Chapter 1 Introduction
Services and Application of Communication Networks Data Communications Network Architectures Internet Standards
Wireless System Lab, NCNU 1 Chapter 1 Introduction
Services and Applications of Communication Networks
Wireless System Lab, NCNU 2 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
E-mail server Exchange of text messages via servers
Wireless System Lab, NCNU 3 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
Web Browsing
Web server Retrieval of multimedia (text, images, audio, and video) information from web servers
Wireless System Lab, NCNU 4 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
Instant Messaging (MSN, Skype)
Direct exchange of text messages
Wireless System Lab, NCNU 5 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
Telephone
Real-time bidirectional voice exchange
Wireless System Lab, NCNU 6 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
Cell phone
Real-time voice exchange with mobile users
Wireless System Lab, NCNU 7 Communication Services & Applications
Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service.
Short Message Service
Fast delivery of short text messages
Wireless System Lab, NCNU 8 Many Other Examples!
Peer-to-peer applications BT, Emule, Foxy file exchange Audio & video streaming Network games On-line commerce Text messaging by PDAs, cell phones (SMS) Voice-over-Internet (VoIP) ……
All these build on the Communication Networks. Communication Networks 與我們的生活息息相關!
9 Wireless System Lab, NCNU 9 Some Important Concepts
What is communication services? applications? Services (服務): basic information transfer capability Internet transfer of individual information Internet reliable transfer of a stream of bytes Real-time transfer of a voice signal
Applications (應用): build on communication service E-mail & WEB build on reliable network service FAX and modems build on basic telephone service
Emerging applications build on multiple network services SMS builds on reliable Internet service and cellular telephone text messaging
Wireless System Lab, NCNU 10 What is Communication Network?
Communication What a wonderful Network cloud!
Includes equipments (hardware & software) and facilities to provide the basic communication service Virtually invisible to the user; Usually represented by a cloud
Equipments (設備) Facilities (設施) Routers, servers, Copper wires, coaxial switches, multiplexers, cables, optical fiber hubs, modems, … How are communication networks designed and operated?
Wireless System Lab, NCNU 11 Communication Network Architecture
Network architecture: a plan that specifies how the network is built and operated
Architecture is driven by the network services
Overall communication process is complex
Network architecture conceptually partitions all communication processes into separate functional areas called layers
Evolution of communication network architecture: telegraph, telephone, and computer networks
Wireless System Lab, NCNU 12 Information Exchange Evolution 百億倍(1011)於 1850 1.0E+14
1.0E+12 ?
1.0E+10
1.0E+08
1.0E+06
per second per 1.0E+04
Informationtransfer 1.0E+02
1.0E+00 1850 1875 1900 1925 1950 1975 2000
Next Telegraph Telephone Internet, Optical Generation networks networks & Wireless networks Internet
Wireless System Lab, NCNU 13 Network Architecture Evolution
Telegraph Networks
Message switching & digital transmission Telephone Networks
Circuit Switching
Analog transmission → digital transmission
Fixed → mobile communications Internet
Packet switching & computer applications Next-Generation Internet
Multiservice packet switching network
Wireless System Lab, NCNU 14 Chapter 1 Introduction
Data Communications and Networks
Wireless System Lab, NCNU 15 1-1 Data Communications
Telecommunication: communication at a distance, including telephone, telegraph, and TV. Tele is Greek for "far“. Data: information presented in whatever form is agreed upon by the parties creating and using the data Data communications: the exchange of data between two devices via some form of transmission medium such as a wire cable, wireless …
Wireless System Lab, NCNU 16 Performance of Data Communications
Data delivery: send data to the correct destination (throughput (Mb/s)) Accuracy: receive data correctly (BER, PER). Timeliness: send data in a timely manner. Delay: voice needs real-time transmissions (150 ms~300 ms). Jitter: delay variation.
Some packets arrive with 30-ms delay and others with 40- ms delay.
Video stream (eg, IPTV) needs small-jitter transmissions.
Wireless System Lab, NCNU 17 Five Components of Data Communications
1. Sender. 2. Receiver. 3. Message: text, digitals, images, audio, and video.
4. Transmission media: the physical path by which a message travels from sender to receiver.
5. Protocol: a set of rules govern data communications. (開車靠左邊、靠右邊。紅燈右轉。)
Which one is your major study area?
