Understanding Multiplexing, Switching, and Service Integration in Communication Networks, Schemes and Mind Maps of Communication

Download Understanding Multiplexing, Switching, and Service Integration in Communication Networks and more Schemes and Mind Maps Communication in PDF only on Docsity!

Communication Networks

MAP-TELE

José Ruela

Network basic mechanisms

Communications networks• Communications networks are used to transport information (data)

exchanged between

end-systems

with the ultimate goal of supporting

a variety of services and distributed applications

• Networks were initially designed and optimized for a specific service
  • The telephone network for the voice service– Broadcast networks for distribution of radio and TV programmes– Computer networks for exchange of data among computers to support

applications like remote access, file transfer, e-mail, etc.

• The current trend is towards carrying traffic (flows) of different

applications or services in the same network infrastructure

• The concept of service integration in public networks started with ISDN

( Integrated Services Digital Network

), which was an evolution of the

digital telephone network IDN (

Integrated Digital Network

), and was

extended to support BISDN (

Broadband ISDN

), which was the driving

force behind the development of ATM (

Asynchronous Transfer Mode

• The Internet was designed for carrying data traffic (on a

best effort

basis)

but is becoming the universal infrastructure for carrying any type oftraffic, such as VoIP (Voice over IP), video streaming, etc.

Resource sharing• At present, the two most ubiquitous networks are the telephone

network and the Internet

• Both the telephone network and computer networks rely on a

transmission

and

switching

infrastructure

• A key issue in networks is the way resources are shared
  • Sharing may be static or dynamic
    • A network is characterized by the multiplexing and switching

techniques (

transfer mode

) it adopts and these are tightly related

• Sharing of transmission resources is accomplished by means of

multiplexing

techniques

• The telephone and computer networks use two different switching

techniques –

Circuit Switching

and

Packet Switching

, respectively,

which are based on rather different paradigms of resource sharing(driven by the type of service they were designed for)

• Circuit Switching is based on static sharing of resources– Packet Switching is based on dynamic sharing of resources

Computer networks• Computers store and process information (digital data), which may

have to be exchanged with other computers (

end-systems

) for many

purposes

• This exchange may require a number of

intermediate systems

• In the first place a transmission system is necessary to move bits

between systems (bits are represented by means of signals)

Point-to-point links

between two systems (e.g., a telephone circuit)

Multipoint links

shared by multiple systems (that listen and broadcast to

the medium)

• Different media may be used for transmission links
  • Guided: copper pairs, coaxial cable, optical fibers– Unguided: free space (radio frequencies, microwaves, infrared)
    • Computer networks may cover geographical areas of different sizes

– WAN –

Wide Area Network

– MAN –

Metropolitan Area Network

– LAN –

Local Area Network

– PAN –

Personal Area Network

Transmission links• Point-to-point • Multipoint (multiple access)

Abstract view of a computer network• A computer network is used to transport data between end-systems,

with some level of service assurance

• A cloud is usually used to represent any type of network that provides

connectivity between systems attached to it

Need for switching• Establishing direct (dedicated) links between pairs of computers is not

practical nor feasible when:

• The number of computers is high, since the number of links necessary to

fully interconnect the computers grows with the square of its number

• Computers are geographically distributed over a wide area (due to the

high communications costs)

• Connectivity requirements are not known in advance, but connectivity

should not be restricted (any to any)

• Traffic is bursty and asynchronous (typical of computer data), which may

lead to underutilization of resources (or even no utilization at all)

• In general, computers must communicate through a switched network
  • In a shared medium (multipoint link), systems are directly connected, but

an arbitration mechanism is required to access the medium withoutconflicts (the medium provides an inherent form of distributed switching)

• When a network is made up of switching nodes (intermediate systems),

they are connected by point-to-point links, typically in a mesh topology

• Hub (multiport repeater) – broadcasts signals received on each input port

(this is logically equivalent to a shared bus and should not be confused witha switch)

Ring

HUB Star

Connectivity – shared media

Bus

Connectivity – single switch• Central switching node (star topology) – traffic is switched between input and

output ports (a switch may be designed to support multicast or broadcast)

Star

• Networks are interconnected by

routers

to form an internet

• The Internet is a worldwide internet based on the TCP/IP protocol

family

A network of networks

Packet Switching• A computer network allows the attached computers (

end-systems

hosts

) to

exchange data and share their resources

• Traffic generated by computers is inherently asynchronous (bursty and

unpredictable) and therefore it is not efficient to reserve and dedicatetransmission resources (circuits) to carry such individual traffic flows

• It is possible and desirable to exploit

statistical multiplexing

to dynamically

share network resources (transmission and switching facilities) amongmany independent traffic flows and thus improve the utilization of resources

• This was the driving force behind the adoption of Packet Switching in

computer networks

• Packet Switching is based on

Asynchronous Time Division Multiplexing

(ATDM), which is more efficient and flexible than Synchronous TimeDivision Multiplexing (STDM) for carrying data traffic or traffic mixes

• When a network carries traffic of different classes, the degree of statistical

multiplexing depends on a trade-off between efficiency and the Quality ofService (QoS) guarantees required by each class

Topics to cover• We shall start by studying the basic technologies that are used in the

core of networks (in particular, in computer networks)

• Multiplexing– Switching
  • Then we discuss how to organize the many functions that must be

performed by end-systems and intermediate systems (networknodes) in support of the communication process

• Network architectures and protocols – protocol layering
  • Finally we shall address a number of specific functions that give

support to data communications and networking

• Framing– Error control (error detection and recovery)– Multiple access– Flow, congestion and admission control– Scheduling– Routing