can support only nonextended networks. could be expected to be meaningful to users. This consisted of a two-byte network number. being chosen by humans. 4 . the interaction between client computers and network servers requires little interaction from the user. For socket numbers. a one-byte node number. Apart from these. Phase 1 therefore has two key limitations: Its network segments can contain no more than 135 hosts and 135 servers. was designed for use in larger internetworks. Instead. who see only the result of these operations.AppleTalk was designed with a transparent network interface—that is. AppleTalk Phase 1. there was no need for users to do anything different to continue accessing the service. nodes. networks. Four basic components form the basis of an AppleTalk network: sockets. a name in AppleTalk mapped directly to a service being provided by a machine. And the same machine could host any number of instances of services of the same type. 5 . where a name translates only to a machine address. without any network connection conflicts. such as Kerberos and Active Directory use DNS SRV records to identify services by name. (Some newer protocols. not including the port number that might be providing a service. Each of these concepts is summarized in the sections that follow.Note that. Thus. their access will break when the service is moved to a different machine. so long as they kept the same service name. because a name translated to an address. but there is no way of guaranteeing that users will follow such a convention. which was entirely separate from the name of the machine itself. if people are accustomed to using a particular machine name to access a particular service. Contrast this with records in the DNS. which is much closer to the AppleTalk model. Fig. services could be moved to a different machine and. which included a socket number as well as a node number.) AppleTalk Network Components AppleTalk networks are arranged hierarchically. Thus. This can be mitigated somewhat by insistence on using CNAME records indicating service rather than actual machine names to refer to the service. and zones.1 illustrates the hierarchical organization of these components in an AppleTalk internetwork. 1 The AppleTalk Internet work consists of a Hierarchy of Components Sockets An AppleTalk socket is a unique. Dynamically assigned sockets are assigned by DDP to socket clients upon request. Socket clients own one or more sockets. Statically assigned sockets are reserved for use by certain protocols or other processes. addressable location in an AppleTalk node. which they use to send and receive datagram. It is the logical point at which upper-layer AppleTalk software processes and the network layer Datagram Delivery Protocol (DDP) interact. These upper-layer processes are known as socket clients. An AppleTalk node can contain up to 254 different socket numbers. Sockets can be assigned statically or dynamically. 6 .Fig. an IBM PC. This device might be a Macintosh computer. The logical cable is comprised of either a single physical cable or multiple physical cables interconnected by using bridges or routers.Fig. a router. Networks An AppleTalk network consists of a single logical cable and multiple attached nodes. AppleTalk networks can be nonextended or extended. a printer. Network 100 and network 7 . Nonextended Networks A nonextended AppleTalk network is a physical network segment that is assigned only a single network number. or some other similar device. which can range between 1 and 1024. Each node in an AppleTalk network belongs to a single network and a specific zone. 2 Socket Clients Use Sockets to Send and Receive Datagram Nodes An AppleTalk node is a device that is connected to an AppleTalk network. Each is discussed briefly in the following sections. Within each AppleTalk node exist numerous software processes called sockets. 1 illustrates a nonextended AppleTalk network.) AppleTalk Phase 1 supports only nonextended networks. Fig. Extended networks can have multiple AppleTalk zones configured on a single network segment. 8 .3. are both valid network numbers in a nonextended network. for example. This configuration is known as a cable range. and a single nonextended network segment cannot have more than one AppleTalk Zone configured on it. and its address must be unique for identification purposes. are both valid in an extended network. AppleTalk cable ranges can indicate a single network number or multiple consecutive network numbers. (A zone is a logical group of nodes or networks. and nodes on extended networks can belong to any single zone associated with the extended network. extended network configurations have replaced nonextended network configurations. each combination of network number and node number in an extended network must be unique. Just as in other protocol suites. The cable ranges network 3-3 (unary) and network 3-6. nonextended network configurations are no longer used in new networks because they have been superseded by extended networks. but as a rule.1 A Nonextended Networks is assigned only one network number Extended Networks An extended AppleTalk network is a physical network segment that can be assigned multiple network numbers. As a rule. Each node number in a nonextended network must be unique.562. Fig. for example. 3. such as TCP/IP and IPX. 3.2 An Extended Network can be assigned multiple network numbers Zones An AppleTalk zone is a logical group of nodes or networks that is defined when the network administrator configures the network. 