Blocking Network :
A multistage network is called blocking if the simultaneous connections of some multiple input-output pairs may result in conflicts in the use of swwitches or communication links.
OMega, baseline,banyan and delta networks.
Some blocking networks are equivalent after graph transformations.In fact, most multistage networks are blocking in nature.In a blocking network, multiple passes through the network may be needed to achieve certain input-output connections.
Non Blocking Network :
A multistage network is called non-blocking if it can perform all possible connection path can always be established between any input-output pair.
Bens network and close network.
Distinguish between blocking and non-blocking message passing :
Blocking message passing Non-blocking message passing 1.Blocking message-passing are referred to as synchronous primitives. 1.Non-blocking message-passing are referred to as asynchronous primitives. 2.When a process calls send it specific a destination & a buffer to send to that destination. While the message is being sent, the sending process is blocked. . 2.If send is non-blocking it returns control to the caller immediately, before the message is sent. 3.faster than non-blocking because doesn't requires extra copy. 3.Slower than blocking technique. 4.CPU time doesn't waste for extra copy.But CPU idles during message transmission 4.CPU time doesn't waste for extra copy. 5.Sender can modify the message buffer until the message has been sent. 5.The sender can't modify the message buffer until the message has been sent. 6.Generally, blocking send without interrupt i.e makes programming simple. 6.Sends with interrupt(makes programming difficult).
Distributed system :
A distributed system is a collection of independent computers that appear to the users of the system as a single computer.That is , distributed system consists of autonomous CPU that work together to make the complete system look like a single computer.Explain with example :
1. As a first example, consider a network of workstations in a university or company department.
2.Second example, consider a factory full of robots, each containing a powerful computer for handling vision, planning, communication and other tasks.
3.Third example, think about a large bank with hundreds of branch of offices all over the world. Each office has a master computer to store local accounts and handle local transactions.
Difference between loosely coupled & tightly coupled system :
Loosely coupled System Tightly coupled System 1.In a loosely coupled system, the inter machine message delay is large & the data rate is low. 1.In Tightly coupled system, the delay time short & the data rate is high. 2.The number of bits per second that can be transferred is short. 2.The number of bits per second that can be transferred is large 3.In loosely coupled ones tend to be used as distributed systems. 3.Tightly-coupled systems tend to be used more as parallel systems. 4.Example:Two computers connected by a 2400 bit/sec modem over the telephone system are certain to be loosely coupled. 4.Example : Two CPU chips on the same printed circuit board and connected by wires etched onto the board are likely to be tightly coupled.
Distinguish between connection-oriented protocol & connectionless network :
connection-oriented protocol connectionless network 1.Connection oriented protocol establishes a virtual circuit. 1.Connectionless mode protocol establishes a datagram. 2.With connection mode, the network can't agree to handle packets idependently. 2.With connectionless mode, the network only agree to handle packets idependently 3.The reliability & convenience of a connection mode is more attractive than the benefits of connectionless mode. 3.The reliability & convenience of a connectionless mode is less attractive than the benefits of connection mode. 4.Example : Connection oriented approach is the X.75 standard used in the telephone system.. 4.Example : The connectionless approach using IP & dropping letter in a mailbox. 5.Sequencing maintains to transfer data. 5.Don't maintain any sequence to transfer data.
Distinguish between frequency division & time division multiplexing :
Frequency division multiplexing Time division multiplexing 1.Frequency division multiplexing(FDM) is an analog technique that can be applied. When the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted. 1.Time division multiplexing(TDM) is a digital technique that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending & receiving devices. 2.In FDM, signals generated by each sending device modulate different carrier frequencies. These modulated signals are the combined into a single composite signal that can be transmitted by the link . 2.In TDM, multiple transmission can occupy a single links by subdiving them & interleaving the portions. 3.FDM is generally used a radio or television set. 3.TDM is generally used for multiplexing digitized voice streams & data streams. 4.Guard bands keep the modulated signals from overlapping & interfering with one another. 4.Guard's bands aren't organized.
