chapter 1 introduction - university of nevada, reno

Introduction 1-1

Chapter 1Introduction

Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith RossAddison-WesleyMarch 2012

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Introduction 1-2

Lecture 2

University of Nevada – RenoComputer Science & Engineering Department

Fall 2015

CPE 400 / 600Computer Communication Networks

Prof. Shamik SenguptaOffice SEM 204

[email protected]://www.cse.unr.edu/~shamik/

Chapter 1: Computer Networks and the Internet

What is computer network: “nuts and bolts” view

1. Numerous connected computing devices: hosts = end systems running network apps

Home network

Institutional network

Mobile networkGlobal ISP

Regional ISP

router

PC

server

wirelesslaptopcellular handheld

wiredlinks

access points

2. communication links fiber, copper,

radio, satellite transmission rate

= bandwidth3. routers: forward

packets (chunks of data)

1-4

Categorization of Computer Networks

• Business Networks• Home Networks • Mobile Networks

1-5

Example Network Applications (1)

A network with two clients and one server(typical client-server connection)

1-6


The client-server model involves requests and replies over the public/private network


Peer-to-peer networking: no fixed clients and servers

6-9

Example wireless network (4)

network infrastructure

wireless hosts laptop, PDA, IP phone run applications may be stationary (non-

mobile) or mobile wireless does not always

mean mobility

Categorization of networks by coverage scale

• Personal area networks (PAN)• Local area networks (LAN)• Metropolitan area networks (MAN)• Wide are networks (WAN)• The Internet (Global network)

1-10

Personal Area Network (PAN)

Bluetooth PAN configuration

Local Area Networks (LAN)

Wireless and wired LANs. (a) 802.11. (b) Switched Ethernet.

Metropolitan Area Networks (MAN)

A metropolitan area network

Wide Area Networks (WAN)

WAN that connects three branch offices in Australia

Coverage scale (contd.)

Classification of interconnected processors by scale

A different categorization of networks

In terms of communication technology

• Unicasting• Broadcasting• Multicasting

What is computer networking: an operational view

Any communication is all about protocol

networking protocol

Hi

HiGot thetime?2:00

Connection req.

Connectionreply.

Get http://www.cnn.com/slide.ppt

<file>time

human protocol

1-17

human protocols:

… specific msgs sent… specific actions taken

when msgs received, or other events

network protocols: machines rather than

humans all communication activity

governed by protocols

protocols define format, order of msgs sent and received among network

entities, and actions taken on msg

transmission, receipt

What is computer networking: an operational view

1-18

1-19

Protocol “Layers”Networks are complex! It is not just two machines communicating!

Millions of components: hosts routers Access networks Physical links

Numerous functionalities

Question:How to manage such vast

amount of components?

Soln: Divide functionalities among multiple layers.

1-20

ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departureairport

arrivalairport

intermediate air-trafficcontrol centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Layering of airline functionality

Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below and above

Another example: Postal Service!

What are the adv. of layering?Network is a huge complex system.

Reduce the design complexity Ease of updating the system change of implementation of layer’s service transparent to

rest of system e.g., Postal service (overnight flight or overnight ground)

1-22

Internet protocol stack

application

transport

network

link

physical

application support host/network applications Email, FTP, HTTP (HTML)

transport process-process data transfer TCP, UDP

network routing of datagrams from src. to destn. IP address, routing protocols

link data transfer between neighboring network elements Ethernet

physical bits “on the wire”

(Compare with the Postal System!)

The TCP/IP Reference Model

1-23

Introduction

ISO/OSI reference model

presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions

session: synchronization, checkpointing, recovery of data exchange

application

presentation

session

transport

network

link

physical

1-24

1-25

sourceapplicationtransportnetwork

linkphysical

HtHn M

segment Htdatagram

destinationapplicationtransportnetwork

linkphysical

HtHnHl MHtHn MHt M

M

networklink

physical

linkphysical

HtHnHl MHtHn M

HtHn M

HtHnHl M

router

switch

Messages, Segments, Datagrams and Frames

message M

Ht M

Hnframe

Encapsulation

message

Introduction

Network core packet switching, circuit switching,

Network structure

1-26

Introduction

mesh of interconnected routers

packet-switching: hosts break application-layer messages into packets forward packets from one

router to the next, across links on path from source to destination

each packet transmitted at full link capacity

The network core

1-27

Introduction

Packet-switching: store-and-forward

takes L/R seconds to transmit (push out) L-bit packet into link at R bps

store and forward: entire packet must arrive at router before it can be transmitted on next link

one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission

delay = 5 sec

more on delay shortly …1-28

sourceR bps destination

123

L bitsper packet

R bps

end-end delay = 2L/R(assuming zero propagation delay)

