Host to network layer in Hindi.

The lowest layer of the TCP/IP model is the host-to-network layer which is concerned with the physical transmission of data. And also known as a network interface layer or link-layer that is a combination of the physical layer and data link layer of the OSI model.

The function of  link-layer are:

• Defines how bits are to be encoded into optical or electrical pulses.

• Accepts IP packets from the network layer and encapsulates them into frames. It synchronizes the transmission of the frames as well as the bits making up the frames, between the sender and the receiver.

•  the transmission mode,i.e simplex, half-duplex, or full-duplex.

•  the topology of the network,i.e bus, star, ring, etc with help of Ethernet, Frame Relay, Token Ring, ATM.

The transport layer is responsible for providing services to the application layer; it receives

services from the network layer.

Access networks and physical media(host):)

Residential access nets and institutional access networks(school, company) and mobile access networks.

Bandwidth (bits per second) of an access network and shared or dedicated.

Enterprise access networks(Ethernet):  Typically used in companies, universities, etc transmission rate are 10 Mbps, 100Mbps, 1Gbps, 10Gbps  .Today, end systems typically connect into Ethernet switch.

Wireless access networks: Shared wireless access network connects the end system to router via base station aka “access point” in wireless LANs and wide-area wireless access.

Host: sends packets of data:)

host sending function: Takes application message data breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth.

packet transmission delay = time needed to transmit L-bit packet into the link=L (bits)/R (bits/sec)

Physical Media:)
Bit: propagates between transmitter/receiver pairs

physical link: what lies between transmitter & receiver

guided media: signals propagate in solid and media are copper, fiber, coaxial.

unguided media: signals propagate freely, e.g radio.

twisted pair (TP): two insulated copper wires are  Category 5 that has 100 Mbps, 1 Gbps Ethernet  and Category 6 that has 10Gbps.

The network core: )

• the mesh of interconnected routers
• packet-switching: hosts break application-layer messages into packets forward packets from one router to the next, across links on the path from source to destination
• each packet transmitted at full link capacity  takes L/R seconds to transmit (push out) L-bit packet into link at R bps
• store and forward: entire packet must arrive at router before it can be transmitted on the next link

queuing and loss: if arrival rate (in bits) to link exceeds transmission rate of link for a period of time. The packets will queue, wait to be transmitted on the link and can be dropped (lost) if memory (buffer) fills up.

Routing: determines the source-destination route taken by packets with help of routing algorithms.

forwarding: move packets from router’s input to appropriate router output.