INTERNETWORKING I
CHAPTER 6 STUDY GUIDE
What does the IEEE 802.2 standard describe?
Breaks the OSI Layer
2 into two separate layers: the MAC and the LLC. It creates the LLC to allow
part of the data link layer to function independently from existing technologies.
It supports both connectionless and connection-oriented services. It manages
communications between devices over a single link on a network. 802.2 also adds
two addressing components (Destination Services Access Point and Source Service
Access Point).
What are the two separate layers of the OSI link layer? What does each do?
MAC (Media Access
Control) – transitions down to the media (cable); it deals with the protocols
that a host follows in order to access the physical media. It also deals with
media access.
LLC (Logical Link
Control) – transitions up to the network layer (layer 3); this allows it to
communicate with upper-level layers.
What is a MAC address?
What is another name for the MAC address?
Flat, physical, BIA
(burned in address), Media Access Control number
At what layer of the OSI model does the MAC address exist?
Where would you find a MAC address?
On the NIC card.
How are MAC addresses represented?
They’re represented by hexadecimal digits.
What are the two parts of a MAC address? What does each part represent?
The first six comprise the Organizational Unique Identifier (OUI) which identifies the manufacturer (assigned by the IEEE). The last six represent a unique ID number for the NIC.
What is the Layer 2 encapsulation process called?
framing
What is each section of a frame called?
What are the six sections of a frame called? Briefly describe what each one does.
·
Address field –
has source and destination address information in it
·
Length/type/control
field – indicates the end (the frame is considered ended after the FCS field);
also sometimes called an end-frame delimiter.
·
Data field – the
information you’re sending
·
Frame check
sequence (FCS) field – contains a number that is calculated by the source
computer and is based on the data in the frame. The destination computer
recalculates the FCS number and compares it with the source FCS number. It is
an error-checking device.
·
Stop frame field
– indicates the end of a frame
What does media access control refer to?
Protocols that determine which computer on a shared medium is allowed to transmit data (access to the media).
What are the two basic categories MAC can be divided into? Briefly describe each one.
Deterministic – uses a form of “taking your turn.” Example is Token Ring. The computer that wants to transmit must get a token in order to gain access to the media. Only one computer (host) at a time can transmit.
Non-deterministic – uses the FCFS approach. The media is shared by all hosts on the network.
Which of the two above types does Ethernet fall into?
What does FCFS stand for? How does it apply to Ethernet?
First Come First Served. Ethernet is a FCFS system because the media is shared by all the hosts on the network. The first host to gain access to the network is the one served. All others must wait until the transmitting host is finished.
What does CSMA/CD stand for? Briefly describe it.
Carrier Sense Multiple Access/Collision Detection. It is the way Ethernet determines if anyone is currently using the media. The computer listens to see if anyone is transmitting. If no one is, then the computer assumes that the media is available and it transmits its data.
Name three common Layer 2 technologies. What is each one’s logical topology?
·
Token Ring –
information flow is controlled in a ring