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 Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 2 Switch 3 Message (Frame) Access Line Trunk Line Server ApplicationClient Application Networks connect applications applications on different computers. Applications are all users care about Networks connect applications applications on different computers. Applications are all users care about

4 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World ServerComputer ClientComputer Switch 1 Switch 2 Switch 3 Message (Frame) Access Line Trunk Line 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 Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 3 Message (Frame) Trunk Line Server ApplicationClient Application The path a frame takes is called its data link The path a frame takes is called its data link Computers (and routers) usually communicate by sending messages called frames Computers (and routers) usually communicate by sending messages called frames Data Link

6 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 4 Message (Frame) Trunk Line Server ApplicationClient Application Switch 2 Switch 1 Switch 3 Frame to Sw1 Frame to Sw1 Frame to Sw2 Frame to Sw2 Frame To Sw3 Frame To Sw3 Frame to Server Frame to Server Switches Switches Forward Frames Sequentially Switches Switches Forward Frames Sequentially

7 Figure 1-5: Ethernet Switch Operation A1-44-D5-1F-AA-4CB2-CD-13-5B-E4-65 Switch D C4-B6-F9 C3-2D-55-3B-A9-4F Port 15 Frame to C3… A1- sends a frame to C3- Frame to C3… Switch sends frame to C3- Switching Table PortHost 10A1-44-D5-1F-AA-4C 13B2-CD-13-5B-E C3-2D-55-3B-A9-4F 16 D C4-B6-F9 Switching Table PortHost 10A1-44-D5-1F-AA-4C 13B2-CD-13-5B-E C3-2D-55-3B-A9-4F 16 D C4-B6-F9 15C3-2D-55-3B-A9-4F C3- is out Port

8 Figure 1-3: Elements of a Network Small Switches (Stacked): Large Switch Both sizes of switches are 48 cm (19 inches) wide

9 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 2 Switch 3 Switch 4 Message (Frame) Access Line Trunk Line Server ApplicationClient Application Wireless Access Points Points Connect Wireless Stations to Switches Wireless Access Points Points Connect Wireless Stations to Switches

10 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 2 Switch 3 Switch 4 Message (Frame) Access Line Trunk Line Server ApplicationClient Application Routers connect networks to the outside world; Treated just like computers in single networks Routers connect networks to the outside world; Treated just like computers in single networks

11 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 2 Switch 3 Switch 4 Message (Frame) Access Line Trunk Line Server ApplicationClient Application Access Lines Connect Computers to Switches Access Lines Connect Computers to Switches

12 Figure 1-3: Elements of a Network Wireless Access Point Mobile Client Router Outside World Server Computer Client Computer Switch 1 Switch 2 Switch 3 Switch 4 Message (Frame) Access Line Trunk Lines Server ApplicationClient Application Trunk Lines Trunk Lines Connect Switches to Switches and Switches to Routers Trunk Lines Trunk Lines Connect Switches to Switches and Switches to Routers Trunk Line

13 Figure 1-4: Packet Switching and Multiplexing Client Computer A Mobile Client Computer B Router D Server Computer C AC BD Access Line Trunk Line Multiplexing Mixes the Messages of Multiple Conversations on a Trunk Line So Packet Switching Reduces the Cost of Trunk Lines Breaking Communications into Small Messages is Called Packet Switching, even if the Messages 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 Characteristics Scope LANs WANs For transmission within a site. Campus, building, and SOHO (Small Office or Home Office) LANs For transmission within a site. Campus, building, and SOHO (Small Office or Home Office) LANs For transmission between sites For transmission between sites Cost per bit Transmitted Low High Typical Speed Unshared 100 Mbps to a gigabit per second to each desktop. Even faster trunk line speeds. Unshared 100 Mbps to a gigabit per second to each desktop. Even faster trunk 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 Management LANs WANs On own premises, so firm builds and manages its own LAN or outsources the Work On own premises, so firm builds and manages its own LAN or outsources the Work Must use a carrier with rights of way for transmission in public Area. Carrier handles most work but Charges a high price. Must use a carrier with rights of way for transmission in public Area. Carrier handles most work but Charges a high price. Choices Unlimited Only those offered by carrier Only those offered by carrier

20 Figure 1-9: Local Area Network (LAN) in a Large Building Multi-floor Office Building The bank has multiple LANs—one at each site The bank has multiple LANs—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 To WAN 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 going out to a computer or to another switch Wire cord going out 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 Bank has multiple facilities connected by multiple WANs Bank has multiple facilities connected by 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. LAN WAN LAN Application Router

26 Figure 1-11: Internets Internet Components –All computers in an internet are called hosts Servers, clients, PDAs, cellphones, etc. Cat Internet 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., ) 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- E )

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 X Network Y Network Z R1 R2 Route A-B Packet A packet goes all the way across the internet; It’s path is its route A packet goes all the way 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) Packet