4 Nodes or Networks in the Same Zone need not be physically Contiguous 9 .Fig. The nodes or networks need not be physically contiguous to belong to the same AppleTalk zone. Fig. 5 AppleTalk Protocols and the OSI Model 10 .AppleTalk Protocols and the OSI Model: Fig. If another machine has that address. and then waits to see if anyone else on the network complains. so for performance purposes the successful address is "written down" in NVRAM and used as the default address in the future. intending to hear back from controllers such as routers. the whole connection would be closed (i. Significant differences from TCP were: • • a connection attempt could be rejected There were no "half-open" connections. usually MAC. only one or two tries are needed before the address effectively become constant. addresses. once one end initiated a tear-down of the connection. This means that in most real-world setups where machines are added a few at a time. not dual simplex).e. When powered on. and keep trying until it finds a free one. It then broadcasts another packet saying "I am selecting this address". ADSP is full-duplex. On a network with many machines it may take several tries before a free address is found. If no address is provided.. it will pick another address. It is functionally equivalent to ARP. 0. AppleTalk Data System Protocol This was a comparatively late addition to the AppleTalk protocol suite. 11 . AARP is a fairly simple system. one is picked at random from the "base subnet". an AppleTalk machine broadcasts an AARP probe packet asking for a network address.Protocols: AppleTalk Address Resolution Protocol AARP resolves AppleTalk addresses to physical layer. done when it became clear that a TCP-style reliable connection-oriented transport was needed. Exactly-once mode was essential for operations which were not idempotent. with no need to set up or tear down connections. it provides services for authenticating users (extensible to different authentication methods including two-way random-number exchange) and for performing operations specific to the Macintosh HFS files system. AppleTalk Session Protocol ASP was an intermediate protocol. The requestor then sent an acknowledgement packet containing a bit mask indicating which of the response packets it received. the responder kept a copy of the response buffers in memory until successful receipt of a release packet from the requestor or until a timeout elapsed. 12 .Apple Filing Protocol The Apple Filing Protocol (AFP). is the protocol for communicating with AppleShare file servers. AppleTalk Transaction Protocol ATP was the original reliable transport-level protocol for AppleTalk. Built on top of AppleTalk Session Protocol. ATP could operate in either "at-least-once" mode or "exactly-once" mode. AFP is still in use in Mac OS X. This way. a full. so the responder could retransmit the remainder. it could respond to duplicate requests with the same transaction ID by resending the same response data. built on top of DDP. An ATP request packet could be answered by up to eight response packets. built on top of ATP. formerly AppleTalk Filing Protocol. reliable connection-oriented protocol like TCP was considered to be too expensive to implement for most of the intended uses of AppleTalk. Thus. ATP was a simple request/response exchange. which in turn was the foundation of AFP. It provided basic services for requesting responses to arbitrary commands and performing out-of-band status queries. without performing the actual operation again. even though most other AppleTalk protocols have been deprecated. It also allowed the server to send asynchronous attention messages to the client. in this mode. At the time it was being developed. such as a file server. As would be expected from Apple. it registered a name for itself on that machine. The Name Binding Protocol (NBP) is a transport layer protocol in the AppleTalk protocol suite that maps the addresses used at lower layers to AppleTalk names. as chosen by a human administrator. it used NBP to query machines to find that service. were built on top of DDP. including the infrastructure protocols NBP. distributed system for managing AppleTalk names. names were truly human readable. such as a print service. An NVE is a network-addressable resource. known as entity types. associated with them. Second. Then later. Two key reasons exist for using entity names rather than addresses at the upper layers. NVEs also have a zone and various attributes.Datagram Delivery Protocol DDP was the lowest-level data-link-independent transport protocol. therefore. Entity names provide a consistent way for users to refer to network resources and services. change regularly. when a client wanted to access that service. 