2a. Introduction to Data Communications and Networking

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2a. Introduction to Data Communications and
Networking
1. Communication Link
2. General Definition 
3. Example of Computer Communication Systems
4. Networking a. Telephone Network b. Computer Networks c. Cable Television d. Wireless Networks.
5. Communication Standards a. System Interconnection
6. OSI/RM
7. Layer Descriptions
8. The TCP/IP Reference Model a. Protocol Hierarchies b. Internet Layer c. Transport Layer d. Application Layer e. Host-to-Network Layer
9. Packet Switching and Circuit Switching
10.Connect-oriented and Conn.less Services (T. pg. 1-84)
       
   
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1. Communication Link
Data Communication Link
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2. General Definitions

• Information is the meaning that a human being
  assigns to data by means of the conventions
  applied to those data.
• Data is a representation of facts, concepts, or
  instructions in a formalized manner suitable for
  communications.
• Signals are the physical encoding of data,
  electric, or electromagnetic means.
• Signals can be
• Analog (continuous in time and amplitude),
• Discrete (discrete in time, continuous in
  amplitude), or
• Digital. A digital signal (discrete in time and
  amplitude),it is a sequence of digital values
  which changes once every interval.

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3. Example of a Computer Communication Systems
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4. Networking

• Communication networks enable many users to
  transfer information in different form of voice,
  video, electronic mail, and computer files.
• a. In Telephone Network
• Circuit switching. Circuit" reefers-one
  telephone conversation along one link.
• Circuit switching occurs at the beginning of new
  telephone call.  
• An electronic interface, coder/decoder (codec) in
  the switch converts the analog signal traveling
  on the link from the telephone set to the switch
  into digital signal-a bit stream.  
• Since the 1980s the transmission links of the
  telephone network have been changing to the
  SONET, or Synchronous Optical Network, standard.
  SONET rates are arranged in the Synchronous
  Transfer Signal (STS).

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Phone connection to digital network

Analog signal

Codec
Switch
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• Carrier Signal Rate in Mbps
• OC-1 STS-1 51,840
• OC-3 STS-3 155,520
• OC-9 STS-9 466,560
• OC-12 STS-12 622,080
• OC-18 STS-18 933,120
• OC-24 STS-24 1244,160
• OC-36 STS-36 1866,240
• OC-48 STS-48 2488,320
• OC-192 STS-192 9853,280
• OC-768 STS-768 39,413,120
  

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• b. Computer or Data Communication Networks
• Data packets
• Packet switching Rules of operations
  (protocols)
• The ARPANET -single packet format and
  addressing scheme. Through the ARPANET was
  evolved into the Internet. ARPANET architecture
  was formalized layered model of OSI
• The packet switching technique in networks is
  based on Multiplexing and/or Multiple Access
  methods of computer interconnections.
• Multiplexing TDM
• FDM (WDM / DWDM)
• Multiple Access Ethernet Network.
• Token Ring Network.
• Fiber
  Distributed Data Interface -
• FDDI-Timed-token mechanism-fixed time of the
  arrivals token  

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Model of the information system
Server
Network
Clients
Broadcast links. Point-to-point (unicast)
links
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LANTopology of theEthernet (a) and Token Ring
networks (b).
A
a
B
IEEE 802.3
b
IEEE 802.5
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Wide Area Network (WAN)
Metropolitan Area Networks (MAN)
MAN represents as a interconnected LANs by
point-to-point communication links. The
interconnection is controlled by switches,
Subnet
Router (Switch)
Client
Links
Host (Server)
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Sprint US backbone network
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• Cable Television, originally known as Community
  Antenna Television or CATV. In CATV the signal
  from one master antenna distributed over a large
  area using coaxial cable and amplifiers. The key
  innovations in cable TV are optical fiber links,
  digital compression techniques, and service
  integration.
• Today cable TV uses frequency-division
  multiplexing to transmit up to 69 analog TV
  channels, each 4.5 MHz wide. Transmission is over
  coaxial cables arranged as a unidirectional tree.
  
• Amplifiers used to compensate for the attenuation
  of the cable signal. The number of TV a channels
  is limited by the bandwidth of coaxial cables.
• Optical fibers are used to transmit the TV
  signals over longer distance. Transmission over
  the fiber is still analog. The signal is fed into
  the coaxial cable network at various points,
  where the optical signal is converted into
  electrical signals. This hybrid fiber/coaxial
  cable distribution system has a longer span and
  better signal quality than a coaxial cable
  network. This network called fiber-to-the-curb
  (FTTC) network.

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• To increase the number of channels, digital
  transmission technology.
• Before transmitting the TV signals, the CATV
  company uses a
• TV codec that converts each signal into a bit
  stream.
• Using Motion Pictures Expert Group (MPEG)
  algorithms,
• the codec compresses the bit stream to
  reduce its rate.
• The bit streams are transmitted over fibers to
  the curb and then distributed by the neighborhood
  coaxial network.
• The compression gain now allows-transmit about
  500 TV channels. MPEG1 standard, TV signal is
  encoded-1.5 Mbps bit stream, which can be
  modulated in a signal that has a bandwidth of
  about 600 kHz.
• Set-up boxes at the user residence perform the
  decompression. This CATV network is still
  unidirectional. Video on demand, Internet access,
  and telephony, the CATV industry is organizing
  bidirectional networks. Such a network connects
  video servers to users by means of control
  messages.
• The user choices these messages to select the
  video program, and the video program is sent over
  the network to the user.

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Residential access cable modems
Diagram http//www.cabledatacomnews.com/cmic/diag
ram.html
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Cable Network Architecture Overview
Typically 500 to 5,000 homes
cable headend
home
cable distribution network (simplified)
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Cable Network Architecture Overview
cable headend
home
cable distribution network (simplified)
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Cable Network Architecture Overview
cable headend
home
cable distribution network
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c. Cable Network Architecture Overview
FDM
cable headend
home
cable distribution network
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d. Wireless Networks.

• The first packet-switched wireless network-
  in 1971- Alohanet, interconnected computers on
  four islands in a star topology
• A first approximation wireless network-
  three main categories
• 1. Components interconnection. Short-range radio.
  Bluetooth network.
• 2. Wireless LANs. Wireless LAN permitting
  per-to-per communications networks. LANs called
  IEEE 802.11, Wireless LAN can operate at bit
  rates up to about 50 Mbps over distances of tens
  of meters.
• 3. Wireless WANs. The radio network used for
  cellular telephones is an example of a
  low-bandwidth wireless wide area system. This
  system has already gone through three
  generations
• a. The first- analog and voice only.
• b. The second- digital and for voice only.
• c. The third- digital and is for both voice and
  data.
• Cellular systems operate below 1 Mbps, but
  the distances between the base station and the
  computer or telephone is measured in kilometers.

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Wireless access networks

• Shared wireless access network connects end
  system to router
• via base station access point
• wireless LANs
• 802.11b
• 50 Mbps, tens of meters
• wireless WAN
• - Cellular systems
• - lt 1Mbps, several km

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5. System interconnection

• An important concept in data communications is
  the interconnections between the communication
  system components. The interconnection could be
  done if
• Physical characteristics of the interconnected
  equipment are fitted to each other.
• It allows manufacturers of different systems to
  interconnect their equipment through standard
  interfaces.
• It also allows software and hardware to integrate
  well and be portable on differing systems.
• So, standards of hardware and software for
  interconnections in systems are necessary.

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Communication Standards

• Computer communication uses different standard
  for different approach.
• The RS-232-C standard is used for the serial port
  of computer devices. This standard is for low bit
  rate transmissions (up to 38 Kbps) over short
  distances (less than 30 m). Transmissions take
  place over untwisted wires.
• A serial link is often used to attach a computer
  to a modem. A modem transmits data by converting
  bits into tones that can be transported by the
  telephone network. The receiving modem then
  converts these tones back into bits, thus
  enabling two computers with compatible modems to
  communicate over the telephone network as if they
  were directly connected by a serial link. Modems
  conforming to new V.90 standard can transmit
  56,000 bps.
• The Synchronous Transmission Standard increases
  the transmission rate. These standards are known
  as Synchronous Data Link Control (SDLC). The main
  idea of SDLC is to avoid the time wasting by
  RS-232-C.
• SDLC groups many data bits into packets.

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• With an open system of standards any company can
  manufacture equipment or write software.
  Companies must cooperate on standards.
• Standard organizations create and administer
  standards. Often competing companies will form a
  committee to create a standard acceptable to all
  interested parties. Then the companies will ask a
  standard organization for formal recognition of
  that standard.
• An example Ethernet, a Local Area Network (LAN)
  system created by Xerox, Intel, and Digital
  Equipment Corporation. These companies asked the
  Institute of Electrical and Electronics Engineers
  (IEEE) to formalize Ethernet, and this becomes
  standard IEEE 802.3.
• United States major standards from industry are
• The American National Standard Institute
  (ANSI), the IEEE, and the Electronic Industries
  Association (EIA). The major governmental
  standards organization is the National institute
  of Standards and Technology (NIST).
• NIST major standards concerns are the
  standard Volt, standard Ampere, time, and
  dimensions for manufactures.

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Open System Interconnection Reference Model
Each layer is a kind of virtual machine, offering
certain services to the layer above
Communication subnet
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Protocol Hierarchies

• The philosopher-translator-secretary architecture.

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Why layering?

• Each layer is a kind of virtual machine, offering
  certain services to the layer above it.
• Layer n on one machine carries on a conversation
  with layer n on another machine. The rules and
  conversations are known as the layer n protocol.
• A protocol is an agreement between the
  communicating parties on how communication is to
  proceed.
• Dealing with complex systems
• Clear structure allows identification,
  relationship of complex systems pieces
• modularization eases maintenance, updating of
  system change of implementation of layers
  service transparent to rest of system

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• The function of layer what task the layer is
  perform, but
• not
  how the layer performs its task.
• The function of interface how a layer will
  communicate
• with the layer
  above it and the layer below it.
• For software interfaces, information may be
  passed in a manner similar to parameter passing.
  The information must be in a particular format
  (a. length, b. the order in which individual
  fields appear within a frame, c. the bit order
  within individual frames).
• The hardware interfaces (physical level) may be
  a. voltages, b. impedance, and c. mechanical
  dimensions.
• Bottom three layers - Communications Subnet. They
  are
• 1. the Physical Layer, (is hardware)
• 2. the Data Link Layer (DLL), (can be a
  mixture of hardware
• 
  and software).
• 3. the Network Layer.
• The Communication Subnet is one of the major
  subjects of
• CS 117 and CS M 171L classes to study.

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Communications Subnet.

• the Physical Layer, is hardware The Physical is
  the actual medium that conveys the bit stream.
  This connects the networks together and carries
  the "ones" and "zeros" (voltage or light pulses).
  Typical questions here are how many volts should
  be used to represent a 1 and how many for 0.
  How many nanoseconds a bit lists,

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• Layer 1 Physical Layer. Transmitted signals are
  modulated electromagnetic waves that propagate
  through medium.
• The medium can be fiber optics, twisted pair
  copper wire, coaxial cable, microwaves,
  satellite, laser beams, or radio waves. Layer 1
  also includes the antennas, cables, satellites,
  and connectors.
• The transmitter converts the bits into signals,
  and the physical layer in the receiver converts
  the signals back into bits. The receiver must be
  synchronized to be able to recover the arrival
  bits. To assist the synchronization, the
  transmitter inserts a specific bit pattern,
  called a preamble, at the beginning of the
  packet.
• The physical layer transmits bits by converting
  them into electrical, electromagnetic waves, or
  optical signal.
• Generally, wireless links are slower than copper
  links, and copper links are slower than optical
  links.

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Physical Media coax, fiber

• Coaxial cable
• copper conductors
• bidirectional
• baseband
• single channel on cable
• broadband
• multiple channel on cable

• Fiber optic cable
• glass fiber carrying light pulses, each pulse a
  bit
• high-speed operation
• high-speed point-to-point transmission (e.g., 5
  Gps)
• low error rate repeaters spaced far apart
  immune to electromagnetic noise

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Physical media radio

• signal carried in electromagnetic spectrum
• no physical wire
• bidirectional
• propagation environment effects
• reflection
• obstruction by objects
• interference

• Radio link types
• terrestrial microwave
• e.g. up to 45 Mbps channels
• LAN (e.g., WaveLAN)
• 2Mbps, 11Mbps
• wide-area (e.g., cellular)
• e.g. 3G hundreds of kbps
• Satellite
• up to 50Mbps channel (or multiple smaller
  channels)
• 270 msec end-end dela

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Communications Subnet (cont)

• 2. the Data Link Layer (DLL) 1. Error control
  2. Flow control 3 Synchronizes the receiver to
  the incoming bit stream 4. Decodes the bit
  stream.
• Sublayer 2a Media Access Control (MAC).
• regulate the access to that shared link
• Sublayer 2b Logical Link Control (LLC).
• Implement error detection or reliable packet
  transmission between computers attached to
• a shared link.
• The MAC and LLC together constitute the data link
  layer to implement a packet transmission service
  with error detection or a reliable packet
  transmission service

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Communications Subnet (cont)

• Layer 3 Network Layer is concerned with routing
  the frame. The three steps of routing are 1.
  Establishing the connection, 2. Maintaining the
  connection, 3. Terminating the connection after
  the data transfer is complete.
• Routing is the function to find the path the
  packets must follow.
• The network layer appends unique network
  addresses of the source and destination
  computers.
• Addressing scheme in packet-switched networks is
  that used by the Internet.
• Circuit-switch networks, like the telephone
  network, use different addressing schemes.
• The network layer uses the transmission over
  point-to-point links provided by the data link
  layer to transmit packets between any two
  computers attached in a network.

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The network edge

• End systems (hosts)
• Run application programs
• Web, email
• at edge of network
• Client/server model
• Client host requests, receives service from
  always-on server
• Web browser/server email client/server

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The Network Core

• Mesh of interconnected routers
• the fundamental question how is data transferred
  through network?
• --circuit switching dedicated circuit per call
  telephone net
• packet-switching data sent thru net in packets

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Circuit Switching

• End-to-end resources reserved for call
• link bandwidth, switch capacity
• dedicated resources no sharing
• circuit-like (guaranteed) performance
• call setup required

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Packet Switching

• Each end-end data stream divided into packets
• users share network resources dynamically
• each packet uses full link bandwidth
• resources used as needed

• Resource contention
• aggregate resource demand can exceed amount
  available bandwidth
• congestion packets queue, wait for link use

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Packet Switching Statistical Multiplexing
10 Mbs Ethernet
C
A
statistical multiplexing
1.5 Mbs
B
queue of packets waiting for output link

• Sequence of A B packets does not have fixed
  pattern ? statistical multiplexing.

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Whats the Internet

• Millions of connected computing devices hosts,
  end-systems
• PCs workstations, servers
• running network applcts
• communication links
• fiber, copper, radio, satellite
• transmission rate bandwidth
• Routers (gateways) forward packets (chunks of
  data)

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Whats a protocol?
Hi
TCP connection req
Hi
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Whats a protocol?

• network protocols
• machines rather than humans
• all communication activity in Internet governed
  by protocols

• human protocols
• whats the time?
• I have a question
• introductions
• specific msgs sent
• specific actions taken when msgs received, or
  other events

protocols define format, order of msgs sent and
received among network entities, and actions
taken on msg transmission, receipt
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Protocol Layers

• Networks are complex!
• many pieces
• hosts
• routers
• links of various media
• applications
• protocols
• hardware, software

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A closer look at network structure

• Network edge applications and hosts
• Network core
• routers
• network of networks
• Access networks, Physical media communication
  links

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Internet protocol stack

• application supporting network applications
• FTP, SMTP, STTP
• transport host-host data transfer -TCP, UDP
  (user datagram protocol)
• Network routing of datagrams from source to
  destination
• IP, routing protocols
• Data link data transfer between neighboring
  network elements
• PPP, Ethernet
• Physical bits on the wire

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Network SoftwareProtocol Hierarchies

• Layers, protocols, and interface services.

