Lecture 2 Flashcards
Describe the Circuit-switching process
1- Circuit establishment: end to end circuit is established before communication.
• 2- Data Transfer: Data is transmitted from one node to another (Transmission can be analogue of digital depending on the network).
• 3- Circuit disconnect: The circuit is disconnected once the transmission is done.
Describe Packet-switching
Messages are broken in packets (-fragmentation)
• Each packet contains addresses and control information
• Each node receives packets, stores them temporarily and forwards them to the next stop (store-and-forward)
Difference between Circuit-Switching and Packet Switching?
Circuit-Switching:
- Dedicated transmission path
- packets are not stored
- fixed bandwidth
Packet-Switching:
-No dedicated path
packets may be stored until delivered
-dynamic use of bandwidth
What is routing?
Station sends the packet to the nearest router.
Each router forwards the packets to the next router
Go over node delay in lectures
Go over node delay in lectures
What is Transmission time?
Transmission Time: The time required so that the router forward the packet to the next node/router
• It depends on the packet size and the link rate/bandwidth
• It is not related to the physical distance between the routers
What is propagation Time?
Propagation Time: It is the time required for a bit to be propagated
• It is related to the distance between the two routers
• It is not related to the packet length and the link rate/bandwidth
Describe packet loss
Queue/buffer in the outgoing link has limited capacity, When the queue is full, packet is lost
A lost packet
o It can be retransmitted from the previous node
o It can be managed at end-to-end
What are some reasons a packet may contain errors?
A packet may contain errors, due
o Multiple transmission in a link
o Noise and interference
o Low power control in the receiver
How does packet delay and loss occur?
Delay:
packets being transmitted
packets queueing
Loss:
(available) buffers: arriving packets dropped (loss) if no free buffers
What is throughput?
Throughput
o Number of bits that can be transmitted within a time window (delay)
o Delay= Propagation Time+ Transmission Time + Queuing
What is Time Division Multiplexing (TDM) ?
Time is divided into very small elementary portions (slots)
The service nodes cyclically reserves in advance one or more slots
What is Frequency Division Multiplexing (FDM)?
- Each device uses different carrier frequencies
* The carrier frequencies are separated by enough bandwidth to accommodate the user’s needs
What is statistical Multiplexing?
- Time division “on-demand”
- Scheduling link per package
- Packets from different sources alternate on the link
- The transferred packets are stored in a temporary buffer, they are serviced by the shared link
