Data Communications (IT105) Part 5

8/2/2019 Data Communications (IT105) Part 5

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STANDARDS

ORGANIZATIONS

Prepared by: Armando V. Barretto


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Standard

Standard is an object or procedure considered by an authority or bygeneral consent as a basis for comparison.

Two Types of Standards

1. Proprietary (closed) standards

Generally controlled and manufactured by one company. Other companies are generally not allowed to manufacture

equipment or write software using these standards.

Advantages are tighter control, easier consensus, andmonopolization.

Disadvantages include lack of choice of customers, higherinvestment, overpricing, and reduced customer protection.

2. Open system standards

Any company can use the standards

In some cases, royalty must be paid to the company who developedthe standard.

Promotes compatibility between vendors equipment and software.

Disadvantages include less product control and increased difficulty

in obtaining agreement between concerned parties.


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Standards Organizations

Institute of Electrical and Electronics Engineers (IEEE) International professional organization founded in the US.

Responsible for 802 series of standards such as 802.3, 802.5 and otherstandards

Electronics Industry Association (EIA)

Anonprofit US trade association that establishes and recommends industrialstandards.

Responsible for developing theRS (recommended standard) series ofstandards, such asRS-232, RS 422, and RS 423

Telecommunications Industry Association (TIA)

A leading trade association in the communications and informationtechnology.

American National Standards Institute (ANSI)

Official standards agency for the US.

Official member of the ISO for the US. Completely private , non profit organization composed of people from

professional societies, industry, government, and consumer group.

European Telecommunications Standards Institute (ETSI) Telecommunications standards organization for Europe


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Internet Architecture Board

A technical advisory group of the Internet Society which oversees thearchitecture and procedures used in Internet.

Internet Engineering Task Force (IETF)

A large international committee of network designers, operators, vendorsand researchers concerned with the evolution and operation of the Internet.

Internet Research Task Force

Promotes research of importance to the evolution of the future internet.

International Standards Organization (ISO) Created in 1946.

International organization for standardization of wide range of subjects

Promotes research of importance to the evolution of the future Ineternet.

Voluntary,non-treaty organization whose membership is comprisedmainly of standards organizations of various countries.

Responsible for Open Systems Interconnect (OSI) model.


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Standards Organizations International Telecommunications Union Telecommunications Sector (ITU-T)

One of the four permanent parts of the International Telecommunications

Union.

The standardization work of ITU dates back toMay 17, 1865, with

International Telegraph Union as its first name.

It was formerly called Consultative Committee on International Telephone

and Telegraph (CCITT).

CCITTwas created in 1956, when theInternational Telephone Consultative

Committee (CCIF, set up in 1924) and theInternational Telegraph

Consultative Committee (CCIT, set up in 1925) were merged to form CCITT. Headquarters is located in Geneva, Switzerland.

CCITTwas renamed toITU in 1993.

Consists ofgovernment authorities from various countries.

Standards organization for the United Nations since 1947.

After a meeting in 1992, the Union was streamlined into three Sectors,

corresponding to its three main areas of activity: Telecommunication

Standardization (ITU-T), Radiocommunication (ITU-R) and

Telecommunication Development (ITU-D).


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Published V series standards for modems such as V.32, V.90, and V.92

PublishedX series standards for data transmission over public networkssuchX.25.

PublishedI and Q series of standards for ISDN.


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ITU Landmark Dates

(Source: ITU)

1837 - Invention of the electric telegraph

1865 - 17 May -Founding of the International Telegraph Union in Paris

by 20 European countries with the adoption of first ITU Convention. First

Telegraph Regulations put in place.

1868 - Vienna First Telegraph Conference. Decision to establish the

headquarters of the Union inBern.

1869 - Publication of the Telegraph Journalbegins. Renamed

Telecommunication Journalin 1934, it is now published under the name

ITU News.

1876 -Alexander Graham Bell patents his invention of the telephone

1885 -Berlin Telegraph Conference. First provisions for international

telephone service

1895 -First signals transmitted by radio-relay system .

1902 - First radio transmissions of the human voice .


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ITU Landmark Dates

(Source: ITU)

1906 - Berlin International Radiotelegraph Conference (Plenipotentiary).

First Radiotelegraph Convention. Worldwide adoption of the SOS

emergency distress signal. First trials of broadcasting (voice and music)

using radiotelephony .

1920 -Birth of sound-broadcasting in the improvised studios of the

Marconi company .

1924 - Creation of International Telephone Consultative Committee

(CCIF)

1925 - Creation of International Telegraph Consultative Committee

(CCIT)

1927 - Washington Radiotelegraph Conference (Plenipotentiary).

Creation of theInternational Radio Consultative Committee (CCIR)

1932 - The organization changes its name from International TelegraphUnion to International Telecommunication Union


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ITU Landmark Dates

(Source: ITU)

1947 - Atlantic City Plenipotentiary Conference. Creation of the

International Frequency Registration Board (IFRB). On 15 November

1947,an agreement between ITU and the newly created United Nations

was approvedby the UN General Assembly and became applicable, on a

provisional basis, from that date.

1948 - ITU headquarters transferred to Geneva.

1949 - The agreement recognizing the International Telecommunication

Union as a UN specialized agency formally entered into force on 1 January

1949.

1956 - Geneva CCIF and CCIT are merged to form CCITT

(International Telegraph and Telephone Consultative Committee)

1957 - Launch of Sputnik-1, the Earths first artificial satellite

1963 -Launch of the worlds first telecommunication satellite, Syncom-1,in geostationary orbit. Geneva first World Space Radiocommunication

Conference

1982 - Nairobi Plenipotentiary Conference. TheIndependent

Commission for Worldwide Telecommunications Development isestablished .


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Series Description

A Organization of the work of ITU-TB Means of expression: definitions, symbols, classification

C General telecommunication statistics

D General tariff principles

E Overall network operation, telephone service, service operation and human factors

F Non-telephone telecommunication services

G Transmission systems and media, digital systems and networksH Audiovisual and multimedia systems

I Integrated services digital network

J Cable networks and transmission of television, sound programme and other multimedia signals

K Protection against interference

L Construction, installation and protection of cables and other elements of outside plant

M Telecommunication management, including TMN and network maintenance

N Maintenance: international sound programme and television transmission circuits

O Specifications of measuring equipment

P Telephone transmission quality, telephone installations, local line networks

Q Switching and signalling

R Telegraph transmission

S Telegraph services terminal equipment

T Terminals for telematic services

U Telegraph switching

V Data communication over the telephone network

X Data networks, open system communications and security

Y Global information infrastructure, Internet protocol aspects and next-generation networks

Z Languages and general software aspects for telecommunication systems

Series of ITU Recommendations (Source: ITU )


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Series of ITU Recommendations (Source: ITU)

Signalling in the international manual service Q.1-Q.3

International automatic and semi-automatic working Q.4-Q.59

Basic Recommendations Q.4-Q.9

Numbering plan and dialling procedures in the international service Q.10-Q.11

Routing plan for international service Q.12-Q.19

General Recommendations relative to signalling and switching systems (national

or international)Q.20-Q.34

Tones for use in national signalling systems Q.35-Q.39General characteristics for international telephone connections and circuits Q.40-Q.47

Signalling for satellite systems Q.48-Q.49

Signalling for circuit multiplication equipment Q.50-Q.59

Functions and information flows for services in the ISDN Q.60-Q.99

Methodology Q.60-Q.67

Basic services Q.68-Q.79Supplementary services Q.80-Q.99

Clauses applicable to ITU-T standard systems Q.100-Q.119

General clauses Q.100-Q.109

Transmission clauses for signalling Q.110-Q.114

Logic and protocols for the control of signal processing network elements and

functions Q.115-Q.115

Abnormal conditions Q.116-Q.119

Specifications of Signalling Systems No. 4, 5, 6, R1 and R2 Q.120-Q.499

Digital exchanges Q.500-Q.599

Introduction and field of application Q.500-Q.509

Exchange interfaces, functions and connections Q.510-Q.539

Design objectives and measurement Q.540-Q.549

Transmission characteristics Q.550-Q.559


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Specifications of Signalling System No. 7 Q.700-Q.799General Q.700-Q.700