13 . NBP provided browse ability ("what are the names of all the services available?") as well as the ability to find a service with a particular name. network addresses are assigned to nodes dynamically and. using names instead of addresses to refer to resources and services preserves the transparency of lower-layer operations to end users. containing spaces. When a service started up on a machine. NBP provided a system for checking that no other machine had already registered the same name. NVEs are referred to by character strings known as entity names. First. that is accessible over the internet work. At this point. RTMP and ZIP. upper and lower case letters. and including support for searching. Socket clients within AppleTalk nodes are known as Network-Visible Entities (NVEs). It provided a datagram service with no guarantees of delivery. All application-level protocols. Name Binding Protocol NBP was a dynamic. each end could only send data to the other end if there was an outstanding ATP request to respond to. each end sent the other an ATP request which basically meant "send me more data". It was built on top of ATP. after which another "send-more-data" request was sent. while the server could respond with any diagnostic messages that might be generated as a result. 14 .Fig. The client's response to the server was to send a block of PostScript code. This use of ATP provided automatic flow control. When a PAP connection was opened. 6 An RTMP Routing Table Contains Information about Each Destination Network Known to the Router Printer Access Protocol PAP was the standard way of communicating with Postscript printers. each router had to send out a list of all the network numbers it knew about and how far away it thought they were. As long as connection modules conform to the signal descriptions of the Physical Layer. handled by separate ATP transactions. Even while it was busy servicing a print job from one client. a zone could include several different discontinuous portions of the network. This was the only part of AppleTalk that required periodic unsolicited broadcasts: every 10 seconds. encapsulates the data in frames. ALAP is also responsible for assigning node numbers to each station on a network. and recognizes when data should be received.PAP also provided for out-of-band status queries. Zone Information Protocol ZIP was the protocol by which AppleTalk network numbers were associated with zone names. the Serial Communications Control chip in the Mac takes care of the AppleTalk port. a PAP server could continue to respond to status requests from any number of other clients. As mentioned previously. The AppleTalk Link Access Protocol (ALAP) must be common to all systems on the network bus and handles the node-to-node delivery of data between devices connected to a single AppleTalk network. and what the job was that it was busy with. signal transmission/ reception and carrier sensing. The ALAP software assigns a random node number when the Mac is booted and keeps that number as long as 15 . "Accounting Department"). A zone was a subdivision of the network that made sense to humans (for example. The Physical Layer has the responsibility of bit encoding/decoding. sends its data. synchronization. Routing Table Maintenance Protocol RTMP was the protocol by which routers kept each other informed about the topology of the network. which happens to be the printer port on current Macs. but while a network number had to be assigned to a topologically-contiguous section of the network. This allowed other Macintoshes on the LAN that were waiting to print to display status messages indicating that the printer was busy. ALAP determines when the bus is free. any transmission medium can be used for the actual network. and network number. The routing tables pair network numbers with the local node number of the bridge through which the shortest path to that net exists. known as an internet. The Datagram Delivery Protocol takes care of assigning socket numbers. so the node number is not enough to identify a network address. several protocols exist to add different types of functionality to the underlying services. node number. A socket is a communication endpoint within a node on the network. While the ALAP protocol provides delivery of data over a single AppleTalk network. to provide a unique identification for every process occurring on the AppleTalk network. for access control. One Mac may have several AppleTalk connections open at one time. An internet can be formed. as well as node numbers and network numbers. The Link Access Protocol uses a method called CSMA/CA or carrier-sense multiple accesses with collision avoidance. all transmitters wait until the bus is idle for a minimum time plus a random amount of added time before transmitting (or retransmitting after a collision). ALAP tries again). As we move on to the Transport Layer. by using a bridge between two. for example. Collision avoidance means that the protocol attempts to minimize collisions between transmitted data packets. In AppleTalk CSMA/CA. The Routing Table Maintenance Protocol (RTMP) allows bridges and internet routers to dynamically discover routes to the different AppleTalk networks in an internet. In addition. AppleTalk networks. Sockets belong to processes or functions that are implemented within software in the node. Carrier sense means that a sending node first listens to the network to hear if any other node is using the bus and defers to the ongoing transmission. AppleTalk's address header (a part of each data packet) is used for identification of a process on the network and consists of a socket number. node numbers are unique only within a single physical network. 16 .it does not conflict with a previously assigned node number (if it does conflict. or more. the Datagram Delivery Protocol (DDP) extends this mechanism to include a group of interconnected AppleTalk networks. so DDP requires that each network be assigned a network number. NBP also introduces the concept of a zone. the type name (e.. The specifications for the AppleTalk Data Stream Protocol (ADSP) have not yet been published (Inside AppleTalk. Central to ASP is the concept of a session. the majority of ZIP is implemented in the bridges of an internet. maintaining and closing sessions. ASP is an asymmetric protocol in that the 17 .g.The AppleTalk Transaction Protocol. 