Introduction to Data Communications

1. Chapter 1 Introduction to Data Communications

2. Introduction The second industrial revolution radically changes the way we communicate virtually eliminating information lag. What problems does this create?

3. Recent Communications History 1834 Samuel Morse invents the telegraph 1876 Alexander Graham Bell makes the first long-distance phone call (10 miles) 1915 First transatlantic and transcontinental telephone service. 1948 Microwave links for telephone calls 1951 direct long distance dialing

4. Communications History Cont. 1962 Fax service is introduced 1965 widespread use of satellite long distance. 1968 Non Bell equipment allowed on phones system 1969 Picturephones 1969 DARPAnet

5. Communications History Cont. 1970 Limited long-distance competition allowed 1984 AT&T is broken up creating a regulatory boundary between local phone service and long distance 1984 Cellular phone service starts 1990�s Cellular phone service explodes

6. Communications History Cont. 1996 Telecommunications Competition and Deregulation Act replaced all federal and state telecommunications law 1997 68 countries sign agreement to allow foreign telecommunications competition

7. Information Systems History 1950�s Batch processing and punch cards 1970�s Real-time transaction-oriented database-driven systems emerge 1990�s Macys is bankrupt in part due to their �old� 1970�s era IS infrastructure Read comparison between Macys and WalMart

8. Components of a Network Server � a device that stores data and often performs functions in addition to storage Client � A terminal or microcomputer from which a user or other application performs a work function Circuit � a wire, or set of wires and devices (modem, router, switch etc�) that carry information from the client to the server

9. Types of Networks LAN � Local Area Network BN � Backbone Network MAN � Metropolitan Network WAN � Wide Area Network Intranet � A network used within an organization Extranet � Access for people from outside

10. Network Models Used to break networks into component functions (layers) which then allows each layer to be addressed independently. The use of layers and different standards (and standards bodies) at these layers allows great flexibility in design, and competition between manufacturers.

11. OSI Model Produced in 1984 Consists of seven layers

12. Internet Model Similar to the OSI model Compresses layers 5-7 into a single layer 5 The textbook author claims the internet model has won the �war�. Is this true?

13. Functions at Layer 4 (TCP) Error detection/correction Linking higher layer software to the network layer Name resolution Breaking messages into pieces small enough to send over the network (MTU

14. Functions at Layer 3 (IP) Responsible for end-to-end routing of messages from sender to receiver Responsible for attaining the next address for messages as they hop from router to router across the internet

15. Functions at Layer 2 Responsible for moving messages from the sender to the receiver within a LAN. Controls the physical layer Formats the messages Provides error detection and correction

16. Functions at Layer 1 Get the signal (electrical signal, light pulse, smoke signal) from one LAN device to the next. This layer includes hardware devices such as modems and hubs.

17. Two Types of Standards Formal Developed by an official industry or government agency These are often slow in developing and follow an already existing de facto standard De facto Emerge in the marketplace and are supported by multiple vendors but have to official standing

18. Standards Making Bodies IEEE The Institute of Electrical and Electronic Engineers Professional organization based in the United States Primarily responsible for existing LAN standards

19. Standards Making Bodies ITU-T Responsible for creating technical standards for the united nations international telecommunications union (ITU) Open to public or private operators of communications networks from more then 200 countries Based in Geneva Switzerland

20. Standards Making Bodies IETF Internet Engineering Task Force Open to everyone Manages consensus-building process through the use of RFC�s Oversees creation of Internet protocols and standards

21. Future Trends Pervasive networking Integration of voice, video and data New information services

22. Chapter 2 Application Layer

23. Application Architectures Host-Based Architectures Commonly a mainframe with terminals Client-Based Architectures Distribute PC based architecture with the computing power at the desktop Client-Server Architecture Applications software divided between desktop PC�s and central servers (fat vs. thin clients)

24. N-tier Architectures Two-tier A client talks to a server (connecting to a web server) Three-tier A client talks to a web server which in turns queries a database server to obtain the requested data N-tier Same concept applied N times

