circuit switching circuit-switched network direct physical connection between two devices ex)...
TRANSCRIPT
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Circuit Switching Circuit-switched network
direct physical connection between two devices ex) phones or computers
shorter links (no, length) than point-to-point connection
The circuit can not be shared by other devices
circuit switches
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Packet SwitchingDatagram Approach
each packet is treated independently from all others packet = datagram datagrams may arrive at their destination out of
order Transport layer reorders the datagrams
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Packet SwitchingSVC(Switched Virtual Circuit)
A virtual circuit is created whenever needed and exists only for the duration of the specific exchange
comparable conceptually to dial-up circuit switching
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Packet SwitchingCircuit switching vs. Virtual Circuit
Path vs. Routephysical path
routing table
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Packet SwitchingCircuit switching vs. Virtual Circuit (cont.)
Dedicated vs. Shared
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Frame Relay Higher data rate at lower cost
the past WAN : leased line or X.25 low data rate Solution : T-lines, mesh network, Frame relay Data rate of Frame relay : 1.544Mbps (T-1) /
44.376Mbps (T-3)
Pure mesh T-line network vs. Frame Relay
lower cost
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Frame Relay Less overhead due to improved transmission media
No need to have a WAN that spends time and resources checking and double checking potential errors
X.25 vs. Frame relay • X.25
– extensive error checking and flow control at the network layer– station-to-station frame checking at the data link layer– overhead for reliability eats up bandwidth
• Frame Relay – does not provide error checking or require acknowledgment in the
data link layer because network become reliable and less error– All error checking is left to network and transport layer protocols– Frame relay traffic : simplified transmission
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X.25 traffic
Frame Relay traffic
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Frame RelayFrame Relay is normally used as a WAN WAN to connect LANs or mainframe computers.
Frame Relay network
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Frame RelayVirtual CircuitsVirtual Circuits
Use a virtual circuit identifier (not physical address) Virtual circuit identifiers in Frame Relay operate at the data
link layer (cf. X.25: network layer) data link connection identifier (DLCI) : local number
Two type of connections in Frame Relay PVC(Permanent Virtual Circuit) Connection SVC(Switched Virtual Circuit) Connection
DLCIs
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Frame Relay LayersPhysical LayerPhysical Layer
No specific protocol
Data Link LayerData Link Layer A simplified version of HDLC called core LAPF
LAPF : LAP for frame mode No extensive error and flow control fields
final(1)/more(0)
a switch informs that congestion has occurred
frame priority for discard
in bottleneck (1:high)
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ISDN Services
provides the means to transfer information (voice, data, video) between users without the network manipulating the content of that information
provides additional functionality to the bearer services and Teleservices
network may change or process the content of data layer 4-7 service
Layer 1-3 services
Three categories
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User Interfaces BRI: Basic Rate Interface for home or small office
2B+D = 192kbps
PRI: Primary rate Interface 23B+D = 1.544Mbps (North America) = T1 30B+D = 2.048 Mbps (Europe) = E1
Subscriber Access to the ISDN
TP local loop
T1
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Broadband ISDN (B-ISDN)
Bit rates for different application
For the services beyond the capabilities of both the BRI and PRI
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ATM ArchitectureVirtual Connection
Connection is accomplished through TP, VP, VC Transmission Paths (TPs)
Physical connection (wire, cable, satellite and so on) Virtual Paths (VPs)
A connection or a set of connection between Switches Virtual Circuits (VCs)
All cells belonging to a single message follow the same VC
TPs > VPs > VCs
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Example of VPs and VCs
ATM ArchitectureTP
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ATM