[學習]網(wǎng)際網(wǎng)路協(xié)定基礎(chǔ)介紹

1、網(wǎng)際網(wǎng)路協(xié)定基礎(chǔ)介紹,Data Communications and Computer Networks: A Business User’s ApproachFifth Edition (Chap 10),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,2,,Internet Protocols,To s

2、upport the Internet and all its services, many protocols are necessarySome of the protocols that we will look at:Internet Protocol (IP)Transmission Control Protocol (TCP)Address Resolution Protocol (ARP)Dynamic Host

3、 Configuration Protocol (DHCP)Network Address Translation (NAT),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,3,,,Internet Protocols (continued),Recall that the Internet with a

4、ll its protocols follows the TCP/IP protocol suite (Internet model)An application, such as e-mail, resides at the highest layerA transport protocol, such as TCP, resides at the transport layerThe Internet Protocol (IP

5、) resides at the Internet or network layerA particular media and its framing resides at the network access (or data link) layer,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,4,

6、,,Internet Protocols (continued),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,5,,,The Internet Protocol (IP),IP prepares a packet for transmission across the InternetThe IP he

7、ader is encapsulated onto a transport data packetThe IP packet is then passed to the next layer where further network information is encapsulated onto it,Data Communications and Computer Networks: A Business User's

8、Approach, Fifth Edition,6,,,,The Internet Protocol (IP) (continued),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,7,,,The Internet Protocol (IP) (continued),Using IP, a router:

9、Makes routing decisions based on the destination addressMay have to fragment the datagram into smaller datagrams (rare today) using Fragment OffsetMay determine that the current datagram has been hopping around the net

10、work too long and delete it (Time to Live),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,8,,,,The Internet Protocol (IP) (continued),Data Communications and Computer Networks: A

11、 Business User's Approach, Fifth Edition,9,,,The Transmission Control Protocol (TCP),TCP layer creates a connection between sender and receiver using port numbersThe port number identifies a particular application o

12、n a particular device (IP address)TCP can multiplex multiple connections (using port numbers) over a single IP line,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,10,,,The Trans

13、mission Control Protocol (TCP) (continued),The TCP layer can ensure that the receiver is not overrun with data (end-to-end flow control) using the Window fieldTCP can perform end-to-end error correctionChecksumTCP all

14、ows for the sending of high priority dataUrgent Pointer,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,11,,,,The Transmission Control Protocol (TCP) (continued),Data Communicati

15、ons and Computer Networks: A Business User's Approach, Fifth Edition,12,,,Internet Control Message Protocol (ICMP),ICMPUsed by routers and nodesPerforms error reporting for the Internet ProtocolICMP reports errors

16、 such as invalid IP address, invalid port address, and the packet has hopped too many times,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,13,,,User Datagram Protocol (UDP),A tra

17、nsport layer protocol used in place of TCPWhere TCP supports a connection-oriented application, UDP is used with connectionless applicationsUDP also encapsulates a header onto an application packet, but the header is m

18、uch simpler than TCP,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,14,,,Address Resolution Protocol (ARP),When an IP packet has traversed the Internet and encounters the destina

19、tion LAN, how does the packet find the destination workstation?Even though a destination workstation may have an IP address, a LAN does not use IP addresses to deliver frames A LAN uses MAC layer addressARP translate

20、s an IP address into a MAC layer address so the frame can be delivered to the proper workstation,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,15,,,Dynamic Host Configuration Pr

21、otocol (DHCP),An IP address can be assigned to a workstation permanently (static assignment) or dynamicallyDynamic IP address assignment is a more efficient use of scarce IP addressesWhen DHCP client issues an IP reque

22、st, DHCP server looks in its static tableIf no entry exists, the server selects an IP address from available pool,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,16,,,Dynamic Hos

23、t Configuration Protocol (DHCP) (continued),The address assigned by DHCP server is temporaryPart of agreement includes specific period of timeIf no time period specified, the default is one hourDHCP clients may negoti

24、ate for a renewal before the time period expires,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,17,,,Network Address Translation (NAT),NAT lets the router represent the entire lo

25、cal area network to the Internet as a single IP addressThus, all traffic leaving the LAN appears as originating from a global IP addressAll traffic coming into this LAN uses this global IP addressThis security feature

26、 allows a LAN to hide all the workstation IP addresses from the Internet,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,18,,,Network Address Translation (NAT) (continued),Since t

27、he outside world cannot see into the LAN, you do not need to use registered IP addresses on an inside LANWe can use the following blocks of addresses for private use:10.0.0.0 – 10.255.255.255172.16.0.0 – 172.31.255.25

