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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
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerServerComputerComputer
ClientClientComputerComputer
Switch1
Switch2
Switch3
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
Networks connect computers: clients (fixed and mobile) and servers
Networks connect computers: clients (fixed and mobile) and servers
5
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch3
Message (Frame)
TrunkLine
Server ApplicationClient Application
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
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch4
Message (Frame)Message (Frame)
TrunkLine
Server ApplicationClient Application
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
Figure 1-3: Elements of a Network
Small Switches (Stacked):
Large Switch
Both sizes of switches are48 cm (19 inches) wide
9
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
Wireless AccessWireless AccessPointsPoints Connect
Wireless Stationsto Switches
Wireless AccessWireless AccessPointsPoints Connect
Wireless Stationsto Switches
10
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
RouterRouter
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
Routers connect networksto the outside world;
Treated just like computersin single networks
Routers connect networksto the outside world;
Treated just like computersin single networks
11
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLine
Server ApplicationClient Application
Access LinesAccess LinesConnect Computers
to Switches
Access LinesAccess LinesConnect Computers
to Switches
12
Figure 1-3: Elements of a Network
WirelessAccess Point
MobileClient
Router
OutsideWorld
ServerComputer
ClientComputer
Switch1
Switch2
Switch3
Switch4
Message (Frame)Message (Frame)
AccessLine
TrunkLines
Server ApplicationClient Application
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
First Bank of Paradise (FBP)
• Annual Revenues: $4.5 Billion
• Operations
– 60 Branches
– 375 ATMs (Automated Teller Machines)
• Network
– 700 Ethernet switches
– 450 Routers
17
First Bank of Paradise (FBP)
• Computers
– 2,300 desktop and notebook user PCs
– 130 Windows servers
– 60 Unix servers
• Information Systems Staff
– 112 people
18
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
19
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
20
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
21
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
22
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
23
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
Figure 1-11: Internets
• 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
Figure 1-11: Internets
• 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)
28
Figure 1-11: Internets
• 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
29
Figure 1-11: Internets
• 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
30
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
31
Figure 1-12: Internet with Three Networks
• 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
32
Figure 1-12: Internet with Three Networks
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
33
Figure 1-12: Internet with Three Networks
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
34
Figure 1-12: Internet with Three Networks
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
35
Figure 1-12: Internet with Three Networks
• 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
Figure 1-12: Internet with Three Networks
• Spelled in lowercase, “internet” is any internet
• Spelled in uppercase, “Internet” is the global Internet
37
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
38
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
39
Figure 1-14: The Internet, internets, Intranets, and Extranets
• 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
40
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
42
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
Figure 1-14: The Internet, internets, Intranets, and Extranets
• 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
Figure 1-14: The Internet, internets, Intranets, and Extranets
• Extranets
– To connect multiple firms• Only some computers from each firm are on the
extranet
– Use TCP/IP standards
“Extra” means “outside”
46
Figure 1-14: The Internet, internets, Intranets, and Extranets
• 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
54
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… …
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
Figure 1-22: The Domain Name System (DNS)
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
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
Figure 1-22: The Domain Name System (DNS)
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
Host Name IP Address … …… …Voyager.cba.hawaii.edu128.171.17.13… …
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
60
61
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?