The network core
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The mesh of interconnected routers
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Packet-switching (think here refers to data packets. Different data exchange )
- the Hosts file application-BREAK INTO Layer messages packets, packets from Forward to The Next One Router, across links (link means between the hosts) on path ( It refers to the path from the source host to the target hosts) from source to destination. -
Packet switching cause delay and maybe loss
– Store and forward cost the time
– Queuing caused by excessive packets in the router costs the time
– Packets may be dropped (lost) if the memory fills up
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TWO Key Network-Core Functions
- the Routing: Determines Source-Where do you want route taken by packets (the algorithm to calculate the path).
- the Forwarding:. The Move packets from Router apos INPUT to Appropriate Router (according to the calculated route the data packets transmitted out routing, the router there are multiple ports.) -
Alternative core: circuit switching (circuit switched)
End-to-End Resources are allocated to and Reserved for "Call" BETWEEN Source and Where do you want.
The In The Diagram, each Link has Four Circuits.
- the Dedicated Resources are NO Sharing, and IT CAN Guarantee the performance.
link proprietary and related resources, not to be shared, to ensure performance.
- Circuit segment idle if not used used by call.
Led to the bringing forward of neutral data on waste of resources.
-Commonly used in traditional telephone networks. -
Two ways of circuit switching: FDM (Frequency-division multiplexing）and TDM (Time-division multiplexing)
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Comparing packet switching and circuit switching:
– Basing on the link with same bandwidth and assuming users have the same bandwidth. Packet switching can make more people use network than circuit switching.
– Packet switching is great for bursty data (数据突发性增长) since it is resource-sharing, simpler without call setup.
– Excessive congestion maybe cause packets delay and loss, and it need protocols to improve the reliability of data transfer and congestion control.
– It’s needed to make packet switch has the circuit-like behavior for solving some problems, like unstable audio or video services. -
Internet Structure: Network of Networks
- End Systems Connect to Internet Via Access ISPs (Internet Service Providers), SUCH AS Residential, Company, and University ISPs.
- Access ISPs in Turn the MUST BE Interconnected, SO that the any TWO hosts CAN the send packets to the each OTHER.
ISP interconnection (two-way), so that any two hosts in the network can transmit packets to each other.
- Network of netwoks become more complex, and evolution was driven by economics and national policies.
References
Sildes of Computer Networking, A Top-Down Approach
