1、網際網路協定基礎介紹Data Communications and Computer Networks: A Business Users ApproachFifth Edition (Chap 10)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition2Internet Protocols To support the Internet and all its services, many protocols are necessary Some of the protocols
2、 that we will look at: Internet Protocol (IP) Transmission Control Protocol (TCP) Address Resolution Protocol (ARP) Dynamic Host Configuration Protocol (DHCP) Network Address Translation (NAT)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition3Internet Protocols (cont
3、inued) 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 highest layer A transport protocol, such as TCP, resides at the transport layer The Internet Protocol (IP) resides at the Internet or network layer
4、 A particular media and its framing resides at the network access (or data link) layerData Communications and Computer Networks: A Business Users Approach, Fifth Edition4Internet Protocols (continued)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition5The Internet Pro
5、tocol (IP) IP prepares a packet for transmission across the Internet The IP header is encapsulated onto a transport data packet The IP packet is then passed to the next layer where further network information is encapsulated onto itData Communications and Computer Networks: A Business Users Approach
6、, Fifth Edition6The Internet Protocol (IP) (continued)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition7The Internet Protocol (IP) (continued) Using IP, a router: Makes routing decisions based on the destination address May have to fragment the datagram into smaller
7、 datagrams (rare today) using Fragment Offset May determine that the current datagram has been hopping around the network too long and delete it (Time to Live)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition8The Internet Protocol (IP) (continued)Data Communications
8、 and Computer Networks: A Business Users Approach, Fifth Edition9The Transmission Control Protocol (TCP) TCP layer creates a connection between sender and receiver using port numbers The port number identifies a particular application on a particular device (IP address) TCP can multiplex multiple co
9、nnections (using port numbers) over a single IP lineData Communications and Computer Networks: A Business Users Approach, Fifth Edition10The 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
10、field TCP can perform end-to-end error correction Checksum TCP allows for the sending of high priority data Urgent PointerData Communications and Computer Networks: A Business Users Approach, Fifth Edition11The Transmission Control Protocol (TCP) (continued)Data Communications and Computer Networks:
11、 A Business Users Approach, Fifth Edition12Internet Control Message Protocol (ICMP) ICMP Used by routers and nodes Performs error reporting for the Internet Protocol ICMP reports errors such as invalid IP address, invalid port address, and the packet has hopped too many timesData Communications and
12、Computer Networks: A Business Users Approach, Fifth Edition13User Datagram Protocol (UDP) A transport layer protocol used in place of TCP Where TCP supports a connection-oriented application, UDP is used with connectionless applications UDP also encapsulates a header onto an application packet, but
13、the header is much simpler than TCPData Communications and Computer Networks: A Business Users Approach, Fifth Edition14Address 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
14、 a destination workstation may have an IP address, a LAN does not use IP addresses to deliver frames A LAN uses MAC layer address ARP translates an IP address into a MAC layer address so the frame can be delivered to the proper workstationData Communications and Computer Networks: A Business Users A
15、pproach, Fifth Edition15Dynamic Host Configuration Protocol (DHCP) An IP address can be assigned to a workstation permanently (static assignment) or dynamically Dynamic IP address assignment is a more efficient use of scarce IP addresses When DHCP client issues an IP request, DHCP server looks in it
16、s static table If no entry exists, the server selects an IP address from available poolData Communications and Computer Networks: A Business Users Approach, Fifth Edition16Dynamic Host Configuration Protocol (DHCP) (continued) The address assigned by DHCP server is temporary Part of agreement includ
17、es specific period of time If no time period specified, the default is one hour DHCP clients may negotiate for a renewal before the time period expiresData Communications and Computer Networks: A Business Users Approach, Fifth Edition17Network Address Translation (NAT) NAT lets the router represent
18、the entire local area network to the Internet as a single IP address Thus, all traffic leaving the LAN appears as originating from a global IP address All traffic coming into this LAN uses this global IP address This security feature allows a LAN to hide all the workstation IP addresses from the Int
19、ernetData Communications and Computer Networks: A Business Users Approach, Fifth Edition18Network Address Translation (NAT) (continued) Since the outside world cannot see into the LAN, you do not need to use registered IP addresses on an inside LAN We can use the following blocks of addresses for pr
