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WELCOME to
COMP 421 /CMPET 401
COMMUNICATIONS and NETWORKING
Class 1
COURSE OUTLINE

Overview of Communications
– Introduction
– Protocols and Architecture

Data Communications
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Data Transmission
Transmission Media
Data Encoding
Data Link Control
Multiplexing
COURSE OUTLINE (continued)
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Local and Wide Area Networks
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LAN & WAN Protocols
Switching Techniques
Bridges and Routers
High Speed Networks
Internetworking
Internet Resources
Network Operating Systems
TELECOMMUNICATIONS
Telecommunications is the technique of transmitting a message from one point to another
knowing how much information, if any, is likely to be lost in the process.
Hence the term TELECOMUNICATIONS covers all forms of distance communications
including:
•Radio
•Telegraph
•Television
•Telephony
•Data Communications
•Computer Networking
The elements of a telecommunication system are:
•Transmitter
•Channel
•Line
•Receiver
The transmitter is a device that transforms or codes the message into a physical
phenomenon called the transmission channel, by its physical nature it is likely to
modify or degrade the signal on it path from the transmitter to the receiver.
TELECOMMUNICATIONS
The receiver has a decoding mechanism capable of recovering the message
within certain limits of signal degradation by the communication channel.
Telecommunication can be point-to-point or point-to-multipoint in which case it is
called conferencing.
Broadcasting is a particular form of telecommunication that is point-to-multipoint
and goes predominantly from the transmitter to the receivers.
Possible imperfections in a communication channel are:
 Shot noise
 Thermal noise
 Latency
 Non linear channel transfer function
 Sudden signal drops
 Bandwidth limitations
 Signal reflections
TELECOMMUNICATIONS
The art of the telecommunications engineer is
to analyze the physical properties of the
transmission channel, and the statistical
properties of the message, in order to design
the most effective coding and decoding mechanisms.
Information theory enables us to evaluate the capacity of a
communication channel according to its bandwidth and signal-tonoise ratio.
The Communications Model
input
information
Input
device
input
data
transmitted
received
signal
signal
Transmission
Transmitter
Receiver
medium
output
information
output
data
Output
Devices
Cloud
Modem
Modem
Workstation
Workstation
Cloud
Workstation
Hub
Hub
Workstation
Communication Tasks

Communication Tasks Include:
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Transmission System Utilization
Interfacing
Signal Generation
Synchronization
Exchange Management
Error Correction and Detection
Flow Control
Addressing
Routing
Recovery
Message Formatting
Security
Network Management
Data Communication Network
Communication
Network Node
Communication
Network
Network Station
Data Communication Networking

Networks are used to link devices together
– Distant - Network is called a Wide Area Network (WAN)

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Circuit Switched
Packet Switched
Frame Relay
ATM
Public Switched Telephone Network (PSTN)
Leased lines
Public switched data network (PSDN)
Integrated services digital network (ISDN)
– Local - Network is called a Local Area Network (LAN)
– Intermediate - Network is called a Metropolitan Area
Network (MAN)
PSTN

modem link via PSTN
PSTN
modem
modem
LAN
hub
station
4th floor
hub
station
3rd floor
hub
2nd floor



confined geographical area
under single management
high data rate
station
1st floor
server
hub
router
Leased lines
• Lease pubic circuits to connect different sites
• Communication channel is private
LAN
leased circuit
Voice
LAN
LAN
Voice
Voice
PSDN
• PSDN is designed specifically for the transmission of data rather than voice
• Communication is shared
PSDN= Public Switched Data Network
LAN
LAN
PSDN
LAN
ISDN
ISDN is an acronym for integrated Services Digital Network
ISDN provides integrated voice and data over the Telephone
company facilities.
3 Telephone
Lines
Computer
Telco
Central
Office
1 ISDN
Line
Telephone
Telco
Central
Office
Fax
Fax
Telephone
Computer
Standards
Standards are required in the telecommunications industry to govern
the physical, electrical and procedural characteristics of communications
equipment.
