Network layer
Network Layer
The network layer is responsible for the source-to destination delivery of a packet, possibly across multiple networks (links). Whereas the data link layer oversees the delivery of the packet between two system on the same network (link), the network layer ensures that each packet gets from its point if origin to its final destination.
If two systems are connected to the same link, there is usually no need for a network layer. However, if the two systems are attached two different networks (link) with connecting devices between the networks (link), there is often a need for the network layer to accomplish source-to-destination delivery. Other responsibilities of the network layer include the following:
Ø Logical addressing. The physical addressing implemented by the data link layer handles the addressing problem locally. If a packet passes the network boundary, we need another addressing system distinguish the source and destination system. The network layer adds a header to the packet coming from the upper layer that, among other thing, includes the logical addresses of the sender and receiver.
Ø Routing. When independent networks or links are connected together to create internetworks (network of networks) or a large network, the connecting devices (called routers or switches) route or switch the packets to their final destination. One of the function of the network layer is to provides this mechanism.
Data link layer
Data link layer
The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. It makes the physical layer appear error-free to the upper layer(network layer). Other responsibilities of the data link layer include the following:
Ø Framing. The data link layer divides the stream of bits received from the network layer into manageable data units called frame.
Ø Physical addressing. If frames are to be distributed to different system on the network, the data link layers add a header to the frame to define the sender and /or receiver of the frame. If the frame is intended for a system outside the sender’s network, the receiver address is the address of the connecting device that connects the network to the next one.
Ø Flow control. If the rate at which the data is absorbed by the receiver is less than the rate produced at the sender, the data link layer imposes a flow control mechanism to prevent overwhelming the receiver.
Ø Error control. The data link layer adds reliability to the physical layer by adding mechanism to detect and retransmit damaged or lost frames. It also uses a mechanism to recognize a duplicate frame. Error control is normally achieved through a trailer added to the end of the frame.
Ø Access control. When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time.
Physical Lyer
Layers in the OSI model
Physical layer
The physical layer coordinates the function required to carry a bit stream over a physical medium. Physical Layer deals with the mechanical and electrical specifications of the interface and transmission media Physical Layer also defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur.
The physical layer is responsible for moving individual bits from one
(NODE) to the next.
Physical layer is concerned with the following
Ø Physical characteristics of interfaces and media. The physical layer defines the characteristics of the interface between the devices and the transmission media. It also defines the type of transmission media.
Ø Representation of bits. The physical layer data consists of a stream of bits (sequence of 0s and 1s ) with no interpretation. To be transmitted bits must be encoded into signals (electrical or optical). The physical layer defines the type of encoding (how 0s and 1s are changed to signals).
Ø Data rate. The transmission rate – the number of bits sent each second –is also defined by the physical layer. In other words, the physical layer defines the duration of a bit, which is how long it lasts.
Ø Synchronization The sender and receiver must not only use the same bit rate but must also be synchronized at the bit level. In other words, the sender and the receiver clocks must be synchronized.
Ø Line configuration. The physical layer is concerned with the connection of devices to the media. In a point-to-point configuration, two devices are connected together through a dedicated link. In a multipoint configuration a link is shared between several devices .
Ø Physical topology. The physical topology define how devices are connected to make a network. Devices can be connected using a mesh topology (every device connected to every other device), a star topology (devices are connected through a central device), a ring topology (each device is connected to the next. Forming a ring), or a bus topology (every device ion a common link)
Ø Transmission mode The physical layer also defines the direction of transmission between two devices: simplex, half duplex. In the simplex mode, only one device can send; the other can only receive. The simplex mode is a one way communication. In the half duplex mode, two devices can send and receive, but not at the same time, in a full-duplex (or simple duplex) mode, two devices can send and receive at the same time.
SIP (Session Initiation Protocol)
SIP (Session Initiation Protocol)
SIP is an application layer protocol designed to be independent of the underlying transport layer; it can run on transmission control protocol (TCP), UDP, or SCTP. It is a text based protocol, incorporating many elements of the HTTP and the SMTP.The session Initiation Protocol is a signaling communication protocol, widely used for controlling multimedia communication sessions such as voice and video calls over IP.
The protocol defines the messages that are sent between peers which govern establishment, terminations and other essential element of call. SIP can be used for creating, modifying, and terminating two party (unicast) or multiparty (multicast) sessions consisting one or several media streams. Other SIP applications include video conferencing, streaming multimedia distribution, instant messaging, presence information, file transfer and online games.