Message transfer part (MTP) Q.701-Q.710

Signalling connection control part (SCCP) Q.711-Q.719

Telephone user part (TUP) Q.720-Q.729

ISDN supplementary services Q.730-Q.739

Data user part Q.740-Q.749

Signalling System No. 7 management Q.750-Q.759

ISDN user part Q.760-Q.769

Transaction capabilities application part Q.770-Q.779

Test specification Q.780-Q.799

Q3 interface Q.800-Q.849

Digital subscriber Signalling System No. 1 Q.850-Q.999

General Q.850-Q.919

Data link layer Q.920-Q.929

Network layer Q.930-Q.939

User-network management Q.940-Q.949

Stage 3 description for supplementary services using DSS1 Q.950-Q.959


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Broadband ISDN Q.2000-Q.2999

General aspects Q.2000-Q.2099

Signalling ATM adaptation layer (SAAL) Q.2100-Q.2199

Signalling network protocols Q.2200-Q.2299

Common aspects of B-ISDN application protocols for access signalling and

network signalling and interworkingQ.2600-Q.2699

B-ISDN application protocols for the network signalling Q.2700-Q.2899

B-ISDN application protocols for access signalling Q.2900-Q.2999

Signalling requirements and protocols for the NGN Q.3000-Q.3999

General Q.3000-Q.3029

Network signalling and control functional architecture Q.3030-Q.3099

Network data organization within the NGN Q.3100-Q.3129

Bearer control signalling Q.3130-Q.3179

Signalling and control requirements and protocols to support attachment in

NGN environmentsQ.3200-Q.3249

Resource control protocols Q.3300-Q.3369

Service and session control protocols Q.3400-Q.3499

Service and session control protocols supplementary services Q.3600-Q.3649

NGN applications Q.3700-Q.3849

Testing for NGN networks Q.3900-Q.3999

Supplements to the Series Q Recommendations Q supplements


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DATA COMMUNICATION OVER THE TELEPHONE NETWORK

General V.1-V.9

Interfaces and voiceband modems V.10-V.34

Wideband modems V.35-V.39

Error control V.40-V.49Transmission quality and maintenance V.50-V.59

Simultaneous transmission of data and other signals V.60-V.99

Interworking with other networks V.100-V.199

Interface layer specifications for data communication V.200-V.249

Control procedures V.250-V.299

Modems on digital circuits V.300-V.399

Supplements to the Series V Recommendations V supplements


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GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND

NEXT-GENERATION NETWORKS

Global information infrastructure Y.100-Y.999

General Y.100-Y.199

Services, applications and middleware Y.200-Y.299

Network aspects Y.300-Y.399Interfaces and protocols Y.400-Y.499

Numbering, addressing and naming Y.500-Y.599

Operation, administration and maintenance Y.600-Y.699

Security Y.700-Y.799

Performances Y.800-Y.899Internet protocol aspects Y.1000-Y.1999

General Y.1000-Y.1099

Services and applications Y.1100-Y.1199

Architecture, access, network capabilities and resource management Y.1200-Y.1299

Transport Y.1300-Y.1399

Interworking Y.1400-Y.1499

Quality of service and network performance Y.1500-Y.1599

Signalling Y.1600-Y.1699

Operation, administration and maintenance Y.1700-Y.1799

Charging Y.1800-Y.1899

IPTV over NGN Y.1900-Y.1999


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Digital networks G.800-G.899

General aspects G.800-G.809Design objectives for digital networks G.810-G.819

Quality and availability targets G.820-G.829

Network capabilities and functions G.830-G.839

SDH network characteristics G.840-G.849

Management of transport network G.850-G.859

SDH radio and satellite systems integration G.860-G.869

Optical transport networks G.870-G.879

Digital sections and digital line system G.900-G.999

General G.900-G.909

Parameters for optical fibre cable systems G.910-G.919

Digital sections at hierarchical bit rates based on a bit rate of 2048 kbit/s G.920-G.929

Digital line transmission systems on cable at non-hierarchical bit rates G.930-G.939

Digital line systems provided by FDM transmission bearers G.940-G.949

Digital line systems G.950-G.959

Digital section and digital transmission systems for customer access to

ISDNG.960-G.969

Optical fibre submarine cable systems G.970-G.979

Optical line systems for local and access networks G.980-G.989Access networks G.990-G.999


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INTEGRATED SERVICES DIGITAL NETWORK

General structure I.100-I.199

Terminology I.110-I.119

Description of ISDNs I.120-I.129

General modelling methods I.130-I.139

Telecommunication network and service attributes I.140-I.149

General description of asynchronous transfer mode I.150-I.199

Service capabilities I.200-I.299

Scope I.200-I.209

General aspects of services in ISDN I.210-I.219

Common aspects of services in the ISDN I.220-I.229

Bearer services supported by an ISDN I.230-I.239

Teleservices supported by an ISDN I.240-I.249

Supplementary services in ISDN I.250-I.259

Overall network aspects and functions I.300-I.399

Network functional principles I.310-I.319

Reference models I.320-I.329

Numbering, addressing and routing I.330-I.339

Connection types I.340-I.349

Performance objectives I.350-I.359

Protocol layer requirements I.360-I.369

General network requirements and functions I.370-I.399


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NETWORKING



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Computer Network

Computer network - two or more computers interconnected with one another for

the purpose of sharing resources such as database, backup device, and others.

The elements of a computer network are (Source: Network Fundamentals

Cisco):

Protocols rules and agreements on how the different parts of the network

will operate. Aprotocol stack is a list or set of protocols used by a system.

Data and Messages information used or transmitted / received in the

network.

Communications medium interconnects the different devices in the

network. It may include copper and fiber optic cables, earths atmosphere, or

free space.

Devices - includes computers, routers, switches, hubs, bridges and others.

Network protocols or networks may be classified as:

Current includes most modern and sophisticated protocols or networks

Legacy includes old protocols/networks which are still being used for some

reasons.

Legendary includes protocols which have become antiquated and are no

longer being used.


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Computer Network

Networks may be classified as:

Intranet network which allows only internal employee access.

Extranet network which allows non-employee access to the network.

Some of the considerations in implementing a network are:

Fault tolerance ability of network to withstand failure in some portion of

the network, which results to better reliability.

Scalability ability of network to grow and react to future changes.

Quality of Service indicates the performance level of services provided bythe network.

Security ability to avoid unauthorized access, use, alteration, or tamperingof any part of the network whether hardware, software or data.


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Classification of Computer Networks According to

Geographic Scope Local Area Network

Computers confined to one building or cluster of buildings

Relatively high speed of transmission

Usually privately owned

Wide Area Network

Computers located outside a building or cluster of buildings

Computers may be located between two or more cities, or between two ormore countries

Usually uses facilities of telecom companies such as T1, E1, ISDN, X.25,Frame Relay, ATM, SDH, SONET.

Metropolitan Area Network

Computers located within a city or cluster of cities

Usually use facilities of telecom or network service providers Global Area Network

Computers located in different countries around the world. Ex. Internet

Personal Area Network (PAN) allow people to transfer data through thehuman body simply by touching each other (future)

Power line area network (PAN) uses ac power lines.


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Classification of Computer Networks According to Type of

Physical Connection

Multipoint or Multidrop (also called Broadcast)

More than two stations and/or devices on the network share a singlecommunications medium

Many or all subscribers of the network receive transmitted messages, andeach message contains an address to identify which subscriber is intendedto receive the message.

May useBroadcast (message is intended for all subscribers) orMulticast(message is intended for a specific group of subscribers)

Point to point Only two stations use a communications medium

Combination of Broadcast and Point to Point


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Classification of Computer Networks or Protocols According

to Type of Connection

Connection Oriented

Communicating devices first setup a logical connection (virtual circuit)before data are transmitted between the two devices.

Designed to provide ahigh degree of reliability for data transmission and

reception. Often provides error control.

Usuallysequence numbers and acknowledgement numbers are used totrack the transmission and reception of data.

Connection is usually terminated with proper acknowledgment between

communicating devices. A telephone call is similar to this type of connection.

Connectionless

Communicating devicesneed not establish an active connection beforedata are transmitted.

Packets of datarely on addresses for it to be able to reach the destination.

Doesnot provide the same high degree of reliability as connectionoriented protocol.

An example would be a packet switch, connectionless network.


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Computer Networks

Network modelcould be: Peer to peer client server all computers share their resources

with all the other computers in the network.

