jozef goetz, 2012 1 copyright © the mcgraw-hill companies, inc. permission required for...
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Jozef Goetz, 2012
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Copyrights @ 2013 by John Wiley & Sons, Inc
Most chapter references are related to Behrouz A Forouzan ed4
expanded by Jozef Goetz, 2012
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ObjectivesObjectivesExam Objective MatrixTechnology Skill Covered Exam Objective Exam Objective
NumberIntroduction to the OSI Model Compare the layers of the OSI and
TCP/IP models.OSI model:•Layer 1—Physical•Layer 2—Data Link•Layer 3—Network•Layer 4—Transport•Layer 5—Session•Layer 6—Presentation•Layer 7—ApplicationClassify how applications, devices, and protocols relate to the OSI model layers.•IP address•Frames•Packets•Cable
1.1
1.2
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ObjectivesObjectivesExam Objective MatrixTechnology Skill Covered Exam Objective Exam Objective
NumberTCP/IP Model Compare the layers of the OSI and
TCP/IP models.TCP/IP model:• Network Interface Layer• Internet Layer• Transport Layer• Application Layer• (Also described as: Link Layer, InternetLayer, Transport Layer, Application Layer)
1.1
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2-1 LAYERED TASKS2-1 LAYERED TASKS
•We use the concept of We use the concept of layerslayers in our daily life. in our daily life. •As an example, let us consider As an example, let us consider two friends who two friends who communicate through postal mail. communicate through postal mail.
•The process of The process of sending a lettersending a letter to a to a friendfriend would be would be complexcomplex if if there were no servicesthere were no services available from the available from the post office. post office.
Sender, Receiver, and CarrierHierarchy
Topics discussed in this section:Topics discussed in this section:
Jozef Goetz, 2012
5 Sending a letter: The concept of layers
There is a hierarchy (order) of different asks: •e.g. at the sender site.
•The letter must be written and dropped in the mailbox before being picked up by the letter carrier and delivered to PO
with the sender and receiver address
sorted and
and sorted
Note: each layer at the sending site uses the services of the layer immediately below it.
Home layer
PO layer
Mailbox layer
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2-2 THE OSI MODEL2-2 THE OSI MODEL
•Established in 1947, the Established in 1947, the International Standards International Standards OrganizationOrganization ( (ISOISO) is a multin) is a multinaational body dedicated to tional body dedicated to worldwide agreement on international standards. worldwide agreement on international standards.
•An ISO standard that covers all aspects of network An ISO standard that covers all aspects of network communications is the communications is the Open Systems InterconnectionOpen Systems Interconnection ((OSIOSI) model. ) model.
•It was first introduced in the late 1970s.It was first introduced in the late 1970s.
Layered ArchitecturePeer-to-Peer ProcessesEncapsulation
Topics discussed in this section:Topics discussed in this section:
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ISO is the organization.OSI is the model.
Note
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Figure 2.1 Seven layers of the OSI model
Mnemonics:Top to bottom
All People Seem To Need Data ProcessingBottom to top
Please Do Not Throw Sausage Pizza Away
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13Figure 2.2 Internet layers
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14Figure 2.3 Peer-to-peer processes
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15Protocol Hierarchies
Layers: Networks are organized as a stack of levels or layers to reduce their design
complexity. Each layer perform a specific collection of well–understood
related functions We build each layer on the one below it. Each layer talks to the ones above & below it Each layer hides underlying details from the one above it – sort of a
virtual machine, offering certain services (operations) to the layer above it Layers differ in number and function from one network to another.
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16 interfaces and protocols Between each pair of
adjacent layers is an interface.
defines what information and services the lower layers makes available to the upper one.
Well defined interfaces and layers provide modularity to a network
Layers or their services (functions) are replaceable
The corresponding layers on different machines are called peers
The peers communicate by using protocols
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17Services to Protocols Relationship
Services is a set primitives (operations) that the layer provides to the layer above it
What functions does this layer provide? Services like an abstract data type in OOD - object oriented design
A protocol is a set of rules governing the format and meaning of the packets and/or msgs that are exchange by the peers entities within a layer.
