Chapter 12: Wide Area Networks
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Transcript of Chapter 12: Wide Area Networks
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Chapter 12:Wide Area Networks
Business Data Communications, 4e
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Wide Area Networking Issues
Trend towards distributed processing architectures to support applications and organizational needs.Expansion of wide area networking technologies and services available to meet those needs.
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WAN Alternatives
SMDS: Switched Mulitmegabit Data Service
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Integrated Network AccessUsing Dedicated Channels
(STDM)
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Integrated Network AccessUsing Public Switched WAN
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Frame Relay Characteristics
Designed to eliminate excessive X.25 overheadControl signaling takes place on a separate logical connection (nodes don’t need state tables for each call)Multiplexing/switching take place at layer 2, eliminating a layer of processingNo hop-by-hop flow/error control
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Traditional Packet Switching
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Frame Relay Operation
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Frame Relay Architecture
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Committed Information Rate - CIR
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ATM - Asynchronous Transfer Mode
Also known as cell relayFaster than X.25, more streamlined than frame relaySupports data rates several orders of magnitude greater than frame relayData on logical connection is organized into fixed-size packets, called cells. No link-by-link error control or flow control.
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Virtual Channels & Virtual Paths
Logical connections in ATM are virtual channels analogous to a virtual circuit in X.25 or a
frame relay logical connection used for connections between two end
users, user-network exchange (control signaling), and network-network exchange (network management and routing)
A virtual path is a bundle of virtual channels that have the same endpoints.
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VP vs. VC
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Advantages of Virtual Paths
Simplified network architectureIncreased network performance and reliabilityReduced processing and short connection setup timeEnhanced network services
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Virtual-Path/Virtual-Channel Characteristics
Quality of service Cell loss ratio, Cell delay variation
Switched and semi-permanent virtual-channel connectionsCell sequence integrityTraffic parameter negotiation and usage monitoring- average rate, peak rate, burstiness, peak duration
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ATM Cell Format
UNI NNI
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ATM Cell Header GFC (Generic Flow Control): 4 bits
Control of cell flow at local user-network interface
Virtual Path Identifier (VPI) 8 bits at UNI, 12 bits at NNI
Virtual Channel Identifier (VCI) : 16 bits VCI functions much as a service access point.
Payload Type (PT) : 3 bits Type of information
Cell Loss Priority (CLP): 1 bit 0: Relative high priority
Header Error Control (HEC): 8 bits To correct single-bit errors And to detect double-bit
errors
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Payload Type (PT)
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ATM Bit Rate Services
Constant bit rate (CBR) Fixed data rate
Variable bit rate (VBR) Sustained rate for normal use Faster burst rate at peak periods
Available bit rate (ABR) Guaranteed minimum rate
Unspecified bit rate (UBR) Best-effort service
Leased lineLeased lineLeased lineLeased line
Voice/videoVoice/videoVoice/videoVoice/video
On-line sessionsOn-line sessionsOn-line sessionsOn-line sessions
E-mailE-mailE-mailE-mail
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ATM Bit Rate Services