Dedicated client server one or more computers are assigned as a

server and the rest of the computers are clients. Network Architecture outlines the way in which a network is arranged

or structured.

Network Topology refers to the appearance or the way a network is

laid out. Network topology could be:

Physical Topology - refers to the physical lay out (geometric

representation) of the computers in a network.

Logical Topology Describes how data actually flow through thenetwork. It refers to the logical layout of the computers in a

network (how computers access other computers in the network)

Hybrid topology combines two or more topologies (star, ring )


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PHYSICAL LAN TOPOLOGY

Bus Topology

Star Topology

Ring Topology

Tree Topology

Mesh

Topology


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Point to Point Topology

Only two stations are connected by a transmission medium.

Advantages

Very simple

Transmission medium is ready for use anytime by the two stations.

Disadvantages

Less stations can communicate with each other.

Point to Point Topology


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Physical Mesh Topology

Every station has a direct two point communication to every otherstation.

Also calledfully connected.

Fully connected circuit requires n(n-1) physical transmission links tointerconnect n stations.

Advantages

Computers can communicate anytime (no traffic)

Robust (Data have alternate routes)

Has more privacy and security

Easier fault isolation

Disadvantages

More expensive and bulkier cabling / communication lines

More communication ports are needed

More cumbersome installation and reconnection

Could have higher total cost of ownership


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Physical Star Topology

Stations are connected directly to a centrally located device such as acomputer or hub which acts like amultipoint connector.

Advantages

If link of one computer fails, others can still communicate Requires less cable and communication ports than mesh topology

Could be less expensive than mesh topology

Easier to install compared to mesh topology

Easier fault isolation compared to bus

Disadvantages

If central hub breaks down, all communications are down

Less robust compared to mesh topology

Often requires more cable than bus


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Physical Bus Topology

It uses amultipoint data communications circuit. All stations are connected to a single transmission medium, which allows all

stations to receive transmitted packets.

Also calledmultidrop, linear bus, or horizontal bus.

Advantages

Requires less cable than other topology

Easier to install compared to other topology

Requires less communication ports than mesh and ring topology Could be less expensive than mesh topology

Disadvantages

Computers could not communicate anytime (because of collision) If cable breaks down, entire network could be disrupted

More difficult fault isolation


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Physical Ring Topology

All stations are connected in tandem (series) to form a closed loop or circle.

Advantages

Requires less cable than mesh topology

Requires less communication ports than mesh topology

Relatively easy to install

Could be less expensive than mesh topology

Disadvantages

Delay is longer for non-adjacent stations.

If one cable breaks down, entire network could be disrupted

Requires more communication port than bus or star topology


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Hybrid Topology

It combines two or more of the traditional topologies to form a larger, morecomplex topology.

Advantages

Combines the benefits of traditional topologies used.

Disadvantages

Combines the disadvantages of traditional topologies used.


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Components of a Network

The different components of a network may be classified as (Source: Network

Fundamentals Cisco):

End devices refers to the equipment which acts as the source or destination ofdata, or both. Examples are servers, computers, printers, VOIP phones, PDAs, andnetwork cameras.

Servers are computers that hold shared files, programs, network operatingsystems, and other resources. Example: file server, printer server.

Clients are computers that access and use network and shared networkresources.

Previously, computers typically havenetwork interface cards (NICs) which

are used to connect a computer to a network. However, the functions of theNICs are now integrated in the main board of most computers.

Intermediary devices refers to equipment which are used by end devices intransferring data across the network. Examples are hubs, switches, bridges, androuters.

Communications or transmission medium / media refers to the cables, earthsatmosphere, or free space through which data are transmitted between devices.

Services and processes refers to the software which run on devices.


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Network Backbones

Building Backbone a network connection that usually carries traffic

between departmental LANs within a single company.

Campus Backbone a network connection used to carry traffic to and from

LANs located in various buildings on a campus.

It normally usesfiber optic cables to minimize interference.


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Multipoint Network Access Methods / Protocols

Random Access Protocols

1. Multiple Access (MA)

2. Carrier Sense Multiple Access (CSMA)

3. Carrier Sense Multiple Access / Collision Detection (CSMA/CD)

4. Carrier Sense Multiple Access / Collision Avoidance(CSMA/CA)

Controlled Access Protocols

1. Reservation2. Token Passing

3. Polling

Channelization Protocols1. Frequency Division Multiple Access (FDMA)

2. Time Division Multiple Access (TDMA)

3. Code Division Multiple Access (CDMA)


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Multipoint Network Access Methods

Random Access Protocols1. Multiple Access (MA)

Any device can send a frame whenever it has one to send,without detecting if there is ongoing transmission or collision.

Pure Aloha was thefirst multiple access methodused. Uses abase station to receive packets from sender and

retransmit packets to ultimate destination.

Acknowledgements are sent to transmitting stations, whichretransmits packets when no acknowledgements are received

within specific period of time.

No longer used widely.

2. Carrier Sense Multiple Access (CSMA)

Station senses transmission medium if there is any existing

transmission before it sends packets, but has no proceduresfor collision.

Station may send packets immediately if medium is idle or itmay send after a certain period of time.

Base station may no longer be used.

No longer used widely.


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Random Access Protocols (continuation)3. Carrier Sense Multiple Access / Collision Detection

(CSMA/CD)

Same as CSMA except that there are procedures if

collisions occur (Computers retransmit data after someperiod of time.)

If collision is sensed, sending station typically sends ajamming signalto inform other stations about the collision.

Time before retransmission may become longer as more

collisions are detected in attempting to transmit packet. Used widely, especially inEthernet.

4. CSMA/CA

Same as CSMA except that stations avoid collision by

waiting by an interframe gap (IFG) amount of time andanotherrandom amount of time, before transmitting packets.

Transmitting station waits for an acknowledgement, andretransmits packet if no acknowledgement is received after acertain period of time.

Used in wireless LANs.


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Controlled Access Protocols1. Reservation

Station makes reservation before sending data.

Each station is allotted areservation time slot on a

reservation frame.2. Token Passing

Atoken is passedfrom one station to another.

Station with token has the right to send data.

Stations used logical ring topology. Used by IBM.

3. Polling Usesprimary stations (control stations) andsecondary

stations. Primary station polls secondary stations if any would want to

transmit data.

All transmissions pass through the primary station.

Used in SDLC (developed by IBM).


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Channelization Protocols1. Frequency Division Multiple Access (FDMA)

Data Link Layer protocol that usesfrequency division multiplexing.

Availablebandwidth (frequency spectrum) is sharedby stations.

Total radio frequency spectrum isdividedinto individual channels.

Used incell phone networks.2. Time Division Multiple Access (TDMA)

Data Link Layer protocol that usestime division multiplexing.

Each station isallotted a certain amount of time (time slot) to transmitpackets.

Used incell phone networks.

3. Code Division Multiple Access (CDMA)

Based onspread spectrum technology.

Only one channel occupies the entire bandwidth of link.

All stations cansend data simultaneously without time sharing orfrequency spectrum sharing.

Each station isassigned a unique code orspreading sequences(sequence of numbers calledchips)

Code is used to manipulate bits to be transmitted.


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CDMA Multiplexer

+1,+1,+1,+1

+1,-1,+1,-1

-1,-1,-1,-1

-1,+1,-1,+1

0, 0, 0, 0

+1,-1, -1, +1

+1,+1,-1,-1

+1,-1,-1,+1

X

+

X

X

X

-1,-1,-3,+1

-1

-1

0

+1

Bit = 0

Bit = 0

Silent

Bit = 1

Station 1

Station 2

Station 3

Station 4

Code A

Code B

Code C

Code D

Encoding rules: 0 = -1, 1= +1, silent = 0


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CDMA Demultiplexer

+1,+1,+1,+1

+1,-1,+1,-1

-1,-1,-3,+1

-1,+1,-3,-1

-1, -1, +3, -1

-1,+1, +3, +1

+1,+1,-1,-1

+1,-1,-1,+1

X

X

X

X

-1,-1,-3,+1

-4

-4

0

+4

Bit = 0

Bit = 0

Silent

Bit = 1

Code A

Code B

Code C

Code D

Decoding rules: 0 = -1, 1= +1, silent = 0

-1

-1

0

+1

Add

Add

Add

Add

Divideby

4

Divideby

4

Divideby

4

Divide

by

4


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Line Discipline

Line discipline refers to the coordination of hop to hop data delivery.

