Semester 4 CCNA 4

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Semester 4 (CCNA 4)

• Wide Area Networks
• WANs

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CHAPTER 2 OBJECTIVES

• Describe the purpose function of WANs
• Describe the various WAN devices
• Describe WAN operation
• Understand WAN encapsulation formats
• Understand WAN link options

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WANs vs. LANsWhats the Difference?

• A LAN operates in a limited geographical area.
• A WAN is a communications network that operates
  beyond a LANs geographic scope, inter-connecting
  LANs.

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The OSI Model

• WANs function at the three lowest layers of the
  OSI reference model
• WANs focus on the physical and data link layer.
• The data link layer is used to describe how
  frames are carried between systems on a single
  WAN data path.

Application
7 6 5 4 3 2 1
Presentation
Session
Transport
Network
WAN Layers
Data Link
Physical
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The WAN Physical Layer

• Describes how to provide electrical, mechanical,
  operational, and functional connections for WAN
  services.
• Also describes the interface between the DTE and
  DCE

SUBSCRIBER
PROVIDER
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WAN STANDARDS
The following agencies define and manage WAN
standards

• International Telecommunication
  Union-Telecommunication Standardization Sector
  (ITU-T)
• International Organization for Standardization
  (ISO)
• Internet Engineering Task Force (IETF)
• Electronic Industries Association (EIA)
• Telecommunications Industries Association (TIA)

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WAN TECHNOLOGIES
Packets may take different physical routes from
source to destination
Physical lines that require no switching
Physical circuit is established for the duration
of the data transfer
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WAN Service Providers

• In order to use WAN services, a company must
  subscribe to an outside WAN service provider. For
  example, a Regional Bell Operating Company
  (RBOC).

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WAN Line Types
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WAN Protocols/Encapsulations

• Frame Relay - Can transmit data very rapidly
  compared to other WAN protocols. Uses simplified
  encapsulation with no error correction mechanisms
  over high-quality digital facilities. Frame
  Relay is the industry standard.
• Point-to-Point Protocol (PPP) - PPP was developed
  by the IETF. PPP contains a protocol field to
  identify the network-layer protocol.
• ISDN - A set of digital services that transmit
  voice and data over existing phone lines.

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WAN Protocols/Encapsulations

• Link Access Procedure, Balanced (LAPB) - For
  packet-switched networks. It can also be used
  over a point-to-point link if the link is
  unreliable or if there is an inherent delay
  associated with the link, such as in a satellite
  link. LAPB provides reliability and flow control
  on a point-to-point basis.
• Cisco/IETF - Used to encapsulate Frame Relay
  traffic. The Cisco option is proprietary and can
  be used only between Cisco routers.
• High-Level Data Link Control (HDLC) - An ISO
  standard, HDLC might not be compatible between
  different vendors because of the way each vendor
  has chosen to implement it. HDLC supports both
  point-to-point and multipoint configurations.

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WAN TERMS -Customer Premises Equipment (CPE)

• Devices physically located on the subscribers
  premises
• Includes both owned and leased equipment.

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WAN TERMS -Point of Demarcation (demarc)

• Point at which the CPE ends and the local loop
  portion of the service begins
• Usually located at the POP

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WAN TERMS -Local Loop (Last Mile)

• Cabling, usually copper wiring, that extends from
  the demarc into the WAN service providers
  central office (CO).

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WAN TERMS -CO Switch (Central Office)

• All local loops in a given area connect to the
  CO.
• A switching facility that provides the nearest
  point of presence for the providers WAN service.

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WAN TERMS -Toll Network

• The collective switches facilities (called
  trunks) inside the WAN providers cloud.

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WAN TERMS -DTE DCE Devices

• Data terminal equipment (DTE)
• Data circuit-terminating equipment (DCE)
• The DTE/DCE interface acts as a boundary where
  responsibility for the traffic passes between the
  WAN subscriber and the WAN provider.
• Examples
• DTE typically a router
• DCE device used to convert the user data from
  the DTE into a form acceptable to the WAN
  services facility (typcially an attached Modem,
  CSU/DSU, or TA/NT1).

