Part 1: Introduction - INET: Internet Network Architectures · What’s the Internet: “Nuts and...
Transcript of Part 1: Introduction - INET: Internet Network Architectures · What’s the Internet: “Nuts and...
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Part 1: Introduction
Goal:
r Review of how the Internet works
r Overview
m Get context
m Get overview, “feel” of the Internet
r Application layer protocols and addressing
r Network layer / Routing
r Link layer / Example
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What’s the Internet: “Nuts and bolts” view
r Millions of connected computing devices: hosts, end-systems
m PC’s workstations, servers
m PDA’s, phones, toasters
running network apps
r Communication linksm Fiber, copper, radio, satellite
r Routers: forward packets (chunks) of data through network
local ISP
company / accessnetwork
regional ISP
routerworkstation
servermobile
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Example access net: Home network
Typical home network components:
r ADSL or cable modem
r router/firewall
r Ethernet
r Wireless access points
wirelessaccess point
wirelesslaptops
router/firewall
cablemodem
to/fromcable
headend
Ethernet(switched)
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What’s the Internet: “Nuts and bolts” view
r Protocols: control sending, receiving of messages
m E.g., TCP, IP, HTTP, FTP, PPP
r Internet: “network of networks”
m Loosely hierarchical
m Public Internet versus private intranet
r Internet standards
m RFC: Request for comments
m IETF: Internet Engineering Task Force
local ISP
companynetwork
regional ISP
routerworkstation
servermobile
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What’s the Internet: A service view
r Communication infrastructure enables distributed applications:
m WWW, email, games, e-commerce, database, voting,
m More?
r Communication services provided:
m Connectionless
m Connection-oriented
r Cyberspace [Gibson]:“a consensual hallucination
experienced daily by billions of operators, in every nation, ...."
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Principles of the Internet
r Edge vs. core (end-systems vs. routers)
m Dumb network
m Intelligence at the end-systems
r Different communication paradigms
m Connection oriented vs. connection less
m Packet vs. circuit switching
r Layered system
r Network of collaborating networks
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A closer look at network structure
r Network edge:applications and hosts
r Network core:m Routers
m Network of networks
r Access networks, physical media:Communication links
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The network edge
r End systems (hosts):m Run application programs
m E.g., WWW, email
m At “edge of network”
r Client/server modelm Client host requests, receives
service from server
m E.g., WWW client (browser)/ server; email client/server
r Peer-2-peer model:m Host interaction symmetric
m E.g.: File sharing
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Network edge: Connection-oriented service
Goal: data transfer between end systems
r Handshake: setup (prepare for) data transfer ahead of time
m Hello, hello back human protocol
m Set up “state” in two communicating hosts
r TCP – Transmission Control Protocol
m Internet’s connection-oriented service
TCP service [RFC 793]
r Reliable, in-order byte-stream data transfer
m Loss: acknowledgements and retransmissions
r Flow control:m Sender won’t overwhelm
receiver
r Congestion control:m Senders “slow down sending
rate” when network congested
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Network edge: Connectionless service
Goal: Data transfer between end systemsm Same as before!
r UDP – User Datagram Protocol [RFC 768]: Internet’s connectionless service
mUnreliable data transfer
mNo flow control
mNo congestion control
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The network core
r Mesh of interconnected routers
r The fundamental question:How is data transferred through net?
m Circuit switching:Dedicated circuit per call: telephone net
m Packet switching: Data sent through net in discrete “chunks”
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Network core: Circuit switching
End-end resources reserved for “call”
r Link bandwidth, switch capacity
r Dedicated resources: no sharing
r Circuit-like (guaranteed) performance
r Call setup required
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Network core: Packet switching
Each end-end data stream divided into packets
r Users’ A, B packets share network resources
r Each packet uses full link bandwidth
r Resources used as needed
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Network core: Packet switching
Packet-switching versus circuit switching: Human restaurant analogy
A
B
C1 GbsEthernet
100 Mbs
45 Mbs
D E
statistical multiplexing
queue of packetswaiting for output
link
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Network core: Packet switching
Resource contention:
r Aggregate resource demand can exceed amount available
r Congestion: Packets queue, wait for link use
r Store and forward: Packets move one hop at a time
mTransmit over link
mWait turn at next link
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Delay in packet-switched networks
Packets experience delay on end-to-end path
r Four sources of delay at each hop
r Nodal processing m Check bit errors
m Determine output link
r Queueingm Time waiting at output
link for transmission
m Depends on congestion level at router
A
B
propagation
transmission
nodalprocessing queueing
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Delay in packet-switched networks
Transmission delay:
r R = link bandwidth (bps)
r L = packet length (bits)
r Time to send bits into link = L/R
Propagation delay:
r d = length of physical link
r s = propagation speed in medium (~2x108 m/sec)
r Propagation delay = d/s
A
B
propagation
transmission
nodalprocessing queueing
Note: s and R are verydifferent quantities!
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Queueing delay
r R = link bandwidth (bps)
r L = packet length (bits)
r A = average packet arrival rate
Traffic intensity = La/R
r La/R ~ 0: average queueing delay small
r La/R -> 1: delays become large
r La/R > 1: more “work” arriving than can be serviced => average delay infinite!
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Packet switching vs. circuit switching
r Great for bursty data
m Resource sharing
m No call setup
r Excessive congestion: Packet delay and loss
m Protocols needed for reliable data transfer,congestion control
r Key question: How to provide circuit-like behavior?
m Bandwidth guarantees needed for audio/video apps
Is packet switching a “slam dunk winner?”
