1、1,Overview: Data communications Networks The Internet Protocols,1. Introduction,2,1.1 Data Communications,Telecommunication communication at a distance, including telephony, telegraphy, and television. Tele”far” Data communications the exchange of data between two or more computing devices Voice, vi
2、deo, and data communications,3,Five components of data communication,4,Data flow (simplex, half-duplex, and full-duplex),5,1.2 Networks,A network is a set of devices (nodes) connected by communication links. A node can be a computer, printer, or any other devices capable of sending/receiving data.,6
3、,Physical Topology,Physical topology refers to the physical appearance of a network.,Categories of topology,7,A fully connected mesh topology (five devices),8,A star topology connecting four stations,9,A bus topology connecting three stations,10,A ring topology connecting six stations,11,A hybrid to
4、pology: a star backbone with three bus networks,12,Categories of Networks,Computer networks can be generally divided into two primary categories: Local Area Network (LAN) Wide Area Network (WAN),13,Local Area Network,A LAN is usually private owned, and is designed to enable local computer users to s
5、hare some valuable computing resources such as printers, software programs, and data.,An isolated LAN connecting 12 computers to a hub in a closet,14,Wide Area Network,A WAN provides the service of transmitting data over long distance.,WANs: a switched WAN and a point-to-point WAN,16,Interconnection
6、 of Networks: Internetwork,Today, an isolated LAN, or WAN is rare. Most of them are interconnected with each other. When two or more networks are connected, they form an internetwok, or internet.,17,A heterogeneous network made of four WANs and two LANs,18,1.3 The Internet,The most notable internet
7、is call the Internet. Internet History: Late 1960s: ARPANET using interface message processors (IMPs) 1969: ARPANET became a reality. 1973: TCPIP,J.F Kurose and K.W. Ross,http:/personalpages.manchester.ac.uk/staff/m.dodge/cybergeography/atlas/historical.html,20,Sprint US backbone network,J.F Kurose
8、and K.W. Ross,21,Source: http:/www.caida.org/tools/visualization/mapnet/Backbones/,US Commercial Backbones,22,23,24,25,The Internet Today (contd),“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs,Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,J.F Kurose an
9、d K.W. Ross,26,The Internet Today (contd),Tier 1 ISP,Tier 1 ISP,Tier 1 ISP,J.F Kurose and K.W. Ross,Connect to the Internet,DSL Cable Modem,Digital Subscriber Line,Digital Subscriber Line (DSL) technology is one of the most popular choice for the Internet access over the exiting local loops. DSL tec
10、hnology is a set of technologies, each differing in the first letter (ADSL, HDSL, VDSL, and SDSL) The set is often referred to as xDSL, where x can be replaced by A, V, H , or S.,28,ADSL,Asymmetric DSL (ADSL) provides higher speed (bit rate) in the downstream direction (from the Internet to the resi
11、dent) than in upstream direction (from the resident to the Internet). ADSL is designed for residential users; it is not suitable for businesses. How to achieve the asymmetric data rates ?,29,Using Existing Local Loops,The existing local loops can handle bandwidths up to 1.1 MHz. But the filter at th
12、e end office restricts the bandwidth to 4 KHz.,30,Channel Division,Typically, an available bandwidth of 1.104 MHz is divided into 256 channels. Each channel uses a bandwidth of 4.312 kHz. Channel 0 Voice Channel 1-5 not used Channel 6-30 upstream vs. Channel 31-255 downstream The effective channel i
13、s determined by a number of factors such as distance, the gauge of the cable, and surrounding environment. Therefore, ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line. Upstream: 0.5 3.5 Mbps and Downstream: 8-24 Mbps Kbps, Mbps, Gbps,31,ADSL m
14、odem,32,ADSL modem is installed at the customers site.,DSLAM,33,Digital subscriber line access multiplexer (DSLAM) is installed at the telephone company site.,In the traditional cable TV network, the cable TV office, called the head end, receives video signals from a regional cable head (RCH), and t
15、hen broadcasts through a distribution network of coaxial cable. The traditional cable TV system used coaxial cable end to end. Therefore, a large number of amplifiers (up to 35 amplifiers) had to be used.,34,Traditional cable TV network,Cable TV Networks Traditional Cable Networks,Cable TV For Data
16、Transfer,Video Band: 54 550 MHz. Each channel needs 6 MHz, so 80 channels. Downstream Data: 550 750 MHz. 6 MHz for a channel The max. downstream data rate for each channel is 30Mbps,35,Division of coaxial cable band,Cable TV For Data Transfer (contd),Upstream Data: 5 42 MHz 6 MHz per channel The max
17、. upstream data rate is 12Mbps,36,Timesharing,Each coax cable is able to serve up 1,000 subscribers. The upstream data bandwidth is 37 MHz, or only six 6 MHz channels. The cable provider allocates one channel for a group of subscribers, , and then uses a timesharing protocol to let this group of sub
18、scribers to share the channel. The downstream band has 33 channels of 6 MHz. Each channel must also be shared between a group of subscribers. If there are data for any of the subscribers in the group, the data are sent to that channel. Each subscriber is sent the data, but only the subscriber with a
