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Transcript
Subject:
Computer Forensics and Cyber Applications
UNIT- I
Prof. Pansare R.B.
Department of Computer Engineering
Contents :
Basics of Computer Networks:
Protocols and Standards, OSI Model, TCP/IP Model, Network topology,
LAN standards, Ethernet (802.3)
Transmission media:
Guided transmission media - Twisted Pair, Coaxial and Fiber-optic cables,
Switching techniques:
Circuit switching, Packet switching and message switching,
Network Hardware Components:
Connectors, Repeaters, hubs, NICs, Bridges and Switches
• Fundamentals of Mac Protocols:
Motivation for a specialized MAC, Fundamentals of MAC protocols,
Sensor MAC Case Study (Protocol overview, Periodic listen and sleep
operations, Schedule selection and coordination, Adaptive listening,
Message passing)
IEEE 802.15.4 protocol:
Physical, MAC layer, naming and addressing, Assignment of MAC
addresses, Distributed assignment of locally unique addresses, content
based and geographic addressing
STANDARDS AND PROTOCOLS
1. Organizations For Communication
Standards
Standards are developed by cooperation among
standards creation committees, forums, and
government regulatory agencies.
Standards Creation Committees
a) International Standards Organization (ISO)
b) International Telecommunications Union (ITU)
c) American National Standards Institute (ANSI)
d) Institute of Electrical and Electronics Engineers (IEEE)
e) Electronic Industries Association (EIA)
f) Internet Engineering Task Force (IETF)
a) International Standards
Organization (ISO)
- A multinational body whose membership is drawn mainly
from the standards creation committees of various
governments throughout the world
- Dedicated to worldwide agreement on international
standards in a variety field.
- Currently includes 82 memberships industrialized nations.
- Aims to facilitate the international exchange of goods and
services by providing models for compatibility, improved
quality, increased quality, increased productivity and
decreased prices.
b) International Telecommunications Union (ITU)
- Also known as International Telecommunications
Union-Telecommunication Standards Sector (ITU-T)
- An international standards organization related to
the United Nations that develops standards for
telecommunications.
- Two popular standards developed by ITU-T are:
i) V series – transmission over phone lines
ii) X series – transmission over public digital
networks, email and directory services and ISDN.
c) American National Standards Institute (ANSI)
- A non-profit corporation not affiliated with US
government.
- ANSI members include professional societies,
industry associations, governmental and regulatory
bodies, and consumer groups.
- Discussing the internetwork planning and
engineering, ISDN services, signaling, and
architecture and optical hierarchy.
d) Institute of Electrical and Electronics Engineers
(IEEE)
- The largest national professional group involved in
developing standards for computing,
communication, electrical engineering, and
electronics.
- Aims to advance theory, creativity and product
quality in the fields of electrical engineering,
electronics and radio.
- It sponsored an important standard for local area
networks called Project 802 (eg. 802.3, 802.4 and
802.5 standards.)
e) Electronic Industries Association (EIA)
- An association of electronics manufacturers in
the US.
- Provide activities include public awareness
education and lobbying efforts in addition to
standards development.
- Responsible for developing the EIA-232-D and
EIA-530 standards.
f) Internet Engineering Task Force (IETF)
- Concerned with speeding the growth and
evolution of Internet communications.
- The standards body for the Internet itself
- Reviews internet software and hardware.
2. Communication Protocols
Definition
-
Protocol is a set of rules that govern all aspect of data communication
between computers on a network.
-
These rules include guidelines that regulate the following characteristics
of a network: access method, allowed physical topologies, types of
cabling, and speed of data transfer.
-
A protocol defines what, how, when it communicated.
The key elements of a protocol are syntax, semantics and timing.
-
Protocols are to computers what language is to humans. Since this article
is in English, to understand it you must be able to read English. Similarly,
for two devices on a network to successfully communicate, they must
both understand the same protocols.
Elements of protocol
i) Syntax
The structure or format of the data.
Eg. A simple protocol;
Sender
address
8 bits
Receiver
address
data
8 bits
64 bits
ii) Semantics
- Refers to the meaning of each
section of bits.
- how is a particular pattern to be interpreted,
and what action is to be taken based on that
interpretation.
Eg. Does an address identify the route to be
taken or the final of the message?
iii) Timing
Refers to two characteristics:
a. When data to be sent
b. How fast it can be sent
Eg. If a sender produces data at 100 Mbps but
the receiver can process data at only 1
Mbps, the transmission will overload the
receiver and data will be largely lost.
Characteristics of protocol
a) Direct / indirect
-
communication between two entities maybe direct
or indirect.
i) point-to-point link
- connection provides a dedicated link between
two devices
- the entities in these systems may
communicate directly that is data and
control information pass directly
between entities with no intervening
active agent.
ii) multipoint link
- connection more than two devices can share a single
link
- The entities must be concerned with the issue of
access control and making the protocol more
complex.
b) Monolithic / structured
- The task of communication between entities
on different systems is too complex to be
handled as a unit.
Eg. An electronic mail package running on two
computers connected by a synchronous HDLC
link. To be structured, the package would need
to include all of the HDLC logic. If the
connection were over a packet-switched
network, the packaged would still need the
HDLC logic to attach it to the network.
c) Symmetric / asymmetric
- Symmetric is the most use in
protocol and involve communication
between peer entities.
- Asymmetry may be dictated by the
logic of an exchange (eg; client and
a server process) the desire to keep
one of the entities or systems as
simple as possible.
d) Standard / nonstandard
If K different kinds of information sources have
to communicate with L types of information
receivers, as many as K x L different protocols
are needed without standards and a total of 2
x K x L implementations are required
If all systems shared a common protocol, only
K+L implementations would be needed.
Common protocol used
Protocol
Acronym
Remarks
Point To Point
PPP
Used to manage network
communication over a
modem
Transfer/Transmission Control Protocol
TCP / IP
Backbone protocol. The
most widely used protocol.
Internetwork package exchange
IPX
Standard protocol for Novell
NOS
NetBIOS extended user interface
NetBEUI
Microsoft protocol that
doesn’t support routing to
other network. Running only
Windows-based clients.
File transfer Protocol
FTP
used to send and received
file from a remote host
Simple mail Transfer protocol
SMTP
Used to send Email over a
network
Hyper text transfer protocol
HTTP
Used for Internet to send
document that encoded in
HTML
Apple Talk
Apple Talk
Protocol suite to network
Macintosh computer and a
peer-to-peer network
protocol
OSI Model
OSI Layers
A way of illustrating how
information functions travels
through network of its 7
layers.
3. Network Protocols
a)
Simple Network Management Protocol (SNMP)
-
Allows simple maintenance and remote monitoring of any
device on a network.
With SNMP, administrators can address issues such as
problems with a network card in a server, a program, or
service on the server, or a device such as a hub or a router.
When managing a network device using SNMP, an
administrator can use the central management system and
the management information base.
The management system allows the administrator to view
performance and operation statistics of the network
devices, enabling him to diagnose a network remotely.
-
b) User Diagram Protocol (UDP) Relay
- A connectionless protocol that operates at the
transport layer of the TCP/IP and OSI models.
- UDP is an unreliable delivery service, it does not
require receiving protocols to acknowledge the
receipt of the packet.
- The advantage of UDP is; it does not concentrate on
establishing a connection, it can transmit more
information in a smaller amount of time than TCP.
c) Virtual LAN(VLAN)
- A logical grouping of network devices or users
that are not restricted to a physical switch
segment.
- The devices or users in a VLAN can be grouped
by function, department, and application,
regardless of their physical segment location.
- A VLAN creates a single broadcast domain that
is not restricted to a physical segment and is
treated like a subnet.
d) Routing Information Protocol (RIP)
- A protocol supplied with UNIX BSD systems.
- Used to transfer routing information between
routers that are located in the same domain.
- RIP uses hop count as a routing metrics.
- Allows the router to determine which path it will use
to send, based on a concept known as distancevector routing.
e) Open Shortest Path First (OSPF)
- A link-state routing protocol based on open
standards. A better description, might be
“determination of optimum path” because this
interior gateway protocol actually uses several
criteria to determine the best route to a destination.
- These criteria include cost metrics, which factor in
such things as route speed, traffic, reliability, and
security.
f) Quality Of Service (QoS)
- Network management traffic
- Provide traffic management on network
particularly during times of congestion or
failure.
- QoS also give preferential treatment if a node
does not reach the worth levels during the
packets transmission.
OSI Model
Communication Architecture
Strategy for connecting host computers and other communicating
equipment.
Defines necessary elements for data communication between
devices.
A communication architecture, therefore, defines a standard for
the communicating hosts.
A programmer formats data in a manner defined by the
communication architecture and passes it on to the
communication software.
Separating communication functions adds flexibility, for example,
we do not need to modify the entire host software to include
more communication devices.
OSI Model
Layer Architecture
Layer architecture simplifies the network design.
It is easy to debug network applications in a layered architecture
network.
The network management is easier due to the layered
architecture.
Network layers follow a set of rules, called protocol.
The protocol defines the format of the data being exchanged, and
the control and timing for the handshake between layers.
OSI Model
Open Systems Interconnection (OSI) Model
International standard organization (ISO) established a committee
in 1977 to develop an architecture for computer communication.
Open Systems Interconnection (OSI) reference model is the result
of this effort.
In 1984, the Open Systems Interconnection (OSI) reference model
was approved as an international standard for communications
architecture.
Term “open” denotes the ability to connect any two systems
which conform to the reference model and associated standards.
