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The Workings of the Internet. CECS 5030 with Cathie Norris, Jennifer Smolka & Gerald Knezek. Overview. Layered Organization Topologies Network Transports Access Methods Routing. ISO/OSI Model . Developed by International Organization for Standardization in 1974

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the workings of the internet

The Workings of the Internet

CECS 5030

with Cathie Norris,

Jennifer Smolka & Gerald Knezek

overview
Overview
  • Layered Organization
  • Topologies
  • Network Transports
  • Access Methods
  • Routing
iso osi model
ISO/OSI Model
  • Developed by International Organization for Standardization in 1974
  • Consists of seven layers
  • Each with unique function
  • Each hands off functions to adjacent layer
  • Modules (layers) may be replaced with another of equal functionality (Xerox vs. Novell, for example)
osi model layers
OSI Model Layers

OSI Layer

Function Provided

Network applications such as file transfer and terminal emulation

Application

Presentation

Data formatting and encryption

Establishment and maintenance of sessions

Session

Provision for end-to-end reliable and unreliable delivery

Transport

Delivery of packets of information, which includes routing

Network

Transfer of units of information, framing, and error checking

Data Link

Physical

Transmission of binary signal

network topologies
Network Topologies
  • Architectural “drawings” that show the overall physical configuration for a given communications system
  • Determine access methods and rules used to design and implement a communication system
  • Represent the drawing of your network cable plant
  • Three main types: star, ring, and bus
network topologies6
Network Topologies
  • Linear Bus - Ethernet/IEEE 802.3 10Base2 and 10Base5
  • Star Wired Bus - Ethernet/IEEE 802.3i 10BaseT
  • Star Wired Ring - Token Ring/IEEE 802.5
  • Dual Counter Rotating Ring - FDDI/ANSI X3T9.5
  • Wireless - Product Specific
star topology

Node

Node

Central Hub

Node

Node

Star Topology
  • First used with the telephone switches
  • Centralized hub with all stations connected
  • No single point of failure effects the whole network, except the hub
  • Oldest and most popular topology
  • Better network management
ring topology
Ring Topology
  • All stations (repeaters) are enclosed in a loop
  • Each receives the signal and repeats it on the other side to its “downstream” neighbor
  • Data is transmitted in one direction only
  • Single point of failure when one station quits repeating
  • Management processes invoked that dynamically remove a station allowing the ring to return to an operational state
ring topology9
Ring Topology

Data Direction

Node

Transmitter

Receiver

Node

Node

Repeater

Node

bus topology
Bus Topology
  • Also known as linear bus
  • Uses a single length of cable with all stations attached to it
  • The network is terminated at its endpoints (not a closed loop)
  • A break on the single cable will bring down all attachments on the network
  • The bus topology is most commonly used for Ethernet networks
bus topology11
Bus Topology

