PC and Industrial Networks

The Evolution of Networks

Welcome to CSET 2200, PC and Industrial Networks. In this course we will examine the

operation of local area networks.

In our examination of local area networks, we will focus on understanding the Open

System Interconnect (OSI) Model and how each of the model layers contribute to data

communications among devices on a network. The reason for doing this is simple:

Almost anyone can build a simple network and get it functioning without sophisticated

knowledge of networking. As long as things work properly, there is very little to be

concerned about. The trouble beings when things do not work as expected, or there is a

problem on the network. Then, understanding how networks operate, especially how

devices communicate becomes critical to troubleshooting on the network. As a result, we

will examine and understand the operation of a network at each layer of the OSI model.

In today’s global economy, there is a strong demand to link multiple local area networks

together. This process is termed internetworking, and involves concepts associated with

wide area networking. We will examine strategies for deploying wide area networks

including network design principles. We will learn to configure the devices that facilitate

and control the movement of data between devices. One such type of device is called a

switch, and we will be working with Cisco switches. We are using Cisco devices

because they are the ―de-facto‖ standard for enterprise networking and they provide a

rich set of features that allow for a great deal of flexibility and options on a network.

With any interconnected network, one of the immediate concerns is not only providing

access to network resources, but of also limiting access to authorized devices. We will

examine the basic principles of network security and access control in this course.

In order to understand where we are at with networking technology, it probably makes

sense to spend some time understanding the state of the technology prior to today, and

how networks have evolved.

Each new phase expands on the functionality of the previous phase.

1960 – 1970:

dumb terminals connected to a host mainframe

processing power resides on the mainframe

characterized by low speed access lines (i.e. serial) to a centralized host allowed

sharing of resources (files, printers) under the direct control of the central

processor.

Major features:

o Monolithic design, dumb terminals, serial data transmission.

o Worked because the only things sent were text based characters; no

graphics.

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o Provided a great deal of data security – concentrated in one spot under the

control of MIS and access could be restricted at devices. Data and

subsystems could be restricted by both users and devices.

o Data comes into a controller and then is ―multiplexed‖ into the system.

The controller is responsible for separating data communications between

the devices.

1970 – 1980:

pc networks – processing power, and memory on the desktop

expensive resources (permanent storage and printing) were shared.

Emergence of the LAN

Interconnecting isolated LANs provides the basis for enterprise wide applications

(i.e. e-mail and file transfer)

Strategic advantage: increased productivity

Minicomputers outside the central office enabled data processing (distributed and

wide-area)

In general: applications from different computing environments remained

separate and independent due primarily to different communication

protocols

o Mainframe: SNA (Systems Network Architecture)

o LANs:

 IPX/SPX (Internetwork Packet Exchange/Sequenced Packet Exchange)

 TCP/IP

IPX/SPX and TCP/IP allowed connections of multiple networks

through routers which facilitated the growth of LANs within

departments and companies.

1980-1990:

Inter-networks tie LANs, WANs together to form a corporate communications

infrastructure

Moves data and voice anywhere within an organization

Routers are a key element: allow or deny communications between LANs and

WANs; removes barriers associated with physical connections.

1990 – 2000:

Global internetworking

o Graphics, imaging, large files, large programs, c/s computing

Requires bandwidth, appropriate traffic routing and security

2000 –

Leveraging the internetwork

o To create intra-networks via Remote Access, VPN’s

o SAS, Cloud Computing

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Network Communications

There are two basic types of communications networks:

Connection-oriented (circuit-switched)

Connectionless (packet-switched)

Connection-oriented is analogous to placing a telephone call.

End to end connection is made and established even if no one is talking.

Provides a guaranteed method of communication.

Once established, nothing can diminish the capacity of the connection.

Circuit costs are fixed, independent of their use.

Connectionless networks take a different approach.

Data to be transferred is broken into packets that are multiplexed into the

bitstream.

Source and destination identifiers are used to move the packets and

reassemble them.

The main advantage is that multiple communications among computers

can proceed concurrently.

The disadvantage is increased activity may result in loading or delays.

Despite the risk of delay, the advantage of this type of network is cost and

performance.

Networks that use packet-switched technologies are divided into two broad

categories:

Local Area Networks (LANs)

Wide Area Networks (WANs)

LAN Characteristics

Operate in a limited geographical environment

Multiple users access high bandwidth media

Privately controlled (i.e. local control of the media)

Locally administered

Why deploy a LAN?

LAN Technologies

Provide the highest speed connections

Lack the ability to span long distances

Experience the lowest rate of delay

Do not need to be intelligent - depends on electronic interfaces to generate

and receive signals.

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LAN Standards

IEEE (Institute of Electrical and Electronic Engineers): http://www.ieee.org

802 (February of 1980)

802.2 - LLC (logical link control system)

802.3 - CSMA/CD (carrier sense multiple access/collision

detection)

802.5 - Token Ring

Ethernet Technology

Invented at Xerox PARC in the early 1970’s.

Standardized by Xerox, Intel, DEC as Ethernet in 1978.

Revised to Ethernet II in 1984

IEEE released a compatible version as 802.3. It is the same as the Ethernet II

standard in providing access to the media.

10Base5 thick (1/2”) coaxial cable

up to 500 meters in length

resistor at each end to prevent reflection of the signal.

utilizes a transceiver that ―tapped‖ into the cable

the transceiver connected to the host adapter via an Attachment Unit

Interface (AUI)

Cons: Cost, not readily relocated, cable costly and difficult to work with.

Pros: Heavy shielding prevented electrical interference

Outer Insulating Jacket

Braided Metal Shield

Polyethylene Filler

Center Wire

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10Base2 thin-wire Ethernet less protection from electrical

interference, shorter distances. eliminated separate transceivers

(integrated onto adapter) BNC connectors easy to use

10BaseT unshielded copper wires 4 pair category 5 cabling

 pairs utilized

 can run on Cat 3 half duplex connect to hub

100 meters between hub and computer same capability as

coaxial, just a different wiring scheme.

10Mb/s—megabits per second not all

capacity available (a highway)

100BaseT Fast Ethernet

great capacity – most pc’s can’t sustain throughput did not change

other parts of the Ethernet standard optimized to allow more

stations, more traffic not faster throughput between a pair of

computers.

100BaseTX – full duplex between switches

10/100 Ethernet auto-negotiation of speed and duplex

100BaseFX (fiber optic)

1000BaseT

Gigabit Ethernet

IEEE 802.3z

4 pair Cat 5; full duplex (switched only)

1000BaseSX

short haul multi-

mode fiber

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Ethernet Characteristics:

Shared bus

Best-effort delivery: hardware provides no mechanism for informing sender

whether packet was delivered.

Carrier Sense Multiple Access/ Collision Detect – access control is

distributed, no central authority for transmission.

(switching to reduce contention) maximum

transmission limits ―hogging‖

minimum idle time between transmissions produces ―sharing‖ random

delays before re-transmit upon collision detection prevent gridlock

(binary exponential)

no CD on full duplex transmissions

Utilizes broadcast technology – all stations receive every transmission host

interface receives all packets. host interface examines the packet and

decides if it should be sent up the stack. host interface discards other

packets. unicast