Collision and Network layer

Collision:
When two network sends frame with same device in a physical layer and transmit simultaneously it will cause collision. So no data pass and require retransmit. Collision event as a situation where each device's digital signals totally interference with one another  on the wire.

Bridge: 
Bridge use to communicate smoothly two different network. A major job of bridge is to reduce collision. A bridge has a CAM (Content Addressable Memory) table.

CAM table has a list of IPs against MAC. When any PC on network transmit data the the data is checked from CAM table and if it is not listed on CAM table than the data inputed. The collision easily reduced on the activity of bridge concept.

The bridge included on Hub and it become Switch now.

Network layer: OSI
OSI layer is hierarchical and there is many advantages on other layer. Here is the layers:
Layer7: Application layer
Layer 6: Presentation layer
Layer 5: Session layer
Layer 4: Transport layer
Layer 3: Network layer
Layer 2: Data Link layer
Layer 1: Physical layer

Application Layer:
Application layer of OSI model works as a interface. It just provide the communication solustion by protocol stack as the networked computers application can communicated each other. Different protocol works for different jobs. Some important job of application layer is:

• File transfer
• Email
• Enable Remote Access
• Client/Server Process
• Information Location 
• There is some protocole name and their jobs:

HTTP: Hypertext Transfer Protocol (Port: 80): HTTP is the protocol to exchange or transfer hypertext.
FTP: File Transfer Protocol: (Port: 21)  is a standard network protocol used to transfer files from one host to another host over a TCP-based network
Telnet (Port: 23) is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection.
DHCP (Port: 67) Dynamic Host Configuration Protocol (DHCP) is a standardized networking protocol used on Internet Protocol (IP) networks for dynamically distributing network configuration parameters, such as IP addresses for interfaces and services. With DHCP computers request IP addresses and networking parameters automatically from a DHCP server, reducing the need for a network administrator or a user from having to configure these settings manually.
DNS (Port: 53) Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities.
SMTP (Port: 25) Simple Mail Transfer Protocol  is an Internet standard for electronic mail (e-mail) transmission
POP (Port: 110) Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection. POP has been developed through several versions, with version 3 (POP3) being the current standard.

IMAP (Port: 140) Internet Message Access Protocol

Presentation layer:
Presentation layer presents data to user.In the nework communication data is sent is a format and the it present in other format. The main job of the layer is
data compression, decompression, encryption, decryption and sometimes multimedia operation.

Session Layer:
When two devices want to communicate with each other a session should be established. Session layer maintain this. Session layer is responsible to setting up, managing and terminate session and keeping data separate. Dialog control also occur at this layer.
There is three different mode of communication
a) Simplex: Only Send
b) Half Duplex: First I will send than you will send
c) Full Duplex: Both send and receive simultanously.

(Class-3 )
(Topic: DoD Model and Layer)
(Next Topic: IPV4)
(Date:08/02/2014)