According to Tomasi, there are two fundamental ways that line disciplineis achieved, namely:

1. ENQ/ACK (Enquiry/Acknowledgment)

Works best in simple networks such as when only two DTEs are

communicating. Initiating station begins a session by transmitting an enquiry (ENQ)

frame to the other station. Frame usually includes the address of theother station.

The other station sends anacknowledgment (ACK) frame if it is readyto receive data, or anegative acknowledgment (NAK) frame if it is notready to receive data.

Destination station acknowledges all messages with an ACK or NAK.

2. Poll/Select

Best suited for centrally controlled networks using multipoint topology,where one station acts as primary or host station and the others assecondary stations.

Primary station polls each station and determines which station shoulduse the transmission medium.


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Flow Control

Flow controlis used to determine how much data should a station send to

another station, and when a station should stop or start sending data to anotherstation.

According to Tomasi, there are two common methods of flow control, namely:

1. Stop and Wait

Transmitting station sends one message then waits for an acknowledgmentbefore sending the next message.

Advantage is its simplicity.

Disadvantage is its slow speed.

2. Sliding Window

Transmitting station can transmit several messages in succession beforereceiving an acknowledgment.

One acknowledgment can be used for several messages.

The term sliding window refers to imaginary receptacles at the source anddestination.

Frames can be acknowledged before the window is filled with data. To keep track of which frames have been acknowledged,modulo n

numbering system is required where each frame transmitted is identifiedwith a sequence number between 0 and n-1.

n is any integer value equal to 2x, where x is the number of bits in the

numbering system.


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Error Control

Error controlincludes both error detection and error correction.

Error detection can be accomplished using VRC, LRC, CRC, or other error

detection techniques.

Error correction isgenerally accomplishedusingAutomatic Repeat Request

(ARQ) :

ARQ can bestop and wait ARQ orsliding windows ARQ.

Sliding window ARQ can be go-back-n frames orselective reject (SREJ).

Withgo-back-n frames, destination tells the source to go back n frames

and retransmit all of them.

Withselective reject ARQ, the destination tells the source to retransmit

only the frame with error.

Open Systems Interconnection (OSI) Model


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Developed byInternational Standards Organization (ISO).

Intended to facilitate the interconnection of similar or different types ofcomputers.

Intended to serve as amodel/framework for developing standards and productsused in interconnecting computers in a network.

The model is applicable for many of the standards widely used today (TCP/IP,Ethernet, and others)

Model has 7 layers

Each layercommunicates with corresponding layer on the other side

Each layer serves as aservice provider to higher layers.

Each layer is independent from other layers.

Each layer encapsulates packets from higher layers with its own controlinformation such as addresses

Theadvantages of layered architecture are: It facilitates peer to peer

communications among protocols, additions and changes in one layer doesnot affect other layers, and development can be done per layer.



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Each layer has a unit of data calledprotocol data unit (PDU).

At thetransmitter, each layeradds its own header and trailer to the protocoldata unit (encapsulation) passed by the immediate layer above it, to create itsown protocol data unit.

At thereceiver, each layerremoves the header and trailer (decapsulation)

added by the corresponding layer at the transmitter, and passed the data to theimmediate layer above it.

Each layer canprovide services to more than one entity in the higher layer byusing aservice access point (SAP).

Information and network information passes from one layer to another through

a layer to layer interface. Layers 4 to 7address the aspects of network toallow for two host computers to

communicate directly.

Layers 1 to 3 are concerned with the actualmechanics of moving the data.


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OSI Model

Computer BComputer A

100 Base T Hub or Switch

Application layer

Presentation Layer

Session layer

Transport Layer

Network Layer

Data Link Layer

Physical layer

7

6

5

4

3

2

1

7

6

5

4

3

2

1

Application layer

Presentation Layer

Session layer

Transport Layer

Network Layer

Data Link Layer

Physical layer


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Physical Layer

Responsible fortransmission methodandactual propagation ofunstructured data bits (1 and 0) through a transmission medium.

Deals withcreation and reception of physical signals such as voltages,current, and optical signals.

Defines allowablecircuit characteristics such as impedance andcapacitance.

Definescommunications media to be used.

Definesmaximum speedof transmission of data.

Defineshow 0 and 1 is represented in signals. Definesconnections, pin assignments, interface parameters, and

timing.

Defines thecarrier system used to propagate signals such as T1 or E1.

May provide switching facilities. Theprotocol data unit (PDU) in this layer is calledbits.

Some standards which operate in the physical layer areRS232, RS422,RS 423, andEthernet (also includes data link layer).

Data Link Layer


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Data Link Layer

Responsible forformatting of frames andproviding error-freecommunications across the physical link connecting stations in thenetwork. .

Producesframes to be transmitted by physical layer.

Provides identity of bits and fields in aframe.

Defines thestart and endof transmission of frames.

Could provide data link layersource and destination addresses(Physical orMedia Access Control (MAC) addresses)

May provide facilities for line discipline ( coordinating hop to hop

delivery of data), error detection and error recovery. May provideflow controlof frames (to prevent overflow of received

frames at receiver memory).

May provide communications mediumaccess control, such asCSMA/CD.

Theprotocol data unit (PDU) in this layer is calledframe.

Used in establishing communications between devices physicallyconnected with one another (such as computer connected toanother computer or router)

Data Link Layer


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Data Link Layer

Error control used could be:

Stop and wait ARQ (Automatic Repeat Request )

ACKis transmitted by receiver for each frame sent.

If there is an error on the frame,no ACK is transmitted.

Sender retransmits if it receives no ACK after preset time.

Go-Back-N ARQ (Automatic Repeat Request) Multiple frames can be sent prior to transmission of ACK.

Sequence numbers are added to frames.

Usessliding windows concept.

If a frame has an error, or timer expires, senderretransmits allpreviously transmitted frame, starting from frame with error.

Selective Repeat ARQ (Automatic Repeat Request)

Same as Go-back-N ARQ, but onlyframe with error is retransmitted.

NACKwhich indicates sequence no. of frame with error is sent byreceiver.

Window size is at most half the size of those used for Go-back-N ARQ.

Range of sequence numbers is expected by receiver.

Forward Error Correction

Data Link Layer


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Data Link Layer

IEEE subdivided data link layer to: Logical Link Control (LLC)

Medium Access Control (MAC)

Standards which operate in the data link layer include:

Asynchronous (Start Stop) protocol SDLC (Synchronous Data Link Control)

Bisync (Binary Synchronous)

HDLC (High Level Data Link Control)

Ethernet (also includes physical layer)

Network Layer


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Network Layer

Provides details that enable the data to be routed between devices inan environment using multiple networks.

Responsible fornetwork addressing anddelivering packets fromultimate source to ultimate destination.

Provides means for routing packets through different portions of

computer network. Providesnetwork layer source address anddestination address.

May provide facilities for error detection and error recovery.

May provideflow control of packets.

Provides upper layers of the hierarchy independence from the datatransmission and switching technologies used to interconnect systems.

Theprotocol data unit (PDU) in this layer is calledpacket.

Standards which operate in the network layer includesIP (InternetProtocol) which is a part of TCP/IP protocol, and IPX (Novell)

Transport layer


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Transport layer

Controls and ensures the end-to-end integrity of the data message

propagated through the network between two devices.

Responsible fordata tracking andprocess to process delivery of entiremessage across the network

Has the ultimate responsibility of providing efficient and error free delivery

of data (not all network layer protocols provide error recovery procedures) Providessegmentation of the data, in which messages are broken into

smaller pieces that can be easily transported across a medium.

Reassembles segments into streams of application data at the receiver.

Generates transport layer addresses which are calledport numbers.

Provides flow controlat the transport layer level.

May or may not establish logical connection on the transport layer level.

Theprotocol data unit (PDU) in this layer is calledsegment.

Standards which operate in the transport layer include TCP (TransmissionControl Protocol) and User Datagram Protocol (UDP) which are part of theTCP/IP protocol,, and SPX (Sequence Packet Exchange) which is aprotocol used by Novell.

Services provided may beconnection oriented (such as TCP) or

connectionless (such as UDP).

