Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level 7 Message : Balqis Please Help Me Identify sender and intended reciever , is there an e-mail app available? Send as electrical signal over category 5 copper wiring at X volt and X Mbps Keep track of how many hops; open the shortest path first ; go to Ip address 192.168.1.2 Make sure all data has arrived intact Inititate and terminate the session according to X protocol Decode data with X decoding key ; use ASCII characters Is the initial connection set up? Put data into frames according to X standard Balqis Please Help Me Identified sender and intended receiver , found available e-mail app. Send as electrical signal over category 5 copper wiring at X volt and X Mbps Keep track of how many hops; open the shortest path first ; go to Ip address 192.168.1.2 Make sure all data has arrived intact Inititated and terminated the session according to X protocol Decode data with X decoding key ; used ASCII characters Initial connection is set up. Decoding data in frames according to X standard
At the receiving node, the layered process that sent the message
on its way is reversed.
The physical layer recalculates the checksum, confirms arrival, and logs in packets.
The network layer recounts incoming packets for security.
The transport layer recalculates the checksum and reassembles the message segments.
The session layer holds the parts of the message until it is complete and sends it to the next layer.
The presentation layer decrypts, expands, and translates the message.
The application layer identifies the recipient, converts the bits into readable characters, and directs the data to the correct application.
INTERMEDIATE NODES An intermediate node calculates and verifies the checksum for each packet. A router might also reroute the message to avoid congestion on the network.
PHYSICAL LAYER The physical layer encodes the packets into the medium that will carry them – such as an analog signal, if the message is going across a telephone line – and sends the packets along that medium.
Provide means for bits to be transmitted across physical com. path.
Defines the electrical and mechanical requirement of com. sys.
Eg. Type of cable to be used, type of connectors to be employed, the bit rate(s) and signal levels to be used.
Defines topology of network
Eg. Bus or ring
DATA-LINK LAYER The data-link layer supervises the transmission. It confirms the checksum, and then addresses and duplicates the packets. This layer keeps a copy of each packet until it receives confirmation from the next point along the route that the packet has arrived undamaged.
Responsible for the source-to-destination delivery of a packet possible across multiple network(links)
Not necessary for 2 sys. in the same network/link.
Adding logical add. (on different network/link) of sender and receiver.
When independent networks or links are connected together to create an internetwork (a network of networks) /a large network, the connecting devices(called routers/gateways ) route the packets to their final destination.
TRANSPORT LAYER The transport layer protects the data being sent. It subdivides the data into segments and creates checksum tests- mathematical sums based on the contents of data- that can be used later to determine whether the data was scrambled. It also makes backup copies of the data. The transport header identifies each segment’s checksum and its position in the message
Responsible for source-to-destination (end-to-end) delivery of the entire message.
Network layer oversees end-to-end delivery of individual packet
Ensure that the whole message arrives intact in order
Adding port add./ service-point add . (process (running prog.) add.) of sender and receiver.
Ensures frames arrive at the destination in their correct order
Provide end-to-end correction and data flow.
SESSION LAYER The session layer opens communications. It sets boundaries (called brackets) for the beginning and end of the message and establishes whether the message will be sent half duplex , with each computer taking turns sending and receiving, or full duplex , with both computers sending and receiving at the same time. The details of these decisions are placed into a session header.
Handles logon and logoff procedures and then it established, and later clear down, the connection between two terminals.
Controls the transfer of messages over network and overall error detection.
Controls how a message starts and finishes.
PRESENTATION LAYER The presentation layer translates the message into a language that the receiving computer can understand (often ASCII, a way of encoding text as bits). This layer also compresses and perhaps encrypts the data. It adds another header specifying the language as well as the compression and encryption schemes.
Concerned with the syntax and semantics of the info. exchange between two sys.
To translate, encrypt, and compress data
APPLICATION LAYER For a message, file, or any other data to travel through a network, it must pass through several layers, all designed to make sure the data gets through intact and accurate. The first layer, the application layer, is the only part of the process a user sees, and even then the user doesn’t see most of the work the application does to prepare a message for sending over a network. The layer converts a message’s data into bits and attaches a header identifying the sending and receiving computers.