OSI Model
OSI Reference Model
The OSI model is now considered the primary Architectural
model for inter-computer communications.
The OSI model describes how information or data makes its way
from application programmes (such as spreadsheets) through a
network medium (such as wire) to another application
programme located on another network.
The OSI reference model divides the problem of moving
information between computers over a network medium into
SEVEN smaller and more manageable problems .
This separation into smaller more manageable functions is known
as layering.
OSI Model
OSI Reference Model: 7 Layers
OSI Model
OSI: A Layered Network Model
The process of breaking up the functions or tasks of networking
into layers reduces complexity.
Each layer provides a service to the layer above it in the protocol
specification.
Each layer communicates with the same layer’s software or
hardware on other computers.
The lower 4 layers (transport, network, data link and physical —
Layers 4, 3, 2, and 1) are concerned with the flow of data from end
to end through the network.
The upper four layers of the OSI model (application, presentation
and session—Layers 7, 6 and 5) are orientated more toward
services to the applications.
Data is Encapsulated with the necessary protocol information as it
moves down the layers before network transit.
OSI Model
Physical Layer
Provides physical interface for transmission of information.
Defines rules by which bits are passed from one system to another
on a physical communication medium.
Covers all - mechanical, electrical, functional and procedural aspects for physical communication.
Such characteristics as voltage levels, timing of voltage changes,
physical data rates, maximum transmission distances, physical
connectors, and other similar attributes are defined by physical
layer specifications.
OSI Model
Data Link Layer
Data link layer attempts to provide reliable communication over
the physical layer interface.
Breaks the outgoing data into frames and reassemble the
received frames.
Create and detect frame boundaries.
Handle errors by implementing an acknowledgement and
retransmission scheme.
Implement flow control.
Supports points-to-point as well as broadcast communication.
Supports simplex, half-duplex or full-duplex communication.
OSI Model
Network Layer
Implements routing of frames (packets) through the network.
Defines the most optimum path the packet should take from the
source to the destination
Defines logical addressing so that any endpoint can be identified.
Handles congestion in the network.
Facilitates interconnection between heterogeneous networks
(Internetworking).
The network layer also defines how to fragment a packet into
smaller packets to accommodate different media.
OSI Model
Transport Layer
Purpose of this layer is to provide a reliable mechanism for the
exchange of data between two processes in different computers.
Ensures that the data units are delivered error free.
Ensures that data units are delivered in sequence.
Ensures that there is no loss or duplication of data units.
Provides connectionless or connection oriented service.
Provides for the connection management.
Multiplex multiple connection over a single channel.
OSI Model
Session Layer
Session layer provides mechanism for controlling the dialogue between
the two end systems. It defines how to start, control and end
conversations (called sessions) between applications.
This layer requests for a logical connection to be established on an enduser’s request.
Any necessary log-on or password validation is also handled by this
layer.
Session layer is also responsible for terminating the connection.
This layer provides services like dialogue discipline which can be full
duplex or half duplex.
Session layer can also provide check-pointing mechanism such that if a
failure of some sort occurs between checkpoints, all data can be
retransmitted from the last checkpoint.
OSI Model
Presentation Layer
Presentation layer defines the format in which the data is to be
exchanged between the two communicating entities.
Also handles
(cryptography).
data
compression
and
data
encryption
OSI Model
Application Layer
1.
Application layer interacts with application programs and is the
highest level of OSI model.
2.
Application layer contains management functions to support
distributed applications.
3.
Examples of application layer are applications such as file
transfer, electronic mail, remote login etc.
OSI Model
OSI in Action
A message begins at the top application
layer and moves down the OSI layers to
the bottom physical layer.
As the message descends, each
successive OSI model layer adds a
header to it.
A header is layer-specific information
that basically explains what functions
the layer carried out.
Conversely, at the receiving end,
headers are striped from the message
as it travels up the corresponding
layers.
TCP/IP Model
OSI & TCP/IP Models
TCP/IP Model
TCP/IP Model
Application Layer
Application programs using the network
Transport Layer (TCP/UDP)
Management of end-to-end message transmission,
error detection and error correction
Network Layer (IP)
Handling of datagrams : routing and congestion
Data Link Layer
Management of cost effective and reliable data delivery,
access to physical networks
Physical Layer
Physical Media
Models and Standards in
Communication
• Communication
– Established standards
– Standards are known as protocols
• Implementation
– A framework is helpful in the design of hardware
and software for communication
– ISO-OSI Model serves this purpose
– ISO-OSI supersedes the TCP/IP model
ISO and OSI Defined
• ISO
– International Standards Organization
• OSI
– Open Systems Interconnect
OSI Model Background
• Introduced in 1978 and revised in 1984
• Formulates the communication process into
structured layers
• There are seven layers in the model, hence the
name the 7-Layer model
• The model acts as a frame of reference in the
design of communications and networking
products
The Layered Approach to
Communication
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
Division of Layers
7. Application
6. Presentation
Upper Layers
5. Session
4. Transport
Middle Layer
3. Network
2. Data Link
Lower Layers
1. Physical
The Function of a Layer
• Each layer deals with one aspect of networking
– Layer 1 deals with the communication media
• Each layer communicates with the adjacent layers
– In both directions
– Ex: Network layer communicates with:
• Transport layer
• Data Link layer
• Each layer formats the data packet
– Ex: Adds or deletes addresses
Role of Layers
Node A
7. Application
6. Presentation
Data In
To/from
Node B
1. Physical
Data Out
Communication Between Layers
7. Application
Data
Encapsulation
6. Presentation
Data
Stripping
5. Session
The Role of Layers in Point-to-point
Communication
Node a
7. Application
1. Physical
Node b
7. Application
1.Physical
Virtual Communication Between
Layers
7. Application
7. Application
3. Network
3. Network
Module Objectives
•
•
•
•
•
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
7. Application Layer
• Purpose
– User application to network service interface
• Examples
– File request from server
– E-mail services
– etc.
Application Layer Function
• General network access
• Flow control
• Error recovery
6. Presentation Layer
• Purpose
– Formats data for exchange between points of
communication
• Ex: Between nodes in a network
• Example:
– Redirector software
• Formats for transmission to the server
Presentation Layer Function
•
•
•
•
•
Protocol conversion
Data translation
Encryption
Character set conversion
Expansion of graphics command
Redirector Example
F:/PUR/ORDER
C:/CORRES/USDA
REDIRECTOR
TO SERVER
TO LOCAL
DISK
5. Session Layer
• Purpose
– Oversee a communication session
• Establish
• Maintain
• Terminate
• Example
Session Layer Function
• Performs name recognition and related
security
• Synchronization between sender and receiver
• Assignment of time for transmission
– Start time
– End time etc.
4. Transport Layer
• Purpose
– Repackage proper and efficient delivery of
packages
• Error free
• In sequence
• Without duplication
• Example
Transport Layer Function
• For sending data
– Repackage the message to fit into packets
• Split long messages
• Assemble small messages
• On receiving data
– Perform the reverse
– Send an acknowledgment to the sender
• Solve packet problems
– During transmission and reception
3. Network Layer
• Purpose
– Addressing and routing the packets
• Example application at the router
– If the packet size is large, splits into small packets
Network Layer Function
• Address messages
• Address translation from logical to physical
– Ex: nganesa ----------> 102.13.345.25
• Routing of data
– Based on priority
– Best path at the time of transmission
• Congestion control
2. Data Link Layer
• Purpose
– Manages the flow of data over the physical media
• Responsible for error-free transmission over
the physical media
• Assures error-free data submission to the
Network Layer
Data Link Layer Function
• Point of origin
– Packages data for transmission over physical line
• Receiving end
– Packages data for submission to the network layer
• Deals with network transmission protocols
– IEEE 802. protocols
Data Link Layer Subdivision
• Improvement to ISO Model
• Logical Link Control (LLC) sub-layer
– Manages service access points (logical link)
– Error and flow control
• Media Access Control (MAC) sub-layer
– Applies directly to network card communication
– Access control
Logical Link Control
Media Access Control Application
• Network Interface Card driver
NETWORK
SOFTWARE
NETWORK
CARD
NIC Driver
facilitates data
transfer
1. Physical Layer
• Purpose
– Deals with the transmission of 0s and 1s over the
physical media
• Translation of bits into signals
• Example
– Pulse duration determination
– Transmission synchronization
– etc.
Physical Layer Function
• Encode bits into signals
– Carry data from the h higher layers
• Define the interface to the card
– Electrical
– Mechanical
– Functional
– Example: Pin count on the connector
Lower Layers Application Areas
• Special significance to network card design
• Applies to general LAN hardware design
– Exceptions
• Routers etc.
• 802. standards
– Centered around the lower layers
– Applies to networks
Layer Operations
• At each layer, additional information is added
to the data packet
• An example would be information related to
the IP protocol that is added at Layer 3
Formatting of Data Through the Layers
Application Header
Network Header
Data Link Header and Trailer
Presentation Header
Session Header
Transport Header
Physical Frame Preamble
Packet : General Format
Header
Trailer
Data
A general concept of packets serves as a prerequisite to
the understanding of the ISO-OSI model.
Some Header Information Added at
Various Layers
•
•
•
•
Packet arrival information
Receiver’s address
Sender’s address
Synchronization character
Data
• Actual data
• May contain error correction code
– Performed on individual characters of the data
– Example: Parity
• Size may vary
– Depending on the protocol
– Example
• 802.3 specifies range of data packet length
Some Trailer Information Added at Various
Layers
• Error correction code
– Character oriented
– VRC (Parity Checking)
• Packet oriented error correction codes
– LRC
– CRC
A Note on CRC
• Used widely
• Sophisticated
– Polynomial of deferent degrees are used for error
correction
– Example: Degrees 16, 32 etc.
