Question

How does the link layer provide guaranteed delivery of frames to its destination?

Answer 1

Data link-layer protocol is used to push a datagram over an individual link. The link-layer protocol describes the format of the units of data being exchanged between the nodes at the ends of the link, as well as the actions that are taken by
these nodes when the data units are sending and receiving.

Units of data interchanged by a link-layer protocol are termed as Frames, and that each link-layer frame hardly encapsulates one network-layer datagram.

The actions performes by the link-layer protocol when sending and receiving frames involves error detection, re transmission, flow control, and random access.

Examples of link-layer protocols include Ethernet, token ring, FDDI, and PPP.

The network layer has the peer-to-peer duty of moving transport-layer elements from the source host to the destination host, a link-layer protocol has the peer-to-peer job of moving a network-layer datagram over a single link in the path.

An important property of the link layer is that , datagram may get handled by various link-layer protocols on the various links in the path.

The network layer must be able to process its peer-to-peer job in the face of a differ in set of individual link layer services.

The services that can be provided by the data link-layer protocol :

• Framing and link access.
• Reliable delivery.
• Flow control.
• Error detection.
• Error correction.
• Half-duplex and full-duplex.

Many services offerd by the link layer consists of robust parallels with services provided at the transport layer.

Both the link layer and the transport layer can offer reliable delivery. Eve though the mechanisms used to support reliable delivery in the two layers are similar, the two reliable delivery services are not the same.

A transport protocol offered consistent delivery between two processes on an end-to-end basis; a reliable link-layer protocol provides the reliable-delivery service between two nodes connected by a single link. Likely, both link-layer and transport-layer protocols can offer flow control and error detection; again, flow control in a transport-layer protocol
is provided on an end-to-end basis, whereas it is offered in a link-layer protocol on a node-to-adjacent-node basis.

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