1 network basics 1.the nine elements of a network 2.lans and wans 3.internets 4.packet switching vs....

1

Network Basics

1. The Nine Elements of a Network

2. LANs and WANs

3. Internets

4. Packet Switching vs. Circuit Switching

1. The Nine Elements of a Network

Although the idea of “network”is simple, you must understand the

nine elements found in most networks

3

Figure 1-3: Elements of a Network

WirelessAccess Point

MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Message (Frame)Message (Frame)

AccessLine

TrunkLine

Server ApplicationClient Application

Networks connectapplicationsapplications on different computers.Applications are all users care about

Networks connectapplicationsapplications on different computers.Applications are all users care about

4



MobileClient

Router

OutsideWorld

ServerServerComputerComputer

ClientClientComputerComputer

Switch1

Switch2

Switch3


AccessLine

TrunkLine


Networks connect computers: clients (fixed and mobile) and servers

Networks connect computers: clients (fixed and mobile) and servers

5



MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch3

Message (Frame)

TrunkLine


The patha frame takes

is called its data link

The patha frame takes

is called its data linkComputers (and routers)

usually communicateby sending messages

called frames

Computers (and routers)usually communicateby sending messages

called frames

Data LinkData Link

6



MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch4


TrunkLine


Switch 2Switch 2

Switch 1Switch 1Switch 3Switch 3

Frameto Sw1Frameto Sw1 Frame

to Sw2Frameto Sw2 Frame

To Sw3FrameTo Sw3 Frame

toServer

Frameto

Server

SwitchesSwitches ForwardFrames Sequentially

SwitchesSwitches ForwardFrames Sequentially

7

Figure 1-5: Ethernet Switch Operation

A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65

Switch

D4-47-55-C4-B6-F9

C3-2D-55-3B-A9-4F

Port 15

Frame to C3…Frame to C3…

A1- sends a frame to C3-A1- sends a frame to C3-

Frame to C3…Frame to C3…

Switch sends frame to C3-Switch sends frame to C3-

Switching TablePort Host10 A1-44-D5-1F-AA-4C13 B2-CD-13-5B-E4-6515 C3-2D-55-3B-A9-4F16 D4-47-55-C4-B6-F9

Switching TablePort Host10 A1-44-D5-1F-AA-4C13 B2-CD-13-5B-E4-6515 C3-2D-55-3B-A9-4F16 D4-47-55-C4-B6-F915 C3-2D-55-3B-A9-4F15 C3-2D-55-3B-A9-4F

C3- is out Port 15C3- is out Port 15

1

2

3

8


Small Switches (Stacked):

Large Switch

Both sizes of switches are48 cm (19 inches) wide

9



MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine


Wireless AccessWireless AccessPointsPoints Connect

Wireless Stationsto Switches

Wireless AccessWireless AccessPointsPoints Connect

Wireless Stationsto Switches

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MobileClient

RouterRouter

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine


Routers connect networksto the outside world;

Treated just like computersin single networks

Routers connect networksto the outside world;

Treated just like computersin single networks

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLine


Access LinesAccess LinesConnect Computers

to Switches

Access LinesAccess LinesConnect Computers

to Switches

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MobileClient

Router

OutsideWorld

ServerComputer

ClientComputer

Switch1

Switch2

Switch3

Switch4


AccessLine

TrunkLines


Trunk LinesTrunk Lines ConnectSwitches to Switches and

Switches to Routers

Trunk LinesTrunk Lines ConnectSwitches to Switches and

Switches to Routers

TrunkLine

13

Figure 1-4: Packet Switching and Multiplexing

ClientComputer A

Mobile ClientComputer B

Router D

ServerComputer C

AC

ACAC

AC

ACAC

BD

BD

BD

BD

AccessLine

Trunk Line

Multiplexing Mixesthe Messages of

Multiple Conversationson a Trunk Line

So Packet SwitchingReduces the Cost of Trunk Lines

Breaking Communications intoSmall Messages is Called

Packet Switching, even if theMessages are Frames

2. LANs and WANs

15

First Bank of Paradise (FBP)

• The book’s running case study

– Composite mid-size bank in Hawaii

– Banks are fairly “typical” firms, although they have stronger need for security

– Warren Chun is the chief information officer (CIO)

– Yvonne Champion is the network manager

16


• Annual Revenues: $4.5 Billion

• Operations

– 60 Branches

– 375 ATMs (Automated Teller Machines)