Some organizations whom exist, at least partially, to create these
standards are:
•The Internet Society
•ISO
•ITU-T (formerly CCITT)
•The ATM Forum
•IEEE
RFC - Request for Comment
Standards
ECMA
EIA
IEEE
ITU-T
CEPT
ANSI
Computer
Industry
Telecommunications
Industry
Proprietary standards
(closed systems)
Interface standards
(multi-vendor systems)
ISO
ITU-T
Integrated computer and
telecommunications industry
International Standards
(Open Systems
Interconnection)
Standards
The Standardization Process of the Internet Organizations is
•Be stable & well understood
•Be technically competent
•Have multiple independent and interoperable
implementations with substantial operational experience
•Enjoy significant public support
•Be recognizable useful in some or all parts of the Internet
The key difference between theses criteria and this used for the
international standards from ISO and ITU-U is the emphasis
on operational experience
Standards
The process a specification goes through to
become a standard is defined by RFC 2026
Proposed
Standard
Internet
Draft
Experimental
Draft
Standard
Internet
Standard
Historic
International
An Example – 802.11 Wireless LAN
802.11
802.11a
802.11b
802.11c
802.11d
802.11e
802.11f
802.11g
802.11h
802.11i
802.11j
802.11k
Initial 1 & 2 Mbps
High Rate 5.7Ghz
5.5 and 11 Mbps
MAC Bridge
Regulating Domains
Quality of Service
Multi-Vendor Inter-Access Port
High Rate 2.4Ghz
Power Control/Frequency Selection
Enhanced Security
4.9-5Ghz in Japan
Radio Resonance Management
TOPOLOGIES
A network topology is the geometric arrangement of nodes and
cable links in a LAN, and is used in two general configurations:
bus and star. These two topologies define how nodes are connected
to one another. A node is an active device connected to the network,
such as a computer or a printer. A node can also be a piece of
networking equipment such as a hub, switch or a router.
A bus topology consists of nodes linked together in a series with
each node connected to a long cable or bus. Many nodes can tap
into the bus and begin communication with all other nodes on that
cable segment. A break anywhere in the cable will usually cause the
entire segment to be inoperable until the break is repaired.
Examples of bus topology include 10BASE2 and 10BASE5.
TOPOLOGY
Bus topology.
Mesh topology A network topology in which there are at least two nodes with two
or more paths between them.
Ring topology: A network topology in which every node has exactly two branches
connected to it.
Star topology: A network topology in which peripheral nodes are connected to a
central node, which rebroadcasts all transmissions received from any peripheral
node to all peripheral nodes on the network, including the originating node.
.
Hybrid topology A hybrid network accrues only when two basic networks are
connected and the resulting network topology fails to meet one of the basic
topology definitions. For example, two star networks connected together exhibit
hybrid network topologies.
Tree topology: A network topology that, from a purely topologic viewpoint,
resembles an interconnection of star networks in that individual peripheral
nodes are required to transmit to and receive from one other node only,
toward a central node, and are not required to act as repeaters or
regenerators.
Computer Networks
A computer network is a system for communication among two or more computers
Computer network may be categorized by Range:
PAN
LAN
MAN
WAN
Computer network applications may be categorized with respect to the functional
relationships between components:
•Client-server
•Multi-tier architecture
•peer to peer
PANs
A personal area network (PAN) is a computer network used for
communication among computer devices (including telephones and
personal digital assistants) close to one person. The devices may or
may not belong to the person in question. The reach of a PAN is
typically a few meters. PANs can be used for communication among
the personal devices themselves (intrapersonal communication), or
for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as
USB and Firewire. Wireless PANs can also be made possible with
network technologies such as IrDA and Bluetooth.
MANs
Metropolitan area networks or MANs are large computer
networks usually spanning a campus or a city. Common technologies
used for this purpose are Asynchronous Transfer Mode, Fiber
distributed data interface and Switched multimegabit data service and
more recently gigabit Ethernet.
