Network and System Unit 4 notes

Transport Layer:
Introduction to TCP/UDP protocols. (C1: Knowledge)

Session, Presentation and Application Layers:

Analyze Session Layer design issues, Presentation Layer design issues (C4: Analysis)

Evaluate Data compression techniques, Cryptography. Application Layer – Distributed application

(client/server, peer to peer, cloud etc.) (C5: Evaluation)

Distinguish World Wide Web (WWW), Domain Name System (DNS), E-mail, File
Transfer Protocol (FTP), HTTP as an application layer protocol (C4: Analysis)

Transport Layer:

Transport Layer protocols

o The transport layer is represented by two protocols: TCP and UDP.
o The IP protocol in the network layer delivers a datagram from a source host to
the destination host.
o Nowadays, the operating system supports multiuser and multiprocessing
environments, an executing program is called a process. When a host sends a
message to other host means that source process is sending a process to a
destination process. The transport layer protocols define some connections to
individual ports known as protocol ports.
o An IP protocol is a host-to-host protocol used to deliver a packet from source
host to the destination host while transport layer protocols are port-to-port
protocols that work on the top of the IP protocols to deliver the packet from the
originating port to the IP services, and from IP services to the destination port.
o Each port is defined by a positive integer address, and it is of 16 bits.
UDP
o UDP stands for User Datagram Protocol.
o UDP is a simple protocol and it provides nonsequenced transport functionality.
o UDP is a connectionless protocol.
o This type of protocol is used when reliability and security are less important than
speed and size.
o UDP is an end-to-end transport level protocol that adds transport-level
addresses, checksum error control, and length information to the data from the
upper layer.
o The packet produced by the UDP protocol is known as a user datagram.

User Datagram Format

The user datagram has a 16-byte header which is shown below:
Where,

o Source port address: It defines the address of the application process that has
delivered a message. The source port address is of 16 bits address.
o Destination port address: It defines the address of the application process that
will receive the message. The destination port address is of a 16-bit address.
o Total length: It defines the total length of the user datagram in bytes. It is a 16-
bit field.
o Checksum: The checksum is a 16-bit field which is used in error detection.

Disadvantages of UDP protocol

o UDP provides basic functions needed for the end-to-end delivery of a

transmission.
o It does not provide any sequencing or reordering functions and does not specify
the damaged packet when reporting an error.
o UDP can discover that an error has occurred, but it does not specify which packet
has been lost as it does not contain an ID or sequencing number of a particular
data segment.

TCP
o TCP stands for Transmission Control Protocol.
o It provides full transport layer services to applications.
 o It is a connection-oriented protocol means the connection established between
both the ends of the transmission. For creating the connection, TCP generates a
virtual circuit between sender and receiver for the duration of a transmission.

Features Of TCP protocol

o Stream data transfer: TCP protocol transfers the data in the form of contiguous
stream of bytes. TCP group the bytes in the form of TCP segments and then
passed it to the IP layer for transmission to the destination. TCP itself segments
the data and forward to the IP.
o Reliability: TCP assigns a sequence number to each byte transmitted and expects
a positive acknowledgement from the receiving TCP. If ACK is not received within
a timeout interval, then the data is retransmitted to the destination.
The receiving TCP uses the sequence number to reassemble the segments if they
arrive out of order or to eliminate the duplicate segments.
o Flow Control: When receiving TCP sends an acknowledgement back to the
sender indicating the number the bytes it can receive without overflowing its
internal buffer. The number of bytes is sent in ACK in the form of the highest
sequence number that it can receive without any problem. This mechanism is also
referred to as a window mechanism.
o Multiplexing: Multiplexing is a process of accepting the data from different
applications and forwarding to the different applications on different computers.
At the receiving end, the data is forwarded to the correct application. This
process is known as demultiplexing. TCP transmits the packet to the correct
application by using the logical channels known as ports.
o Logical Connections: The combination of sockets, sequence numbers, and
window sizes, is called a logical connection. Each connection is identified by the
pair of sockets used by sending and receiving processes.
o Full Duplex: TCP provides Full Duplex service, i.e., the data flow in both the
directions at the same time. To achieve Full Duplex service, each TCP should have
sending and receiving buffers so that the segments can flow in both the
directions. TCP is a connection-oriented protocol. Suppose the process A wants
to send and receive the data from process B. The following steps occur:
 o Establish a connection between two TCPs.
o Data is exchanged in both the directions.
o The Connection is terminated.