Introduction

Packet Switching: queueing delay, loss

A

B

CR = 100 Mb/s

R = 1.5 Mb/s D

Equeue of packetswaiting for output link

1-29

queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of

link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up

Introduction

Alternative core: circuit switchingend-end resources allocated

to, reserved for “call”between source & dest:

In diagram, each link has four circuits. call gets 2nd circuit in top

link and 1st circuit in right link.

dedicated resources: no sharing circuit-like (guaranteed)

performance circuit segment idle if not used

by call (no sharing) Commonly used in traditional

telephone networks1-30

Introduction

Circuit switching: FDM versus TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

1-31

Introduction

Packet switching versus circuit switching

example: 1 Mb/s link each user:

• 100 kb/s when “active”

• active 10% of time

circuit-switching: 10 users

packet switching allows more users to use network!

Nusers

1 Mbps link

1-32

Introduction

great for bursty data resource sharing simpler, no call setup

excessive congestion possible: packet delay and loss protocols needed for reliable data transfer, congestion

control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (will discuss about this more

later…)

is packet switching a “clear winner?”

Packet switching versus circuit switching

1-33

Internet structure: network of networks

End systems connect to Internet via access ISPs (Internet Service Providers) Residential, company and university ISPs

Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other

Resulting network of networks is very complex Evolution was driven by economics and national policies

Let’s take a stepwise approach to describe current Internet structure


Question: given millions of access ISPs, how to connect them together?

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet


Option: connect each access ISP to every other access ISP?

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

connecting each access ISP to each other directly doesn’t

scale: O(N2) connections.


accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

Option: connect each access ISP to a global transit ISP? Customerand provider ISPs have economic agreement.

globalISP


accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

But if one global ISP is viable business, there will be competitors ….

ISP B

ISP A

ISP C


accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

But if one global ISP is viable business, there will be competitors …. which must be interconnected

ISP B

ISP A

ISP C

IXP

IXP

peering link

Internet exchange point


accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet

… and regional networks may arise to connect access nets to ISPS

ISP B

ISP A

ISP C

IXP

IXP

regional net

1-41


roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and

Wireless), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

1-42

Tier-1 ISP: e.g., Sprint

1-43


“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

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISPTier-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.

1-44


“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 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

1-45


a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Introduction

Delay, loss, throughput in networks

1-46

Introduction

How do loss and delay occur?

packets queue in router buffers packet arrival rate to link (temporarily) exceeds output link

capacity packets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets dropped (loss) if no free buffers

1-47

Introduction

Four sources of packet delay

dproc: nodal processing check bit errors determine output link typically < msec

A

B

propagation

transmission

nodalprocessing queueing

dqueue: queueing delay time waiting at output link

for transmission depends on congestion

level of router

dnodal = dproc + dqueue + dtrans + dprop

1-48

Introduction

dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R

dprop: propagation delay: d: length of physical link s: propagation speed in medium

(~2x108 m/sec) dprop = d/sdtrans and dprop

very different

Four sources of packet delay

propagation

nodalprocessing queueing

dnodal = dproc + dqueue + dtrans + dprop

1-49

A

B

transmission

Introduction

Packet loss queue (aka buffer) preceding link in buffer has finite

capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node,

by source end system, or not at all

A

B

packet being transmitted

packet arriving tofull buffer is lost

buffer (waiting area)

1-50

Introduction

Throughput

throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time

server, withfile of F bits

to send to client

link capacityRs bits/sec

link capacityRc bits/sec

server sends bits (fluid) into pipe

pipe that can carryfluid at rateRs bits/sec)

pipe that can carryfluid at rateRc bits/sec)

1-51

Introduction

Throughput: Internet scenario

10 connections (fairly) share backbone bottleneck link R bits/sec

Rs

Rs

Rs

Rc

Rc

Rc

R

per-connection end-end throughput: min(Rc,Rs,R/10)

in practice: Rc or Rsis often bottleneck

1-52

Metric Units (1)

The principal metric prefixes1-53

Metric Units (2)

The principal metric prefixes1-54

chapter 1 introduction - university of nevada, reno

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