TeIecommunications Network Fundamentals

Technical Foundations of Telecommunications

There are five main building blocks in a telecomm network
-	Terminals
-	Transmission Links
-	Nodes and Switches
-	Transmission Methods and Procedures
-	Architecture and Standards

Specifically, we will discuss:
-	Digital Communications
-	The Components of a Network
-	Types of Networks
-	Uses of Networks
-	Transmission Media
-	Bandwidth
-	Transmission Speeds

Digital Communications
-	Information technology (IT) – computers, database management and telecomm
-	Key concept: the ability to represent any form of information as one of two conditions – on or off.
-	Key terms:
-	digital coding – the use of bits to represent info
-	bit/Byte – an 0 or 1 – a group (usually 8) of bits
-	standards – agreements on formats, procedures, and interfaces
-	ASCII – American Standard Code for Information Interchange – the most common digital standard
-	Digital transmission v. analog transmission
-	Faster speeds, greater accuracy, improved error  checking, more accurate storage and retrieval, less expensive to buy and maintain

The Components of a Network
-	Terminals and workstations
-	A variety of devices with varying intelligence
-	Transmission links
-	The whole variety of media
-	Transmission methods – protocols
-	Different techniques for handling data
-	Nodes and Switches
-	Coordination of data traffic
-	Network Architecture
-	The master blueprint for all the network standards

Types of Networks
-	Two main distinctions: geography and public v. private
-	Local Area Network (LAN)
-	Campus/Metropolitan Area Network (MAN)
-	Wide Area Private Network (WAN)
-	Public Voice Network (PSTN)
-	Public Data Networks (PDNs)
-	Value-added Networks (VANs)
-	Virtual Private Networks (VPNs)

Uses of Networks
-	Large companies use a variety of networks at once
-	Switched Megabit Data Services (SMDS) – hot item
-	High-speed data communications on demand
-	Ideal for bursty images and audio/video
-	Competition, Integration and convergence are all made possible and enhanced by digital networks
-	LANs v. WANs – built on different technology bases
-	LANs emerged from desktop PCs
-	WANs evolved from long distance telephony
-	The key task is to link LANs to WANs

Transmission Media
-	A Wire, a Cable, or a Radio Signal
-	Electromagnetic Spectrum
-	Holds new broadband possibilities
-	Any Message through Any Medium

Bandwidth
-	Carrying Capacity of a Transmission Link
-	Kilo, Mega, Giga, and Terahertz
-	Channels – More Than Television
-	One TV channel – 6 megahertz
-	Fiber optics – 30 to 400 terahertz
-	Microwave – 2 to 25 gigahertz
-	Wireless broadband – 40 to 50 gigahertz

Transmission Speeds
-	Usually Stated as Rates
-	Bits Per Seconds (bps) – the standard measure
-	Typical phone line delivers 9,600 bps unimproved
-	Kilobits Per Second (kbps) – 1000 bps
-	Historically the most common transmission rates are 56 kbps and 64 kbps
-	Megabits Per Second (mbps) – 1,000,000 bps
-	T1’s the Industry Standard For High Speed, Long Distance Data Transmission – 1.544 mbps
-	Gigabits Per Second (gbps) – billion bps
-	Fiber Optics: SONET, Gigabit Ethernet, 10 Gigabit Ethernet
-	Terabits Per Second (tbps) – who knows what the future holds?
-	Text v. Graphics
-	One page memo – 15,000 bits
-	High-res image of the memo – 100,000 bits
-	Data Compression
-	Based on the principle of redundancy
-	Example: digital HDTV
-	Compressed signal Is 1/200 the size of the uncompressed signal
-	Will transform the economics of broadcast and cable television
-	The Bandwidth Revolution

Terminals

Dumb Terminals v. Intelligent Terminals
-	Input/Output Devices that interface with humans
-	Single-purpose (telegraph key) to multi-purpose:
-	The PC: Stand-alone to Dumb Terminal to Intelligent Workstation

Operating Systems
-	Software That Manages All Aspects of Applications
-	DOS, Windows, MacOS, variations of Unix
-	Network Operating Systems (NOS) control the operation of LANs
-	Operating System Wars:
-	Microsoft, Apple, IBM, Linux, Unix
-	Higher Level Functions – despite decentralization trends, transactional databases remain on mainframes
-	UNIX – More effective use of hardware resources, better portability and multitasking

Other Types of Terminals
-	Barcode scanners, machine tools, sensors, alarms
-	Key concept: Shift the intelligence as far out in the network as possible for ease of use
-	Adapters – Ethernet cards, for example
-	Distributed Processing – shares the workload in computing and communication
-	Client/Server Computing – dynamic workflow of data and software
-	Cooperative Processing – extends client/server computing to complex transactions

Transmission Links

The paths between terminal devices
-	Information carrying capacity depends on:
-	Strength of the signal, bandwidth of the link
-	Over the air
-	Terrestrial and satellite microwave, traditional broadcast (UHF – HDTV), broadcast broadband
-	Twisted pair wire
-	Standard for many applications – cost effective
-	Coaxial cable
-	Expensive, stiff, well-shielded
-	Fiber optic cable
-	Fully digital, laser device pulses on or off
-	Modems
-	Modulate/demodulate analog to digital and back
-	Will never go away as long as we use microwave signals
-	Repeaters
-	Check, regenerate digital signals
-	Every 40-50 miles for fiber, every six miles for coax