• CRC-32 is a more stringent error checking
procedure than CRC-16
Some of the Major Components of the
Data Packet
Receiver’s
Address
Control
Data
Data
Error
Correction
Protocol
Start/synch
Information
Sender’s
Address
Standardizing Packet Formatting
• Packets must conform to a standard in order for the
nodes in a network to be able to communicate with
one another
• The International Standards Organization (ISO) has
provided a reference model
• Standards are established for operations at each
layer of the ISO/OSI model in the form of protocols
IEEE Background
• Institution of Electrical and Electronic
Engineers (IEEE)
– A professional non-profit organization
• Project group 802
– Responsible for setting standards relating to the
physical link of the network
IEEE 802 Focus
• OSI Reference
– Data Link layer
– Physical layer
• Areas
– Network cards and cables
– Network electronic/optical/ wireless communication
standard as they apply to the lower two layers mentioned
above
– WAN connectivity
Upper Layer Focus
•
•
•
•
IETF
W3C
ISO/IEC
The above agencies focus on setting standards
on higher level protocol
– TCP, IP etc.
IEEE 802 Committees And
Responsibilities
• 802.1
– Internetworking
• 802.2
– Logical Link Control (LLC)
• 802.3
– CSMA/CD
• 802.4
– Token Bus LAN
IEEE 802 Committees and Responsibilities
(Cont.)
• 802.5
– Token Ring LAN
• 802.6
– Metropolitan Area Network
• 802.7
– Broadband Technical Advisory Group
• 802.8
– Fiber-Optic Technical Advisory Group
IEEE 802 (Cont.)
• 802.9
– Integrated Voice/Data Networks
• 802.10
– Network Security
• 802.11
– Wireless Networks
• 802.12
– Demand Priority Access LANs
– Ex: 100BaseVG-AnyLAN
OSI Sub-Layer Reference to IEEE 802
Standards
Logical
Link
Control
(LLC)
802.2
802.1 for
both.
Media
Access
Control
(MAC)
802.3
802.4
802.5
802.12
Network Topologies
Objectives
• Describe the basic and hybrid LAN physical
topologies, and their uses, advantages and
disadvantages
• Describe the backbone structures that form
the foundation for most LANs
Simple Physical Topologies
• Physical topology: physical layout of nodes on a
network
• Three fundamental shapes:
– Bus
– Ring
– Star
• May create hybrid topologies
• Topology integral to type of network, cabling
infrastructure, and transmission media used
Bus
• Single cable connects all network nodes
without intervening connectivity devices
• Devices share responsibility for getting data
from one point to another
• Terminators stop signals after reaching end of
wire
– Prevent signal bounce
• Inexpensive, not very scalable
• Difficult to troubleshoot, not fault-tolerant
Bus (continued)
Advantages of Bus Topology
• Works well for small networks
• Relatively inexpensive to implement
• Easy to add to it
Disadvantages of
Bus Topology
• Management costs can be high
• Potential for congestion with network traffic
Ring
Simple Physical Topologies
• Physical topology
– Physical layout of a network
• A Bus topology consists of a single cable—called a
bus— connecting all nodes on a network without
intervening connectivity devices
Advantages of Bus Topology
• Works well for small networks
• Relatively inexpensive to implement
• Easy to add to it
Disadvantages of
Bus Topology
• Management costs can be high
• Potential for congestion with network traffic
Simple Physical Topologies
• Ring topology
– Each node is connected to the two nearest nodes so the entire
network forms a circle
– One method for passing data on ring networks is token passing
• Active topology
– Each workstation transmits data
Advantages of Ring Topology
• Easier to manage; easier to locate a defective
node or cable problem
• Well-suited for transmitting signals over long
distances on a LAN
• Handles high-volume network traffic
• Enables reliable communication
Disadvantages of
Ring Topology
• Expensive
• Requires more cable and network equipment
at the start
• Not used as widely as bus topology
– Fewer equipment options
– Fewer options for expansion to high-speed
communication
Star
Simple Physical Topologies
• Star topology
– Every node on the network is connected through a
central device
Star (continued)
• Any single cable connects only two devices
– Cabling problems affect two nodes at most
• Requires more cabling than ring or bus networks
– More fault-tolerant
• Easily moved, isolated, or interconnected with other
networks
– Scalable
• Supports max of 1024 addressable nodes on logical
network
Advantages of Star Topology
•
•
•
•
•
Good option for modern networks
Low startup costs
Easy to manage
Offers opportunities for expansion
Most popular topology in use; wide variety of
equipment available
Disadvantages of
Star Topology
• Hub is a single point of failure
• Requires more cable than the bus
Hybrid Physical Topologies:
Star-Wired Ring
Star-Wired Bus
Backbone Networks: Serial Backbone
• Daisy chain: linked series of devices
– Hubs and switches often connected in daisy chain
to extend a network
• Hubs, gateways, routers, switches, and bridges
can form part of backbone
• Extent to which hubs can be connected is
limited
Backbone Networks: Serial Backbone
(continued)
Distributed Backbone
Collapsed Backbone
Parallel Backbone
Logical Topologies
• Logical topology: how data is transmitted between
nodes
– May not match physical topology
• Bus logical topology: signals travel from one network
device to all other devices on network
– Required by bus, star, star-wired physical topologies
• Ring logical topology: signals follow circular path
between sender and receiver
– Required by ring, star-wired ring topologies
Topology
• The physical topology of a network refers to the
configuration of cables, computers and other
peripherals.
• The main types of network topologies are:
–
–
–
–
Linear Bus
Star
Ring
Tree or Hybrid
Linear Bus topology
• A linear bus topology consists of a main run of cable with a
terminator at each end. All servers workstations and
peripherals are connected to the linear cable
Star topology
• A star network is
designed with each
node (file server,
workstation, peripheral)
connected directly to a
central network hub or
server
Ring topology
• A ring network is one
where all workstations
and other devices are
connected in a
continuous loop. There is
no central server
Tree or hybrid topology
• A tree or hybrid topology
combines characteristics
of linear bus and star
and/or ring topologies.
• It consists of groups of
star-configured
workstations connected
to a linear bus backbone
cable
Network Operating Software
• Network operating systems coordinate the activities of multiple
computers across a network
• The two major types of network
OS are:
– Peer-to-peer
– Client/server
Peer to peer network OS
– In peer to peer network OS, there is no file
server or central management source; all
computers are considered equal
– Peer to peer networks are design primarily
for small to medium LANS
– AppleShare and Windows for Workgroups are
examples of programs that can function as
peer to peer
Client/Server network OS
– Client/server network OS centralise
functions and applications in one or
more dedicated file servers.
– The file server provides access to
resources and provides security
– Novel Netware and Windows NT
Server are examples of client/server
network operating systems
Ethernet
Outline
Multiple Access and Ethernet Intro
Ethernet Framing
CSMA/CD protocol
Exponential backoff
Shared Access Networks are Different
• Shared Access Networks assume multiple nodes on
the same physical link
– Bus, ring and wireless structures
– Transmission sent by one node is received by all others
– No intermediate switches
• Need methods for moderating access (MAC
protocols)
– Fairness
– Performance
– How can this be done?
Multiple Access Methods
• Fixed assignment
– Partition channel so each node gets a slice of the bandwidth
– Essentially circuit switching – thus inefficient
– Examples: TDMA, FDMA, CDMA (all used in wireless/cellular
environments)
• Contention-based
– Nodes contends equally for bandwidth and recover from collisions
– Examples: Aloha, Ethernet
• Token-based or reservation-based
– Take turns using the channel
– Examples: Token ring
A Quick Word about Token Ring
• Developed by IBM in early 80’s as a new LAN
architecture
– Consists of nodes connected into a ring (typically via
concentrators)
– Special message called a token is passed around the
ring
• When nodes gets the token it can transmit for a limited time
• Every node gets an equal opportunity to send
– IEEE 802.5 standard for Token Ring
• Designed for predictability, fairness and reliability
– Originally designed to run at either 4Mbps and
16Mbps
• Still used and sold but beaten out by Ethernet
Our Focus is Ethernet
• History
–
–
–
–
Developed by Bob Metcalfe and others at Xerox PARC in mid-1970s
Roots in Aloha packet-radio network
Standardized by Xerox, DEC, and Intel in 1978
LAN standards define MAC and physical layer connectivity
• IEEE 802.3 (CSMA/CD - Ethernet) standard – originally 2Mbps
• IEEE 802.3u standard for 100Mbps Ethernet
• IEEE 802.3z standard for 1,000Mbps Ethernet
• CSMA/CD: Ethernet’s Media Access Control (MAC) policy
– CS = carrier sense
• Send only if medium is idle
– MA = multiple access
– CD = collision detection
• Stop sending immediately if collision is detected
Ethernet Standard Defines Physical Layer
• 802.3 standard defines both MAC and physical layer
details
Metcalfe’s original
Ethernet Sketch
Ethernet Technologies: 10Base2
•
•
10: 10Mbps; 2: under 185 (~200) meters cable length
Thin coaxial cable in a bus topology
•
Repeaters used to connect multiple segments
–
Repeater repeats bits it hears on one interface to its other interfaces: physical layer device only!