25. Advantages of Client-Server Scalability N-tiered architecture gives a high degree of scalability Cost of infrastructure A set of smaller micro or mini computers and the associated software is often far less expensive then a mainframe approach

26. World Wide Web Create in 1989 at the CERN lab in Geneva Switzerland by Tim Berners-Lee A graphical interface was developed in 1993 by a team of students led by Marc Andreessen at the NCSA lab at the University of Illinois Adoption of the technology was immediate and rapid

27. Electronic Mail One of the earliest applications on the Internet (Early �killer� app) Cost and speed are among it�s strengths when compared with �snail mail� Important protocols and extensions to understand SMTP (Simple Mail Transfer Protocol) IMAP (Internet Message Access Protocol) MIME (Multipurpose Internet Mail Extension)

28. Other Important Applications Listserv A mailing list of users who have joined to discuss a topic or receive specific information updates Usenet A repository of articles on many different subjects

29. Other Important Applications FTP � File Transfer Protocol Provides the ability to transfer data to and from systems (primarily used in conjunction with UNIX servers) Telnet Provides the ability to login to a server from anywhere within a connected network The name is derived from making a TELephone connection via the NETwork.

30. Chapter 3 Physical Layer

31. Components in Physical Layer Media Wires, fiber-optic strands Wireless Special-purpose devices Modems Repeaters/hubs

32. Circuits Physical Circuit Twisted pair cable, fiber, wireless link Exclusively committed to your data Logical Circuit One of several, perhaps many circuits on a single physical circuit Channel 12 on TV is a logical circuit, it rides on a coaxial cable or wireless (a physical circuit) along with many other logical circuits

33. Types of Data Digital Two possible values for any data bit (1 or 0) In a fiber circuit a light being on could represent a �1� while off represents a �0� In a copper circuit 5 volts could represent �1� while 0 volts represents �0� Analog Signals are shaped like sound waves and are constantly changing

34. Modem/Codec MOdulate/DEModulate Translates digital data into a form that can be transmitted across an analog circuit such as a standard telephone line COder/DECoder Translates analog information into a form that can be transmitted across a digital circuit

35. Circuit Configuration Point-to-Point A circuit with a device at each end Home modem Multipoint A single device at one end with many devices at the other end with either time-slicing or circuit switching

36. Data Flow Simplex One way transmission (i.e. cable TV) Half-duplex Communication in both directions, only one way at a time (i.e. walkie-talkie) Full-duplex Communication in both ways, at the same time (i.e. telephone)

37. Communication Media Guided media Twisted-pair, coaxial, fiber-optic Wireless media Radio, infrared, satellite

38. Fiber Optic Multi mode Attenuation (weakening of the signal) Dispersion (spreading of the signal) Single mode Must use the precision of lasers as opposed to LED�s

39. Coding Character A symbol with a constant understood meaning Byte A group of (typically) eight bits that is treated as a character ASCII (American Standard Code for Information Interchange) 7 or 8 bit code (typically 8)

40. Transmission Modes Parallel All bits are sent simultaneously, in a 32-bit system then there must be paths to send all 32 bits at the same time Serial Each bit is sent one at a time,

41. Digital Transmission Transmission of 1�s and 0�s With electricity this can be voltages with perhaps 0 volts representing a zero and 5 volts representing a 1 (unipolar) With light this can be using the state of the light with perhaps off representing a 0 and on representing a 1

42. Manchester Encoding Used in Ethernet Unipolar coding scheme with a twist Voltage moving from a lower level to a higher level represents a �1� Voltage moving from high to low is a �0�

43. Analog Transmission Telephone systems were originally designed to carry analog transmissions, electrical representations of the human voice Three key characteristics Amplitude Frequency Phase

44. Modulation A carrier wave (ugly noise heard when modems are negotiating) is sent between modems, the shape of the wave is altered to represent 1�s and 0�s These �shape changes� are referred to as modulation

45. Modulation Techniques Amplitude Modifying the height of the wave Frequency Modifying the frequency (the number of waves per second) of the wave Phase Modifying the point in phase at which the wave starts

