Topic 2: The Open System Interconnection (OSI) Model & Network Protocols.
OSI Model - SRM Institute of Science and Technology4).pdf · Open Systems Interconnection (OSI)...
Transcript of OSI Model - SRM Institute of Science and Technology4).pdf · Open Systems Interconnection (OSI)...
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OSI Model
UNIT‐I
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TCP/IP Protocol Suite 2
OSI MODEL
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Communication ArchitectureStrategy for connecting host computers and othercommunicating equipment.
Defines necessary elements for data communicationbetween devices.
A communication architecture, therefore, defines astandard for the communicating hosts.
A programmer formats data in a manner defined by thecommunication architecture and passes it on to thecommunication software.
Separating communication functions adds flexibility, forexample, we do not need to modify the entire host softwareto include more communication devices.
OSI Model
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Layer ArchitectureLayer architecture simplifies the network design.
It is easy to debug network applications in a layeredarchitecture network.
The network management is easier due to the layeredarchitecture.
Network layers follow a set of rules, called protocol.
The protocol defines the format of the data beingexchanged, and the control and timing for the handshakebetween layers.
OSI Model
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Open Systems Interconnection (OSI) Model
International standard organization (ISO) established acommittee in 1977 to develop an architecture for computercommunication.
Open Systems Interconnection (OSI) reference model is theresult of this effort.
In 1984, the Open Systems Interconnection (OSI) referencemodel was approved as an international standard forcommunications architecture.
Term “open” denotes the ability to connect any twosystems which conform to the reference model andassociated standards.
OSI Model
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OSI Reference Model
The OSI model is now considered the primary Architecturalmodel for inter‐computer communications.
The OSI model describes how information or data makes itsway from application programmes (such as spreadsheets)through a network medium (such as wire) to anotherapplication programme located on another network.
The OSI reference model divides the problem of movinginformation between computers over a network mediuminto SEVEN smaller and more manageable problems .
This separation into smaller more manageable functions isknown as layering.
OSI Model
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OSI Reference Model: 7 Layers
OSI Model
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TCP/IP Protocol Suite 8
Chapter Outline
3.1 Wired Local Area Network
3.2 Wireless LANs
3.3 Point-to-Point WANs
3.4 Switched WANs
3.5 Connecting Devices
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TCP/IP Protocol Suite 9
3-1 WIRED LOCAL AREA NETWORKS
A local area network (LAN) is a computer network that isdesigned for a limited geographic area such as abuilding or a campus. Although a LAN can be used asan isolated network to connect computers in anorganization for the sole purpose of sharing resources,most LANs today are also linked to a wide area network(WAN) or the Internet.
The LAN market has seen several technologiessuch as Ethernet, token ring, token bus, FDDI, and ATMLAN, but Ethernet is by far the dominant technology.
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TCP/IP Protocol Suite 10
Topics Discussed in the Section
IEEE Standards
Frame Format
Addressing
Ethernet Evolution
Standard Ethernet
Fast Ethernet
Gigabit Ethernet
Ten‐Gigabit Ethernet
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TCP/IP Protocol Suite 11
Figure 3.1 IEEE standard for LANs
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TCP/IP Protocol Suite 12
Figure 3.2 Ethernet Frame
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TCP/IP Protocol Suite 13
Figure 3.3 Maximum and minimum lengths
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TCP/IP Protocol Suite 14
Minimum length: 64 bytes (512 bits)
Maximum length: 1518 bytes (12,144 bits)
Note
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TCP/IP Protocol Suite 15
Figure 3.4 Ethernet address in hexadecimal notation
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TCP/IP Protocol Suite 16
Figure 3.5 Unicast and multicast addresses
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TCP/IP Protocol Suite 17
The broadcast destination address is a special case of the multicast address
in which all bits are 1s.
Note
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TCP/IP Protocol Suite 18
The least significant bit of the first byte defines the type of address.
If the bit is 0, the address is unicast; otherwise, it is multicast.
