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Thursday, March 31, 2016

Different functions of different ATM layers

OSI Layer ATM Layer ATM Subnet Sunctionality
3/4 AAL CS Providing the standard interface(Convergence).
2/3 ATM Flow Control cell header generation/extraction virtual circuit/path management cell multiplexing/demultiplexing.
2 TC Cell rate decoupling header checksum generation & verification cell generation packing/unpacking cells from the enclosing envelope frame generation.
1 Physical. PMD Bit timing physical network access.
CS = Convergence sublayer

SAR = Segmentation and reassembly sublayer

TC = Transmission Convergence sublayer

PMD = Physical medium dependent sublayer
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Comparison of LS and DV algorithms Message complexity


• LS: with n nodes, E links, O(nE)
msgs sent

• DV: exchange between neighbors
only

convergence time varies
Speed of Convergence

• LS: O(n2) algorithm requires
O(nE) msgs

may have oscillations

• DV: convergence time varies

may be routing loops

count-to-infinity problem
Robustness: what happens if router
malfunctions?

LS:

node can advertise incorrect link
cost

each node computes only its own
table

DV:

DV node can advertise incorrect
path cost

each node’s table used by others

error propagate thru network
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Distance Vector Algorithm

 Distance Vector Algorithm

Bellman-Ford Equation (dynamic programming)
Define
dx(y) := cost of least-cost path from x to y

Then
dx(y) = min {c(x,v) + dv(y) }
where min is taken over all neighbors v of x


Distance Vector Algorithm

Dx(y) = estimate of least cost from x to y

Distance vector: Dx = [Dx(y): y є N ]

Node x knows cost to each neighbor v: c(x,v)

Node x maintains Dx = [Dx(y): y є N ]

Node x also maintains its neighbors’ distance vectors

For each neighbor v, x maintains
Dv = [Dv(y): y є N ]

Basic idea:

Each node periodically sends its own distance vector estimate to
neighbors

When a node x receives new DV estimate from neighbor, it updates its
own DV using B-F equation:
Dx(y) ← minv{c(x,v) + Dv(y)} for each node y ε N

Under minor, natural conditions, the estimate Dx(y) converge to the
actual least cost dx(y)

Stan Kurkovsky

Distance Vector Algorithm

Iterative, asynchronous: each
local iteration caused by:

local link cost change

DV update message from
neighbor

Distributed:

each node notifies neighbors only
when its DV changes

neighbors then notify their
neighbors if necessary

Each node:

wait for (change in local link
cost of msg from neighbor)
recompute estimates

if DV to any dest has
changed, notify neighbors
8

Stan Kurkovsky

Distance Vector: link cost changes

Link cost changes:

node detects local link cost change

updates routing info, recalculates
distance vector

if DV changes, notify neighbors

“Good news travels fast”

At time t0, y detects the link-cost change, updates its DV, and informs its
neighbors.

At time t1, z receives the update from y and updates its table. It computes a
new least cost to x and sends its neighbors its DV.

At time t2, y receives z’s update and updates its distance table. y’s least costs
do not change and hence y does not send any message to z.

x z
4 1
50
y
1
Stan Kurkovsky

Distance Vector:
link cost changes

Link cost changes:

good news travels fast

bad news travels slow - “count to infinity” problem!

44 iterations before algorithm stabilizes

Poissoned reverse:

If Z routes through Y to get to X :

Z tells Y its (Z’s) distance to X is infinite (so Y won’t route to X via Z)

will this completely solve count to infinity problem?
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Dijkstra's algorithm

Dijkstra's algorithm

From Wikipedia, the free encyclopedia
Not to be confused with Dykstra's projection algorithm.
Dijkstra's algorithm
Dijkstra's algorithm runtime
Dijkstra's algorithm to find the shortest path between a and b. It picks the unvisited vertex with the lowest distance, calculates the distance through it to each unvisited neighbor, and updates the neighbor's distance if smaller. Mark visited (set to red) when done with neighbors.
Class Search algorithm
Data structure Graph
Worst case performance O(|E| + |V| \log|V|)