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Packet-switched networks: Routing
r Goal: Move packets among routers from source to destination
r Datagram network:m Destination address determines next hop
m Routes may change during session
m Analogy: Drive towards dst. and ask for directions
r Virtual circuit network:m Fixed path determined at call setup time, remains fixed through call
m Each packet carries tag (virtual circuit ID);Tag determines next hop
m Routers maintain per-call state
m Analogy: Fixed driving instructions
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What’s a protocol?
Human protocols:
r “What’s the time?”
r “I have a question!”
… introductions
… specific msgs sent
… specific actions taken when msgs received, or other events
Network protocols:
r machines rather than humans
r all communication activity in Internet governed by protocols
Protocols define format, order of msgs sent and received among network entities, and actions taken
on msg transmission, receipt
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Protocol “layers”
Networks are complex!
r Many “pieces”:
m Hosts
m Routers
m Links of various media
m Applications
m Protocols
m Hardware, software
Question:
Is there any hope of organizing structure of
network?
Or at least in our discussion of networks?
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Why layering?
Dealing with complex systems:
r Explicit structure allows identification, relationship of complex system’s pieces
m Layered reference model for discussion
r Modularization eases maintenance, updating of system
m Change of implementation of layer’s service transparent to rest of system
m E.g., change in gate procedure does not affect rest of system
r Layering considered harmful?
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Protocol “Layers”
Networks are complex!
r many “pieces”:
m hosts
m routers
m links of various media
m applications
m protocols
m hardware, software
Question:
Is there any hope of organizingstructure of network?
Or at least our discussion of networks?
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Why layering?
Dealing with complex systems:
r Explicit structure allows identification, relationship of complex system’s pieces
m Layered reference model for discussion
r Modularization eases maintenance, updating of system
m Change of implementation of layer’s service transparent to rest of system
m E.g., change in gate procedure doesn’t affect rest of system
r Can layering be considered harmful?
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Internet protocol stack
r Application: Supporting network applications
r Transport: Host-host data transfer
r Network: Uniform format of packets, routing of datagrams from source to destination
r Link: Data transfer between neighboring network elements
r Physical: Bits “on the wire”
application
transport
network
link
physical
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Layering: Logical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
Each layer:
r Distributed
r “Entities”implement layer functions at each node
r Entities perform actions, exchange messages with peers
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Layering: Logical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
E.g., transport
r Take data from application
r Add addressing, reliability check info to form “datagram”
r Send datagram to peer
r Wait for peer to ack receipt
r Analogy: post office
data
transport
transport
ack
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Layering: Physical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
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Protocol layering and data
Each layer takes data from above
r Adds header information to create new data unit
r Passes new data unit to layer below
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnH l
M
M
M
M
Ht
HtHn
HtHnH l
message
segment
datagram
frame
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Internet protocol stack
r Application: Supporting network applications
r Transport: Host-host data transfer
r Network: Uniform format of packets, routing of datagrams from source to destination
r Link: Data transfer between neighboring network elements
r Physical: Bits “on the wire”
application
transport
network
link
physical
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What makes the Internet so sexy
r Applications can be deployed by anybody that is connected to the Internet(Fundamentally different to the Telephone world)
r Multi-service network: Everything over the Internet• Every application protocol over IP
• IP over any network technology
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TCP/IP Protocol structure
Transport(Hosts)
Network
Link
Application(Processes)
IP
TCP UDP
Telnet FTP
DNSHTTP SMTP
FDDI ATM
Tokenring Ethernet
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Internet structure: Network of networks
r Roughly hierarchical
r At center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage
m 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)
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Internet structure: Network of networks
r “Tier-2” ISPs: smaller (often regional) ISPs
m 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
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Internet structure: Network of networks
r “Tier-3” ISPs and local ISPs
m 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
localISP
localISP
localISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier-3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
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Example Tier-1 ISP: Sprint
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Internet structure: Network of networks
r 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
localISP
localISP
localISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Try traceroute!
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Internet philosophy
r Interconnect networks
m Accross multiple different technologies
r Requirements on these networks
m Minimal assumption about network capabilities => some data should be transmitted from time to time
⇒ „Best Effort“ paradigma
r High survivability
m Mesh
m Intermediate nodes do not maintain per host state
=> „End-to-end“ paradigma
r Layering with simple application interface
m Sockets
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Internet design philosophy
In order of importance:
m Connect existing networks
m Survivability
m Support multiple types of service
m Must accommodate a variety of networks
m Allow distributed management
m Allow host attachment with a low level of effort
m Be cost effective
m Allow resource accountability
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Internet terminology
r internetm Collection of packet switched networks interconnected by routers running the IP/TCP protocols
r The „Internet“m Public Internet (in contrast to Intranets)
r End system == host attached to network
r Router = gateway = intermediate systemm Routes packets between its attached networks
r Firewall (device placed at network boundaries)m Restricts packet flows to improve security
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Internet terminology (2.)r Name
m Identifies an object (e.g., an end system)
r Addressm Identifies where an object is located (here IP address)
r Name to address translation (and vice versa)m Links names and addresses
• mail.zrz.TU-Berlin.DE � 130.149.4.15
r Interfacem Network attachment (≥ 1 interfaces = multihomed)
r Routem How to get to an objects location
r Network prefix m Set of addresses