communication networks - technische universität...

Communication Networks Winter 2017/18

Prof. Jochen Seitz 1

Communication Networks

Chapter 2 – Fundamentals

Communication Networks: 2. Fundamentals 30

Overview

1. Communication Network

2. Standardization

3. Communication Associations

4. Communication Architectures

5. Telecommunication Services and Protocols

6. ISO/OSI Basic Reference Model




Example of a Telecommunication Network (Repetition)



LAN 1

Wireless LAN 3

MobileUsers

LAN 2

Backbone

URL Web Page


Components

• Terminal Equipment (End Nodes)

User interface to communication service

Host for applications / server

Source and/or sink of information flows

• Switching Equipment (Intermediate Nodes)

Forwarding of information

Routing decision

• Physical Media

Links between

terminal equipment and switching equipment

switching equipment and terminal equipment

Need for international standards




Communication Service


NetworkTerminal

EquipmentTerminal

Equipment

Tele Service

Bearer Service

User Network Interface (UNI)

Application / User Interface



Main Task

• Transmission of information from one terminal equipment to another

Information transmission for different applications / use cases

Information transmission on demand to an arbitrary terminal equipment

Possibly, transformation of information required


Network

Speech Communication

Transmission of Bits




Fully Meshed Network

• Direct links between all end nodes of the network

• No switching equipment needed

• For communication simply select the correct link

• For n end nodes: ½ (n * (n-1)) links required


End Node1

End Node2

End Node3

End Node4

End Node5

End Node6

End Node7Example:

• Network of 7 end nodes• 21 links


Partially Meshed Network

• At least one path through the network for all pairs of end nodes

• Switching equipment on the path forwards information accordingly

Communication association between end devices / users

Control of communication association required

Resources in the network might be limited


Network



2. Standardization

Standardization Bodies (I)

• International Standardization Organizations

International Organization for Standardization (ISO)

ISO Reference Model for Open Systems Interconnection (OSI)

International Telecommunication Union (ITU)

Telecommunication Standardization Sector, ITU-T

Radiocommunication Sector, ITU-R

Telecommunication Development Sector, ITU-D

Institute of Electrical and Electronics Engineers (IEEE)

• Regional / National Standardization Organizations

European Telecommunication Standards Institute (ETSI)

American National Standards Institute (ANSI)

Deutsches Institut für Normung (DIN)


2. Standardization

Standardization Bodies (II)

• Standardization of the Internet

Internet Engineering Task Force

large number of working groups and informal discussion groups (BoF – Birds of a Feather)

working groups organized into areas by subject matter

area directors, together with the IETF Chair, form the Internet Engineering Steering Group (IESG)

• Special Interest Groups (SIGs)

Bluetooth-SIG

Ecma International (former European Computer Manufacturers Association)

The Open Group (former OSF and X/Open)

ZigBee Alliance




2. Standardization

Standardization by ISO

• Working Groups

Meetings each 6 to 9 months

National bodies need to agree on concepts to be standardized

• Process

Draft Proposal (DP)

Draft International Standard (DIS)

International Standard (IS)

• International Reconcilement


ISO

TechnicalCommittee (TC)

SubCommittee(SC)

Working Group(WG)

… … … …

… … … …

… … … …

2. Standardization

Standardization in the Internet

• IETF responsible for standardization

• IESG controls standardization process

• Two results

Request for Comments (RFC)

For Your Information (FYI)

• For each draft standard, two interoperable and independent implementations must exist


Proposal

Proposed Standard

Draft Standard

Full Standard

Experimental

Informal



2. Standardization

Standards of the Internet – Examples

RFC Title Date

RFC 768 User Datagram Protocol (UDP) August 1980

RFC 791 Internet Protocol (IP) September 1981

RFC 792 Internet Control Message Protocol (ICMP) September 1981

RFC 793 Transmission Control Protocol (TCP) September 1981

RFC 959 File Transfer Protcol October 1985

RFC 1945 Hypertext Transfer Protocol – HTTP/1.0 May 1996

RFC 2460 Internet Protocol, Version 6 (IPv6) Specification December 1998

RFC 8212 Default External BGP (EBGP) Route Propagation Behavior without Policies

July 2017


see http://www.ietf.org

3. Communication Association

Communication Association

• Temporary service provided by the network to transfer information from one UNI to some freely selected UNI