The drawback of Remote Procedure Call(RPC) :
In RPC, pointers & complex data s tructures are hard to pass
Global variables are difficult to use.
The extraxt semantics of RPC are tricky because clients & servers can fail independently of one another.
Implementing RPC efficiently is not staightforward & requires careful throught.
The failure occur in RPC systems :
1.The client is unable to locate the server.
2.The request message from the client to the server is lost.
3.The reply message from the server to the client is lost.
4.The server crashes after receiving a request.
5.The client crashes after sending a request.
Coordinate Universal Time(UTC) :
An external time source that is often used as a reference for synchronization computer clocks with real time is the Coordinated Universal Time(UTC). The UTC is an international standard .May standardbodies disseminate UTC signals by radio, telephone,and satellite.For instance, the WWW radio station in the United States and the Geostationary Opeartional Environmental Satellite(GEOS) are two such standard bodies.Commercial devices(called time providers) are available to receive and interrupt these signals.Computers equipped with time provider devices can synchronize their clocks with these timing signals.
Distributed deadlock :
Two kinds of distributed deadlocks : communication deadlocks and resource deadlock. A communication deadlock occurs, for example, when process A is trying to send a message to processn B, which in turn is trying to send one to process C, which trying to send one A.There are carious scenarios in which this situation leads to deadlock, such as no bufer being available.A resource deadlock occurs when processors arr fighting over exclusive access to I/O devices, files, locks, or other resources.
The difference between UMA & NUMA model :
UMA Model NUMA Model 1.In a UMA multiprocessor modl, all processors uniformaly share the physical memory. 1.A NUMA multiprocessor is a shared-memory system in which the access times various with the location of the memory word. 2.All processors have equal access time all memory words, which is why it is called uniform memory access . 2.The shared memory is physically distributed to all processors, called local memories. 3.Each processor may use a private cache. 3.Cache memory doesn't involve. 4.Example : sequent symmetry S-81. 4.Example : BBN Butterfly & The cadre System.
The difference between CRCW & ERCW :
CRCW ERCW 1.Allows either concurrent reads or concurrent writes at the same time. 1.Allows either exclusive read or concurrent writes to the same memory location. 2.CRCW model is the most popular. 2.ERCW is less popular than CRCW model. 3.CRCW algorithm runs faster than an equivalent ERCW algorithm. 3.ERCW algorithm is slower than an equivalent CRCW algorithm. 4.Writing conflicts are occurred in CRCW model. 4.Writing conflicts are occurred in ERCW model.
Grain Packing :
When a program is partitioned into little parts, then each part of that program is called gain.
Suppose there are 100 instructions in a program.Now it is partitioned into 5 parts. In this condition it means that the number of grains is 5 and the grain size is 20.
After grain packing task, we have to decide which grain will execute after one grain i.e.We have to maintain here here a scheduling process of grain execution of the program. This process is known as scheduling.
Clock synchronization :
Every computer needs a timer mechanism to keep track of current time and also for various accounting purposes such as calculation the time spent by a process in CPU utilization, disk I/O and so on. So that the corresponding user can be charged properly.
Clock synchronization is needed :
In a distributed system, an application may have processes that concurrently run on multiple nodes of the system.For correct results, several such distributed applications require that the clocks of the nodes are synchronized with each other.
In a distributed system, synchronized clocks also enable one to measure the duration of distributed actibities that start on one node and terminate on another node.
For instance, calculating the time taken to transmit a message from one node to another at any arbitary time.
The disadvantages of Tokn ring algorithm :
Process failure : A process failure the system cause the logical ring to break.In such a situation, a new logical ring must be established to ensure the continued circulation of the token among other process.
Lost token : If the token is lost, a new token must be generated.Therefore, the algorithm must also have mechanisms to detect and regenerated a lost toke.One method to solve this problem is to designate one of the process on the ring as a "monitor process.
Coordinator failure : When the coordinator coodinates all the nodes within the token, then some problem of network some time the coordinator may fail.