46. Amplitude Modulation

47. Frequency Modulation

48. Phase Modulation

49. Two-bit Amplitude Modulation

50. Modulation Techniques The various modulation techniques discussed can be combined as well QAM (Quadrature Amplitude Modulation) Combines eight phases (three bits) and two amplitudes (one bit) for a total of four bits TCM (Trellis Code Modulation) Similar to QAM but can transmit up to ten bits per symbol

51. Bits Baud and Symbol Bits (specifically bits per second) are generally the important measurement in data communications as symbols are composed of bits There is a common misconception that these terms are interchangeable, baud refers to the number of symbols per second as opposed to the number of bits per second

52. Voice Circuit Capacity Home analog phone lines have a bandwidth range from 0 to 4000 Hz The human ear can detect sounds up to ~14,000 Hz so very high pitch sounds can�t be transmitted over an analog phone line Digital circuits used to tie analog phone lines together have a bandwidth of 64,000 bits per second (bps)

53. Modem Technologies V.34+ Transmits up to 33,600 bps V.44 (Compression) Builds a dictionary of character combinations being sent over the circuit When a combination is repeated the dictionary reference is sent as opposed to the characters Average throughput is ~ 6:1

54. Codec Converts Analog data into a digital form for transmission over a digital system and back The analog signal is translated into a binary number This digital signal is an approximation of the original with the quality depending on the resolution by either increasing the amplitude levels or increasing the sampling rate

55. Telephone Transmission The �local loop� is the circuit from the phone company CO (the building between 3rd and 4th streets and Chestnut and Hazel streets) uses analog transmission Once the signal reaches the phone company office it is converted to digital form and is then sent to it�s destination CO Even local calls are converted to digital

56. Pulse Code Modulation PCM is used in phone company CODEC�s in North America PCM samples the data 8,000 times (twice the highest frequency within the phone system Eight bits are generated for each sample, thus the phone system uses the 8 bits * 8,000 samples for a data rate of 64,000 bps

57. ADPCM Adaptive Differential Pulse Code Modulation Similar to PCM except it only sends the difference between the former and the new signal Data rates as low as 8Kbps can be obtained, 32Kbps is the lowest providing sufficient quality so that the user doesn�t notice The use of ADPCM is the reason that some users can�t get a modem connection above 26,200 bps

58. Analog/Digital Modems Uses PCM backward Sends 8,000 samples per second Uses 7 bits (one is lost for control purposes 7 bits * 8,000 samples = 56,000 bits V.92 modems do this in each direction and due to technical constraints are limited to ~52,000 bps downstream and ~42,000 bps upstream

59. Multiplexing Using one high-speed circuit to carry the traffic of multiple lower-speed circuits FDM TDM WDM (form of FDM) DWM (combination of FDM and TDM) Has reached 1.25 terabits already and is expected to reach 1 petabit within a few years

60. Frequency Division Multiplexing

61. Time Division Multiplexing

62. Inverse Multiplexing Using a series of lower-speed circuits to connect two high-speed circuits together Technology has been proprietary until just recently The BONDING (Bandwidth ON Demand Interoperability Networking Group) standard is allowing vendors to interoperate today but this is still in its infancy

63. Inverse Multiplexing

64. Digital Subscriber Line Much of the available bandwidth in the local loop has gone unused for many years DSL uses this bandwidth by applying FDM to create three circuits comprised of the original phone line, a upstream data circuit and a downstream data circuit TDM and PM are also used to obtain various data rates and features

65. Chapter 4 Data Link Layer

66. Media Access Control A mechanism used to control when computers transmit Important when using half-duplex circuits or multipoint configurations Two fundamental approaches Controlled Access Contention

67. Controlled Access X-ON/X-OFF Polling Roll Call Polling: one device in the circuit is a �master� and checks with each other device on its wire to see if they have something to say Hub Polling (token passing): one computer starts the poll and passes it to the next, when a computer with something to say receives the �token� then it can send its data

68. Contention The opposite of controlled access, each device listens to see if someone else is talking, if not then it sends carrier and starts to talk CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is used in Ethernet networks

