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Computer Networks Cheat Sheet by

OSI stands for Open Systems Interconnection. It has been developed by ISO– International Organization for Standardization, in the year 1984. It is a seven-layer architecture with each layer having specific functionality to perform.

OSI Layers

Data Units
Applic­ation Layer
Mail Services, Directory Services, FTAM
Presen­tation Layer
Encryp­tio­n/D­ecr­yption, Compre­ssion
Session Layer
Session Establ­ish­ment, Synchr­oni­zation, Dialog Controller
Transport Layer
Segments, Datagram
Network Layer
Traffic control, Fragme­nta­tion, Routing
Data Link Layer
Flow control, Error control, Access control
Physical Layer
Bit Synchr­oni­zation, Bit rate control, Physical Topologies

OSI x TCP/IP Model

Types of Networks

Personal Network is a network consisting of only a small number of devices owned by an indivi­dual.
A local area network is a network that covers a small area (for example, a company’s network).
A wide Area Network is a network that includes many devices and covers a large area. Usually collec­tively owned.
MAN stands for Metrop­olitan Area Network. It is a computer network that connects a findnumber of LANs to form a larger network so that the computer resources can be shared.

Network Topologies

Bus Topology
A bus topology, also called a line topology, is a type of network topology in which all network devices are connected through a central RJ-45 network cable or coaxial cable.
Ring Topology
A ring topology is a type of network topology in which each device is connected to two other devices on either side using RJ-45 or coaxial cables.
Star Topology
A star topology is a network topology in which each element of the network is physically connected to a central node such as a router, hub, or switch. In a star topology, hubs act as servers, and connecting nodes act as clients.
Mesh Topology
In a mesh topology, each node is connected to at least one other node and often to multiple nodes. Each node can send and receive messages from other nodes.
Tree Topology
A tree topology is a hybrid network topology in which star networks are interc­onn­ected by bus networks. Tree networks are hierar­chical and each node can have any number of child nodes.
Hybrid Topology
A hybrid topology is a type of network topology that uses two or more different network topolo­gies. These topologies can include mixed bus topolo­gies, mesh topolo­gies, ring topolo­gies, star topolo­gies, and tree topolo­gies.

Advantages vs. Disadv­antages Network Topologies

- It is the easiest network topology for connecting periph­erals or computers in a linear fashion.
- It works very effici­ently well when there is a small network.
- The length of cable required is less than a star topology.
- It is easy to connect or remove devices in this network without affecting any other device.
- Very cost-e­ffe­ctive as compared to other network topology i.e. mesh and star
- It is easy to understand topology.
- Easy to expand by joining the two cables together.

- Bus topology is not great for large networks.
- Identi­fic­ation of problems becomes difficult if the whole network goes down.
- Troubl­esh­ooting individual device issues is very hard.
- Need termin­ators are required at both ends of the main cable.
- Additional devices slow the network down.
- If the main cable is damaged, the whole network fails or splits into two.
- Packet loss is high.
- This network topology is very slow as compared to other topolo­gies.

- It is very reliable – if one cable or device fails then all the others will still work
- It is high-p­erf­orming as no data collisions can occur
- Less expensive because each device only need one I/O port and wishes to be connected with hub with one link.
- Easier to put in
- Robust in nature
- Easy fault detection because the link are often easily identi­fied.
- No disrup­tions to the network when connecting or removing devices.
- Each device requires just one port i.e. to attach to the hub.
- If N devices are connected to every other in star, then the amount of cables required to attach them is N. So, it’s easy to line up.

- Requires more cable than a linear bus .
- If the connecting network device (network switch) fails, nodes attached are disabled and can’t partic­ipate in network commun­ica­tion.
- More expensive than linear bus topology due to the value of the connecting devices (network switches)
- If hub goes down everything goes down, none of the devices can work without hub.
- Hub requires more resources and regular mainte­nance because it’s the central system of star .
- Extra hardware is required (hubs or switches) which adds to cost
- Perfor­mance is predicated on the one concen­trator i.e. hub.

