Introduction1-1 COSC6377: Computer Networks Rong Zheng [email protected] Computer Networking: A Top...
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Transcript of Introduction1-1 COSC6377: Computer Networks Rong Zheng [email protected] Computer Networking: A Top...
Introduction 1-1
COSC6377: Computer Networks
Rong [email protected]
Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2004.
Introduction 1-2
Introduction
Overview of the course Basic concepts and structures in
computer networking Network architecture
Introduction 1-3
What’s the Internet: “nuts and bolts” view End systems
Host computer Network applications
Access networks Local area networks communication links
Network core: routers network of networks
local ISP
companynetwork
regional ISP
router workstation
servermobile
Introduction 1-4
What’s the Internet: “nuts and bolts” view Protocols define format, order
of msgs sent and received among network entities, and actions taken on msg transmission, receipt e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of networks” loosely hierarchical public Internet versus private
intranet Internet standards
RFC: Request for comments IETF: Internet Engineering
Task Force
local ISP
companynetwork
regional ISP
router workstation
servermobile
Introduction 1-5
Network Components (Examples)
Fibers
Coaxial Cable
Links Interfaces Switches/routers
Ethernet card
Wireless card
Large router
Switch
Introduction 1-6
Introduction 1-7
Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T,
Cable and Wireless), national/international coverage treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
NAP
Tier-1 providers also interconnect at public network access points (NAPs)
Introduction 1-8
Tier-1 ISP: e.g., Sprint
Sprint US backbone network
Seattle
Atlanta
Chicago
Roachdale
Stockton
San Jose
Anaheim
Fort Worth
Orlando
Kansas City
CheyenneNew York
PennsaukenRelay
Wash. DC
Tacoma
DS3 (45 Mbps)OC3 (155 Mbps)OC12 (622 Mbps)OC48 (2.4 Gbps)
Introduction 1-9
Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other, interconnect at NAP
Introduction 1-10
Internet structure: network of networks
“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
Introduction 1-11
Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Introduction 1-12
Protocol “Layers”Networks are
complex! many “pieces”:
hosts routers links of various
media applications protocols hardware,
software
Question: Is there any hope of organizing structure of
network?
Or at least our discussion of networks?
Introduction 1-13
An Imaginary 2-tier
New application has to interface to all existing media adding new application requires O(m) work, m = number of media
New media requires all existing applications be modified adding new media requires O(a) work, a = number of applications
Total work in system O(ma) eventually too much work to add apps/media
Application end points may not be on the same media!
SMTP SSH FTP
Packetradio
Coaxial cable
Fiberoptic
Application
TransmissionMedia
HTTP
Introduction 1-14
Solution: Indirection Solution: introduce an intermediate layer that provides
a single abstraction for various network technologies O(1) work to add app/media Indirection is an often used technique in computer science
SMTP SSH NFS
802.11LAN
Coaxial cable
Fiberoptic
Application
TransmissionMedia
HTTP
Intermediate layer
Introduction 1-15
Network Architecture
Architecture is not the implementation itself
Architecture is how to “organize” implementations
what interfaces are supportedwhere functionality is implemented
Architecture is the modular design of the network
Introduction 1-16
Software Modularity
Break system into modules:Well-defined interfaces gives flexibility
can change implementation of modulescan extend functionality of system by
adding new modulesInterfaces hide information
allows for flexibilitybut can hurt performance
Introduction 1-17
Network Modularity
Like software modularity, but with a twist:Implementation distributed across
routers and hostsMust decide both:
how to break system into moduleswhere modules are implemented
Introduction 1-18
Layering
Layering is a particular form of modularization
The system is broken into a vertical hierarchy of logically distinct entities (layers)
The service provided by one layer is based solely on the service provided by layer below
Rigid structure: easy reuse, performance suffers
Introduction 1-19
ISO OSI Reference Model ISO – International Standard Organization OSI – Open System Interconnection Seven layers
Lower two layers are peer-to-peer Network layer involves multiple switches Next four layers are end-to-end
Application
Presentation
Session
Transport
Network
Datalink
Physical
Application
Presentation
Session
Transport
Network
Datalink
Physical
Network
Datalink
Physical
Physical medium A Physical medium B
Host 1 Intermediate switch Host 2
Introduction 1-20
Key Concepts
Service – says what a layer does Ethernet: unreliable subnet
unicast/multicast/broadcast datagram service IP: unreliable end-to-end unicast datagram service TCP: reliable end-to-end bi-directional byte stream
service
Service Interface – says how to access the service E.g. UNIX socket interface
Protocol – says how is the service implemented a set of rules and formats that govern the
communication between two peers
Introduction 1-22
Functions of the Layers Service: Handles details of application
programs. Functions:
Service: Controls delivery of data between hosts.
Functions: Connection establishment/termination,
error control, flow control, congestion control, etc.
Service: Moves packets inside the network. Functions: Routing, addressing, switching, etc.
Service: Reliable transfer of frames over a link. Functions: Synchronization, error control, flow
control, etc.
telnet, ftp, emailwww, NFS
TCP, UDP
IP, ICMP, OSPFRIP, BGP
Ethernet, WiFiT1
ApplicationLayer
TransportLayer
NetworkLayer
(Data) LinkLayer
Introduction 1-23
Internet Protocol Architecture
FTPprogram
TCP
IP
EthernetDriver
EthernetDriver
ATMDriver
IP
FTPprogram
TCP
IP
ATMDriver
FTP protocol
TCP protocol
IP protocol IP protocol
Ethernetprotocol
ATMprotocol
Introduction 1-24
Internet Protocol Architecture
MPEG Servierprogram
UDP
IP
EthernetDriver
EthernetDriver
ATMDriver
IP
MPEG Playerprogram
UDP
IP
ATMDriver
RTP protocol
UDP protocol
IP protocol IP protocol
Ethernetprotocol
ATMprotocol
Introduction 1-25
messagesegment
datagram
frame
sourceapplicatio
ntransportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHnHl M
HtHn M
HtHnHl M HtHnHl M
router
switch
Encapsulation
Introduction 1-26
Hourglass
Note: Additional protocols like routingprotocols (RIP, OSPF) needed to makeIP work
Introduction 1-27
Implications of Hourglass
A single Internet layer module:Allows all networks to interoperate
all networks technologies that support IP can exchange packets
Allows all applications to function on all networks
all applications that can run on IP can use any network
Simultaneous developments above and below IP
Introduction 1-28
Reality
Layering is a convenient way to think about networks
But layering is often violatedFirewallsTransparent cachesNAT boxes
Introduction 1-29
Thinking Exercise – Interplanetary Internet Network entities:
Ground stations Satellites, space stations at
near-Earth orbit 600 kilometers (~ 2s)
Mars rovers take ~ 10 to 30 min
Planets farther away? Objective:
Interconnect with earth-bound networks?
http://www.spectrum.ieee.org/WEBONLY/publicfeature/aug05/0805inte.html