How the Internet Works? ( TCP/IP, DNS, HKIX ) CSC1720 Introduction to Internet Essential Materials
How computers send data? Channel Protocol Connection method Address CSC1720 Introduction to Internet 2
Outline Internet Hardware Modem, Wired, Hubs, Switches Basic Internet Structure Postal service analogy Internet Software IP address, Subnets Network Protocol DNS, WINS and Domains HKIX and HARNET CSC1720 Introduction to Internet 3
Communication Channel what kind of media? Telephone line (Twist pair, Optical fiber) Modulator-Demodulator (Modem( Modem) Digital Subscriber Line (DSL( DSL) Cable modem Satellite, Microwave Wireless connection (IR, RF) CSC1720 Introduction to Internet 4
Different medium Twisted pair RJ45 connector Coaxial cable BNC connector Fiber optic cable Different cabling length Optic > coaxial > Twisted pair CSC1720 Introduction to Internet 5
Use Modem Digital data - 10101010101 Telephone line Analog data Modulation / De-modulation E.g. CU Dialup Pool (56kbps max.) CSC1720 Introduction to Internet 6
Use Digital Subscriber Line (DSL) Traditional phone line ADSL modem Why ADSL? CSC1720 Introduction to Internet 7
Why ADSL? Asymmetric DSL A slower upstream (upload) can trade off a faster downstream (download) speed. 128 to 640 kbps (upstream) 1.5M to 5M bps (downstream) E.g. PCCW - Netvigator CSC1720 Introduction to Internet 8
Use Cable Modems Use coaxial cable to carry TV signal and High speed Internet access CSC1720 Introduction to Internet 9
Satellite & Microwave Satellite systems Use satellites orbiting above the Earth to relay signals from one part of a WAN to another, cause 0.5 to 5 sec delays. Microwave Costly to install but cheaper than satellite. It is very useful for connecting networks that are separated by a barrier, such as a highway or a lake. CSC1720 Introduction to Internet 10
Use Cellular Phone / Palm Mobile computing Latest technology Bluetooth A wireless technology CSC1720 Introduction to Internet 11
Using A Computer To Interconnect Networks Special-purpose purpose computers are used to interconnect networks. Using standard hardware (CPU, memory, and network interfaces) Running special-purpose purpose software CSC1720 Introduction to Internet 12
Network Interface Card NIC Physically connects a computer to the transmission medium on a network. What is device driver? NIC comes with different drivers for different types of operating systems. A driver is the software that allows the operating system to communicate with the network interface card. What is the major difference between an expensive, 3Com, and a cheap, Filand,, NIC? CSC1720 Introduction to Internet 13
Hardware/Physical/MAC (Media Access Control) address When a NIC is manufactured, the card is given a unique hardware address. It never changes. CSC1720 Introduction to Internet 14
Routers Interconnecting computers are called routers by using the same protocol. Determining where to send packets Router CSC1720 Introduction to Internet 15
Hubs A network cable connects a computer via a network card to a hub. Provides a central location. CSC1720 Introduction to Internet 16
Ports A hub contains sockets or ports. Some LED indicates information transferred through the port. CSC1720 Introduction to Internet 17
Ethernet Repeater A repeater is a device that strengthens and retransmits signals on a network. CSC1720 Introduction to Internet 18
Network Architecture It refers how information transfers on networks. Ethernet It the most popular architecture used to build networks. Least expensive and easiest to setup Token-ring architecture It was developed by IBM in 1984. They are popular found in large organizations, such as banks and insurance companies. Others: ARCnet,, AppleTalk, CSC1720 Introduction to Internet 19
Ethernet & Token Ring Ethernet, Fast Ethernet, Gigabit Ethernet (transmit data at 1Gbps). CSC1720 Introduction to Internet 20
Postal Services You have to write a complete address on the envelope specifying the country, state, city, district, street,, and so on. After put the letter put into the mailbox, it will be delivered (routed) to its destination in a hierarchical way. HK Post Office knows the letter is sent to US, without concerning the actual address to be routed within US. CSC1720 Introduction to Internet 21
Basic Internet Structure The Internet works in a similar way as postal services. Roughly speaking, you may consider US, UK, HK, China and so on, as individual networks connecting to each other. Each network is further divided into smaller sub- networks such as CUHK, HKU, UST, and so on. CUHK has its academic departments, etc. The different pieces of the Internet are connected by a set of computers (Gateways) Translates between protocols CSC1720 Introduction to Internet 22