Distances
Data
between 5 and 50 km
rate above 1 Mbps
Standards:
IEEE 802.6 DQDB, FDDI, and ATM
LANs (Local Area Networks)
Maximum
distance not more than a few kms
Ownership
by a single organization
Transmission
speed of at least several Mbps (tens to hundreds are
economical)
Some widely used standards include:
IEEE
803.3 - Ethernet
IEEE
803.5 - Token ring
FDDI
ATM
An
important issue in broadcast LANs is the allocation of the shared channel
(media access control)
Control
may be static (time division multiplexing) or dynamic (contention or
arbitration)
WANs (Wide Area Networks)
Often a network is located in multiple physical locations.
Wide area networking combines multiple LANs that are
geographically separate. This is accomplished by
connecting the different LANs using services such as
dedicated leased phone lines, dial-up phone lines both
synchronous and asynchronous, satellite links, and data
packet carrier services. Wide area networking can be as
simple as a modem and remote access server for employees
to dial into, or it can be as complex as hundreds of branch
offices globally linked using special routing protocols and
filters to minimize the expense of sending data sent over
vast distances.
WAN
WAN
(Wide Area Network)
Spans
entire states or countries
Data
rate of 1.544 (T1), and 45 (T3) Mbps
common
Higher
data rates are available with the wide
deployment of ATM backbone networks
Often
owned by multiple organizations
WAN
Usually
separate communications functions from application
functions
Transmission
Switching
lines: circuits, channels or trunks
elements:
Specialized
computers connecting two or more circuits
Intermediate
Systems, Packet Switching Node, Data
Switching Exchange, Router, etc.
Intermediate
systems store a complete packet before
forwarding it
•store-and-forward; packet switched; point-to-point
network
Computer Networks
Computer Networks may be implemented using a variety of network protocol
stack architectures computer buses or combinations of media and protocol layers
incorporating one or more of the following:
ARCNET
DECNET
Ethernet
IP
TCP
AppleTalk
Token Ring
IPX
FDDI
HSSI
ATM
RS-232
USB
Firewire
X.25
Blue Tooth
WiFi
Frame Relay
Network Software
Network
This
The
software is highly structured
technique has been immensely successful
key is Layered design
Each
layer provides a service to the layer above
Each
layer hides details of how the service is provided to
the layer above
Nth layer on one machine “talks to” or interacts with
the Nth layer on another machine
The
Understanding Services and Protocols
Protocol
is set of rules about the format and meaning of data
units exchanged by peers
Protocol
is used by entities to implement services
Protocol
and/or its implementation can change and as long as
the Service (interface) remains unchanged, higher layers are
happy and continue to work
Like
in abstract data types or object orientation, we decouple
interface and implementation
Protocols
Although each network protocol is different, they all share the
same physical cabling. This common method of accessing the
physical network allows multiple protocols to peacefully
coexist over the network media, and allows the builder of a
network to use common hardware for a variety of protocols.
This concept is known as "protocol independence," which
means that devices that are compatible at the physical and data
link layers allow the user to run many different protocols over
the same medium.
Protocols
A Structured Set of Modules implements the
communications function
File Transfer
Application
Files and file transfer commands
File Transfer
Application
Communications
Service Module
Communications related data units
Communications
Service Module
Network Access
Module
Network
Interface Logic
Network Access
Module
Comms
\Network
Network
Interface Logic
That structure is referred to as a Protocol Architecture
Protocols
The Key Elements of Protocols are:
•SYNTAX
- Data format and signal levels
•SEMANTICS- Control information for coordination
& error handling
•TIMING
- speed matching and sequencing
Network Software - Protocols
Conventions
and rules governing this interaction are specified by
the Layer N Protocol
A protocol
is an agreement about how communications are to
proceed
Without
a protocol, communication can be difficult or even
impossible
E.g.