19、 matched address will keep the data.,37,Cable modem (CM),38,39,1.4 Protocols,Protocols Syntax Semantics Timing,40,40,Signal: analog and digital Network performance,2. Data and Signals,41,41,2.1 ANALOG AND DIGITAL,Analog signals vs. Digital signals,Comparison of analog and digital signals,42,42,2.2 A
20、nalog Signals Simple Analog Signals,A sine wave,Peak amplitude the strength of the signal (volts). Frequency the # of cycles in 1 s (Hz). Phase the initial position of the signal (degrees or radians).,43,43,2.3 Digital Signals,Two digital signals: one with two signal levels and the other with four s
21、ignal levels,44,Bit Rate,Bit rate is the number of bits sent in 1 second It is expressed in bits per second (bps),45,Transmission of Digital Signals,Baseband transmission sending a digital signal over a channel directly.,45,Baseband transmission,46,Transmission of Digital Signals (contd),Broadband t
22、ransmission changing the digital signal to an analog signal for transmission (modulation). a channel with a bandwidth not starting from zero.,46,47,48,49,2.4 Network Performance,One important issue in networking is the performance of the networkhow good is it? Bandwidth, throughput, latency (delay)
23、In networking, we use the term bandwidth in two contexts bandwidth in hertz bandwidth in bits per second,49,50,More on Performance,Throughput is a measure of how fast we can actually send data through a network.,50,51,More on Performance,Latency or delay defines how long it takes for an entire frame
24、 to completely arrive at the destination from the time the first bit was sent out from the source. Latency made of four components: propagation time, transmission time, queuing time, and processing delay.,Latency time = propagation time + transmission time + queuing time + processing delay,51,52,Mor
25、e on Latency,Propagation time measures the time required for a bit travel from the source to the destination. Transmission time of a message depends on the size of the message and the bandwidth of the channel.,Propagation time = Distance Propagation speed,Transmission time = Message Size Bandwidth,5
26、2,53,3. Transmission Media,Classes of transmission media,3.1 GUIDED MEDIA,Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and
27、 transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light.,54,Twisted-Pair Cable,Twist cancel out the noise. Unshielded Twisted-Pair (UTP) and Shielded Twisted-Pair (STP),55,Twisted-pair cable,UTP and STP cables,56,Categorie
28、s of unshielded twisted-pair cables,57,UTP connector,58,Coaxial Cable,59,Coaxial cable,Categories of coaxial cables,60,BNC connectors,61,Fiber-Optic Cable,62,Fiber construction,Optical fiber,63,64,Fiber types,Connectors,There are three common types of connectors for fiber-optic cables: Subscriber Ch
29、annel (SC) connector, Straight-Tip (ST) connector and MT-RJ connector.,65,Fiber-optic cable connectors,Applications,Fiber-optic is often found in backbone networks because of its wide bandwidth. Some cable TV companies use a combination of optical fibers and coaxial cable. Local Area Networks such a
30、s 100Base-FX network and 1000Base-X also use fiber-optic cable.,66,Source: http:/www.caida.org/tools/visualization/mapnet/Backbones/,US Commercial Backbones,Advantages and Disadvantage Of Optical Fiber,Higher bandwidth Less Signal Attenuation Immunity to electromagnetic interference Resistance to co
31、rrosive materials Light weight Greater immunity to tapping Cost,68,3.2 Unguided Media: Wireless,Unguided media transport electromagnetic waves without using a physical conductor Wireless Communication. The electromagnetic spectrum, ranging from 3 KHz to 900 THz, is used for wireless communication.,6
32、9,Electromagnetic spectrum for wireless communication,Propagation methods,70,There are three general ways in which unguided signals can travel from the source to dest.: ground propagation, sky propagation, and line-of-sight propagation.,Bands,71,The section of the electromagnetic spectrum defined as
33、 radio waves and micro waves is divided into eight ranges, called bands.,Wireless transmission waves,72,Radio Waves,Electromagnetic waves ranging in frequencies between 3KHz and 1GHz are normally called radio waves. Radio waves are omnidirectional, can travel long distances, and penetrate walls.,73,
34、Therefore, they are very commonly used in multicasting communications (e.g. radio station, television, and paging systems). The radio wave band is relatively narrow, 1 GHz, leading to a low data rate for digital communication.,Microwaves,Electromagnetic waves have frequencies between 1 and 300 GHz a
35、re called microwaves. Microwaves are unidirectional. Microwave propagation is line-of-sight: the sending and receiving antennas need to be in direct sight of each other. Very high-frequency microwaves cannot travel very long distance (repeaters are needed for long distance communication) and penetra
36、te walls. The microwave band is relatively wide, almost 299 GHz. Therefore , a high data rate is possible. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.,74,Infrared,Electromagnetic waves, with frequencies from 300GHz to 400THz, are called infrared waves. Infrared waves cannot penetrate walls and are useless for long-range communication. Short-range communication: remote control and wireless keyboard, mice, printers.,75,