- In this data flows in one direction which reduces the chance of packet collis­ions.
- In this topology additional workst­ations can be added after without impacting perfor­mance of the network.
- Equal access to the resources.
- There is no need of server to control the connec­tivity among the nodes in the topology.
- It is cheap to install and expand.
- Minimum collision.
- Speed to transfer the data is very high in this type of topology.
- Due to the presence of token passing the perfor­mance of ring topology becomes better than bus topology under heavy traffic.
- Easy to manage.
- Ring network is extremely orderly organized where every device has access to the token and therefore the opport­unity to transmit.

- Due to the Uni-di­rec­tional Ring, a data packet (token) must have to pass through all the nodes.
- If one workst­ation shuts down, it affects whole network or if a node goes down entire network goes down.
- It is slower in perfor­mance as compared to the bus topology
- It is Expensive.
- Addition and removal of any node during a network is difficult and may cause issue in network activity.
- Difficult to troubl­eshoot the ring.
- In order for all the computer to commun­icate with each other, all computer must be turned on.
- Total dependence in on one cable.
- They were not Scalable.

- Failure during a single device won’t break the network.
- There is no traffic problem as there is a dedicated point to point links for every computer.
- Fault identi­fic­ation is straig­htf­orward.
- This topology provides multiple paths to succeed in the destin­ation and tons of redund­ancy.
- It provides high privacy and security.
- Data transm­ission is more consistent because failure doesn’t disrupt its processes.
- Adding new devices won’t disrupt data transm­iss­ions.
- This topology has robust features to beat any situation.
- A mesh doesn’t have a centra­lized authority.

- It’s costly as compared to the opposite network topologies i.e. star, bus, point to point topology.
- Instal­lation is extremely difficult in the mesh.
- Power requir­ement is higher as all the nodes will need to remain active all the time and share the load.
- Complex process.
- The cost to implement mesh is above other select­ions.
- There is a high risk of redundant connec­tions.
- Each node requires a further utility cost to think about.
- Mainte­nance needs are challe­nging with a mesh.

- This topology is the combin­ation of bus and star topology.
- This topology provides a hierar­chical as well as central data arrang­ement of the nodes.
- As the leaf nodes can add one or more nodes in the hierar­chical chain, this topology provides high scalab­ility.
- The other nodes in a network are not affected if one of their nodes gets damaged or does not work.
- Tree topology provides easy mainte­nance and easy fault identi­fic­ation can be done.
- A callable topology. Leaf nodes can hold more nodes.
- Supported by several hardware and software vendors.
- Point-­to-­point wiring for individual segments.
- Tree Topology is highly secure.
- It is used in WAN.
- Tree Topology is reliable.

- This network is very difficult to configure as compared to the other network topolo­gies.
- The length of a segment is limited & the limit of the segment depends on the type of cabling used.
- Due to the presence of a large number of nodes, the network perfor­mance of tree topology becomes a bit slow.
- If the computer on the first level is erroneous, the next-level computer will also go under problems.
- Requires a large number of cables compared to star and ring topology.
- As the data needs to travel from the central cable this creates dense network traffic.
- The Backbone appears as the failure point of the entire segment of the network.
- Treatment of the topology is pretty complex.
- The establ­ishment cost increases as well.
- If the bulk of nodes is added to this network, then the mainte­nance will become compli­cated.

- This type of topology combines the benefits of different types of topologies in one topology.
- Can be modified as per requir­ement.
- It is extremely flexible.
- It is very reliable.
- It is easily scalable as Hybrid networks are built in a fashion which enables easy integr­ation of new hardware compon­ents.
- Error detecting and troubl­esh­ooting are easy.
- Handles a large volume of traffic.
- It is used to create large networks.
- The speed of the topology becomes fast when two topologies are put together.

- It is a type of network expensive.
- The design of a hybrid network is very complex.
- There is a change in the hardware to connect one topology with another topology.
- Usually, hybrid archit­ectures are larger in scale so they require a lot of cables in the instal­lation process.
- Hubs which are used to connect two distinct networks are very costly. And hubs are different from usual hubs as they need to be intell­igent enough to work with different archit­ect­ures.
- Instal­lation is a difficult process.