Noise – distortion that makes a signal inaccurate
-	Claude Shannon first defined "signal to noise ratio"
-	2X is inherently noisy, fiber is virtually noiseless
-	1/100 second spark (impulse noise) can distort 100 bits at 9.6 kbps line -- more on faster lines
-	Network software can be too slow to catch errors in modern high-speed transmissions
-	Bit error rates -- the measure of quality in a network
-	One error per million bits is barely acceptable
-	Fiber is one error per billion bits

Nodes and Switches

First, a few definitions:
-	Switch – computers or microprocessors that direct information streams over alternative paths
-	Node – a functional unit connecting transmission lines; usually contains one or many switches
-	Multiplexer – device that aggregates small/slow data streams onto a high-capacity/fast line
-	Hierarchical Configuration – switches move traffic to successively higher bandwidth as the traffic load increases – then gradually back down to destination

Cabling and Switches:
-	Networks are a maze of cables and switches – difficult to keep track of and change
-	Smart Hubs
-	fastest growing part of the telecomm industry
-	combines many functions in one box
-	Hot swappable – capable of being replaced while the network is running
-	Bridges – connect identical networks
-	Routers – connect dissimilar networks that conform to the OSI model
-	Gateways – connect completely dissimilar networks

Intelligence in Switches
-	Switches run the gamut from:
-	High-end computers switching hundreds of thousands of phone calls a minute, to
-	A simple bridge between LANs
The most intelligent switches are capable of:
-	Error handling
-	Accounting and control
-	Message format conversion
-	Analog-to-digital conversion
-	Prevention of unauthorized access
-	Fault detection and diagnosis

Transmission Methods and Procedures

Protocols
-	Telecommunications protocols are the equivalent of a socially acceptable interpersonal interaction
-	The orderly rules and procedures for efficient transport of information
-	The basis of a protocol is a frame that encapsulates the user's data
-	Protocols are built in layers
-	Lowest layer establishes the connection
-	Highest layer interprets and formats data
-	A complete protocol has six functions
-	Initiation of communication
-	Character identification and grouping
-	Message or conversation identifier
-	Link control
-	Error detection and correction
-	Termination of communication

Duplex and Half-duplex Transmission
-	Full duplex – signals are carried both directions simultaneously
-	Half-duplex – two-way alternate transmission

Circuit Switching v. Packet Switching
-	In circuit switching:
-	A fixed path connects the sender and receiver
-	The path is dedicated (used exclusively) for the duration of the transmission
-	Circuit is used inefficiently during pauses
-	Is the basis for telephony and for IBM's main telecommunications architectures
-	In packet switching:
-	Information is digitized and divided into packets
-	Each packet is sent separately, out of order, over various routes
-	An efficient use of transmission facilities
-	Transmission links are not dedicated
-	Packet switching is commonly used in public data networks
-	Newer forms of fast packet switching
-	Frame relay – packets are framed with standard headers, accuracy is checked only at beginning and end of transmission
-	Cell relay – ATM, for example: packets of all kinds are divided into uniform size and framed

Synchronous and Asynchronous Transmission
-	Asynchronous:
-	No regular timing relationship between terminals
-	Start and stop bits are used with each character or group of characters
-	Good for e-mail and other bursty transmissions
-	Synchronous:
-	Terminals are synchronized in time
-	Specified intervals for data and control information
-	Good for large, continuous blocks of data

Protocol Converters
-	Devices that use hardware and software to:
-	Modify the bit stream to adapt to the protocols of the next device or leg of the network
-	Nowadays, they are built into switches, smart hubs, and intelligent workstations

Network Architecture and Standards

Integration and Standards
-	Integration is the combination of telecommunications, computing, end databases
-	Integration requires compatibility
-	Compatibility requires standards
-	Standards – there are thousands:
-	Physical interfaces (RJ-11, RJ-45, USB, Firewire)
-	Higher level standards:
-	Message formats
-	Network procedures
-	Types of transmission

Architecture as Blueprint
-	The architecture is:
-	The set of design principles, and
-	The choice of standards
-	An effective architecture:
-	Integrates services, applications, data, and networks
-	Eliminates duplication, incompatibility, and
redundancy
-	Takes advantage of economies of scale
-	Ensures seamlessness and transparency

Open Systems
-	Open standards are independent of equipment, software, and suppliers
-	Open systems use standards to make seamless and transparent integration possible
-	A standard Is considered open if:
-	It is fully defined
-	It has proved to be stable in products
-	Its interfaces are published for use by all
-	No single party controls its development/use

The Open Systems Interconnection (0SI) Reference Model
-	Developed by the International Standards Organization (ISO)
-	Reference – guides development of products, does not define a specific product
-	Establishes rules that permit data exchange between dissimilar networks
-	Consists of seven layers – each represents an element in electronic communication

Network Topologies
-	Topology refers to the physical structure of a network
-	There are five main topologies:
-	Star – all nodes connect to a central device
-	Bus – all nodes connect to a common linear transmission medium
-	Ring – all nodes connect to a circular, closed transmission medium
-	Mesh – direct connections between pairs of nodes
-	Hierarchical – a mesh network with fewer direct connections – the connections are made between higher and lower volume networks

LANs and WANs

To recap, there are five main building blocks in a telecomm network:
-	Terminals
-	Transmission links
-	Nodes and switches
-	Transmission methods and procedures
-	Architecture and standards

The five building blocks are generic:
-	They apply to both LANs and WANs
-	They apply to both voice and data
-	LANs and WANs are competitive and cooperative technologies
-	WANs were the original core of telecommunications operations and networks
-	LAN technology was a response to PC in the workplace
-	LANs became the driver behind business innovation
-	Making WANS as fast as LANs the current focus
-	Now, the key is interoperability