10BaseT and 100BaseT
• 10/100 Mbps rate
• T stands for Twisted Pair
• Hub(s) connected by twisted pair facilitate “star topology”
– Distance of any node to hub must be < 100M
Physical Layer Configurations for 802.3
• Physical layer configurations are specified in three parts
• Data rate (10, 100, 1,000)
– 10, 100, 1,000Mbps
• Signaling method (base, broad)
– Baseband
• Digital signaling
– Broadband
• Analog signaling
• Cabling (2, 5, T, F, S, L)
–
–
–
–
5 - Thick coax (original Ethernet cabling)
F – Optical fiber
S – Short wave laser over multimode fiber
L – Long wave laser over single mode fiber
Ethernet Overview
• Most popular packet-switched LAN technology
• Bandwidths: 10Mbps, 100Mbps, 1Gbps
• Max bus length: 2500m
– 500m segments with 4 repeaters
• Bus and Star topologies are used to connect hosts
– Hosts attach to network via Ethernet transceiver or hub or switch
• Detects line state and sends/receives signals
– Hubs are used to facilitate shared connections
– All hosts on an Ethernet are competing for access to the medium
• Switches break this model
• Problem: Distributed algorithm that provides fair access
Ethernet Overview (contd.)
• Ethernet by definition is a broadcast
protocol
– Any signal can be received by all hosts
– Switching enables individual hosts to
communicate
• Network
layer
packets
are
transmitted
over
64
48
48
16
32
an Ethernet by
encapsulating
Src
Dest
Preamble
Type
Body
CRC
addr
addr
• Frame Format
Switched Ethernet
• Switches forward and filter frames based on LAN addresses
– It’s not a bus or a router (although simple forwarding tables are maintained)
• Very scalable
– Options for many interfaces
– Full duplex operation (send/receive frames simultaneously)
• Connect two or more “segments” by copying data frames between them
– Switches only copy data when needed
• key difference from repeaters
• Higher link bandwidth
– Collisions are completely avoided
• Much greater aggregate bandwidth
– Separate segments can send at once
Ethernet Frames
• Preamble is a sequence of 7 bytes, each set to “10101010”
– Used to synchronize receiver before actual data is sent
• Addresses
– unique, 48-bit unicast address assigned to each adapter
• example: 8:0:e4:b1:2
• Each manufacturer gets their own address range
– broadcast: all 1s
– multicast: first bit is 1
• Type field is a demultiplexing key used to determine which
higher level protocol the frame should be delivered to
• Body can contain up to 1500 bytes of data
A Quick Word about Aloha Networks
• Developed in late 60’s by Norm Abramson at Univ. of Hawaii (!!)
for use with packet radio systems
– Any station can send data at any time
– Receiver sends an ACK for data
– Timeout for ACK signals that there was a collision
• What happens if timeout is poorly timed?
– If there is a collision, sender will resend data after a random backoff
• Utilization (fraction of transmitted frames avoiding collision for
N nodes) was pretty bad
– Max utilization = 18%
• Slotted Aloha (dividing transmit time into windows) helped
– Max utilization increased to 36%
Ethernet’s MAC Algorithm
• In Aloha, decisions to transmit are made without paying
attention to what other nodes might be doing
• Ethernet uses CSMA/CD – listens to line before/during sending
• If line is idle (no carrier sensed)
– send packet immediately
– upper bound message size of 1500 bytes
– must wait 9.6us between back-to-back frames
• If line is busy (carrier sensed)
– wait until idle and transmit packet immediately
• called 1-persistent sending
• If collision detected
– Stop sending and jam signal
– Try again later
State Diagram for CSMA/CD
Packet?
No
Sense
Carrier
Send
Detect
Collision
Yes
Discard
Packet
attempts < 16
attempts == 16
Jam channel
b=CalcBackoff();
wait(b);
attempts++;
Collisions
Collisions are caused when two adaptors transmit at the same
time (adaptors sense collision based on voltage differences)
• Both found line to be idle
• Both had been waiting to for a busy line to become idle
A starts at
time 0
A
A
B
B
Message almost
there at time T when
B starts – collision!
How can we be sure A knows about the collision?
Collision Detection
• How can A know that a collision has taken place?
–
–
–
–
There must be a mechanism to insure retransmission on collision
A’s message reaches B at time T
B’s message reaches A at time 2T
So, A must still be transmitting at 2T
• IEEE 802.3 specifies max value of 2T to be 51.2us
– This relates to maximum distance of 2500m between hosts
– At 10Mbps it takes 0.1us to transmit one bit so 512 bits (64B) take 51.2us to send
– So, Ethernet frames must be at least 64B long
• 14B header, 46B data, 4B CRC
• Padding is used if data is less than 46B
• Send jamming signal after collision is detected to insure all hosts see collision
– 48 bit signal
Collision Detection contd.
A
B
A
B
A
B
time = 0
time = T
time = 2T
Exponential Backoff
• If a collision is detected, delay and try again
• Delay time is selected using binary exponential backoff
– 1st time: choose K from {0,1} then delay = K * 51.2us
– 2nd time: choose K from {0,1,2,3} then delay = K * 51.2us
– nth time: delay = K x 51.2us, for K=0..2n – 1
• Note max value for k = 1023
– give up after several tries (usually 16)
• Report transmit error to host
• If delay were not random, then there is a chance that sources
would retransmit in lock step
• Why not just choose from small set for K
– This works fine for a small number of hosts
– Large number of nodes would result in more collisions
MAC Algorithm from the Receiver Side
• Senders handle all access control
• Receivers simply read frames with acceptable
address
– Address to host
– Address to broadcast
– Address to multicast to which host belongs
– All frames if host is in promiscuous mode
Fast and Gigabit Ethernet
• Fast Ethernet (100Mbps) has technology very similar to
10Mbps Ethernet
– Uses different physical layer encoding (4B5B)
– Many NIC’s are 10/100 capable
• Can be used at either speed
• Gigabit Ethernet (1,000Mbps)
–
–
–
–
–
–
Compatible with lower speeds
Uses standard framing and CSMA/CD algorithm
Distances are severely limited
Typically used for backbones and inter-router connectivity
Becoming cost competitive
How much of this bandwidth is realizable?
Experiences with Ethernet
• Ethernets work best under light loads
– Utilization over 30% is considered heavy
• Network capacity is wasted by collisions
• Most networks are limited to about 200 hosts
– Specification allows for up to 1024
• Most networks are much shorter
– 5 to 10 microsecond RTT
• Transport level flow control helps reduce load (number of
back to back packets)
• Ethernet is inexpensive, fast and easy to administer!
Ethernet Problems
• Ethernet’s peak utilization is pretty low (like
Aloha)
• Peak throughput worst with
– More hosts
• More collisions needed to identify single sender
– Smaller packet sizes
• More frequent arbitration
– Longer links
• Collisions take longer to observe, more wasted bandwidth
– Efficiency is improved by avoiding these conditions
Why did Ethernet Win?
