TCP/IPTCP/IP Dr. ClincyLecture 21 Ch 2: TCP/IP and OSI Lecture 2.

Dr. Clincy Lecture 2 1

TCP/

IP

Ch 2: TCP/IP and OSI

Lecture 2


TCP/

IP

OSI

• Open Systems Interconnection

• Developed by ISO(International Organization for Standardization)

• Contains seven layers

• Application

• Presentation

• Session

• Transport

• Network

• Data Link

• Physical


TCP/

IP

OSI Reference Model ?

• Bottom 3 layers• Responsible for

getting the info to the destination

• Top 4 layers• Responsible for the

creation and interpretation of the info

• Bottom 3 layers• Responsible for getting

the info to the destination• Called Network Support

Layers

• Transport Layer• Links the bottom layers

with the top layers• Ensures what the bottom

layers have transmitted is usable by the top layers

• Top 3 layers• Responsible interoperability

among unrelated software systems

• Called User Support Layers

Your Author’s Perspective Your Professor’s Perspective


TCP/

IP

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


TCP/

IP

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


TCP/

IP

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)


TCP/

IP

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.


TCP/

IP

OSI Network Layer• Responsible for routing of messages through networks

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

• Handles routing among different networks

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

• No need for routing with in the same network (LAN)

• Routing across “internetworks”

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


TCP/

IP

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


TCP/

IP

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)

Z

A

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


TCP/

IP

Recap – OSI bottom 3 layers

• Network

• Data Link

• Physical

Data Comm Layers


TCP/

IP

OSI Upper Layers• Application

• Presentation

• Session

• Transport

• Peer-to-Peer Processes …..

• End-to-End nodes only


TCP/

IP

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


TCP/

IP

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)


TCP/

IP

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).


TCP/

IP

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


TCP/

IP

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.)


TCP/

IP

Recap – Two General Objectives of Networking ?

Lower Layers – getting the signal/data/info from one place to the next

Upper Layers – creating and interpreting the signal, data or info


TCP/

IP

A ZB C Q T

7

1

3

1

Tx Rx

Intermediate Nodes

What happens at the End and Intermediate Nodes ?


TCP/

IP

– 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


TCP/

IP

An exchange using the OSI model

Explain encapsulation and decapsulation


TCP/

IP

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


TCP/

IP

Summary of OSI Layers


TCP/

IP

OSI in Action: Outgoing File Transfer• The File Transfer Program issues

a command to the Application Layer

• Application passes it to Presentation, which may reformat, encrypt, encode, compress, passes to Session (adds overhead)

• Session requests a connection, passes to Transport (adds overhead)

• Transport breaks file into chunks, adds error-checking and flow-control info, process-to-process, passes to Network (adds overhead)

• Network selects the data’s route (internetworking), passes to Data Link (adds overhead)

• Data Link adds error-control and flow-control info, passes to Physical (adds overhead)

• Physical translates bits to signal and transmits the signal, which includes information added by each layer


TCP/

IP

OSI in Action: Incoming File Transfer• Physical receives signal and

translates to bits, passes to Data Link

• Data Link checks for errors and performs flow control on bits, formulates bits into some formation (frames), passes to Network

• Network verifies routing (if intermediate node, determines next hop), passes to Transport

• Transport checks for errors and performs flow control on the chunks, reassembles the chunks, passes to Session

• Session determines if transfer is complete, may end session, passes to Presentation

• Presentation may reformat, perform conversions, decode, decrypt, decompress, pass to Application layer

• Application presents results to user (e.g. updates FTP program display)


TCP/

IP

How TCP/IP maps to OSI ??


TCP/

IP

TCP/IP Model

Explain Suite and Stack Concept

Protocols for different underlying technologies – this is key

SCTP


TCP/

IP

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


TCP/

IP

Physical Address ExamplePhysical Address Example

Most local area networks use a 48-bit (6 bytes) physical address written as 12 hexadecimal digits, with every 2 bytes separated by a hyphen as shown below:

07-01-02-01-2C-4B A 6-byte (12 hexadecimal digits) physical address


TCP/

IP

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


TCP/

IP

IP Address ExampleIP Address Example

An Internet address (in IPv4) is 32 bits in length, normally written as four decimal numbers (or 4 octal numbers), with each number representing 1 byte. How many bits is a byte ? A nibble ??

The numbers are separated by a dot. Below is an example of such an address. Call “dot notation”

132.24.75.9Example of IPv6 Address (128 bits):


TCP/

IP

Addresses in TCP/IP

Application Specific Address

Converts to a part address


TCP/

IP

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

Add IP address

Overhead (H2, T2) added for what ?


TCP/

IP

Port Address Example Port Address Example

As we will see in Chapters 11 and 12, a port address is a 16-bit address represented by one decimal number as shown below.

753 A 16-bit port address


TCP/

IP

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

Signals

Bits

Frames

Datagrams (Packets)

Segments

Messages


TCP/

IP

For entertainment purposes – if time permits….

• If time permits (15 minutes maybe), illustrate how the US Postal System is very similar to how networking works

• Will help students better understand (versus memorize) networking

Lower Layers – getting the signal from one place to the next

Upper Layers – creating and interpreting the signal, data or info

US Postal System Analogy

TCP/IPTCP/IP Dr. ClincyLecture 21 Ch 2: TCP/IP and OSI Lecture 2.

Documents

Transcript of TCP/IPTCP/IP Dr. ClincyLecture 21 Ch 2: TCP/IP and OSI Lecture 2.