• Requirements:

Addressing of the UNI / user

Fulfillment of user / application requirements:

throughput / goodput

delay / delay variation (jitter)

reliability (bit errors / packet loss / communication breakdown)

security / authenticity / trustworthiness

availability

…





Communicating Entities

• Man–to–Man

one-way (e-mail) or dialogue (telephony, chat)

text (e-mail, chat) or speech (telephony)

synchronous (telephony) or asynchronous (e-mail, chat)

• Man–to–Machine

client/server-based applications (www, online banking, …)

peer-to-peer applications (gnutella, …)

• Machine–to–Machine

distributed processes for smart home, industry 4.0, internet of things…

pervasive computing


Number of Communication Entities



Number ofSenders

Number ofReceivers

CommunicationAssociation

Example

1 1 Unicast lecture (?)

1 1 Dialogue telephony

1 1 < n < all Multicast pay TV

1 all Broadcast “normal” TV

m > 1 1 Concast tele-voting

m > 1 n > 1 Multipeer video conference

1 n > 1 Anycast DHCP



Communication Links



Universal Serial Bus (USB)(serial transmission)

Centronix(8 bis in parallel)

Serial Communication

Parallel Communication

01000001

01000001

1 0 0 0 0 0 1 0

1 bit per time interval,1 physical link

8 bits per time interval,8 physical links

t

t

Direction of Communication



Simplex Duplex Half Duplex

- Radio / TV Broadcast- Fire Detector- Sensor Node

- Telephony- Internet- Video Game

- Citizen‘s Band- Walkie-Talkie




Order of Delivery

• According to sending sequence (First In, First Out (FIFO))

• FIFO + Priorities

• Random delivery order


Network3 2 1 3 1 2

Quality ofService Many criteria

Optimization of all criteria at the same time not possible



Suitability:• Complexity• Scalability• Usability

Performance:•Signal Runtime•Response Time•Throughput

Costs:• Investment Costs• Operating Costs

Reliability:• Transmission Errors• Comm. Breakdown

• Service Reliability

Security:•Information Integrity•Confidentiality•Authenticity•Non-Repudia-

bility




Principles

• Different components in a communication architecture with dedicated functionality:

Interface to the physical medium

Interface to the application / user

Several communication entities

to realize the required communication service

to provide the required quality of service

• Structured in a layered architecture


Interface to thePhysical Medium

Interface to theApplication / User

CommunicationEntities


The Layered Approach

• Refinement of „Communication Entities“ layer arbitrary number of layers

• Each layer

offers service to the upper layer

utilizes service of the lower layer

• Advantages

Concentration on a specific communication aspect in each layer

Exchange of a layer without side effect on the other layers


CommunicationEntities

Layer X

Layer X-1

Layer X-2

Layer X-n+1

Layer X-n

…



Point-to-Point Physical Medium



Physical Medium

Physical Transmission Channel

Medium Access Point Medium Access Point

Sender Receiver

Shared Physical Medium



Physical Medium


Sender A Receiver A2Receiver A1 Receiver B1 Sender B



Layer i

Abstract Medium for Layer i

The Layers



Application Application

Physical Medium

Service Access Point (SAP)

Horizontal Communication

Horizontal Communication

Ver

tica

lCo

mm

un

ica

tio

n

Ver

tica

lCo

mm

un

ica

tio

n

Interface

Service and Protocol (I)


5. Telecommunication Service and Protocol

Service Provider 1 Service Provider 2

Service User 1 Service User 2

Protocol

Serv

ice

Serv

ice

Layer i

Layer i+1

System A System B




Service and Protocol (II)

• Peer entities on one layer

utilize the service of the layer below (if there is one)

offer their service to the layer above (if there is one)

only know the interface to the service beneath, but not its implementation

communicate with each other according to specific rules

receive input

generate events

• Service offered by a layer is based on the cooperation of the communicating peer entities in the layer


Telephony Service (I)



Telephony Service

Pick Up

Dial Tone

Enter theTelephone Number

Ringing Tone

End of Ringing Tone

Hang UpConversation

Pick Up

Ringing

Hang Up

Busy Tone

Time



Telephony Service (II)