Wireless System Lab, NCNU 18 Data Flow Types
Simplex Half-duplex Full-duplex
Wireless System Lab, NCNU 19 Simplex
Unidirectional, as on a one-way street. Only one device uses the entire capacity to send data in one direction. Examples? Examples: broadcast, TV, input, output, keyboards and monitors.
Wireless System Lab, NCNU 20 Half-Duplex
Bidirectional, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive. Examples? Examples: walkie-talkies, ham radio.
Wireless System Lab, NCNU 21 Full-Duplex
Bidirectional, both stations can transmit and receive simultaneously (like a two-way street with both direction traffic). Transmissions in two directions share the whole channel capacity. The full-duplex mode is used when two devices want to send and receive all the time. Examples? Examples: telephone, video conferencing.
Wireless System Lab, NCNU 22 Chapter 1 Introduction
Network Architectures
Wireless System Lab, NCNU 23 1-2 Networks
Network: a set of devices (often referred to as nodes) connected by communication links Node: can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes Most networks are distributed processing Network criteria
Performance: throughput, delay
Reliability (可靠度)
Security (安全性)
Wireless System Lab, NCNU 24 Physical Structures of Networks
Types of Connections:
Point-to-Point (點對點)
Multipoint/Multidrop (點對多點)
• Microwave or satellite links • TV remote control • ADSL.
• Medium is shared by multiple nodes. • Ethernet connected by coaxial cables. • Cable modem.
Wireless System Lab, NCNU 25 Physical Topology (拓墣)
Wireless System Lab, NCNU 26 A Fully Connected Mesh Topology
Fully-connected: Each nodes is connected to each other. Better reliability, security and privacy. However, each node needs (n-1) ports. n(n - 1)/2 duplex physical links are needed for fully connection. Expensive. Backbone connections between regional networks.
Wireless System Lab, NCNU 27 A Star Topology
Each device has a link only to a central controller (hub). The controller acts as an exchange. Less expensive, one port and one connection for a node. Robustness issue:
One link failure only affects one node.
However, if the hub goes down, the whole system is dead.
Wireless System Lab, NCNU 28 A Bus Topology
Only one backbone is needed to connect all the nodes. Less expensive. A fault or break in the bus cable stops all transmission, even between devices on the same side.
The damaged area reflects signals back in the direction of origin, thereby creating noise. (Cable end is needed.) Difficult recovery and fault isolation. (需要查線)
Wireless System Lab, NCNU 29 A Ring Topology
Only one backbone is needed to connect all the nodes. Repeater can amplify the signal along the ring. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Fault recovery is easy. Unidirectional traffic can be a disadvantage. A break in the ring disables the entire network.
Dual ring can overcome this issue.
Wireless System Lab, NCNU 30 A Hybrid Topology
Star + bus
Wireless System Lab, NCNU 31 Categories of Networks
Local area network (LAN): Less than 2 miles. Metropolitian area network (MAN): Metropolitan wide, tens of miles. Wide area network (WAN): Worldwide. Router WAN Switch Switch Router WAN Router Gateway Router Ethernet LAN Switch Hub Hub Switch MAN Hub BS
Switch Ring LAN Wireless LAN
Wireless System Lab, NCNU 32 An Isolated LAN Connecting Computers to a Hub
The most common LAN topologies are bus, ring, and star. Mesh topology is too expensive. Examples: Labs, offices, department.
Wireless System Lab, NCNU 33 Wide Area Networks (WANs)
Long-distance transmission over large geographic areas (a country, a continent, or even the whole world).
Switched WAN
Point-to-point WAN
Wireless System Lab, NCNU 34 Wide Area Networks (WANs)
Switched WAN
Usually as the backbones that connect many networks.
Switched WAN connects the end systems (e.g., a router (internetworking connecting device) to another LAN or WAN).
Examples: TANET.
Wireless System Lab, NCNU 35 TANET
TANET (台灣學術網路)主要分為數個網路區域，由該區域的負責 學校來管理網路相關事宜，而在各區域之間，連有骨幹線路。
台北區域網路中心：台灣大學計資中心、政治大學電算中心
桃園區域網路中心：中央大學電算中心
竹苗區域網路中心：交通大學計網中心、清華大學計通中心
台中區域網路中心：中興大學電算中心
雲嘉區域網路中心：中正大學電算中心
台南區域網路中心：成功大學電算中心
高屏區域網路中心：中山大學電算中心
花蓮區域網路中心：東華大學資訊與網路中心
台東區域網路中心：台東大學電算中心
Wireless System Lab, NCNU 36 Wide Area Networks (WANs)
Point-to-point WAN
Usually, as a dial-up line that connects a home computers connects home computer or a small LAN to Internet service provider (lSP).