69. Network Errors Two types of network errors Data loss Data corruption Three approaches to dealing with errors Prevention Detection Correction

70. Sources of Errors Line noise, distortion Line outages Impulse noise Cross-talk Attenuation Intermodulation noise Jitter

71. Error Prevention Shielded cabling Cable location Cable selection (fiber vs. twisted pair) Cable installation and maintenance

72. Error Detection Parity Longitudinal redundancy checking Polynomial checking Checksum Cyclic Redundancy Check 16-bit CRC used in TCP 32-bit CRC used in Ethernet

73. Error Correction via Retrans. Stop-and-wait ARQ Continuous ARQ

74. Forward Error Correction Sufficient redundant data is included within the transmission to correct errors without retransmission Used heavily in satellite transmission

75. Ethernet Protocols Ethernet (IEEE 802.3) Byte-count protocol Destination, length, LLC, SNAP, CRC-32 Point-to-Point Protocol (PPP) Address Protocol Message length = 1,500 bytes

76. Bridging/Switching MAC-layer address table for each interface Addresses behind a port are stored in memory Ethernet frames are checked at each interface to determine if they should be forwarded

77. Transmission Efficiency Transmission efficiency = total information bits/total bits Throughput = transmission efficiency adjusted for errors and retransmissions TRIB

78. Chapter 5 Network and Transport Layers

79. TCP/IP TCP Layer 4 Provides error detection (CRC-16) Breaks data into appropriate size blocks (MTU) IP Provides routing and addressing IPv4 (32-bit address) IPv6 (128-bit address)

80. TCP Ports A computer can have multiple applications running, i.e. a machine can be running both a web server and an email server Commonly used ports SMTP � port 26 WWW � port 80 FTP � port 21 Telnet � port 23

82. Packetizing Taking an outgoing message with a length too great to fit within the data-link maximum frame length (MTU) and breaking the message into appropriate lengths Function is performed by the transport layer With IPv4 the packet size is set for the local LAN and is adjusted if the message is sent across a link that requires a smaller MTU

83. Connection-oriented Routing A specific route �virtual route� is determined when the session is created A SYN packet is sent to create the virtual circuit A FIN packet is sent to tear the circuit down

84. Connectionless Routing Uses UDP instead of TCP Packets can travel different routes Commonly used with applications such as DNS and DHCP which are not likely to send a packet that will have to be broken into pieces

85. Quality of Service A special type of connection-oriented routing Classes of service are established and each application is assigned one of the classes Applications such as VoIP and video-conferencing may be in a higher priority class then SMTP or WWW

86. Internet Addresses Assigned by ICANN (Internet Corporation for Assigned Numbers and Names) Blocks of network addresses are assigned to organizations Often a large block of addresses are assigned to an organization These large blocks of addresses are broken into smaller blocks referred to as �subnets�

87. Subnets There are many possible combinations when dividing a network address block into subnets It is also possible to merge two adjacent networks together into a single �supernet� Whether dividing a network into subnets or combining two or more networks into a supernet the subnet mask is the key

88. Subnet Mask A subnet mask is a string of 1�s and 0�s A subnet mask of 255.255.255.0 indicates the first three bytes of the IP address are part of the network Another way of looking at this subnet mask would be 11111111.11111111.11111111.00000000 A 1 indicates the corresponding bit in the IP address is part of the network designation

89. Dynamic Addressing DHCP (Dynamic Host Configuration Protocol) When the computer is started it sends a message requesting that a DHCP server provide an IP address and other configuration allowing the computer to communicate via IP

90. Layer 2 Address Resolution ARP (Address Resolution Protocol) Broadcast Message (all 1�s) Whoever has IP address xxx.xxx.xxx.xxx send me your Ethernet address

91. Domain Name Service An Internet phone book When typing in www.csuchico.edu DNS will translate this application-layer address to the network-layer address of 132.241.82.24

92. Routing Packets are routed between networks based on a set of routing tables The routing tables can be manually programmed (static routing) or created by a routing protocol (dynamic routing) Routing Protocols Distance Vector (RIP) Link State (OSPF)