TCP Segment Format

Where,

o Source port address: It is used to define the address of the application program
in a source computer. It is a 16-bit field.
o Destination port address: It is used to define the address of the application
program in a destination computer. It is a 16-bit field.
o Sequence number: A stream of data is divided into two or more TCP segments.
The 32-bit sequence number field represents the position of the data in an
original data stream.
o Acknowledgement number: A 32-field acknowledgement number acknowledge
the data from other communicating devices. If ACK field is set to 1, then it
specifies the sequence number that the receiver is expecting to receive.
o Header Length (HLEN): It specifies the size of the TCP header in 32-bit words.
The minimum size of the header is 5 words, and the maximum size of the header
is 15 words. Therefore, the maximum size of the TCP header is 60 bytes, and the
minimum size of the TCP header is 20 bytes.
o Reserved: It is a six-bit field which is reserved for future use.
 o Control bits: Each bit of a control field functions individually and independently.
A control bit defines the use of a segment or serves as a validity check for other
fields.

There are total six types of flags in control field:

o URG: The URG field indicates that the data in a segment is urgent.
o ACK: When ACK field is set, then it validates the acknowledgement number.
o PSH: The PSH field is used to inform the sender that higher throughput is needed
so if possible, data must be pushed with higher throughput.
o RST: The reset bit is used to reset the TCP connection when there is any
confusion occurs in the sequence numbers.
o SYN: The SYN field is used to synchronize the sequence numbers in three types
of segments: connection request, connection confirmation ( with the ACK bit
set ), and confirmation acknowledgement.
o FIN: The FIN field is used to inform the receiving TCP module that the sender has
finished sending data. It is used in connection termination in three types of
segments: termination request, termination confirmation, and acknowledgement
of termination confirmation.
o Window Size: The window is a 16-bit field that defines the size of the
window.
o Checksum: The checksum is a 16-bit field used in error detection.
o Urgent pointer: If URG flag is set to 1, then this 16-bit field is an offset
from the sequence number indicating that it is a last urgent data byte.
o Options and padding: It defines the optional fields that convey the
additional information to the receiver.

Differences b/w TCP & UDP

Basis for TCP UDP

Comparison
 Definition TCP establishes a virtual circuit UDP transmits the data directly to
before transmitting the data. the destination computer without
verifying whether the receiver is
ready to receive or not.

Connection Type It is a Connection-Oriented It is a Connectionless protocol

protocol

Speed slow high

Reliability It is a reliable protocol. It is an unreliable protocol.

Header size 20 bytes 8 bytes

acknowledgement It waits for the acknowledgement It neither takes the

of data and has the ability to acknowledgement, nor it
resend the lost packets. retransmits the damaged frame.

Session, Presentation and Application Layers:

Design issues in Session Layer




Session Layer is one of the Seven Layers of OSI Model. Physical layer, Data Link
Layer and Network Layer lack some services such as establishment of a session between
communicating systems. This is managed by Session Layer which particularly behaves as
a dialog controller between communicating system thus facilitating interaction between
them.
Before looking into design issues, here are some of functions of Session Layer:

1. Dialog Control –
Session layer allows two systems to enter into a dialog exchange mechanism
which can either be full or half-duplex.
2. Managing Tokens –
The communicating systems in a network try to perform some critical
operations and it is Session Layer
which prevents collisions which might occur while performing these operations
 which would otherwise result in a loss.

3. Synchronization –
Checkpoints are the midway marks that are added after a particular interval
during stream of data
transfer. These points are also referred to as synchronization points. The
Session layer permits process to add these checkpoints.
For example, suppose a file of 400 pages is being sent over a network, then it is
highly beneficial to set up a checkpoint after every 50 pages so that next 50
pages are sent only when previous pages are received and acknowledged.
Design Issues with Session Layer :

1. Establish sessions between machines –

The establishment of session between machines is an important service
provided by session layer. This session is responsible for creating a dialog
between connected machines. The Session Layer provides mechanism for
opening, closing and managing a session between end-user application
processes, i.e. a semi-permanent dialogue. This session consists of requests and
responses that occur between applications.
2. Enhanced Services –
Certain services such as checkpoints and management of tokens are the key
features of session layer and thus it becomes necessary to keep enhancing these
features during the layer’s design.
3. To help in Token management and Synchronization –
The session layer plays an important role in preventing collision of several
critical operation as well as ensuring better data transfer over network by
establishing synchronization points at specific intervals. Thus it becomes
highly important to ensure proper execution of these services.