Telephone conversation, Postal addresses
Network Software - Protocols
The
set of protocols and layers together make up the Network
Architecture
A Network Architecture
Specification must provide enough
information to allow implementation in hardware/software
Implementation
specific details are not part of the
architecture and should be irrelevant for inter-operation
With
one protocol per layer we have a Protocol Stack
Network Software - Protocols
Information
is not actually transferred directly
between peer layer N entities
Peer
layer N entities carry on a virtual
communication using the services of the layers
below
Layer
N passes data and control information down
to (or receives data and control from) Layer N-1
until the physical medium is reached
The benefits of Layered Protocols
Network Architectures,
Protocols and Protocol stacks are the
Fundamentals of Computer Networks
They
form the foundation for the very considerable
success of computer networks in the real world
Multilayer
communications protocols allow
ready
adaptation of successful protocols to new
technology (prevent obsolescence)
migration of protocols from software implementation
(slow) to hardware (fast) as they evolve

More Benefits of Layered Protocols
Separate
data and control information
Support
differing levels of abstraction (message, packet,
frame) with different sizes
Allow
segmentation of large messages
Peer
process abstraction facilitates reduction of difficult
design task (a network architecture) into smaller manageable
tasks (protocol layer architecture)
Typically
lower layer protocols of “network software” are
implemented in silicon (hardware)
Network Software - Interfaces & Services
Interfaces
exist between each layer
Interface
defines which primitive functions and services layer N-1
provides to layer N
Want
layers to:
Perform
a well defined, logically related set of functions
Minimize
the amount of information needed to pass between
layers
Keep
interfaces “clean” to allow easy and transparent
replacement of layers
The 3 Layer Model
•Network access Layer - This layer is concerned with the
exchange of data between the
computer and the network
•Transport Layer
-
This layer is concerned with
reliable and orderly exchange of
data
•Application Layer
-
This layer provides the logic
required to support the
various user applications
A Simple Architecture
Application
() () ()()
Transport
Network
Access
SAPs
Network
Address
Application
Comms
Network
() () ()()
Transport
Network
Access
Application
() () ()()
Transport
Network
Access
•Each computer contains software at all three layers.
•Every entity on the network must have a unique address
•Actually two layers of addressing are required
•A unique network address
•Each application of the computer must have a unique address
•This application address allows the transport layer to support
applications on each computer and are known as
Service Access Points (SAPs)
Simplified Architecture
Computer A
Computer B
Application Protocol
Application
Application
Transport Protocol
Transport
Transport
Network
Access
Network
Access
Protocol
Comms
\Network
Network
Access
Protocol
Network
Access
PDUs
Protocol Data Unit (PDU) - is the combination of data from the next
higher layer and control information
Application data
Transport
header
Application
data
Transport
header
Application
data
Transport protocol
data unit (TPDU)
Network Transport
header
header
Application
data
Network Transport
header
header
Application
data
Network protocol
data unit (NPDU)
 control info + data in each layer = protocol data unit (PDU)
Network Operation
Information in Transport Header
Destination SAP - Tells the destination Transport layer to whom to deliver the message
Sequence Number - Tells the destination what order the PDU was sent
by numbering them
Error-Detection Code - The sending transport sends a code that is a function of the contents
of the PDU. The receiving entity performs the same calculation
and compares the two numbers.
