1, the network layer transport unit: Datagram!
Features:
- Routing and packet forwarding
- Heterogeneous network interconnection
- Congestion Control
Data exchange:
Circuit-switched and packet-switched [blog talking about easy to understand! ]
Circuit switched: establishing a connection - release a communication connection ---
[Message entire bit stream continuously from a direct source end point, if transmitted in a conduit. ]
advantage:
- [Little communication delay circuit switching connection-oriented, once the connection is established, data can better reach the receiver via a physical connection path, so a small transmission delay;]
- Orderly transfer
- There is no conflict
- And real time
Disadvantages:
- A long time to establish a connection
- Line exclusive, inefficient use
- Inflexibility
- Error-control capabilities
Packet switching:
Store and Forward
advantage:
- No need to establish a link: [does not take up a whole, but a section of]
Disadvantages:
Packet switching is packet switching improved version! [Parallel packet forwarding mechanism, so there will be more than the exchange of messages to save time! ]
to sum up:
VC and data packets:
Reference: virtual circuit network datagram network
Virtual circuit network:
When two computers communicate, it should first establish a connection (i.e.: establishing a VC (Virtual Circuit) in a packet exchange), and then both transmits the packet along the virtual circuit established. This way, the group does not need to complete filling of the destination host address of the head, but only need to fill this VC number corresponding to, thus reducing the overhead of the packet.
VC to reach the terminal via the network service if the re-use reliable transmission protocol, packets can be transmitted sequentially without error, where the loss of the repeat is not present. FIG like between the two hosts are grouped in the exchange must be pre-established virtual circuits.
VC number of data packets refers to what?
When two machines communicate with each other to establish a virtual circuit, according to the data packets virtual circuit number by the lookup table virtual circuit switches and an output line to get it, and further transmits data to the destination
VC network using the network will become the core of the complex, you need to go through all the nodes of this circuit is to safeguard, if the virtual circuit is opened, then the data will be lost, only to re-establish a virtual circuit. Internet pioneers that computer has a strong error handling capabilities, thus proposed the idea of a connectionless: data network reported.
Datagram networks:
The web does not need to establish a connection before sending a packet. Each packet (IP data packets) transmitted independently, regardless of the packet (unnumbered) in its front. The network layer does not provide a quality of service guarantee. In other words, the transmitted packet may be wrong, lost, duplicated and disorder (not in order to reach the terminal), the time limit does not guarantee packet delivery. Since the end of the transmission network does not provide reliable transmission service, which makes routers in the network is relatively simple, so that reduce the burden on the core network, and the price is relatively low.
If the communication between host processes require reliable data delivery, then (error detection, flow control, etc.) by the transport layer is responsible for a host in the network. This design has taken a number of benefits: the network is relatively low cost, flexible operation mode, can be applied to a variety of applications.
The current Internet can be developed to today's scale, it is because the use of this design idea. OSI system supporters had urged suitable for reliable transmission VC network, but it has already become history.
Network architecture TCP / IP system is provided datagram network services.
VC network datagram network distinction:
Wang:
From another:
