Chapter 2: Networks

1
Chapter 2 Networks

• COMP 2073
• Week 3
• Winter 2003
• Professor Kona Sirohi
• Email ksirohi_at_gbrownc.on.ca

2
Networks - Basics

• A network consists of two or more computers
  connected to each other to share data.
• Networks makes sharing of data much faster and
  efficient.
• Networks also allow use of shared hardware
  resources such as printers etc.
• Two types of networks are LAN and WAN
• In LAN, computers are connected to one another in
  one physical location.
• In WAN, computers from different geographic
  locations can connect to each other.

3
Networks Basics (contd)

• All networks have certain general components,
  functions and features. These include
• Computers that provide shared resources to
  network users (Servers)
• Computers that access shared network resources
  provided by the servers (Clients)
• Hardware resources provided by the server
  (Printers and other peripherals)
• Shared software (Applications, documents, audio,
  video etc)

4
Networks Basics (contd)

• Networks can be divided into two categories
• Peer-to-peer Network No dedicated servers, no
  hierarchy among computers. Sharing capabilities
  are defined at the individual level.
• Server-based Network A dedicated server acts as
  a leader and computers act as clients. The server
  provides sharing permissions to individual
  clients.
• The decision to deploy one network over the other
  depends on the size of the organization, the
  level of security needed and the level of
  administration support needed.
• Streaming media solutions should always follow
  the second option.

5
Various LAN Topologies

• Token Ring
• Ethernet
• Fast Ethernet
• Gigabit Ethernet
• Fiber Distributed Data Interface(FDDI)
• Asynchronous Transfer Mode(ATM)
• (Click on each hyperlink to learn more about
  these topologies)

6
Token Ring

• This topology uses a token-passing mechanism to
  pass information. Computers pass information to
  another in a cycle.
• A token, which is a special bit pattern, travels
  around the circle. To send a message, a computer
  catches the token, attaches a message to it, and
  then lets it continue to travel around the
  network.

Contd
7
Token Ring(contd)

• Initially, token ring networks used a data
  transfer rate of 4 Mbps, which have now been
  upgraded to 16 Mbps.
• This method is not a supported technology for
  streaming media.
• If a single client is not operation in the
  network, the whole data transmission stops.
• If a single client uses its allocated bandwidth
  to run other applications, the transmission of
  data slows down significantly.

8
Ethernet (also called IEEE 802.3)

• Ethernet uses either a star or a bus topology and
  is a widely used base for network technologies.
• It normally operates with a transmission rate of
  10 Mbps.

Contd
9
Ethernet (contd)

• Ethernet uses Collision Sense Multiple Access/
  Collision Detection (CSMA/CD) algorithm which can
  be described as below
• Listen over the medium before you transmit.
• If the medium is idle, then transmit.
• If the medium is busy, wait until idle, then
  transmit immediately.
• Look for collision.
• If a collision is detected, wait for a random
  period of time and then reattempt.

10
Fast Ethernet

• It uses combination of 100BaseT (this is the most
  common standard today) and 100VG-AnyLan standard.
• The data transmission rate is 100 Mbps.
• 100VG-AnyLAN uses a demand priority scheme.
  Demand priority works like a traffic signal the
  hub polls each client to determine if it has
  data to transmit and then allows transmission in
  order.
• This method generates fewer collisions.

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Example of 100VG-AnyLan method

• If there is a request waiting on port one and
  port
• three the hub begins by servicing port one.
• Next, the hub checks to make sure that no new
• requests have come in for port two, the next in
• line. Assuming no requests have come in, the
• hub proceeds to service the request on port
• three. If a request came in from ports two and
• four while the request at port three was being
• serviced, port four would be the next one
• serviced and then the hub would start back at
• port one. This "round-robin technique" allows
• equal access to network media.

12
Gigabit Ethernet

• This operates with a data rate of 1000 Mbps.
• Its fully compatible with existing Ethernets.
• Used as server connection and backbone
  connections.
• Uses CSMA/CD algorithm.

13
Fiber Distributed Data Interface(FDDI)

• FDDI networks are enhanced token-passing
  networks, and support data rates of up to 100
  Mbps.
• Uses fiber-optic cable to transmit digital data.
• FDDI networks are typically used as backbones for
  wide-area networks.
• FDDI uses dual-ring architecture to provide
  redundancy in case of a failure.
• An extension to FDDI, called FDDI-2, supports the
  transmission of voice and video information as
  well as data.

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Asynchronous Transfer Mode (ATM)

• It is a broadband network topology used to
  transfer high volumes of data within LAN and WAN.
• It allows to integrate voice, video and data.
• Common data rates used by ATMs are OC-3(155 Mbps)
  and OC-12(622 Mbps).
• It is a connection oriented technology - Every
  cell with the same source and destination travels
  over the same route.
• Perhaps the best networking topology but the
  cost of deployment is substantially high.
• Commonly used for connecting various segments of
  a network together.

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Asynchronous Transfer Mode (ATM)
16
Various WAN Technologies

• Digital Subscriber Line (DSL)
• Asynchronous Transfer Mode (ATM)
• Integrated Services Digital Network (ISDN)
• X.25
• Frame Relay
• Cable Modems
• Analog Modems
• T1 Lines

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Digital Subscriber Line (DSL)

• DSL, which stands for Digital Subscriber Line,
  provides high-speed remote network access using
  regular telephone lines.
• The total bandwidth data transfer speed ranges
  between 56 Kbps to 14 Mbps.
• Some versions of DSL support concurrent voice and
  data over the same phone line.
• It is a dedicated line between the end-user and
  the phone company and its always on for use.

18
Digital Subscriber Line (DSL contd...)
19
Asynchronous Transfer Mode (ATM)

• ATM is also used in WAN environments. Most of the
  new backbone segments added to the Internet, use
  ATM topology.
• ATM is designed for high-performance multimedia
  networking.
• The benefits of ATM are the following
• High performance
• Dynamic bandwidth
• Support for multimedia
• Scalability in speed and network size
• Common LAN/WAN architecture
• International standards compliance

20
Integrated Services Digital Network(ISDN)

• ISDN, which stands for Integrated Services
  Digital Network, is a system of digital phone
  connections which has been available for over a
  decade.
• An ISDN modem established a much faster
  connection to the remote machine than an analog
  modem.
• Voice and data are carried by two bearer channels
  (B channels) occupying a bandwidth of 64 kbps
  each (total of 128 Kbps).
• A data channel (D channel) handles signaling at
  16 kbps or 64 kb/p, depending on the service
  type.

21
X.25

• X.25 is an international standard developed for
  point-to-point transmission of data.
• It uses packet-switching technology, which is
  very much different from IP-based technology.
• Used to connect terminals to mainframe computer
  systems.
• The technology performs constant error checks
  rectifications if any, and thus creates overheads
  on the network.
• Not used so widely these days.

22
Frame Relay

• This is a packet-switched architecture similar to
  X.25. It also works on a network that uses
  IP-based technology.
• Used mostly with digital technology, where the
  probability of an error is less.
• It provides better stability and less error
  checking, making it a faster technology.
• It is widely used to connect point-to-point
  segments on the WAN.

23
Cable Modem

• Its a new technology that offers high-speed
  network access over traditional cable television
  systems.
• Cable modems share the same bandwidth among many
  customers using the same fiber-optic line.
• It follows asymmetrical design that means
  downstream is greater than upstream.

24
Analog Modem

• They use standard plain old telephone service
  (POT) lines.
• The bandwidth is between 28 Kbps and 56 Kbps.
• A large number of users connect to the Internet
  using analog modem.
• They also work in asymmetric fashion.

25
T1 Lines

• These are digital circuits used by the corporate
  world for connecting to remote networks.
• Its a standard digital line that carries both
  voice and data at equal up and downstream rate.
• The bandwidth is guaranteed 1.544 Mbps.
• Its extremely reliable and much faster than the
  ordinary telephone line.
• Very popular with many corporate sectors for over
  a decade now.

26
Internet Protocols

• Streaming media technology, apart from using some
  special protocols, use the very same protocols
  that are used to transmit documents over a
  network.
• They rely on Transmission Control Protocol /
  Internet Protocol (TCP/IP) architecture.
• Some common network protocols are
• IP (Internet Protocol)
• UDP (User Datagram Protocol)
• HTTP (Hyper Text MarkUp Language)

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IP (Internet Protocol)

• IP is a network-layer protocol responsible for
  transmitting blocks of data called datagram from
  sources to destinations.
• Source and destinations have a fixed length,
  unique identification number called IP address.
  IP address are divided into five major classes
• Class A from 1.0.0.0 to 127.0.0.0. Mostly used
  by ISPs for their large and complex network.
• Class B from 128.0.0.0 to 191.255.0.0. Used in
  mid-sized networks such as college campuses etc.
• Class C from 192.0.0.0 to 223.255.255.255. Used
  by small networks in an enterprise.
• Class D from 224.0.0.0 to 239.0.0.0, Used for
  multicasts.
• Class E from 240.0.0.0 to 248.0.0.0. Used for
  experimental purposes.

28
UDP (User Datagram Protocol)

• It is a standard, low-head, connectionless,
  host-to-host protocol that is used over
  packet-switched communication networks.
• It allows an application program on one machine
  to send datagram to an application program on
  another machine.
• The connectionless service allows the transfer of
  information among subscribers without the need
  for end-to-end establishment procedures.
• The term connectionless refers to the fact that a
  connection to the destination host is not
  required. If any UDP application sends messages
  to a host, it does not know whether the host
  received the message because the host does not
  respond with an acknowledgment by default.

29
HTTP (Hyper Text Transfer Protocol)

• This protocol facilitates the transfer of
  hypertext-based files between local and remote
  systems.
• This protocol is used to transmit web-pages
  across the Internet.

30
Streaming Media Protocols

• All the three streaming media technologies use
  either TCP/IP, UDP or HTTP protocols to transfer
  data packets between the host server and the
  client media player.
• These technologies use a 3 level rollover
  mechanism for transferring data
• First UDP is used as a preferred mode of
  transferring data packets.
• If UDP cannot be used because of Firewall issues,
  then TCP is used.
• Windows media player rolls over from TCP to HTTP
  automatically whereas RealPlayer and QuickTime
  needs manual rollover.

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Networks - Advanced
32
Streaming Protocols

• QuickTime and RealVideo use the RTSP protocol,
  that provides a framework to enable the
  controlled, on-demand delivery of real-time data.
• This protocol is intended to
• Control multiple data delivery sessions
• Provide a means for choosing delivery channels
  such as UDP, Multicast UDP and TCP and
• Provide a means of choosing delivery mechanism.

Contd
33
Streaming Protocols (contd)

• Microsoft uses its own MMS protocol.
• MMS is the default method of connecting to
  Windows Media Unicast Service.
• Both RTSP and MMS can handle clients request
  (such as Play, Stop, Fast Forward or Rewind) over
  TCP.
• Both protocols ensure that media packets arrive
  in a format recognized by the player.
• Data Packets are carried over either UDP, TCP or
  HTTP by using the rollover mechanism.

Contd
34
Streaming Protocols (contd)

• A significant factor in facilitating streaming
  data in a healthy network is to properly map the
  network topology and determine the capabilities
  of the network.
• Hubs often suffer increased collision from a
  consistent streaming of data because they
  broadcast to every port.
• Switches perform better in Multicast traffic
  handling by transmitting the signal to the
  designated IP address.

35
Creation of Streaming Media

• Capture the audio and video contents.
• Convert it to a computer-format.
• Encoding Conversion of video or audio content
  into a computer format is known as Encoding.
• It uses mathematical algorithms to compress the
  information into smaller media format for
  streaming it live or archiving it for on-demand
  viewing.
• Distribute and Stream Once the content has been
  encoded, this format can either be streamed live
  or archived for on-demand broad

Contd
36
New Culture

• The challenge is
• to help people feel comfortable while recording,
• produce the information using new media tools,
• create applications that will be easy to use and
• encourage the users to start using these
  applications to replace the conventional phone
  calls, faxes, face-to-face meetings etc.
• Enterprises must provide basic training for the
  video and IT personnel in the process of creating
  and delivering digital media.
• Standards and workflow templates should become a
  part of our daily routine for consistent and
  quality delivery of the final product.

37
New Roles

• New business roles must be created, not only to
  develop and maintain the digital infrastructure
  but also to maintain an environment that promotes
  and supports the use of the new media. The roles
  can be
• Digital Media Support creates the streaming
  content, understands audio, video and networking
  issues, create templates to be used in the
  production, encode live streams and create
  interactive applications to display the archived
  contents.
• Producer or Coordinator Coordinates the
  production of the content, receives pre-recorded
  content from various departments, ensure that
  media is properly converted and submitted into
  the corporate network.
• Content Distribution Ethernet is the preferred
  LAN topology to distribute Unicast and Multicast
  productions.

38
Choosing a Streaming Architecture

• Centralized Architecture
• Few low user concurrent remote sites.
• High bandwidth network between remote users and
  server.
• Normally servers live broadcasting.
• Multicast enabled between server and remote sites.

• Distributed Architecture
• Many remote sites with high user concurrency at
  those sites.
• Comparatively low WAN bandwidth between clients
  and server.
• Normally hosts media on-demand content.
• Multicast not enabled between the remote sites.

39
Centralized Architecture

• Hosts a farm of media servers at a single
  location, supporting all the users from the same
  location.
• Can be used only when there are few low user
  concurrent remote sites.
• Allows simple content management.
• Allows more efficient use of hardware.
• Allows single-site management. No need to
  redirect users to different servers.
• Does not scale very well.
• Increases load on the central location.
• Does not allow efficient use of WAN bandwidth.

40
Centralized Architecture
41
Distributed Architecture

• Involves placing several servers known as
  splitters, reflectors or stations in strategic
  locations to server the users.
• User requests are directed to the closest server.
• Creates a more fault-tolerant, scalable media
  on-demand solution.
• It can extend multicasts to parts of the network
  where multicast is not possible otherwise.
• Introduces technical challenges as to how the
  user be redirected to the nearest server.

42
Distributed Architecture
WAN
WAN
Creation
Distribution
Playback
43
Content Delivery Network (CDN)

• CDN emerged as a result of poor delivery of
  content on the Internet.
• CDN provides an architecture of web-based network
  elements, arranged for efficient delivery of
  digital content.
• CDN provides an arranged set of distributed
  caching, load-balancing and web-request
  redirection service.
• CDN ensure that based on user proximity and
  server load, the content is served in the most
  efficient manner.
• CDN benefits the content provider as well as the
  network connectivity providers.

44
Content Delivery Network (Contd..)
Load Balancer redirects user to the closest media
server.
Cache server finds media in cache storage and
sends stream to user. Cache server cannot find
the media.
Cache server requests media from the original
media server.
Client Requests media
Original media server sends media to cache server.
Cache server sends the media to the user
45
Content Delivery Network (contd..)

• Benefits of CDN
• Reduces the response-time delays by minimizing
  the number of stops a request has to make from
  the content source.
• CDN brings order and quality of service to the IP
  backbone.
• Load-balancing can be facilitated by the CDN
  network provider it directs the traffic to the
  least loaded server.
• Recently, CDNs are using application-layer
  switching software that not only examine the IP
  of the client but also calculate the specific
  response time of the content being requested.This
  helps in efficient delivery of the content.

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What is Quality of Service(QoS)?

• QoS refers to the performance of a specified set
  of rules to deliver high-quality transmission
  over a communication system.
• QoS is indicted by certain parameters like
  signal-to-noise ration, bit-error-ratio, message
  throughput rate and call blocking probability.
• RSVP, the Reservation Protocol, is one of the
  mechanisms available for Q0S. Others schemes are
  Diff-Serv and IP Precedence.
• If the protocol chosen for QoS on the local loop
  is not same as the backbone, then QoS translation
  software is required specially for interactive
  video applications.

47
How does Streaming Video work?

• Regardless of the technology used, all streaming
  technologies follow the same schema
• Live Feed captured by encoder
• Encoder transmits to Media server or Media server
  pulls media on-demand from storage.
• User Requests media from the Web server.
• Web Server requests streams from media server
  and sends back to the user.

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How Streaming Video works?(Contd..)

• The Source media is either located on a storage
  or is captured live by a camera.
• Video and audio cables transfer the audio-video
  signal from the source device to a capture card
  on the encoding workstation.
• The capture card converts the analog signals to
  digital signals.
• The software encoder detects the digital signal
  and converts it into streaming format.
• This formatted signal is either sent to the
  distribution server or is captures as a file.
• The Media server responds to user requests that
  are made by using a web-page.
• The Media server servers the LAN users as well as
  distributes the signal to other media servers
  over WAN.

49
Firewall Issues

• A firewall is a hardware, software or a
  combination of both for providing security to
  computer networks.
• Firewalls act an interface between two networks
  and regulates traffic between them to protect the
  network from electronic attacks originating from
  external network.

50
Firewall Issues

• Isolates internal and external traffic.
• Makes internal addresses invisible and
  inaccessible directly from outside.
• Allows only authorized traffic to come in after
  proper checking.
• Facilitates encrypted connections.
• Filters outgoing traffic for security and network
  use rules.
• Filters incoming traffic for rouge data like
  viruses, spam etc.

51
Firewall Issues

• Blocks forbidden external services and addresses.
• Provides login service for authorized users.
• Caches network traffic.
• Converts between different network protocols.
• Diverts traffic for cost-optimizing, network
  planning etc.
• Provides consistent open entry to internal
  network.
• Facilitates public network address and connection
  sharing.