It is known as Internet Protocol Suite means this conceptual framework communication protocol used on Internet. It is mostly called by TCP/IP model because TCP (Transmission Control Protocol) and IP (Internet Protocol) were the important protocols used by DoD model. TCP/IP consists of layers such as Network Interface, Internet, Transport and Application Layer.
Now we can deeply look inside each TCP/IP Layers
Network Interface Layer of TCP/IP
Network Interface Layer (Network Access Layer) corresponds to the Physical and data link layer of the OSI model. Network access layer can do all the function that done by physical and data link layer such as using wiring standards, physical addressing, and synchronizing.
Internet Layer of TCP/IP
Internet layer maps to the network layer of the OSI model. TCP/IP is mainly focused on Internet Protocol (IP) were as OSI can have IP, IPX and AppleTalk.
IPv4 Header
DoD originally developed IP and now we are using IPv4 and IPv6, IPv4 is about 32 bit wide.IPv4 header is comprised of 13 fields in which 12 fields are required and one field is optional.
| IPv4 Header Field | Size in bits | Description |
|---|---|---|
| Version |
4
|
Used to describe the version IP;0100 in version means IPv4 |
| Header Length |
4
|
This field specifies header length minimum 160 bits |
| Type of Service |
8
|
Used as QoS marking. Also known as Differentiated Service Code Point (DSCP) used to give more priority to certain packets |
| Total Length |
16
|
Grant total of IP packet size measured in bytes. Range from 20 to 65535 bytes. |
| Identification |
16
|
Used to identify fragment that belong to same packet. All fragments from one packet have same Identification number. |
| IP Flags |
3
|
Used as Flag for segmentation |
| Fragment Offset |
13
|
Fragment Offset allows the destination host to reassemble the Fragments in the proper order. |
| Time To Live |
8
|
Limits the lifespan of packet, its value is decremented as it passes through router; Helps to reduce routing loops. |
| Protocol |
8
|
Used to identify which upper layer protocol is used. |
| Header Checksum |
16
|
Used to check errors. |
| Source Address |
32
|
Sender IPv4 address |
| Destination Address |
32
|
Receiver IPv4 address |
| IP Optional Field |
32
|
Optional field have various parameters. |
TCP/IP Transport Layer
Transport layer of TCP/IP maps to the layer 4 of the OSI layer. This layer encompasses of two protocols TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) which are connection-oriented and connectionless protocols respectively.TCP Header Format
TCP is one of the protocols used by DoD model. TCP is a Connection-Oriented protocol so it can provide reliable end-to-end communication. It can do functions such as segmentation, sequencing, acknowledgments and flow control.
| TCP Header Field | Size in bits | Description |
|---|---|---|
| Source Port |
16
|
Specify the TCP port number used by the sender |
| Destination Port |
16
|
Specify the TCP Port used in the Destination |
| Sequence Number |
32
|
Sequence Number (SYN) used to send segments which have this SYN to ensure that all segments is transmitted it use SYN |
| Acknowledgment Number |
32
|
ACK is used by receiver; it means that segment up that is received and ready for next segment. If ACK5 means it received segments up to 5. Now ready for segment 5. |
| Offset |
4
|
Used to indicate where the data begins. |
| Reserved |
6
|
Reserved for future use. Must be zero. |
| TCP Flags |
6
|
Also known as control bit used. To control transmission through TCP. |
| Window |
16
|
Indicate window size in bytes that means amount of data that can be transmitted without receiving ACK |
| Checksum |
16
|
Used to check errors in header and data. |
| Urgent Pointer |
16
|
Communicate with current value of urgent pointer as an offset from the sequence number in the segment. |
| TCP Options |
32
|
TCP option or some parameters to control the data transmission. |
UDP Header Format
UDP is a lightweight protocol which is connectionless and unreliable. UDP has little overhead because don’t have to segment and sequence the data and not need to setup virtual circuit for data transmission. We don’t have to wait for acknowledgments from the receiver so UDP is very fast compared to TCP. And this is mainly used in steaming audio and video.
| UDP Header Fields | Size in bytes | Description |
|---|---|---|
| Source Port |
16
|
Port number of the sender |
| Destination Port |
16
|
Port address to the packet is addressed to. |
| UDP Length |
16
|
UDP header and data length in bytes. |
| UDP Checksum |
16
|
An optional field used for checking error. Not optional at IPv6 traffic. |
TCP UDP Comparison
| TCP | UDP |
|---|---|
| Connection-Oriented | Connectionless |
| Setup Virtual Circuit | Don’t need virtual circuits |
| Reliable | Unreliable |
| Acknowledgement | No acknowledgement |
| Segmentation | No Segmentation |
| Sequencing | No sequencing |
| Flow Control | No flow control |
TCP/IP Application Layer
The main difference between OSI and TCP/IP model is that it have a single application layer, it can perform all things done by application, presentation and session layers of OSI model. This reduces complexity of developer and network administrator in classifying protocol.TCP/IP Protocols
Now we are going to look some important protocols used in networks. We can manage user traffic to access multiple services of a server by assigning different port numbers to each request. We are also going to look some well-known (1-1023) port numbers also. Clients initiating the connection normally uses source port higher than 1023 such ports is known as Ephemeral Ports.| Protocol | Description | TCP Ports | UDP ports |
| HTTP | Hypertext Transfer Protocol used to retrieve contents of a web page | 80 | |
| HTTPS | Hypertext Transfer Protocol Secure used to retrieve contents of a web page securely | 443 | |
| Telnet | Used to connect remote host | 23 | |
| DNS | Domain Name Server used to resolve IP address of a domain | 53 | 53 |
| FTP | File Transfer Protocol used to retrieve file from server | 21 | |
| SSH | Secure Shell used to connect remote site securely | 22 | |
| TFTP | Trivial File Transfer Protocol used to share file with remote host | 69 | |
| SMTP | Simple Mail Transfer Protocol used to send mail to server | 25 | |
| DHCP | Dynamic Host Configuration Protocol used to allocate dynamic IP address and details to devices on the network. | 67 | |
| NTP | Network Time Protocol used to synchronize clock in a device on the network | 123 | |
| SNTP | Simple Network Time Protocol a less accurate version of NTP | 123 | |
| POP3 | Post Office Protocol version 3 used to retrieve mail from server | 110 | |
| LDAP | Lightweight Directory Access Protocol used to access directories on the network | 389 | |
| IMAP4 | Internet message Access Protocol version 4 used to retrieve mail from the server | 143 | |
| RDP | Remote Desktop Protocol developed by Microsoft in order to control desktop of remote host | 3389 | |
| RTSP | Real Time Streaming Protocol used to stream videos and audios from media servers | 554 | 554 |
Jas Jashim Author and Founder of ccnaguru.com.He is electronics and communication engineer by education, working in networking field.Started this blog as an hobby to help you in ccna studies.
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