• Network

– 700 Ethernet switches

– 450 Routers

17


• Computers

– 2,300 desktop and notebook user PCs

– 130 Windows servers

– 60 Unix servers

• Information Systems Staff

– 112 people

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Figure 1-8: LANs Versus WANs

CharacteristicsCharacteristics

ScopeScopeLANsLANs WANsWANs

For transmission withina site. Campus, building, and SOHO(Small Office or HomeOffice) LANs

For transmission withina site. Campus, building, and SOHO(Small Office or HomeOffice) LANs

For transmissionbetween sites

For transmissionbetween sites

Cost per bit TransmittedCost per bit Transmitted LowLow HighHigh

Typical SpeedTypical SpeedUnshared 100 Mbps to a gigabit per second to eachdesktop. Even fastertrunk line speeds.

Unshared 100 Mbps to a gigabit per second to eachdesktop. Even fastertrunk line speeds.

Shared 128 kbps to several megabits per second trunk line speeds

Shared 128 kbps to several megabits per second trunk line speeds

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Figure 1-8: LANs Versus WANs

Characteristics

ManagementManagement

LANs WANsWANs

On own premises, sofirm builds andmanages its own LANor outsources theWork

On own premises, sofirm builds andmanages its own LANor outsources theWork

Must use a carrier withrights of way for transmission in publicArea. Carrier handles most work butCharges a high price.

Must use a carrier withrights of way for transmission in publicArea. Carrier handles most work butCharges a high price.

ChoicesChoices UnlimitedUnlimited Only those offered bycarrier

Only those offered bycarrier

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Figure 1-9: Local Area Network (LAN) in a Large Building

Multi-floorOffice Building

The bank has multipleLANs—one at each site

The bank has multipleLANs—one at each site

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Figure 1-9: Local Area Network (LAN) in a Large Building

Router Core Switch

Workgroup Switch 2

Workgroup Switch 1

Wall Jack

ToWAN

Wall Jack

Server

Client

Frames from the client to the server go through Workgroup Switch 2, through the Core Switch, through Workgroup Switch 1, and then to the server

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Figure 1-10: Workgroup Switch(19 inches / 48 cm Wide)

48 cm (19 in.)Workgroup Switch

with 16 ports

Wire cord goingout to a computer

or to another switch

Wire cord goingout to a computer

or to another switch

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Figure 1-7: The First Bank of Paradise’s Wide Area Networks (WANs)

Operations

Headquarters

North Shore

OC3 Private Leased Line

T3

T3

Bank has multiplefacilities connectedby multiple WANs

Bank has multiplefacilities connectedby multiple WANs

Frame Relay Network

Branch Office

3. Internets

25

Figure 1-11: Internets

• Single LANs Versus Internets

– In single networks (LANs and WANs), all devices connect to one another by switches—our focus so far.

– In contrast, an internet is a group of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet.

LANLAN WANWAN LANLAN

Application Application

Router Router

26


• Internet Components

– All computers in an internet are called hosts• Servers, clients, PDAs, cellphones, etc.

Cat

InternetInternet

Client PC(Host)

Cellphone(Host)

VoIP Phone(Host)

PDA(Host)

Server(Host)

27


• Hosts Have Two Addresses

• IP Address– This is the host’s official address on its internet– 32 bits long

– Expressed for people in dotted decimal notation (e.g., 128.171.17.13)

• Single-Network Addresses– This is the host’s address on its single network– Ethernet addresses, for instance, are 48 bits long

– Expressed in hexadecimal notation (e.g., AF-23-9B-E8-67-47)

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• Networks are connected by devices called routers

– Switches provide connections within networks, while routers provide connections between networks in an internet.

• Frames and Packets

– In single networks, message are called frames

– In internets, messages are called packets

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• Packets are carried within frames

– One packet is transmitted from the source host to the destination host

• Its IP destination address is that of the destination host

– In each network, the packet is carried in (encapsulated in) a frame (Figure 1-12)

– If there are N networks between the source and destination hosts, there will be one packet and N networks between the source and destination hosts, there will be one packet and N frames for a transmission

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Figure 1-12: Internet with Three Networks

Host B

Host A

Network XNetwork Y

Network Z

R1

R2

Route A-B

PacketPacket

A packet goes all theway across the internet;

It’s path is its route

A packet goes all theway across the internet;

It’s path is its route

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• Messages in single networks (LANs or WANs) are called frames

• Message in internets are called packets

– Travel from the source host to the destination host across the entire internet

• Within a single network, the packet is encapsulated in (carried in) the network’s frame

