The Network layer of the OSI Model basically defines logical addressing and the ways that packets are moved from source to destination on a network. The functions of the Network layer can be broken down as follows:
Path determination between source and destination nodes on different networks
Routing messages between networks
Controlling congestion on the subnet
Translating logical addresses into physical addresses
Logical Address Construction
||Total Address Length
||Bits in Network Portion
||Bits in Host Portion
||Class A – 8
Class B – 16
Class C – 24
|Class A – 24
Class B – 16
Class C – 8
||32 or less (only
significant digits listed)
|48 bits (MAC address)
||16 or less (indicates one
or many in cable range)
|8 bits or less
Routing protocols support routed protocols. A routing protocol is used to pass messages between routers for maintaining and updating routing tables. Examples of routing protocols are RIP, IGRP, OSPF, EIGRP.
Routed protocols are used to carry end-user traffic across the internetwork. Examples of routed protocols are IP and IPX Read more »
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The Data Link layer performs a number of separate activities, including:
Access to the physical medium
Different data link layer specifications define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control.
Physical addressing, is not to be confused with network or IP addresing. The physical address defines how devices are labeled in the data link layer. This physical address is most commonly called the Media Access Control (MAC) address. The MAC address is a unique number assigned by the manufacturer. This numbering system is actually administered by one of the networking governing bodies.
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The Physical Layer has two responsibilities; it sends bits and receives bits.
The Physical layer specifications specify the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating a physical link between end systems.
The physical layer is usually a combination of software and hardware programming and may include electromechanical devices.
All wireing, power, cabling and connections are part of the physical layer. Without the physical layer functioning properly none of the upper layers will respond correctly.
* transmits raw bit stream over physical cable
* defines cables, cards, and physical aspects
* defines NIC attachments to hardware, how cable is attached to NIC
* defines techniques to transfer bit stream to cable
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