SIP work in conjunction with several other application layer protocols that identify and carry the session media identification and negotiation is achieved with session description protocol (SDP). For the transmission of media stream a(voice, video) SIP typically employs the Real-Time transport protocol (RTP), which many be secured with the secure Real-Time transport protocol (RTP). For secure transmissions of SIP message the protocol may be encrypted with transport layer security TLS.
NNTP (Network News Transport Protocol)
NNTP (Network News Transfer Protocol)
The News Transport Protocol (NNTP) is an application protocol used for
transporting Usenet news articles (net news) between news server and for
reading and posting articles by end client application.
Usenet was originally designed based on the UUCP network, with most
article transfer taking place over direct point to point telephone link between
news sever and which were powerful time sharing systems. Readers and posters logged
into this computer reading the article directly from the local disc.
As local area network and internet participation it became describe to
allow news readers to be run on personal computers connected to local networks.
Because distributed files system were not yet widely available, a news protocol
was developed based on the client server model. It resembled the simple Mail Transfer
Protocol (SMTP), but was tailored for exchanging news group article.
A news reader, also known as a news client, is a software application
that reads article on Usenet, either directly from the news server's disks or
via the NNTP. The well-known TCP port 119 is reserved for NNTP. When client
connect to a news server with transport layer security (TLS), TCP port 563 is
used. This is sometimes referred to as NNTPS.
In October 2006, the IETF released RFC 3977 which updates the NNTP protocol
and codifies many of the additions over the years since RFC977.
Domain Name System
DNS (Domain Name System)
The
Domain Name System is a hierarchical distributed naming system for computers,
services, or any resource connected to internet or a private network. It
associates various information with domain names assigned to each of the
participating entities. Most prominently, it translates easily memorized domain
name to the numerical IP addresses needs for the purpose of locating computer
services and devices worldwide. By providing a worldwide, distributed
keyword-based redirection service, the Domain Name System is an essential component
of the functionality of the internet.
An
often-used analogy to explain the Domain Name System is that it serves as the
phone book for the internet by translating human-friendly computer hostnames
into IP addresses. For example the domain name www.example.com
translates to the addresses 192.163.0.10 (IPv4) and 2001:500:88:200::10 (IPv6).
Unlike a phonebook the DNS can be quick updated, allowing a service's location
on the network to change without effecting the end users, who continue to use
the same hostname. Users take advantage of this when they use meaningful
uniform resource locator (URL) and E-mail addresses without having to known how
the computer actually locates the services.
The
Domain Name System distributes the responsibility of assigning domain names and
mapping those names to IP addresses by designating authoritative name serves
for each domain. Authoritative name servers are assigned to be responsible for
their particular domain and in turn can assign other authoritative name servers
for their sub-domains. This mechanism has made the DNS distributed and fault
tolerant and has held avoid the need for a single central register to be
continually consulted and updated. Additionally the responsibility for
maintaining and updating the master record for the domain is spread among many
domain name registers, who compete for the end-user's (the domain-owner's)
business. Domain can be moved from one registrar to other registrar at any time.
The
Domain Name System also specifies the technical functionality of this data base
service. It defines the DNS protocol, a detailed specification of the data
structures and data communication exchanges used in DNS, as part of the
internet protocol suit.
What is Protocol?
Protocols
A
communication protocol is (Networking protocol) is a system of digital message
formats and rules for exchanging messages in or between computing system and in
telecommunications. A protocol may have a formal description. Protocol may include
signaling, authentication and error detection and correction capability.
In
a routing protocol, it specifies that how routers communicate with each other
and with the other types of machines. Protocols are determines and enable the
routes between the nodes on a computer network. Algorithms determine the
specific choice of routing. A router has knowledge only the direct attached
networks and a protocol shares information about the neighbors immediate and
then throughout the network. A router can understand the network topology
through the protocol. So we can say that a protocol is playing very important
role in a network. Although, there are many types of protocols.
Types of protocols
There
are many types of protocols for different purpose in networking.
Routing protocols
IS-IS,
OSPF, IGRP and EIGRP, RIP, BGP,
Internet protocols
Application Layer
DHCP,
DHCPv6, DNS, FTP, HTTP, IMAP, IRC, LDAP, MGCP, NNTP, BGP, NTP, POP, RPC, RTP,
RTSP, RIP, SIP, SMTP, SNMP, SOCKS, SSH, Telnet, TLS/SSL, XMPP.
Transport Layer
TCP, UDP, DCCP, SCTP, RSVP, TP-TCP, NC, MTP
Network Layer
IP(IPv4,IPv6),
ICMP, ICMPv6, ECN, IGMP, IPSec, GGP.
Link Layer
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