exam 2 part 3

Explain what a router does, at each hop along a path.

Accepts a frame from the network medium. De-encapsulates the frame to expose the encapsulated packet. Re-encapsulates the packet into a new frame. Forwards the new frame on the medium of the next network segment.

· What are the primary LAN topologies used today?

An extended star extends this topology by interconnecting multiple Ethernet switches. The star and extended topologies are easy to install, very scalable (easy to add and remove end devices), and easy to troubleshoot. Early star topologies interconnected end devices using Ethernet hubs.

· Differentiate between full-duplex and half-duplex communication. Know what types of devices make use of each.

Half-duplex communication Both devices can transmit and receive on the media but cannot do so simultaneously. WLANs and legacy bus topologies with Ethernet hubs use the half-duplex mode. Half-duplex allows only one device to send or receive at a time on the shared medium. Click play in the figure to see the animation showing half-duplex communication. Full-duplex communication Both devices can simultaneously transmit and receive on the shared media. The data link layer assumes that the media is available for transmission for both nodes at any time. Ethernet switches operate in full-duplex mode by default, but they can operate in half-duplex if connecting to a device such as an Ethernet hub. Click play in the figure to see the animation showing full-duplex communication.

media access control

Implements this sublayer (IEEE 802.3, 802.11, or 802.15) in hardware. It is responsible for data encapsulation and media access control. It provides data link layer addressing and it is integrated with various physical layer technologies.

· What types of organizations create Data Link Layer standards?

Institute for Electrical and Electronic Engineers (IEEE). International Telecommunications Union (ITU). International Organizations for Standardization (ISO). American National Standards Institute (ANSI).

· What is another name for a MAC address?

physical address

header

a frame field that contains frame start, addressing, type, control.

data

contains the frame payload (ex, packet header, segment header, and the data

· What type of topology is considered, when accessing the media?

contention bases access

· Differentiate between controlled access and contention-based access by explaining how each works. Explain advantages and disadvantages of each.

controlled access: In a controlled-based multiaccess network, each node has its own time to use the medium. These deterministic types of legacy networks are inefficient because a device must wait its turn to access the medium. Examples of multiaccess networks that use controlled access include the following: Legacy Token Ring Legacy ARCNET contention bases access: In contention-based multiaccess networks, all nodes are operating in half-duplex, competing for the use of the medium. However, only one device can send at a time. Therefore, there is a process if more than one device transmits at the same time. Examples of contention-based access methods include the following: Carrier sense multiple access with collision detection (CSMA/CD) used on legacy bus-topology Ethernet LANs Carrier sense multiple access with collision avoidance (CSMA/CA) used on Wireless LANs

· Why is Layer 2 divided into sublayers? List the sublayers and differentiate between them.

destination NIC and source NIC

error detection

included after the data to form the trailer

addresses

indicates the source and destination nodes on the media

· Differentiate between a logical and physical topology.

logical is a dataflow of topology. The topology of a network is the arrangement and relationship of the network devices and the interconnections between them.

encapsulation

media access control is responsible for this

· Does the same access control method apply to all media?

no not the same one

· List the services carried out by Layer 2.

provides the addressing used in transporting a frame across a shared local media. Device addresses at this layer are referred to as physical addresses.

topology

the arrangement, or the relationship, of the network devices and the interconnections between them.

collision

the mechanism used by Ethernet to control access and allocate shared bandwidth among stations that want to transmit at the same time on a shared medium. Because the medium is shared, a mechanism must exist where two stations can detect that they want to transmit at the same time.

trailer

the trailer determines if the frame arrived without error. It places a logical or mathematical summary of the bits that comprise the frame in the trailer.

frame start

used to identify the beginning and end limits of the frame

frame stop

used to identify the beginning and end limits of the frame

· Do networks usually have the same type of topology logically and physically?

yes