1、網(wǎng)際網(wǎng)路協(xié)定基礎介紹Data Communications and Computer Networks: A Business Users ApproachFifth Edition (Chap 10) 牛牛文庫文檔分享2Internet ProtocolsTo support the Internet and all its services, many protocols are necessarySome of the protocols that we will look at:Internet Protocol (IP)Transmission Control Protocol (T

2、CP)Address Resolution Protocol (ARP)Dynamic Host Configuration Protocol (DHCP)Network Address Translation (NAT) 牛牛文庫文檔分享3Internet Protocols (continued)Recall that the Internet with all its protocols follows the TCP/IP protocol suite (Internet model)An application, such as e-mail, resides at the high

3、est layerA transport protocol, such as TCP, resides at the transport layerThe Internet Protocol (IP) resides at the Internet or network layerA particular media and its framing resides at the network access (or data link) layer 牛牛文庫文檔分享4Internet Protocols (continued) 牛牛文庫文檔分享5The Internet Protocol (I

4、P)IP prepares a packet for transmission across the InternetThe IP header is encapsulated onto a transport data packetThe IP packet is then passed to the next layer where further network information is encapsulated onto it 牛牛文庫文檔分享6The Internet Protocol (IP) (continued) 牛牛文庫文檔分享7The Internet Protocol

5、 (IP) (continued)Using IP, a router: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 network too long and delete it (Time to Live) 牛牛文

6、庫文檔分享8The Internet Protocol (IP) (continued) 牛牛文庫文檔分享9The Transmission Control Protocol (TCP)TCP layer creates a connection between sender and receiver using port numbersThe port number identifies a particular application on a particular device (IP address)TCP can multiplex multiple connections (usi

7、ng port numbers) over a single IP line 牛牛文庫文檔分享10The Transmission 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 allows for the sending of hig

8、h priority dataUrgent Pointer 牛牛文庫文檔分享11The Transmission Control Protocol (TCP) (continued) 牛牛文庫文檔分享12Internet Control Message Protocol (ICMP)ICMPUsed by routers and nodesPerforms error reporting for the Internet ProtocolICMP reports errors such as invalid IP address, invalid port address, and the p

9、acket has hopped too many times 牛牛文庫文檔分享13User Datagram Protocol (UDP)A transport 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 much sim

10、pler than TCP 牛牛文庫文檔分享14Address Resolution Protocol (ARP)When an IP packet has traversed the Internet and encounters the destination 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 fram

11、es A LAN uses MAC layer addressARP translates an IP address into a MAC layer address so the frame can be delivered to the proper workstation 牛牛文庫文檔分享15Dynamic Host Configuration Protocol (DHCP)An IP address can be assigned to a workstation permanently (static assignment) or dynamicallyDynamic IP add

12、ress assignment is a more efficient use of scarce IP addressesWhen DHCP client issues an IP request, DHCP server looks in its static tableIf no entry exists, the server selects an IP address from available pool 牛牛文庫文檔分享16Dynamic Host Configuration Protocol (DHCP) (continued)The address assigned by D

13、HCP server is temporaryPart of agreement includes specific period of timeIf no time period specified, the default is one hourDHCP clients may negotiate for a renewal before the time period expires 牛牛文庫文檔分享17Network Address Translation (NAT)NAT lets the router represent the entire local area network

14、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 allows a LAN to hide all the workstation IP addresses from the Internet 牛牛文庫文檔分享18Network Address T

15、ranslation (NAT) (continued)Since the 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: 55 55 55 牛牛文庫文檔分享19Network Address Translation (NAT) (continued)When a user on the inside sends a

16、packet to the outside, the NAT interface changes the users 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 is droppedUnless NAT has a service table of fixed IP address mappings

17、This service table allows packets to originate from the outside 牛牛文庫文檔分享20Tunneling 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 created?One possible

18、 technique is to create a virtual private network (VPN)VPN creates a secure connection through the Internet by using a tunneling protocol 牛牛文庫文檔分享21The World Wide WebThe World Wide Web (WWW) immense collection of Web pages and other resources that can be downloaded across the Internet and displayed

19、on a workstation via a Web browser 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 牛牛文庫文檔分享22Locating a Document on the InternetEvery document on the Internet ha

20、s a unique Uniform Resource Locator (URL)All URLs consist of four parts:Service typeHost or domain nameDirectory or subdirectory informationFilename 牛牛文庫文檔分享23Locating a Document on the Internet (continued) 牛牛文庫文檔分享24Locating a Document on the Internet (continued)When a user, running a Web browser,

21、enters a URL, how is URL translated into an IP address?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 address, the server at next level wil

22、l 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 of domain name, root server will query server at domain names locationWhen domains server returns results, they are p

23、assed back through chain of servers (and their caches) 牛牛文庫文檔分享25IP AddressesAll 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-bit address on every NIC is the physical, or permanent addressComp

24、uters, networks, and routers use the 32-bit binary address, but a more readable form is the dotted decimal notation 牛牛文庫文檔分享26IP Addresses (continued)For example, the 32-bit binary address10000000 10011100 00001110 00000111translates toin dotted decimal notation 牛牛文庫文檔分享27Creating Web Pages (continu

25、ed) 牛牛文庫文檔分享28Creating Web Pages (continued) 牛牛文庫文檔分享29Electronic Mail (E-Mail)E-mail programs can create, send, receive, and store e-mails, as well as reply to, forward, and attach non-text filesMultipurpose Internet Mail Extension (MIME) is used to send e-mail attachmentsSimple Mail Transfer Proto

26、col (SMTP) is used to transmit e-mail messagesPost Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrieve e-mail messages 牛牛文庫文檔分享30File Transfer Protocol (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 brows