Design Issues in Presentation Layer

The syntax and the semantics of the information exchanged between two
communication systems is managed by the presentation layer of the OSI Model.
Before going through the design issues in the presentation layer, some of its main
functions are:
1. Translation –
It is necessary that the information which is in the form of numbers,
characters and symbols needs to be changed to the bit streams. The
presentation layer handles the different encoding methods used by different
machines .It manages the translation of data between the format of network
requires and computer.
 2. Encryption –
The data encryption at the transmission end as well as the decryption at the
receiver end is managed by the presentation layer.
3. Compression –
In order to reduce the number of bits to be transmitted, the presentation layer
performs the data compression. It increases efficiency in case of multimedia
files such as audio, video etc.
Design issues with Presentation Layer :
1. Standard way of encoding data –
The presentation layer follows a standard way to encode data when it needs to
be transmitted. This encoded data is represented as character strings, integers,
floating point numbers, and data structures composed of simple components.
It is handled differently by different machines based on the encoding methods
followed by them.
2. Maintaining the Syntax and Semantics of distributed information –
The presentation layer manages and maintains the syntax as well as logic and
meaning of the information that is distributed.
3. Standard Encoding on the wire –
The data structures that are defined to be exchanged need to be abstract along
with the standard encoding to be used “on the wire”.

Evaluate Data compression techniques

Ever since humans learned to communicate and exchange information, they
have done their best to reduce the length or size of the information. Prior to the
digital age, techniques like morse code were implemented. Later, telephones
came into being, and voice transmission underwent innovations like cutting off
high frequencies. Fast-forward to the present era – we are now dealing with
information in digital form with the velocity, veracity, and volume increasing
exponentially. As a result, data compression has become essential for efficient
storage and transmission.

Why compress data?

Storing, managing, and transferring data becomes essential in data
communication and other data-driven solutions. This is because no matter the
degree of advancement in computer hardware (RAM, ROM, GPU) and forms of
communication (internet), these resources are scarce.
To utilize these resources efficiently, the data is often required to be
compressed, i.e., reduced to a smaller size without losing any or losing minimal
information.
Varied kinds of data can be compressed. This includes numbers, text, video,
images, audio, or even programs and software. These data types can be reduced
in different ratios, such as 2:1, which means a data file with a 100 MB size can
take up only 50MB of disk space after compression. This compression, also
known as compaction, is performed through various compression techniques.
What is data compression technique?
data compression techniques refer to the use of specific formulas and carefully
designed algorithms used by a compression software or program to reduce the
size of various kinds of data. There are particular types of such techniques that
we will get into, but to have an overall understanding, we can focus on the
principles.
The use of data compression techniques greatly helps in reducing the time for a
file transfer, the cost of storage, and traffic in the network.
Types of data compression techniques
While one can refer to this data compression technique PDF[source], to know
about the various type of techniques available, the two common types that
always stand out are:
1. Lossy
2. Lossless
Lossy compression
To understand the lossy compression technique, we must first understand the
difference between data and information. Data is a raw, often unorganized
collection of facts or values and can mean numbers, text, symbols, etc. On the
other hand, Information brings context by carefully organizing the facts.
To put this in context, a black and white image of 4×6 inches in 100 dpi (dots
per inch) will have 2,40,000 pixels. Each of these pixels contains data in the
form of a number between 0 to 255, representing pixel density (0 being black
and 255 being white).
This image as a whole can have some information like it is a picture of the
16th president of the USA- Abraham Lincoln. If we display an image in 50 dpi,
i.e., in 60,000 pixels, the data required to save the image will reduce, and
perhaps the quality too, but the information will remain intact. Only after
considerable loss in data, we can lose the information.
With the above understanding of the difference between data and information,
we now can comprehend Lossy compression. As the name suggests, Lossy
compression loses data, i.e., gets rid of it to reduce the size of the data.
Advantages and disadvantages of Lossy Compression
 Advantage:
The advantage of lossy compression is that it’s relatively quick, can reduce the
file size dramatically, and the user can select the compression level. It is
beneficial for compressing data like images, video, and even audio by taking
advantage of the limitation of the human sense. This is because of the limit of
our eyes and ears as they cannot perceive a difference in the quality of an image
and audio before a certain point.

