managing computer and communication networks
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Managing Computer and Communication Networks. Part1 Dr. Hamid Reza Naji. Motivation for Networks. Information Access Sharing of Resources Facilitate Communications. What A Network Includes. Transmission hardware Special-purpose hardware devices interconnect transmission media - PowerPoint PPT PresentationTRANSCRIPT
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Managing Computer and Communication Networks
Part1
Dr. Hamid Reza Naji
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• Information Access
• Sharing of Resources
• Facilitate Communications
Motivation for Networks
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• Transmission hardware• Special-purpose hardware devices
– interconnect transmission media– control transmission– run software protocol
• Software Protocol– encodes/decodes and formats data– detects and corrects problems
What A Network Includes
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• Provides communication that is– Reliable– Fair– Efficient– From one application to another
• Automatically detects and corrects– Data corruption– Data loss– Duplication– Out-of-order delivery
• Automatically finds optimal path from source to destination
What A Network Does
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Point-to-point - Individual connections between pairs of machines.
Broadcast Networks - Single channel with multiple machines connected to it.
Packets - Messages - the "chunk" of data transmitted from one machine to the
next.
Addressing - One to one: Packet contains specific target address. Broadcasting: All machines on the network receive and process the
packet. Multicasting: A subset of machines receive and process the packet.
Issues we’ll be dealing with
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view messaging in terms of the transmission distance
100 meter Building -- Local area network 10 kilometer City -- Metropolitan area network 1K kilometer Country -- Wide area network 10K kilometer Continents -- Internet
transmission distance
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• Dedicated– fixed bandwidth– route fixed at setup– idle capacity wasted– network state
Circuit Switching
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• Best Effort– end-to-end control– multiplexing technique– re-route capability– congestion problems
Packet Switching
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LANs are:Privately owned. Can be up to several kilometers long;Run at speeds of 10, 100, or more Mbps.Low delay. High reliability.Requires collision arbitration.
Ethernet:IEEE 802.3.Bus based broadcast network with decentralized control at 10 or 100 Mbps.
Token Ring:IEEE 802.5Ring based broadcast network with token arbitration at 4 or 16 Mbps.
Network Hardware
LOCAL AREA NETWORKS
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MANS are:Larger version of LAN ("city" wide).Public or private / data or voice.Broadcast Can be distinguished from LANs based on wiring mechanism.
Network Hardware
METROPOLITAN AREA NETWORKS
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WANS are: Networks spanning large distances.
Hosts or End Systems - Machines running user applications.
(Communication) Subnet -Connections between hosts - transmission lines + switches.A "locality" understanding each other's addresses.
Circuits/Channels/Trunks -Transmission lines move the bits.
Network Hardware
WIDE AREA NETWORKS
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Router - Generic term for switching computers.
Point-to-point/Store-and-forward/Packet-switched -Moving through a series of routers, packets are received at a
router, stored there, then forwarded to the next router.
Network Hardware
WIDE AREA NETWORKS
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WirelineString, Copper (Twisted Pair, Coax), Optical Fiber
WirelessSound, Light, Infrared, RF, Microwave
• Used where computer is mobile or far away from wires.• Only few Mbps / higher error rates / interference.
Network Hardware
Media
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• Layers - The concept that network software is organized
functionally into levels. A level on one host talks to the same level on another host (its peer).
• Protocol - The protocol is the convention or standard that a layer
uses to talk to the other layer. An agreement or standard on the conversation.
PROTOCOL HIERARCHIES
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PROTOCOL HIERARCHIES
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PROTOCOL HIERARCHIES
• Physical Medium - Underneath the layers is the wire or fiber or whatever.
• Interface - Defines the services that one layer offers another
(either up or down.)
Important that each layer perform specific actions.
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• Network architecture -
A set of layers and protocols. It contains details on what happens in the layer and what the layer says to its peer.
• Protocol stack -
A list of protocols used by a system, one protocol per layer.
PROTOCOL HIERARCHIES
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• Both Directions Simultaneous• Simplex No No• Half duplex Yes No• Full duplex Yes Yes
• o Number of logical channels per connection• o Error control. • o Flow control.• o Breaking up messages into a smaller chunks (and • reassembly.)• o Multiplexing messages on same connection.• o Routing - how to get from one host to another.
DESIGN ISSUES FOR THE LAYERS
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DESIGN ISSUES FOR THE LAYERS
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• Purpose of each layer is to provide services to the layer above it.
• Entities / Peer entities -• Active element in each layer (processor / IO chip). • Peer entity = layer N entity <--> layer N entity.• Layer N entity provides service for layer N + 1.
• Service providers and users -• Layer N is a provider for user N + 1.
• SAPs (Service Access Points) -• Entry points in N that layer N + 1 can access.• Has an address that uniquely identifies it.
INTERFACES AND SERVICES
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• IDUs (Interface Data Unit) -• The information from N + 1 provided at the SAP.• Made up of SDU + control information.
• SDUs (Service Data Unit) -• The portion of the IDU that will be passed up to the peer entity.
• PDUs (Protocol Data Unit) -• The SDU may be broken up into PDUs, that being the chunk
size
for further transmission.
INTERFACES AND SERVICES
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INTERFACES AND SERVICES
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• Connection oriented service -
Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in.
» Connection Setup» Data Transfer» Connection Termination
CONNECTION-ORIENTED SERVICES
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• Connectionless service -
Like the post office. Each message has the entire address on it. Each message may follow a different route to its destination. Ordering is not important
CONNECTIONLESS SERVICES
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• Quality of service -• Will the message arrive?? • A reliable connection-oriented service guarantees success.• Message sequence - message boundaries and order are maintained.• Byte streams - messages are broken up or combined; flow is bytes. • Can pair mechanism with upper-layer requirements (matching).
CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:
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• Datagram Service – Like junk mail. It's not worth the cost to determine if it
actually arrived. Needs a high probability of arrival, but 100% not required. Connectionless, no acknowledgment.
• Acknowledged datagram service - As above, but improved reliability via acknowledgment.
• Request-reply service -Acknowledgment is in the form of a reply.
CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:
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CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:
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• Primitives are:• The operations available to an entity. Possibilities
include:• Request -- An entity want some work done.• Indication -- An entity is told about an event.• Response -- An entity wants to respond to
an event.• Confirm -- Response to earlier request has come back.
SERVICE PRIMATIVES
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• Example of Connectionless Protocol:
• Data-request |--------->| Data-indication• Data-indication |<---------| Data-request
• Example of Connection-oriented Protocol: (needs connection establishment)
• Connect-request |--------->| Connect-indication• Connect-confirm |<---------|
• Data-request |--------->| Data-indication• Data-indication |<---------| Data-request
• Disconnect-request |--------->| Disconnect-indication• Disconnect-confirm |<---------|
SERVICE PRIMATIVES
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• THE RELATIONSHIP OF SERVICES TO PROTOCOLS:
• Services are primitives that a layer provides for the layer above it.
• Protocols are rules governing the meaning of frames/packets/messages exchanged with the peer entity.
SERVICE PRIMATIVES
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Layering
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Reference Models
Headers, Data, and Trailers
Encapsulation
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THE OSI REFERENCE MODEL
OSI == Open Systems Interconnection
Developed by ISO == International Standards Organization
Principles used to develop OSI Layering:1. Need a layer for each different level of operation.2. Each layer performs a well defined function.3. Each layer has a standard.4. Layer boundaries should minimize data flow across
those boundaries.5. The right number of layers - don't put too many functions
together, but not too many layers either.
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THE OSI REFERENCE MODEL
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• Physical Layer -
• Purpose -- Transmits raw bits across a medium.
• Electrical -- Concerns are voltage, timing, duplexing, connectors, etc.
THE OSI REFERENCE MODEL
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• Data Link Layer -
• Framing -- Breaks apart messages into frames. Reassembles frames into messages. • Error handling -- solves damaged, lost, and duplicate frames.• Flow control -- keeps a fast transmitter from flooding a slow receiver.• Gaining Access -- if many hosts have usage of the medium, how is access
arbitrated.
THE OSI REFERENCE MODEL
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• Network Layer -
• Routing -- What path is followed by packets from source to destination. Can be based on a static table, when the connection is created, or dynamic when each packet is sent.
• Congestion -- Controls the number packets in the subnet.
• Accounting -- Counts packets/bytes for billing purposes.
• Heterogeneity -- Interfacing so one type of network can talk to another.
THE OSI REFERENCE MODEL
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• Transport Layer -
• Reliability -- Ensures that packets arrive at their destination. Reassembles out of order messages.
• Hides network -- Allows details of the network to be hidden from higher level layers.
• Service Decisions -- What type of service to provide; error-free point to point, datagram, etc.
• Mapping -- Determines which messages belong to which connections.
• Naming -- "Send to node xyz" must be translated into an internal address and route.
• Flow control -- keeps a fast transmitter from flooding a slow receiver.
THE OSI REFERENCE MODEL
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• Session Layer –
• Sessions -- Provides services that guarantee a particular message. For instance, a login session could be logged.
• Synchronization-- Provide way to subdivide a long mechanism for reliability.
THE OSI REFERENCE MODEL
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• Presentation Layer -
Prettiness
-- Syntax and semantics of information transmitted.
--Understands the nature of the data being
transmitted.
--Converts ASCII / EBCDIC.
THE OSI REFERENCE MODEL
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• Application Layer -
• Interfacing -- Terminal type translation.
• File transfer -- Programs able to understand directory structures and naming conventions and map them onto various systems.
THE OSI REFERENCE MODEL
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Data Transmission in the OSI Model -
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THE TCP/IP REFERENCE MODEL
Used in the Internet. Common mechanism that is surpassing the OSI Model.
Internet Layer - The IP (Internet Protocol) does delivery and congestion control.
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• Transport Layer - Allows peer entities to communicate.
• TCP -- Transmission Control Protocol provides a reliable connection oriented protocol that delivers a byte stream from one node to another. Guarantees delivery and provides flow control.
• UDP -- User Datagram Protocol provides an unreliable connection-less protocol for applications that provide their own.
• Application Layer - Terminal -- Telnet File transfer -- FTP The Web -- HTTP
THE TCP/IP REFERENCE MODEL
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LAYERS
Transport Network
OSI ConnectionlessConnection-Oriented Connection-Oriented
TCP Connectionless Connectionless Connection-Oriented
COMPARISON OF REFERENCE MODELS
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• NOVELL NETWARE: Heavily used in PC world.
• Proprietary protocol stack Network layer -- IPX - unreliable connectionless Transport layer -- NCP (Network Core Protocol)
- connection oriented• Naming and Addressing --• SAP (Service Advertising Protocol) - Servers
advertise their address to router machines. Clients, when booted, ask for location of nearest server.
Example Networks
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Example Networks
THE INTERNET:• Growing exponentially.• All nodes run TCP/IP. Means that all nodes have an
IP address by which they can be contacted.• Services provided include:
o e-mail o news o remote login
o file transfer o the web
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ISO (International Standards Organization)
ANSI (American National Standards Institute)
NIST (National Institute of Standards and Technology)
IEEE (Institute of Electrical and Electronics Engineering)
IAB (Internet Architecture Board)
Standards