- Количество слайдов: 20
Comparison of Various Network Models to OSI o IBM SNA o DECnet DNA o Apple. Talk o Xerox XNS o Novell Netware o Banyan Vines
IBM SNA o IBM networking today consists of essentially two separate architectures that branch, more or less, from a common origin. Before contemporary networks existed, IBM's Systems Network Architecture (SNA) ruled the networking landscape, so it often is referred to as traditional or legacy SNA.
o IBM SNA model components map closely to the OSI reference model. The descriptions that follow outline the role of each SNA component in providing connectivity among SNA entities. o Data link control (DLC)—Defines several protocols, including the Synchronous Data Link Control (SDLC) protocol for hierarchical communication, and the Token Ring Network communication protocol for LAN communication between peers o Path control—Performs many OSI network layer functions, including routing and datagram segmentation and reassembly (SAR) o Transmission control—Provides a reliable end-to-end connection service, as well as encrypting and decrypting services
o Data flow control—Manages request and response processing, determines whose turn it is to communicate, groups messages, and interrupts data flow on request o Presentation services—Specifies data-transformation algorithms that translate data from one format to another, coordinate resource sharing, and synchronize transaction operations o Transaction services—Provides application services in the form of programs that implement distributed processing or management services o SNA does not define specific protocols for its physical control layer. The physical control layer is assumed to be implemented via other standards.
DECNet o DECnet is a group of data communications products, including a protocol suite, developed and supported by Digital Equipment Corporation (Digital). The first version of DECnet, released in 1975, allowed two directly attached PDP-11 minicomputers to communicate.
The OSI, DECnet, and TCP Are All Supported by DECnet/OSI DNA Ph. V
Apple. Talk o Apple. Talk, a protocol suite developed by Apple Computer in the early 1980 s, was developed in conjunction with the Macintosh computer. o Apple. Talk's purpose was to allow multiple users to share resources, such as files and printers. The devices that supply these resources are called servers, while the devices that make use of these resources (such as a user's Macintosh computer) are referred to as clients. Hence, Apple. Talk is one of the early implementations of a distributed client/server networking system. o The Apple. Talk Protocol Suite Maps to Every Layer of the OSI Model
Xerox Network Systems o The Xerox Network Systems (XNS) protocols were created by the Xerox Corporation o in the late 1970 s and early 1980 s. They were designed to be used across a variety of communication media, processors, and office applications. Several XNS protocols resemble the Internet Protocol (IP) and Transmission Control Protocol (TCP) entities developed by the Defense Advanced Research Projects Agency (DARPA) for the U. S. Department of Defense (Do. D).
o Because of its availability and early entry into the market, XNS was adopted by most of the early LAN companies, including Novell, Inc. ; Ungermann-Bass, Inc. (now a part of Tandem Computers); and 3 Com Corporation. Each of these companies has since made various changes to the XNS protocols. Novell added the Service Advertisement Protocol (SAP) to permit resource advertisement and modified the OSI Layer 3 protocols (which Novell renamed IPX, for Internetwork Packet Exchange) to run on IEEE 802. 3 rather than Ethernet networks. o Ungermann-Bass modified RIP to support delay as well as hop count, and made other small changes. Over time, the XNS implementations for PC networking have become more popular than XNS as it was designed by Xerox. o Although the XNS design objectives are the same as those for the OSI reference model, the XNS concept of a protocol hierarchy is somewhat different from that provided by the OSI reference model, as Figure 33 -1 illustrates.
Novell Netware o Net. Ware is a network operating system (NOS) that provides transparent remote file access and numerous other distributed network services, including printer sharing and support for various applications such as electronic mail transfer and database access. o Net. Ware specifies the upper five layers of the OSI reference model and, as such, runs on any media-access protocol (Layer 2). o Additionally, Net. Ware runs on virtually any kind of computer system, from PCs to mainframes.
o Net. Ware was developed by Novell, Inc. , and was introduced in the early 1980 s. o It was derived from Xerox Network Systems (XNS)
Banyan Vines o Banyan Virtual Integrated Network Service (VINES) implements a distributed network operating system based on a proprietary protocol family derived from the Xerox Corporation's Xerox Network Systems (XNS) protocols. o VINES uses a client/server architecture in which clients request certain services, such as file and printer access, from servers.
o Media Access n The lower two layers of the VINES stack are implemented with a variety of well-known media-access mechanisms, including High-Level Data Link Control (HDLC), X. 25, Ethernet, and Token Ring. o Network Layer n VINES uses the VINES Internetwork Protocol (VIP) to perform Layer 3 activities (including internetwork routing). VINES also supports its own Address Resolution Protocol (ARP), its own version of the Routing Information Protocol (RIP)—called the Routing Table Protocol (RTP)— and the Internet Control Protocol (ICP), which provides exception handling and special routing cost information. ARP, ICP, and RTP packets are encapsulated in a VIP header. o VINES Internetwork Protocol n VINES network layer addresses are 48 -bit entities subdivided into network (32 bits) and subnetwork (16 bits) portions. The network number is better described as a server number because it is derived directly from the server's key (a hardware module that identifies a unique number and the software options for that server). The subnetwork portion of a VINES address is better described as a host number because it is used to identify hosts on VINES networks
Reference o http: //www. cisco. com/univercd/cc/td/doc/ cisintwk/ito_doc/index. htm