Telephony Service

Pick Up

Dial Tone


Ringing Tone

End of Ringing Tone

Hang UpConversation

Pick Up

Ringing

Hang Up

Busy Tone

Time

Telephony Service (I)



Pick Up

Dial Tone


Ringing Tone

End of Ringing Tone

Hang UpConversation

Pick Up

Ringing

Hang Up

Busy Tone

Time

Network

Disconnect

Response

Disconnect




Definition of Service

• Service = set of functions in one layer

delivered by cooperating entities of the layer communicating according to a specific Protocol

offered at the Services Access Point (SAP) of the layer

defined by a set of Service Primitives and rules for their usage

• Service Primitive types

Request

Indication

Response

Confirmation


Illustration of a Telecommunication Service



Abstract Medium Mi

Communi-catingEntity

Ii+11

Communi-catingEntity

Ii+12

Communi-catingEntityIi+1

N-1

Communi-catingEntityIi+1

N

…

ServiceInterfaceof Layer i

ServiceAccessPoint (SAP)

Exchange ofServicePrimitives



Layer i


Service of Layer i

• Set of functions offered by layer i at its Service Access Point vertical communication

• Delivered by peer entities in layer i communication with each other utilizing the service of layer i-1 horizontal communication

• Entities of layer i+1 only know the service interface of layer i


Entity 1of Layer i+1

Ii+11


Ii+12


Ii1


Ii2

SAP of Layer i SAP of Layer i

Protocol

Different Kinds of Services

Confirmed Service

• Confirmed by service user

Unconfirmed Service

• Initiated by the service user

• Initiated by the service provider



Request

Indication

Response

Confirmation

Indication

Request

IndicationIndication




Connection-oriented Service

• Three phases:

Connection Establishment

Creation of context in terminal and switching equipment

Data Transmission

Based on established context

Connection Release

Deletion of context

Deallocation of resources


DisconnectRequest Disconnect

IndicationC

on

nec

tio

nR

elea

se

DataRequest Data

Indication

DataRequest Data

IndicationDa

taTr

an

smis

sio

n

ConnectRequest Connect

Indication

ConnectConfirmation

ConnectResponseC

on

nec

tio

nEs

tab

lish

men

t


Connection End Points

• Connection End Point (CEP) = Identification of a connection within a SAP


Layer i


Ii+11


Ii+13


Ii1


Ii2


Protocol


Ii+12


Ii+14

Connection End Point




Datagram Service

• Connectionless service:

„shoot and pray“

no phases for connection setup/release required

no creation of context in the network

no guarantee for ordered delivery

unconfirmed service


Data.Indication2

Data.Request1

Data.Indication1

Data.Request2

Protocol



Abstract Medium Mi


Ii+11


Ii+12

Entity 1of Layer i

Ii1

Entity 2of Layer i

Ii2


Protocolof Layer i

Abstract Medium Mi-1

ServiceInterfaceof Layer i

ServiceInterface

of Layer i-1




The Idea Behind Protocols

• Rules for concurrently running cooperating entities

• Enhancement of the quality (QoS) and the funcitons of the layer below

• Distributed algorithm

• Important problem:

Failures and faults in the lower layer must be taken into account

• Specification of protocols:

In most cases only for two entities

(Extended) Finite State Machine ((E)FSM)

Message Sequence Chart (MSC)



Protocol Function

• Elementary atomic function to be included

in different communication architectures

in different protocols

in different layers

• Cannot be further divided into parts




Protocol Function “Encapsulation”



Abstract Medium Mi

Entity Ii+11 Entity Ii+1

2

Entity Ii1 Entity Ii

2Protocolof Layer i


User Information User Information

User Information User Information

Protocol Function “Segmentation and Reassembly”



Abstract Medium Mi

Entity Ii+11 Entity Ii+1

2


2Protocolof Layer i


User InformationUser Information




Protocol Function “Connection Management”

• Connection establishment

• Connection maintenance resource allocation

• Connection release

• Handling of connection breakdowns

• Handling of “orphaned” connection

• Further tasks related to connection management

Addressing

Address mapping



Protocol Function “Routing”