Note
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TCP/IP Protocol Suite 19
Define the type of the following destination addresses:a. 4A:30:10:21:10:1Ab. 47:20:1B:2E:08:EEc. FF:FF:FF:FF:FF:FF
SolutionTo find the type of the address, we need to look at the secondhexadecimal digit from the left. If it is even, the address is unicast. If itis odd, the address is multicast. If all digits are F’s, the address isbroadcast. Therefore, we have the following:a. This is a unicast address because A in binary is 1010 (even).b. This is a multicast address because 7 in binary is 0111 (odd).c. This is a broadcast address because all digits are F’s.
Example 3.1
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TCP/IP Protocol Suite 20
Show how the address 47:20:1B:2E:08:EE is sent out on line.
SolutionThe address is sent left-to-right, byte by byte; for each byte, it issent right-to-left, bit by bit, as shown below:
Example 3.2
← 11100010 00000100 11011000 01110100 00010000 01110111
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TCP/IP Protocol Suite 21
Figure 3.6 Ethernet evolution through four generations
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• Carrier Sense• Listen to the wire is anybody talking
• No – transmit
• Yes – say nothing– Try again later
• Multiple Access• Possible for two to hear nothing and transmit at the same time
• Possible collision
• What to do when a collision occurs• Shutup
• Wait a while
• Try again
TCP/IP Protocol Suite 22
CSMA/CD ‐ Carrier Sense Multiple Access with Collision Detection
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TCP/IP Protocol Suite 23
Figure 3.7 Space/time model of a collision in CSMA
T ime T ime
BA C D
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TCP/IP Protocol Suite 24
Figure 3.8 Collision of the first bit in CSMA/CD
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TCP/IP Protocol Suite 25
In the standard Ethernet, if the maximum propagation time is25.6 μs, what is the minimum size of the frame?
SolutionThe frame transmission time is Tfr = 2 × Tp = 51.2 μs. Thismeans, in the worst case, a station needs to transmit for aperiod of 51.2 μs to detect the collision. The minimum size ofthe frame is 10 Mbps × 51.2 μs = 512 bits or 64 bytes. This isactually the minimum size of the frame for Standard Ethernet,as we discussed before.
Example 3.3
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TCP/IP Protocol Suite 26
Figure 3.9 CSMA/CD flow diagram
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TCP/IP Protocol Suite 27
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TCP/IP Protocol Suite 28
Figure 3.10 Standard Ethernet implementation
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TCP/IP Protocol Suite 29
STP – Shielded twisted pair (copper)Fiber – Fiber optic cable (glass)UTP – Unshielded twisted pair (copper)
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TCP/IP Protocol Suite 30
Figure 3.11 Fast Ethernet implementation
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TCP/IP Protocol Suite 31
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TCP/IP Protocol Suite 32
In the full-duplex mode of Gigabit Ethernet, there is no collision;
the maximum length of the cable is determined by the signal attenuation
in the cable.
Note
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TCP/IP Protocol Suite 33
Figure 3.12 Gigabit Ethernet implementation
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TCP/IP Protocol Suite 34
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TCP/IP Protocol Suite 35
Pin No. conductor color Name
1 white and orange TX_D1+
2 orange TX_D1‐
3 white and green RX_D2+
4 blue BI_D3+ **
5 white and blue BI_D3‐ **
6 green RX_D2‐
7 white and brown BI_D4+ **
8 brown BI_D4‐ **
Ethernet Pin OutPC to Hub
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Ethernet Crossover CablePC to PC
TCP/IP Protocol Suite 36
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Current Technology
• Used to be:• Wrong cable – no communications
• Now:• Ethernet adapters sense the cabling and auto configure themselves
• Auto‐MDIX
TCP/IP Protocol Suite 37
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TCP/IP Protocol Suite 38
3-2 WIRELESS LANS
Wireless communication is one of the fastestgrowing technologies. The demand for connectingdevices without the use of cables is increasingeverywhere. Wireless LANs can be found on collegecampuses, in office buildings, and in many publicareas. In this section, we concentrate on twowireless technologies for LANs: IEEE 802.11wireless LANs, sometimes called wireless Ethernet,and Bluetooth, a technology for small wireless LANs.