Session Layer


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y

Responsible for jobmanagement tracking andnetwork availability(Data storage and processor capacity).

Provides logical connection entities at the application layer.

Provides means for establishment or reestablishment of connection

between user applications. Logon and log off procedures.

Creates and maintains dialogs between source and destination.

Includes services for virtual connections between applications,synchronization of data flow for recovery purposes, creation of

dialogue units and activity units, connection parameter negotiation,and partitioning services into functional groups.

Provides means ofgraceful termination of connection between userapplications.

Presentation Layer


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Presentation Layer

Provides independence to the application processes byaddressing anynecessary code or syntax conversion.

Transforms data into a form that the application layer can use.

Handles syntax and semantics used by application layer.

Syntax refers to the structure or format of the data within themessage.

Semantics refers to the meaning of each section of the data.

May providecode conversion.

May providedata compression/decompression.

May encrypt data to be transmitted anddecrypt received data.

May provide virtual terminaltranslation services.

Examples: converting an EBCDIC-coded text file to an ASCII-coded

file.

Presentation Layer


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Some standards which operate in this layer are:

QuickTime - used for video and audio. Motion Picture Experts Group (MPEG) - used for video

compression and coding.

Graphics Interchange Format (GIF) used for compression and

coding for graphic images. Joint Photographic Experts Group (JPEG) used for compression

and coding for graphic images.

Tagged Image File Format (TIFF) - used for coding graphic

images.

Application Layer


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pp y

Analogous to General manager of the network.

Provides distributed information services and controls the sequence of

activities of the applications.

Provides support for end user applications such as:

file transfer

electronic mail

remote login

accessing resources of other computers

Serves as end user interface

Manages application processes

Theprotocol data unit (PDU) in this layer is calleddata.

Example is FTP (file transfer protocol) which is a part of TCP/IP TCP/IP protocol suite contains protocols for network, transport, and

application layers.

Application Layer


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pp y

Protocols which operate in the Application layer are:

FTP (file transfer protocol) which is a part of TCP/IP used to

transfer files.

Domain Name System (DNS) used to resolve Internet names to IP

addresses. Hypertext Transfer Protocol (HTTP) used to transfer files that make

up the web pages of the World Wide Web.

Simple Mail Transfer Protocol (SMTP) used for transferring email

messages. Telnet used for terminal emulation.

Cisco Three Layer Model


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Cisco is a company producing network devices such as routers and switches.

Cisco defines three layers for its computer network model, namely: Core Layer the highest layer in the model. It is responsible for:

transporting large amounts of data traffic reliably and quickly.

Distribution Layer (workgroup layer) responsible for:

Communications point between the access layer and core layer Determining the fastest way to handle service requests

Providing security and network policies

Defining broadcast and multicast domains

Access Layer - responsible for: Access control

Creation of separate collision domains

Workgroup connectivity

TCP/IP Three Layer Model Model


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TCP/IP protocol suite was developed by the Department of Defense of the US

before the development of the OSI model. Thethree layers of thethree layer TCP/IP modelare:

Application layer functions like the session layer, presentation layer, andapplication layer of the OSI model

Transport Layer similar to the transport layer of the OSI model. Network Layer (Internet layer or internetwork layer) similar to the

network layer of the OSI model.

Thetwo layers below the network layer arenot specified in the TCP/IPprotocol suite.

TCP/IP Four Layer Model


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The four layer of the four-layer TCP/IP Model are:

Process Layer provides application support. Host-to host Layer services the process and Internet layers to handle the

reliability and session aspects of the data transmission.

Internet Layer (network layer) contains information that pertains to how

data can be routed through the network . Network Access Layer provides means of physically delivering data

packets using frames or cells.


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Physical Layer Standards / Protocols


Ph i l L S d d / P l


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Physical Layer Standards / Protocols

RS232 (EIA) / CCITT V.24 and V.28

RS422 (EIA) / CCITT V.11

RS423 (EIA) / CCITT V.10 RS485 (EIA)

Ethernet (Physical layer portion; Ethernet also has data link layer

standards)

Manchester Encoding Centronics Parallel Interface

IEEE 1284 Standard

USB Standard

IEEE 1394 Standard

EIA RS232 / CCITT or ITU V.24 And V.28


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Developed byElectronics Industry Association (EIA) of US. RS stands forRecommended Standard.

Official name isInterface Between Data Terminal Equipment AndData Communications Equipment Employing Serial Binary DataInterchange.

Variously known asEIA RS-232, EIA 232, and TIA 232. Various revisions areRS232 C, RS232 D, RS232 E and TIA-232-F.

Developed as an interface standardfor a data terminal equipment(DTE) and a data communications equipment (DCE).

Defines the following:

electrical signals used and control signals circuit impedance and maximum transmission speed

Commonly used to connect modems to DTEs

May be used to connect two DTEs over short distances (50 feet or less)

Maximum data rate is20,000 baud. Standard defines the use ofDB25 (25 pin) connectors.

Currently used in different types of connectors such as DB9 or DIN 8

V.24 is for functional specifications and V.28 is for electricalspecifications

RS232 / V.24 And V.28


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Single ended (unbalanced) operation.

Bipolar (uses non-return to zero bipolar encoding)

For the transmitter (driver):

+5 volts to +15 volts indicate a 0 (negative logic)

-5 volts to -15 volts indicate a 1 (negative logic)

For the receiver: +3 volts to +25 volts indicate a 0 (negative logic)

-3 volts to -25 volts indicate a 1 (negative logic)

-3 volts to +3 volts is undefined

Difference between transmitter and receiver voltages is callednoisemargin.

Positive voltage indicates the activation of control signals (positive logic)

Load impedance should be between3000 to 7000 ohms

Typical interconnecting cable length is50 feet (15 meters)

Maximum load capacitance is2500 pf, which typically limits theinterconnecting cable length to 50 feet. Typical interconnecting cableshave capacitance of 50 pF per foot, thus a total load capacitance of 2500pF will be reached if 50 feet of cable is used.

Driver output resistance 300 ohms maximum

RS232 / V.24 And V.28


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RS232 signals are divided into the followingfive groups:

A used for ground

B used for data

C used for control

D- used for timing (clocking)

S used for secondary channel

There aretwo full duplex channels in a 25 pin RS232 interface, although

some manufacturers do not used the full RS232 implementation (secondary

channel and other primary channel control signals are not used).

RS232 Pin Assignments Using DB25 Connector


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Pin No. Function

1 Frame Ground 10Negative DC Test

Voltage

19Sec. Request To

Send2

Transmitted Data

(TD)11 20

Data Terminal

Ready (DTR)

3Received Data

(RD)12

Sec. Carrier

Detect21

Signal Quality

Detect

4Request to Send

(RTS)

13Sec. Clear To

Send

22Ring Indicator

(RI)5

Clear To Send

(CTS)14

Sec. Transmitted

Data23

Data Rate

Select

6Data Set Ready

(DSR)15

Transmitter

Clock24

Ext. Transmitter

Clock

7 Signal Ground 16Sec. Received

Data

25 Busy

8Carrier Detect

(CD)17

Receiver

Clock

9Positive DC Test

Voltage18

Function FunctionPin No. Pin No.


Protective ground (GWG, FG, or CG) chassis or earth ground. Usually


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g g yconnected to signal ground (pin 7), but not always.

Transmit Data or Send Data (TD or TxD) (from DTE) where data fromDTE is transmitted to the modem.

Receive Data (RD or RxD) (from DCE) where data from the modem (datafrom remote DTE) is received by the DTE.

Request to Send (RS or RTS) (from DTE) informs DCE that DTE wants totransmit data.

Clear to Send (CS or CTS) (from DCE) informs DTE that it can transmitdata.

Data Set Ready or Modem Ready (DSR or MR) - (from DCE) informs DTEthat DCE and communications channel is ready for data transmission andreception.

Signal Ground (common, SG or GND) signal reference line for all signals.

Carrier Detect (CD) or Receive Line Signal Detect (RLSD, CD, or DCD)(from DCE) informs DTE that DCE is receiving carrier signal from remotemodem.

Transmitter Clock or Transmit Signal Element Timing (TSET, SCT-DCE)(from DCE) where transmit clock generated from the DCE is passed to theDTE. (for synchronous transmission)

Receive Clock or Receiver Signal Element Timing (RSET or SCR) (fromDCE) where recovered clock by modem is passed to DTE. (Used for

synchronous transmission.)