- Hybrid Topology helps in keeping the full diversity of the computer network.
- Hybrid Topology is helpful when we require more than one topology in the system.
- Hybrid Topology helps in reducing the cost of the overall system.
- Hybrid Topology helps in easily running the system.
- Hybrid Topology is widely used in educat­ional instit­utes, research organi­zat­ions, finance sectors, etc.

Type of Multip­lexers

Frequency Division Multip­lexing (FDM)
The frequency spectrum is divided into logical channels and each user has exclusive access to his channel. It transmits signals in several different frequency ranges and multiple video channels over a single cable. Each signal is modulated onto a different carrier frequency and the carrier freque­ncies are separated by guard bands.
Time Division Multip­lexing (TDM)
Each user gets full bandwidth for a short period of time on a regular basis. The entire channel is dedicated to her one user, but only for a short time.
Wavelength Division Multip­lexing
This is the same as FDM but applied to fiber, with the difference that here the operating frequency is much higher, actually in the optical range. Due to its extremely high bandwidth, fiber optic has great potential.

Network Devices

Any device, such as a workst­ation, laptop, tablet, or smartp­hone, that is used to access a network.
Provides resources to network users, including email, web pages, or files.
A Layer 1 device that does not perform any inspection of traffic. A hub simply receives traffic in a port and repeats that traffic out of all the other ports.
A Layer 2 device that makes its forwarding decisions based on the destin­ation Media Access Control (MAC) address. A switch learns which devices reside off which ports by examining the source MAC address. The switch then forwards traffic only to the approp­riate port, and not to all the other ports.
A Layer 3 device that makes forwarding decisions based on Internet Protocol (IP) addres­sing. Based on the routing table, the router intell­igently forwards the traffic out of the approp­riate interface.
Can operate at both Layer 2 and Layer 3. Also called a Layer 3 switch, a multilayer switch is a high-p­erf­ormance device that can switch traffic within the LAN and for- ward packets between subnets.
Media can be copper cabling, fiber-­optic cabling, or radio waves. Media varies in its cost, bandwidth capacity, and distance limita­tion.
Analog Modem
Modem is short for modula­tor­/de­mod­ulator. An analog modem converts the digital signals generated by a computer into analog signals that can travel over conven­tional phone lines.
Broadband Modem
A digital modem used with high-speed DSL or cable Internet service. Both operate in a similar manner to the analog modem, but use higher broadband freque­ncies and transm­ission speeds.
Access Point
A network device with a built-in antenna, transm­itter, and adapter that provides a connection point between WLANs and a wired Ethernet LAN. APs usually have several wired RJ-45 ports to support LAN clients. Most small office or home office (SOHO) routers integrate an AP.

IEEE Standards

IEEE 802
IEEE 802.1
LAN/MAN Bridging and management
IEEE 802.1s
Multiple spanning tree
IEEE 802.1 w
Rapid reconf­igu­ration of spanning tree
IEEE 802.1x
Port-based network access control
IEEE 802.2
Logical Link Control (LLC)
IEEE 802.3
CSMA/CD access method (Ethernet)
IEEE 802.3ae
10 Gigabit Ethernet
IEEE 802.4
Token passing bus access method and Physical layer specif­ica­tions
IEEE 802.5
Token Ring access method and Physical layer specif­ica­tions
IEEE 802.6
Distri­buted Queue Dual Bus (DQDB) access method and Physical layer specif­ica­tions (MAN)
IEEE 802.7
Broadband LAN
IEEE 802.8
Fiber Optic
IEEE 802.9
Isochr­onous LANs (standard withdrawn)
IEEE 802.10
Intero­perable LAN/MAN Security
IEEE 802.11
Wireless LAN MAC and Physical layer specif­ica­tions
IEEE 802.11a
Wireless with speed upto 54 Mbps
IEEE 802.11b
Wireless with speed upto 11 Mbps
IEEE 802.11g
Wireless with speed upto 54 Mbps
IEEE 802.11n
Wireless with speed upto 600 Mbps
IEEE 802.12
Demand­-pr­iority access method, physical layer and repeater specif­ica­tions
IEEE 802.13
not used
IEEE 802.14
Cable modems (proposed standard was withdrawn)
IEEE 802.15
Wireless Personal Area Network (WPAN)
IEEE 802.16
Wireless Metrop­olitan Area Network (Wireless MAN)
IEEE 802.17
Resilient Packet Ring (RPR) Access