The algorithm exists in many variants; Dijkstra's original variant found the shortest path between two nodes,[2] but a more common variant fixes a single node as the "source" node and finds shortest paths from the source to all other nodes in the graph, producing a shortest-path tree.
For a given source node in the graph, the algorithm finds the shortest path between that node and every other.[3]:196–206 It can also be used for finding the shortest paths from a single node to a single destination node by stopping the algorithm once the shortest path to the destination node has been determined. For example, if the nodes of the graph represent cities and edge path costs represent driving distances between pairs of cities connected by a direct road, Dijkstra's algorithm can be used to find the shortest route between one city and all other cities. As a result, the shortest path algorithm is widely used in network routing protocols, most notably IS-IS and Open Shortest Path First (OSPF). It is also employed as a subroutine in other algorithms such as Johnson's.
Dijkstra's original algorithm does not use a min-priority queue and runs in time O(|V|^2) (where |V| is the number of nodes). The idea of this algorithm is also given in (Leyzorek et al. 1957). The implementation based on a min-priority queue implemented by a Fibonacci heap and running in O(|E|+|V|\log|V|) (where |E| is the number of edges) is due to (Fredman & Tarjan 1984). This is asymptotically the fastest known single-source shortest-path algorithm for arbitrary directed graphs with unbounded non-negative weights. However, specialized cases (such as bounded/integer weights, directed acyclic graphs etc) can indeed be improved further as detailed in § Specialized variants.
In some fields, artificial intelligence in particular, Dijkstra's algorithm or a variant of it is known as uniform-cost search and formulated as an instance of the more general idea of best-first search.[4]


Algorithm

  • Assign to every node a tentative distance value: set it to zero for our initial node and to infinity for all other nodes.
  • Set the initial node as current. Mark all other nodes unvisited. Create a set of all the unvisited nodes called the unvisited set.
  • For the current node, consider all of its unvisited neighbors and calculate their tentative distances. Compare the newly calculated tentative distance to the current assigned value and assign the smaller one. For example, if the current node A is marked with a distance of 6, and the edge connecting it with a neighbor B has length 2, then the distance to B (through A) will be 6 + 2 = 8. If B was previously marked with a distance greater than 8 then change it to 8. Otherwise, keep the current value.
  •  When we are done considering all of the neighbors of the current node, mark the current node as visited and remove it from the unvisited set. A visited node will never be checked again.
  • If the destination node has been marked visited (when planning a route between two specific nodes) or if the smallest tentative distance among the nodes in the unvisited set is infinity (when planning a complete traversal; occurs when there is no connection between the initial node and remaining unvisited nodes), then stop. The algorithm has finished.
  • Otherwise, select the unvisited node that is marked with the smallest tentative distance, set it as the new "current node", and go back to step 3.
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Write down the network layer design issues

Network Layer : The layer that responsible source to destination to delivery of packet
multiple network is called network layer.

Characteristics :
i) Logical addressing
ii) Routing
iii) Connecting different network.


The network layer design issues :

1) Store and formed packet switching.

2) Service provided to the transport layer.

3) Implementation of connectionless service. 

4) Implementation of connection-oriented source.

5) Comparison of virtual circuit and datagram submits.


1) Store and formed packet switching : 
                                                           Store and forward operation : -
i) Host transmits packet to router across LAN or oval point to point link.

ii) Packet is stored on router until fully arrived and processed.

iii) Packet is forward to next router.

2) Service provide to transport layer : 
                                                          The network layer services have been designed with the goals : -

i) The advice should independent of router telenet

ii) The transport layer should be shilded from the number type and topology of the router present.

iii) The network addresses maid arailable to transport 


3) Implementation of connectionless service : 
                                                                    Connectionless service is offered packets are injected into the subnet individually and routed idependently of each other. Each packet is transmitted idenpendently.

Connectionless service used in network layer ID and transport layer.

Packet are frequently called datagram connectionless service is largly for data communication the internet.


4) Implementation of connection-oriented service : -

Connection-oriented service is used a path from the source router to the destination router must be established before any data packet can be sent.

                 Connection oriented service also called virtual circuit service. This service used network layer for ATM. It also used in transport layer for TCP.


A connection must be established before any can be sent packets order preserved logical connection is also established here. 



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Wednesday, March 30, 2016

Name the ATM layers and their functions or, Different function of different ATM layer

ATM : 
            ATM stands for Asynchronous Transfer mode. It is a stream line packet transfer interface that makes the use of fixed size packet called cells.It results in an efficient method for transmission over high speed network. It also known as cell relay. It is a connection oriented network.

Features : 

(1) ATM involves the transfer of data in discrete chunks/cells

(2) ATM allows multiple logical connection to be multiplexed over a single physical interface.

(3) ATM is a stream line protocol with minimal or minimum error and flow control capabilities.

(4) It provides high data rate ranging 25-6Mbps to 622Mbps.

(5) It is switable for high data traffic

(6) Reliability and fidelity of modern digital facilities.


Name of the ATM Layer : 

                                              ATM uses a different protocol architecture than of frame relay, X.25 etc.
It has four different layer and three different management plane.