20、ivate use: 10.0.0.0 10.255.255.255 172.16.0.0 172.31.255.255 192.168.0.0 192.168.255.255Data Communications and Computer Networks: A Business Users Approach, Fifth Edition19Network Address Translation (NAT) (continued) When a user on the inside sends a packet to the outside, the NAT interface change
21、s the users inside address to a global IP address This change is stored in a cache When the response comes back, the NAT looks in cache and switches the addresses back If not, the packet is dropped Unless NAT has a service table of fixed IP address mappings This service table allows packets to origi
22、nate from the outsideData Communications and Computer Networks: A Business Users Approach, Fifth Edition20Tunneling Protocols and Virtual Private Networks (VPNs) The Internet is not normally a secure system If someone wants to use the Internet to access a corporate computer system, how can a secure
23、connection be created? One possible technique is to create a virtual private network (VPN) VPN creates a secure connection through the Internet by using a tunneling protocolData Communications and Computer Networks: A Business Users Approach, Fifth Edition21The World Wide Web The World Wide Web (WWW
24、) immense collection of Web pages and other resources that can be downloaded across the Internet and displayed on a workstation via a Web browser and is the most popular service on the Internet Basic Web pages are created with the Hypertext Markup Language (HTML) Hypertext Transport Protocol (HTTP)
25、is protocol to transfer a Web pageData Communications and Computer Networks: A Business Users Approach, Fifth Edition22Locating 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 Host or domain name Direc
26、tory or subdirectory information FilenameData Communications and Computer Networks: A Business Users Approach, Fifth Edition23Locating a Document on the Internet (continued)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition24Locating a Document on the Internet (conti
27、nued) When a user, running a Web browser, enters a URL, how is URL translated into an IP address? Domain Name System (DNS) large, distributed database of URLs and IP addresses The first operation performed by DNS is to query a local database for URL/IP address information If local server does not re
28、cognize address, the server at next level will be queried Eventually root server for URL/IP addresses will be queried If root server has answer, results are returned If root server recognizes domain name but not extension in front of domain name, root server will query server at domain names locatio
29、n When domains server returns results, they are passed back through chain of servers (and their caches)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition25IP Addresses All devices connected to Internet have 32-bit IP address associated with them Think of the IP addre
30、ss as a logical address (possibly temporary), while the 48-bit address on every NIC is the physical, or permanent address Computers, networks, and routers use the 32-bit binary address, but a more readable form is the dotted decimal notationData Communications and Computer Networks: A Business Users
31、 Approach, Fifth Edition26IP Addresses (continued) For example, the 32-bit binary address10000000 10011100 00001110 00000111translates to128.156.14.7in dotted decimal notationData Communications and Computer Networks: A Business Users Approach, Fifth Edition27Creating Web Pages (continued)Data Commu
32、nications and Computer Networks: A Business Users Approach, Fifth Edition28Creating Web Pages (continued)Data Communications and Computer Networks: A Business Users Approach, Fifth Edition29Electronic Mail (E-Mail) E-mail programs can create, send, receive, and store e-mails, as well as reply to, fo
33、rward, and attach non-text files Multipurpose Internet Mail Extension (MIME) is used to send e-mail attachments Simple Mail Transfer Protocol (SMTP) is used to transmit e-mail messages Post Office Protocol version 3 (POP3) and Internet Message Access Protocol (IMAP) are used to hold and later retrie
34、ve e-mail messagesData Communications and Computer Networks: A Business Users Approach, Fifth Edition30File Transfer Protocol (FTP) Used to transfer files across the Internet User can upload or download a file The URL for an FTP site begins with ftp:/ The three most common ways to access an FTP site
35、 are: Through a browser Using a canned FTP program Issuing FTP commands at a text-based command promptData Communications and Computer Networks: A Business Users Approach, Fifth Edition31Remote Login (Telnet) Allows a user to remotely log in to a distant computer site User usually needs a login and
36、password to access a remote computer site User saves money on long-distance telephone chargesData Communications and Computer Networks: A Business Users Approach, Fifth Edition32Voice Over IP The transfer of voice signals using a packet-switched network and the IP protocol Voice over IP (VoIP) can b
37、e internal to a company (private VoIP) or can be external using the Internet VoIP consumes many resources and may not always work well, but can be cost-effective in certain situationsData Communications and Computer Networks: A Business Users Approach, Fifth Edition33Voice Over IP (continued) 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 telephone (need gateways)
