Download - WAN Technologies Chapter 14
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WAN TechnologiesChapter 14
Switched Networks
Circuit Switch Virtual Circuit Switch Packet Switch
Switched Networks
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Switched Networks
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Circuit Switched Network
• Circuit from A to M could be dynamic• Circuit from A to M could be permanent• Once set up, looks like a Point-to-Point circuit
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Switched Virtual Circuits
• A form of switched circuits
• May be dynamic or permanent
• For any session data path is fixed
• Two very popular Switched Virtual Circuit technologies: Frame Relay Asynchronous Transfer Mode (ATM)
• These are Data Link technologies
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Frame Relay
• High speed wide area network service
• Designed to accept and deliver frames
• Frames up to 8k bytes
• Actual data transported over traditional telephony circuits (T1, T3)
• Often used to interconnect LANs over wide geographical areas
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Frame Relay
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Frame Relay
Virtual Circuit Identifier (VCI)
In Frame Relay, VCI is called Data Link Connection Identifier (DLCI)
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Asynchronous Transfer Mode (ATM)
• Designed by the Telecommunications Industry• Designed to support all existing and future
telecommunications services Voice, high speed data, video
• Connection oriented to ensure predictable delivery – quality of service
• Designed to support all forms of networking• Designed to include a LAN architecture• Defines different levels of service – (QoS)
CBR – Continuous Bit Rate VBR – Variable Bit Rate ABR – Available Bit Rate UBR – Unspecified Bit Rate
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ATM
• Basic data unit is fixed frame called a cell • A cell carries 48 bytes of data plus 5 bytes of
identification• A composite circuit between 2 ATM switches
delivers a fixed rate of cells• Any virtual circuit is made up of a certain number
of equally spaced cells per second. Ex. A voice circuit (64Kbps) would be 166 equally
spaced cells A T1 would be 2020 equally spaced cells
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ATM CELL
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ATM
• ATM was intended to be the universal communications architecture
• Why isn’t it dominant today? Cost – end user equipment is expensive Cell Overhead – 10 per cent Complexity of Quality of Service (QoS) Overtaken but enhancements to Ethernet
• Gigabit Ethernet and beyond• MultiProtocol Label Switching (MPLS)
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Switched Virtual Networks
• These architectures present the view of a point to point circuit to the end client
• Thus, various WAN protocols can be run over then Point-to-Point Protocol (PPP) HDLC
• At upper layers, any protocol stack can also be used, including the Internet Protocol