Frame

Truck(frame)

Package(Packet)PacketPacket

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Mobile ClientHost

ServerHost

Switch

SwitchX2

SwitchX1

Switch

Router R1D6-EE-92-5F-C1-56

Network XRoute A-BRoute A-B

A route is a packet’spath through the internet

A route is a packet’spath through the internet

Details inNetwork X

Details inNetwork X

Data linkA-R1

Data linkA-R1

A data Link is aframe’s path through

its single network

A data Link is aframe’s path through

its single network

In Network X, the Packet is Placed in Frame X

PacketFrame X

Host A10.0.0.23

AB-23-D1-A8-34-DD

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Router R1

Router R2AF-3B-E7-39-12-B5

PacketFrame Y

ToNetwork X

ToNetwork Z

Network Y

Data LinkR1-R2

RouteA-B

Details inNetwork Y

Details inNetwork Y

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Host Bwww.pukanui.com

1.3.45.11155-6B-CC-D4-A7-56

Mobile Client Host

SwitchZ1

Switch

SwitchZ2

Switch

PacketFrame Z

Network Z

Router R2

Router

Data LinkR2-B

Details inNetwork Z

Details inNetwork Z

Mobile ClientComputer

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• In this internet with three networks, in a transmission,

– There is one packet

– There are three frames (one in each network)

• If a packet in an internet must pass through 10 networks,

– How many packets will be sent?

– How many frames must carry the packet?

36


• Spelled in lowercase, “internet” is any internet

• Spelled in uppercase, “Internet” is the global Internet

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10000000101010110001000100001101 10000000101010110001000100001101

Figure 1-13: Converting IP Addresses into Dotted Decimal Notation

Divided into 4 bytes. Theseare segments.

10000000 10101011 00010001 0000110100001101

Dotted decimal notation(4 segments separated bydots)

Dotted decimal notation(4 segments separated bydots)

IP Address (32 bits long)

Convert each byte todecimal (result will bebetween 0 and 255)*

128 171 17 1313

*The conversion process is described in the Hands On section at the end of the chapter.

128.171.17.13128.171.17.13

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Figure 1-14: The Internet, internets, Intranets, and Extranets

• The Global Internet

– As noted earlier,

• Spelled with a lowercase i, internet means any internet

• Spelled with a uppercase I, Internet means the global Internet

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• The Internet (Figure 1-18)

– Host computers

– Internet service providers (ISPs)• Required to access the Internet• Carry your packets across the Internet• Collect money to pay for the Internet

– The Internet backbone consists of many ISPs• ISPs interconnect at Network access points (NAPs) to

exchange cross-ISP traffic

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Figure 1-17: The Internet

User PC’sInternet Service

Provider

Webserver’sInternet Service

Provider

ISP ISP

User PCHostComputer

WebserverHost

Computer

NAP = Network Access Point

Router

NAPNAPNAPNAP

NAPNAPISP

ISP

Internet Backbone(Multiple ISP Carriers)

AccessLine

AccessLine

41

Figure 1-17: The Internet

User PC’sInternet Service

Provider

Webserver’sInternet Service

Provider

ISP ISP

User PCHostComputer

WebserverHost

NAP = Network Access Point

Router

NAPNAPNAPNAP

NAPNAPISP

ISP

Internet Backbone(Multiple ISP Carriers)

AccessLine

AccessLine

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Figure 1-18: Subnets in an Internet

LAN 1LAN 2

LAN Subnet10.1.x.x

WANSubnet

123.x.x.x

LAN Subnet60.4.3.x

LAN Subnet10.2.x.x

LAN Subnet10.3.x.x

LAN Subnet60.4.15.x

LAN Subnet60.4.7.x

Note: Subnets are single networks (collections of switches, transmission lines)

RouterR1

Router R3

RouterR4

Router R2

LAN Subnet60.4.131.x

43

Figure 1-19: Terminology Differences for Single-Network and Internet Professionals

By Single-NetworkProfessionals

By InternetProfessionals

By InternetProfessionals

Single Networks AreCalled

Networks SubnetsSubnets

Internets Are CalledInternets Are Called InternetsInternets NetworksNetworks

In this book, to avoid confusion,

we will call internets “internets”

and subnets “single networks”

44


• Intranets

– An intranet is an internal internet for use within an organization

– Based on the TCP/IP standards created for the Internet

“Intra” means “within”

