EE 122 Lecture 25 Review Ion Stoica December 6 2001 Overview A taxonomy of communication networks Router Architecture in Packet Switching Networks Layering End to end argument istoica cs berkeley edu 2 A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Communication Network Switched Communication Network CircuitSwitched Communication Network Broadcast Communication Network PacketSwitched Communication Network Datagram Network Virtual Circuit Network istoica cs berkeley edu 3 Broadcast vs Switched Communication Networks Broadcast communication networks Information transmitted by any node is received by every other node in the network Examples usually in LANs Ethernet Wavelan Problem coordinate the access of all nodes to the shared communication medium Multiple Access Problem Switched communication networks Information is transmitted to a sub set of designated nodes Examples WANs Telephony Network Internet Problem how to forward information to intended node s this is done by special nodes e g routers switches running routing protocols istoica cs berkeley edu 4 A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Communication Network Switched Communication Network CircuitSwitched Communication Network Broadcast Communication Network PacketSwitched Communication Network Datagram Network Virtual Circuit Network istoica cs berkeley edu 5 Circuit Switching Three phases 1 circuit establishment 2 data transfer 3 circuit termination If circuit not available Busy signal Example telephone networks istoica cs berkeley edu 6 Timing in Circuit Switching Host 1 Node 1 Node 2 Host 2 processing delay at Node 1 propagation delay between Host 1 and Node 1 Circuit Establishment Data Transmission propagation delay between Host 2 and Node 1 DATA Circuit Termination istoica cs berkeley edu 7 Circuit Switching A node switch in a circuit switching network incoming links Node istoica cs berkeley edu outgoing links 8 Circuit Switching Multiplexing Demultiplexing Frames Slots 0 1 2 3 4 5 0 1 2 3 4 5 Time divided in frames and frames divided in slots Relative slot position inside a frame determines which conversation the data belongs to E g slot 0 belongs to red conversation Need synchronization between sender and receiver In case of non permanent conversations Need to dynamic bind a slot to a conservation How to do this If a conversation does not use its circuit the capacity is lost istoica cs berkeley edu 9 A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Communication Network Switched Communication Network CircuitSwitched Communication Network Broadcast Communication Network PacketSwitched Communication Network Datagram Network Virtual Circuit Network istoica cs berkeley edu 10 Packet Switching Data are sent as formatted bit sequences so called packets Packets have the following structure Header Data Trailer Header and Trailer carry control information e g destination address check sum Each packet is passed through the network from node to node along some path Routing At each node the entire packet is received stored briefly and then forwarded to the next node Store and Forward Networks Typically no capacity is allocated for packets istoica cs berkeley edu 11 Packet Switching A node in a packet switching network incoming links Node outgoing links Memory istoica cs berkeley edu 12 Packet Switching Multiplexing Demultiplexing Data from any conversation can be transmitted at any given time A single conversation can use the entire link capacity if it is alone How to tell them apart Use meta data header to describe data istoica cs berkeley edu 13 A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Communication Network Switched Communication Network CircuitSwitched Communication Network Broadcast Communication Network PacketSwitched Communication Network Datagram Network Virtual Circuit Network istoica cs berkeley edu 14 Datagram Packet Switching Each packet is independently switched each packet header contains destination address No resources are pre allocated reserved in advance Example IP networks istoica cs berkeley edu 15 Timing of Datagram Packet Switchi ng Host 1 transmission time of Packet 1 at Host 1 Node 1 Packet 1 Packet 2 Packet 3 Host 2 Node 2 propagation delay between Host 1 and Node 2 Packet 1 Packet 2 Packet 3 processing delay of Packet 1 at Node 2 Packet 1 Packet 2 Packet 3 istoica cs berkeley edu 16 Datagram Packet Switching Host C Host D Host A Node 1 Node 2 Node 3 Node 5 Host B Node 6 Node 7 Host E Node 4 istoica cs berkeley edu 17 A Taxonomy of Communication Networks Communication networks can be classified based on the way in which the nodes exchange information Communication Network Switched Communication Network CircuitSwitched Communication Network Broadcast Communication Network PacketSwitched Communication Network Datagram Network Virtual Circuit Network istoica cs berkeley edu 18 Virtual Circuit Packet Switching Hybrid of circuit switching and packet switching data is transmitted as packets all packets from one packet stream are sent along a pre established path virtual circuit Guarantees in sequence delivery of packets However Packets from different virtual circuits may be interleaved Example ATM networks istoica cs berkeley edu 19 Virtual Circuit Packet Switching Communication with virtual circuits takes place in three phases 1 VC establishment 2 Data transfer 3 VC disconnect Note packet headers don t need to contain the full destination address of the packet istoica cs berkeley edu 20 Timing of Datagram Packet Switchi ng Host 1 Node 1 Host 2 Node 2 propagation delay between Host 1 and Node 1 VC establishment Packet 1 Packet 2 Data transfer Packet 3 Packet 1 Packet 2 Packet 3 Packet 1 Packet 2 Packet 3 VC termination istoica cs berkeley edu 21 Datagram Packet Switching Host C Host D Host A Node 1 Node 2 Node 3 Node 5 Host B Node 6 Node 7 Host E Node 4 istoica cs berkeley edu 22 Packet Switching vs Circuit Switching Most important advantage of packet switching over circuit switching Ability to exploit statistical multiplexing Efficient bandwidth usage ratio between peek and average rate is 3 1 for audio and 15 1 for data traffic However packet
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