Cables (according to IEEE)

Ethernet Standards
Data Rate
Cable Fiber Type
Maximum Distance
Ethernet (10Bas­e-FL)
10 Mbps
50m or 62.5um Multimode @ 850nm
Fast Ethernet (100Ba­se-FX)
100 Mbps
50m or 62.5um Multimode @ 1300nm
Fast Ethernet (100Ba­se-SX)
100 Mbps
50m or 62.5um Multimode @ 850nm
Gigabit Ethernet (1000B­ase-SX)
1000 Mbps
50m Multimode @ 850nm
Gigabit Ethernet (1000B­ase-SX)
1000 Mbps
62.5um Multimode @ 850nm
Gigabit Ethernet (1000B­ase-LX)
1000 Mbps
50m or 62.5um Multimode @ 1300nm
Gigabit Ethernet (1000B­ase-LX)
1000 Mbps
9um Singlemode @1310nm
Gigabit Ethernet (1000B­ase-LH)
1000 Mbps
9um Singlemode @1550nm

Types of Ethernet Networks

Common Name
Informal IEEE Standard Name
Formal IEEE Standard Name
Cable Type, Maximum Length
10 Mbps
Copper, 100 m
100 Mbps
Fast Ethernet
Copper, 100 m
1000 Mbps
Gigabit Ethernet
Fiber, 5000 m
1000 Mbps
Gigabit Ethernet
Copper, 100 m
10 Gbps
10 Gig Ethernet
Copper, 100 m

Transm­ission Media (Guided Media)

Type of Media
Twisted Pair Cable
It is a superi­mposed winding of two separately insulated conduc­tors. As a rule, several such pairs are grouped together in a protective cover. They are the most widely used transm­ission media.
Coaxial Cable
It has a PVC or Teflon insulating layer and an outer plastic sheath containing two parallel conduc­tors, each with a separate conformal protective cover.
Optical Fiber Cable
It uses the concept of light reflection through a glass or plastic core. The core is surrounded by a less dense glass or plastic shell called the cladding. Used to transfer large amounts of data.
Stripline is a transverse electr­oma­gnetic (TEM) transm­ission line medium invented by Robert M. Barrett at the Air Force Cambridge Research Center in the 1950s. Stripline is the earliest form of planar transm­ission line.
Conductive material is separated from the ground plane by a dielectric layer.

Mode of Commun­ication

Simplex Mode
In simplex mode, commun­ication is one-way, like one-way. Only one of the two devices on the link can transmit, the other can only receive. Simplex mode allows data to be sent in one direction using the full capacity of the channel.
Televi­sio­n/Radio Signal
Half-D­uplex Mode
In half-d­uplex mode, each station can both transmit and receive, but not at the same time. When one device transmits, the other device can only receive and vice versa. Half-d­uplex mode is used when simult­aneous commun­ication in both directions is not required.
Full-D­uplex Mode
In full-d­uplex mode, both stations can transmit and receive at the same time. In full-d­uplex mode, signals in one direction share the capacity of the link with signals in the other direction. This sharing can be done in two ways: Either the link must contain two physically separate transm­ission paths, one for sending and the other for receiving. Or the capacity is divided between signals traveling in both direct­ions.
Telephone call

Layers and their uses

Web server, Mail Server, browser, mail client
Web server, Mail Server, browser, mail client
Web server, Mail Server, browser, mail client
TCP, UDP, SPX, AppleTalk
Router, Firewall (Layer 3), Switch
Data Link
ARP, ATM, CDP, FDDI, Frame Relay, HDLC, MPLS, PPP, STP, Token Ring
Bridge, Switch (Layer 2)
Bluetooth, Ethernet, DSL, ISDN, 802.11 Wi-Fi

Collision Detection

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
In this method, after sending a frame, the station monitors the media to see if the transm­ission was succes­sful. If succes­sful, the transm­ission is termin­ated, otherwise the frame is retran­smi­tted.
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
The basic idea behind CSMA/CA is that stations must be able to receive while transm­itting in order to detect collisions from different stations. A collision in a wired network nearly doubles the energy of the received signal, allowing stations to detect a potential collision.
It was developed for wifi, but can also be used for shared media. Multiple stations can transmit data at the same time, which can lead to collisions and data corrup­tion.

