Business data communications 5e by stallings chapter 12

Chapter 12: Circuit Switching and Packet Switching Business Data Communications, 5e Switching Techniques • Data transmitted through a network of intermediate switching nodes, which are not concerned with content • End devices receiving data are stations; switching devices are nodes • A collection of nodes is a communication network • A switched communication network routes data from one station to another through nodes Business Data Commun ications, 5e Switched Network Characteristics • Some nodes connect only to other nodes for switching of data; other nodes have one or more stations attached as well • Node-station links are generally dedicated pointto-point links; ode-node links are usually multiplexed links • Usually, the network is not fully connected; however, it is desirable to have more than one possible path through the network for each pair of stations to enhance reliability Business Data Commun ications, 5e Types of Switched Networks • Two different technologies – Circuit switching – Packet switching • Differ in the way the nodes switch information from one link to another between source and destination Business Data Commun ications, 5e Circuit-Switching Stages • Circuit establishment • Data transfer – point-to-point from endpoints to node – internal switching/multiplexing among nodes • Circuit disconnect Business Data Commun ications, 5e Circuit Establishment • Station requests connection from node • Node determines best route, sends message to next link • Each subsequent node continues the establishment of a path • Once nodes have established connection, test message is sent to determine if receiver is ready/able to accept message Business Data Commun ications, 5e Data Transfer • Point-to-point transfer from source to node • Internal switching and multiplexed transfer from node to node • Point-to-point transfer from node to receiver • Usually a full-duplex connection throughout Business Data Commun ications, 5e Circuit Disconnect • When transfer is complete, one station initiates termination • Signals must be propagated to all nodes used in transit in order to free up resources Business Data Commun ications, 5e Circuit Switching Characteristics • Channel capacity is dedicated for the duration of a connection, even if no data are being transferred • Once the circuit is established, the network is effectively transparent to the users, resulting in negligible delays • Developed to handle voice traffic but is now also used for data traffic Business Data Commun ications, 5e Circuit Switching Applications • Public Telephone Network (PSTN) • Private Branch Exchanges (PBX) • Private Wide Area Networks (often used to interconnect PBXs in a single organization) • Data Switch Business Data Commun ications, 5e 10 Network Management Signals • Used for the maintenance, troubleshooting, and overall operation of the network • These signals cover a broad scope, and it is this category that will expand most with the increasing complexity of switched networks Business Data Commun ications, 5e 18 In-Channel Signaling • Traditionally, control signals were carried on the same channel as the call to which the control signals relate • Drawbacks – Information transfer rate limited – Delay between entering a number and establishing a connection Business Data Commun ications, 5e 19 Common-Channel Signaling • Control signals are carried over paths completely independent of the voice channels • One independent control signal path can carry the signals for a number of subscriber channels (i.e is a “common control channel” for these channels) Business Data Commun ications, 5e 20 Softswitch Architecture • A general-purpose computer running specialized software that turns it into a smart phone switch • Cost significantly less and can provide more functionality • Can convert digitized voice bits into packets, opening transmission options (e.g voice over IP) • Physical switching function: media gateway (MG) • Call processing logic: media gateway controller (MGC) Business Data Commun ications, 5e 21 Traditional Circuit Switching Illustration Business Data Commun ications, 5e 22 Softswitch Architecture Illustration Business Data Commun ications, 5e 23 Packet-Switching Networks • Developed in 1970s for long-distance data transmission due to circuit switching limitations – In user/host data connection the line is often idle, so circuit-switching is inefficient – Circuit-switching requires both devices to transmit and receive at the same data rate, limiting interconnection options Business Data Commun ications, 5e 24 Packet Switching Operation • Data is broken into packets, each of which can be routed separately • Advantages: better line efficiency, signals can always be routed, prioritization option • Disadvantages: transmission delay in nodes, variable delays can cause jitter, extra overhead for packet addresses Business Data Commun ications, 5e 25 Packet Switching Illustration Business Data Commun ications, 5e 26 Packet-Switching Techniques • Datagram – each packet treated independently and referred to as a datagram – packets may take different routes, arrive out of sequence • Virtual Circuit – preplanned route established for all packets – similar to circuit switching, but the circuit is not dedicated Business Data Commun ications, 5e 27 Packet-Switched Routing • • • • Adaptive routing changes based on network conditions Factors influencing routing are failure and congestion Nodes must exchange information on network status Tradeoff between quality and amount of overhead Business Data Commun ications, 5e 28 Packet-Switched Congestion Control • When line utilization is >80%, queue length grows too quickly • Congestion control limits queue length to avoid througput problems • Status information exchanged among nodes • Control signals regulate data flow using interface protocols (usually X.25) Business Data Commun ications, 5e 29 WANs for Voice • Requires very small and nonvariable delays for natural conversation difficult to provide this with packet-switching • As a result, the preferred method for voice transmission is circuit-switching • Most businesses use public telephone networks, but some have implemented private voice networks • VoIP uses packet transmission over Internets and intranets; it is enjoying gradually growing acceptance as an alternative Business Data Commun ications, 5e 30 WANs for Data • • • • • Public packet-switched networks Private packet-switched networks Private leased lines Public circuit-switched networks Private circuit-switched networks (interconnected digital PBXs) • ISDN (integrate packet and circuit switching) Business Data Commun ications, 5e 31 WAN Considerations • Nature of traffic – stream generally works best with dedicated circuits – bursty better suited to packet-switching • Strategic and growth control limited with public networks • Reliability greater with packet-switching • Security greater with private networks Business Data Commun ications, 5e 32 ... (MGC) Business Data Commun ications, 5e 21 Traditional Circuit Switching Illustration Business Data Commun ications, 5e 22 Softswitch Architecture Illustration Business Data Commun ications, 5e. .. overhead for packet addresses Business Data Commun ications, 5e 25 Packet Switching Illustration Business Data Commun ications, 5e 26 Packet-Switching Techniques • Datagram – each packet treated... channel equipment) Business Data Commun ications, 5e 13 Types of Control Signals • Supervisory • Address • Call Information • Network Management Business Data Commun ications, 5e 14 Supervisory