Node

Node

Node

star wired bus topology

Node

Node

Node

Node

Node

Node

Concentrator Hub

Star-Wired Bus Topology
  • Each node is attached to hub
  • When one node fails, it doesn’t affect the other nodes
  • The hub is a single point of failure for all nodes
  • Hub failure causes all nodes to lose connectivity
physical media
Physical Media
  • Physical media provide the connections between network devices that make networking possible
  • There are four main types of physical media in widespread use today:
    • Coaxial Cable
    • Twisted Pair
    • Fiber Optic Cable
    • Wireless Media
thick coaxial cable
Thick Coaxial Cable
  • Used in the first Ethernet networks
  • Type RG-11 / 10Base5
  • Usually orange/black
  • Thickness of a small garden hose
  • Very expensive and heavy cable
  • Two strands along the axis
  • Conductor down the center
  • Insulator surrounds conductor
  • Shielded mesh serves as outside
thin coaxial cable
Thin Coaxial Cable
  • Alternative to Thick Ethernet Cable
  • Type RG-58 / 10Base2 / “Cheapnet”
  • Usually black
  • Thickness of a pencil
  • More flexible than thick Ethernet
  • Reduced the cost of the cabling
  • Flexible
twisted pair cable
Twisted Pair Cable
  • Phone Systems
  • Twisted Pair Cable consists of two copper wires, usually twisted around each other to cancel out any noise in the circuit
  • Two main type of Twisted Pair Cabling
    • Shielded Twisted Pair (STP)
    • Unshielded Twisted Pair (UTP)
shielded twisted pair stp
Shielded Twisted Pair (STP)
  • Shielded twisted pair is the original media used for token ring networks
  • STP can be used for high-speed networks, such as FDDI or ATM, where shielding is important
unshielded twisted pair utp
Unshielded Twisted Pair (UTP)
  • Most commonly used twisted pair cable
  • Uses common telephone wire
  • UTP was standardized by the IEEE 802.3 committee in October of 1990
  • UTP for LANs is now classified as:
    • Category 3 - used for LANs up to 10 Mbps
    • Category 4 - used for LANs up to 16 Mbps
    • Category 5 - used for LANs up to 100 Mbps
fiber optic cable
Fiber Optic Cable
  • Uses light signals transmitted over a very thin filament, usually made of glass
  • Advantage over other types of media
    • security against eavesdropping
    • immunity to interference
    • maximum length of a single segment
  • Most expensive of all media
wireless media
Wireless Media
  • Connect your computer to your cell phone?
  • Problems with stability of connection
  • Have wireless for a long time
  • Commercial Satellite
    • Geostationary Orbit
    • Microwave Wavelength
    • Expensive
wireless media21
Wireless Media
  • A number of wireless media are used in internetworking, e.g.:
    • Microwave
    • Commercial Radio wave
    • Infrared signaling (Palm Synching)
concentrators hubs
Concentrators/Hubs
  • Hubs allow multiple users to be connected to a single network as a shared device
  • The more users on a hub the slower the response time
network transports
Network Transports
  • Ethernet / Fast Ethernet / IEEE 802.3
  • Token Ring / IEEE 802.5
  • FDDI / FDDI/ANSI X3T9.5
  • Wireless/IEEE 802.11
how ethernet works
How Ethernet Works
  • Sent the message and listens for a response
  • An access method based on the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) algorithm
  • Cooperative effort between Digital, Intel, and Xerox produced Ethernet version 1.0 in 1980
how ethernet works26
How Ethernet Works
  • Ethernet was adopted with modifications by the standards committees IEEE 802.3 and ANSI 8802/3
  • Most widely used network system today
normal ethernet operation
Normal Ethernet Operation

B

C

Address mismatch

packet discarded

Address mismatch

packet discarded

Send data

to node D

Address match

packet processed

Transmitted packet seen

by all stations on the LAN

(broadcast medium)

A

D

Data

final ethernet issues
Final Ethernet Issues
  • Ethernet is an access method that strictly adheres to the CSMA/CD algorithm
  • Ethernet is a multiprotocol solution
  • Ethernet is usually hardware (firmware), not software
how token ring works
How Token Ring Works
  • Token Ring controls which PC can send messages by passing a token from station to station around the ring
  • When a PC wants to transmit it will replace the token with a “frame” (message)
  • The frame is passed from PC to PC until it reaches its destination
how token ring works30
How Token Ring Works
  • The destination PC makes a copy of the “frame” (message) and marks the frame to indicate that it got the message
  • The frame circulates around the network until it gets back to the sender
  • The sender, seeing that the message has been received, replaces it with a new token
wide area network wan topologies
Wide Area Network (WAN) Topologies
  • Dedicated Circuits
    • 56Kb
    • T-1
    • DS-3
  • Frame-Relay
    • 56Kb to T-1 speeds
  • Integrated Services Digital Network (ISDN)
inter networking
Inter-networking
  • Networks have their restrictions
    • Thick coaxial cable maximum length is 500 meters
    • LANs are broadcast-oriented
    • Proper network design is impossible using repeaters
inter networking33
Inter-networking
  • Properly extending the LAN requires special devices known as bridges and routers
    • A LAN that uses bridges is called an extended LAN
    • A LAN that uses routers is called an internet or inter-network
    • A gateway between dissimilar networks
inter networking34
Inter-networking
  • Bridges and routers are data-forwarding devices that forward packets to one or more LANs
    • They allow for more efficient networks to be designed
inter networking categories
Inter-networking Categories