32 Figure 1-12: Internet with Three Networks Mobile Client Host Server Host Switch X2 Switch X1 Switch Router R1 D6-EE-92-5F-C1-56 Network X Route A-B A route is a packet’s path through the internet A route is a packet’s path through the internet Details in Network X Details in Network X Data link A-R1 Data link A-R1 A data Link is a frame’s path through its single network A data Link is a frame’s path through its single network In Network X, the Packet is Placed in Frame X Packet Frame X Host A AB-23-D1-A8-34-DD

33 Figure 1-12: Internet with Three Networks Router R1 Router R2 AF-3B-E B5 Packet Frame Y To Network X To Network Z Network Y Data Link R1-R2 Route A-B Details in Network Y Details in Network Y

34 Figure 1-12: Internet with Three Networks Host B B-CC-D4-A7-56 Mobile Client Host Switch Z1 Switch Z2 Switch Packet Frame Z Network Z Router R2 Router Data Link R2-B Details in Network Z Details in Network Z Mobile Client Computer

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

Figure 1-13: Converting IP Addresses into Dotted Decimal Notation Divided into 4 bytes. These are segments Dotted decimal notation (4 segments separated by dots) Dotted decimal notation (4 segments separated by dots) IP Address (32 bits long) Convert each byte to decimal (result will be between 0 and 255)* *The conversion process is described in the Hands On section at the end of the chapter

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’s Internet Service Provider Webserver’s Internet Service Provider ISP User PC Host Computer Webserver Host Computer NAP = Network Access Point Router NAP ISP Internet Backbone (Multiple ISP Carriers) Access Line Access Line

41 Figure 1-17: The Internet User PC’s Internet Service Provider Webserver’s Internet Service Provider ISP User PC Host Computer Webserver Host NAP = Network Access Point Router NAP ISP Internet Backbone (Multiple ISP Carriers) Access Line Access Line

42 Figure 1-18: Subnets in an Internet LAN 1 LAN 2 LAN Subnet 10.1.x.x WAN Subnet 123.x.x.x LAN Subnet x LAN Subnet 10.2.x.x LAN Subnet 10.3.x.x LAN Subnet x LAN Subnet x Note: Subnets are single networks (collections of switches, transmission lines) Router R1 Router R3 Router R4 Router R2 LAN Subnet x

43 Figure 1-19: Terminology Differences for Single- Network and Internet Professionals By Single-Network Professionals By Internet Professionals By Internet Professionals Single Networks Are Called Networks Subnets Internets Are Called Internets Networks 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 PC A3-4E-CD F DHCP Server DHCP Request Message: “My 48-bit Ethernet address is A3-4E-CD F”. Please give me a 32-bit IP address.” Pool of IP Addresses

51 Figure 1-21: Dynamic Host Configuration Protocol (DHCP) Client PC A3-4E-CD F DHCP Server DHCP Response Message: “Computer at A3-4E-CD F, your 32-bit IP address is ”. (Usually other configuration parameters as well.) Pool of IP 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 ( ) – 子網路遮罩 ( ) – 預設通訊閘 ( ) – 領域名稱伺服器 ( ) –… winipcfg (Win 98/Me) ipconfig /all (Win 2000/XP)

控制台  網路和網際網路連線

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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 NameIP Address…… Voyager.cba.hawaii.edu … Host NameIP Address…… Voyager.cba.hawaii.edu … DNS Table 1. Client Host wishes to reach Voyager.cba.hawaii.edu; Needs to know its IP Address 2. Sends DNS Request Message “The host name is Voyager.cba.hawaii.edu” Voyager.cba.hawaii.edu Local DNS Host

57 Figure 1-22: The Domain Name System (DNS) Host NameIP Address…… Voyager.cba.hawaii.edu … Host NameIP Address…… Voyager.cba.hawaii.edu … DNS Table 4. DNS Response Message “The IP address is ” Voyager.cba.hawaii.edu Client sends packets to DNS Host looks up IP address DNS Host

58 Figure 1-22: The Domain Name System (DNS) Host NameIP Address…… Voyager.cba.hawaii.edu … Host NameIP Address…… Voyager.cba.hawaii.edu … DNS Table Client Host 1. DNS Request Message Anther DNS Host Local DNS Host 3. DNS Response Message The local DNS host sends back the response; the user is unaware that other DNS hosts were involved The local DNS host sends back the response; the user is unaware that other DNS hosts were involved If local DNS host does not have the target host’s IP address, it contacts other DNS hosts to get the IP address If local DNS host does not have the target host’s IP address, it contacts other DNS hosts to get the IP address 2. Request & Response

59 NCNU Campus Network DHCP Server DNS Server Proxy Servers TANet HiNet Web Filter (1) (2) (3) (4) (5) Example: Web Browsing Router Switch

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62 nslookup

4. Packet Switching vs. Circuit Switching

64 A Simple Switching Network Station Node

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 Packet Switching: Virtual-Circuit Approach

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?