Transm­ission Media (Unguided Media)

Type of Media
Radio waves
hese are easy to generate and can penetrate buildings. There is no need to align the transmit and receive antennas. Frequency Range: 3kHz – 1GHz AM radios, FM radios, and cordless phones use radio waves for transm­ission.
Multip­lexer types: line-o­f-sight transm­ission. H. Transm­itting and receiving antennas should be placed properly. The distance a signal travels is directly propor­tional to the height of the antenna. Frequency Range: 1GHz – 300GHz They are mainly used for mobile telephony and television distri­bution.
Infrared is used for short distance commun­ica­tion. Obstacles cannot be penetr­ated. This prevents interf­erence between systems. Frequency Range: 300GHz – 400THz It is used in TV remote controls, wireless mice, keyboards, printers, etc.

Computer Network Protocols

Network Protocol
Port Number
A family of protocols that specify how devices on the same network segment format and transmit data.
44818, 2222
Wi-Fi or WLAN
A family of protocols that deal with wireless transm­­is­sion.
Splits data into packets (reass­embles later). Error checking is also included, as the acknow­led­gment is expected to be sent within a specified timeframe.
User Datagram Protocol
Every device has an IP address. Packets are “addre­ssed” to ensure they reach the correct user.
Used to access web pages from a web server.
uses encryption to protect data.
File Transfer Protocol: Handles file uploads and downloads, transf­erring data and programs.
SMTP server has a database of user email addresses. Internet Message Access Protocol: Handles incoming mail.
Internet Message Access Protocol: Process incoming mail.
ARP finds a host’s hardware address (also known as MAC (Media Access Control) address) based on its known IP address.
DNS is the host name for the IP address transl­ation service. DNS is a distri­buted database implem­ented on a hierarchy of name servers. It is an applic­ation layer protocol for messaging between clients and servers.
FTPS is known as FTP SSL which refers to File Transfer Protocol (FTP) over Secure Sockets Layer (SSL) which is more secure from FTP. FTPS also called as File Transfer Protocol Secure.
POP3 is a simple protocol that only allows downlo­ading messages from your Inbox to your local computer.
Session Initiation Protocol was designed by IETF and is described in RFC 3261. It’s the protocol of applic­ation layer that describes the way to found out Internet telephone calls, video confer­ences and other multimedia connec­tions, manage them and terminate them.
The SMB protocol was developed by Microsoft for direct file sharing over local networks.
SNMP is an applic­ation layer protocol that uses UDP port numbers 161/162. SNMP is also used to monitor networks, detect network errors, and sometimes configure remote devices.
SSH (Secure Shell) is the permis­sions used by the SSH protocol. That is, a crypto­graphic network protocol used to send encrypted data over a network.
VNC stands for Virtual Network Commun­ica­tion.
Remote Procedure Call (RPC) is a powerful technique for building distri­buted client­-server based applic­ations. It is based on extending tradit­ional calls to local procedures so that the called procedure does not have to be in the same address space as the calling procedure.
1024 to 5000
NFS uses file handles to uniquely identify the file or directory on which the current operation is being performed. Internet Control Message Protocol (ICMP) to provide error control. Used for reporting errors and admini­str­ative queries.
Internet Control Message Protoc­ol(­ICMP) to provide an error control. It is used for reporting errors and management queries.
Bootstrap Protocol (BOOTP) is a network protocol used by network management to assign IP addresses to each member of that network in order to join other network devices through a main server.
Dynamic Host Config­uration Protocol (DHCP) is an applic­ation layer protocol. DHCP is based on a client­-server model, based on discov­eries, offers, requests, and ACKs.
Network Address Transl­ation (NAT) is the process of transl­ating one or more local IP addresses into one or more global IP addresses, or vice versa, in order to provide Internet access to local hosts.
Point-­to-­Point Protocol (PPP) is basically an asymmetric protocol suite for various connec­tions or links without framing. H. Raw bit pipe. PPP also expects other protocols to establish connec­tions, authen­ticate users, and carry network layer data as well.
Routing Inform­ation Protocol (RIP) is a dynamic routing protocol that uses hop count as a routing metric to find the best path between source and destin­ation networks.
