Group9_deadlock:GO BACK N ARQ contd..

Go-Back-N ARQ is a more efficient use of a connection than Stop-and-wait ARQ, since unlike waiting for an acknowledgement for each packet, the connection is still being utilized as packets are being sent.
In other words, during the time that would otherwise be spent waiting, more packets are being sent. However, this method also results in sending frames multiple times, if any frame was lost or damaged, or the ACK acknowledging them was lost or damaged, then that frame and all following frames in the window (even if they were received without error) will be re-sent. To avoid this, Selective Repeat ARQ can be used.

Selective Repeat ARQ: The receiver process keeps track of the sequence number of the earliest frame it has not received, and sends that number with every ACK it sends. If a frame from the sender does not reach the receiver, the sender continues to send subsequent frames until it has emptied its window. The receiver continues to fill its receiving window with the subsequent frames, replying each time with an ACK containing the sequence number of the earliest missing frame. Once the sender has sent all the frames in its window, it re-sends the frame number given by the ACKs, and then continues where it left off.

Group9_deadlock:GO BACK N ARQ

Go-Back-N ARQ is a specific instance of the Automatic Repeat-reQuest (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an ACK packet from the receiver.

The receiver process keeps track of the sequence number of the next frame it expects to receive, and sends that number with every ACK it sends. The receiver will ignore any frame that does not have the exact sequence number it expects, whether that frame is a past duplicate of a frame it has already ACK’ed, or whether that frame is a future frame past the lost packet it is waiting for. Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to sequence number of the last ACK it received from the receiver process and fill its window starting with that frame and continue the process over again.
NOTE:
1) Packets transmitted continuously (when available) without waiting for ACK, up to N outstanding, un ACK’ed packets.

2) Receiver:
-ACK packet if correctly received and in-order, pass to higher layer.
-NACK or ignore (possibly discard) corrupt or out-of-order packet.

3) Sender :
-If NACK received, or timeout, for packet n, begin resending from n all aver again
-Cumulative ACK: ACK of n implicitly acknowledges up through n.

group9_deadlock:notes on GO BACK N

there are following features of GO BACK N.
• Requires no buffering of packets at the receiver.
• Window size = N
– Sender cannot send packet i+N until it has received the ACK for packet i.
• Receiver operates just like in Stop and Wait.
– Receive packets in order
– Receiver cannot accept packet out of sequence
• The transmitter has a “window” of N packets that can be sent without acknowledgments.
• Sender must buffer up to N packets while waiting for their acknowledge.
• Sender must re-send entire window in the event of an error.
• Packets can be numbered modulo M where M > N.
– Because at most N packets can be sent simultaneously.
• Receiver can only accept packets in order.
– Receiver must deliver packets in order to higher layer
– Cannot accept packet i+1 before packet i
– This removes the need for buffering
– This introduces the need to re-send the entire window upon error
• The major problem with Go Back N is this need to re-send the entire window when an error occurs. This is due to the fact that the receiver can only accept packets in order

group9_deadlock:GO BACK N ARQ

Go-Back-N ARQ is a specific instance of the Automatic Repeat-request (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an acknowledge packet from the receiver.
Go Back N allows the transmission of new packets before earlier ones are acknowledged. It uses a window mechanism where the sender can send packets that are within a “window” (range) of packets.
The receiver process keeps track of sequence number of the next frame it expects to receive, and sends that number with every acknowledge it sends. The receiver will ignore any frame that does not have the exact sequence number it expects whether that frame is a “past” duplicate of a frame it has already acknowledged or whether that frame is a “future” frame past the last packet it is waiting for. Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to sequence number of the last acknowledge it received from the receiver process and fill its window starting with that frame and continue the process over again.

Group9_deadlock:interaction blog

topic:- ip utilities

q 1) why cant ip address stored on datalink layer (q asked – anita bs)
ans) The datalink layer is hardware and contents cannot be changed, as ip address are dynamically assigned using reference of subnet mask and host default gateway it cant be stored on datalink layer( ans by bhaskar)

q 2) how does port number signify the domain? (q by ankan adhikari)
ans) every protocol has a unique port number, they differ for different domains, eg http is 80 as default, ftp as 21, and ftp for .org varies. so each domain like .net, .chinchic(china), .org, .uk, .in will have respective port numbers.( answer by bhaskar)

q 3) what do you mean by multi homing??(q by murgesh kalyani)
ans) Multihoming is a method to increase the reliability of the IP address. in this method we assigned multiple IP address to a connection end SCTP,so that if one fails but all the connection will not fail. (answer by Lalit)

q 4) will the port number of domain be checked from the main server or other procedure? (q asked ankan adhikari)
ans) There will be a cache table which contains all the default and mainly used domains, so if its in this table then no problem, or else it has to go the main server and get the port number(answer by bhaskar)

q 5) will the MAC checked everytime it has to transfer data( by phanesh)
ans) yes it has to be checked each time (in correct)(by bhaskar)
The router will contain a arp cache table from where the MAC address is retrieved and directed to all the computers connected and the computer requested will accept the packet and the rest computer ignore it. process is called broadcasting

q 6) how will communication happen if we change our ip address to a proxy? (q by ramya)
ans) The communication happens basically from the subnet mask or default gateway, the subnet number is appended once data leave a router or a subnet mask,so even if ip address is changed to proxy the communication happens through the gate way address.(ans by bhaskar)

q 7) why are udp small packets?(q by nishitha)
ans)(incorrect answer) udp are small because it acts as connection oriented so that data is packed into large packet and sent together.
(correct ans) upd is connection less protocol used for faster communication. when we are watching video it has to come on time. if it comes late it has to be discarded.so the small packets are sent even if there is no connection.