A protocol relates to the implementation of the service and as such is not visible to the user of the service
Entities use protocols to implement their service definition
The services and the protocols are completely decoupled Protocols can be changed but the service can remain the same
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Figure 2.3 The interaction between layers in the OSI model
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems
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19Protocols
Protocols:1. Define data types for transmission2. Provide different services (a set of
operations) Initiate a connection Transmit data Terminate a connection
Are layered to form architectures
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21Figure 2.4 An exchange using the OSI model
Each layer in the sending device •adds its own info (header) to the msg it receives from the layer just above it and •passes the whole package to the layer below
At the receiving device, the msg is unwrapped layer by layer (the msg moves back up throught the OSI layers):
•i.e. the headers and trailers (T2) attached to it at the corresponding sending layer are removed, and actions appropriate to that layer are taken
Header contains information that describes what each layer of the OSI Model should do with the data
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22Data as It Moves Through OSI Layers, Sent by One Computer and
Received by Another
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Figure 2.4 An exchange using the Internet modelEncapsulation concept: level N – 1 is not aware which part of the packet is data and which part is the header
•A packet at level 5 is encapsulated in packet at level 4. •Level 4 is not aware which part of the encapsulated packet is data and which part •is the header. •The packet in level 4 is encapsulated in packet at level 3, and so on.
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24Protocol encapsulation
e-mail client
TCP server
IP server
ethernetdriver/card
user X
e-mail server
TCP server
IP server
ethernetdriver/card
user Y“Hello”
“Hello”
“Hello”
“Hello”
“Hello”
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25Encapsulation/De-encapsulation
The process of moving data between layers of the OSI Model
Encapsulation:Data > segment >packet > frame >bits
De-encapsulation:Bits > frame >packet > segment> data
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26How Data Is Referred to in the OSI Model
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1. The physical layer is responsible for transmitting individual bits from one
node to the next.
Note:Note:
Physical Layer PL 1
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28 Physical layer
•Defines physical means that are used to transmit data:•Cable standards – e.g. copper wiring•Wireless standards – e.g. radio frequencies•Fiber optic standards – e.g. light pulses
•Concerned with the characteristics of the physical medium to transfer row bits over a communication channel.
•Deals with •mechanical, •electrical, •functional, •procedural and •timing interfaces, and •the physical medium itself.
•Example of device: HUB
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29Physical layer duties
1. Physical characteristics of interfaces and media• Plug types, materials etc.
2. Representation (encoding) of bits• E.g. TTL 5v = 1, 0 = 0v, RS232C 1 = -12v, 0 = +12v• Sensitivity of receivers, e.g. minimum voltage for 1 in RS232C is -3v
3. Data Rate/Transmission Rate• How many bits per second
4. Synchronization of bits• Not only the bit rate but when does a char or frame/packet starts
and ends5. Transmission mode: simplex, half-duplex, or full-duplex6. Physical topology: mesh, star, bus, ring, or hybrid
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Shows relationship of it to other layers
Data Link Layer DDL 2
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31Figure 2.7 Node (hop)-to-node (hop) delivery by the DLL
The data link layer is responsible for transmitting frames from one node to the next (of the same network).
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Data Link Layer DDL 2 - point-to-point connection Deals with transforming a raw line into a
line that appears free of errors to the network layer.
It accomplishes with breaking up the data into data frames, transmit the frames sequentially, and then receiving acknowledgements back.
This layer also deals with different hardware speeds by slowing some transmissions if the other end can’t keep up.
How much buffer space the receiver has? How the error is handled?
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33Data link layer duties:
•Framing• the data link layer DLL divides the stream of bits into manageable data units called frames
• Physical Addressing• adds a header to the frame containing sender and/or receiver address
• Flow Control• Controls how fast a transmitter can send to a receiver
• Error Control• Detection and recovery from error conditions or lost frames
•Achieved through a trailer T2 added to the end of the frame• (Medium) Access Control
• who has control over the link at any given time•Fair access to shared data link networks e.g. Ethernet
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34Data Link Layer of OSI Model Can move frames from one adjacent
computer to another, cannot move frames across routers
Encapsulation = frame
Requires a unique MAC address. or physical address e.g. 11-00-68-BF-F8-EA
Protocols defined include Ethernet Protocol and Point-to-Point Protocol (PPP)
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35Data Link Layer of OSI Model
Device example: Switch Two sublayers:
Logical Link Control (LLC) and the Media Access Control (MAC)
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LLC and MAC Sublayers Logical Link Control (LLC)
Data Link layer addressing, flow control, address notification, error correction
Media Access Control (MAC) Determines which computer has access to
the network media at any given time Determines where one frame ends and the
next one starts, called frame synchronization
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37Figure 2.19 Example 1
•In Figure below a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header.