45


• Extranets

– To connect multiple firms• Only some computers from each firm are on the

extranet

– Use TCP/IP standards

“Extra” means “outside”

46


• Intranets, Extranets, and the Internet

– Confusingly, both intranets and extranets can use the Internet for some of their transmission capacity

47

Figure 1-15: Routers(19 inches / 48 cm Wide)

48

Figure 1-16: Small Router for a Branch Office (19 inches / 48 cm Wide)

49

Figure 1-20: IP Address Management

• Every Host Must Have a Unique IP address

– Server hosts are given static IP addresses (unchanging)

– Clients get dynamic (temporary) IP addresses that may be different each time they use an internet

• Dynamic Host Configuration Protocol (DHCP)

– Clients get these dynamic IP addresses from Dynamic Host Configuration Protocol (DHCP) servers

50

Figure 1-21: Dynamic Host Configuration Protocol (DHCP)

Client PCA3-4E-CD-59-28-7F

DHCPServer

DHCP Request Message:“My 48-bit Ethernet address is A3-4E-CD-59-28-7F”.

Please give me a 32-bit IP address.”

Pool ofIP Addresses

51

Figure 1-21: Dynamic Host Configuration Protocol (DHCP)

Client PCA3-4E-CD-59-28-7F

DHCPServer

DHCP Response Message:“Computer at A3-4E-CD-59-28-7F,

your 32-bit IP address is 11010000101111101010101100000010”.(Usually other configuration parameters as well.)

Pool ofIP Addresses

52

動態主機組態協定 (DHCP)

• Dynamic Host Configuration Protocol

• 自動設定電腦的– IP 位址 (163.22.20.223)

– 子網路遮罩 (255.255.255.0)

– 預設通訊閘 (163.22.20.254)

– 領域名稱伺服器 (163.22.2.1)

– …

• winipcfg (Win 98/Me)

• ipconfig /all (Win 2000/XP)

53

12

3

控制台網路和網際網路連線

55

Figure 1-20: IP Address Management

• Domain Name System (DNS) (Figure 1-22)

– IP addresses are official addresses on the Internet and other internets

– Hosts can also have host names (e.g., cnn.com)

• Not official—like nicknames

– If you only know the host name of a host that you want to reach, your computer must learn its IP address

• DNS servers tell our computer the IP address of a target host whose name you know. (Figure 1-22)

56

Figure 1-22: The Domain Name System (DNS)

Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …


DNS Table1.Client Host

wishes to reachVoyager.cba.hawaii.edu;

Needs to knowits IP Address

2. Sends DNS Request Message“The host name is Voyager.cba.hawaii.edu”

Voyager.cba.hawaii.edu128.171.17.13

LocalDNSHost

57




DNS Table

4. DNS Response Message“The IP address is 128.171.17.13”

Voyager.cba.hawaii.edu128.171.17.13

5.Client sends packets to

128.171.17.13

3.DNS Hostlooks up

IP address

DNSHost

58




DNS Table

Client Host

1. DNS Request Message

Anther DNS Host

LocalDNSHost

3. DNS Response Message

The local DNS hostsends back the response;the user is unaware that

other DNS hosts were involved

The local DNS hostsends back the response;the user is unaware that

other DNS hosts were involved

If local DNS host does nothave the target host’s IP address,

it contacts other DNS hoststo get the IP address

If local DNS host does nothave the target host’s IP address,

it contacts other DNS hoststo get the IP address

2.Request &Response

59

NCNUNCNUCampus Campus NetworkNetwork

DHCPServer

DNSServer

ProxyServers

TANetHiNet

Web Filter

(1)

www.google.com

(2)

(3)(4)

(5)

Example: Web Browsing

Router

Switch

62

nslookup

4. Packet Switching vs. Circuit Switching

64

A Simple Switching Network

StationStation

NodeNode

65

Switching

• Fully Connected vs. Switching Network

• What does “switching” mean?