Group9_deadlock:mandatory

Group name : deadlock

Member names:

bhaskar kumar b naidu-1ms07is014
dheeraj pai -1ms07is026
lalit kumar sharma -1ms07is040

Group A project : ip utilities

Group B project : Go back wait ARQ

Group A project presentation: Oct 7 2009 ( completed)

Group B project presentation: Nov 18 2009(not completed )

Group A project ppt uploaded : yes

Group B project ppt uploaded : No

Group A project report : No

Group B project report: No

Group A problems faced and solved : NO

Group B problems faced and solved : NO

Group9_Deadlock:Ppt

group9_dead lock:TCP/IP utilities

TCP/IP UTILITIES:

• ARP: ARP stand for Address Resolution Protocol. This provides IP to Ethernet addresses. Each hardware card has an address coded in. This allows deletion and addition to the ARP cache. The switches to be used can be obtained by just typing arp at a DOS command prompt. Displays and modifies entries in the Address Resolution Protocol (ARP) cache, which contains one or more tables that are used to store IP addresses and their resolved Ethernet or Token Ring physical addresses. There is a separate table for each Ethernet or Token Ring network adapter installed on your computer.
• Nbtstat: Displays the local NetBIOS name table, a table of NetBIOS names registered by local programs, and the NetBIOS name cache, a local cache listing of NetBIOS computer names that have been resolved to IP addresses. Ex- If you and your friend have WIN servers <the same or some that share> inserted in your network or connection setup and have log onto network checked then the Wins server will register you when you log on.  If the other person’s computer name is Alpha then typing Nbtstat -a Alpha will provide that computers IP address.
• Netstat: This utility provides the connection both the local and remote, ports and the state of the connection. It has several switches which maybe found by typing netstat /? from the command prompt. It provides the IP addresses and the ports of the remote computer(S) to which the socket is connected. If a port has not been established it is indicated by a *. It shows the the port numbers as well as IP address for the local computer. It provides the type of protocol being used for the connection(s). It provides a status of the connection. Is it established ?? is it closed ?? or is it waiting ?? and more.
• PING: This is a simple diagnostic tool to verify connection and also used quite frequently as a troubleshooting tools. The available switches can be obtained by typing ping from command prompt. Ping is the primary TCP/IP command used to troubleshoot connectivity, reachability, and name resolution. Is also used to keep connections alive. This is sometimes frowned upon. There are several utilities which will issue ping commands at regular intervals.
• Route: This command is very useful if using networking. It allows you to view and manipulate the routing tables. It is a very useful tool for diagnosing and modifying networking routing issues. It is what specifies where packages are sent to reach places. It is the first place to look when you run into problems like “host unreachable or not found” in a network environment.
• Tracert: This is a utility which allows you to see the route taken by packages from yourself to a destination. It also show the time it takes. It can also be used to determined the IP address of a service were you only know the name. It does this by sending out packets with varying TTL (time to live). Each way station along the route is supposed to decrease the TTL value by 1 before passing it on. When the count reaches Zero, the router will return respond to the sender that the time was exceeded. Thus, the first packet is sent with a TTL (hop count) of 1 and then incremented until the destination is reaches.
• Winipcfg: A very useful little utility. Use Start —->Run and type in winipcfg. It will tell you your present IP address and your subnet mask. If you click “more info” it will also provide the DNS (Domain names servers) and WINS servers if you have any.

GROUP9_dead lock:TCP/IP model v/s OSI model

Both OSI and TCP/IP reference models are based on the concept of a stack of protocols. The functionality of the layers is almost similar. In both models the layers are there to provide an end-to-end network independent
transport service to processes wishing to communicate with each other.

The Two models have many differences. An obvious difference between the two models is the number of layers: the OSI model has seven layers and the TCP/IP has four layers. Both have (inter) network, transport, and application layers, but the other layers are different. OSI uses strict layering, resulting in vertical layers whereas TCP/IP uses loose layering resulting in horizontal layers. The OSI model supports both connection less and connection-oriented communication in the network layer, but only connection-oriented communication at the transport layer. The TCP/IP model has only one mode in network layer (connectionless), but supports both modes in the transport layer. With the TCP/IP model, replacing IP by a substantially different protocol would be virtually impossible, thus, defeating one of the main purposes of having layered protocols in the first place.

group9_dead lock:Transmission control protocol

TCP is one of the main protocols in TCP/IP networks. TCP/IP was developed in the 1970s and adopted as the protocol standard for ARPANET (the predecessor to the Internet) in 1983.Whereas the IP protocol deals only with packets. TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.It is a popular network debugging tool used to intercept and display packets transmitted or received on a network.TCPdump is one of those tools that network and systems administrators alike reach for whenever they need to take a look at the actual network packets. The TCP/IP suite provides two transport methods and also ensures that data arrive intact and complete. It is used for everything that must arrive in perfect form.

The TCP transport layer 4 sends packets to IP network layer 3, which adds its own header and delivers a “datagram” to a data link layer 2 protocol such as Ethernet, ATM or SONET. Datagram is the unit of data or packet, transmitted in a TCP/IP network. Each datagram contains source and destination addresses and data.