Some common concepts of computer network

Chapter Four

1. Routers forwarding: the packet from one input port of a router to link a suitable output link interface of a local action , involves only the packet from the router link into a link to be transmitted;

2. The router routing: refer to a packet from source to destination end path network-wide operation , involving all routers ;

3. Packet Switch: a general packet switching device,, according to the header value of the packet from an input link interface transmitting packets to an output link interface.
   

4. ATM service model: Constant Bit Rate CBR (Costant bit rate) service ; Available Bit Rate ABR (Available bit rate) service;

5. CBR: look like so that there is a network connection between the sending and receiving hosts dedicated fixed bandwidth transmission link. Suitable for real-time , constant bit rate audio and video streams.

6. ABR: guaranteed minimum cell rate (the MCR) , or higher than the MCR (there is sufficient free resources);

7. Internet service provided by the network layer: a single service that best-effort service (best-effort service), similar to the ** "There is no service" **.
   

8. VC VC: between the source and destination of a logical connection paths : a series of links and routers; multiple virtual circuits can be created simultaneously.

9. VC number: the number of each segment of the link on the path, on each link VC number may be different .
   Each link uses a different VC number of advantages; reduce the length of the packet header field VC; simplify the process of establishing virtual circuits.

10. Network layer and the transport layer connection establishment distinction:
    the connection establishment of the transport layer: involves only two end systems , communicate with each other and negotiate jointly determine parameters of the connection. Routers in the network does not know the transport layer connection.
    The network layer virtual circuit established: in between the two end systems routers on the path to be involved in the establishment of virtual circuits , and each router is fully aware of all virtual circuits elapsed .

11. Signaling message: sending an indication to the network end system packet start and termination of virtual circuits , and the message delivery between the router for establishing a virtual circuit.

12. Router configuration: inputs : ** achieve physical layer and data link layer functions related to the input link. Output port : Remove the packet storage memory in the output port, and transfer it to the output link.
    , Switch fabric : the packet from the input port switching (forwarding) to the output port, routing processor ;

13. Thread HOL (head-of-the-line) blocking: input queue is located behind a packet of a packet blocking thread (even if the output port is free), wait for the switch fabric transmission;
    

14. Datagram service: in a transmission between a given source and destination different packets may take different routes.
    VC services: using the same paths in all packets between a given source and destination. They are packet-switched network

15. Default router: connected to a host a first router , the access network to the access router is the default, the source router : default router of the source host, the destination router : destination host default router

16. Reversal toxicity: mainly used to avoid "routing loops" phenomenon; as: If y by z x destination routing, tells the z y, x is the distance to its infinite (i.e. tell y z, Dz (x) ∞ =)
    Y is not believed to path x z, it will not attempt to routing via z x.
    
    Three or more nodes of the circuit: not detect reversal of toxicity;

17. DV algorithm : Each node only neighbors exchange, get new cost neighbors and inform their neighbors of the current lowest rates available, know the cost of each link of the network **** needs O (nE) telegrams and O ( n2) search , incorrect calculation values will spread to the entire network.
    LS algorithm : Each node and all other nodes broadcast exchanges, only informing the cost directly connected link. Direct exchange between the two neighbors packet convergence is slow. You may experience routing loop, or count to infinity problem. There is a certain robustness.

18. AS AS: by region of the system, running in the same AS routers routing algorithm is the same .

19. Gateway Router: interconnection of AS. Responsible for forwarding packets to a destination outside of this AS to forward packets within the AS according to another AS routers.

20. AS an internal routing protocols :
    the RIP Routing Information Protocol (DV algorithm): based on the distance vector routing protocol
    OSPF Open Shortest Path First (LS algorithm): The cost of the Dijkstra shortest path algorithm, is a link state protocol.
    Inter-AS routing protocols :
    BGP Border Gateway Protocol: Routing protocol based on the distance vector. Neighboring BGP routers exchange routing information.