28、5192.168.0.0 – 192.168.255.255,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,19,,,Network Address Translation (NAT) (continued),When a user on the inside sends a packet to the

29、outside, the NAT interface changes the user’s inside address to a global IP addressThis change is stored in a cacheWhen the response comes back, the NAT looks in cache and switches the addresses backIf not, the packet

30、 is droppedUnless NAT has a service table of fixed IP address mappingsThis service table allows packets to originate from the outside,Data Communications and Computer Networks: A Business User's Approach, Fifth Edi

31、tion,20,,,Tunneling Protocols and Virtual Private Networks (VPNs),The Internet is not normally a secure systemIf someone wants to use the Internet to access a corporate computer system, how can a secure connection be cr

32、eated?One possible technique is to create a virtual private network (VPN)VPN creates a secure connection through the Internet by using a tunneling protocol,Data Communications and Computer Networks: A Business User'

33、;s Approach, Fifth Edition,21,,,The World Wide Web,The World Wide Web (WWW) – immense collection of Web pages and other resources that can be downloaded across the Internet and displayed on a workstation via a Web browse

34、r and is the most popular service on the InternetBasic Web pages are created with the Hypertext Markup Language (HTML)Hypertext Transport Protocol (HTTP) is protocol to transfer a Web page,Data Communications and Compu

35、ter Networks: A Business User's Approach, Fifth Edition,22,,,Locating a Document on the Internet,Every document on the Internet has a unique Uniform Resource Locator (URL)All URLs consist of four parts:Service type

36、Host or domain nameDirectory or subdirectory informationFilename,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,23,,,,Locating a Document on the Internet (continued),Data Comm

37、unications and Computer Networks: A Business User's Approach, Fifth Edition,24,,,Locating a Document on the Internet (continued),When a user, running a Web browser, enters a URL, how is URL translated into an IP addr

38、ess?Domain Name System (DNS) – large, distributed database of URLs and IP addressesThe first operation performed by DNS is to query a local database for URL/IP address informationIf local server does not recognize add

39、ress, the server at next level will be queriedEventually root server for URL/IP addresses will be queriedIf root server has answer, results are returnedIf root server recognizes domain name but not extension in front

40、of domain name, root server will query server at domain name’s locationWhen domain’s server returns results, they are passed back through chain of servers (and their caches),Data Communications and Computer Networks: A

41、Business User's Approach, Fifth Edition,25,,,IP Addresses,All devices connected to Internet have 32-bit IP address associated with themThink of the IP address as a logical address (possibly temporary), while the 48-

42、bit address on every NIC is the physical, or permanent addressComputers, networks, and routers use the 32-bit binary address, but a more readable form is the dotted decimal notation,Data Communications and Computer Netw

43、orks: A Business User's Approach, Fifth Edition,26,,,IP Addresses (continued),For example, the 32-bit binary address10000000 10011100 00001110 00000111translates to128.156.14.7in dotted decimal notation,Dat

44、a Communications and Computer Networks: A Business User's Approach, Fifth Edition,27,,,Creating Web Pages (continued),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,28,,,Crea

45、ting Web Pages (continued),Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,29,,,Electronic Mail (E-Mail),E-mail programs can create, send, receive, and store e-mails, as well as r

46、eply to, forward, and attach non-text filesMultipurpose Internet Mail Extension (MIME) is used to send e-mail attachmentsSimple Mail Transfer Protocol (SMTP) is used to transmit e-mail messagesPost Office Protocol ver

47、sion 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrieve e-mail messages,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,30,,,File Transfer Pr

48、otocol (FTP),Used to transfer files across the InternetUser can upload or download a fileThe URL for an FTP site begins with ftp://…The three most common ways to access an FTP site are:Through a browserUsing a canne

49、d FTP programIssuing FTP commands at a text-based command prompt,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,31,,,Remote Login (Telnet),Allows a user to remotely log in to a

50、distant computer siteUser usually needs a login and password to access a remote computer siteUser saves money on long-distance telephone charges,Data Communications and Computer Networks: A Business User's Approach

51、, Fifth Edition,32,,,Voice Over IP,The transfer of voice signals using a packet-switched network and the IP protocolVoice over IP (VoIP) can be internal to a company (private VoIP) or can be external using the Internet

52、VoIP consumes many resources and may not always work well, but can be cost-effective in certain situations,Data Communications and Computer Networks: A Business User's Approach, Fifth Edition,33,,,Voice Over IP (cont

53、inued),Three basic ways to make a telephone call using VoIP:PC to PC using sound cards and headsets (or speakers and microphone)PC to telephone (need a gateway to convert IP addresses to telephone numbers)Telephone to