 Disadvantage:
The disadvantage of lossy is that decompression of data compressed through
lossy will not return the same data (in terms of quality, size, etc.). Still, it will
hold similar information (this, in fact, is useful in some instances, such as
streaming or downloading content on the internet). However, on the flip side,
constant downloading and uploading of a file can compress and consequently
distort it beyond the point of recognition, causing permanent information loss.
Similarly, if a severe level of compression is used by the user, then the output
file might not be anywhere close to the original input file.
Lossless Compression
Lossless compression, unlike lossy compression, doesn’t remove any data;
instead, it transforms it to reduce its size. To understand the concept, we can
take a simple example.
There is a piece of text where the word ‘because’ is repeated quite often. The
term is comprised of seven letters, and by using a shorthand or abbreviated
version of it like ‘bcz’, we can transform the text. This information of replacing
‘because’ with ‘bcz’ can be stored in a dictionary for later use (during
decompression).
 Methodology: While lossy compression removes redundant or
unnoticeable pieces of data to reduce the size, lossless compression
transforms it through encoding it by using some formula or logic.
Here’s how lossless compression works.
Advantages and disadvantages of Lossless Compression
 Advantage:
There are types of data where lossy compression is not feasible. For example, in
a spreadsheet, software, program, or any data comprised of factual text or
numbers, lossy cannot work as every number might be essential and can’t be
considered redundant as any reduction will immediately cause loss of
information. Here lossless compression becomes crucial as, upon
decompression, the file can be restored to its original state without losing any
data.
 Disadvantage:
There is a limit to data compression. If data is already compressed, then
compressing it again will result in little to no reduction in its size. Also, it is less
effective against larger file sizes.
Following are the most common data compression models-

Lossless compression technique models

The most common models based on lossless technique are-
1. RLE (Run Length Encoding)
2. Dictionary Coder (LZ77, LZ78, LZR, LZW, LZSS, LZMA, LZMA2)
3. Prediction by Partial Matching (PPM)
 4. Deflate
5. Content Mixing
6. Huffman Encoding
7. Adaptive Huffman Coding
8. Shannon Fano Encoding
9. Arithmetic Encoding
10. Lempel Ziv Welch Encoding
11. ZStandard
12. Bzip2 (Burrows and Wheeler)

Lossy compression technique models-

The most common models based on the lossy technique are-
1. Transform coding
2. Discrete Cosine Transform
3. Discrete Wavelet Transform
4. Fractal Compression
What is Cryptography in Computer
Network?
Cryptography refers to the science and art of transforming messages to make
them secure and immune to attacks. It is a method of storing and transmitting
data in a particular form so that only those for whom it is intended can read and
process it. Cryptography not only protects data from theft or alteration but can
also be used for user authentication.

Components
There are various components of cryptography which are as follows −

Plaintext and Ciphertext

The original message, before being transformed, is called plaintext. After the
message is transformed, it is called ciphertext. An encryption algorithm
transforms the plaintext into ciphertext; a decryption algorithm transforms the
ciphertext back into plaintext. The sender uses an encryption algorithm, and the
receiver uses a decryption algorithm.
Cipher

We refer to encryption and decryption algorithms as ciphers. The term cipher is

also used to refer to different categories of algorithms in cryptography. This is
not to say that every sender-receiver pair needs their very own unique cipher
for secure communication. On the contrary, one cipher can serve millions of
communicating pairs.

Key

A key is a number (or a set of numbers) that the cipher, as an algorithm,

operates on. To encrypt a message, we need an encryption algorithm, an
encryption key, and plaintext. These create the ciphertext. To decrypt a
message, we need a decryption algorithm, a decryption key, and the ciphertext.
These reveal the original plaintext.

Types
There are two types of cryptography which are as follows −

Symmetric Key Cryptography

In symmetric-key cryptography, the same key is used by both parties. The

sender uses this key and an encryption algorithm to encrypt data; the receiver
uses the same key and the corresponding decryption algorithm to decrypt the
data.

Asymmetric-Key Cryptography

In asymmetric or public-key cryptography, there are two keys: a private key

and a public key. The private key is kept by the receiver. The public key is
announced to the public.

