Chapter 1 Flashcards
What is the idea behind layering in the OSI model
That each layer is responsible for providing a service to the layer above by using the services of the layer below
What is the communication between layer *n *and layer *n - 1 *known as?
interface
What is the 1st Layer in the OSI Model
Physical
What is the second layer in the OSI Model
Data Link
What is the third layer in the OSI model?
Network
What is the 4th layer in the OSI model
Transport
What is the 5th layer in the OSI model
Session
What is the 6th layer in the OSI model
Presentation
What is the 7th Layer in the OSI model
Application
What is the goal of the Presentation Layer
To agree on representations for data.
What method of presentation does the Presentation Layer standardize on?
ASN.1 (Abstract Syntax Notation 1)
What is bit stuffing and how does it work
Bit stuffing is a technique used to mark the start and end of a frame. In bit stuffing 6 1’s are used to denote the start and end of a frame. If 6 1’s are included in the data portion of a frame, after 5 1’s are transmitted the transmitting node knows to add a 0 into the data. The receiving node knows that once 5 1’s are received, followed by a 0 and another 1, it should remove the 0 and parse the date portion as if 6 1’s were being transmitted.
What are two methods used to denote the beginning and end of a packet?
1) bit stuffing
2) using different physical signals for data bits, than for markers
As it pertaines to layering, what is an envelope and when is it applied
An envelope is information glued onto the beginning/end of a packet for interpretation by a certain layer of the OSI model. These are known as the header and footer
Each layer communicates with its peer layer through a ____
Protocol Data Unit (PDU)
What kind of PDU’s does the data link layer use to communicate?
LPDU
What kind of PDU is used to communicate with at the Network Layer?
NPDU
Which kind of PDU is used to communicate with at the Transport Layer?
TPDU
When layer N+1 gives information to layer n for transmission, what is the information known as?
An SDU, or Service Data Unit. The layer term is prepended to elminiate ambiguity (e.g. PSDU, SSDU, TSDU, NSDU…etc)
Does an NSDU have a Network Layer envelope?
No, an NSDU defines the TPDU after it has been handed to the Network Layer. A packet that already has the Network Layer envelope added to it would be known as an NPDU if it resides at the network layer, or an LSDU if it resides at the Data Link Layer.
What two functions does a connectionless service offer layer n?
1) it accepts packets for transmission from layer n
2) it delivers pacets to layer n
In a connection-oriented service, what three phases does communication consist of?
1) Connection Setup
2) Data Transfer
3) Connection Release
Does a service that is purely datagram make a guarantee about delivery?
No, datagram, aka best-effort, accepts data but makes no guarantee about it’s delivery.
What does a reliable service guarantee
That data will be delivered in the order transmitted, without corruption, duplication, or loss.
What are the two forms of service tramsission
1) reliable
2) datagram (aka best-effort)
In a connectionless network layer, does it make sense to utilize a reliable service?
No, only datagram service makes sense in this instance because by definition nothing is keeping track of what gets delivered.
Are IP, IPX, DECnet, CLNP, and AppleTalk examples of connection oriented or connectionless network layers?
connectionless
