TocH Institute of Science & Technology
Time:2Hr Computer Science & Engineering Max Marks : 50
Code:CS 802 Subject: Distributed Computing RegNo:………………..
PART A
Answer all questions
Each question carries 3 marks
Solution set
1. What are the two variants of the interaction model?
Synchronous
Asynchronous
In synchronous systems, time to execute each step, message transmission
time and local clock drift rates are within certain bounds ,where as in
asynchronous, these parameters has no bounds.
2. Differentiate between Mobile Devices and Mobile Agents.
Mobile Agent is a running program including code and data that
travels from one computer to another in a network carrying out a task on
someone’s behalf , such as collecting information eventually returning with
results, where a mobile device is a physical tangible entity.
3. Differentiate between process omission failure and communication
omission failure.
A process crash is related to POF.
COF – if it deosn’t transmit a message from sender’s buffer to receiver
buffer
4. What is a ROR?
When a client wants to invoke a method in remote object, a remote object
reference (ROR) is send along with an invocation message in order to
specify which object is to be invoked.
5. Differentiate between marshalling and unmarshalling.
Marshalling is the process of taking a collection of data items and
assembling them into a form suitable for transmission in a meassage.
Unmarshalling is a process of disassembling them on arrival to produce
an equivalent collection of data items at the destination
6. Differentiate between RPC and LRPC.
Instead of RPC parameters being copied from kernel and user address
space involved, client and server are able to pass arguments and return
values directly via an Argument stack or A stack. The same stack is used
by client and server stubs. In LRPC, arguments are only copied once,
when they are marshaled into A stack. In an equivalent RPC, they are
copied 4 times: from the client stub into a message, from the message
into a kernel buffer, from the kernel buffer to the server message, from
the message to server stub’s stack.
7. What do you mean by copy-on-write?
Suppose a memory region is shared by 2 processes P1 and P2. Initially all
page frames assosciated with the region are shared between 2 processe’s
page tables. If a thread in either process attempts to modify the data , a
hardware exception called page fault is generated. Lets say process P2
attempted the write. The page fault handler allocates a new frame for
process P2 and copies the orginal frame data into it byte for byte. The old
frame number is replaced by new frame number in one process’s page
table and old page frame no is left in other process’s page table. The two
corresponding page in processes P1 and P2 are then each made writable
once more at the hardware level. After this, process P2’s modifying
instruction is allowed to proceed.
See fig in text (Page 233)
8. What do you mean by a null RPC?
A null RPC is defined as an RPC without parameters that executes a null
procedure and returns no values. They measure a fixed overhead, the
latency. The total RPC call time experienced by a client , has to be
accounted for the actions of the OS and user –level RPC run time code
9. Explain the relationship between RPC delay and packet size.
The delay is roughly proportional to the size until the size reaches at about
network packet size. Beyond that at least one packet has to be sent , to carry
the extra data and delay increases rapidly.
See fig in text (Page 249)
10. What are the different types of transparencies that are related to
distributed file system?
Access: Program written to operate on local files are able to access remote
files without modification
Location: Client program should see a uniform file name space
Mobility: Neither client programs or system administration tables may be
changed when files are moved
Performance: Client program should perform satisfactorally when load on
the service varies within a specified range
Scaling: The service can be exapanded with a incremental growth to deal
with a range of loads and network sizes.
PART B
Answer any two questions
Each question carries 10 marks.
11. Explain the implementation of RMI in detail.
12. Explain interprocess communication in Unix in detail .
13. Explain the File Service Architecture of a Distributed File System in
detail .
************ All the best ***********