•
•
•
•
•
•
There are LOTS of LAN protocols
Price
Performance
Availability
Ease of use
Scalability
Transmission Media
Overview
• Guided - wire
• Unguided - wireless
• Characteristics and quality determined by
medium and signal
• For guided, the medium is more important
• For unguided, the bandwidth produced by the
antenna is more important
• Key concerns are data rate and distance
Design Factors
• Bandwidth
– Higher bandwidth gives higher data rate
• Transmission impairments
– Attenuation
• Interference
• Number of receivers
– In guided media
– More receivers (multi-point) introduce more
attenuation
Electromagnetic Spectrum
Guided Transmission Media
• Twisted Pair
• Coaxial cable
• Optical fiber
Transmission Characteristics of Guided
Media
Frequency
Range
Typical
Attenuation
Typical
Delay
Repeater
Spacing
Twisted pair
(with loading)
0 to 3.5 kHz
0.2 dB/km @
1 kHz
50 µs/km
2 km
Twisted pairs
(multi-pair
cables)
Coaxial cable
0 to 1 MHz
0.7 dB/km @
1 kHz
5 µs/km
2 km
0 to 500 MHz
7 dB/km @ 10
MHz
4 µs/km
1 to 9 km
Optical fiber
186 to 370
THz
0.2 to 0.5
dB/km
5 µs/km
40 km
Twisted Pair
Twisted Pair - Applications
• Most common medium
• Telephone network
– Between house and local exchange (subscriber
loop)
• Within buildings
– To private branch exchange (PBX)
• For local area networks (LAN)
– 10Mbps or 100Mbps
Twisted Pair - Pros and Cons
•
•
•
•
Cheap
Easy to work with
Low data rate
Short range
Twisted Pair - Transmission
Characteristics
• Analog
– Amplifiers every 5km to 6km
• Digital
– Use either analog or digital signals
– repeater every 2km or 3km
•
•
•
•
Limited distance
Limited bandwidth (1MHz)
Limited data rate (100MHz)
Susceptible to interference and noise
Near End Crosstalk
• Coupling of signal from one pair to another
• Coupling takes place when transmit signal
entering the link couples back to receiving pair
• i.e. near transmitted signal is picked up by
near receiving pair
Unshielded and Shielded TP
• Unshielded Twisted Pair (UTP)
– Ordinary telephone wire
– Cheapest
– Easiest to install
– Suffers from external EM interference
• Shielded Twisted Pair (STP)
– Metal braid or sheathing that reduces interference
– More expensive
– Harder to handle (thick, heavy)
UTP Categories
• Cat 3
– up to 16MHz
– Voice grade found in most offices
– Twist length of 7.5 cm to 10 cm
• Cat 4
– up to 20 MHz
• Cat 5
– up to 100MHz
– Commonly pre-installed in new office buildings
– Twist length 0.6 cm to 0.85 cm
• Cat 5E (Enhanced) –see tables
• Cat 6
• Cat 7
Comparison of Shielded and
Unshielded Twisted Pair
Attenuation (dB per 100 m)
Frequency
(MHz)
Category 3
UTP
Category 5
UTP
1
2.6
2.0
4
5.6
16
13.1
150-ohm
STP
Near-end Crosstalk (dB)
Category 3
UTP
Category 5
UTP
150-ohm
STP
1.1
41
62
58
4.1
2.2
32
53
58
8.2
4.4
23
44
50.4
25
—
10.4
6.2
—
41
47.5
100
—
22.0
12.3
—
32
38.5
300
—
21.4
—
—
—
31.3
Twisted Pair Categories and Classes
Category 3
Class C
Category 5
Class D
Bandwidth
16 MHz
100 MHz
Cable Type
UTP
Link Cost
(Cat 5 =1)
0.7
Category
5E
Category 6
Class E
Category 7
Class F
100 MHz
200 MHz
600 MHz
UTP/FTP
UTP/FTP
UTP/FTP
SSTP
1
1.2
1.5
2.2
Coaxial Cable
Coaxial Cable Applications
• Most versatile medium
• Television distribution
– Ariel to TV
– Cable TV
• Long distance telephone transmission
– Can carry 10,000 voice calls simultaneously
– Being replaced by fiber optic
• Short distance computer systems links
• Local area networks
Coaxial Cable - Transmission
Characteristics
• Analog
– Amplifiers every few km
– Closer if higher frequency
– Up to 500MHz
• Digital
– Repeater every 1km
– Closer for higher data rates
Optical Fiber
Optical Fiber - Benefits
• Greater capacity
– Data rates of hundreds of Gbps
•
•
•
•
Smaller size & weight
Lower attenuation
Electromagnetic isolation
Greater repeater spacing
– 10s of km at least
Optical Fiber - Applications
•
•
•
•
•
Long-haul trunks
Metropolitan trunks
Rural exchange trunks
Subscriber loops
LANs
Optical Fiber - Transmission
Characteristics
• Act as wave guide for 1014 to 1015 Hz
– Portions of infrared and visible spectrum
• Light Emitting Diode (LED)
– Cheaper
– Wider operating temp range
– Last longer
• Injection Laser Diode (ILD)
– More efficient
– Greater data rate
• Wavelength Division Multiplexing
Optical Fiber Transmission Modes
Frequency Utilization for Fiber
Applications
Wavelength (in
vacuum) range
(nm)
Frequency
range (THz)
820 to 900
366 to 333
1280 to 1350
234 to 222
1528 to 1561
1561 to 1620
Band
label
Fiber type
Application
Multimode
LAN
S
Single mode
Various
196 to 192
C
Single mode
WDM
185 to 192
L
Single mode
WDM
Attenuation in Guided Media
Wireless Transmission Frequencies
• 2GHz to 40GHz
–
–
–
–
Microwave
Highly directional
Point to point
Satellite
• 30MHz to 1GHz
– Omnidirectional
– Broadcast radio
• 3 x 1011 to 2 x 1014
– Infrared
– Local
Antennas
• Electrical conductor (or system of..) used to radiate
electromagnetic energy or collect electromagnetic energy
• Transmission
–
–
–
–
Radio frequency energy from transmitter
Converted to electromagnetic energy
By antenna
Radiated into surrounding environment
• Reception
– Electromagnetic energy impinging on antenna
– Converted to radio frequency electrical energy
– Fed to receiver
• Same antenna often used for both
Radiation Pattern
• Power radiated in all directions
• Not same performance in all directions
• Isotropic antenna is (theoretical) point in
space
– Radiates in all directions equally
– Gives spherical radiation pattern
Parabolic Reflective Antenna
• Used for terrestrial and satellite microwave
• Parabola is locus of point equidistant from a line and a point
not on that line
– Fixed point is focus
– Line is directrix
• Revolve parabola about axis to get paraboloid
– Cross section parallel to axis gives parabola
– Cross section perpendicular to axis gives circle
• Source placed at focus will produce waves reflected from
parabola in parallel to axis
– Creates (theoretical) parallel beam of light/sound/radio
• On reception, signal is concentrated at focus, where detector
is placed
Parabolic Reflective Antenna
Antenna Gain
• Measure of directionality of antenna
• Power output in particular direction compared
with that produced by isotropic antenna
• Measured in decibels (dB)
• Results in loss in power in another direction
• Effective area relates to size and shape
– Related to gain
Terrestrial Microwave
•
•
•
•
•
Parabolic dish
Focused beam
Line of sight
Long haul telecommunications
Higher frequencies give higher data rates
Satellite Microwave
• Satellite is relay station
• Satellite receives on one frequency, amplifies or
repeats signal and transmits on another
frequency
• Requires geo-stationary orbit
– Height of 35,784km
• Television
• Long distance telephone
• Private business networks
Satellite Point to Point Link
Satellite Broadcast Link
Broadcast Radio
•
•
•
•
•
Omnidirectional
FM radio
UHF and VHF television
Line of sight
Suffers from multipath interference
– Reflections
Infrared
•
•
•
•
Modulate noncoherent infrared light
Line of sight (or reflection)
Blocked by walls
e.g. TV remote control, IRD port
Wireless Propagation
• Signal travels along three routes
– Ground wave
• Follows contour of earth
• Up to 2MHz
• AM radio
– Sky wave
• Amateur radio, BBC world service, Voice of America
• Signal reflected from ionosphere layer of upper atmosphere
• (Actually refracted)
– Line of sight
• Above 30Mhz
• May be further than optical line of sight due to refraction
• More later…
Ground Wave Propagation
Sky Wave Propagation
Line of Sight Propagation
Refraction
• Velocity of electromagnetic wave is a function of density of material
– ~3 x 108 m/s in vacuum, less in anything else
• As wave moves from one medium to another, its speed changes
– Causes bending of direction of wave at boundary
– Towards more dense medium
• Index of refraction (refractive index) is
– Sin(angle of incidence)/sin(angle of refraction)
– Varies with wavelength
• May cause sudden change of direction at transition between media
• May cause gradual bending if medium density is varying
– Density of atmosphere decreases with height
– Results in bending towards earth of radio waves
Optical and Radio Horizons
Line of Sight Transmission
• Free space loss
– Signal disperses with distance
– Greater for lower frequencies (longer wavelengths)
• Atmospheric Absorption
–
–
–
–
Water vapour and oxygen absorb radio signals
Water greatest at 22GHz, less below 15GHz
Oxygen greater at 60GHz, less below 30GHz
Rain and fog scatter radio waves
–
–
–
–
Better to get line of sight if possible
Signal can be reflected causing multiple copies to be received
May be no direct signal at all
May reinforce or cancel direct signal
• Multipath
• Refraction
– May result in partial or total loss of signal at receiver
Free
Space
Loss
Multipath Interference
Overview
• Characteristics and quality determined by:
– Medium
– Signal
• Medium
– Guided - wire
– Unguided - wireless
• For Guided Medium
– The medium is more important
• For Unguided
– The bandwidth produced by the antenna is more important
• Key concerns are data rate and distance
Design Factors
•
Bandwidth
–
•
Transmission impairments
–
•
Attenuation
Interference
–
•
Higher bandwidth gives higher data rate
Issue especially in case of unguided medium
Number of receivers
–
–
Unicast (one sender, one receiver)
Multicast (multiple receivers can introduce more errors)
Guided Transmission Media
• Twisted Pair
• Coaxial Cable
• Optical Fiber
Transmission Characteristics of Guided
Media
Frequency
Range
Typical
Attenuation
Typical Delay
Repeater
Spacing
Twisted pair
(with loading)
0 to 3.5 kHz
0.2 dB/km @
1 kHz
50 µs/km
2 km
Twisted pairs
(multi-pair
cables)
Coaxial cable
0 to 1 MHz
0.7 dB/km @
1 kHz
50 µs/km
2 km
0 to 500 MHz
7 dB/km @ 10
MHz
4 µs/km
1 to 9 km
Optical fiber
186 to 370
THz
0.2 to 0.5
dB/km
5 µs/km
40 km
Twisted Pair
Twisted Pair Architecture
Two Insulated copper wires
Issues:
(1) Interference due to unwanted electrical coupling of two copper
(2) Interference due to unwanted electrical coupling between the neighboring
twisted pairs
Twisted Pair Applications
• Most commonly used medium
• Telephone network
– Between house and local exchange (subscriber
loop)
• Within buildings
– To private branch exchange (PBX)
• For local area networks (LAN)
– 10Mbps or 100Mbps
Twisted Pair - Pros and Cons
• Advantages
– Less expensive
– Easy to work with
• Disadvantages
– Low data rate
– Short range
Twisted Pair (TP) Characteristics
• Analog transmission
– Amplifiers every 5km to 6km
• Digital transmission
– Use either analog or digital signals
– repeater every 2km or 3km
• TP is Limited
– Distance
– Bandwidth
– Data rate
• Susceptible to interference and noise
– Easy coupling of electromagnetic fields
Unshielded and Shielded TP
• Unshielded Twisted Pair (UTP)
– Ordinary telephone wire
– Less expensive
– Weak immunity against noise and interference
– Suffers from external EM interference
• Shielded Twisted Pair (STP)
– An extra metallic sheath on each pair
– Relatively more expensive
– Provide better performance than UTP
• Increased Data rate
• Increased Bandwidth
UTP Categories
• Cat 3
– up to 16MHz
– Voice grade found in most offices
– Twist length of 7.5 cm to 10 cm
• Cat 4
– up to 20 MHz
• Cat 5
– up to 100MHz
– Commonly pre-installed in new office buildings
– Twist length 0.6 cm to 0.85 cm
• Cat 5E (Enhanced) –see tables
• Cat 6
• Cat 7
Coaxial Cable
Coaxial Cable Architecture
Coaxial Cable Applications
• Television (TV) signals distribution
– Ariel to TV
– Cable TV
• Long distance telephone transmission
– Can carry 10,000 voice calls simultaneously
– Being replaced by fiber optic
• Short distance computer systems links
– Local area networks (LAN)
– Metropolitan area network (MAN)
Coaxial Cable Characteristics
• Analog
– Amplifiers every few km
– Closer if higher frequency
– Up to 500MHz
• Digital
– Repeater every 1km
– Closer for higher data rates
• Problem
– Inter-modulation noise
– Thermal noise
Optical Fiber
Optical Fiber Architecture
Optical Fiber Benefits
• Greater capacity
– Data rates of hundreds of Gbps
• Smaller size & weight
– Made up of extremely thin fibers
• Lower attenuation
– Electromagnetic isolation
• Greater repeater spacing
– 10s of km at least
Optical Fiber - Transmission
Characteristics
• Operational range
– 1014 to 1015 Hz
• Light source
– Light Emitting Diode (LED)
• Cheaper
• Wider operating temperature range
• Last longer
– Injection Laser Diode (ILD)
• Operates on laser principle
• More efficient
• Greater data rate
• Wavelength Division Multiplexing (WDM)
Transmission Media
Transmission medium and physical layer
Classes of transmission media
GUIDED MEDIA
Guided media, which are those that provide a conduit
from one device to another, include twisted-pair cable,
coaxial cable, and fiber-optic cable.