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Data Terminal Ready (DTR) (from DTE) informs DCE that DTE is

available and ready to transmit and receive data.

Signal Quality Detect (SQD) (from DCE) a low signal indicates poor

signal being received by DCE.l.

Ring Indicator (RI) - (from DCE) indicates that DCE is receiving a

call from a remote modem (for dial up modems).

Data Signal Rate Selector (DSRS) (from DTE) used to select one of

two transmission rates.

External Transmit clock or Transmit Signal Element Timing (TSET,

SCT-DTE) (from DTE) transmit clock used for synchronous

transmission if transmit clock from DCE is not used.

Secondary channel signals are similar to primary channel signals.


If a DTE is to be connected to a DCE s ch as a modem all pins in the


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If a DTE is to be connected to a DCE such as a modem, all pins in the

DTE connector are connected to thesame pin number in the DCEconnector.

If a DTE is to be connected to another DTE directly (without using

DCEs), transmit data (pin 2) of one DTE must be connected to receive

data (pin 3) of the other DTE, and vice versa. Control pins must be properly connected to other pins in such a way that

the required control signals are asserted. Usually pins 4 and 5 are

connected , and pins 6, 8, and 20 are connected (on the same connector).

(These are not part of the RS232 specifications, but are being practiced inthe field).

RS232 Signal Level


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0 volts

+ 25 volts

+ 3 volts

- 3 volts

- 25 volts

Notes:

1. + 3 volts to +25 volts indicate a logical 0

2. -3 volts to - 25 volts indicate a logical 1

3. -3 volts to + 3 volts is undefined

RS449 Standard

D l d b El t i I d t A i ti (EIA)


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Developed byElectronics Industry Association (EIA).

Also known asEIA-449 orTIA-449,

Intended to replace RS232.

Definesmechanical specifications only.

Defines the use of37 pin (DB37) (for primary channel) and 9 pinconnectors (DB9) (for secondary channel)

Used forRS422 and RS 423 standards, which are electrical

specifications.

Not readily adopted by the industry and the standard isno longerbeing recommended for use.

Replaced by RS 530 standard also known as EIA/ TIA 530.

RS449 Standard


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Pin

No.Function

1

23

4

5

6

7

8

9

10

11

12

13

14

1516

17

18

19

Shield

Signaling RateUnassigned

Transmit Data

Transmit Timing

Receive Data

Request to Send

Receive Timing

Clear to Send

Local Loopback

Data Mode

Terminal Ready

Receiver Ready

Remote Loopback

Incoming CallRate Selector

Terminal Timing

Test Mode

Signal Ground

20

2122

23

24

25

26

27

28

29

30

31

32

33

3435

36

37

Receive Common

UnassignedTransmit Data

Transmit Timing

Receive Data

Request to Send

Receive Timing

Clear to Send

Terminal in Service

Data Mode

Terminal Ready

Receiver Ready

Select Standby

Signal Quality

New SignalTerminal Timing

Standby Indicator

Transmit Common

First Segment Second Segment

FunctionPin

No.

DB-37 Connector DB-9 Connector

Pin

No.

1

23

4

5

6

7

8

9

Function

Shield

Secondary Receiver ReadySecondary Transmit Data

Secondary Receive Data

Signal Ground

Receive Common

Secondary Request To Send

Secondary Clear To Send

Transmit Common

RS 530 (Also called EIA 530 or TIA 530)


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Developed by EIA.

Also known as EIA/ TIA 530.

Defines mechanical specifications only.

Generally uses a25-pin connector.

Used for RS422 and RS 423 standards.

Used to replace RS 449.

RS422 / CCITT V.11 Standard


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RS-422 is American National Standards Institute (ANSI) standardANSI/TIA/EIA-422-B

CCITT / ITU-T standard is V.11

Defines electrical signals only.

Used with RS/EIA/TIA 449 and RS/EIA/TIA 530 standard. Used for distances longer than what RS232 can handle.

Usesdifferential transmission and reception

Uses balanced transmission (each signal uses two wires)

2 wires are used for transmit, two wires for receive. Specification itselfdoes not set an upper limit on data rate

Could be used for data rate of100 Kbaud at 4000 feet

Could be used for data rate of10 Million baud at 40 feet

Currently use RS 530, RS449, DB25, DB9 or other connectors. Not compatible with RS232.

Note: some books generally define maximum cable length is 200 feet(60 m) and maximum data rate of 2.048 Mbps.

RS423 / CCITT V.10 Standard

RS/EIA/TIA 423


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RS/EIA/TIA-423

is a standard for serial communications. ITU / CCITT version is V.10.

It uses unidirectionalsending driver, and allows for up to 10 receivers.

Defines electrical signals.

Used for distances longer than what RS232 can handle.

Usesdifferential transmission and reception.

Uses unbalanced transmission (Signal lines have one commonground line)

3 wires are used for transmit and receive .

Could be used for data rate of1 Kbaud at 4000 feet.

Could be used for data rate of100 Kbaud at 40 feet.

Signals arecompatible with RS232.

Note: some books generally define maximum cable length is 200 feet

(60 m) and maximum data rate of 2.048 Mbps.

RS422 and RS423 Signal Level


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0 volts

+ 6 volts

+ 200 milivolts

- 200 milivolts

- 6 volts

Notes:

1. + 200 milivolts to + 6 volts indicate a logical 0

2. - 200 milivolts to - 6 volts indicate a logical 1

3. - 200 milivolts to + 200 milivolts is undefined

RS485

EIA 485 also known as TIA/EIA 485 or RS 485 is a standard


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EIA-485, also known as TIA/EIA-485 or RS-485, is a standarddefining the electrical characteristics of drivers and receivers for use in

balanced digital multipoint systems.

It can span up to4000 feet or just over 1200 meters.

The two ends of the cable have atermination resistor connected

across the two wires.

Centronics Parallel Interface


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Original specifications were established by Centronics, which was a

company that produced and sell printers.

Used forconnecting printers to computers.

Could be used forshort distances only (10 meters or less) Voltages used are TTL (Transistor Transistor Logic)l evels.

Transmission of data is unidirectional.

Centronics Parallel Interface


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Pin No. Function

1 Frame Ground 10

Acknowledge

Line

2 Data Line 11 Busy

3 Received Data 12 Paper End

4 Request to Send 13 Select Line

5 Clear To Send 19 to 31 Return Lines

6 Data Set Ready 32 Fault Line

7 Signal Ground

8 Carrier Detect

9Positive DC Test

Voltage

FunctionPin No.

Data Line

Data Line

Data Line

Data Line

Data Line

Data Line

Data Line

IEEE 1284 Standard (Parallel Interface)

TheIEEE 1284 standard is designed forparallel transmission of data.

It allows faster throughput compared to Centronics Parallel Interface Standard


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It allowsfaster throughput compared to Centronics Parallel Interface Standard,

but isbackward compatible with Centronics interface.

It allowsbidirectional data flow unlike the original Centronics interface.

It has theoretical maximum throughput of4 megabytes per second.

IEEE 1284 can operate in five modes: Compatibility Mode, also known as Centronics standard.

Nibble Mode is an interface that allows the device to transmit data four bits at

a time.

Byte Mode, also known as "Bi-Directional is a half-duplex mode that allowsthe device to transmit eight bits at a time .

Enhanced Parallel Port (EPP) is a half-duplex bi-directional interface

designed to allow devices like printers, scanners, or storage devices to transmit

large amounts of data.

Extended Capability Port (ECP) is a half-duplex bi-directional interface

similar to EPP, except that PC implementations use direct memory access.

IEEE 1284 Standard (Parallel Interface)


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Universal Serial Bus (USB) Standard

Used to establishcommunication s between devices and a host controller .

Can connect peripherals such as mouse, printers, hard disks and others to a


82/161

p p , p ,

computer.

USB was intended for easier connection of external devices to PCs by replacing

the connectors at the back of PCs.

Unlike serial or parallel ports of PCs, USB portsprovide electric power to

connected devices.

Maximum length of cables is 5 meters.

USB supports the following signaling rates:

A low-speed rate of 1.5 Mbit/s is defined by USB 1.0.

Thefull-speed rate of 12 Mbit/s is definedby USB 1.1.

