Sept 2017 osi and tcp ip protocols

Network Integration(Multimedia)

Communication ArchitectureStrategy for connecting host computers and other communicating equipment.Defines necessary elements for data communication between devices.A communication architecture, therefore, defines a standard for the communicating hosts.A programmer formats data in a manner defined by the communication architecture and passes it on to the communication software.Separating communication functions adds flexibility, for example, we do not need to modify the entire host software to include more communication devices.

Layer ArchitectureLayer architecture simplifies the network design.It is easy to debug network applications in a layered architecture network.The network management is easier due to the layered architecture.Network layers follow a set of rules, called protocol.The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers.

Open Systems Interconnection (OSI) Model

International standard organization (ISO) established a committee in 1977 to develop an architecture for computer communication.Open Systems Interconnection (OSI) reference model is the result of this effort.In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture.Term “open” denotes the ability to connect any two systems which conform to the reference model and associated standards.

OSI Reference ModelThe OSI model is now considered the primary Architectural model for inter-computer communications.The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network.The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems .This separation into smaller more manageable functions is known as layering.

OSI Reference Model: 7 Layers

OSI: A Layered Network ModelThe process of breaking up the functions or tasks of networking into layers reduces complexity.Each layer provides a service to the layer above it in the protocol specification. Each layer communicates with the same layer’s software or hardware on other computers. The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

Physical LayerProvides physical interface for transmission of information.

Defines rules by which bits are passed from one system to another on a physical communication medium.Covers all - mechanical, electrical, functional and procedural - aspects for physical communication.Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

Data Link LayerData link layer attempts to provide reliable communication over the physical layer interface.

Breaks the outgoing data into frames and reassemble the received frames.Create and detect frame boundaries.Handle errors by implementing an acknowledgement and retransmission scheme.Implement flow control.Supports points-to-point as well as broadcast communication.Supports simplex, half-duplex or full-duplex communication.

Network LayerImplements routing of frames (packets) through the network.

Defines the most optimum path the packet should take from the source to the destinationDefines logical addressing so that any endpoint can be identified. Handles congestion in the network.Facilitates interconnection between heterogeneous networks (Internetworking).The network layer also defines how to fragment a packet into smaller packets to accommodate different media.

Transport LayerPurpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers.

Ensures that the data units are delivered error free.Ensures that data units are delivered in sequence.Ensures that there is no loss or duplication of data units.Provides connectionless or connection oriented service.Provides for the connection management.Multiplex multiple connection over a single channel.

Session LayerSession layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications.

This layer requests for a logical connection to be established on an end-user’s request.Any necessary log-on or password validation is also handled by this layer.Session layer is also responsible for terminating the connection.This layer provides services like dialogue discipline which can be full duplex or half duplex.Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint.

Presentation LayerPresentation layer defines the format in which the data is to be exchanged between the two communicating entities. Also handles data compression and data encryption (cryptography).

Application Layer1. Application layer interacts with application programs and is the

highest level of OSI model.2. Application layer contains management functions to support

distributed applications.3. Examples of application layer are applications such as file

transfer, electronic mail, remote login etc.

OSI Model

OSI in ActionA message begins at the top application layer and moves down the OSI layers to the bottom physical layer. As the message descends, each successive OSI model layer adds a header to it. A header is layer-specific information that basically explains what functions the layer carried out. Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

OSI Model

TCP/IP MODEL

OSI & TCP/IP Models

TCP/IP Model

Application LayerApplication programs using the network

Transport Layer (TCP/UDP)Management of end-to-end message transmission,

error detection and error correction

Network Layer (IP)Handling of datagrams : routing and congestion

Data Link LayerManagement of cost effective and reliable data delivery,

access to physical networks

Physical LayerPhysical Media

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IP Address Classes

• IP addresses are divided into 5 classes, each of which is designated with the alphabetic letters A to E.

• Class D addresses are used for multicasting.• Class E addresses are reserved for testing &

some mysterious future use.

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IP Address Classes (Cont.)

• The 5 IP classes are split up based on the value in the 1st octet:

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IP Address Classes (Cont.)

• Using the ranges, you can determine the class of an address from its 1st octet value.

• An address beginning with 120 is a Class A address, 155 is a Class B address & 220 is a Class C address.

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Are You the Host or the Network?

• The 32 bits of the IP address are divided into Network & Host portions, with the octets assigned as a part of one or the other.

Network & Host RepresentationBy IP Address Class

Class Octet1 Octet2 Octet3 Octet4

Class A Network Host Host Host

Class B Network Network Host Host

Class C Network Network Network Host

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Are You the Host or the Network? (Cont.)

