practical routers and switches (including tcp/ip and ethernet) for engineers and technicians

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Practical Routers & Switches (Including TCP/IP and Ethernet) for Engineers & Technicians


Topics

• Overview

• Network Communication

• Types of Networks

• Open Systems

• Interoperability/Internetworking

• IEEE Standards

• Topologies

• Media Access Control


Network Connection Methodologies

Two basic methods of communicationfor data exchange between computersand peripherals:• Circuit Switched

• Packet Switched


Full tim e exclusive connection estab lishedacross netw ork for duration of each call.

Typica lD ata F low s Low utilization

Circuit Switched Data

one shared circu it

Packet Assem blerD isassem bler

Packet Sw itched N etw ork

Packet Switched Data

Typica lD ata F low s

S w itch1

Sw itch2

Sw itchn

BA

A

B

C

D

E

F

H igher utiliza tion

D ataeg. Address

A to E B to D C to F etc

00100111 00101101 10101101


Circuit Switched

• Analogous to establishing a digital phone connection.

• Once connection is established, communication links is dedicated to user.

• No other communications/network activity affects circuit capacity.


Packet Switching

• Used extensively in computer and related systems.

• Data is divided into small units (“Packets”) and multiplexed onto a common high speed circuit.


Types of Networks


Local Area Networks

500m m ax

LAN (10 Base 5) exam ple


WAN Concept


Open Systems Interconnection

Application

Presentation

Session

Transport

Network

Data L ink

Physica l

The OSI Reference Model


Open Systems Interconnection

Application

Presentation

Session

Transport

N etw ork

D ata L ink

Physica l

Application

Presentation

Session

Transport

N etw ork

D ata Link

Physica l

Process A Process B

Communication Channel

Physica lD ata

B its

Fram es

Application PD U

Presentation PD U

Session PD U

Transport PD U

Packets


PH

PH

M essage

M essage

M essage

M essage

M essage

M essage

A H

AH

AH

AH

AH

AH

AH

PH

PH

PH

PH

SH

SH

SH

SH

SHTH

TH

TH

THN H

N H

N HD LH

D LHPre N T

N T

N T

D LT

D LT

Post

App lica tion

P resen ta tion

Session

Transport

N etw ork

D a ta L ink

P ysica l

Protocol C ontro l In fom ation(PC I) or H eader

M essage

M essage


Descriptions of the Seven OSI Layers

• Application Layer (7)

• Presentation Layer (6)

• Session Layer (5)

• Transport Layer (4)

• Network Layer (3)

• Data Link Layer (2)

• Physical Layer (1)


Interoperability• Defined as:

“the ability of two different networks to work together”– How networks can communicate and share data,

even though they may have different architectures.– Also used to refer to the ability of different

software products to work together in the same environment


Simplified OSI / RM

User

Physical

Data Link

Application

.

.

.

.

.

.

.

.

.

.

Object oriented messagesbroadcast, point-to-point

Token-pass, addressing,error-checking

Twisted pair, fibre opticbus, star

Function blocks etc"Layer 8"

Fieldbus Layer Model


Physical Topologies

• Physically, there are three structures:– Bus– Star– Ring

• Others ie hybrids are possible

• The logical topology may not reflect the physical!


Bus Topology

Server


Bus Topology• Advantages

– Uses relatively little cable compared to other topologies

– Easy to add or remove nodes– Simple & flexible architecture– Broadcast messages are easy– Failure of node does not affect network– Inexpensive cable and connectors


Bus Topology

• Disadvantages– Security problem - every node “hears” every message– No automatic acknowledgment of messages– Failure diagnosis can be difficult– No automatic regeneration of signals


Star Topology

Node Node

NodeNodeNode

Node

Hub


Star Topology

• Advantages– Troubleshooting & fault isolation are easy– Easy to add / remove nodes & modify cable layout– Failure of a node does not isolate any other– Central hub allows monitoring for management

purposes

• Disadvantages- Hub fails - network fails!- Can require a lot of cabling


Ring Topology

Node

Node

Node

Node

Node

Node


Ring Topology

• Advantages

- Physical ring has minimal cable requirements

- No wiring centre needed

- Message can be automatically acknowledged

- Each node can regenerate the signal

• Disadvantages- If a node fails, the ring fails- Diagnosis & fault finding is difficult- Adding /removing nodes disrupts network- Limit on distance between nodes


Media Access• Networks are for sharing!

• Each node will be connected to the shared media via a Network Interface Card (also called NI adapter)

• The card must be compatible with:– Cable, or medium, type– Computer bus– Access method


LAN Access

• Only one node can transmit at a time

• Two main methods are in current use– Contention– Token Passing


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practical routers and switches (including tcp/ip and ethernet) for engineers and technicians

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