Knowt
Circuit & Packet switching cram
Circuit Switching
This is now most often used for a traditional telephone system. A dedicated line is made between the ‘sender’ and ‘receiver’ and ‘tied up’ (noone else can access that line). When data is sent from A to B, the line is made, data is transferred then the connection is terminated. Private data networks also use this method of data transmission.
Pros | Cons |
Only one line is dedicated to this. | Not a flexible way of transmission. |
Data transmission is faster. | Noone else can use the channel. |
The whole bandwidth is made available. | The channel is always present, even while it is not in use. |
Data arrives in sequence. | Requires greater bandwidth. |
Data cannot get lost. | Initial setup takes time. |
This method is good for real-time data transmission. |
Packet Switching
In this method of transmission, the data is broken up into ‘packets’ and sent independently, not always arriving in sequence. Each follows its own path, then is reassembled at the destination. Their paths are selected by routers which chose a path according to the number of packets, and a referral to a ‘routing table’ which holds the data for each packet. It then chooses the shortest route available.
Pros | Cons |
No need to ‘tie’ a line. | Protocols are more complex. |
Can re-route packets. | If packets get lost, they must be resent, which causes slowness in data transmission. |
Expands on options for the use of traffic. | Not good for real-time transmission. |
Can have high data transmission. | Must shara a bandwidth with others. |
Uses digital networks. | Need a large space of RAM to reassemble the packets. |
Packets
A system for hopping is used to overcome the problem of lost packets. Here are some key points:
a packet can only hop a finite number of times
once it has reached a certain limit, it is deleted by the next router, a fact determined by the routing table
A system for error checking is also in place for packet switching, here are some key points of this:
a parity check/checksum value is added to the packet header
it is then calculated at the destination. If it is incorrect, a request is sent to resend the packet
priority values are sometimes added to a header
Here are some features of a packet header:
IP address of its source
IP address of its destination
Current hop number
length of packet in bytes
number of packets in the message
its sequence number for reassembly
checksum value
Routing Tables
These contain the information for the shortest/best routes. The router looks first at the header of the current packet, then at the routing table, which gives the information for where to send the packet next. Here are some of the features of a routing table:
number of hops
MAC address of next router
metrics (cost assigned to routes in order to find the best one)
Net destination (Net ID/pathway)
Gateway details
Netmask (for generating Net ID)
Interface (which locally available interface the packet is intended to reach for the gateway)
Circuit & Packet switching cram
Circuit Switching
This is now most often used for a traditional telephone system. A dedicated line is made between the ‘sender’ and ‘receiver’ and ‘tied up’ (noone else can access that line). When data is sent from A to B, the line is made, data is transferred then the connection is terminated. Private data networks also use this method of data transmission.
Pros | Cons |
Only one line is dedicated to this. | Not a flexible way of transmission. |
Data transmission is faster. | Noone else can use the channel. |
The whole bandwidth is made available. | The channel is always present, even while it is not in use. |
Data arrives in sequence. | Requires greater bandwidth. |
Data cannot get lost. | Initial setup takes time. |
This method is good for real-time data transmission. |
Packet Switching
In this method of transmission, the data is broken up into ‘packets’ and sent independently, not always arriving in sequence. Each follows its own path, then is reassembled at the destination. Their paths are selected by routers which chose a path according to the number of packets, and a referral to a ‘routing table’ which holds the data for each packet. It then chooses the shortest route available.
Pros | Cons |
No need to ‘tie’ a line. | Protocols are more complex. |
Can re-route packets. | If packets get lost, they must be resent, which causes slowness in data transmission. |
Expands on options for the use of traffic. | Not good for real-time transmission. |
Can have high data transmission. | Must shara a bandwidth with others. |
Uses digital networks. | Need a large space of RAM to reassemble the packets. |
Packets
A system for hopping is used to overcome the problem of lost packets. Here are some key points:
a packet can only hop a finite number of times
once it has reached a certain limit, it is deleted by the next router, a fact determined by the routing table
A system for error checking is also in place for packet switching, here are some key points of this:
a parity check/checksum value is added to the packet header
it is then calculated at the destination. If it is incorrect, a request is sent to resend the packet
priority values are sometimes added to a header
Here are some features of a packet header:
IP address of its source
IP address of its destination
Current hop number
length of packet in bytes
number of packets in the message
its sequence number for reassembly
checksum value
Routing Tables
These contain the information for the shortest/best routes. The router looks first at the header of the current packet, then at the routing table, which gives the information for where to send the packet next. Here are some of the features of a routing table:
number of hops
MAC address of next router
metrics (cost assigned to routes in order to find the best one)
Net destination (Net ID/pathway)
Gateway details
Netmask (for generating Net ID)
Interface (which locally available interface the packet is intended to reach for the gateway)