• Each Network is assigned a network address & every device or interface (such as a router port) on the network is assigned a host address.

• There are only 2 specific rules that govern the value of the address.

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Are You the Host or the Network? (Cont.)

• A host address cannot be designated by all zeros or all ones.

• These are special addresses that are reserved for special purposes.

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Class A Addresses

• Class A IP addresses use the 1st 8 bits (1st Octet) to designate the Network address.

• The 1st bit which is always a 0, is used to indicate the address as a Class A address & the remaining 7 bits are used to designate the Network.

• The other 3 octets contain the Host address.

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Class A Addresses (Cont.)

• There are 128 Class A Network Addresses, but because addresses with all zeros aren’t used & address 127 is a special purpose address, 126 Class A Networks are available.

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• There are 16,777,214 Host addresses available in a Class A address.

• Rather than remembering this number exactly, you can use the following formula to compute the number of hosts available in any of the class addresses, where “n” represents the number of bits in the host portion:

(2n – 2) = Number of available hosts

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• For a Class A network, there are:224 – 2 or 16,777,214 hosts.

• Half of all IP addresses are Class A addresses.• You can use the same formula to determine the

number of Networks in an address class.• Eg., a Class A address uses 7 bits to designate the

network, so (27 – 2) = 126 or there can be 126 Class A Networks.

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Class B IP Addresses

• Class B addresses use the 1st 16 bits (two octets) for the Network address.

• The last 2 octets are used for the Host address.

• The 1st 2 bit, which are always 10, designate the address as a Class B address & 14 bits are used to designate the Network. This leaves 16 bits (two octets) to designate the Hosts.

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Class B IP Addresses (Cont.)

• So how many Class B Networks can there be?• Using our formula, (214 – 2), there can be

16,382 Class B Networks & each Network can have (216 – 2) Hosts, or 65,534 Hosts.

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Class C IP Addresses

• Class C addresses use the 1st 24 bits (three octets) for the Network address & only the last octet for Host addresses.the 1st 3 bits of all class C addresses are set to 110, leaving 21 bits for the Network address, which means there can be 2,097,150 (221 – 2) Class C Networks, but only 254 (28 – 2) Hosts per Network.

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Class C IP Addresses (Cont.)

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Special Addresses

• A few addresses are set aside for specific purposes.

• Network addresses that are all binary zeros, all binary ones & Network addresses beginning with 127 are special Network addresses.

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Special Addresses (Cont.)

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• Within each address class is a set of addresses that are set aside for use in local networks sitting behind a firewall or NAT (Network Address Translation) device or Networks not connected to the Internet.

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• A list of these addresses for each IP address class:

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Subnet Mask

• An IP address has 2 parts:– The Network identification.– The Host identification.

• Frequently, the Network & Host portions of the address need to be separately extracted.

• In most cases, if you know the address class, it’s easy to separate the 2 portions.

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Subnet Mask (Cont.)

• With the rapid growth of the internet & the ever-increasing demand for new addresses, the standard address class structure has been expanded by borrowing bits from the Host portion to allow for more Networks.

• Under this addressing scheme, called Subnetting, separating the Network & Host requires a special process called Subnet Masking.

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Subnet Mask (Cont.)

• The subnet masking process was developed to identify & extract the Network part of the address.

• A subnet mask, which contains a binary bit pattern of ones & zeros, is applied to an address to determine whether the address is on the local Network.

• If it is not, the process of routing it to an outside network begins.

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Subnet Mask (Cont.)

• The function of a subnet mask is to determine whether an IP address exists on the local network or whether it must be routed outside the local network.

• It is applied to a message’s destination address to extract the network address.

• If the extracted network address matches the local network ID, the destination is located on the local network.

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Subnet Mask (Cont.)

• However, if they don’t match, the message must be routed outside the local network.

• The process used to apply the subnet mask involves Boolean Algebra to filter out non-matching bits to identify the network address.

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Default Standard Subnet Masks

• There are default standard subnet masks for Class A, B and C addresses:

Subnetting Concepts

• Revise: binary nos., boolean operators AND• Phone number analogy still works!

(401) 555-7777• Host ID: divided into Subnet ID and Host ID• Need to communicate which part is subnet ID• 32 bit binary number called “Subnet mask”• The bits of the mask in any given subnetted network

are chosen so that the bits used for either the network ID or subnet ID are ones, while the bits used for the host ID are zeroes.