•These are the only addresses needed. The rest of the header contains other information needed at this level. •The trailer usually contains extra bits needed for error detection
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Network Layer NL 3
Shows relationship of it to other layers
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39Figure 2.9 Source-to-destination delivery across different networks
The network layer is responsible for the delivery of packets from the original source to the final destination (across different network).
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Network Layer 3 Controls the operation of the subnet.
A key design issue is - determining how packets are routed.
Packet routing may be static (based on static tables ex. determined from a
terminal session) or dynamic (determined for each packet), depending
on the type of network.
Other issues: congestion control, quality of service: (delay, transit time etc.), overcome protocol differences
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41Network Layer of OSI Model
Responsible for moving packets (data) from one end of the network to the other, called end-to-end communications
Device example: Router Routing is the ability of various network
devices and their related software to move data packets from source to destination
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42Network layer duties
1. Source to Destination Delivery• Beyond the same link• Interconnected basic different networks
2. Logical Addressing such as IP e.g. 192.45.0.120• if packet passes the network boundary we need to distinguish
the source and destination network by adding header with the logical sender and receiver addresses
• so we separate from physical addressing at data link• logical addresses need to be assigned to every computer on a
network• the logical addresses doesn’t change
3. Routing/Internetworking• determine how to get from the source to the destination• connecting devices (routers or switches ) are used to route to
the proper destination
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43Figure 2.20 Example 3
•In Figure we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN.
•Because the two devices are located on different networks, we cannot use physical addresses only;
•the physical addresses only have local jurisdiction.
•What we need here are universal addresses that can pass through the LAN boundaries?
•The network (logical) addresses have this characteristic.
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Transport layer TL 4
The transport layer is responsible for delivery of a segment (message) from
one process to another.
Note: Note: NetworkNetwork L.L. deliver deliver individualindividual packets packets, it , it doesn't recognize doesn't recognize any relationship any relationship between packetsbetween packets which belonged to which belonged to some segmentssome segments..
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45Figure 2.11 Reliable process-to-process delivery of a message
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46Transport Layer of OSI Model
Takes data from higher levels of OSI Model and breaks it into segments that can be sent to lower-level layers for data transmission
Conversely, reassembles data segments into data that higher-level protocols and applications can use
Also puts segments in correct order (called sequencing ) so they can be reassembled in correct order at destination
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47 Transport Layer TL 4 Serves as the interface between the Session and
Network layers.
The Transport Layer is responsible for breaking up larger data (messages) from the session
layer into (smaller messages) segments and then sending them across the network layer making sure the all pieces arrive correctly to the
destination
The transport layer is a true end-to-end layer, all the way from the source to the destination
A program on the source machine carries on a conversation with the similar program on the destination machine
In the lower layers, the protocols are between each machine and its immediate neighbors, not between the ultimate source and destination.
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48Transport layer duties
1. Port addressing• Process (running program) on one computer
delivers a message (msg) to a specific process on the other.• To identify the process the port address is
provided to the TL
2. Segmentation and reassembly control• Sending large amounts of data needs to be
managed by breaking down into transmissible segments • Each segment contains a sequence # in order to
reassemble data (message) at the destination
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49Transport layer duties
3. Connection control• a phone call like service (connection oriented service
- such as TCP to ensure destination received segments) or
• a postcard like service without verification (connectionless service - such as UDP to send segments without assurance of delivery ) – e.g. VoIP, video – data-streaming apps
4. Flow control• End to End control at a process level
5. Error control• End to End error control rather than a single link• Make sure no error (damage, loss, or duplicates) at the
receiving TL
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50Figure. Example 3. Internet Model
Figure shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process).
•Since the data size is larger than the network layer can handle, the data (message) are split into two segments, each segment retaining the port addresses (j and k).
Then in the network layer, network addresses (A and P) are added to each packet.
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Session layer SL 5
The session layer is responsible for dialog control and synchronization.
