Circuit Switching and Packet Switching

Circuit Switching and Packet Switching ENTC 345 Dr. Ana Goulart Assistant Professor

Announcements • Reading: Stallings • Chapter 1 and 2 • Chapter 10 • TA: Aninda@neo.tamu.edu • Office hours: Mondays 5 to 8 pm (T 101) • Hw # 1 due today

Review • M/M/1 example – incoming link information • Hw#1: Examples of simulations and applications • How was the first lab?

On Opnet – Traffic • Applications and Profiles Application Models: generate typical application traffic patterns Examples: FTP Email Remote Login Video Conferencing Database HTTP Print Voice Custom Standard applications

On Opnet • Standard applications • Client/Server Model • Two-tier architecture * Sessions: single conversation between client/server * Traffic organized into sessions request Client Server response

Applications and Profiles • Applications: simple traffic sources, or complex protocols, or discrete set of tasks • Application Profile: user’s behavior • Specify application he/she uses • how long and how often

Applications and Profiles Application Profile: user’s behavior • Example: start time, duration, repeatability, parallel applications or serial applications Profile 1 : Serial Email HTTP Email HTTP FTP Profile 2 : Parallel Email FTP

Application Model Hierarchy Profile Profile Object Application Application Object Tasks Task Object (Custom applications) Phase

Lab 1 – Small Internetwork Application and Profile Objects – database

Steps: • Create application – add row 1 • Create profile – set attributes • Workstation object - Assign profile to desired workstations • Server object – assign service type (application) • Example: How would you model the traffic at the library’s subnet?

A Network Configuration ISP (page 30 - Stallings) R Internet Residential user Subscriber connection R R R ATM switch Firewall host Ethernet switch R Private WAN Server LAN PCs

Wide Area Network Important concepts: Circuit switching Packet switching Frame relay ATM (Asynchronous Transfer Mode)

Wide Area Networks Important concepts: Circuit switching – - fixed routes, dedicated path between 2 stations - on each link, a logical channel is dedicated to the connection - data transmitted along the dedicated path as rapidly as possible Packet switching – - data sent in a sequence of packets - each packet passed from node to node along some path - at each node, the entire packet is received, stored briefly and transmitted to next node

Circuit Switching A B - data transmitted along the dedicated path as rapidly as possible

Packet Switching A R Internet R R R B At each node, the entire packet is received, stored briefly and transmitted to next node What is the primary framework to model this behavior and analyze delays?

Circuit switching x Packet switching Timing of events: Queuing delay Call request signal Pkt 1 Pkt 2 Circuit establishment Propagation delay Pkt 3 Time Time Transmission delay Call accept signal Data A B C D B C D A Packet switching Circuit switching

Delays in Circuit switching Timing of events: Call request signal Circuit establishment After connection is established, Information is transmitted at a fixed data rate. Node delays are negligible. Advantages? Disadvantages? Time Propagation delay Data B C D A Packet switching Circuit switching

Circuit switching x Packet switching Timing of events: Queuing delay Call request signal Pkt 1 Pkt 2 Pkt 3 Circuit establishment Propagation delay Time Time Transmission delay Call accept signal Data A B C D B C D A Packet switching Circuit switching

Packet switching delays Pkt 1 Transmission delay Total delay from A to B Propagation delay Queuing delay + Processing Pkt 1 What is the Throughput? A B C Packet switching

Throughput Pkt 1 Transmission delay T = Total delay from A to B Propagation delay Queuing delay + Processing Pkt 1 What is the Throughput? L = size of packet (bits) Throughtput = L / T A B C Packet switching

Throughput What else can impact the throughput? - Packet losses - The type of recovery mechanism Pkt 1 Transmission delay X T = Total delay from A to B Propagation delay Queuing delay + Processing What is the Throughput? L = size of packet (bits) Throughput = L / T As delay increases, the throughput decreases B A Packet switching

Impact of packet size • Effect of packet size on transmission time (figure 10.11, page 314 Stallings) • Smaller packets => higher service rate (or smaller transmission times) • Service rate on the outgoing link • μ = Capacity (bits/sec) Packet size (bits/packet)

Virtual Circuit Packet Switching • Datagram packet switching • No dedicated route for the conversation or session • Virtual Circuit Packet Switching • Dedicated route for the conversation or session • Additional Call setup delay

Virtual Circuit switching (internal) Timing of events: Call request signal Circuit establishment Time Call accept signal Pkt 1 Data Pkt 2 Pkt 3 B C D A Circuit switching Packet switching

Virtual circuits (external) • Logical path (or connections) between two stations Example: X.25 standard Physical level – interface between station and packet switched network Link level – reliable data transfer across the physical link (LAP-B) Network level – virtual circuit service, enables users to set-up logical connections Packet switching Network

Frame relay • Designed to eliminate the overhead of X.25 • Virtual circuits or logical connections carried at the link layer • Call control signaling (separate) • No hop-by-hop flow control (error and flow control should be taken care by another higher layer protocol

Circuit Switching and Packet Switching