Network Models to OSI

prunelimitNetworking and Communications

Oct 23, 2013 (4 years and 8 months ago)


Comparison of Various
Network Models to OSI




Xerox XNS

Novell Netware

Banyan Vines


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.

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.

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

Path control

Performs many OSI network layer functions,
including routing and datagram segmentation and
reassembly (SAR)

Transmission control

Provides a reliable end
connection service, as well as encrypting and decrypting

Data flow control

Manages request and response
processing, determines whose turn it is to communicate,
groups messages, and interrupts data flow on request

Presentation services

Specifies data
algorithms that translate data from one format to another,
coordinate resource sharing, and synchronize transaction

Transaction services

Provides application services in
the form of programs that implement distributed
processing or management services

SNA does not define specific protocols for its physical
control layer. The physical control layer is assumed to be
implemented via other standards.


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
minicomputers to communicate.

The OSI, DECnet, and TCP Are All
Supported by DECnet/OSI DNA Ph. V


AppleTalk, a protocol suite developed by Apple Computer in
the early 1980s, was developed in conjunction with the
Macintosh computer.

AppleTalk'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,
AppleTalk is one of the early implementations of a
distributed client/server networking system.

The AppleTalk Protocol Suite Maps to Every Layer of the
OSI Model

Xerox Network Systems

The Xerox Network Systems (XNS) protocols
were created by the Xerox Corporation

in the late 1970s and early 1980s. 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

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 3Com 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.

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

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

Novell Netware

NetWare 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.

NetWare specifies the upper five layers of the OSI
reference model and, as such, runs on any media
protocol (Layer 2).

Additionally, NetWare runs on virtually any kind of
computer system, from PCs to mainframes.

NetWare was developed by Novell, Inc.,
and was introduced in the early 1980s.

It was derived from Xerox Network
Systems (XNS)

Banyan Vines

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.

VINES uses a client/server architecture in which
clients request certain services, such as file and
printer access, from servers.

Media Access

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.

Network Layer

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

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.

VINES Internetwork Protocol

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