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Session Layer SL 5 Allows users on different machines to establish
a session, manage and terminate session. Session services provide:
dialog control (who transmits next)• provides communications between 2 Ps in simplex, half-
duplex, or full-duplex synchronization (checkpointing long transactions
so they can continue after a crash), adjournment, termination and restart or recovery
• SL allows to add checkpoints, or synchronization points, to a stream data in order if a crash happens during the retransmission send one from the last checkpoint
• e.g. 2000 pages are sent, but a crash happens at page 123, so pages are needed to resend are 101 to 125
token management (preventing the same critical operation at the same time).
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Handles the syntax and semantics of the info exchanged between systems.
Presentation Layer 6
The presentation layer is responsible for translation, compression, and encryption.
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Presentation Layer PL 6
1. Manages translation Allows data to move from one machine
to another while retaining the appropriate format.
allows higher-level data structure (e.g., banking records), to be defined into a
common format at the sender and send it to the receiver which converts into its receiver-dependent format.
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Presentation Layer PL 6
2. Encryption The sender transforms the orginal info to
another form (to protect from interception or eavesdropping) and sends msg out over the network
Decryption reverses to its orginal form at the receiver
e.g. Secure Socket Layer (SSL) and IPSec (ure)
3. Compression Reduces the # of bits
Important for sending text, audio, and video
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The application layer is responsible for providing network services (access
to the network) to the user.
Application Layer 7
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57Application Layer Contains protocols that are often
needed by users, such as HTTP.
The application layer is the most abstract layer and is closest to the user.
The user is most likely to interact with the application layer than any other layer in the model.
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58Application Layer Provided services:
network virtual terminal to logon to a remote host
file transfer, access and mgmnt access to a remote host to make changes and read data retrieve/send files from/to a remote host
mail services for e-mail forwarding and storage E-mail program may use POP3 (Post Office Protocol version
3) to read e-mails and SMTP (Simple Mail Transport Protocol) to send e-mails
directory services database access for global info about services etc.
Firefox web browser uses HTTP (Hyper-Text Transport Protocol)
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Summary of layers !
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The OSI Reference Model
This is the “International Standards Organization Open Systems Interconnection Reference Model”, or the ISO OSI Reference Model.
We will call it the OSI model.
There is a protocol defined for each layer by the ISO.
The protocols are rarely used anymore, but the model is very relevant.
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61Principles behind the model.
1. • Layers should be created where abstraction is needed.
2. • Each layer should perform a well-defined function.
3. • The function of the layer should be chosen while defining protocols.
4. • The layer boundaries should be chosen to minimize the information flow across the interfaces.
5. • There should not be too many or too few layers.
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OSI The OSI itself is not a network
architecture because it does not specify exact services and protocols to be used in each layer.
It just tells what each layer should do
However ISO produced standards for all the layers, although these are not part of the reference model itself
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Reference Models.The OSI reference model.
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2-4 TCP/IP 2-4 TCP/IP PROTOCOLPROTOCOL SUITE (Internet Model) SUITE (Internet Model)
•The The layerslayers in the in the TCP/IPTCP/IP protocol suite protocol suite do notdo not exactly exactly matchmatch those in the OSI model. those in the OSI model. •The The original TCP/IP protocol suiteoriginal TCP/IP protocol suite was defined as was defined as having four layers: having four layers: host-to-network, internet, transporthost-to-network, internet, transport, , and and applicationapplication. . •However, when TCP/IP is compared to OSI, we can say However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of that the TCP/IP protocol suite is made of five layersfive layers: : physical, data link, network, transportphysical, data link, network, transport, and , and applicationapplication..
Physical and Data Link LayersNetwork LayerTransport LayerApplication Layer
Topics discussed in this section:Topics discussed in this section:
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65The TCP/IP Reference Model
– the model itself is not much use but the protocols are widely used
This data communication model was first defined in 1974 when the internet was still part of ARPANET.
Major Goals: The Army-driven design was meant to allow the computer
network to communicate even if a part of the network was down.
This would allow the network to continue to work in the case of a war.
The military was also worried about lost connections. They did not want a connection to die as long as the
source and destination machines were alive, even if some of the machines in the middle were lost.
This put further requirements on any protocol that might be created.
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The TCP/IP reference model. The host-to-network layer is undefined in this
model. They leave out all of the underlying layers, leaving the
implementation up to whoever creates the network.
