Networking (OSI, TCP/IP)

IP address

Today we use IPv4 address.
  1. Private address
  2. Loopback address: 127.0.0.0 - 127.255.255.255. (Commonly used 127.0.0.1)
  3. Multicast Address: 224.0.0.0 - 239.255.255.255. (data sent to many but not all)
  4. Experimental use: 240.0.0.0 - 255.255.255.255.

Data flow in IP address

When we get internet connection through Router to computer/mobile, the ISP assigns a public IP address with port number (ex. 12.13.14.15:12345) to the WAN port of the router. Then the router will generate a private IP address for itself and for all other devices connected to this router through LAN port of the router. This private IP of the router is called the Default Gateway. If the private IP is of class C range (192.168.x.x), then first 3 octet of any private IP and default gateway will be same (which is network id).

In IPv4 addressing we use both idea of classful and classless addressing (VLSM). Look at the above image and consider my IP address is 192.168.1.152. It is class C address. So the mask/subnet mask will be 255.255.255.0. Hence, we find the network address 192.168.1.0. Network address is used to identify the network. It is not assigned to the router. When a data packet comes to the router, then the router matches the network address with it's routing table.

  • Class A - Mask 255.0.0.0
  • Class B - Mask 255.255.0.0
  • Class C - Mask 255.255.255.0
Subnet mask is used for sub network of VLSM.

So the first address (192.168.1.0) is the network address and the last address 192.168.1.255) is the broadcast address for this network.

Variable Length Subnet Masking (VLSM)

Consider, an administrator have 192.168.1.0/24 network. Mask is 24 bit. It have three different departments:

Step - 1: 

Make a list of Subnets possible. If you decide for Class C sub-netting then your list will be below:

Step - 2:

Sort the requirements of IPs in descending order (Highest to Lowest).
  1. Sales 100
  2. Purchase 50
  3. Accounts 25
  4. Management 5

Step - 3:

Allocate the highest range of IPs to the highest requirement, so let's assign 192.168.1.0 /25 (255.255.255.128) to Sales department. And then repeat this step.
Total no. of hosts = 2n-1.

NAT and PAT


Video URL: https://www.youtube.com/watch?v=QBqPzHEDzvo

OSI model

There are seven layers in OSI (Open System Interconnection) model:
  • 7. Application (HTTP, HTTPS, FTP, DHCP, SMTP, Telnet, POP3)
  • 6. Presentation (Translation, Compression, Encryption)
  • 5. Session (Authentication, Authorization)
  • 4. Transport (TCP, UDP)
  • 3. Network (IP)
  • 2. Datalink (MAC address)
  • 1. Physical
Functions of top three layers is done by operating system. Switching network are of two types:
  • 1. Circuit switching: Channel will be dedicated. Connection oriented. Example - Telephone network.
  • 2. Packet switching: No dedicated channel. Connection less. Data are divided into packet. Example TCP/IP internet.

  • 1. Connection oriented: Acknowledgement signal is sent by receiver computer.
  • 2. Connection less: No Acknowledgement.

Though TCP & UDP both are used in internet (which is connection less), TCP is connection oriented. MAC address is used for data communication in the same network.
Video URL: https://www.youtube.com/watch?v=vv4y_uOneC0

Network devices

  • Repeater: Repeater is used to transmit signal to a remote place. Repeater increase the strength of a weak signal to it's original state. It is a two port devices.
  • Hub: Hub is similar to Repeater except Hub has more than two port. Signal coming through any port is broadcasted to all other ports. Used in a LAN.
  • Bridge: Two port device. It can Identify MAC address. It works on Datalink layer of OSI model. It connects two LANs.
  • Switch: Similar to Bridge except Switch has more than two port. Signal coming through any port is passed to a single destination ports because it can identify MAC address. It is used in a single LAN. It connects multiple multiple devices to form a LAN.
  • Router: It connects two or more similar (Same protocol) networks. It can identify the IP address. Router works on network layer of OSI model. ISP like ks network gives a public IP address to WAN port of Router. Then Router generates a local IP for itself on LAN side. So, it has two IP. During data transmission Router performs (NAT & PAT) operation. Is is used in LAN & WAN. It connects multiple Switches.
  • Gateway: It connects two or more dissimilar (Different protocol) networks. Example Communication between PC network with a 3270 mainframe device and NetWare network.

Generations of wireless cellular technology

Different generations of wireless cellular technology (mobile telecommunications).
1g
  • Introduced in the 1980s.
  • The first commercially automated cellular network (the 1G generation) was launched in Japan by Nippon Telegraph and Telephone (NTT) in 1979.
  • Standards: Nordic Mobile Telephone (NMT). Advanced Mobile Phone System (AMPS) in North America and Australia.
  • The radio signals used by 1G networks are analog.
  • Speed: 2.4 kbps
2g
  • Standard: GSM in Finland
  • The main difference between the two mobile telephone systems (1G and 2G), is that the radio signals used by 1G network are analog, while 2G networks are digital.
  • Speed:64 Kbps.
  • Searvices introduced are : data service (Alias-Internet, Bearer service), SMS, MMS
2.5g
  • GPRS: General Packet Radio Service
3g
  • Speed: 144 kbps-2 mbps.
  • Service: Due to high data speed: video call, mobile TV, mobile game.
  • Standards: CDMA2000, WCDMA, UMTS
4g
  • Speed: 100 Mbps - 1 Gbps
  • Service: Video conferencing, 3d television, high-definition Mobile TV.
  • Standard: LTE
5g
  • 5G is a generation currently under development.
  • Speed: 

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