Which layer is responsible for data flow between the source and destination?

Data Link Layer (2)

The data link layer takes the packet from the network layer and breaks it into frames. The header in this layer provides the source and destination MAC addresses. It is the data link layer that will convert the data into binary digits such as 1 and 0 and then prepare them for the physical layer. This layer has to be aware of what type of network interface card (NIC) is being used in order to prepare the packet in a certain way. A frame prepared for Ethernet format would not be understood by a network set up with Token Ring. Thus, this layer takes the network interface into consideration before con-verting the packet. Cyclic redundancy Checking (CRC) is another feature found in the data link layer that provides the ability to detect if a received frame was damaged. This checking feature is normally done by the LAN switch or WAN frame relay switch.

Layer 2 devices that operate at this level are switches and bridges. They work by guiding the traffic to a destination based on the MAC address. The MAC address is a unique series of numbers and letter used to identify a certain network card. They are sometimes referred to as the physical address because this address is hard coded into the network card. A switch can direct traffic to the correct computer only if it's aware of what port the computer's network card is attached. This is done by the computer presenting the MAC address from its network card to the switch when it first comes online.

There are a variety of protocols that work at this layer. Some are used by hosts and others by network devices such as switches. STP (Spanning tree protocol) and RSTP (Rapid spanning tree protocol) are examples of protocols used by switches in this layer. They provide the ability to make sure there is only one layer 2 path to get to a destination. PPP (Point-to-point protocol) and L2TP (Layer 2 Tunneling protocol) are used by hosts. PPP provides the ability for a host to make a connection with a remote side using a modem. L2TP allows a host to connect to a remote side using a secure connection.

Layer 2: Data Link

The data link layer is responsible for maintaining the data link between two hosts or nodes. Its characteristics and functions are as follows:

Defines and manages the ordering of bits to and from data segments called packets

Management of frames, which contains data arranged in an organized manner, which provides for an orderly and consistent method of sending data bits across the medium

Responsible for flow control, which is the process of managing the timing of sending and receiving data so that it doesn't exceed the capacity of the physical connection

Responsible for error notification, including receiving and managing error messaging related to physical delivery of packets

Network devices that operate at this layer include Layer 2 switches (switching hubs) and bridges.

The data link layer is divided into two sublayers:

Logical Link Control (LLC) sublayer provides the logic for the data link. Thus, it controls the synchronization, flow control, and error checking functions of the data link layer.

Media Access Control (MAC) sublayer provides control for accessing the transmission medium. It is responsible for moving data packets from one network interface card (NIC) to another, across a shared transmission medium. Physical addressing is handled at the MAC sublayer. MAC is also handled at this layer. This refers to the method used to allocate network access to computers and prevent them from transmitting at the same time, causing data collisions. Common MAC methods include Carrier Sense Multiple Access/Collision Detection (CSMA/CD), used by Ethernet networks, Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA), used by AppleTalk networks, and token passing, used by Token Ring and Fiber Distributed Data Interface (FDDI) networks.

EXAM WARNING

A MAC address consists of six hexadecimal numbers. The highest possible hexadecimal number is FF:FF:FF:FF:FF:FF, which is a broadcast address. The first three bytes contain a manufacturer code and the last three bytes contain a unique station ID. You can view the MAC address on most systems with the following commands.

Windows ME, 9x: winipcfg (navigate the graphical user interface (GUI) to find the MAC address)

Windows NT, XP, Vista, 2000, 2003, 2008: ipconfig/all

Linux: ifconfig -a

3.1.5 Layer 3: Network Layer

The data link layer implements a packet link between computers attached to a common link. As we explained in our discussion of store-and-forward packet switching (see section 2.6.2), when computers are connected by a collection of point-to-point links, they must figure out where to send the packets that they receive: whether to send them out over another link and, if so, which one. (See Figure 3.6.) This function–finding the path the packets must follow–is called routing. Routing is one of the main functions of the network layer. The network layer appends unique network addresses of the source and destination computers. An important addressing scheme in packet-switched networks is that used by the Internet. Circuit-switched networks, like the telephone network, use different addressing schemes.

Thus, the network layer uses the transmission over point-to-point links provided by the data link layer to transmit packets between any two computers attached in a network.

What layer is responsible for transferring data between the source and destination computers?

Which layer is responsible for data flow?

What layers gets data from a source network to the destination network?

Which layer is responsible for source to destination delivery in a network model?