Ahigh-speed rate of 480 Mbit/s is defined by USB 2.0

A SuperSpeed rate of 4800 Mbit/s (5 Gbps) is defined by USB 3.0

Wireless USB is the new wireless extension to USB. It utilizes the commonWiMedia* Ultra-wideband (UWB) radio platform developed by the WiMedia

Alliance.

IEEE 1394 Interface Standard (Also called Firewire)

TheIEEE 1394 interface is a serial bus interface standard for high-speed

communications such as data transfer.


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It is used in personal computers, video cameras, audio players and other devices.

The interface is also called FireWire (Apple), i.LINK (Sony), and Lynx (Texas

Instruments.

It can replace SCSIin many applications.

FireWire is also available in wireless, fiber optic and coaxial versions using

isochronous protocols.

It is theHigh Definition Audio-Video Network Alliance (HANA) standard

connection interface for A/V (audio/visual) component communication and

control.

Apple's other code-name for FireWire was "Chefcat.

FireWire 400 (IEEE 1394-1995) can transfer data between devices at 100, 200, or

400 Mbit/s.

FireWire 800 (IEEE 1394b-2002) allows transfer rate of786.432 Mbit/s.

FireWire S1600 allows transfer rate of1.6 Gbit/s .

Firewire S3200 allows transfer rate of3.2 Gbit/s.

Manchester Encoding (Digital Biphase or Diphase)

Manchester encoding (also calledPhase Encoding, orPE) is a signaling method

wherein there is achange in voltage in themiddle of the bit time.


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It hasno DC component, and isself clocking, which means that it may be

inductively or capacitively coupled, and that aclock signal can be recoveredfrom

the encoded data.

A voltage change fromnegative (low) to positive (high) represents logic 1, while a

voltage change frompositive (high) to negative (low) represents a logic 0.

Manchester encoding is the signaling standard for 10Base-T Ethernet.

O volt

O volt

O volt

+V

+V

+V

-V

Data

clock

Manchester Code

(802.3 convention-opposite of Thomas

convention))

1 1 0 0 1 0 1 0Binary digits

from information

source

4B5B Coding

4b5b is a line code that maps4-bit symbols to 5-bit symbols to achieve DC-

balance.


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It provides enoughsignal changes to allowclock recovery.

Used inFiber Distributed Data Interface (FDDI) and 100 Base TX Ethernet.

5B/6B Coding

5b/6b is a line code that maps5 bit symbols to 6-bit symbols to achieve DC-

balance


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It provides enoughsignal changes to allowclock recovery.

8B/10B Coding 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-

balance

I id h i l h ll l k


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It provides enoughsignal changes to allowclock recovery. It was developed by IBM in 1983 and was patented in 1984.

It is also used in USB 3.0 and Gigabit Ethernet except for 1000Base-T(twistedpair).

It isDC-free.


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Data Link Layer Standards /Protocols


Data Link Layer Standards / Protocols

A h (St t St ) t l


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Asynchronous (Start Stop) protocol

XMODEM

YMODEM


SDLC (Synchronous Data Link Control)


Point to Point Protocol (PPP)

Ethernet (contains data link and physical layer protocols) IEEE 802.5 Token Ring (contains data link and physical layer

protocols)

XMODEM Asynchronous data link protocolused for low speed data transfer.

Designed for transferring files between computers over the public switched


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Designed for transferring files between computers over thepublic switchedtelephone network.

Usesasynchronous data and asynchronous modems.

Useshalf duplex stop and wait protocol.

The four fields for XMODEM arestart of header (SOH) field, header field,data field, and error detection field.

The first byte of the header is the sequence number.

A similar protocol called YMODEMwas developed.


Synchronous transmission protocoldeveloped by IBM.

Sometimes calledbisynchronous communications.

Character oriented protocol (Sync flag uses a character)


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Character oriented protocol(Sync flag uses a character).

Withcharacter oriented protocol, receiver interprets a frame of data as a group ofsuccessive bits combined into predefined patterns of fixed length, usually eight bitseach.

Control characters are interpreted as such no matter where they are located in theframe.

Character oriented protocols are sometimes calledbyte oriented protocol.

Usespoll/select format to control data transmission. Primary station polls secondarystations and devices connected to secondary stations.

Poll could begeneral (for all devices connected to a secondary station) orspecific (for only one device connected to a secondary station).

Message could be apoll, aselection, anacknowledgment, ormessage with data.

Uses half duplex (Stop and Wait) flow control, which makes it inefficient for linksprone to errors and those with long delays.

Receiving DTE must sendpositive or negative acknowledgements beforeanother frame is sent by transmitter.

Could be used forfaster data transmission compared to asynchronous (start stop)if huge amount of data is transmitted.

Relativelyslow compared to SDLC.

Hasseveral variations.

Bisync (Binary Synchronous) With Bisync, each line control unit canserve many computers, printers or other

devices. Each station and each device on a station has its own address.


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Telecommunications

Facilities PC

(Device 1)

PC

(Device 2)

Synchronous

Modem

Primary

Station

Synchronous

Modem

FEP is a DTE which directs traffic to

and from many different circuits, which

could have different parameters, such

as codes, and data formats.

LCU is a DTE that directs traffic

between one data communication

medium and a relatively few terminals

which uses the same protocols,

character codes, and other parameters

Line control

Unit 2 (LCU)Synchronous

Modem

PC

(Device 1)

PC

(Device 2)

Line control

Unit 1 (LCU)

Secondary Station 2

Secondary Station 1

Typical Bisync Frame For General Poll

EOTPAD SYNSYN SPA SPA PADENQPAD SYNSYN


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Ageneral pollis sent by a primary station to a specific secondary station (linecontrol unit) to ask if there is any device connected to the station which wouldwant to transmit data.

First PAD (Leading PAD) used for bit / clock synchronization betweentransmitter and receiver. Could have a value of10101010 (AA Hex) or01010101 (55 Hex).

Second PAD is a string of 1s which is used as time fill so that secondarystations can clear and be ready for the succeeding fields.

Last PAD trailing PAD with a value ofFF Hex. Used to ensure thatRLSD(Receive Line Signal Detect) in the receive modem is held long enough forentire message to be demodulated.

SYN (Sync character) used for character synchronization betweentransmitter and receiver.

SYNcould have a value of32 (HEX) for EBCDIC or 16 (HEX) forASCII.

SYNcharacters are alwaystransmitted in pairs to preventmisinterpretation of a SYN character in the data portion of the frame when

a string of bits similar to the SYN character is present in the data portion.

Typical Bisync Frame For General Poll

EOTPAD SYNSYN SPA SPA PADENQPAD SYNSYN


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EOTPAD SYNSYN SPA SPA PADENQ

EOT (End of Transmission) in this case used as clearing character to place allsecondary stations into line monitor mode.

SPA (Station Polling Address) used to indicate the address of the secondarystation (line control unit) being polled.

Two SPAs are transmitted for error detection (character redundancy).

ENQ (Enquiry) format or line turnaround character which initiates a line

turnaround. signifies a general poll for all devices connected to the station (line control

unit). Any device which needs to send data can answer the poll from the primarystation.

PAD SYNSYN

Typical Bisync Frame For Specific Poll

EOTPAD SYNSYN SPA SPA DADA PADENQPAD SYNSYN


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EOTPAD SYNSYN SPA SPA DADA PADENQ

Aspecific pollis sent by a primary station to a specific device connected to asecondary station (line control unit) to ask if that device needs to transmit

data. All fields arethe same as those for Bisync general pollexcept thefield for

was replaced with DA.

DA (Device Address) signifies the address of a specific device connected

to the secondary station (line control unit). Two DAs are transmitted for error detection (character redundancy).

Only the device with the specific DA address can respond to the pollfrom the primary station.

PAD SYNSYN

Typical Bisync Frame For Selection

EOTPAD SYNSYN SSA SSA DADA PADENQPAD SYNSYN


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EOTPAD SYNSYN SSA SSA DADA PADENQ

Aselection frame is sent by a polled device to the primary station to indicatethe address of the other device to which the polled device wants to

communicate with. The selected device may or may not be connected to thesame secondary station (line control unit)

The fields arethe same as those used forpoll frame except the Station PollAddress (SPA) wasreplaced with Station Selection Address (SSA).

