WAN Technologies

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WAN Technologies
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WAN Technologies

• Access technologies
• Plain Old Telephone Service (POTS)
• T-Carrier
• Digital Subscriber Line (DSL)
• Cable Modems
• ISDN
• Transport technologies
• Frame Relay
• SONET
• ATM

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Access Technologies
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Plain Old Telephone Service (POTS)
Local Loop
Digital
Digital
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T-Carrier

• High speed technology used to replace analog
  circuits in the PSTN
• Channelized T-Carrier
• Uses Synchronous TDM to combine 64 Kbps (DS-0)
  channels
• Unchannelized T-Carrier
• Allows channels of different sizes to be
  multiplexed
• For example, one channel of 1.536 Mbps or 2 at
  384 Kbps and one of 768 Kbps

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North American Digital Hierarchy
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T-Carrier
T-Carrier circuits are dedicated point-to-point
circuits
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T-Carrier WAN Design

• T-Carrier are dedicated, point-to-point
  connections
• You pay for the bandwidth 24 hours of data
  whether you use it or not
• Its considered two ended because you connect two
  specific sites
• Expensive but reliable

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Star WAN
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Hierarchical or Tiered WAN
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Fractional T1
Fractional T1 allows customers to obtain an
arbitrary number of DS-0 channels for lower than
T1 data rates.
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Digital Subscriber Line (DSL)

• Uses existing twisted pair local loop wire
• Very susceptible to local loop conditions
• Distance from CO
• Splices, mixed wire gauges
• Bridge taps, load coils
• Uses FDM so that POTS signals can coexist with
  DSL signal

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Digital Subscriber Line (DSL)
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DSL
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Cable Modems

• Uses CATV network
• Data signals are multiplexed with video signals
• Potential data rates up to 36 Mbps downstream and
  3.6 Mbps upstream
• PC connects to cable modem using 10BaseT so
  effective maximum data rate is 10 Mbps
• Most CATV networks must be upgraded because they
  were originally designed as downstream only
• Some systems use POTS for upstream traffic
• Similar to Ethernet

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Cable Modems
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Integrated Services Digital Network (ISDN)

• Conceived as a means of replacing the PSTN with
  an all digital network
• Although more successful in other parts of the
  world, ISDN has never achieved a high level of
  adoption

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ISDN Channels

• D Channel
• Operate at 16 or 64 Kbps
• Used for network signalling
• B Channel
• Operate at 64 Kbps (DS-0)
• H Channel
• H0 384 Kbps, H1 1.536 Mbps, H2 1.92 Mbps

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ISDN Services

• Basic Rate Interface (BRI)
• 2 B Channels 1 D Channel (2BD)
• Up to 128 Kbps (sometimes up to 144 Kbps)
• Primary Rate Interface (PRI)
• Usually 23 B Channels 1 (64 Kbps) D Channel
  (23BD)
• Up to 1.544 Mbps

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Frame Relay

• Frame Relay is the packet switching portion of
  ISDN
• Has become one of the most common types of WAN
  connections
• Scalable bandwidth up to 45 Mbps (T3)
• Point-to-Multipoint connections
• Relatively mature and reliable

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Frame Relay Network
FRND Frame Relay Network Device FRAD Frame
Relay Assemble/Disassembler
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Frame Relay Virtual Circuits

• Frame Relay can use PVCs or SVCs but usually only
  PVCs are implemented
• Each VC is identified by a Data Link Connection
  Identifier (DLCI)
• DLCIs are similar to Layer 2 addresses except
  that DLCIs are only locally significant

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DLCIs in Frame Relay Network
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Bandwidth on Demand

• Frame Relay uses statistical TDM so it is able to
  temporarily allocate higher bandwidth to data
  streams that require it
• Committed Information Rate (CIR) is the bandwidth
  the carrier guarantees to provide over a VC
• VCs are either symmetrical or asymmetrical
• Committed Burst Rate (CBR) is the bandwidth over
  and above the CIR the carrier agrees to carry
  when bandwidth is available
• Frames above the CIR are marked as Discard
  Eligible meaning the switched can discard them if
  the network is congested

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Star using Frame Relay
Single T1 connection with two VCs.
Asymmetric VCs allow user to scale bandwidth to
each sites requirements.
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Ring (or Mesh) using Frame Relay
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Transport Services

• Used inside the carriers networks but arent
  offered as services to customers as often

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SONET

• The principle transport technology for most WAN
  and some Campus networks
• Capable of very high data rates
• Very reliable
• Flexible allocation of bandwidth to many
  different types of signals
• Strong international standard

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SONET Paths and Channels
Virtual Path - End-to-end communication
circuit Virtual Tributary Tributary carries a
specific signal (e.g. T1) within a Virtual
Path Virtual Channel Exists within a Virtual
Tributary
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SONET Digital Hierarchy
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SONET Digital Hierarchy
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Linear SONET
Add-Drop Multiplexer
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Star SONET
Digital Cross Connect
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Ring SONET
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Asynchronous Transfer Mode (ATM)

• ATM was designed from the ground up to handle
  real-time as well as data transmissions
• ATM offers Quality of Service (QoS) levels so
  that real time data such as voice can be
  transmitted on the same network as data

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ATM and the OSI Model
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ATM Physical Layers(just a sample)

• Token Ring
• Fibre Channel
• SONET at OC-3 and OC-12
• DS-1, DS-3, E-1, E-3

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ATM LAN or WAN

• ATM is used most often in WANs but was designed
  to be used in LANs or WANs
• ATM in LANs is most often uses as a campus
  network backbone
• The goal was to have a single architecture from
  the LAN to the WAN
• This would greatly simplify network integration

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Cells

• Rather than variable length frames, as with other
  LAN architectures, ATM uses fixed length cells
• Cells consists of a 5 byte header and a 48 byte
  payload

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Advantages of Cells

• Fixed length simplifies hardware design and
  operation
• Cells can be switches more efficiently than
  variable length frames
• More predictable transmission times
• Less jitter
• Easier to combine multiple data streams

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Disadvantages of Cells

• Since cells are much smaller than IP packets, the
  IP packets must be segmented to fit within
  multiple cells
• Because header data is added to every cell the
  transmission efficiency is reduced
• This reduction in efficiency is called the cell
  tax

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ATM Service Classes

• Constant Bit Rate
• Very low variable latency, very low error rate
• Fixed bandwidth allocated to the data stream
• Variable Bit Rate Real Time
• Slightly more variation in latency allowed
• Variable Bit Rate Non-Real Time
• More variation in latency allowed
• Available Bit Rate
• Use whatever bandwidth is available
• Unspecified Bit Rate
• No specifications

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Virtual Circuits

• Virtual Channel Connection (VCC)
• A connection between end nodes
• Virtual Path Connection (VPC)
• Can contain multiple VCCs
• Can be established permanently between two points
  and VCCs created within it as needed
• For example, a VPC is established between two
  office sites and a VCC is created whenever data
  is transmitted between the sites

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VPs and VCs
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ATM Virtual Circuit
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ATM/SONET
IP
Network Layer
ATM
Data Link Layer
SONET/SDH
Physical Layer
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Packet over SONET/SDH (POS)
IP
Network Layer
PPP in HDLC Framing
Data Link Layer
SONET/SDH
Physical Layer