Circuit Switching

1
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
2
Packet Switching

• Datagram 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

3
Packet Switching

• SVC(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

4
Packet Switching

• Circuit switching vs. Virtual Circuit
• Path vs. Route

physical path
routing table
5
Packet Switching

• Circuit switching vs. Virtual Circuit (cont.)
• Dedicated vs. Shared

6
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)

lower cost
Pure mesh T-line network vs. Frame Relay
7
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

8
X.25 traffic
Frame Relay traffic
9
Frame Relay

• Frame Relay is normally used as a WAN to connect
  LANs or mainframe computers.

Frame Relay network
10
Frame Relay

• Virtual 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
11
Frame Relay Layers

• Physical Layer
• No specific protocol
• Data Link Layer
• A simplified version of HDLC called core LAPF
• LAPF LAP for frame mode
• No extensive error and flow control fields

frame priority for discard in bottleneck (1high)
a switch informs that congestion has occurred
final(1)/more(0)
12
ISDN Services
Three categories
network may change or process the content of data
? layer 4-7 service
provides additional functionality to the bearer
services and Teleservices
provides the means to transfer information
(voice, data, video) between users without the
network manipulating the content of that
information
Layer 1-3 services
13
Subscriber Access to the ISDN

• User Interfaces
• BRI Basic Rate Interface for home or small
  office
• 2BD 192kbps
• PRI Primary rate Interface
• 23BD 1.544Mbps (North America) T1
• 30BD 2.048 Mbps (Europe) E1

TP local loop
T1
14
Broadband ISDN (B-ISDN)

• For the services beyond the capabilities of both
  the BRI and PRI

15
ATM Architecture

• Virtual 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 gt VPs gt VCs
16
ATM Architecture
TP
Example of VPs and VCs
17
ATM