Station Selection Address (SSA) specifies the secondary station address towhich the selected device is connected.

Device Address (DA) indicates the address of the selected device.

Aselected device can respond to a selection with either apositiveacknowledgment (it can communicate with the device making the selection) or

negative acknowledgment (it cannot communicate with the device making theselection).

PAD SYNSYN

Typical Bisync Frame For Data Transmission

PAD PAD SYNSYN STX DATA BCCETB /

ETXPADPAD


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Frame is used fortransmitting data from one device to another device.

PAD used for bit synchronization between transmitter and receiver. Could

have a value of 10101010 or 01010101 SYN (Sync character) used for character synchronization between transmitterand receiver.

SYNcould have a value of32 (HEX) for EBCDIC or 16 (HEX) for ASCII.

SYNcharacters are alwaystransmitted in pairs to prevent misinterpretation

of a SYN character in the data portion of the frame when a string of bitssimilar to the SYN character is present in the data portion.

STX (Start of text) used to indicate that succeeding field contains data.

ETB (End of Transmission Block) indicates end of block of data transmitted.

ETX (End of Text) indicates end of multiple blocks of data. BCC (Block Check Character) used to detect errors. It typically usesLRC for

ASCIIand CRC-16 for EBCDIC.

Typical Bisync Frame For Acknowledgment

PAD SYNSYN DLE 0 PAD


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Positive Acknowledgment is sent by receiving station to transmitting station toindicate that there was no error on the received message frame based on theBCC.

Negative Acknowledgment is sent by receiving station to transmitting stationto indicate that there was an error on the received message frame based on the

BCC.

Positive Acknowledgment Frame (even numbered blocks)

PAD SYNSYN DLE NAK PAD

Negative Acknowledgment Frame

PAD SYNSYN DLE 1 PAD

Positive Acknowledgment Frame (odd numbered blocks)

DLE (Data Link Escape) used to indicate that next

field contains control

characters rather than data


Synchronous transmission protocol developed by IBM for use in Systems

Network Architecture (SNA). It was the first bit oriented synchronous protocol


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( ) It was the firstbit oriented synchronous protocol.

Abit oriented protocolis a discipline forserial-by-bit information transfer overa communications channel.

Withbit oriented protocol, data is transmitted as a series of successive bits thatmay be interpreted individually on a bit-by-bit basis or in groups of several bitsrather than in a fixed-length group of n bits.

Sync is determined by sequence of bits containing 01111110 in binary or 7E inHexadecimal.

Can transfer data usingsimplex, half duplex, or full duplex. Can supportpoint to point or multipoint topologies.

Can be used forcircuit switch or packet switch networks.

Usesfull duplex flow control.

Usessliding window ARQ for error correction. Frames are generally limited to256 characters.

EBCDIC was the originalcharacter code used for SDLC.


Thetwo types of nodes for SDLC are theprimary station andsecondary

station.Primary station controls the data exchange on the communications


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Primary station controls the data exchange on the communicationschanneland issues commands.

Could be used forfaster data transmission compared to asynchronous (startstop) if huge amount of data is transmitted.

Thethree transmission states for SDLC are:

Transient exists before and after each line turnaround.

Idle a secondary station assumes that the circuit is in the idle state afterreceiving 15 or more consecutive 1s.

Active exists whenever either the primary of a secondary station istransmitting data or control information.

International Standards Organization modified SDLC and createdHighLevel Data Link Control (HDLC).

SDLC became a subset of HDLC (High Level Data Link Control).

International Telecommunications Union (ITU) modified HDLC and createdLink Access Procedure (LAP).

IEEE modified HDLC and createdIEEE 802.2.

Typical SDLC I (Information) Frame

An I (Information) frame contains user data.


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Ending

Flag

Frame

CheckSequence

Payload

(User Data) Starting FlagControl

Secondary

StationAddress

NR P/F FINS

1 byte2 or 4 bytes1 byte 1 byteN bits 1 byte

FI = 0 (b7) indicates frame is information frame

NS = Send sequence numberNR = Receive sequence number

P/F = Poll / Final

Typical SDLC S (Supervisory) Frame An S (Supervisory) frame does not contain user data, but it could be used to

assist in the transfer of data.

It can be used toconfirm previously receivedinformation frames, conveyreadyb diti f t ti lli h i t ti h i f ti


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EndingFlag

FrameCheck

Sequence

Starting FlagControl

SecondaryStation

Address

NR P/F FI Information

Frame

1 byte2 or 4 bytes1 byte 1 byte1 or 2 bytes

FI = 10 (b7 and b6) (indicates frame is supervisory frame)

P/F = Poll / Final

NR = Receive sequence number

Code = 00 (b5 and b4) indicates receiver is ready to receive data (RR)

= 10 (b5 and b4) indicates receiver is not ready to receive data

= 01 (b5 and b4) indicates a negative acknowledgement (NAK) (reject) for

received data

= 11 (b5 and b4) indicates selective negative acknowledgement (NAK) (reject)

for received data

Code

or busy conditions of stations,polling when primary station has no information

to send.

Typical SDLC U (Unnumbered) Frame

A U (Unnumbered) frame does not contain user data, but it is used to send

commands (frames from primary station) andresponses (frames from

secondary stations.


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Ending

Flag

Frame

Check

Sequence

Management

InformationStarting Flag

Control

Secondary

Station

Address

1 byte2 or 4 bytes1 byte 1 byte1 byte

FI = 11 indicates frame is unnumbered frame

Code = corresponds to a command or response

P/F = Poll / Final

Code P/F FICode

It is used to sendnetwork controlandstatus information.

SDLC Frame

Format of frame from primary station issimilar to that of a secondary station.

Starting flag indicates start of frame (has a value of 01111110 or 7E Hex)


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a a a ( a a va 0 0 )

Used for character synchronization

Bit stuffing is used when data contains a series of bits same as starting orending flag.

Secondary Station Address contains secondary station address to which frame must go to, or from which

frame came from Address 00 Hex is used for network testing and is never used for secondary

stations. It is callednull address.

AddressFF Hex is thebroadcast address (frame intended for all secondarystations.

Can be one or several bytes long Control Field used forpolling, confirming received frames, and other

functions.

NR (Receive sequence number) Indicates the number of the next information frame thetransmitting station

expects to receive, or the number of the next information frame thereceiving station will transmit.

Used also to indicatestatus of previously received frames.

SDLC Frame

P/F (poll bit (P) or final (F) bit)

1 indicates that the frame sent by primary station needs a reply from thesecondary station,


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or 1 indicates that the frame is the last frame sent by a secondary station tothe primary station.

NS (Send or transmit sequence number)

defines sequence number of frame currently being sent. Used to reconstruct data and to identify missing frames or frames with errors. FI (Frame identifier)

identifies if the frame is I, S, or U FI = 0 indicates an information frame

FI = 10 indicates a supervisory frame FI = 11 indicates an unnumbered frame Payload

contains users data Frame check sequence

contains error detection information such as CRC. Ending flag indicates end of frame (also has a value of 01111110) can also be used as starting flag of next frame


HDLC is a superset of the SDLCprotocol and thus uses the functionalities

of the SDLC protocol.It d t d f SDLC t l


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It was adopted from SDLC protocol.

It supports half-duplex and full duplex communication over point-to-point ormultipoint links.

It uses ARQ. Has two common modes of transmission

Normal response mode (NRM)

Hasone primary station (one which issues commands), and one ormore secondary stations

Uses point to point or multipoint link

Asynchronous balance mode (ABM)

Each station can be a primary or secondary station

Uses point to point link


Has three types of frames Information frames (I frames)


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Information frames (I frames)

Used to transport user data and control information

Supervisory frames (S frames)

Used only to transport control information

Unnumbered frames (U frames)

Reserved for system management


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Typical HDLC S Frame

EndingFrame Secondary

1 byte or

more2 or 4 bytes1 byte 1 byte1 or 2 bytes


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Ending

FlagCheck

Sequence

Starting FlagControl

Station

Address

NR P/F FIInformation

Frame

FI = 10 (indicates frame is supervisory frame)

P/F = Poll / Final

NR = Receive sequence number

Code = 00 indicates receiver is ready to receive data (RR)

= 10 indicates receiver is not ready to receive d

Documents

Data Communications (IT105) Part 5