• Selection of the “optimal” physical medium interface and of the next node

• Different criteria

(monetary) cost

data rate

availability / reliability

delay / number of intermediate hops to the destination

current load

…

• Optimum might vary according to current network state

• Probably duplication of sent information

flooding

multicast





Protocol Function “Data Transfer”

• Desired: ordered data transfer

data is delivered in the same order as it was sent

data might have to be reordered after receiving

• Desired: different priorities for different data

“normal” versus “expedited” data transfer

no overtaking of important data by normal data

data might have to be reordered before forwarding


Protocol Function “Load Control”



Load Control

Flow ControlNetwork Overload

Control

Congestion Control Traffic Control

on terminalenvironments

in the network

preventivelyreactively



Protocol Function “Error Detection and Correction”

Error Detection

• Redundancy

Parity

Checksum

• Acknowledgements

Stop & Wait

Credit-based

• Timeout

• Numbering of packets

Sequence control

Error Correction

• Redundancy

Forward Error Correction (FEC)

• Retransmission

Selectively

Go-back-N

• Reset

• Abort



Layer i

Protocol Function “Multiplex and Bundling”

Multiplex

• One entity serves several entities on the layer above

Bundling

• On entity utilizes the services of several entities in the layer below



Entity Ii+11

Entity Ii1

Entity Ii+12

Layer i

Entity Ii+11


2



Protocol Function “Shared Medium Access”

Controlled Medium Access

• Alternatives

centrally controlled

without central control(e.g. token based)

• No collision

• Problem: Part of bandwidth might be unused

Arbitrary Medium Access

• No central control

• Each nodes decides whether it may send

• Problem: Collisions possible



Combination: Hybrid Medium Access


Protocol Function “Synchronization”

• Different contexts:

Signal level

clock, sensing, …

Medium Access

time slots, start of sending after last transmission

Transmission

start and end (bits, octets, frames, packets, …)

Connection

establishment, release

Data transfer

progress of data transfer in case of restart

…





The ISO/OSI Basic Reference Model

• Standardization of protocols and services to implement open systems(OSI = Open Systems Interconnection)

• Base for interoperability of components of different companies

• Nota bene: ISO/OSI Basic Reference Model is mainly a framework to explainand classify communication architectures

• Implementation especially in public networks, but not relevant any more

• Important standard:

ISO/IEC IS 7498: Information Processing Systems – Open Systems Interconnection –

Basic Reference Model, International Standard, October 15, 1994

Adopted by CCITT resp. ITU-T in recommendation X.200



Principles

• OSI End System Terminal system that adheres to the ISO/OSI standard

• (N)-Layer All entities/instances in the layer N

• (N)-Entity Implementation of a process providing the service of the layer N

Might be instantiated several times in one open system in one layer

• Peer Entities Cooperating entities in one layer to deliver a certain service


End System A End System B

(N)-Layer(N)-Entity (N)-Entity



Connection and Association

(N)-Connection

• Relation between two or more (N+1)-Entities

• Connection established between (N)-CEPs in

the (N)-SAPs

• (N)-Entities offer connection-oriented service

(N)-Association

• Cooperative relation between two or more

(N)-Entities

• Can be based on

(N)-Connection

connectionless service of (N)-Layer



Entity IN+11 Entity IN+1

2

Entity IN1 Entity IN

2

(N+1)-Association

(N)-Connection

Generic Communication over SAP



(N-1)-Layer

(N+1)-LayerSAP

(N)-Layer

SAP

(N)-SDU (N)-ICI

(N-1)-SDU (N-1)-ICI

(N)-IDU

(N-1)-ICI

(N-1)-IDU

(N)-PCI

(N)-PDU

(N )-PCI (N)-SDU



Data and Information Units

• (N)-IDU Interface Data Unit exchanged between (N+1)- and (N)-Entities

via an (N)-SAP

composed of (N)-ICI and (N)-SDU

• (N)-ICI Interface Control Information exchanged between (N+1)- and (N)-Layer

used to control service delivery

contains e.g. addresses

• (N)-SDU Service Data Unit consists of information to be transparently

transferred between (N)-SAPs

• (N)-PCI Protocol Control Information exchanged between Peer Entities of the

(N)-Layer

used to control protocol functions

contains e.g. sequence numbers, check

sums etc.

