1. Network Protocols and Standards

2. Introduction
Whether it’s wired or wireless, most data communications today happens by way of packets of information travelling over one or more networks. However before these networks can work together, they must use a common protocol, or a set of rules for transmitting and receiving these packets of data.
One of the most widely used protocol is the Transmission Control Protocol/Internet Protocol (TCP/IP). There is also, a generic protocol model used in describing network communications known as the Open System Interconnection (OSI) model is useful for comparing and contrasting different protocols.

3. Open System Interconnection Model (OSI)
The OSI model is a standard of the International Organization for Standardization (ISO). It is a general-purpose concept for discussing or describing how computers communicate with one another over a network.
It’s seven-layered approach to data transmission which divides the many operations up into specific related groups of actions at each layer.

4. Seven Layers of the OSI
All of the necessary and desirable operations required are grouped together in a logical sequence at each of the layers. Each layer is responsible for specific functions:
Application Layer (7th Layer)
Presentation Layer (6th Layer)
Session Layer (5th Layer)
Transport Layer (4th Layer)
Network Layer (3rd Layer)
Data Link Layer (2nd Layer)
Physical Layer (1st Layer)

5. Application Layer
It allows you to use an application to communicate for example with the operating system of the server i.e. using your browser to interact with the server operating system which in turn gets the data you requested for.
This layer works with the application software to provide communications functions as required. It verifies the availability of a communications partner and the resources to support any data transfer. It also works with end applications such as Domain Name Service (DNS),File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), Internet message access protocol (IMAP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), Telnet,

6. Presentation Layer
This layer is responsible for coding and decoding data.
This layer checks the data to ensure that it is compatible with the communications resources. It ensures compatibility between the data formats at the applications level and the lower levels. It also handles any needed data formatting or code conversion, as well as data compression and encryption.

7. Session Layer
This layer helps with the task of carrying information from one node (workstation) to the other. However a session has to be established before data can be transferred from one node to the other.
In short the session layer software handles authentication and authorization functions. It also manages the connection between the two communicating devices, establishing a connection, maintaining the connection, and ultimately terminating it. This layer verifies that the data is delivered as well.

8. Transport Layer
The layer allows for data to be broken into smaller packets for distribution to other node.
This layer provides quality of service (QoS) functions and ensures the complete delivery of the data. The integrity of the data is guaranteed at this layer via error correction and similar functions

9. Network Layer
This layer makes it possible to connect two dissimilar networks. The layer performs this function through packet routing via logical addressing and switching functions.

10. Data Link Layer
This is where we assign meaning to electrical signals in a network. The layer determines the size and format of data sent to printers and other devices on the network.
It also defines errors and correction schemes to ensure that data is sent and received correctly
It package and unpacks the data in frames

11. Physical Layer
It is the physical part of the network such as wires and cables. It also handles the electrical signals that transmits the data throughout the network.  
It defines the logic levels, data rate, physical media, and data conversion functions that make up the bit stream of packets from one device to another.

12. OSI Model

13. How OSI Works
The transmitting computer software gives the data to be transmitted to the applications layer, where it is processed and passed from layer to layer down the stack with each layer performing its designated functions. The data is then transmitted over the physical layer of the network until the destination computer or another device receives it. At this point the data is passed up through the layers again, each layer performing its assigned operations until the data is used by the receiving computer’s software.

14. How OSI Works
During transmission, each layer adds a header to the data that directs and indentifies the packet. This process is called encapsulation. The header and data together form the data packet for the next layer that, in turn, adds its header and so on.
The combined encapsulated packet is then transmitted and received. The receiving computer reverses the process, de-encapsulating the data at each layer with the header information directing the operations. Then, the application finally uses the data. The process is continued until all data is transmitted and received

15. Points to Note about OSI
 First, the OSI model is just that, a model. Its use is not mandated for networking, yet most protocols and systems adhere to it quite closely. It is mainly useful for discussing, describing, and understanding individual network functions.
Second, not all layers are used in some simpler applications. While layers 1, 2, and 3 are mandatory for any data transmission, the application may use some unique interface layer to the application instead of the usual upper layers of the model

16. TCP/IP Protocol
Transmission Control Protocol/Internet Protocol(TCP/IP) was developed during the 1960s as part of the America’s Department of Defense’s (DoD) Advanced Research Projects Agency (ARPA) effort to build a nationwide packet data network. It was first used in UNIX-based computers in universities and government installations. Today, it is the main protocol used in all Internet operations.

17. TCP/IP Based Networks
TCP/IP based networks play an important role in computer networks. Its based on an open specification that is not controlled by any vendor.
The term TCP/IP is not limited to just these two protocols. Its also used to refer to a group of protocols related to the TCP/IP protocol such as User Datagram Protocol (UDP), File Transfer Protocol (FTP)

18. Layers of TCP/IP Protocol
TCP/IP also is a layered protocol but does not use all of the OSI layers, though the layers are equivalent in operation and function. The network access layer is equivalent to OSI layers 1 and 2.
The Internet Protocol layer is comparable to layer 3 in the OSI model. The host-to-host layer is equivalent to OSI layer 4. These are the TCP and UDP (user datagram protocol) functions.
Finally, the application layer is similar to OSI layers 5, 6, and 7 combined.