93. Routing Protocols Interior routing protocols RIP, OSPF, EIGRP Exterior routing protocols OSPF, BGP Autonomous System

94. Multicasting Three types of messages Unicast Broadcast Multicast IGMP (Internet Group Management Protocol) Each participating computer uses a common data-link layer address

95. TCP/IP Example Work through the entire TCP/IP example at the end of chapter 5 Known addresses, same subnet Known addresses, different subnet Unknown addresses TCP connections

96. Chapter 6 Local Area Networks

97. Why Use a LAN? Information Sharing Email File access Video conferencing Resource Sharing Printers Applications servers

98. Dedicated Server vs. Peer-to-Peer Dedicated Server One or more server computers permanently assigned to being a network server File servers Print servers Peer-to-Peer No dedicated server

99. LAN Components NIC (Network Interface Card) Network cables Twisted pair UTP/STP See Category Ratings in Technology Focus Coaxial cables BALUNs Fiber-optic cables Single-mode vs. multi-mode

100. LAN Components Cont. Network hubs Network bridges/switches Network routers Network Operating System Server/client software Network profile Storage Area Networks (SAN) Network Attached Storage (NAS)

101. Ethernet (IEEE 802.3) Topology Logical vs. physical The logical topology of a traditional Ethernet network is a bus The physical topology is often a star

102. Media Access Control With a bus topology there must be a mechanism to either prevent, or detect and deal with, collisions on the media CSMA/CD Full-duplex Ethernet

103. Types of Ethernet 10Base-5 10Base-2 10Base-T 100Base-T 10/100 Ethernet 1000Base-T

104. Switched Ethernet The switch replaces the hub in the network The hub repeats every bit of data out every port The switch sends the data out the port which is connected to the message recipient The switch uses a forwarding table that contains the Ethernet addresses of the computers connected to each port

105. Wireless Ethernet IEEE 802.11 The WEP standard has been completely cracked Uses CSMA/CA for media control Subject to the �hidden node� problem Has VCSM (Virtual Carrier Sense Method) as an option to work around the hidden node problem

106. Types of Wireless Ethernet IEEE 802.11b DSSS � Allows speeds from 1 � 11 Mbps depending on distance and interference FHSS � Allows speeds from 1 � 2 Mbps IEEE 802.11a The standard is still incomplete Data rate is likely to be 54 Mbps on first iteration Actual throughput will likely be ~20Mbps

107. Other Wireless Technologies Infrared wireless Requires line of site or white ceilings and walls with diffused infrared Bluetooth Slated to become standardized as IEEE 803.15 Short range networks referred to as piconets with no more then 8 devices Uses controlled access media access control Less then 1Mbps throughput

108. Reducing Network Demand Placing heavily-used applications or data modules on each client computer Network segmentation � note this is really increasing supply rather then reducing demand

109. Chapter 7 Backbone Networks

110. Backbone Network Components Bridges Operating at the data-link layer (MAC address) Routers Operating at the network layer (IP address) Gateways Operating at the transport layer (note that this disagrees with the authors table 7-1)

111. Backbone Network Components Collapsed backbone Chassis-based Rack-based VLAN�s Port-based MAC-based IP-based Application-based

112. ATM Four key differences between Ethernet and ATM in the backbone 53-byte fixed-length cells No error correction Virtual Channel addressing as opposed to fixed addresses with the path and circuit numbers Built in Class-of-Service (CoS) and Quality-of-Service (QoS)

113. ATM Classes of Service CBR VBR-RT VBR-NRT ABR UBR LANE vs. MPOA SVC vs. PVC

114. Chapter 8 MAN�s and WAN�s

115. MAN�s Generally constrained to a city or small region between 3 and 30 miles Generally deployed via either wireless technology or services leased from a carrier Moderate levels of regulation

116. WAN�s Connecting over potentially great distances Generally deployed via circuits leased from Common Carriers Very heavily regulated within North America and usually even worse oversees

117. Circuit Switched Networks Usually depicted by a cloud with your organizations data traveling with many others across the same physical circuits POTS ISDN BRI PRI Broadband