The TCP/IP internet layer is similar in functionality to the OSI network layer.
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Figure 2.16 TCP/IP and OSI model p.43-44
•The 5th layer deals with the Internet services provided by various applications.
•The first 4 layers deal with the communication between hosts.
•Layers 3 and 4 are fully implemented in the operating systems kernel on most existing systems.
•The first 2 layers are network hardware specific, the others are work independently of the physical layer
•Most of the 1st layer is handled by hardware (communication medium used, attachments of hosts to the medium).
•The rest of the 1st layer and all the 2nd layer is handled by the (Network Interface Card) NIC card in a host.
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Network Modelswith approximate mapping between the two
•The 5th layer deals with the Internet services provided by various applications.
•The first 4 layers deal with the communication between hosts.
•Layers 3 and 4 are fully implemented in the operating systems kernel on most existing systems.
•The first 2 layers are network hardware specific, the others are work independently of the physical layer
•Most of the 1st layer is handled by hardware (communication medium used, attachments of hosts to the medium).
•The rest of the 1st layer and all the 2nd layer is handled by the (Network Interface Card) NIC card in a host.
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69Internet Layer. The requirements resulted in a complex network led to
choice of a packet-switching network based on a connectionless internetwork layer.
The Internet (Network) Layer is responsible for injecting packets into any network and have them travel to their destination.
Order of arrival is not important to the internet layer – they packets can be sorted out later by the higher layers.
The internet layer defines an official packet format for and protocol called Internet Protocol (IP).
the major issue is packet routing to avoid congestion.
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70Transport Layer.The transport layer is intended to allow two
machines to carry on a conversation, just like the OSI transport layer.
There are two end-to-end protocols defined for this:
– TCP (Transmission Control Protocol) reliable, byte stream connection-oriented
for application without errors – file transfer
– UDP (User Datagram Protocol) unreliable, connectionless
for applications that don’t need TCP’s sequence or flow control and wish to provide their own
used for client/server request reply queries in which prompt delivery is more important than accurate delivery,
such as a transmitting speech or video
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The Application layer contains all of the higher-level protocols
Network Interface Layer has Link Layer synonym– FTP – file transfer TFTP - Trivial File Transfer Protocol - used for automated transfer of configuration
or boot files between machines in a local
environment– SMTP – e-mail– DNS - Domain Name System– NNTP - Network News Transfer Protocol– HTTP - Hypertext Transfer Protocol
TCP/IP Model and its Relation to Protocols of the TCP/IP Suite
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72The TCP/IP Protocol Suite IGMP - Internet Group
Management Protocol handles multicasting
ICMP - Internet Control Message Protocol
Handles errors and control messages.
Protocol is used to forward information, primarily error messages.
To see if a computer is running, the `ping' program sends an echo request, which is part of ICMP.
ARP -Address Resolution Protocol is a protocol for mapping an Internet Protocol IP address to a physical machine address that is recognized in the local network.
For example, in IP Version 4, the most common level of IP in use today, an address is 32 bits long.
In an Ethernet LAN, however, addresses for attached devices are 48 bits
1st -2nd layer is handled by the Network Interface Card -NIC card
RARP - Reverse Address Resolution Protocol is a protocol by which a physical machine in a LAN can request to learn its IP address from a gateway server's Address Resolution Protocol (ARP) table or cache.
A network administrator creates a table in a LAN’s gateway router that maps the physical machine (addresses) into IP addresses.
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73Comparing OSI and TCP/IP Models
Both are: based on the concepts of a stack of
independent protocols
the layers up through transport layers provide an end-to-end network-independent transport service
the layers above transport are application-oriented users
Jozef Goetz, 2012
74Comparing OSI and TCP/IP Models• The differences between the TCP/IP (4 layers)
and OSI (7 layers) models.• OSI model clearly defined the distinction
between services, interfaces (specifies what the parameters are and what result to expect) and protocols, where the TCP/IP model does not.
• Protocols can easily be replaced in the OSI model (as long as it provides the offered services), but not in the TCP/IP model.
This fits in nicely with OO programming concepts as the layer (an object) hide information and has a set of methods (services) that processes outside the object can invoke
The code internal to the object is its protocol and it is not visible outside the object
Abstraction hides details of one layer from others
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75Comparing OSI and TCP/IP Models
• The OSI model has no biases for protocols, but the OSI model was overly general and did not help with the creation of new protocols.