Application

Gateways

Presentation

Session

Transport

Network

Routers

Data Link

Bridges

Physical

Repeaters

repeaters
Repeaters
  • Extend the network by interconnecting multiple segments
  • Have transformed into wiring concentrators (hubs)
  • Low cost
  • Can be used to interconnect different wiring types but not different access methods
    • e.g. Coax to twisted pair
bridge designs
Bridge Designs
  • Cascaded
    • Locates on bridge next to another in a pillar fashion
  • Backbone
    • For networks with many LANs
    • Backbone cable is run vertically in building’s riser
    • LAN “ribs” run on each floor
  • Star
    • Used in wide area networks or remote bridged networks
cascaded
Cascaded

Terminal Server

Workstation

Terminal

Host

Cable segment 1

Cable segment 2

Cable segment 3

File Server

backbone
Backbone

Workstation

Floor 20

Host

Fiber

backbone

Workstation

Terminal

Floor 1

slide40
Star

California

Serial line

Serial line

Texas

North Carolina

Serial line

Virginia

introduction to routers
Introduction to Routers
  • Routers are data forwarding devices but operate differently than a bridge
  • Routers separate networks into regions.
    • Each region is assigned a unique network number
  • These network numbers are unique for each network they are assigned to
  • Packet forwarding is based on these network Ids
  • Routers route packets based on a protocol as well as a network ID
  • Most routers today are multiprotocol in that one box can forward different protocol packets
  • Routers, like bridges, can be used locally or remotely
routing
Routing
  • Most network protocols were designed with network-layer routing
  • Routers base forwarding decisions on an embedded network number in the network layer header of the packet
  • Network numbers can be thought of as area codes in the phone system
    • Must use the area code to call different areas
  • Any number of end stations may be assigned to one network number
    • Most routers do not keep track of individual end stations’ addresses
  • Network numbers group network stations into one or more network numbers
  • Taken as a whole, routers combine networks and form internets
routers operation
Routers - Operation

Node D

Router sends

packet directly

to the end station

MAC address

for the router

Network 2

C

Destination

network

number

is different

Router Z

B

Find router

and give packet

to the router

Network 1

Node A

Node P

Destination network address is local

transmit packet directly to the end station

routing diagram
Routing Diagram

G

Network 4

Router X

H

F

E

Network 3

Router Y

D

Network 2

C

MAC Addresses

Router Z

B

Network 1

A

multiprotocol routers
Multiprotocol Routers
  • LANs currently operate with many different types of protocols
    • Apple Computers can use AppleTalk
    • UNIX workstations use TCP/IP
    • Client/Server applications could use Novell NetWare
  • To require one router for each protocol on the LAN is not efficient
  • Multiprotocol routers were invented to handle this
    • Arrived around 1986
    • Routes not only based on the network IDs but are able to pass the packet to the correct protocol processor by examining the Type of packet
gateways
Gateways
  • Complex devices that provide for a protocol translation during data forwarding
  • Examples are:
    • TCP/IP to SNA
    • asynchronous to synchronous serial stream
  • Gateways differ from bridges and routers
    • Perform protocol translation of the incoming packet to match the outgoing stream
references

From Networking 101Jim Cabral, Puget Technology Group, Inc. &

Tammy Ruth, Children’s Hospital and Medical Center

cabralje@pugettech.com

truth@chmc.org

References

www.pugettech.com