In public-key encryption/decryption, the public key that is used for encryption is

different from the private key that is used for decryption. The public key is
available to the public, and the private key is available only to an individual.

Application Layer
The application layer is an abstraction layer that defines the
interface methods and shared communication protocols used
by hosts in a communications network. It is the layer closest to
the end-user.
Client-Server Model
The Client-server model is a distributed application structure that partitions task or
workload between the providers of a resource or service, called servers, and service
requesters called clients. In the client-server architecture, when the client computer
sends a request for data to the server through the internet, the server accepts the
requested process and deliver the data packets requested back to the client. Clients do
not share any of their resources. Examples of Client-Server Model are Email, World
Wide Web, etc.
How the Client-Server Model works ?
In this article we are going to take a dive into the Client-Server model and have a look
at how the Internet works via, web browsers. This article will help us in having a solid
foundation of the WEB and help in working with WEB technologies with ease.
 Client: When we talk the word Client, it mean to talk of a person or an
organization using a particular service. Similarly in the digital world
a Client is a computer (Host) i.e. capable of receiving information or using a
particular service from the service providers (Servers).
 Servers: Similarly, when we talk the word Servers, It mean a person or
medium that serves something. Similarly in this digital world a Server is a
remote computer which provides information (data) or access to particular
services.
So, its basically the Client requesting something and the Server serving it as long as its
present in the database.
How the browser interacts with the servers ?
There are few steps to follow to interacts with the servers a client.
 User enters the URL(Uniform Resource Locator) of the website or file. The
Browser then requests the DNS(DOMAIN NAME SYSTEM) Server.
 DNS Server lookup for the address of the WEB Server.
 DNS Server responds with the IP address of the WEB Server.
 Browser sends over an HTTP/HTTPS request to WEB Server’s
IP (provided by DNS server).
 Server sends over the necessary files of the website.
 Browser then renders the files and the website is displayed. This rendering is
done with the help of DOM (Document Object Model)
interpreter, CSS interpreter and JS Engine collectively known as the JIT or
(Just in Time) Compilers.
Advantages of Client-Server model:
 Centralized system with all data in a single place.
 Cost efficient requires less maintenance cost and Data recovery is possible.
 The capacity of the Client and Servers can be changed separately.
Disadvantages of Client-Server model:
 Clients are prone to viruses, Trojans and worms if present in the Server or
uploaded into the Server.
 Server are prone to Denial of Service (DOS) attacks.
 Data packets may be spoofed or modified during transmission.
 Phishing or capturing login credentials or other useful information of the user
are common and MITM(Man in the Middle) attacks are common.

P2P (peer-to-peer) architecture: It has no dedicated server in a data center.

The peers are the computers which are not owned by the service provider. Most of the
peers reside in the homes, offices, schools, and universities. The peers communicate
with each other without passing the information through a dedicated server, this
architecture is known as peer-to-peer architecture. The applications based on P2P
architecture includes file sharing and internet telephony.

Features of P2P architecture

o Self scalability: In a file sharing system, although each peer generates a
workload by requesting the files, each peer also adds a service capacity by
distributing the files to the peer.
o Cost-effective: It is cost-effective as it does not require significant server
infrastructure and server bandwidth.

Cloud
1. The application layer, which is at the top of the stack, is where the actual
cloud apps are located. Cloud applications, as opposed to traditional
applications, can take advantage of the automatic-scaling functionality to
gain greater performance, availability, and lower operational costs.
2. This layer consists of different Cloud Services which are used by cloud users.
Users can access these applications according to their needs. Applications are
divided into Execution layers and Application layers.
 3. In order for an application to transfer data, the application layer determines
whether communication partners are available. Whether enough cloud
resources are accessible for the required communication is decided at the
application layer. Applications must cooperate in order to communicate, and
an application layer is in charge of this.
4. The application layer, in particular, is responsible for processing IP traffic
handling protocols like Telnet and FTP. Other examples of application layer
systems include web browsers, SNMP protocols, HTTP protocols, or HTTPS,
which is HTTP’s successor protocol.

Protocols in Application Layer




The application layer is present at the top of the OSI model. It is the layer through which
users interact. It provides services to the user. Application layer performs several kinds of
functions which are requirement in any kind of application or communication process.
In computer networks, "www" stands for the World Wide Web.
The World Wide Web is an information space on the internet
where documents and other web resources are identified by
Uniform Resource Locators (URLs), which are often referred to
as web addresses. The "www" prefix is commonly used to
denote a web server or a website.

