Upload
buck-hicks
View
323
Download
18
Embed Size (px)
Citation preview
Internetworking Concept Internetworking Concept and Architectural Modeland Architectural Model
Chapter 3Chapter 3
Looked at low-level details of transmission Looked at low-level details of transmission across individual data networksacross individual data networks
Raise level of abstractionRaise level of abstraction System that hides underlying details while System that hides underlying details while
providing universal communication servicesproviding universal communication services Result: high level abstraction; framework for Result: high level abstraction; framework for
all design decisionsall design decisions
Later chapters:Later chapters: Use the abstraction to build layers of internet Use the abstraction to build layers of internet
communication softwarecommunication software Show how applications use the comm systemShow how applications use the comm system
Application-Level Application-Level InterconnectionInterconnection
Two approaches to hiding detailsTwo approaches to hiding details Have applications do the workHave applications do the work Hide details in the operating systemHide details in the operating system
Application-level connections require Application-level connections require application gatewaysapplication gateways Application running on each computer in the Application running on each computer in the
networknetwork Understands details of network connectionsUnderstands details of network connections
Seems natural at first, but:Seems natural at first, but: New functionality means new application New functionality means new application
program for every computerprogram for every computer New network hardware means modifying all New network hardware means modifying all
existing programsexisting programs With hundreds or thousands of networks, no way With hundreds or thousands of networks, no way
to write all possible application programsto write all possible application programs Intermediate application programs between the Intermediate application programs between the
source and destination must operate correctlysource and destination must operate correctly
Network-Level InterconnectionNetwork-Level Interconnection
Alternative to application-levelAlternative to application-level
Provides a mechanism to deliver small Provides a mechanism to deliver small data packets from source to destinationdata packets from source to destination
No intermediate application programsNo intermediate application programs
Several advantagesSeveral advantages Efficient (scheme maps onto underlying HW)Efficient (scheme maps onto underlying HW) Separates data communication from applicationsSeparates data communication from applications Flexible (allows general-purpose comm facilities)Flexible (allows general-purpose comm facilities) Modifying network does not affect applicationsModifying network does not affect applications
Key is abstraction of Key is abstraction of internetworkinginternetworking InternetworkInternetwork (internet) concept is powerful (internet) concept is powerful Detaches comm from network technologiesDetaches comm from network technologies Hides low-level details from userHides low-level details from user Drives software design decisionsDrives software design decisions Helps handle physical addresses and routesHelps handle physical addresses and routes
Motivation for internetworking comes from Motivation for internetworking comes from two observations:two observations: No single network hardware technology can No single network hardware technology can
satisfy all needssatisfy all needsExample: LAN vs WANExample: LAN vs WAN
Users desire universal interconnectionUsers desire universal interconnection
Goal: Goal: Build unified interconnection of networks to Build unified interconnection of networks to
support universal communicationsupport universal communicationEach network has own technologiesEach network has own technologies
Software between networks and application Software between networks and application programs gives impression of single large networkprograms gives impression of single large network
Internet PropertiesInternet PropertiesUniversal serviceUniversal service
Hidden underlying architectureHidden underlying architecture
No forced network interconnection topologyNo forced network interconnection topology Adding network should be easyAdding network should be easy Intermediate networks not directly connected to Intermediate networks not directly connected to
source or destination computerssource or destination computers
Set of shared, universal machine identifiersSet of shared, universal machine identifiers
Operations and applications independent of Operations and applications independent of underlying network technologiesunderlying network technologies
RoutersRoutersUse a special computer to connect Use a special computer to connect networksnetworks Called Called internet gatewaysinternet gateways or or internet routersinternet routers IP router & IP gateway used interchangeablyIP router & IP gateway used interchangeably
Routers must know the topology beyond Routers must know the topology beyond the networks to which it connectsthe networks to which it connectsKey:Key: Routers use the destination Routers use the destination networknetwork, not the , not the
destination computer, for forwarding packetsdestination computer, for forwarding packets
Will study in detail in later chaptersWill study in detail in later chapters
For now:For now: Assume it is possible and practical for Assume it is possible and practical for
routers to do their jobrouters to do their job Also assume that only routers connect Also assume that only routers connect
physical networksphysical networks
User’s ViewUser’s ViewWant user to see only one network to Want user to see only one network to which all machines are connectedwhich all machines are connected
Network level interconnections means:Network level interconnections means: Applications that communicate run without Applications that communicate run without
change on any computerchange on any computer Internet SW worries about physical Internet SW worries about physical
connectionsconnections
TCP/IP internet protocols treat all TCP/IP internet protocols treat all networks equallynetworks equally
Internetworking SummaryInternetworking SummaryInternet is more than collection of networks Internet is more than collection of networks interconnected by computersinterconnected by computers
Need conventions that allow communicationNeed conventions that allow communication
Need universal identifiers and set of Need universal identifiers and set of procedures for moving data to destinationprocedures for moving data to destination
IP routers (or gateways) connect networks IP routers (or gateways) connect networks and forward packetsand forward packets
Details As Yet UnansweredDetails As Yet Unanswered
Form of internet addresses?Form of internet addresses?How addresses relate to Ethernet, ATM, etc.?How addresses relate to Ethernet, ATM, etc.?What does a packet look like?What does a packet look like?What if packets come too fast for a computer or What if packets come too fast for a computer or router to handle?router to handle?How do routers learn routes?How do routers learn routes?How do multiple applications executing con-How do multiple applications executing con-currently on one computer send/receive currently on one computer send/receive packets to multiple destinations without packets to multiple destinations without problems?problems?