Lecture 3 Flashcards
What is circuit switching?
A dedicated channel (known as circuit) is established for the duration of the transmission.
That circuit between the hosts can be made of one or more physical links.
An example being the PSTN Telephony system - where multiple wire segments are linked together to create an unbroken line for each phone call.
What is packet switching?
Data is transferred by dividing the data into individual (small) packets and are transmitted via a medium that may share multiple communication sessions.
No path or resources are reserved, packets are routed on-the-fly.
What does ATM stand for?
Asynchronous Transfer Mode (ATM).
What is ATM?
A Layer 2 cell relay protocol designed by the ATM Forum.
A telecom concept for the carriage of complete user traffic, including voice, data and video signals.
Similar to circuit switching, ATM uses signaling protocol to establish circuit before data communication commences.
Similar to packet switching as well, ATM is based on statistical multiplexing.
How does ATM benefit itself?
It uses both circuit and packet switching.
It has a small packet (cell) size meaning less transmission delay.
Fixed route for all packets of the connection.
Flexible bandwidth and statistical multiplexing.
High transmission efficiency
What does logical connection first established mean?
Route from the source to the destination is chosen.
The same route is used for all cells (fixed size) of the connection.
Benefits of virtual circuit?
No routing decision for every cell
No dedicated path reserved
What is the transmission path (TP)?
TP is hte physical transmission connection medium - the cable, wireless /etc.
What is a virtual path (VP)?
VP provides connection(s) between switches.
What does a VP consist of?
Multiple Virtucal Circuits (VCs) that logically connect the same two points.
What is the fixed size of a cell?
53 Bytes - 48 bytes payload + 5 bytes header.
What are the problems with a cell?
They have a reduced header functionality.
There is no sequence number or destination and source address.
What does UNI stand for?
User-Network Interface (UNI)
What does NNI stand for?
Network-Network Interface (NNI)
What is the cell format at UNI?
GFC - 4 - Generic Flow Control VPI - 8 - Virtual Path Identifier VCI - 16 - Virtual Circuit Identifier PT - 3 - Payload Type CLP - 1 - Cell Loss Priority HEC - 8 - Header Error Check
What is the cell format at NNI?
VPI - 12 - Virtual Path Identifier VCI - 16 - Virtual Circuit Identifier PT - 3 - Payload Type CLP - 1 - Cell Loss Priority HEC - 8 - Header Error Check
How is switching done in ATM?
Based on the VPI / VCI.
What does AAL stand for?
Application Adaptation Layer