Topics discussed in this section:
Twisted-Pair Cable
Coaxial Cable
Fiber-Optic Cable
Twisted-pair cable
UTP and STP cables
Table 7.1 Categories of unshielded twisted-pair cables
UTP connector
Coaxial cable
Categories of coaxial cables
Fiber optics: Bending of light ray
Optical fiber
Propagation modes
Modes
Fiber types
Fiber construction
Fiber-optic cable connectors
UNGUIDED MEDIA: WIRELESS
Unguided media transport electromagnetic waves
without using a physical conductor. This type of
communication is often referred to as wireless
communication.
Topics discussed in this section:
Radio Waves
Microwaves
Infrared
Electromagnetic spectrum for wireless communication
Propagation methods
Bands
Wireless transmission waves
Omnidirectional antenna
Unidirectional antennas
Wireless Channels
• Are subject to a lot more errors than guided
media channels.
• Interference is one cause for errors, can be
circumvented with high SNR.
• The higher the SNR the less capacity is available
for transmission due to the broadcast nature of
the channel.
• Channel also subject to fading and no coverage
holes.
Circuit Switching and Packet
Switching
Overview
• Networks are used to interconnect many devices.
• We have checked with Local Area Networks.
• Now, wide area networks
– Since the invention of the telephone, circuit switching has been the
dominant technology for voice communications.
– Since 1970, packet switching has evolved substantially for digital data
communications. It was designed to provide a more efficient facility
than circuit switching for bursty data traffic.
• Two types of packet switching:
– Datagram (such as today’s Internet)
– Virtual circuit (such as Frame Relay, ATM)
Switched Communications Networks
• Long distance transmission between stations (called “end
devices”) is typically done over a network of switching nodes.
• Switching nodes do not concern with content of data. Their
purpose is to provide a switching facility that will move the
data from node to node until they reach their destination (the
end device).
• A collection of nodes and connections forms a
communications network.
• In a switched communications network, data entering the
network from a station are routed to the destination by being
switched from node to node.
Simple Switching Network
Switching Nodes
• Nodes may connect to other nodes, or to
some stations.
• Network is usually partially connected
– However, some redundant connections are
desirable for reliability
• Two different switching technologies
– Circuit switching
– Packet switching
Circuit Switching
• Circuit switching:
– There is a dedicated communication path between two stations (endto-end)
– The path is a connected sequence of links between network nodes. On
each physical link, a logical channel is dedicated to the connection.
• Communication via circuit switching has three phases:
– Circuit establishment (link by link)
• Routing & resource allocation (FDM or TDM)
– Data transfer
– Circuit disconnect
• Deallocate the dedicated resources
• The switches must know how to find the route to the
destination and how to allocate bandwidth (channel) to
establish a connection.
Circuit Switching Properties
• Inefficiency
– Channel capacity is dedicated for the whole duration of a connection
– If no data, capacity is wasted
• Delay
– Long initial delay: circuit establishment takes time
– Low data delay: after the circuit establishment, information is
transmitted at a fixed data rate with no delay other than the
propagation delay. The delay at each node is negligible.
• Developed for voice traffic (public telephone network) but can
also applied to data traffic.
– For voice connections, the resulting circuit will enjoy a high percentage
of utilization because most of the time one party or the other is talking.
– But how about data connections?
Public Circuit Switched Network
Subscribers: the devices that attach to the network.
Subscriber loop: the link between the subscriber and the network.
Exchanges: the switching centers in the network.
End office: the switching center that directly supports subscribers.
Trunks: the branches between exchanges. They carry multiple voice-frequency
circuits using either FDM or synchronous TDM.
Packet Switching Principles
• Problem of circuit switching
– designed for voice service
– Resources dedicated to a particular call
– For data transmission, much of the time the
connection is idle (say, web browsing)
– Data rate is fixed
• Both ends must operate at the same rate during the
entire period of connection
• Packet switching is designed to address these
problems.
Basic Operation
• Data are transmitted in short packets
– Typically at the order of 1000 bytes
– Longer messages are split into series of packets
– Each packet contains a portion of user data plus some control info
• Control info contains at least
– Routing (addressing) info, so as to be routed to the intended
destination
– Recall the content of an IP header!
• store and forward
– On each switching node, packets are received, stored briefly (buffered)
and passed on to the next node.
Use of Packets
Advantages of Packet Switching
• Line efficiency
– Single node-to-node link can be dynamically shared by many packets
over time
– Packets are queued up and transmitted as fast as possible
• Data rate conversion
– Each station connects to the local node at its own speed
• In circuit-switching, a connection could be blocked if there
lacks free resources. On a packet-switching network, even
with heavy traffic, packets are still accepted, by delivery delay
increases.
• Priorities can be used
– On each node, packets with higher priority can be forwarded first.
They will experience less delay than lower-priority packets.
Packet Switching Technique
• A station breaks long message into packets
• Packets are sent out to the network sequentially,
one at a time
• How will the network handle this stream of
packets as it attempts to route them through the
network and deliver them to the intended
destination?
– Two approaches
• Datagram approach
• Virtual circuit approach
Datagram
• Each packet is treated independently, with no
reference to packets that have gone before.
– Each node chooses the next node on a packet’s path.
•
•
•
•
Packets can take any possible route.
Packets may arrive at the receiver out of order.
Packets may go missing.
It is up to the receiver to re-order packets and
recover from missing packets.
• Example: Internet
Datagram
Virtual Circuit
• In virtual circuit, a preplanned route is
established before any packets are sent, then all
packets follow the same route.
• Each packet contains a virtual circuit identifier
instead of destination address, and each node on
the preestablished route knows where to forward
such packets.
– The node need not make a routing decision for each
packet.
• Example: X.25, Frame Relay, ATM
Virtual
Circuit
A route between stations is
set up prior to data transfer.
All the data packets then
follow the same route.
But there is no dedicated
resources reserved for the
virtual circuit! Packets need
to be stored-and-forwarded.
Virtual Circuits v Datagram
• Virtual circuits
– Network can provide sequencing (packets arrive at the same order)
and error control (retransmission between two nodes).
– Packets are forwarded more quickly
• Based on the virtual circuit identifier
• No routing decisions to make
– Less reliable
• If a node fails, all virtual circuits that pass through that node fail.
• Datagram
– No call setup phase
• Good for bursty data, such as Web applications
– More flexible
• If a node fails, packets may find an alternate route
• Routing can be used to avoid congested parts of the network
Comparison of
communication
switching
techniques
Switching Networks
• Long distance transmission is typically done
over a network of switched nodes
• Nodes not concerned with content of data
• End devices are stations
– Computer, terminal, phone, etc.