1). The Echo Protocol is mainly meant for network maintenance functions. The concept of zones is provided to assist the establishment of departmental or other user-understandable grouping of the entities of the internet.g. Most of ZIP’s services are transparent to the normal (non-bridge) node. In the Session Layer.. This transaction-oriented protocol can be contrasted to other types of transport layers which support a two-way link between clients that can act as though they had an error-free hardwired link between them. the AppleTalk Session Protocol (ASP) is a general protocol designed to interact with ATP to provide for establishing. which is an arbitrary subset of networks in an internet where each network is in one and only one zone. or ATP. printer). 1986). The Echo Protocol (EP) is a simple protocol that allows any node to send data to any other node on an AppleTalk internet and receive an echoed copy of that data in return. ADSP is designed to provide byte-stream data transmission in a full duplex mode between any two sockets on an AppleTalk internet. two network entities. Bldg. The basic function of the Name Binding Protocol (NBP) is the translation of a character string name into the internet address of the corresponding client. AppleTalk names consist of three fields: the object name (e. Dave). is part of the Transport Layer and is responsible for controlling the transactions (flow of data) between requestor and responder sockets. current version dated July 14.g. can set up an ASP session between themselves (identified by a unique session’s identifier). A key feature of the network is that most objects are accessible by name rather than by address (better for the user). The Zone Information Protocol (ZIP) is used to maintain an internet-wide mapping of networks to zone names. ZIP is used by the Name Binding Protocol to determine which networks belong to a given zone. one in a workstations and the other in a server.. and the zone name (e. However. AFP has been finalized with the introduction of the AppleShare file server software from Apple. The specifications for the AppleTalk Filing Protocol (AFP) have not been generally publicized.workstation initiates the session connection and issues sequences of commands. to which the server responds. however. Other network nodes. the server may not send commands to the workstation. 7 illustrates a basic ZIT. ZIP is used primarily by AppleTalk routers. ZITs are lists maintained by ZIP that map specific network numbers to one or more zone names. 18 . The Zone Information Protocol (ZIP) is a session layer protocol in the AppleTalk protocol suite that maintains network number-to-zone name mappings in AppleTalk routers. which uses AFP. Fig. use ZIP services at startup to choose their zone. ZIP maintains a zone information table (ZIT) in each router. AFP is a presentation layer protocol designed to control access to remote file systems. Each ZIT contains a network number-to-zone name mapping for every network in the internetwork. 4 kbit/s. known as Ether Talk and Token Talk respectively. The boxes are designed so that the continuity of the trunk cable and the network is maintained even if a device is disconnected from the network by unplugging it from the connection box. but at the time the additional cost and complexity of networking on PC machines was such that it was common that Macs were the only networked machines in the office. Ethernet and Token Ring were also supported. Ether Talk in particular gradually became the dominant implementation method for AppleTalk as Ethernet became generally popular in the PC industry throughout the 1990s. The system was slow by today's standards.Physical implementation: The initial default hardware implementation for AppleTalk was a high-speed serial protocol known as LocalTalk that used the Macintosh's built-in RS-422 ports at 230. PhoneNet was considerably less expensive to install and maintain. One common replacement for LocalTalk was PhoneNet. LocalTalk used a splitter box in the RS-422 port to provide an upstream and downstream cable from a single port. a 3rd party solution (from a company called Farallon) that also used the RS-422 port and was indistinguishable from LocalTalk as far as Apple's LocalTalk port drivers were concerned. but ran over two unused wires in existing phone cabling. Other physical implementations were also available. Additional devices can be added to the network at any time simply by plugging them into the boxes. An Ethernet network could also run AppleTalk and TCP/IP simultaneously Advantages: One of the advantages of AppleTalk relates to the design of these connection boxes. The physical layout of an AppleTalk network can therefore be designed by locating the connection boxes where desired without worrying if a device will be initially connected to each one of the boxes. 19 . MAHAKAL INSTITUTE OF TECHNOLGY UJJAIN A SEMINAR REPORT On APPLE TALK The seminar project submitted to Rajiv Gandhi Proudyogiki Vishwavidhyalaya. Bhopal Towards partial fulfillment of the Degree of Bachelor of Engineering in Computer Science Submitted to: Submitted by: 20 .