• (N)-PDU Protocol Data Unit exchanged between (N)-Entities on

utilizing the service of the (N-1)-Layer

composed of (N)-PCI and (N)-SDU

corresponds to the (N-1)-SDU



Exchange of Data Units



(N+1)-Layer

SAP

(N)-IDU

SAP

(N-1)-Layer

SAPSAP

Entity 1of Layer N

IN1

Entity 2of Layer N

IN2

Protocol of Layer N

(N)-IDU

(N-1)-IDU (N-1)-IDU

(N)-PDU

(N)-Service

(N-1)-Service



Layer 7 (A Layer)

Layer 6 (P-Layer)

Layer 5 (S-Layer)

Layer 4 (T-Layer)

Layer 3 (N-Layer)

Layer 2 (DL-Layer)

The OSI Layers



Layer 1 (Ph-Layer) Physical Layer

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application LayerApplication-

orientedLayers

Transport-oriented

Layers

Service Primitives



Layer Service Primitive

Ph -Connect .Req (Request)

DL -Data .Ind (Indication)

N -Disconnect .Rsp (Response)

T -UserAbort .Cnf (Confirmation)

… -…

(N)-Service.Primitve

Note: Service Primitives in Application Layer named according to the relatedApplication Service Element (ASE)



Communication Example



DL-Connect.ReqDL-Connect.Ind

DL-Connect.RspDL-Connect.Cnf

DL-Data.Req

DL-Data.IndDL-Data.Req

DL-Data.Ind

DL-Disconnect.Req

DL-Disconnect.Ind

Co

nn

ect

ion

Esta

blis

hm

en

tD

ata

Tran

sfe

rC

on

ne

ctio

nR

ele

ase


Transport-oriented Layers

• Do not consider the contents of the transported information

• Only deal with bit sequences

• Apply the same procedures to all transported information

• Consist of the following layers

Transport Layer

Network Layer

Data Link Layer

Physical Layer


Layer 4 (T-Layer)

Layer 3 (N-Layer)

Layer 2 (DL-Layer)

Layer 1 (Ph-Layer)

Transport-oriented

Layers




Physical Layer

• Transfers (unstructured) bit sequences in form of physical signals

• Implements channel coding

• Defines the physical interfaces (connectors, jacks, sockets, …)

• Might not be able to deal with transmission errors


Physical Medium


Physical Layer Entity 1

Physical Layer Entity 2

Bits Bits

Physical Signals Eventually Disturbed Physical Signals

Transmission over PhysicalLayerTaken from F. Halsall (2000)



Transmitted Data

Transmitted Signal

Sampling Instants

Received Data

0 1 1 110 0 0

0 1 0 110 0 0

+V

-V

Bit Error

Typical Received Signal




Data Link Layer

• Responsible for detection and correction of bit errors

For detection: adding redundancy (parity bits, cyclic redundancy check, …)

For correction: several mechanisms

Forward Error Correction (FEC)

Acknowledgements

Sequence Numbers

Timeout & Retransmission

Flow Control

Reset

• Medium Access Control (MAC) for shared medium

• Addressing receiver (especially in case of a shared medium) e.g. MAC address

• Control information and user information frame structure:


Header User Data Trailer

Intermediate System End System AEnd System A


Network Layer

• Links several point-to-point associations (of the Data Link Layer) to an and system association


• Is responsible for finding the optimal path through the network (routing) and forwarding the information on this path

• Should control network load

• Works connection-oriented or connectionless

• Is based on world-wide unique addresses (e.g. telephone number or IP address)

Network LayerEntity 1

Data Link LayerEntity 1




Data Link Association Data Link Association

Network Association

DL LayerEntity

2.1

DL LayerEntity

2.2



End System AEnd System A

Transport LayerEntity 1

Transport LayerEntity 3


Transport Layer

• Data transfer between different pairs of applications on the end systems

• Abstracts from the underlying networking technologies

• Adds Quality of Service (QoS) to the service provided by the Network Layer as required by the applications

• Works connection-oriented or connectionless


Intermediate System




DL LayerEntity

2.1



Data Link Association Data Link AssociationDL LayerEntity

2.2


Application-Oriented Layers

• Depend on the application and its semantics

• Are aware of the kind of information to be transferred (not just bits)