Basic Internet Structure (depicted) CSC1720 Introduction to Internet 23
Postage over the Internet When delivering information via the Internet, the information is split into small units called data packets (1500 byte each) When a packet is sent from US to a particular host in CUHK. The packet is first delivered to Hong Kong, then is further transmitted to CUHK, then is further transmitted to the appropriate department, finally arrived to the specific host. The data is reassembled at the destination. The data packet is continuously being switched from the source to destination. The Internet is said to be Packet Switching Network. CSC1720 Introduction to Internet 24
Packet Switching Network CSC1720 Introduction to Internet 25
Packet switching example Figure 16.1 An example internet with four networks connected by routers. Figure 16.2 Cars from two roads merging onto another road are analogous to packets from two networks merging onto a third network. CSC1720 Introduction to Internet 26
IP address Each host in the Internet is assigned to a specific and unique number for identification. This number is called the IP address of the specific host. This number is divided into 4 parts for improving the readability. The range of each number is between 0 and 255. E.g. 0.0.0.0 255.255.255.255 For example, the host orchid.cse.cuhk.edu.hk has has its IP address of 137.189.91.60 CSC1720 Introduction to Internet 27
Network Number / Host Number IP addresses are split into 2 parts A network number + a host number For example, 137.189 is the network number of CUHK, 91.60 is the host number of the host orchid.cse.cuhk.edu.hk Network numbers are assigned by a central authority, the Internet Corporation for Assigned Names and Numbers (ICANN). CSC1720 Introduction to Internet 28
Network Classes There are 5 classes of IP address Class A comprises networks 1.0.0.0 to 127.255.255.255, the network address is in first quad. It allows roughly 16 million hosts per network. Class B comprises network 128.0.0.0 to 191.255.255.255, the network address is in the first two quads. It allows for 16,382 networks with up to 64K hosts. CSC1720 Introduction to Internet 29
Network Classes Class C comprises networks 192.0.0.0 to 223.255.255.255, with the network number contained in the first three quads. It allows about 2 million networks with up to 254 hosts in each network. Class D and E are falling into the range of 224.0.0.0 to 254.0.0.0 which are reserved for multicast address and for special purpose use. CSC1720 Introduction to Internet 30
Subnet The Internet is structured hierarchically. CUHK consists of many academic departments and administrative bodies. IP allows you to subdivide a network into several subnets. E.g. CSE and CSC are two subnets inside CUHK. Each subnet is identified by a subnet number. E.g. we have a different way to interpret the IP address 137.189.91.60 137.189 refers to the network number of CUHK, 91 refers to the subnet number of CSE, 60 refers to the host number of orchid. CSC1720 Introduction to Internet 31
Subnet example in CUHK CSC1720 Introduction to Internet 32
Subnet Mask 252 254 = 1111 1100 1111 1110 CSC1720 Introduction to Internet 33
Dynamic Host Configuration Protocol (DHCP) A Protocol for assigning dynamic IP address to devices on a network. It is built on client and server models. Server is the machine running DHCPD. Client can be any network devices. Advantage? Eliminates manual configuration of network parameters and utilizes the use of IP address CSC1720 Introduction to Internet 34
IP Routing The process of transmitting a data packet from the source to the destination via a series of intermediate stations is called Routing. IP routing works as follow: Each data packet is labeled with IP address of the destination host 137.189.90.184 1500 bytes Data here CSC1720 Introduction to Internet 35
IP Packet Includes Header, payload, data CSC1720 Introduction to Internet 36
Packets Are Not The Same Size Packets may be any size up to the maximum. Can be as small as a single keystroke Can be larger, depending on application CSC1720 Introduction to Internet 37