Subnetting Concepts (Cont)

• Subnet Bit Is A One: In this case, we are ANDing either a 0 or 1 in the IP address with a 1. If the IP address bit is a 0, the result of the AND will be 0, and if it is a 1, the AND will be 1. In other words, where the subnet bit is a 1, the IP address is preserved unchanged.

Subnet Bit Is A Zero: Here, we are ANDing with a 0, so the result is always 0 regardless of what the IP address is. Thus, when the subnet bit is a 0, the IP address bit is always cleared to 0.

• A router that performs this function is left with the address of the subnet. Since it knows from the class of the network what part is the network ID, it also knows what subnet the address is on.

• Bit Allocation Example– We can decide to use 1 bit for the subnet ID and 15 bits for the host

ID. If we do this, then the total number of subnets is 21 or 2: the first subnet is 0 and the second is 1. The number of hosts available for each subnet is 215-2 or 32,766.

Example: IP Subnetting

• Requirements– Class, how many hosts, scalability, min, max

Subnetting Design Trade-Off For Class C Networks

• Class C Custom Subnet Mask Calculation Example – 3 for subnet ID and 5 for host ID

Express Subnet Mask In “Slash Notation”: 255.255.255.224 is equivalent to “/27”.

Determining Host Address for each Subnet

VLSM

• Variable-length subnet masks were developed to allow multiple levels of subnetted IP addresses within a single network

• The routing protocol you use must support VLSM– Open Shortest Path First (OSPF)– Enhanced Interior Gateway Routing Protocol (EIGRP)– Routing Information Protocol version 2 (RIPv2)

• VLSM is crucial for an effective IP addressing plan

VLSMBenefits of VLSM

• More efficient use of IP addresses– Without use of VLSM, a single subnet mask must be

implemented with an entire Class A, B, or C network• Greater capacity to use router summarization – Allows more hierarchical levels within an addressing plan

• Isolation of topology changes from other routers

VLSMBenefits of VLSM

VLSM Permits Flexible, Efficient Subnet Address Allocation

VLSMCIDR and Route Summarization

• The definition of classless inter-domain routing (CIDR):– Allocation of one or more blocks of Class C network numbers to each

network service provider– Organizations using the network service provider for Internet

connectivity are allocated bitmask-oriented subsets of the provider’s address space as required

• CIDR (“cider”) was developed to address the problem of IP address space running out and core Internet routers running out of capacity

• Route summarization is the representation by a single network of a group of contiguous networks


Route Summarization of

Contiguous Subnets of a Class

B Network


Route Summarization of Contiguous Subnets of a Class B Network (continued)

• Router D in previous slide has these networks in its routing table– 172.16.12.0/24– 172.16.13.0/24– 172.16.14.0/24– 172.16.15.0/24

• To calculate the summary route:– Find the number of highest-order bits that match in all addresses– Locate where the common pattern of digits ends– Count the number of common bits; this is the length of the summary

route


Route Summarization of Contiguous Subnets of a Class B Network (continued)

• Follow these guidelines when calculating summary routes:– Addresses that do not share the same number of bits as the prefix length

of the summary route are not included in the summarization block– The IP addressing plan is hierarchical in nature to allow router to

aggregate the largest number of IP addresses into a single summary route

– IP networks can only be summarized in 2n networks (for some n), where the last octet of the first network in the sequence is divisible by 2n

VLSMRoute Aggregation

• By using a prefix length instead of an address class to determine the network portion of the address, CIDR allows routers to aggregate routing information– Shrinks routing table– One address and mask combination can represent the routes to multiple

networks• Route aggregation is used more loosely than CIDR; describes

the summarization of classful networks • Without CIDR, routers must maintain tables for individual

networks

VLSMSupernetting

• The practice of using a summary network to group multiple classful networks into a single address is called supernetting– Subnetting breaks down a classful network– Supernetting pastes together classful networks

• With Class A and B address space almost exhausted, large organizations requested multiple Class C network addresses from their service providers

• A block of contiguous Class C addresses can appear as a single large network, or supernet

VLSMSupernetting

• Supernetting and route aggregation are similar– Route aggregation is used in the context of summarizing

routes with BGP– Supernetting is a term used when the summarized

networks are under common administrative control• Many networking professionals use the terms

“route summarization” and “route aggregation” interchangeably

VLSMCIDR Example

CIDR Permits the Aggregation of Several Classful Networks into a Single Route Advertisement

Sept 2017 osi and tcp ip protocols

Engineering

Transcript of Sept 2017 osi and tcp ip protocols