intro to course and architecture models data communications
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INTRO TO COURSE
AND
ARCHITECTURE MODELS
Data Communications
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Intro to TDC 460
Masters degree is now called Network Engineering and Management
Prereqs: Java, TDC 311 or CSC 373, TDC 261, TDC 363
Foundation: TDC 460 (updated), TDC 463, TDC 464 (updated)
Advanced: TDC 477 (security), TDC 511 (practicum), TDC 560, TDC 563
Electives: 5 coursesCapstone: TDC 594
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System Architectures
We have already been introduced to the various types of communications systems Telephone Internet Television Cable TV and modems LANs (wired and wireless) Wireless WAN
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System Architectures
Let’s look at these system architectures in more detail
What are the models that support each architecture?
What type of code conversions must be performed?
What protocols support these models?Where is the convergence?
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What is a Protocol?
For two entities to communicate successfully, they must “speak the same language”.
What is communicated, how it is communicated, and when it is communicated must conform to some mutually acceptable conventions.
These conventions are referred to as a protocol.
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Key Elements of a Protocol
Syntax Data formats Signal levels
Semantics Control information for coordination Error handling
Timing Speed matching (between sender and receiver) Sequencing (the right commands in the right
order – closely related to semantics)
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Network Architecture
The task of communication is broken up into modules
For example, a file transfer could use many modules: The file transfer interface that the user runs (FTP) The module that makes sure the file arrives at the
destination exactly the same as when it left the source The module that gets the packets from one router to
another The module that get each packet from the user’s
computer to the network The module that converts 1s and 0s to voltages
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TCP/IP Protocol Suite
Dominant commercial protocol architectureSpecified and extensively used before OSIDeveloped by research funded by U.S.
Department of DefenseUsed by the Internet
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TCP/IP Suite Architecture
No official model, but a working one. Application layer Host to host or transport layer Internet layer Network access layer Physical layer
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TCP/IP Physical Layer
Physical interface between data transmission device (e.g. computer) and transmission medium or network
Characteristics of transmission mediumSignal levelsData ratesetc.
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TCP/IP Network Access Layer
Exchange of data between end system and network
Frame createdDestination address providedError checking code providedPossible services like priority invoked
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TCP/IP Internet Layer (IP)
Systems may be attached to different networks
Routing functions across multiple networksImplemented in end systems and routers
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TCP/IP Transport Layer (TCP)
Reliable delivery of data (error-free)Ordering of deliveryImplemented in end systems only (not
implemented in routers)
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TCP/IP Application Layer
Support for user applicationse.g. HTTP, SMTP, FTP, SNMP
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OSI Model
Open Systems InterconnectionDeveloped by the International Organization
for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standard
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OSI - The Model
A layer modelEach layer performs a subset of the
required communication functionsEach layer relies on the next lower layer to
perform more primitive functionsEach layer provides services to the next
higher layerChanges in one layer should not require
changes in other layers
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OSI as Framework for Standardization
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OSI Layers
ApplicationPresentationSessionTransportNetworkData LinkPhysical
What is the function of each OSI layer?
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The OSI Environment19
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Figure 2.16 TCP/IP and OSI model
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Questions
What TCP/IP layer handles addressing?What OSI layer handles voltage conversions?What TCP/IP layer handles email?What OSI layer handles routing?What TCP/IP layer handles end-to-end
connections?What OSI layer handles session connections?What TCP/IP layer handles synchronization?
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SNA
IBM’s Systems Network ArchitectureCreated in the 1970sBeing replaced with TCP/IP but still out
there a little bitSeven layers which map fairly closely to
OSIGood website:
http://www.cisco.com/univercd/home/home.htm
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Novell
Novell NetWare’s architecture used to rely heavily on IPX and SPX protocols
Starting with NetWare version 5, IP became the default protocol replacing IPX
NetWare protocol suite maps to the following OSI layers:
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Telephony Architecture
SubscribersLinesCentral officesTrunksLATAsSS7Switching centers
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Standards
Required to allow for interoperability between equipment
Advantages Ensures a large market for equipment and
software Allows products from different vendors to
communicateDisadvantages
Freeze technology May be multiple standards for the same thing
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Standards Organizations
Internet SocietyISOITU-T (formally CCITT)IEEEANSI
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Functions of Standards
1. Encapsulation2. Segmentation and reassembly3. Connection control4. Ordered delivery5. Flow control6. Error control7. Addressing8. Multiplexing9. Transmission services
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Encapsulation
Addition of control information to data Address information Error-detecting code Protocol control
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Segmentation (Fragmentation)
Data blocks are of bounded sizeApplication layer messages may be largeNetwork packets may be smallerSplitting larger blocks into smaller ones is
segmentation (or fragmentation in TCP/IP) ATM blocks (cells) are 53 octets long Ethernet blocks (frames) are up to 1526 octets
longCheckpoints and restart/recovery
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Why Fragment?
Advantages More efficient error control More equitable access to network facilities Shorter delays Smaller buffers needed
Disadvantages Overheads Increased interrupts at receiver More processing time
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Connection Control
Connection EstablishmentData transferConnection terminationMay be connection interruption and
recoverySequence numbers used for
Ordered delivery Flow control Error control
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Connection Oriented Data Transfer33
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Ordered Delivery
Packets may traverse different paths through network
Packets may arrive out of orderSequentially number packets to allow for
ordering
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Flow Control
Done by receiving entityLimit amount or rate of data Stop and waitCredit systems
Sliding window
Needed at application as well as network layers
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Error Control
Guard against loss or damageError detection
Sender inserts error detecting bits Receiver checks these bits If OK, acknowledge If error, discard packet
Retransmission If no acknowledge in given time, re-transmit
Performed at various levels
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Addressing Level
Level in architecture at which entity is named
Unique address for each end system (computer) and router
Network level address IP or internet address (TCP/IP) Network service access point or NSAP (OSI)
Process within the system Port number (TCP/IP) Service access point or SAP (OSI)
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Figure 2.18 Relationship of layers and addresses in TCP/IP
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Figure 2.19 Physical addresses
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Figure 2.20 shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.
Example 2.3
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Figure 2.20 IP addresses
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Figure 2.21 shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.
Example 2.4
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Figure 2.21 Port addresses
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Addressing Mode
Usually an address refers to a single system Unicast address Sent to one machine or person
May address all entities within a domain Broadcast Sent to all machines or users
May address a subset of the entities in a domain Multicast Sent to some machines or a group of users
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Multiplexing
Supporting multiple connections on one machine
Mapping of multiple connections at one level to a single connection at another Carrying a number of connections on one fiber optic
cable Aggregating or bonding ISDN lines to gain bandwidth
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Transmission Services
Priority e.g. control messages
Quality of service Minimum acceptable throughput Maximum acceptable delay
Security Access restrictions
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Review Questions
What are the layers of the TCP/IP protocol suite? The OSI model?
What is meant by encapsulation?Trace an FTP command as it moves down
through the layers, across the medium, and up the layers on the receiving side.
What are the functions of standards?
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