Open Shortest Path First (OSPF) is a link-state routing protocol used to find the best path between a source and destin­ation router using its own shortest path first).
Enhanced Interior Gateway Routing Protocol (EIGRP) is a dynamic routing protocol used to find the best path and deliver packets between any two Layer 3 devices.
Border Gateway Protocol (BGP) is a protocol used to exchange Internet routing inform­ation and is used between ISPs in different ASes.
Spanning Tree Protocol (STP) is used to create a loop-free network by monitoring the network, tracking all connec­tions, and shutting down the least redundant connec­tions.
0 to 255
RARP, stand for Reverse Address Resolution Protocol, is a computer networ­k-based protocol used by client computers to request IP addresses from a gateway server’s Address Resolution Protocol table or cache.
The D-channel LAPD or Link Access Protocol is basically the Layer 2 protocol normally required for the ISDN D-channel. It is derived from the LAPB (Link Access Protocol Balanced) protocol.
IP Security (IPSec) is a standard suite of Internet Engine­ering Task Force (IETF) protocols between two commun­ication points on IP networks to provide data authen­tic­ation, integrity, and confid­ent­iality. It also defines encrypted, decrypted, and authen­ticated packets.
ASCII (American Standard Code for Inform­ation Interc­hange) is the standard character encoding used in teleco­mmu­nic­ations. The ASCII repres­ent­ation “ask-ee” is strictly a 7-bit code based on the English alphabet. ASCII codes are used to represent alphan­umeric data.
EBCDIC (Extended Binary Encoded Decimal Interc­hange Code) (prono­unced “ehb-s­uh-dik” or “ehb-k­uh-­dik”) is an alphan­umeric binary code developed by IBM to run large-­scale computer systems .
X.25 PAD
X.25 is an Intern­ational Teleco­mmu­nic­ation Union Teleco­mmu­nic­ation Standa­rdi­zation Sector (ITU-T) protocol standard simply for Wide Area Network (WAN) commun­ica­tions that basically describes how the connec­tions among user devices and network devices are establ­ished and mainta­ined.
High-Level Data Link Control (HDLC) commonly uses the term “frame” to denote units or logs of units of data that are frequently transm­itted or transm­itted from one station to another, express. Each frame on the link must start and end with a flag sequence field (F).
SLIP stands for Serial Line Internet Protocol. It is a TCP/IP implem­ent­ation which was described under RFC 1055 (Request for Comments).
Link Access Procedure (LAP) is basically considered as an ITU family of Data Link Layer (DLL) protocols that are subsets of High-Level Data Link Control (HDLC). LAP is partic­ularly derived from IBM’s System Develo­pment Life Cycle (SDLC).
Network Control Protocol (NCP) is a set of protocols that are part of Point-­to-­Point Protocol (PPP).
Mobile IP
Mobile IP is a commun­ication protocol (created by extending the Internet Protocol, IP) that allows a user to move from one network to another using the same her IP address.
Voice over Internet Protocol (VoIP), is a technology that allowing you to make voice calls over a broadband Internet connection instead of an analog (regular) phone line. Some VoIP services allow you to call people using the same service, but others may allow you to call anyone.
Lightw­eight Directory Access Protocol (LDAP) is an internet protocol works on TCP/IP, used to access inform­ation from direct­ories. LDAP protocol is basically used to access an active directory.
GRE or Generic Routing Encaps­ulation is a tunneling protocol developed by Cisco. It encaps­ulates IP packets i.e. delive­rable inner packets into outer packets.
The HTTP headers Author­ization header is a request type header that used to contains the creden­tials inform­ation to authen­ticate a user through a server. If the server responds with 401 Unauth­orized and the WWW-Au­the­nticate header not usually.
Encaps­ulation security payload, also abbrev­iated as ESP plays a very important role in network security. ESP or Encaps­ulation security payload is an individual protocol in IPSec.
Network News Transfer Protocol (NNTP) is the underlying protocol of UseNet, which is a worldwide discussion system which contains posts or articles which are known as news.
DCOM- Distri­buted Component Object Model– helps remote object via running on a protocol known as the Object Remote Procedure Call (ORPC).
Internet Relay Chat (IRC) is an Internet applic­ation that was developed by Jakko Oikarinen in Finland. Chat is the most convenient immediate way to commun­icate with others via Internet.