19. Layers of TCP/IP Protocol

20. TCP Layer
The TCP layer packages the data into packets. It then adds a header to the data packet which includes source and destination addresses, a sequence number, an acknowledgment number, a check sum for error detection and correction, and some other information. The header is 20 octets (octet = 8 bits)

21. TCP Layer
At the receiving end of the link, TCP reassembles the packets in the correct order and routes them up the stack to the application. TCP can retransmit a packet if an error occurs. In any case, TCP’s main job is just to pack and unpack the data and provide some assurance of the reliable transmission of error-free data. The IP layer actually transmits the TCP packet.

22. IP Layer
The IP layer transmits the data over the physical-layer connection. IP adds its own header to the packet. The header comprises 32 octets again grouped in 32-bit words which includes source and destination addresses.
These are the well-known IP addresses that we see in dotted decimal format ( ). This is the address assigned to the device by the Internet Assigned Numbers Authority (IANA).

23. IP version 4 and 6
Currently 32 bit address header that is used in IP version 4 (IPv4). Since the IANA has run out of 32-bit addresses (232 of them!), a newer version is rapidly being adopted. IPv6 uses 128-bit addresses. With 2128 addresses, there should be enough for all of the planet’s computers, tablets, and smart phones as well as all of the devices that may be connected to form the so-called Internet of Things (IoT)

24. Network Access Layer
Once the IP header is added to the data, it is transferred to the Network Access layer. This layer repackages the data again into Ethernet packets or some other protocol for final physical transmission. The Ethernet packets are then reconfigured again for transmission over a DSL or cable TV connection or over a wide-area network using Sonet or optical transport network (OTN).

25. TCP/IP Networks
When you configure the TCP/IP protocol on a computer, an IP address, subnet mask, and usually a default gateway are required in the TCP/IP configuration settings
The success of TCP/IP as the network protocol of a network such as the internet is largely because of its ability to connect together networks of different sizes and systems of different types. These networks are arbitrarily defined into three main classes (along with a few others) that have predefined sizes, each of which can be divided into smaller subnet.
A subnet mask is used to divide an IP address into two parts. One part identifies the host (computer), the other part identifies the network to which it belongs. .

26. IP Address
An IP address is a 32-bit number that uniquely identifies a host (computer or other device, such as a printer or router) on a TCP/IP network.
IP addresses are normally expressed in dotted-decimal format, with four numbers separated by periods, such as

27. IP Address
For a TCP/IP wide area network (WAN) to work efficiently as a collection of networks, the routers that pass packets of data between networks do not know the exact location of a host for which a packet of information is destined.
Routers only know what network the host is a member of and use information stored in their route table to determine how to get the packet to the destination host's network. After the packet is delivered to the destination's network, the packet is delivered to the appropriate host.

28. IP Address
For this process to work, an IP address has two parts. The first part of an IP address is used as a network address, the last part as a host address. If you take the example and divide it into these two parts you get the following:
Network address
.132 Host address

29. Subnet Mask
The second item, which is required for TCP/IP to work, is the subnet mask. The subnet mask is used by the TCP/IP protocol to determine whether a host is on the local subnet or on a remote network.
In TCP/IP, the parts of the IP address that are used as the network and host addresses are not fixed, so the network and host addresses above cannot be determined unless you have more information.
This information is supplied in another 32-bit number called a subnet mask. In this example, the subnet mask is It is not obvious what this number means unless you know that 255 in binary notation equals ; so, the subnet mask is:

30. Network Class
IP addresses are divided into classes. The most common of these are classes A, B, and C. Classes D and E exist, but are not generally used by end users. Each of the address classes has a different default subnet mask. You can identify the class of an IP address by looking at its first octet. 

31. Network Classes
Class A networks use a default subnet mask of and have as their first octet. The address is a class A address. Its first octet is 10, which is between 1 and 127, inclusive
Class B networks use a default subnet mask of and have as their first octet. The address is a class B address. Its first octet is 172, which is between 128 and 191, inclusive.
Class C networks use a default subnet mask of and have as their first octet. The address is a class C address. Its first octet is 192, which is between 192 and 223, inclusive.

32. Subnetting
 Class A, B, or C TCP/IP network can be further divided, or sub-netted. This becomes necessary as you reconcile the logical address scheme of the Internet (the abstract world of IP addresses and subnets) with the physical networks in use by the real world.
A system administrator who is allocated a block of IP addresses may be administering networks that are not organized in a way that easily fits these addresses. For example, you have a wide area network with 150 hosts on three networks (in different cities) that are connected by a TCP/IP router. Each of these three networks has 50 hosts. You are allocated the class C network This means that you can use the addresses to for your 150 hosts.

33. Subnetting
You should now be able to give IP addresses to 254 hosts. This works fine if all 150 computers are on a single network. However, your 150 computers are on three separate physical networks. Instead of requesting more address blocks for each network, you divide your network into subnets that enable you to use one block of addresses on multiple physical networks.

34. Default Gateway
If a TCP/IP computer needs to communicate with a host on another network, it will usually communicate through a device called a router. In TCP/IP terms, a router that is specified on a host, which links the host's subnet to other networks, is called a default gateway. 

35. END OF LECTURE