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WAN Devices

• Routers - devices that implement network service
  (routers are also LAN devices)
• WAN Switches - multiport networking device, which
  typically switches such traffic as Frame Relay,
  X.25, and Switched Multimegabit Data Service
  (SMDS).
• Modems - device that interprets both digital and
  analog signals by modulating and demodulating the
  signal, enabling data to be transmitted over
  voice-grade telephone lines.

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WAN Device Symbols

• Routers
• WAN switches
• Communication servers
• Modems - CSUs, DSUs, TA/NT1 devices that
  interface ISDN services (DCE Devices)

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WAN DevicesCSU/DSU(Channel Service
Unit/Digital Service Unit)

• A digital interface device that connects end-user
  equipment to the local digital telephone loop
• A CSU/DSU adapts the physical interface on a DTE
  device to the interface of a DCE device.
• A CSU/DSU provides signal timing
• provides a barrier for electrical interference
  from either side of the unit
• When routers are connected to a leased line, they
  need a CSU/DSU between them and the leased line
• CSU/DSUs are sometimes integrated in the router

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WAN TECHNOLOGIES
Packets may take different physical routes from
source to destination
Physical lines that require no switching
Physical circuit is established for the duration
of the data transfer
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Dedicated WAN Technology

• Dedicated lines are leased from WAN service
  providers
• Dedicated lines provide full-time service
• A Router Port, CSU/DSU, and Service provider
  circuit is required for each leased line
  connection.
• Bit rate capacity of a T1 line is 1.544 Mbps.
• Fractional T1 Lines are T1 lines that are used in
  increments of 64k.
• Uses carry data, voice, video provide core WAN
  connectivity and LAN to LAN connectivity

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Point-to-Point Serial Links

• Protocol that provides router-to-router and
  host-to-network connections over synchronous and
  asynchronous circuits.
• Provides dedicated, full-time connectivity.
• The Service Provider reserves Point-to-Point
  links for the private use of the customer

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Point-to-Point WAN Encapsulations and Frame
Formats

• PPP Technical Overview
• Standard serial line encapsulation
• Protocol type specified
• Authentication (PAP CHAP)
• HDLC Technical Overview
• Ciscos default serial line encapsulation
• Proprietary (uses a 2-byte proprietary type code)
• HDLC is NOT interoperable with other vendors
  equipment)

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WAN Packet-switching

• A WAN switching method in which packets may take
  different routes on the way to the destination
• The most common packet-switched network type is
  Frame Relay

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FRAME RELAY OVERVIEW

• Packet-switching data communications technology
• Designed to be used over high-speed, high quality
  digital facilities
• No error checking or reliability
• A cost effective alternative to point-to-point
  WAN designs
• Sites can be connected to all other sites by a
  virtual circuit
• A data-link connection identifier (DLCI)
  identifies a PVC
• Each router requires only one physical interface
  to the carrier

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FRAME RELAY OVERVIEW

• Frame Relay - Information contained in frames
  shares bandwidth with other WAN Frame Relay
  subscribers.
• Frame Relay is a statistical multiplexed service
  which uses Layer 2 identifiers and permanent
  virtual circuits.
• Frame Relay packet switching uses Layer 3 routing
  with sender and receiver addressing contained in
  the packet.

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CIRCUIT-SWITCHED NETWORK

• A type of network in which a physical path is
  obtained for and dedicated to a single connection
  between 2 end-points in the network for the
  duration of the connection.
• A circuit-switched pathway is an actual physical
  pathway through the network
• Requires relatively low bandwidth (connections
  brought up only when needed)
• Examples include basic telephone service and ISDN
• ISDN is used primarily to connect remote and
  mobile users or for a backup

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ISDN OVERVIEW

• 2 types of ISDN service
• PRI Primary Rate Interface
• BRI Basic Rate Interface
• BRI is composed of 2 B (bearer) channels and 1 D
  (delta) channel (2B D)
• B channels operate at 64 kbps and are used to
  carry voice or data traffic
• The D channel is a 16 kbps signaling channel used
  to carry instructions on how to handle the B
  channels.