• A collection of nodes and connections is a
communications network
• Data routed by being switched from node to
node
Nodes
• Nodes may connect to other nodes only, or to
stations and other nodes
• Node to node links usually multiplexed
• Network is usually partially connected
– Some redundant connections are desirable for
reliability
• Two different switching technologies
– Circuit switching
– Packet switching
Circuit Switching
• Dedicated communication path between two
stations
• Three phases
– Establish
– Transfer
– Disconnect
• Must have switching capacity and channel
capacity to establish connection
• Must have intelligence to work out routing
Circuit Switching - Applications
• Inefficient
– Channel capacity dedicated for duration of
connection
– If no data, capacity wasted
• Set up (connection) takes time
• Once connected, transfer is transparent
• Developed for voice traffic (phone)
Public Circuit Switched Network
Circuit Establishment
Circuit Switching Principles revisited
• Circuit switching designed for voice
– Resources dedicated to a particular call
– Much of the time a data connection is idle
– Data rate is fixed
• Both ends must operate at the same rate
Packet Switching: Basic Operation
• Data transmitted in small packets
– Longer messages split into series of packets
– Each packet contains a portion of user data plus
some control info
• Control info
– Routing (addressing) info
• Packets are received, stored briefly (buffered)
and past on to the next node
– Store and forward
Packet-Switched Network
Use of Packets
Advantages
• Line efficiency
– Single node to node link can be shared by many packets over time
– Packets queued and transmitted as fast as possible
• Data rate conversion
– Each station connects to the local node at its own speed
– Nodes buffer data if required to equalize rates
• Packets are accepted even when network is busy
– Delivery may slow down
• Priorities can be used
Switching Technique
• Station breaks long message into packets
• Packets sent one at a time to the network
• Packets handled in two ways
– Datagram
– Virtual circuit
Datagram
•
•
•
•
•
Each packet treated independently
Packets can take any practical route
Packets may arrive out of order
Packets may go missing
Up to receiver to re-order packets and recover
from missing packets
Datagram
Diagram
Network Hardware and Physical
Media
• Network hardware
includes:
–
–
–
–
Computers
Peripherals
Interface cards and
Other equipment needed
to perform data processing
and communications
within the network
File servers
• A very fast computer with
a large amount of RAM
and storage space along
with a fast network
interface card
• The network operating
system software resides
on this computer
Workstations
• All computers connected
to the file server on a
network are called
workstations
Network interface cards
• The network interface card (NIC)
provides the physical connection
between the network and the
computer workstation.
• Most NICs are internal with the
card fitting into an expansion slot
in the computer.
• Three common network interface
connections are Ethernet cards,
Local Talk connectors and Token
Ring cards
Ethernet cards
• The most common
Network Interface Cards
are Ethernet cards
• They contain connections
for either coaxial or
twisted pair cables, or
both
Co-axial cable
Twisted pair
cable
Concentrators / Hubs
• A concentrator is a device
that provides a central
connection point for
cables from workstations,
servers and peripherals
• Hubs are multi-slot
concentrators
Switches
• hubs provide an easy way to scale
up and shorten the distance that
the packets must travel to get from
one node to another
• they do not break up the actual
network into discrete segments.
That is where switches come in.
Switches (continued)
• A vital difference between a hub and a switch is
– all the nodes connected to a hub share the bandwidth among themselves.
– while a device connected to a switch port has the full bandwidth all to itself.
• Think of a switch as a ‘clever’ hub
Repeaters
• A signal loses strength as it passes along a cable,
so it is often necessary to boost the signal with a
device called a repeater
• A repeater might be a separate device, or might
be part of a concentrator
Bridges
• A bridge is a device that allows you to
segment a large network into two smaller,
more efficient networks
An example of a network with a bridge
Router
Hub
Bridge
Hub
Internet
Segment
Node
Routers
• A router translates information from one network to another
• The router directs traffic to prevent “head-on” collisions
• If you have a LAN that you want to connect to the Internet,
you will need a router to serve as the translator between
information on your LAN and the Internet
Routers (continued)
Physical Media
• Physical media provide the connections
between network devices that make
networking possible
• There are four main types of physical
media in widespread use today:
– Coaxial Cable
– Twisted Pair
– Fiber Optic Cable
LAN Technologies
Ethernet
Physical Media :10 Base5
10 Base2
10 BaseT
10 BaseFL
- Thick Co-axial Cable with Bus Topology
- Thin Co-axial Cable with Bus Topology
- UTP Cat 3/5 with Tree Topology
- Multimode/Singlemode Fiber with Tree
Topology
Maximum Segment Length
10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend
the network)
10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend
the network)
10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the
network)
Thick Coaxial Cable
•
•
•
•
•
•
•
•
•
Used in the first Ethernet networks
Type RG-11 / 10Base5
Usually orange/black
Thickness of a small garden hose
Very expensive and heavy cable
Two strands along the axis
Conductor down the center
Insulator surrounds conductor
Shielded mesh serves as outside
Thin Coaxial Cable
•
•
•
•
•
•
•
Alternative to Thick Ethernet Cable
Type RG-58 / 10Base2 / “Cheapnet”
Usually black
Thickness of a pencil
More flexible than thick Ethernet
Reduced the cost of the cabling
Flexible
Coaxial cable connectors
• The most common type of connector used with
coaxial cables is the BNC connector
Twisted Pair Cable
• Phone Systems
• Twisted Pair Cable consists of two copper
wires, usually twisted around each other to
cancel out any noise in the circuit
• Two main type of Twisted Pair Cabling
– Shielded Twisted Pair (STP)
– Unshielded Twisted Pair (UTP)
Shielded Twisted Pair (STP)
• STP is the original media used for token ring networks
• STP can be used for high-speed networks, such as FDDI or ATM, where
shielding is important.
RJ-45
Unshielded Twisted Pair (UTP)
• UTP has four pairs of wires inside the jacket
• Each pair is twisted with a different number of twists per
inch to help eliminate interference from adjacent pairs
UTP (Continued)
• Most commonly used twisted pair cable
• Uses common telephone wire
• UTP was standardized by the IEEE 802.3
committee in October of 1990
• UTP for LANs is now classified as:
– Category 3 - used for LANs up to 10 Mbps
– Category 4 - used for LANs up to 16 Mbps
– Category 5 - used for LANs up to 100 Mbps
Fiber Optic Cable
• Fiber optic cabling consists of a center glass core
surrounded by several layers of protective materials
• It transmits light rather than electronic signals
• It is the standard for connecting networks between
buildings, due to its immunity to the effects of moisture and
light
Fiber Optic (continued)
• Fiber optic cable has the ability to transmit signals over
much longer distances than coaxial or twisted pair
• It can also carry information at vastly greater speeds
• Fiber optic cable is more difficult to install than other
cabling
Wireless LANS
– Wireless networks use high frequency radio signals to communicate
between the workstations and the fileserver or hubs.
– Disadvantages of wireless networks are:
•
•
•
•
they are expensive (relatively),
provide poor security,
are susceptible to interference and
are slower than cabled networks
MAC Layer in WSNs
Outline
•
•
•
•
•
•
Introduction to MAC
MAC attributes and trade-offs
Scheduled MAC protocols
Contention-based MAC protocols
Case studies
Summary
Introduction to MAC
• The role of medium access control (MAC)
– Controls when and how each node can transmit in
the wireless channel
• Why do we need MAC?
– Wireless channel is a shared medium
– Radios transmitting in the same frequency band
interfere with each other – collisions
– Other shared medium examples: Ethernet
Where Is the MAC?
• Network model from Internet
Application layer
Transport layer
End-to-end reliability, congestion control
Network layer
Routing
Link/MAC layer
Physical layer
Per-hop reliability, flow control, multiple access
Packet transmission and reception
• A sublayer of the Link layer
– Directly controls the radio
– The MAC on each node only cares about its
neighborhood
Media access in wireless
• In wired link,
– Carrier Sense Multiple Access with Collision
Detection
– send as soon as the medium is free, listen into the
medium if a collision occurs (original method in IEEE
802.3)
• In wireless
– Signal strength decreases in proportional to at least
square of the distance
– Collision detection only at receiver
– Half-duplex mode
– Furthermore, CS is not possible after propagation
range
What’s New in Sensor Networks?
• A special wireless ad hoc network
–
–
–
–
–
–
Large number of nodes
Limited computation ability and RAM
Battery powered
Topology and density change
Nodes for a common task
In-network data processing
Primary Concerns of MAC Attributes
• Collision avoidance
– Basic task of a MAC protocol
– Determine when and how to access the medium
• Energy efficiency
– One of the most important attributes for sensor
networks, since most nodes are battery powered
– Affect the overall node lifetime
Primary Concerns of MAC Attributes
• Scalability and adaptivity
– Network size, node density and topology change
• Deployed ad-hoc and operate in uncertain
environments
• Nodes die
• Nodes join later
• Nodes move
– Good MAC accommodates changes gracefully
Other Concerns of MAC Attributes
• Channel utilization
– How well is the channel used?
– Also called bandwidth utilization or channel
capacity
• Latency
– Delay from sender to receiver
– Its importance depends on application
– single hop or multi-hop
Other Concerns of MAC Attributes
• Throughput
– The amount of data transferred from sender to
receiver in unit time
– Affected by efficiency of collision avoidance, channel
utilization, latency, control overhead…
Energy Efficiency in MAC Design
• Energy is primary concern in sensor networks
• What causes energy waste?
– Collisions
• Retransmission
– Long idle time
Dominant factor
• Idle listening consumes 50—100% of the power for
receiving
Energy
• What causes energy waste?