• Must be directly controlled by the application

• Consist of the following layers:

Application Layer

Presentation Layer

Session Layer


Layer 7 (A Layer)

Layer 6 (P-Layer)

Layer 5 (S-Layer)

Application-oriented

Layers




Session Layer

• Allows organizing and synchronizing the dialogue of two applications

• Is built on sessions which abstract from network connectivity


• Controls the exchange of information (which application entity might send information at a specific point in time)

• Provides synchronization points for restarting whenever the connectivity is interrupted during transmission

t

Session

Transport Layer Connections


Presentation Layer

• Provides coding of information so that the receiver understands the syntax and the semantics of the transmitted bits

• Is based on abstract data syntax forms which the application can choose from

• Transfers information according to the associated transfer syntax

• Overcomes the ambiguity and heterogeneity of different syntaxes in various operating systems or processor architectures


End System A End System B

Presentation Layer

Entity 1

Presentation Layer

Entity 2

0 1 1 0 0 0 1 0 1 1 0 0 1 0 1 0 0 0 0 1 1 0 1 1 1 1 0 0 0 0 1 0 1 1 0 0 1




Application Layer

• Provides a set of different services suitable for different applications

File Transfer, Access and Management (FTAM)

Message Handling System (MHS, ISO/OSI E-Mail)

Remote Operations (ROSE)

Association Control (ACSE)

• Consists of several Application Service Elements (ASEs) forming an application layer entity

Common Application Service Element (CASE)

Specific Application Service Element (SASE)

• Single Association Control Function (SACF) to control the cooperation of ASEs

• Multiple Association Control Function (MACF) to control several SACFs


The Seven Layers



Layer 7 Entity

Layer 6 Entity

Layer 5 Entity

Layer 4 Entity

Layer 3 Entity

Layer 2 Entity

Layer 1 Entity

Layer 3 Entity

Layer 2 Entity

Layer 1 Entity

Layer 2 Entity

Layer 1 Entity

Layer 7 Entity

Layer 6 Entity

Layer 5 Entity

Layer 4 Entity

Layer 3 Entity

Layer 2 Entity

Layer 1 Entity

NetworkEnd System A End System B



Encapsulation



Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Sen

dR

eceive

Data

Data

Data

Data

Data

Data

Data

Bits

AH

PH

SH

TH

NH

DLTDLH

AH Application Header NH Network HeaderPH Presentation Header DLH Data Link HeaderSH Session Header DLT Data Link TrailerTH Transport Header

Comparison with the Internet Protocol Suite



Application Layer

Transport Layer

Internet Layer

Network-to-HostLayer

Network to host interface implemented on the network cardin the device (subsumes Data Link and Physical Layer)

Routing and forwarding in the Internet –layer of the Internet Protocol

Data transfer end-to-endbetween two applications on two computers

Application specific functions concentrated in one layer only(subsumes Session, Presentation and Application Layer)




Theoretic Model: Three Layer Architecture

• Less processing overhead

• Prevention of redundant functions

• High performance networking

• But: not compatible to current architectures / best practice


Application-orientedLayer

Transport-orientedLayer

Network AccessLayer

Corresponds to OSI layers 5 – 7

Corresponds to OSI layers 2b – 4

Corresponds to OSI layers 1 – 2a

References

• Halsall, Fred (2005): Computer Networking and the Internet. 5th edition. Harlow, England: Addison-Wesley.

• Halsall, Fred (2000): Data Communications, Computer Networks and Open Systems. 4th edition, reprint. Harlow: Addison-Wesley.

• Kurose, James F.; Ross, Keith W. (2017): Computer Networking. A Top-Down Approach. 7th edition. Hoboken, New Jersey: Pearson.

• Nutt, Gary J. (1992): Open Systems. Englewood Cliffs, N.J.: Prentice-Hall (Prentice-Hall Series in Innovative Technology).

• Stallings, William (2014): Data and Computer Communications. 10th edition. Upper Saddle River, N.J.: Pearson.

• Tanenbaum, Andrew S.; Wetherall, David J. (2011): Computer Networks. 5th edition. Boston: Pearson Prentice Hall.


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