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The relationship between a service and a
protocol
A set of layers and protocols is called network
architecture. A list of protocols used by a
certain system, one protocol per layer, is called
a protocol stack.
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Correspondence of OSI and TCP/IP Reference models
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Protocols and networks in the TCP/IP model
initially
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Mixed OSI and TCP/IP layers

• Each layer takes data from above
• adds header information to create new data unit
• passes new data unit to layer below

source
destination
message
segment
datagram
frame
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Layering physical communication
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• The Internet Layer is the glue that holds the
  whole architecture together. Its job is to permit
  hosts to inject packets into any network and have
  them travel independently to the destination
  (potentially on a different network). They may
  even arrive in different order than they were
  sent, in which case it is the job of higher
  layers to rearrange them, if in-order delivery is
  desired.
• The internet layer defines an official packet
  format and protocol called IP (Internet
  Protocol). The job of the internet layer is to
  deliver IP packets where they are supposed to go.
  Packet routing is clearly the major issue here,
  as is avoiding congestion. For these reason, it
  is possible to say that
• the internet layer is similar in functionality
  to the OSI network layer.

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• The Transport Layer is designed to allow the
  source and destination hosts to carry on a
  conversation, just as in the OSI transport layer.
  
• Two end-to-end transport protocols are
• 1. TCP (Transport Control Protocol), is a
  reliable connection-oriented protocol that allows
  a byte stream originating on one machine to be
  delivered within error on any other machine in
  the Internet. It fragments the incoming byte
  stream into discrete messages and passes each one
  on the internet layer. At the destination, the
  receiving TCP process reassembles the received
  messages into the output. TCP also handles flow
  control.
• 2. UDP (User Datagram Protocol), is an
  unreliable, connectionless protocol for
  application that do not want TCPs sequencing or
  flow control and wish to provide their own. It is
  also widely used for one-shot, client-server-type
  request-reply queries and applications in which
  prompt delivery is more important than accurate
  delivery, such as transmitting speech or video.

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Connectionless and Connection-Oriented Services

• Internet, generally TCP/IP network provide two
  types of services to its applications
• 1. connectionless services
• 2. connection-oriented services

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Connection-oriented service

• Goal data transfer between end systems
• handshaking setup (prepare for) data transfer
  ahead of time
• Hello, hello back human protocol
• set up state in two communicating hosts
• TCP - Transmission Control Protocol
• Internets connection-oriented service

• TCP service RFC 793
• reliable, in-order byte-stream data transfer
• loss acknowledgements and retransmissions
• flow control
• sender wont overwhelm receiver
• congestion control
• senders slow down sending rate when network
  congested

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Connectionless service

• Goal data transfer between end systems
• same as before!
• UDP - User Datagram Protocol
• Internets connectionless service
• unreliable data transfer
• no flow control
• no congestion control

• Apps using TCP
• HTTP (Web), FTP (file transfer), Telnet (remote
  login), SMTP (email)
• Apps using UDP
• streaming media, teleconferencing, Internet
  telephony

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• The Application Layer
• The TCP/IP model does not have session or
  presentation layers.
• On top of the transport layer is the application
  layer. It contains all the higher-level
  protocols. The early ones included virtual
  terminal (TELNET), file transfer (FTP), and
  electronic mail (SMTP). The virtual terminal
  protocol allows a user on one machine to log onto
  a distant machine and. Electronic mail was
  originally just a kind of file transfer, but
  later a specialized protocol (SMTP) was developed
  for it. Many other protocols have been added to
  these over the years, the Domain Name System
  (DNS) for mapping host names onto their network
  addresses, NNTP, the protocol for moving USENET
  news articles around, and HTTP, the protocol for
  fetching pages on the World Wide Web, and many
  others.

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Circuit Switching FDMA and TDMA
TDMA
frequency
time
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Packet Switching

• resource contention
• aggregate resource demand can exceed amount
  available
• congestion packets queue, wait for link use
• store and forward packets move one hop at a time
• transmit over link
• wait turn at next link

• each end-end data stream divided into packets
• user A, B packets share network resources
• each packet uses full link bandwidth
• resources used as needed

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Layering logical communication

• transport
• take data from application layer
• add addressing, reliability check info to form
  datagram
• send datagram to peer
• wait for peer to ack receipt
• analogy post office

transport
transport
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Layering logical communication

• Each layer
• distributed
• entities implement layer functions at each node
• entities perform actions, exchange messages with
  peers