Line leased from a telephone or cable CATV provider.
This type of WAN is often used to provide Internet access.
Wireless System Lab, NCNU 37 Metropolitan Area Networks (MAN)
MAN: size between LAN and WAN. It normally covers the area inside a town or a city. For customers who need a high-speed connectivity, normally to the Internet, and MAN have endpoints spread over a city or part of city. Example:
High-speed DSL.
Cable TV network.
Wireless System Lab, NCNU 38 Interconnection of Networks: Internetwork
Actually, a LAN, a MAN, or a LAN are not isolated; they are connected to one another. When two or more networks are connected, they become an internetwork, or internet.
Wireless System Lab, NCNU 39 Chapter 1 Introduction
Internet
Wireless System Lab, NCNU 40 The internet
The internet: a network of networks The internet has revolutionized many aspects of our daily lives. Different network types merged for data transfer between computers. Each network has its protocols and is possibly built on different technologies. Internetworking protocols: required to enable communications between computers attached to different networks. Internet v.s. internet.
Internet: TCP/IP networks.
Wireless System Lab, NCNU 41 Hierarchical Organization of the Internet
The internet has come a long way since the 1960s. The internet today is not a simple hierarchical structure. Made up of many wide- and local- area networks joined by devices and stations.
NAP: network access point
Wireless System Lab, NCNU 42 Internet Protocol (IP)
Routers to interconnect different networks. Host computers prepare IP packets and transmit them over their attached network. Routers forward IP packets across networks Best-effort IP transfer service, no retransmission.
Net 1 Net 2
Router
Wireless System Lab, NCNU 43 Addressing & Routing in Internet
Hierarchical address: Net ID + Host ID IP packets routed according to Net ID (Ethernet protocol is based on the Host ID) Routers compute routing tables using distributed algorithm H
H Net 3 G Net 1 G G G Net 5 Net 4 H Net 2 G G H Wireless System Lab, NCNU 44 Names and IP Addresses
Routing is done based on 32-bit IP addresses Dotted-decimal notation
140.116.139.36 (IP address of NCKU) Hosts are also identified by name
Easier to remember
Hierarchical name structure
com.ncnu.edu.tw Domain Name System (DNS) provided conversion between names and IP addresses
nslookup.
www.ncnu.edu.tw 163.22.6.200
Wireless System Lab, NCNU 45 Transport Protocols
Host computers run two kinds of transport protocols on top of IP to enable process-to-process communications User Datagram Protocol (UDP) enables best-effort transfer of individual block of information Transmission Control Protocol (TCP) enables reliable transfer of a stream of bytes
Transport Protocol
Internet
Wireless System Lab, NCNU 46 Internet Applications
All Internet applications run on TCP or UDP TCP: HTTP (web); SMTP (e-mail); FTP (file transfer; telnet (remote terminal) UDP: DNS, RTP (voice & multimedia) TCP & UDP incorporated into computer operating systems Any application designed to operate over TCP or UDP will run over the Internet!!!
Wireless System Lab, NCNU 47 Chapter 1 Introduction
Standards
Wireless System Lab, NCNU 48 Standards
A very important thing for the internet. New technologies very costly and risky Standards allow players to share risk and benefits of a new market Reduced cost of entry Ensure interoperability Increase network effect 一財貨的需求量隨著相容性產品消費量(使用量)的增加而增加。
當使用即時通訊的人數越來越多時，網路效果就會越大，雖然 新推出的通訊軟體可能有較好的效能與功能，但是礙於已經有 許多人使用，就不太會想要再轉換到新的平台上。
Example: 802.11 wireless LAN products
Wireless System Lab, NCNU 49 Standards Bodies
Internet Engineering Task Force (IETF) Internet standards development Request for Comments (RFCs): www.ietf.org International Telecommunications Union (ITU) International telecom standards IEEE 802 Committee Local area and metropolitan area network standards (e.g., 802.11, 802.16, 802.3) Industry Organizations WiMax Forum, WiFi Alliance, World Wide Web Consortium
Wireless System Lab, NCNU 50 Summary
Medium access control regulates sharing of broadcast medium. IP addresses identify host in internet.
Transfer of packets across a packet network
Distributed calculation of routing tables Internetworking across multiple networks using routers Transport protocols for end-to-end communications Applications that build on the transfer of messages between computers.
Wireless System Lab, NCNU 51