When you enter a web address into a browser, it typically

includes the "www" as part of the URL. For example,
"www.example.com" is a common format for a web address.
The "www" indicates that the resource is part of the World
Wide Web. However, it's important to note that not all websites
require the "www" prefix. Many websites can be accessed with
or without it, and some modern websites may prefer to use the
domain name directly without the "www."
In the context of the Domain Name System (DNS), the "www"
subdomain is just one of many possible subdomains. The DNS is
responsible for translating human-readable domain names (like
www.example.com) into IP addresses that computers use to
locate each other on a network.

In summary, "www" is a widely recognized and used prefix in

URLs to indicate a resource on the World Wide Web. It has
become a standard convention, but it is not mandatory for
accessing websites, and some websites may choose not to use
it in their URLs.

FTP

FTP stands for File Transfer Protocol . It is the protocol that actually lets us transfer
files. It can facilitate this between any two machines using it. But FTP is not just a
protocol but it is also a program.FTP promotes sharing of files via remote computers
with reliable and efficient data transfer. The Port number for FTP is 20 for data and 21
for control.

SMTP

It stands for Simple Mail Transfer Protocol . It is a part of the TCP/IP protocol. Using a
process called “store and forward,” SMTP moves your email on and across networks. It
works closely with something called the Mail Transfer Agent (MTA) to send your
communication to the right computer and email inbox. The Port number for SMTP is
25.

DNS
It stands for Domain Name System. Every time you use a domain name, therefore, a
DNS service must translate the name into the corresponding IP address. For example,
the domain name www.abc.com might translate to 198.105.232.4.
The Port number for DNS is 53.

HTTP/HTTPS

HTTP stands for Hypertext Transfer Protocol and HTTPS is the more secured version
of HTTP, that’s why HTTPS stands for Hypertext Transfer Protocol Secure. This
protocol is used to access data from the World Wide Web. The Hypertext is the well-
organized documentation system that is used to link pages in the text document.
 HTTP is based on the client-server model.
 It uses TCP for establishing connections.
 HTTP is a stateless protocol, which means the server doesn’t maintain any
information about the previous request from the client.
 HTTP uses port number 80 for establishing the connection.

Feature www (World DNS (Domain Email FTP (File Transfer HTTP (Hypertext
Wide Web) Name (Electronic Protocol) Transfer Protocol)
System) Mail)
Purpose Indicates Translates Facilitates Enables file Facilitates
resources on domain electronic transfer transfer of web
the Web. names to IPs. messaging content
Function Identifies web Facilitates IP Enables email Facilitates file Governs transfer
servers/websit address communicati transfers. of web content.
es. lookup. on.
Communic Retrieves web Resolves Text and file- File transfer Requesting and
ation Type content. domain based between systems. receiving web
names. messages. data.
Protocols Typically uses Primarily Uses SMTP, Uses FTP or SFTP Primarily uses
Used HTTP/HTTPS. uses DNS POP3, IMAP protocols. HTTP/HTTPS.
protocol. protocols.
Data Hypertext, Translated IP Text and file Various file types. Hypertext,
Format multimedia addresses. attachments. multimedia
content. content.
Example www.example. Resolving user@exampl ftp:// http://
com www.exampl e.com example.com/ www.example.co
e.com file.txt m
Connectio Stateful Stateless Stateless Stateless Stateless
n Type (persistent (request- (store-and- (command- (request-
connection). response). forward). response). response).
Security Can use DNSSEC Encryption Supports secure Can use HTTPS for
SSL/TLS for enhances during transit variants like FTPS, secure
 secure security. (TLS). SFTP. communication.
browsing.
Port Defaults to Defaults to Defaults to Defaults to ports Defaults to port
Number port 80 for port 53. ports 25, 110, 20, 21 for data 80 for HTTP, 443
HTTP, 443 for 143 for SMTP, and control. for HTTPS.
HTTPS. POP3, IMAP.
User Typically uses No direct Requires user Requires user Can use various
Authentica username/pas user authenticatio authentication for authentication
tion sword, or authenticatio n (login access. methods.
other n. credentials).
authentication
methods.