IP Routing For example, when a packet is routing to orchid.cse.cuhk.edu.hk (137.189.91.60), the network number is extracted as 137.189 which is the network number of CUHK. The packet is then sent to HK and then to CUHK. Inside CUHK, the subnet number is examined and it is 91 which is the subnet number of CSE. Then it is sent to CSE. Inside CSE, the host number is examined and it is 60 which is the host number of orchid. Finally, it is routed to the destination. CSC1720 Introduction to Internet 38
IP enough for routing? A single packet is limited in length, usually 1-15001 1500 bytes. Network may lose packets, or damage the data in transit. Packets may arrive out of sequence (different routing path). TCP is used to solve the problems. CSC1720 Introduction to Internet 39
Protocol and Addressing To communicate over the Internet, the computers must: use a common language or a protocol to govern the exchange of messages. have a way to address one another. Protocol: specifies exact format, order of messages sent and received among network entities, and actions taken on message transmission and receipt. Addressing: defines where to deliver the messages. CSC1720 Introduction to Internet 40
Protocol and Addressing TCP/IP model CSC1720 Introduction to Internet 41
Protocol and Addressing Internet has a large collections of protocols organized in a layering model. Application: : enables the user, whether human or software, to access the network. Transport: : responsible for source-to to-destination (end-to to-end) data transfer. Network: : responsible for routing packets from source-to to-dest across multiple networks. Data link: : responsible for data transfer between neighboring network elements. Physical: : coordinates the functions required to transmit a bit stream over a physical medium. CSC1720 Introduction to Internet 42
Protocol and Addressing Lower layer adds header to the data from upper layer. Header includes addressing and other fields. L5 data L5 data CSC1720 Introduction to Internet 43
Protocol Stack - Open Systems Interconnection (OSI) model CSC1720 Introduction to Internet 44
Protocol and Addressing TCP/IP Protocol Suite. CSC1720 Introduction to Internet 45
What is TCP/IP? TCP would be in charge of the breaking up the packets and messages then reassembling them at the destination, and the IP would be responsible for transmitting the individual packets.. For example: the TCP protocol would split up the letter and place it into multiple envelops, while the IP protocol would be in charge of addressing the envelop and making sure it arrived at its proper destination. from Where Wizards Stay Up Late CSC1720 Introduction to Internet 46
TCP/IP A protocol is a collection of rules for formatting, ordering, and error-checking data sent across a network. In 1974, Vincent Cerf and Robert Kahn developed the Transmission Control Protocol (TCP) which was further split into the Internet Protocol (IP) and TCP in 1978. In 1982, DoD adopted TCP/IP as the standard protocol in the Internet. Because the significance of TCP/IP in the history of the Internet, Cerf and Kahn are considered to be the Father of the Internet. CSC1720 Introduction to Internet 47
Transmission Control Protocol - TCP Basic functions Decompose a lengthy data into multiple packets for transmission Error detection, ensure validity Packet loss? No problem, packet retransmission CSC1720 Introduction to Internet 48
Sequence Numbers TCP breaks the information into multiple packets. Each packet is associated with a sequence number for identification. 137.189.90.184 Number 1 Data here 137.189.90.184 Number 2 Data here 137.189.90.184 Number 3 Data here Each packet is individually routed in the Internet, and arrive in random order. The data is reassembled in the correct order according to the sequence number. CSC1720 Introduction to Internet 49
Packet Retransmission A packet may be lost during the transmission across the Internet (host down, link failure, ) When the destination host has been waiting for a particular packet for a certain time (timeout), it will request the source host to retransmit the packet. There is no need to retransmit all data packets. Instead, only the missing packet, which is identified by the sequence number, needs to be retransmitted. CSC1720 Introduction to Internet 50
Error detection - Checksums Transmission errors occur even if a data packet is received by the destination successfully. How to ensure the data is correctly received? A method to detect possible transmission errors. At the destination, checksum is recalculated based on the received data. The attached checksum and the newly calculated checksum are compared. Mismatch means there is transmission errors occurred. CSC1720 Introduction to Internet 51
