-= NEO ERUDITION =-

                  Introduction to Internetworking
               _____________________________________



The traditional computer communications enviroment in the
mid 1960's and early 1970's had centerd around a host computer called
a mainframe.

In this centralized computing enviroment, unintelligent terminals
used low-speed access lines to communicate with the centralized host.

IBM's computers with Systems Network Architecture (SNA) networks using
multidrop lines, and X.25 public data networks, are typical examples 
of this type of networking enviroment.

Accessing resources, running programs, and copying files are relatively 
straightforward tasks on a single computer.

The computer identifies the requesting user and the desired destination
device or program and coordinates access between them. 

* I will elaborate how this process is carried out further into the 
  lecture.


Coordinating resources becomes a much more complex task from 2 
computers and on. Transferring information requires tasks such as:

-addressing
-error detection
-error correction
-synchronization 
-transmission coordination.

                          

As businesses realized the flexabillity and power of these devices ,
their use increased.

Initially PC's were standalone devices, each requiring its own resources
such as disk space and printers.

Local Area Networks (LANs) *as was described in section 1* evolved
to connect Personal Computers (PCs) together and thus allow
the sharing of such expensive devices.

Early LANs were isolated but organizations quickly realized the 
strategic importance of interconnecting them.

These internetworks provided the basis for enterprise-wide applications
such as Electronic Mail (e-mail) and FTP (File Transfer Protocol).

>From this evolution in networking , In the 1970 and 1980's minicomputers
and shared Wide Area Networks (WANs) evolved.

Minicomputers were often located away from the Central Data Center.
Their proccessing power allowed for the emergence of distrubuted data
processing

The Digital Equipment Corporation (DEC) and VAX (Virtu Access eXtension)
systems and DECnet networking are typical of this era.

In general, however, applications remained separate and independent,
and differnt communications protocols were developed.

                          
Todays networks are a mixture of old and new technologies.

IBM networks operate in parallel with the newer LAN interconnected
networks, electronic commerce, and messaging systems.

Organizations have used local networks, public data networks, 
leased lines, and high speed mainframe channels on an oppurtunististic
basis, with little regard for overall integration and consistencey.

Moving applications from central hosts to distributed servers has
generated new networking requirements and changing traffic patterns.

The approach to computer communications in most organuizations is 
changing rapidly in response to new technologies, evolving business
requirements, and the need for "Instant" knowledge transfer.

To meet these requirements, the internetwork must be flexible, scalable,
and adaptable to suit any organization level.

Internetworks tie LANs and WANs, computer systems, software, and
related devices together to form the corporate communications
infrastructure.

An internetwork moves information anywhere within a corporation
and to external suppliers and customers.

By serving as the organization's *information highway*, the internetwork
has become a key strategic asset and a competitive advantage.

Note: An internetwork is sometimes referd to as an "internet" , NOT to
      be mistaken as the Internet its self.

                       


Todays sophisticated users are placing more and more demands on
networks.

Networks need deal with:
-Graphics and Imaging
-Bulky Files and Software
-Client-Server computing
-Heavy network traffic


while users are demanding:
-Higher bandwidth
-bandwidth on demand
-low lag
-Integration of Voice, Data and Video.

Future global internetworks will provide even greater bandwidth for
new emerging applications.

Many of these applications have mulitmedia requirements of 
high definition imaging, full motion video, and digitized audio.

Modern network administrators make their own demands of internetworks ,
such as:
-connectivity
-reliable performance
-management control

And so the internetwork must be able to connect many seperate, and 
usually differnt, networks in order to serve the organization depending
on it.

It must be able to do this regardless of the range of media attachments,
transmisson speeds, and other technical details.

The intenetwork need be reliable. The organization depends on such
internetwork tools as:
-Operator interface
-the abillity to distribute network software updates
-Utilities to log and monitor performance
-Functions to secure access to resources

Organizations must also be able to effectivley manage its network.

The Adminstrator need to be able to control how the critical resources,
such as color printers, are located. 

They also need to be able to straightforwardley perform troubleshooting
tasks. Expanding internetworks demand fexible administrators.

Expansion and consolidation efforts may mean overcomming physical
or geographical boundaries.

                         

LANs are designed to operate within a limited geographic area.

This could be within a building or floor of a building.

LANs connect mulitple desktop devices.  ( such as PCs)

These devices can access high-bandwidth media via the LAN.

Workstations connected to LANs generally have full-time access to
local services, such as the afore mentioned printers.

When an organisation operates a LAN it purchases whatever media and
connections are used in the LAN.

The organisation can privately control the LAN as it chooses.

Devices that may be located on a LAN would include:
-repeaters
-bridges
-hubs
-Ethernet Switches
-Routers
-Gateways
-Asyncronous Transfer Mode (ATM) switches

Repeaters regenerate and propagate signals from one network segment
to another. They do not change or analyze the address or data in anyway.
they simpley pass the data along.

Briges are intelligent devices used to connect differnt LANs together.
In addition to regenerating and propagating a signal, as a repeater does,
a bridge forwards packets of data based on a Media Access Control
(MAC) address. Bridges may also be used to filter traffic.

They can determin the source and destination involved in the transfer
of packets. They read the specific physical address of a packet on one
network segment and then decide to filter out the packet or forward it
to another network segment.

Using hubs allows you to concentrate on LAN connections.

You can then connect the devices to the hub using twisted pair
copper media.

Ethernet switches offer full-duplex dedicated bandwidth to LAN
segments or desktops.

Routers are concerned with the routing of packets across a network.
They can perform all the functions of a bridge as well as much more
complex tasks.

Routers open up the data packet and make routing decisions based on the
contents of the packet.

Gateways link networks that have differnt protocols.

They can change an entire protocol stack into another.
They do this by using protocol conversion and routing servies.

Gateways examine the entire packet, including the data portion, in order
to translate incompatible protocols. Such as a conversion from ATM cells
to Frame Relay frames.

ATM switches provide high-speed cell switching.

They use a cell relay technology wich combines the advantages of 
conventional circuit- and packet-based systems.

                            

WANs operate beyond the scope of a LANs geographic scope.

They usually use the services of local telecommunications carriers
such as Regional Bell Operating Companies (RBOCs), Sprint, and MCI.

Organisations pay the carrier or service provider of their choice
for connections used in the WAN.

The carriers are usually regulated by tariffs.

WANs allow access over serial interfaces (usually a LAN-to-WAN device)
operating at lower speeds.

However since an organisation must pay for services used it may restrict
access for certain workstations.

also, all WAN services are not available in all locations.

Like LANs, WAN devices include:
-routers
-ATM switches
-X.25 ( or Frame Relay Switches )
-modems , channel service , Units/Data Service Units (CSU/DSU), Terminal
adpaters/Network, Termination 1 (TA/NT1) devices.
-communications servers
-multiplexors

X.25/Frame Relay switches are used to connect to public data communications
services.

Modems are used to interface voice-grade services.

CSU/DSU devices interface T1/E1 services.

TA/NT1 devices interface Integrated Services Digital Network (ISDN)
services.

Communications servers conentrate dial-in and dial-out user
communications.

Multiplexors allow a WAN facility to be shared among several demand
channels.

-EOF


RatDance :: NeoErudition Administator
http://neoerudition.hypermart.net
neoerudition@videotron.ca