intro to course and architecture models data communications

INTRO TO COURSE

AND

ARCHITECTURE MODELS

Data Communications

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

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

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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