Intro to WAN

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Intro to WAN

• CNAP _at_ VCC
• Semester 4, Chapter 2

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Service providers

• Central Office (CO) Each telephone connects to a
  single point called a CO.
• Local Loop (LP) The line that connects the
  customer to the CO.
• Local Exchange Carrier (LEC) The company that
  operates the local loop and owns the Co.
• Local Access Transport Area (LATA) Limited
  Geographic areas served by LECs.

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Service providers

• Inter Exchange Carriers (IXC) Long distance
  carriers that connect COs.
• Regional Bell Operating Companies (RBOC)
  Companies that served LECs such as Bell south,
  Bell Atlantic, and Southwestern Bell.
• Competitive Local Exchange Carriers (CLECs)
• http//www.learntcpip.com/InternetRuns/default.htm
  

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WAN Connection Types

• Asynchronous VS. Synchronous Transmission
• Asynchronous means without respect to time. No
  clock or timing source is needed to keep both the
  sender and receiver synchronized. Sender must
  signal the start and the stop of each character.
• Synchronous common timing signal is used
  between hosts.

5
WAN Connection Types

• Dedicated Connectivity
• Circuit-Switched Networks
• Packet Switched Networks

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Dedicated Connection

• Continuously available point-to-point link
  between two sides.
• Provides a single pre-established WAN path from
  the customer premises, through the carrier
  network to a remote network.
• Offer high speed of up to 45 Mbps.
• Ideal for high volume environment with
  steady-rate traffic patterns.
• Very expensive Includes a fixed fee for
  local-loop access for both locations and a
  distance fee for linking those two location.
• Dedicated leased lines require synchronous serial
  connection

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Dedicated Connection

• A CSU/DSU is classified as a data communication
  equipment (DCE) that provides signal timing and
  interfaces with the router or Data Terminal
  Equipment (DTE)
• Fully meshed WAN is too costly to build using
  only dedicated lines
• Typically connections on a dedicated network
  operates at the following speeds
• 56Kbps
• 64kbps
• T1 (1.544 Mbps)
• T3 (44.736 Mbps)

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Dedicated Connection

• A DTE such as the router connects to a DCE such
  as CSU/DSU using one of the following standards
• EIA/TIA-232
• EIA/TIA-449
• V.35
• X.21
• EIA-530
• When connecting a router to an analog modem,
  EIA/TIA-232 standards compliant cabling and
  asynchronous interfaces are used. When
  connecting the router to digital modem, V.35
  standard compliant cabling and synchronous
  interfaces are used.

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Circuit-Switched Connections

• A dedicated physical circuit is temporarily
  established for each communication session.
• Initial setup signal is used to establish the
  circuit, and a teardown signal brings the circuit
  down when transmission is complete.
• Plain Old Telephone Service (POTS) is the most
  common circuit-switched technology.
• The temporary dedicated circuit does not get
  established until you place a call.

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Circuit-Switched Connections

• Provide mobile and home users with access to a
  central site or to an ISP.
• Normally circuit-switched connections are used
  as backup links, or to link branch offices with
  low vloume or periodic traffic to a companys
  central office.

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Circuit-Switched Connections

• Circuit-switched connections can be costly if
  left continuously established. For that reason
  routers that are connected to a circuit-switched
  network use dial-on-demand routing.
• With DDR, a router places a call only when it
  detects interesting traffic.
• Typical Circuit-Switched connections include the
  following
• Asynchronous Serial (POTS)
• ISDN Basic Rate Interface (BRI)
• ISDN Primary Rate Interface (PRI)

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Asynchronous Serial Connections

• Offer inexpensive WAN service through the
  existing telephone network.
• Modem is required at each end of the connection
• Provides a throughput of less than 56 kbps.
• Used to connect home users or mobile users to
  corporate network

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Asynchronous Serial Connections

• Some routers are designed with dozens of
  asynchronous lines to support a large number of
  dial-in users
• Routers that act as concentration points for
  dial-in and dial-out calls are called access
  servers.
• To receive or place an asynchronous serial call,
  a router must have at least one asynchronous
  serial interface such as the auxiliary port.

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ISDN Connections

• Circuit-Switched Synchronous Connections
• Dial up connection that provide WAN access when
  needed.
• Offers more bandwidth than asynchronous dial-up
  connections.
• ISDN offers to levels of service BRI, and PRI.

15
Packet-Switched Networks

• Unlike leased lines and circuit-switched
  connections, packet switching does not rely on a
  dedicated point-to-point connection through the
  carrier network.
• Allows service providers to support multiple
  customers over the same physical lines.
• Typically, customers connect to the packet
  switched network through a leased line, such as a
  T1 or a fractional T1.
• Frame Relay is the most common packet-switched
  WAN service in the United States.

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Packet-Switched Networks

• In a packet-switched network, the provider
  configures its switching equipment to create
  virtual circuits that provide end-to-end
  connectivity.
• VCs can be permanent or they could be established
  on demand.
• A frame rely VC offers a speed of up to T3 line
• Les control because the WAN facilities are
  shared, but also les cost

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Packet-Switched Networks

• A single synchronous serial connections can
  support several logical VCs in a point to
  mulitipoint configuration.
• Thus packet switching makes a full or partial
  mesh topology relatively affordable.
• However frame relay does not offer the degree of
  reliability , flexibility and security afforded
  by dedicated lines
• Therefore, dedicated lines are the preferred WAN
  service for mission critical traffic and
  continuous high volume exchanges.

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WAN Encapsulation Protocols

• Routers encapsulate packets with layer 2 frame
  before sending them across a WAN link.
• The data link protocol that is used depends in
  part on what type of WAN connection is deployed.
  

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WAN layer 2 Protocols

• Point-To-Point Used for router-to-route and
  host-to network connections over synchronous and
  asynchronous circuits.
• Serial Line Internet Protocol forerunner to
  PPP.
• HDLC HDLC implementations are proprietary.
  When connecting routers from different vendors
  use PPP.

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WAN layer 2 Protocols

• X.25 Provides the standards that regulate how a
  DCE, and a DTE should communicate in a public
  data network. X.25 provides extensive error
  detection and windowing.
• Frame Relay High performance, packet switched
  WAN protocol that does not provide error
  detection.
• ATM Cell Relay in which multiple service types
  such as voice, video, or data are conveyed in
  fixed-length cells.

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Selecting Appropriate WAN Service
22

• A worksite within a company can be categorized
  as
• A central site
• A branch office
• Or a telecommuter site

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LAB

• Connecting a T1 line
• Routing over a T1 line.
• Configuring a CSU/DSU
• Connecting a DCE to a DTE