IPv6 (IP version 6) Major changes: More addresses IP address size from 32 bits to 128 bits Simplified IP headers Reduction of header fields in IP packet Added security features CSC1720 Introduction to Internet 52
IPX/SPX Protocol IPX/SPX makes up the protocol suite that is used to transfer information on networks running the Novell NetWare operating system. Internetwork Packet Exchange (IPX) - Transfer information between devices. Sequenced Packet Exchange (SPX) - An extension of the IPX protocol. CSC1720 Introduction to Internet 53
NetBEUI Protocol NetBIOS Extended User Interface Is a network protocol used on small local area networks. A very small and efficient protocol, use little computer resources. NetBIOS Network Basic Input/ nput/output utput System Develop by IBM and allow computers to communicate with each other on a network. CSC1720 Introduction to Internet 54
Why DNS? What is DNS? Domain Name System IP address is difficult to remember. 137.189.92.1 is which machine? Names are given to each computer on the Internet for the convenience of human users. Besides IP addresses, all internet applications allow users to use computer names. CSC1720 Introduction to Internet 55
Computer names on the NET How does it look like? DNS administrators is responsible to name computers/group in their own subnet. Each level of responsibility is called a domain. Domains are separated by dots cse.cuhk.edu.hk www.intel.com CSC1720 Introduction to Internet 56
Domain name and Host name Each domain can create or change whatever belongs to it. CUHK can create any new domain, cse CSE can buy a new computer and name it as robin, orchid, any other name. Two computers may have the same name if they are in different domains. orchid.cse.cuhk.edu.hk orchid.ie.cuhk.edu.hk CSC1720 Introduction to Internet 57
Domain Name System (DNS) Each node in the tree has a label - a string with a maximum of 63 characters. a domain name - a sequence of labels separated by dots. CSC1720 Introduction to Internet 58
How does DNS work? DNS server = DNS service? CSC1720 Introduction to Internet 59
Domain Example - CUHK CSC1720 Introduction to Internet 60
IP vs Domain Name CSC1720 Introduction to Internet 61
Most Common hostname Figure 18.1 The fifty most common names assigned to computers on the Internet in 2000. CSC1720 Introduction to Internet 62
Top Level Domains The Internet Corporation for Assigned Names and Numbers (ICANN) define the Top Level Domains. CSC1720 Introduction to Internet 63
ISO 3166 Country Codes Partial list Full list CSC1720 Introduction to Internet 64
Windows Internet Naming Service (WINS) Like DNS, WINS also resolves names and IP addresses except that the look up by WINS is specific for Windows computers. Dynamic Win2k use DNS to replace WINS CSC1720 Introduction to Internet 65
HKIX Hong Kong Internet exchange http://www.hkix.net Operated by Information Technology Services Centre (ITSC) of CUHK interconnect the Internet Access Providers (IAPs( IAPs) ) in Hong Kong No need to route via US for local connections. CSC1720 Introduction to Internet 66
HARNET Why? Connect 7 Universities. Manage by the Joint Universities Computer Centre (JUCC) CSC1720 Introduction to Internet 67
HARNET configuration Try this link: http://www.cuhk.edu.hk/hkix/harnet www.cuhk.edu.hk/hkix/harnet/ CSC1720 Introduction to Internet 68
HARNET in CUHK HARNET connect to US is 12M and a connection of 5M to HKT as backup. Our connection to HARNET is dual 12Mbps. With the following additional connections: a secondary link to Hong Kong Telecom Netplus which is 2Mbps inbound and 10Mbps outbound shared with other projects, Internet services for CUHK alumni and SchoolNet; a third link provided by UUNET (Worldcom( Worldcom) ) which is 2Mbps inbound & outbound; and a direct ATM/155Mbps connection to Hong Kong Internet exchange (HKIX), which was set up and is operated by ITSC of CUHK CSC1720 Introduction to Internet 69
Summary What should be considered if you install or update a network? Plan: : the size, the budget Determine: : the network design Select: : the transmission media Choose: : the network hardware, devices Install: : the network OS, drivers Configure: : server & client computers Test: : the final network Maintain: : the network reliability, admin CSC1720 Introduction to Internet 70
References Computer Networks A. S. Tanenbaum (Prentice Hall) The End. Thank you for your patience! CSC1720 Introduction to Internet 71