Dr. Clincy Lecture 1

Internet

Security

CS 4491 Internet Security

Dr. Clincy

Networking Fundamentals

Note: I am still “tweaking” your syllabus in trying to get to 16 or 17 lectures with 50% online

Dr. Clincy Lecture 2

Internet

Security

Internet – Consists of various technologies• LAN Examples: Ethernet, Token Ring, Wireless and

FDDI Ring

• Point-to-Point WAN Examples: Telephony Modem, DSL, Cable/Modem, T-Lines, and SONET

• Switched WAN Examples: X.25, Frame Relay and ATM

Briefly explain the difference between packet switch networks and circuit switch networks

Dr. Clincy Lecture 3

Internet

Security

Internet uses TCP/IP for internetworking – why ?

• Bottom Line: what makes TCP/IP so great and unique from other network protocols ??:– Network Technology Independence – independent of a

particular vendor’s hardware

– Universal Interconnection – any 2 computers connected to the internet can communicate – each computer has a unique internationally recognized address

– End-to-End Acknowledgements – acknowledgements between the source and destination versus intermediate nodes

– Application Protocol Standards – TCP/IP provides services (or software) to applications needing lower level communication services

• In understanding TCP/IP, one must understand OSI

Dr. Clincy Lecture 4

Internet

Security

Why Study OSI?

• Still an excellent model for conceptualizing and understanding protocol architectures

• More granularity in functionality - more functional delineation

• Key points:– Modular

– Hierarchical (chain of command, pecking order)

– Boundaries between layers (called interfaces)

NOTE: the protocols or functionality with in the layer could change however, the interface remains the same – this facilitates the flexibility

Dr. Clincy Lecture 5

Internet

Security

OSI

• Open Systems Interconnection

• Developed by ISO(International Organization for Standardization)

• Contains seven layers

• Application

• Presentation

• Session

• Transport

• Network

• Data Link

• Physical

Dr. Clincy Lecture 6

Internet

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A ZB C Q T

7

1

3

1

Tx Rx

Intermediate Nodes

What happens at the End and Intermediate Nodes ?

Dr. Clincy Lecture 7

Internet

Security

– between different layers on the same node or stack (INTERFACE)– between similar layers on different nodes or stacks (PEER-TO-PEER

PROCESSES)

Recap - OSI’s Layered Approach

Dr. Clincy Lecture 8

Internet

Security

OSI Reference Model ?

• Bottom 3 layers• Bottom 3 layers responsible for getting the info to the destination• (Bottom 3 layers): at the lower levels of the model protocols define

the electrical and physical standards• (Bottom 3 layers) at the lower levels, the bit ordering, the

transmission of the bits, and error detecting and correcting are defined

• Top 4 layers• at the higher levels of the model, the protocols define the data

formatting, message syntax, dialogue management, message sequences and info presentation

Dr. Clincy Lecture 9

Internet

Security

OSI Physical Layer• Responsible for transmission of bits

• Always implemented through hardware

• Encompasses mechanical, electrical, and functional interfaces

• Encoding issues: how 0’s and 1’s are converted to signals

• Transport medium: Coaxial, Twisted Pair, Optical, etc..

• Transmission Rate/Data Rate – how fast to send bits

• Transmission mode: transmission direction (simplex, duplex)

• Physical Topology: network layout

Dr. Clincy Lecture 10

Internet

Security

OSI Data Link Layer• Responsible for error-free, reliable transmission of

data

• Framing, Flow control, Error control (detection/correction)

• Makes use of physical address because with in the same network

Network Layer

Data Link Layer

Physical Layer

Actually sends the packets (groups of frames) from node to node using a routing algorithm

Takes raw data (bits) and transform them into frames, error control, etc.

Transmit and receive the raw data (bits)

Dr. Clincy Lecture 11

Internet

Security

OSI Data Link LayerHigh Level View of Data Link Layer’s Functions: 1. Take raw bits and transform them into frames or packets

(up) 2. Perform error detection on packets prior to them being sent

(down) 3. Perform error checking on packets received (up) 4. If error is encountered, the Data Link Layer notifies the

sender 5. Make sure not too much traffic is sent from the transmitter

to the receiver (flow control) In general, the bullet items above deal with creating a “transmission line” To achieve the functions above, we must have STANDARDS.

