Comparison of VirtualCircuit and Datagram Subnets Definitions Packet
Comparison of Virtual-Circuit and Datagram Subnets Definitions • Packet-分组 • Datagrams-数据包 • Datagram subnet-数据包子网 • VC(virtual circuit)-虚电路 • Virtual circuit subnet-虚电路子网 • 路由表及路由算法 第 4章 网络互联与广域网
Store-and-Forward Packet Switching fig 5 -1 The environment of the network layer protocols. 第 4章 网络互联与广域网
Datagram Packet Switching Packet 1 Packet 2 第 4章 网络互联与广域网
Datagram networks a) b) no call setup at network layer routers: no state about end-to-end connections – c) no network-level concept of “connection” packets forwarded using destination host address – packets between same source-dest pair may take different paths application transport network 1. Send data link physical application transport 2. Receive datanetwork data link physical 第 4章 网络互联与广域网
Virtual Circuit Packet Switching Packet 第 4章 网络互联与广域网
Virtual circuits: signaling protocols a) b) c) used to setup, maintain teardown VC used in ATM, frame-relay, X. 25 not used in today’s Internet application transport 5. Data flow begins 4. Call connected network data link 1. Initiate call physical 第 4章 网络互联与广域网 6. Receive dataapplication 3. Accept calltransport 2. incoming callnetwork data link physical 17
Pros and Cons of datagram and VC • Router memory space VS bandwidth • Setup time VS address parsing/analyzing time • The amount of table space • Quality of Service-congestion control • Vulnerability 第 4章 网络互联与广域网
Routing Algorithms (2) Conflict between fairness and optimality. 第 4章 网络互联与广域网
Shortest Path Routing • Labels on the arcs represent the cost (e. g. , distance, delay) • Select a newly reachable node at the lowest cost during each step, and add the edge to that node, to the tree built so far. 第 4章 网络互联与广域网
Flooding Dijkstra's algorithm to compute the shortest path through a graph. 第 4章 网络互联与广域网
Distance Vector Routing • The previous protocols are static • They do not take the current network load into account • Dynamic protocols • Distance Vector Routing (DVR) • Look at the costs that your direct neighbors are advertising to get a packet to the destination • Select the neighbor those advertised cost, added with the cost to get to that neighbor, is the lowest. • Advertise that new cost to the other neighbors. 第 4章 网络互联与广域网
Distance Vector Routing (2) • Good news propagate really fast • Bad news are slow • Count-to-infinity problem • All routers increase their route up to infinity 第 4章 网络互联与广域网
Link State Routing • Distance vector routing was used in the ARPANET until 1979, when it was replaced by Link State Routing Broadcast info on the entire network topology to all routers, and let each of them calculate a sink tree to the other routers • Each router must do the following: 1. Discover its neighbors, learn their network address. 2. Measure the delay or cost to each of its neighbors. 3. Construct a packet telling all it has just learned. 4. Send this packet to all other routers. 5. Compute the shortest path to every other router. 第 4章 网络互联与广域网
Measuring Line Cost A subnet in which the East and West parts are connected by two lines. 第 4章 网络互联与广域网
Hierarchical Routing Hierarchical routing. 第 4章 网络互联与广域网
Connecting Networks A collection of interconnected networks. 第 4章 网络互联与广域网
Concatenated Virtual Circuits Internetworking using concatenated virtual circuits. 第 4章 网络互联与广域网
Connectionless Internetworking A connectionless internet. 第 4章 网络互联与广域网
Tunneling a packet from Paris to London. 第 4章 网络互联与广域网
Tunneling (2) Tunneling a car from France to England. 第 4章 网络互联与广域网
- Slides: 32