OSI Protocols

Applic­ation Layer Protocols

TELNET: Telnet stands for Teleco­mmu­nic­ations Network. This protocol is used for managing files over the Internet. It allows the Telnet clients to access the resources of Telnet server. Telnet uses port number 23.

DNS: DNS stands for Domain Name System. The DNS service translates the domain name (selected by user) into the corres­ponding IP address. For example- If you choose the domain name as www.ab­, then DNS must translate it as (random IP address written just for unders­tanding purposes). DNS protocol uses the port number 53.

DHCP: DHCP stands for Dynamic Host Config­uration Protocol. It provides IP addresses to hosts. Whenever a host tries to register for an IP address with the DHCP server, DHCP server provides lots of inform­ation to the corres­ponding host. DHCP uses port numbers 67 and 68.

FTP: FTP stands for File Transfer Protocol. This protocol helps to transfer different files from one device to another. FTP promotes sharing of files via remote computer devices with reliable, efficient data transfer. FTP uses port number 20 for data access and port number 21 for data control.

SMTP: SMTP stands for Simple Mail Transfer Protocol. It is used to transfer electronic mail from one user to another user. SMTP is used by end users to send emails with ease. SMTP uses port numbers 25 and 587.

HTTP: HTTP stands for Hyper Text Transfer Protocol. It is the foundation of the World Wide Web (WWW). HTTP works on the client server model. This protocol is used for transm­itting hypermedia documents like HTML. This protocol was designed partic­ularly for the commun­ica­tions between the web browsers and web servers, but this protocol can also be used for several other purposes. HTTP is a stateless protocol (network protocol in which a client sends requests to server and server responses back as per the given state), which means the server is not respon­sible for mainta­ining the previous client’s requests. HTTP uses port number 80.

NFS: NFS stands for Network File System. This protocol allows remote hosts to mount files over a network and interact with those file systems as though they are mounted locally. NFS uses the port number 2049.

SNMP: SNMP stands for Simple Network Management Protocol. This protocol gathers data by polling the devices from the network to the management station at fixed or random intervals, requiring them to disclose certain inform­ation. SNMP uses port numbers 161 (TCP) and 162 (UDP).

Presen­tation Layers Protocols

Apple Filing Protocol (AFP): Apple Filing Protocol is the propri­etary network protocol (commu­nic­ations protocol) that offers services to macOS or the classic macOS. This is basically the network file control protocol specif­ically designed for Mac-based platforms.

Lightw­eight Presen­tation Protocol (LPP): Lightw­eight Presen­tation Protocol is that protocol which is used to provide ISO presen­tation services on the top of TCP/IP based protocol stacks.

NetWare Core Protocol (NCP): NetWare Core Protocol is the network protocol which is used to access file, print, directory, clock synchr­oni­zation, messaging, remote command execution and other network service functions.

Network Data Repres­ent­ation (NDR): Network Data Repres­ent­ation is basically the implem­ent­ation of the presen­tation layer in the OSI model, which provides or defines various primitive data types, constr­ucted data types and also several types of data repres­ent­ations.

External Data Repres­ent­ation (XDR): External Data Repres­ent­ation (XDR) is the standard for the descri­ption and encoding of data. It is useful for transf­erring data between computer archit­ectures and has been used to commun­icate data between very diverse machines. Converting from local repres­ent­ation to XDR is called encoding, whereas converting XDR into local repres­ent­ation is called decoding.

Secure Socket Layer (SSL): The Secure Socket Layer protocol provides security to the data that is being transf­erred between the web browser and the server. SSL encrypts the link between a web server and a browser, which ensures that all data passed between them remains private and free from attacks.