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ISDN OVERVIEW
Connects 4-wire ISDN subscriber to 2-wire local
loop
Device compatible with ISDN network
Device NOT compatible with ISDN
Connects non-ISDN devices to the ISDN network
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Time-division Multiplexing (TDM)

• The process of allocating bandwidth to different
  sources on the same media is known as TDM.
• By multiplexing traffic into fixed time slots,
  TDM avoids congested facilities and variable
  delays.

• Basic telephone services and ISDN use TDM
  circuits.

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Dial on Demand Routing (DDR)

• A technique with which a router can dynamically
  initiate and close circuit-switched sessions as
  transmitting end stations need them.
• DDR allow a standard telephone connection or an
  ISDN connection only when required by the volume
  of network traffic
• In DDR, the connection is brought up only when a
  specific type of traffic (interesting traffic)
  initiates the call or a backup link is needed

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Physical vs. Virtual Circuits

• Physical Circuit
• The messages take one route through the cloud
• Virtual Circuit
• The messages takes the best available route in
  the cloud

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Virtual Circuits

• A virtual circuit is a pathway through a
  packet-switched network that appears to be a
  dedicated, physically connected circuit.
• A virtual circuit-switched connection is a
  dedicated logical connection that allows sharing
  of the physical path among many multiple virtual
  circuit connections.
• Virtual circuits are connection-oriented

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WAN Virtual Circuits

• A virtual circuit is a logical circuit - as
  opposed to a point-to-point circuit - created to
  ensure reliable communication between two network
  devices.
• Two types of virtual circuits
• switched virtual circuits (SVCs)
• permanent virtual circuits (PVCs)

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SWITCHED VS. PERMANENT VIRTUAL CIRCUITS

• Switched virtual circuits (SVCs) - SVCs are very
  much like telephone calls a connection is
  established, data is transferred and then the
  connection is released. Each DTE on the network
  is given a unique DTE address which can be used
  much like a telephone number.
• Permanent virtual circuits (PVCs) - a PVC is
  similar to a leased line in that the connection
  is always present. The logical connection is
  established permanently by the Packet Switched
  Network administration. Therefore, data may
  always be sent, without any call setup.

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WAN Virtual Circuits

• SVCs are dynamically established on demand and
  terminated when transmission is complete.
• SVCs increase bandwidth used due to the circuit
  establishment and termination phases, but
  decrease the cost associated with constant
  virtual-circuit availability.
• Communication over an SVC consists of three
  phases
• data transfer
• circuit termination
• circuit establishment

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WAN Virtual Circuits

• PVC is a permanently established virtual circuit.
• PVCs are used for constant data transfer.
• PVCs decrease bandwidth use associated with the
  establishment termination of virtual circuits.
• PVCs increase costs due to constant
  virtual-circuit availability.

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IP Telephony Voice over IP (VoIP)

• Telephony is traditionally carried out using a
  conventional phone and connections using
  circuit-switching techniques (PSTN).
• The Internet uses packet-switching techniques.
• Packets that move around the Internet contain
  header info including source destination
  address of the packet and a data section
  including text, graphics, or digitized voice.
• Whats the difference?
• Circuit-switching dedicated end-to-end path
• Packet-switching message is chopped up and each
  packet is sent individually and possibly over
  different routes

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IP Telephony Voice over IP (VoIP)

• VoIP uses IP based networks rather than the
  traditional public telecommunication
  infrastructure
• The simultaneous delivery of voice and data over
  a single communications link using the Internet
  Protocol

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Semester 4 V 2.1.2

• Wide Area Networks
• WANs
• The End