– Switching Circuits/Fabric

– Switching Behavior

• Switch

– Switching Hub

– Layer-2 Switch

– Layer-3, 4 Switch

• Switch vs. Router

66

Circuit Switching

• Dedicated path between two stations

– Connected sequence of links between nodes

– E.g telephone network

• Communication involves three phases

– Circuit establishment

– Data transfer

– Circuit disconnect

67

Circuit Establishment

• Station A to node 4 requesting connection to station E

• Circuit from A to 4 usually dedicated line

• Node 4 finds next leg to node 6

• Based on routing information, availability, cost, node 4 selects circuit to node 5

• Allocates a free channel

– TDM [time-division multiplexing]

– FDM [frequency-division multiplexing]

• Node 4 requests connection to E

• And so on

Circuit: Channel / Link

Multiplexing

68

Data Transfer

• Data may be digital (e.g., terminal to host) or analog (e.g., voice)

• Signaling and transmission may each be digital or analog

• Path is A-4 circuit, internal switching through 4, 4-5 channel, internal switching through 5, 5-6 channel, internal switching through 6, 6-E circuit

• Generally, full duplex (data in both directions)

69

Circuit Disconnect

• Connection terminated

– Usually by one of the stations

• Signals to 4, 5, and 6 to de-allocate resources

70

Circuit Switching - Notes

• Connection established before data transmission begins• Channel capacity must be available and reserved. • Nodes must have capacity to handle connection• Switches must have intelligence to make allocations and devise

route• Can be inefficient

– Capacity dedicated for duration of connection• Even if no data are being transferred

– For voice, utilization high, but still doesn’t approach 100%– For terminal connection, may be idle most of the time– Delay prior to data transfer for call establishment– Once circuit established, network transparent to users– Data transmitted at fixed rate

• No delay other than propagation• Delay at node negligible

71

Packet Switching – Circuit Switching Issues

• Designed for voice

• Resources dedicated to particular call

• For voice, high utilization

– Most of the time, someone is talking

• For data

– Line idle much of the time

– Constant data rate• Limits interconnection of variety of host computers

and terminals

72

Packet Switching – Basic Operation

• Data are transmitted in short blocks, called packets, typical upper bound 1000 octets (bytes)

• Longer messages broken up into series of packets

• Transmitting computer sends message as sequence of packets.

• Packet includes control information including destination station.

• Packets sent to node to which sending station attaches

• Node stores packet briefly, determines next leg of route, and queues packet to go out on that link

• When link is available, packet is transmitted to next node

• All packets eventually work their way through network

73

Figure 1.2 The Use of Packets

74

Packet Switching – Advantages

• Line efficiency greater

– Node-to-node link dynamically shared by many packets

• Data-rate conversion

– Each station connects to its node at its proper data rate

– Nodes act as buffers

• Packets accepted, even under heavy traffic, but delivery delay increases

– Circuit switching networks would block new connections

• Priorities can be used

75

Packet Switching – Disadvantages

• Delay

– Transmission delay equal to length of packet divided by incoming channel rate

– Variable delay due to processing and queuing

• Packets may vary in length, take different routes, …

– May be subject to varying delays

– Overall packet delay can vary substantially (jitter)

– Not good for real-time applications like voice and real-time video

• Overheads including address of destination, sequencing information added to packet

– Reduces capacity available for user data

• More processing required at node

76

Switching Techniques

• Datagram– Each packet is treated independently.

• Virtual Circuit

– Sending packets via a preplanned route, similar to circuit switching.

77

Switching Technique - Datagram• Datagram: each packet treated independently

– No reference to packets that have gone before– Each node chooses next node on path– Packets with same destination address do not follow same route– May arrive out of sequence– Exit node or destination restores packets to original order– Packet may be destroyed in transit– Either exit node or destination detects loss and recovers

• Call setup avoided

• For an exchange of a few packets, datagram quicker

• More flexible. – E.g. Routing away from the congestion– Delivery is inherently more reliable

• If a node fails, subsequent packets may be re-routed

78

Packet Switching:Datagram Approach

79

Switching Technique –Virtual Circuit

• Preplanned route established before packets sent• All packets follow same route • Similar to circuit in circuit-switching network

– Hence virtual circuit

• Each packet has virtual circuit identifier– Nodes on route know where to direct packets– No routing decisions

• Not dedicated path, as in circuit switching– Packet still buffered at node and queued for output – Routing decision made once for that virtual circuit

• Network may provide services related to virtual circuit– Sequencing and error control

• Packets should transit more rapidly• If node fails, all virtual circuits through node lost

80

PacketSwitching:Virtual-CircuitApproach

81

Discussion

• Data comm. Vs. Voice comm.

• What if the Internet is circuit-switching?

• What if the telephone network is packet-switching?

• The failure of WAP

• The success of Skype?

1 network basics 1.the nine elements of a network 2.lans and wans 3.internets 4.packet switching vs....

Documents

networksmall switches

ethernet switch operationa1

different computers

idea of network

network basicsthe

data linkcomputers

outside worldtreated

routersusually communicateby