– Overhearing unnecessary traffic
• Can be a dominant factor of energy waste when
– Heavy traffic load
– High node density
– Control packet overhead
• Reduce effective goodput
– Computation complexity
– With Motes, radio and CPU are two major energy
consumers
Hidden terminal problem
• Hidden terminals
–
–
–
–
A sends to B, C cannot receive A
C wants to send to B, C senses a “free” medium (CS fails)
collision at B, A cannot receive the collision (CD fails)
A is “hidden” for C
A
B
C
Exposed terminal problem
• Exposed terminals
– B sends to A, C wants to send to D
– C has to wait, CS signals a medium in use
– but A is outside the radio range of C, thus waiting
is not necessary
– C is “exposed” to B
A
B
C
D
Energy Efficiency in Contention
Protocols
Energy Efficiency in Contention Protocols
• Contention-based protocols need to work
hard in all directions for energy savings
– Reduce idle listening – support low duty cycle
– Better collision avoidance
– Reduce control overhead
– Avoid unnecessary overhearing
Sensor Mac: Case Studies
Case Study 1: S-MAC
• By Ye, Heidemann and Estrin
• Tradeoffs
Latency
Fairness
• Major components in S-MAC
– Periodic listen and sleep
– Collision avoidance
– Overhearing avoidance
– Message passing
Energy
Coordinated Sleeping
• Problem: Idle listening consumes significant
energy
• Solution: Periodic listen and sleep
listen
sleep
listen
sleep
• Turn off radio when sleeping
• Reduce duty cycle to ~ 10% (120ms on/1.2s off)
Latency
Energy
Coordinated Sleeping
• Schedules can differ
Node 1
Node 2
listen
sleep
listen
listen
sleep
sleep
listen
sleep
• Prefer neighboring nodes have same schedule
— easy broadcast & low control overhead
Schedule 1
Schedule 2
Border nodes:
two schedules or
broadcast twice
Coordinated Sleeping
• Schedule Synchronization
– New node tries to follow an existing schedule
– Remember neighbors’ schedules
— to know when to send to them
– Each node broadcasts its schedule every few periods
of sleeping and listening
– Re-sync when receiving a schedule update
• Periodic neighbor discovery
– Keep awake in a full sync interval over long periods
Coordinated Sleeping
• Adaptive listening
– Reduce multi-hop latency due to periodic sleep
– Wake up for a short period of time at end of each
transmission
2
1
3
4
RTS
CTS
listen
CTS
listen
t1
Reduce latency by at least half
listen
t2
Periodic Listen and Sleep
• Choosing schedules
– The node randomly choose time to go to sleep.
– The node receives and follows its neighbor’s schedule by setting its
schedule to be the same.
– If the nodes receives a different schedule after it selects its own
schedule, it adopts its own schedule.
Periodic Listen and Sleep
• Maintaining synchronization
– Update schedule by sending a SYNC packet
periodically.
• SYNC packet contains address of the sender and the
time of its next sleep.
– The new node follows the same procedure to
choose schedule.
• The initial listen period should be long enough.
S-MAC: Coordinated Sleeping
Neighbor Discovery
• chance of failing to discover an existing neighbor
– corrupted SYNC packet, collisions, interference
– sensor – border of two schedules; discovers only the first
schedule, if schedules do not overlap
• Periodically, listen for the complete SP
– frequency?
• - if a sensor has no neighbors
• S-MAC experimental values:
– SP = 10 seconds
– Neighbor discovery period = 2 minutes, if at least 1 nbr
S-MAC: Coordinated Sleeping
Maintaining Synchronization
• Listen is split into 2 parts – for SYNC and RTS/CTS
• Once RTS/CTS is established, data sent in sleep interval
Listen
Receiver
for SYNC
for RTS
for CTS
Sleep
S-MAC: Coordinated Sleeping
Example Scenarios
Listen
Receiver
for SYNC
for RTS
for CTS
Sleep
Tx SYNC
Sender 1
CS
Tx RTS
Got CTS
Send data
CS
Sender 2
Tx SYNC
CS
Sender 3
Tx RTS
CS
Got CTS
Send data
S-MAC: Collision Avoidance
• S-MAC is based on contention
• Similar to IEEE 802.11 ad hoc mode (DCF)
– Physical and virtual carrier sense
– Randomized backoff time
– RTS/CTS for hidden terminal problem
– RTS/CTS/DATA/ACK sequence
S-MAC: Collision Avoidance
• Collision avoidance
– The same procedure as 802.11.
– To adopt RTS/CTS exchange and physical/virtual
carrier sense.
– Randomized carrier sense time.
Overhearing Avoidance
• Problem: Receive packets destined to others
• Solution: Sleep when neighbors talk
• Who should sleep?
– All immediate neighbors of sender and receiver
• How long to sleep?
– The duration field in each packet informs other
nodes the sleep interval
Overhearing Avoidance
• To avoid overhearing by letting interfering nodes go to sleep
after they hear a RTS or CTS packet.
• Who must go to sleep?
E
C
A
B
D
F
– All immediate neighbors of both the sender and receiver should sleep.
• Sleep until NAV becomes zero.
Message Passing
• Problem: Sensor net in-network processing
requires entire message
• Solution: Don’t interleave different messages
– Long message is fragmented & sent in burst
– RTS/CTS reserve medium for entire message
– Fragment-level error recovery — ACK
— extend Tx time and re-transmit immediately
• Other nodes sleep for whole message time
Fairness
Energy
Msg-level latency
Message Passing
• Only one RTS and CTS packet are used to send the fragmented
long packet.
– To avoid control overhead.
• To do overhearing avoidance..
– Each RTS/CTS/DATA/ACK packet has its duration field.
– The duration field include expected transmission time of all fragment.
– Sleep until NAV becomes zero.
S-MAC: An Energy-Efficient MAC Protocol
• S- MAC protocol designed specifically for sensor networks to
reduce energy consumption while achieving good scalability
and collision avoidance by utilizing a combined scheduling
and contention scheme
• The major sources of energy waste are:
–
–
–
–
collision
overhearing
control packet overhead
idle listening
• S-MAC reduce the waste of energy from all the sources
mentioned in exchange of some reduction in both per-hop
fairness and latency
IEEE 802.15.4
and Zigbee Overview
Topics
•
•
•
•
•
802.15.4
ZigBee
Competing Technologies
Products
Some Motorola Projects
IEEE 802.15.4 Applications Space
• Home Networking
• Automotive Networks
• Industrial Networks
• Interactive Toys
• Remote Metering
Some needs in the sensor
networks
Thousands of sensors in a small space Wireless
but sensors are frequently stand alone Low Power
and sensors are frequently isolated Moderate Range.
Some of the challenges facing the standards committee
802.15.4 General Characteristics
Data rates of 250 kb/s, 40 kb/s and 20 kb/s.
Star or Peer-to-Peer operation.
Support for low latency devices.
Fully handshaked protocol for transfer reliability.
Low power consumption.
Frequency Bands of Operation
16 channels in the 2.4GHz ISM* band
10 channels in the 915MHz ISM band
1 channel in the European 868MHz band.
* ISM: Industrial, Scientific, Medical
802.15.4 / ZigBee Architecture
Applications
ZigBee
IEEE 802.15.4 MAC
IEEE 802.15.4
868/915 MHz
PHY
IEEE 802.15.4
2400 MHz
PHY
• Packet generation
• Packet reception
• Data transparency
• Power Management
IEEE 802.15.4 PHY Overview
Operating Frequency Bands
868MHz / 915MHz
PHY
2.4 GHz
PHY
2.4 GHz
Channel 0
Channels 1-10
868.3 MHz
902 MHz
Channels 11-26
2 MHz
928 MHz
5 MHz
2.4835 GHz
IEEE 802.15.4 PHY Overview
Packet Structure
PHY Packet Fields
•
•
•
•
Preamble (32 bits) – synchronization
Start of Packet Delimiter (8 bits)
PHY Header (8 bits) – PSDU length
PSDU (0 to 1016 bits) – Data field
Preamble
Start of
Packet
Delimiter
6 Octets
PHY
Header
PHY Service
Data Unit (PSDU)
0-127 Octets
802.15.4 Architecture
Applications
ZigBee
IEEE 802.15.4 MAC
IEEE 802.15.4
868/915 MHz
PHY
IEEE 802.15.4
2400 MHz
PHY
• Channel acquisition
• Contention mgt
• NIC address
• Error Correction
IEEE 802.15.4 MAC Overview
Design Drivers
Extremely low cost
Ease of implementation
Reliable data transfer
Short range operation
• Very low power consumption
Simple but flexible protocol
IEEE 802.15.4 MAC Overview
Typical Network Topologies
IEEE 802.15.4 MAC Overview
Device Classes
• Full function device (FFD)
– Any topology
– Network coordinator capable
– Talks to any other device
• Reduced function device (RFD)
– Limited to star topology
– Cannot become a network coordinator
– Talks only to a network coordinator
– Very simple implementation
IEEE 802.15.4 MAC Overview
Star Topology
PAN
Coordinator
Master/slave
Full function device
Reduced function device
Communications flow
IEEE 802.15.4 MAC Overview
Peer-Peer Topology
Point to point
Full function device
Cluster tree
Communications flow
IEEE 802.15.4 MAC Overview
Combined Topology
Clustered stars - for example,
cluster nodes exist between rooms
of a hotel and each room has a
star network for control.
Full function device
Reduced function device
Communications flow
IEEE 802.15.4 MAC Overview
General Frame Structure
PHY Layer
MAC
Layer
Payload
Synch. Header
(SHR)
MAC Header
(MHR)
PHY Header
(PHR)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
MAC Service Data Unit
(MSDU)
MAC Protocol Data Unit (MPDU)
PHY Service Data Unit (PSDU)
MAC Footer
(MFR)
IEEE 802.15.4 MAC Overview
Traffic Types
• Periodic data
– Application defined rate (e.g. sensors)
• Intermittent data
– Application/external stimulus defined rate (e.g. light
switch)
• Repetitive low latency data
– Allocation of time slots
802.15.4 Architecture
Applications
• Network Routing
• Address translation
• Packet
Segmentation
• Profiles
ZigBee
IEEE 802.15.4 MAC
IEEE 802.15.4
868/915 MHz
PHY
IEEE 802.15.4
2400 MHz
PHY
ZigBee Stack Architecture
Typical ZigBee-Enabled Device Design
Typical design consist of RF IC and 8-bit
microprocessor with peripherals connected to an
application
Wireless Technology Comparison Chart
34KB /14KB
356 mA