Session Layer Protocols

AppleTalk Data Stream Protocol (ADSP): ADSP is that type of protocol which was developed by Apple Inc. and it includes a number of features that allow local area networks to be connected with no prior setup. This protocol was released in 1985.
This protocol rigorously followed the OSI model of protocol layering. ADSP itself has two protocols named: AppleTalk Address Resolution Protocol (AARP) and Name Binding Protocol (NBP), both aimed at making system self-c­onf­igu­ring.

Real-time Transport Control Protocol (RTCP): RTCP is a protocol which provides out-of­-band statistics and control inform­ation for an RTP (Real-time Transport Protocol) session. RTCP’s primary function is to provide feedback on the quality of service (QoS) in media distri­bution by period­ically sending statis­tical inform­ation such as transm­itted octet and packet counts or packet loss to the partic­ipants in the streaming multimedia session.

Point-­to-­Point Tunneling Protocol (PPTP): PPTP is a protocol which provides a method for implem­enting virtual private networks. PPTP uses a TCP control channel and a Generic Routing Encaps­ulation tunnel to encaps­ulate PPP (Point­-to­-Point Protocol) packets This protocol provides security levels and remote access levels comparable with typical VPN (Virtual Private Network) products.

Password Authen­tic­ation Protocol (PAP): Password Authen­tic­ation Protocol is a passwo­rd-­based authen­tic­ation protocol used by Point to Point Protocol (PPP) to validate users. Almost all network operating systems, remote servers support PAP. PAP authen­tic­ation is done at the time of the initial link establ­ishment and verifies the identity of the client using a two-way handshake (Clien­t-sends data and server in return sends Authen­tic­ati­on-ACK (Ackno­wle­dge­ment) after the data sent by client is verified comple­tely).

Remote Procedure Call Protocol (RPCP): Remote Procedure Call Protocol (RPCP) is a protocol that is used when a computer program causes a procedure (or a sub-ro­utine) to execute in a different address space without the programmer explicitly coding the details for the remote intera­ction. This is basically the form of client­-server intera­ction, typically implem­ented via a reques­t-r­esponse messag­e-p­assing system.

Sockets Direct Protocol (SDP): Sockets Direct Protocol (SDP) is a protocol that supports streams of sockets over Remote Direct Memory Access (RDMA) network fabrics.
The purpose of SDP is to provide an RDMA-a­cce­lerated altern­ative to the TCP protocol. The primary goal is to perform one particular thing in such a manner which is transp­arent to the applic­ation.

Transport Layer Protocols

Transm­ission Control Protocol (TCP)
User Datagram Protocol (UDP)
Stream Control Transm­ission Protocol (SCTP)
Datagram Congestion Control Protocol (DCCP)
AppleTalk Transa­ction Protocol (ATP)
Fibre Channel Protocol (FCP)
Reliable Data Protocol (RDP)
Reliable User Data Protocol (RUDP)
Structured Steam Transport (SST)
Sequenced Packet Exchange (SPX)

Data Link Layer Protocols

Synchr­onous Data Link Protocol (SDLC)
High-Level Data Link Protocol (HDLC)
Serial Line Interface Protocol (SLIP)for encoding
Point to Point Protocol (PPP)
Link Access Procedure (LAP)
Link Control Protocol (LCP)
Network Control Protocol (NCP)

Physical Layer Protocols

Ethernet with 1000BA­SE-T.
Ethernet with 1000BA­SE-SX.
Ethernet at 100BaseT.
Synchr­onous Digital Hierar­chy­/Op­tical Synchr­oni­sation.
Physic­al-­layer variations in 802.11.
Networking for contro­llers.
U.S. Serial Bus

Network Layer Services

The process of encaps­ulating data (also called payload) received from upper layers of the network into network layer packets at the source and decaps­ulating the payload from the network layer packets at the destin­ation is called packet­iza­tion.
Routing and Forwarding
These are two other services provided by the network layer. A network has many routes from a source to a destin­ation. The network layer sets some strategies for finding the best possible route. This process is called routing.


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