Dr. Clincy Lecture 12

Internet

Security

OSI Network Layer• Responsible for routing of messages through networks

• Concerned with type of switching used (circuit v. packet)

• Handles routing among different networks (Routing across “internetworks”)

• NOTE: with in the same network, only the DATA LINK layer is needed – amongst multiple networks, the NETWORK LAYER and routing are needed

• Makes use of logical address vs physical address because not with in same network

Dr. Clincy Lecture 13

Internet

Security

OSI Network Layer

Transport

Network Layer

Data Link Layer

Concerned with an error-free end-to-end flow of data

Actually sends the packets (groups of frames) from node to node using a routing algorithm

Takes raw data (bits) and transform them into frames

Dr. Clincy Lecture 14

Internet

Security

OSI Network Layer

High Level View of Network Layer’s Functions: 1. Transmitting data packets through a network in a timely

manner 2. There are more than one route between the source and

destination, the network layer chooses the best route (next hop) based on some criteria.

3. Makes sure the network does not become congested when

link or node failures occur. Passes data between two networks (differing networks)

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A

Examples - Node Cost - Link Cost - Distance - Spare Cap. - Low Util.

Dr. Clincy Lecture 15

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OSI Upper Layers• Application

• Presentation

• Session

• Transport

• Peer-to-Peer Processes …..

• End-to-End nodes only

Dr. Clincy Lecture 16

Internet

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OSI Transport Layer• Isolates messages from lower and upper layers

• Breaks down message size (segmentation) (down) and performs re-assembly (up)

• Monitors quality of communications channel (oversee all hops)

• Selects most efficient communication service necessary for a given transmission (could change over hops)

• Flow and Error control for Source and Sink

Dr. Clincy Lecture 17

Internet

Security

OSI Session Layer• Establishes logical connections between systems

(up/down)

• Manages log-ons, password exchange, log-offs (up/down)

• Terminates connection at end of session (up/down)

Dr. Clincy Lecture 18

Internet

Security

OSI Session Layer

The Session Layer is responsible for (1) dialogue management, (2)synchronization and (3) activity management.

Dialogue Management – an example is, querying a database. Let theDB sit on a remote server and the query is invoked from the client –the entire process of sending the query and receiving the data isconsidered “dialogue management”.

Synchronization – at the session layer, “synch points” can beinserted in the data being transmitted. If network failures occur, thedata would be re-transmitted starting at the last synch point.

Activity Management – involves sending special messages at thebeginning and end of an activity. These messages can help thereceiver determine when to start processing (after all data isreceived).

Dr. Clincy Lecture 19

Internet

Security

OSI Presentation Layer• Provides format and code conversion services

• Examples – File conversion from ASCII to EBDIC

– Invoking character sequences to generate bold, italics, etc on a printer

• The source and sink could operate using different encoding schemes – the presentation layer makes the translations

• Security

• Compression

Dr. Clincy Lecture 20

Internet

Security

OSI Application Layer• Provides access to network for end-user (end-user

being a human being or software application)

• User’s capabilities are determined by what items are available on this layer (ie. remote log-in, file transfer, email service, directory service, etc.)

Dr. Clincy Lecture 21

Internet

Security

An exchange using the OSI model

Explain encapsulation and decapsulation

Dr. Clincy Lecture 22

Internet

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COMPLEXITY TO CONSIDER

• Any particular node in an internetwork can be functioning as follows simultaneously:

• Tx to other internetwork nodes

• Rx from other internetwork nodes

• Intermediate node to some other internetwork nodes

Dr. Clincy Lecture 23

Internet

Security

How TCP/IP maps to OSI ??

Dr. Clincy Lecture 24

Internet

Security

Physical addresses

• Physical address is also known as the link address

• Physical address can be different sizes (depend on the network)

• Unicast type physical addresses – single Rx

• Multicast type physical address – multiple Rxs

• Broadcast type physical address – all Rxs can pickup message

Dr. Clincy Lecture 25

Internet

Security

IP Addresses can be either unicast, multicast or broadcast types

Going from network A physical address 10 to network P physical address 95.

Can’t use the physical address because different networks

The network layer address contains the uniqueness we need from source to sink. Network layer address is A-P

Unit at this layer - datagram

Explain communications at the network layer

Dr. Clincy Lecture 26

Internet

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Addresses in TCP/IP

Application Specific Address

Converts to a part address

Dr. Clincy Lecture 27

Internet

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Port addressesAddresses of sending and receiving processes (j and k)

Add IP address

Overhead (H2, T2) added for what ?

Dr. Clincy Lecture 28

Internet

Security

Relation-ship betweenLayers, Addresses, and Units in TCP/IP

Signals

Bits

Frames

Datagrams (Packets)

Segments

Messages