Layer :
             It consists three layer. These are : 

(i) Physical layer    

(ii) ATM layer   

 (iii)  ATM Adaptive layer


i) Physical Layer :
                                 Physical layer defines the specification of transmission medium and signal encoding mechanism.It also specifies data rate, bit timing roltages and various other issues.

ii) ATM Layer : 
                           ATM layer defines the transmission of data in a fixed size cell. It also defines the mechanism of logical connection. if provides the layout of a cell and its header format. It has the packet transfer capabilities and condition control.

iii) ATM Adaption Layer :
                                                The layer above the ATM layer allows the user to send packet layer than a cell. This layer segmentic the packet that are transmitted and reassembless them at the other and this layer individually take care of every layer cell.

The AAL modes higher layer information into the ATM cells and called information from ATM cells to deliver in the higher layer.

Plane : 
              It has three planes. There are : -

i) User Plane

ii) Control Plane

iii) Management Plane



i) User Plane :
                           It deals with data transport flow control error control and other user transmitions.

ii) Control Plane :
                                           It deals with connection control and flow and error control.

iii) Management Plane :
                                           It deals with plane management performs the management function related to the systems as a where it also provide and destination between the plane.  


 
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Describe Issues for network layer

Describe Issues for network layer : 

1)Addressing : 
                           *Specify a specific destination

2) Data transfer :
                               *Data only travel in one direction

                               *In other data can go both nays

3) Error Control : 
                                *Here Physical communication circuits are not  perfect.

                                *many error detecting and error connecting codes are known but data ends of tree connection must agree on which one is used.

4) Flow Control : 
                               *Of every level is try how to trees a fast sender frame swamping a slow receiver with data.

                               *Some involves tinds of feedback from receiver to tree sender either directly or indirectly about tree receiver  current situation.
                             
                                *Other, tree sender agreed on transmission, this process is flow control

5) Multiplexing and Demultiplexing :
                                                                  *When it is expensive to set up a separate connection for each pair of communicating, process tree underlying layer may deside to use tree same connection for multiple and demultiple.

6) Routing : 
                          *When tree are multiple data between source and destination a route must be choose.

                           *Sometimes tree decission must be split over two or move layers.


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Data Encryption Algorithm

Data Encryption Algorithm : The main purpose of encryption algorithm is to provide the following :-

1) Authentication : Provide one's identity before granting access.

2) Privacy and confidentiality : Ensure that outsides cannot read data intended for specific parties.

3) Integrity : Ensure that message has not be modified in any way before it arrives to tree intended recipient.

4) Non-repodiation : Ensure that message is truly originated from tree sender.

Data Encryption Prons/Advantages : 

*  Separation 

* No data breack

* Encryption is on tree data

* Encryption equals confidentiability


Data Encryption Cons/Disadvantages : 

* Encryption keys

Expense

* Unrealistic requirements

* Compatibility
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What is Data Encryption?Types of Encryption

Data Encryption : Data encryption is the act of changing electronic information into an unreadable state by using algorithms or ciphers. Originally, data encryption was used for passing government and military information electronically. Over time as the public has begun to enter and transmit personal, sensitive information over the internet, data encryption has become more widespread. Nowadays web browsers will automatically encrypt text when connecting to a secure server. You can tell you are on a secure, encrypted website when the URL begins with "https", meaning Hypertext Transmission Protocol, Secure.


There are three basic encryption methods: hashing, symmetric cryptography, and asymmetric cryptography. Hashing, for example, is very resistant to tampering, but is not as flexible as the other methods. All three forms of encryption rely on cryptography, or the science of scrambling data.

Hashing Encryption :

The first encryption method, called hashing, creates a unique, fixed-length signature for a message or data set. Hashes are created with an algorithm, or hash function, and people commonly use them to compare sets of data. Since a hash is unique to a specific message, even minor changes to that message result in a dramatically different hash, thereby alerting a user to potential tampering.

Symmetric Methods :

Symmetric cryptography, also called private-key cryptography, is one of the oldest and most secure encryption methods. The term "private key" comes from the fact that the key used to encrypt and decrypt data must remain secure because anyone with access to it can read the coded messages.

Asymmetric Forms :

Asymmetric, or public key, cryptography is, potentially, more secure than symmetric methods of encryption. This type of cryptography uses two keys, a "private" key and a "public key," to perform encryption and decryption.
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What are these application of Bluetooth?

 These application of Bluetooth :

i) Headset

ii) Handsgree telephony

iii) Stereo quality audio video

iv) Digital camera to a TV

v) Portable musical player to head phone.
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