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TCP/IP Protocol Suite 39
Topics Discussed in the Section
IEEE 802.1
MAC Sublayer
Addressing Mechanism
Bluetooth
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TCP/IP Protocol Suite 40
Figure 3.13 Basic service sets (BSSs)
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TCP/IP Protocol Suite 41
Figure 3.14 Extended service sets (ESSs)
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• Carrier Sense• Listen to the wire is anybody talking
• No – transmit
• Yes – say nothing– Try again later
• Multiple Access• Possible for two to hear nothing and transmit at the same time
• Possible collision
• How to avoid a collision (politeness)• I want to talk
• Ok talk
• Everyone else shut up
TCP/IP Protocol Suite 42
CSMA/CA ‐ Carrier Sense Multiple Access with Collision Avoidance
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TCP/IP Protocol Suite 43
Figure 3.15 CSMA/CA flow diagram
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TCP/IP Protocol Suite 44
Figure 3.16 CSMA/CA and NAV
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TCP/IP Protocol Suite 45
Figure 3.19 Hidden station problem
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TCP/IP Protocol Suite 46
The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.
Note
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TCP/IP Protocol Suite 47
Figure 3.20 Use of handshaking to prevent hidden station problem
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TCP/IP Protocol Suite 48
3-3 POINT-TO-POINT WANS
A second type of network we encounter in theInternet is the point-to-point wide area network. Apoint-to-point WAN connects two remote devicesusing a line available from a public network such asa telephone network. We discuss traditional modemtechnology, DSL line, cable modem, T-lines, andSONET.
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TCP/IP Protocol Suite 49
Topics Discussed in the Section
65K Modems
DSL Technology
Cable Modem
T Lines
SONET
PPP
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TCP/IP Protocol Suite 50
Figure 3.26 56K modem
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TCP/IP Protocol Suite 51
ADSL is an asymmetric communication technology designed for residential users; it
is not suitable for businesses.
Note
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TCP/IP Protocol Suite 52
Figure 3.27 Bandwidth division
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TCP/IP Protocol Suite 53
Figure 3.28 ADSL and DSLAM
DSLAM – Digital subscriber line access multiplexer ADSL ‐ Asymmetric digital subscriber line
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TCP/IP Protocol Suite 54
Figure 3.29 Cable bandwidth
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TCP/IP Protocol Suite 55
Figure 3.30 Cable modem configuration
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TCP/IP Protocol Suite 56
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TCP/IP Protocol Suite 57
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TCP/IP Protocol Suite 58
Figure 3.31 PPP frame
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TCP/IP Protocol Suite 59
3-4 SWITCHED WANS
The backbone networks in the Internet can beswitched WANs. A switched WAN is a wide areanetwork that covers a large area (a state or acountry) and provides access at several points to theusers. Inside the network, there is a mesh of point-to-point networks that connects switches. Theswitches, multiple port connectors, allow theconnection of several inputs and outputs.
Switched WAN technology differs from LANtechnology in many ways.
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TCP/IP Protocol Suite 60
3-5 CONNECTING DEVICES
LANs or WANs do not normally operate in isolation.They are connected to one another or to theInternet. To connect LANs and WANs together weuse connecting devices. Connecting devices canoperate in different layers of the Internet model. Wediscuss three kinds of connecting devices: repeaters(or hubs), bridges (or two-layer switches), androuters (or three-layer switches).
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TCP/IP Protocol Suite 61
Topics Discussed in the Section
Repeaters
Bridges
Routers
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TCP/IP Protocol Suite 62
Figure 3.40 Connecting devices
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TCP/IP Protocol Suite 63
Figure 3.41 Repeater or hub
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TCP/IP Protocol Suite 64
A repeater forwards every bit; it has no filtering capability.
Note
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TCP/IP Protocol Suite 65
A bridge has a table used in filtering decisions.
Note
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TCP/IP Protocol Suite 66
A bridge does not change the physical (MAC) addresses in a frame.
Note
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TCP/IP Protocol Suite 67
Figure 3.42 Bridge
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TCP/IP Protocol Suite 68
Figure 3.43 Learning bridge
M MM M
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TCP/IP Protocol Suite 69
A router is a three-layer (physical, data link, and network) device.
Note
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TCP/IP Protocol Suite 70
A repeater or a bridge connects segments of a LAN.
A router connects independent LANs or WANs to create an internetwork (internet).
Note
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TCP/IP Protocol Suite 71
Figure 3.44 Routing example
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TCP/IP Protocol Suite 72
A router changes the physical addresses in a packet.
Note