• OSI supports: connectionless and connection-oriented in the
network layer, but only connection-oriented in the transport layer,
providing no choice to the user.
• TCP/IP supports: only connectionless in the network layer, but both in the transport layer, giving user a
choice (TCP, UDP).
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76Comparing OSI and TCP/IP Models
The OSI reference model was devised before the corresponding protocols were invented
With TCP/IP the protocols came first, and the model was just a description of the existing protocols
So protocols fit perfectly
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77A Critique of the OSI Model and Protocols
Why OSI did not take over the world
Bad timing Competing TCP/IP was already there
Bad technology 7 layers choice more political than technical,
layer 5 and 6 nearly empty, 2 and 3 are overfull Functions: addressing, flow control, error
control are in each layer instead error control must be done in the
highest layer Bad implementations
Initially because of the enormous complexity
In contrast TCP/IP was part of Berkeley UNIX and free
Bad politics
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Bad Timing
The apocalypse of the two elephants.
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79A Critique of the Models and Protocols
• OSI1. – Arrived late on the scene2. – Model was too complex and the protocols were flawed 3. (some stuff appears in multiple levels)4. – Poor implementation (no good example)5. – Poorly marketed
• TCP/IP1. – model is just an explanation of what was already
implemented2. – model is not useful for describing any other
protocol3. – model does not clearly define layers4. – model is not complete5. – lead to the introduction of other poorly implemented
protocols
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80A Critique of the TCP/IP Reference Model
Problems:1. Service, interface, and protocol not
distinguished what is required by good software engineering practice to
distinguish between the specification and the implementation
2. Not a general model3. Host-to-network “layer” not really a layer
• in the normal sense of the term as used in the context of layered protocols
• It is an interface between layer 2 and 3
4. Doesn’t distinguish the physical and data link layers.
These are completely different. They are not a separate layers.
5. Minor protocols deeply firmly established (entrenched), hard to replace
Jozef Goetz, 2012
81A Critique of the Models and Protocols.
In summaryOSI – The model, minus the session and
presentation layers, is exceptionally useful.
TCP/IP – The protocol is in wide use and is accepted
virtually everywhere.
The Rest of the Course:• Focus on the useful layers of the OSI model while
ignoring the ISO protocols.
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2-5 ADDRESSING2-5 ADDRESSING
Four levels of addresses are used in an internet Four levels of addresses are used in an internet employing the TCP/IP protocols: employing the TCP/IP protocols: physicalphysical, , logicallogical, , portport, , and and specificspecific..
Physical AddressesLogical AddressesPort AddressesSpecific Addresses
Topics discussed in this section:Topics discussed in this section:
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Figure 2.17 Addresses in TCP/IP
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Figure 2.18 Relationship of layers and addresses in TCP/IP
e.g. URLUniversal Resource Locator
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Figure 2.19 Physical addresses
•In Figure 2.19 a node with physical address 10 sends a frame to a node with physical address 87. •The two nodes are connected by a link (bus topology LAN). •As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.
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Most local-area networks use a 48-bit (6-byte) physical address (or MAC addresses) written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:
Example 2.2
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
Jozef Goetz, 2012
87Wide Area Networks
Relation between hosts on LANs and the subnet. The subnet consists of routers and
transmission lines. A router is a specialized piece of switching hardware
that is responsible for determining the direction that data packets should be sent.
Routers are responsible for directing data down transmission lines from one LAN to another.
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88Wide Area Networks
A stream of packets from sender to receiver. A subnet is organized according to the principle called Store-
and-forward or Packet-switched subnet– The message is broken down into smaller packets to send.– Each packet is sent out onto the network.– As a packet arrives at a router, it is stored there until the outgoing line
is free. It is then sent on it’s way.– All the packets make take the same or different routes depending on if
they are individually routed or not.
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Figure: IP addresses
•Figure 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 3 networks (only two are shown in the figure).
•So each router has 3 pairs of addresses, one for each connection.
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Figure 2.21 Port addresses
•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.
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Example 2.5
As we will see in Chapter 23, a port address is a 16-bit (2 byte) address represented by one decimal number as shown.
753A 16-bit port address represented
as one single number.