118. Dedicated Circuit Networks Dedicated circuits or dedicated bandwidth within carrier circuits Ring Architecture Star Architecture Mesh Architecture

119. T Carrier Services Based on the 64Kbps channel required for a digitized voice connection T1 � 24 channels * 64Kbps = 1.536 Mbps Control information is included bringing the total circuit bandwidth for a stand-alone T1 to 1.544 Mbps T3 � 28 T1�s � 28 * 1.544Mbps = 43.008Mbps With control information = 44,736Mbps

120. SONET SONET is a North American standard but the ITU recently adopted the SDH standard set which is nearly identical OC-1 = 51.84Mbps OC-3 = 3*OC-1 = 155.52 Mbps OC-12 = 12*OC-1 = 622.08 Mbps

121. Packet Switched Networks X.25 � older standard now seldom used in North America ATM Frame Relay Ethernet/IP Networks

122. Virtual Private Networks Intranet Used to connect your organizations office via the Internet Extranet In addition to your organizations office you may also include other organizations with which you do business Access Remote access for employees

123. Chapter 9 The Internet

124. Internet Structure Internet architecture NAP�s, MAE�s, and ISP�s POP�s Peering Autonomous systems

125. Internet Access Technologies DSL Digital Subscriber Line Uses the local-loop A modem is placed in the home converting the data from the DSL format to Ethernet ADSL G.Lite VDSL

126. Internet Access Technologies Cable Modems DOCSIS Shared media means users compete with each other for bandwidth and unscrupulous neighbors could intercept your data Throughput suffers due to hardware compatibility issues that stem from cable TV infrastructure differences

127. Wireless Fixed wireless Wireless DSL Satellite Mobile Wireless WAP WAE

128. Internet Governance ISOC (Internet SOCiety) www.isoc.org IETF (Internet Engineering Task Force) IESG (Internet Engineering Steering Group) Each IETF working group is chaired by a member of the IESG IAB IRTF

129. Internet Domain Name Reg. Internet name and address registration was handled by John Postel until his death in 1998 In 1998 ICANN (Internet Corporation for Assigned Names and Numbers) was formed In 1999 ICANN established the SRS and has now authorized more then 80 companies to issue Internet names and numbers

130. Internet 2 Next Generation Internet vBNS Abilene CA*net 3

131. Chapter 10 Network Security

132. Why Networks Need Security The average cost to companies for a single security breach is slightly less then $1M This is a minor cost when compared to the loss of customer confidence The text indicates that 24 hours of downtime would cost Bank of America $50M

133. Types of Security Threats Disruptions Minor cable breaks to earthquakes Unauthorized Access More often the work of an employee then an outside hacker

134. Network Controls Controls are processes or steps to reduce or eliminate threats Three types of controls Controls that prevent threats Controls that detect threats Controls that correct threats

135. LAN Security Although sometimes overlooked a good first step is to ensure that the LAN hardware is physically secure Firewalls Packet-level Application-level NAT (Network Address Translation)

136. LAN Security Encryption Symmetric DES Triple DES AES Asymmetric (PKI) PGP (Pretty Good Privacy) SSL (Secure Sockets Layer) IPSec (IP Security)

137. Detecting Unauthorized Access IDS (Intrusion Detection Systems) Network-based Host-based Application-based Two IDS Techniques Misuse detection Anomaly detection

138. Chapter 11 Network Design

139. Network Design Process Traditional design process Building Block Design Process Needs analysis Technology design Cost assessment Why network projects fail Management focus 11-2

140. Request For Proposal Background information Network requirements Service requirements Bidding process Information required from vendor

141. Chapter 12 Network Management

142. Network Management Tasks performed by the network manager Five key management tasks Key network management skills Configuration management

143. Performance & Failure Statistics Availability MTBF MTTRepair Policy-Based Management Service-Level Agreements

144. Cost Management Sources of cost TCO (Total Cost of Ownership) $8,000 - $12,000 per device per year? $1,500 - $3,500 per device per year? (NCO) Five steps to reduce network costs

145. Network Management Tools Three types of network management software Device management System management Application management SNMP MIB RMON