What is Data Link Layer?
Definition: Data Link Layer is layer 2 of the OSI reference model that using in computer network. DLL layer consists more complication and complicated functionalities and liabilities. This layer helps to hide all details of their all hardware and finally it represents to upper layer like as source of communication. Data link layer performs all task in between two hosts, they get link directly with medium of communication.
The main goal of the data link layer is to move all datagram over an individual node. At the receiving side, DLL layer grabs all data from hardware device which are electrical signal form, and then it assembles them into frame format and finally further proceeds to upper layer.
Data link layer consists two different sublayers like as Media Access Control (MAC) sub layer and the Logical Link Control (LLC) sub layer. MAC sub layer helps to handle device interaction (control of media). And other side LLC subs layer deals with addressing and multiplexing in several sections like as error control, flow control, and protocols.
Protocols of Data Link Layer
Here, we will discuss various protocols that used in the Data Link Layer; like as:
Data Link Layer Examples of Protocols
You can say examples of those protocols; below explain each one:
Data Link Layer Protocols List:
- Synchronous Data Link Protocol (SDLC)
- High Level Data Link Protocol (HDLC)
- Serial Line Interface Protocol (SLIP)
- Point to Point Protocol (PPP)
- Link Control Protocol (LCP)
- Link Access Procedure (LAP)
- Network Control Protocol (NCP)
Synchronous Data Link Protocol (SDLC): This protocol introduced by IBM in 1970 that associated part of Systems Network Architecture. SDLC protocol helps to attach remotely devices with mainframe computers at centralized point may be point to point otherwise point to multi point connections. Main role of SDLC protocol is to ensure that all data units must arrived appropriately and with correct flow from one network unit to further network unit.
High Level Data Link Protocol (HDLC): HDLC protocol introduced by ISO in 1979. It gets adopt like as associated part of X.25 network system. It is based on SDLC and delivers both reliable and unreliable services. This is bit oriented protocol that accepted for both communications like as point to point and multipoint.
Serial Line Interface Protocol (SLIP): SLIP is a simply protocol that added with framing byte at the end of IP packet. It designs for transmitting data unit in between the Internet service provider as well as home network users based over the dial up connection. It doesn’t support to error correction and detection mechanism.
Point to Point Protocol (PPP): PPP protocol is using where to need transfer multiprotocol data in between two different directly linked computer systems. This is also simply byte oriented protocol that is mostly using for broadband communications. It has massive load and higher speed.
It also supports to error detection system, and produces 2 protocols like as LCP and NCP. LCP protocol is going to use for bringing line up negotiation of options as well as bringing them down. NCP mostly uses for negotiating network-layer protocols.
Link Control Protocol (LCP): LCP protocol introduced by IEEE 802.2.2, and its main role is to deliver HDCL style services over Local Area Network. LCP is simply PPP protocol that uses for transferring of data frames into different areas like as establishing of connection and testing.
Link Access Procedure (LAP): LAP protocols are simply DLL protocols which needed for data framing and transmission of data over the P2P links. LAP has few reliability service features. LAP protocol has three variants like as LAPB (Link Access Procedure Balanced), LAPD (Link Access Procedure D-Channel), and LAPF (Link Access Procedure Frame-Mode Bearer Services).
Network Control Protocol (NCP): NCP protocol was a traditional protocol that used by ARPANET,. This provides various features to users like as getting to access computers. As well as, other devices at remote area and move files in between multiple computers. NCP is always present in every higher layer protocol as well as supported by PPP protocol. But, NCP get alter with TCP/IP in 1980.
Data Link Layer Function and Services
There are several responsibilities of data link layer: below explain each one –
Framing & Link Access
Data link layer grabs all packets from the network layer and encapsulates those packets into Frames, and then it moves every frame with bit by bit over the network hardware devices. On the receiver side, DLL receives all signals from hardware devices and collects them into again Frame form.
Addressing
Data link layer produces all addressing mechanism system of layer 2. And, then entire hardware addresses get mark as unique at the link. It allows them for encoding into hardware at once of manufacturing.
Synchronization
After sending of all frames on the link and then both machines must synchronized for transferring to acquire the position.
Error Control
Due to few issues, some signals are getting problems in transition and bits get flip. To identify those errors and precede them to recover for getting original data bits, and then it delivers error reporting mechanism system forward to sender end’s.
Flow Control
If, multiple stations presents on the similar link with their different speed or capacity. Data link layer enables with flow control that both machine are capable to swap own data on similar speed.
Multi-Access
DLL may be higher possibility of collision, if host want to try transfer data on shared link. Data link layer offers CSMA/CD mechanism to enable ability of accessing the shared media among multiple Systems.
Data Link Layer Devices
There are several devices which are using in the Data Link Layer; below explain each one:
Bridge: Bridge is electronic device that is using in the computer networking. This network device helps to establish interconnection along with another bridge under similar protocol.
Switches: Network switch is a hardware device that works at the data link layer of OSI model. And, it helps to link multiple devices over the network. It uses various packet switching for receiving, sending data packets over the entire network.
Modem: Modem stands for “Modulator – De-modulator“, that used for moving data from one computer network to other computer networks via telephone lines.
Modulator helps to convert all data from digital form to analog form over the transmitting point, and other end De-Modulator offer the functionality for converting the similar from analog mode to digital mode at receiving mode.
Network Interface Card: It is also known as “Network Interface Controller“, “Network Adapter” or “LAN Adapter“. NIC is a circuit board that is installed in the computer systems which deliver dedicated network connection with computer.