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The physical addresses change from hop to hop,but the logical and port addresses usually remain the same.
Note
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93Summary: Difference between UDP
and TCP internet protocol (IP) traffichttp://www.cyberciti.biz/faq/key-differences-between-tcp-and-udp-protocols/
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) is a transportation protocol that is one of the core protocols of the Internet protocol suite. Both TCP and UDP work at transport layer TCP/IP model and both have very different usage.
Difference between TCP and UDPTCP: Reliability: TCP is connection-oriented protocol. When a file or
message send it will get delivered unless connections fails. If connection lost, the server will request the lost part. There is no corruption while transferring a message.
UDP: Reliability: UDP is connectionless protocol. When you a send a data or message, you don't know if it'll get there, it could get lost on the way. There may be corruption while transferring a message.
TCP: Ordered: If you send two messages along a connection, one after the other, you know the first message will get there first. You don't have to worry about data arriving in the wrong order.
UDP: Ordered: If you send two messages out, you don't know what order they'll arrive in i.e. no ordered
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and TCP internet protocol (IP) trafficTCP: Heavyweight: - when the low level parts of the TCP "stream" arrive in
the wrong order, resend requests have to be sent, and all the out of sequence parts have to be put back together, so requires a bit of work to piece together.
UDP: Lightweight: No ordering of messages, no tracking connections, etc. It's just fire and forget! This means it's a lot quicker, and the network card / OS have to do very little work to translate the data back from the packets.
TCP: Streaming: Data is read as a "stream," with nothing distinguishing where one packet ends and another begins. There may be multiple packets per read call.
UDP: Datagrams: Packets are sent individually and are guaranteed to be whole if they arrive. One packet per one read call.
TCP: Examples: World Wide Web (Apache TCP port 80), e-mail (SMTP TCP port 25 Postfix MTA), File Transfer Protocol (FTP port 21) and Secure Shell (OpenSSH port 22) etc.
UDP: Examples: Domain Name System (DNS UDP port 53), streaming media applications such as IPTV or movies, Voice over IP (VoIP), Trivial File Transfer Protocol (TFTP) and online multiplayer games etc
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SummaryThe physical layer is responsible for transmitting a bit stream over a physicalmedium. It is concerned with
a. physical characteristics of the mediab. representation of bitsc. type of encodingd. synchronization of bitse. transmission rate and modef. the way devices are connected with each other and to the links
The data link layer is responsible fora. framing data bitsb. providing the physical addresses of the sender/receiverc. data rate controld. detection and correction of damaged and lost frames
The network layer is concerned with delivery of a packet across multiple networks;therefore its responsibilities include
a. providing host-to-host addressingb. Routing
The transport layer oversees the process-to-process delivery of the entire data (message).
It is responsible fora. dividing the message into manageable segmentsb. reassembling it at the destination,c. flow and error control
The application layer services include, file transfer, remote access, shared databasemanagement, and mail services
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SummaryAddresses
The physical address is the local address of a node; it is used by the data link layer to deliver data from one node to another within the same network.
The logical address defines the sender and receiver at the network layer and is used to deliver messages across multiple networks.
The port address (service-point) identifies the application
process on the station.
The application layer services include file transfer, remote access, shared database management, and mail services
The application, presentation, and session layers of the OSI model are represented by the application layer in the Internet model.
The lowest four layers of OSI correspond to the Internet model layers.
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Secretary X
Mail Room X
Postman X
Post office X
CEO X
Secretary Y
Mail Room Y
Postman Y
Post office Y
CEO Y“Lunch?”
“Lunch?”
“Lunch?”
“Lunch?”
“Lunch?”
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HTTP
TCP
IP
ethernet
Host A
IP
ethernet
Router R
link
HTTP
TCP
IP
ethernet
Router W
Host B
IP
ethernetlink
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OSI units
Address Layer Data Unit Delivery7 ApplicationLayer Data (Messages)6 PresentationLayer Data (Messages)5 SessionLayer Data (Messages)
port #'s 4 TransportLayer TCP Segments, UDP diagrams Process To Process //End to Endlog.address IP 3 NetworkLayer Packet/Datagram Source Host to Destination HostMAC phAddress 2 DataLinkLayer Frames Point to Point //Hop to Hop
1 PhysicalLayer
<=The TCP/IP model reference to be used in our lectures