Part 1: Introduction - INET: Internet Network Architectures · What’s the Internet: “Nuts and bolts”view Protocols: control sending, receiving of messages E.g., TCP, IP, HTTP,

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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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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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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


linkphysical


linkphysical


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


linkphysical


linkphysical


linkphysical


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


linkphysical


linkphysical


linkphysical


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


linkphysical


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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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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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 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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r A packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



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

Documents

Part 1: Introduction - INET: Internet Network Architectures · What’s the Internet: “Nuts and bolts”view Protocols: control sending, receiving of messages E.g., TCP, IP, HTTP,