Network Operation
Information in Network Header
Destination Computer Address - Tells the network to which computer the
data is to be delivered
Facilities Requests - Tells the network to make use of certain facilities (i.e. Priority)
Operation of Protocol Architecture
Source X
Destination Y
Record
Application
Transport
Record
DSAP
DSAP
Application
Transport
Transport PDU
Network
Access
DHost
DHost
Packet
Network
Access
Network Operation
•Computer X desires to send a record to computer Y
•Computer X hands the record via a procedure call to the Transport layer
•The Transport layer adds its header creating the Transport PDU
•This is passed down to the Network layer
•The Network layer adds its header creating the Network PDU
•The Network accepts the network PDU from X and delivers it to Y
•The network access module in Y receives the PDU and strips off the header
•It transfers the transport PDU to its transport layer
•The Transport layer examines the transport header and on the basis of the
SAP field delivers the enclosed record
The components of a basic Network
Why establish a computer network
•Program and file sharing
•Network resource sharing
•Database sharing
•Economical expansion of the PC base
•Workgroup capabilities
•Centralized management
•Security
•Interconnectivity
•Enhancement of corporate structure
Distributed computing
Access methods in a distributed
computing environment
A local area network (LAN) and an
internetwork
A network communication model
Circuit Switching
Circuit-switched is a type of network in which a physical path is obtained for
and dedicated to a single connection between two end-points in the network
for the duration of the connection. Ordinary voice phone service is circuitswitched. The telephone company reserves a specific physical path to the
number you are calling for the duration of your call. During that time, no
one else can use the physical lines involved.
Circuit Switching
Circuit-switched networks have been rapped for not having the
resiliency and redundancy to reroute traffic that runs into a fiber or
wire cut, because they don't have as many dispersed points of
presence as IP networks have.
But the big problem for enterprises running circuit-switched networks
is that first stretch that connects them to the public network - a
vulnerable mile, or two or three, that links them to a solitary central
office shared by several carriers and service providers
That's a vulnerability that circuit-switched networks share with Ethernet, IP,
data-only and sometimes even cable networks. If a tornado, earthquake, ice
storm or terrorist attack disables that shared central office or the lines
leading to it, all data and voice communications for miles around could stop
dead in their routes.
Circuit Switching
Packet Switching
Packet switching is a communications paradigm in which packets
(messages or fragments of messages) are individually routed
between nodes, with no previously established communication path
Packet-switched describes the type of network in which relatively
small units of data called packets are routed through a network
based on the destination address contained within each packet.
Breaking communication down into packets allows the same data
path to be shared among many users in the network. This type of
communication between sender and receiver is known as
connectionless (rather than dedicated). Most traffic over the Internet
uses packet switching and the Internet is basically a connectionless
network.
Packet Switching
Another type of digital network that uses packet-switching is the X.25
network, a widely-installed commercial wide area network protocol.
Internet protocol packets can be carried on an X.25 network. The
X.25 network can also support a virtual circuit in which a logical
connection is established for two parties on a dedicated basis for
some duration. A permanent virtual circuit (PVC) reserves the path on
an ongoing basis and is an alternative for corporations to a system of
leased lines. A permanent virtual circuit is a dedicated logical
connection but the actual physical resources can be shared among
multiple logical connections or users.
Packet Switching
Analogous to a physical packet sent through the post with the
address written on the outside, this provides the information the
network (the postal service) needs to get the packet to the correct
destination.
Packets are routed to their destination through the most expedient
route (as determined by some routing algorithm). Not all packets
travelling between the same two hosts, even those from a single
message, will necessarily follow the same route.
The destination computer reassembles the packets into their
appropriate sequence. Packet switching is used to optimize the use
of the bandwidth available in a network and to minimize the latency.
Ethernet, X.25 and Frame relay are international standard layer 2
packet switching networks.
The Internet is a packet-switched network, running the Internet
protocol layer 3 protocol over a variety of other network technologies.
Also called connectionless.
Internet
The Internet is a system of linked networks that are
worldwide in scope and facilitates data communication
service such as remote login, file transfer, electronic mail,
the World Wide Web and newsgroups.
With the meteoric rise of demand for connectivity, the
Internet has become the communications highway for
millions of users. The Internet was initially restricted to
military and academic institutions in its infancy but now it
is a full-fledged information channel for any and all forms
of information and commerce. Internet websites now
provide personal, educational, political and economic
resources to every corner of the planet.
Intranet
With the advancements made in browser-based software
for the Internet, there is now a phenomenon developed by
private organizations called an intranet. An intranet is a
private network utilizing Internet-type tools, but available
only within that organization. For large organizations, an
intranet provides an easy access mode to corporate
information for employees.