osi network model layers€¦ · in the seven-layer osi model of computer networking, the network...
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Introduction to Network Layer
OSI Network Model Layers
Hakan Murat SAĞLAM2009513018
EEE 448 Computer Networks Class
Network Layer (Layer 3)
In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers, since it knows the address of neighboring network nodes, and it also manages quality of service (QoS), and recognizes and forwards local host domain messages to the Transport layer (layer 4). The data link layer (layer 2) is responsible for media access control, flow control and error checking.
The network layer provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host via one or more networks, while maintaining the quality of service functions.
Wikipedia
The main tasks of the network layer is one of providing cross-network addresses, the routing and the construction and updating of routing tables and the fragmentation of data packets. But the negotiation and ensure a certain quality of service falls within the remit of the network layer.
Popular Network Layer Protocols
DDP Datagram Delivery Protocol
DVMRP Distance Vector Multicast Routing Protocol
ICMP Internet Control Message Protocol
IGMP Internet Group Management Protocol
IPsec Internet Protocol Security
IPv4/IPv6 Internet Protocol
IPX Internetwork Packet Exchange
PIM-DM Protocol Independent Multicast Dense Mode
PIM-SM Protocol Independent Multicast Sparse Mode
RSMLT Routing Information Protocol
Shortest Path Bridging
TCP/IP Model
The OSI Model we just looked at is just a reference/logical model. It was designed to describe the functions of the communication system by dividing the communication procedure into smaller and simpler components. But when we talk about the TCP/IP model, it was designed and developed by Department of Defense (DoD) in 1960s and is based on standard protocols. It stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a concise version of the OSI model. It contains four layers
Protocol Data Unit (PDU)
Sample Datalink Frame and Sample Outgoing E-Mail Frame
Router
A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. Data sent through the internet, such as a web page or email, is in the form of data packets. A packet is typically forwarded from one router to another router through the networks that constitute an internetwork until it reaches its destination node.A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the network address information in the packet to determine the ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey.
Routing Algorithm
A routing algorithm is a set of step-by-step operations used to direct Internet traffic efficiently. When a packet of data leaves its source, there are many different paths it can take to its destination. The routing algorithm is used to determine mathematically the best path to take.
Different routing algorithms use different methods to determine the best path. For example, a distance vector algorithm calculates a graph of all available routes by having each point (called a node) determine the "cost" of travelling to each immediate neighbor. This information is collected for every node to create a distance table; which is used to determine the best path to from any one node to another.
Routing TableA routing table is a set of rules, often viewed in table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed. All IP-enabled devices, including routers and switches, use routing tables.
A routing table contains the information necessary to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination. When a packet is received, a network device examines the packet and matches it to the routing table entry providing the best match for its destination. The table then provides the device with instructions for sending the packet to the next hop on its route across the network.
Routing TableNetwork Address: The destination address has four parts: host address, subnet mask, network address and default gateway.
Netmask: Netmask is the most important entry in a routing table. It is used to decide the portion of the network address that matches the route to be accessed.
Gateway: This is the address of the router or local network card. It is used as the exit and entrance point to the network or PC.
Interface: This network card's address, which is used as a destination. Other devices over a network use the interface to send the data.
Metric: In networks, a metric is used to choose and determine the best route from source to destination. It is sometimes called a hop counter. Within a local area network, usually only one hop is counted.
IP Address Basics
An IP address is a number identifying of a computer or another device on the Internet. It is similar to a mailing address, which identifies where postal mail comes from and where it should be delivered. IP addresses uniquely identify the source and destination of data transmitted with the Internet Protocol.
IPv4 and IPv6 Addresses
IPv4 addresses are 32 bits long (four bytes). An example of an IPv4 address is 216.58.216.164, which is the front page of Google.com.
The maximum value of a 32-bit number is 232, or 4,294,967,296. So the maximum number of IPv4 addresses, which is called its address space, is about 4.3 billion. In the 1980s, this was sufficient to address every networked device, but scientists knew that this space would quickly become exhausted. Technologies such as NAT have delayed the problem by allowing many devices to use a single IP address, but a larger address space is needed to serve the modern Internet.
A major advantage of IPv6 is that it uses 128 bits of data to store an address, permitting 2128 unique addresses, or 340,282,366,920,938,463,463,374,607,431,768,211,456. The size of IPv6's address space — 340 duodecillion — is much, much larger than IPv4.
IP Address ClassesWith an IPv4 IP address, there are five classes of available IP ranges: Class A, Class B, Class C, Class D and Class E, while only A, B, and C are commonly used. Each class allows for a range of valid IP addresses, shown in the following table.
Class Address range Supports
Class A 1.0.0.1 to 126.255.255.254
Supports 16 million hosts on each of 127 networks.
Class B 128.1.0.1 to 191.255.255.254
Supports 65,000 hosts on each of 16,000 networks.
Class C 192.0.1.1 to 223.255.254.254
Supports 254 hosts on each of 2 million networks.
Class D 224.0.0.0 to 239.255.255.255
Reserved for multicast groups.
Class E 240.0.0.0 to 254.255.255.254
Reserved for future use, or research and development purposes.
Ranges 127.x.x.x are reserved for the loopback or localhost, for example, 127.0.0.1 is the loopback address. Range 255.255.255.255broadcasts to all hosts on the local network.
Static vs. Dynamic IP Addresses
IP addresses are assigned in two different ways. They may be dynamically assigned (they can change automatically) or statically assigned (they're intended not to change, and must be changed manually). Most home networks use dynamic allocation. Your router uses DHCP(Dynamic Host Configuration Protocol) to temporarily assign, or "lease," an IP address to your device. After a period of time, this lease "expires," and the router renews your old address or assigns you a new one, depending on the needs of the network and the configuration of the router.
How data is sent to an IP address on another network
The diagram illustrates how your home computer might obtain an IP address and send data to an IP address on another network.
Thank you for listening.References we get support
https://osi-model.com
İTÜ Bilgisayar Mühendisliği Bölümü Dr. Sema Oktuğ Protokoller ve Katmanlı Yapı: OSI, TCP/IP Referans Modelleri
https://www.cozumpark.com/routing-temelleri-yonlendirme-temelleri/
https://www.aboutdebian.com/network.htm
https://www.slashroot.in/difference-between-segments-packets-and-frames
https://www.computerhope.com/jargon/r/routing-algorithm.htm
https://searchnetworking.techtarget.com/definition/routing-table
https://www.techopedia.com/definition/13207/routing
https://www.ilkertemir.com/index.php?s=IP+Yonlendirme
https://www.computerhope.com/jargon/i/ip.htm
Questions?
Hakan Murat Sağlam
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I would also like to thank Doç. Dr. Turgay İBRİKÇİ