CS4700/CS5700 Fundaments of Computer Networks

Transcription

1 CS4700/CS5700 Fundaments of Computer Networks Lecture 4: Fundamental network design issues Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica, Hui Zhang Alan Mislove amislove at ccs.neu.edu Northeastern University 1

2 A Generic Switch incoming links Switch outgoing links Alan Mislove amislove at ccs.neu.edu Northeastern University 2

3 A Generic Switch incoming links Switch outgoing links How to Demultiplex? Alan Mislove amislove at ccs.neu.edu Northeastern University 2

4 A Generic Switch incoming links Switch outgoing links How to Demultiplex? How to Multiplex? Alan Mislove amislove at ccs.neu.edu Northeastern University 2

5 A Generic Switch incoming links Switch outgoing links How to Demultiplex? How to Switch? How to Multiplex? Alan Mislove amislove at ccs.neu.edu Northeastern University 2

6 Circuit Switching: Multiplexing/ Demultiplexing Frames Slots = Alan Mislove amislove at ccs.neu.edu Northeastern University 3

7 Circuit Switching: Multiplexing/ Demultiplexing Frames Slots = Time divided in frames and frames divided in slots Alan Mislove amislove at ccs.neu.edu Northeastern University 3

8 Circuit Switching: Multiplexing/ Demultiplexing Frames Slots = 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 Needs synchronization between sender and receiver Alan Mislove amislove at ccs.neu.edu Northeastern University 3

9 Circuit Switching: Multiplexing/ Demultiplexing Frames Slots = 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 Needs synchronization between sender and receiver In case of non-permanent conversations Needs to dynamic bind a slot to a conservation How to do this? Alan Mislove amislove at ccs.neu.edu Northeastern University 3

10 Circuit Switching: Multiplexing/ Demultiplexing Frames Slots = 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 Needs synchronization between sender and receiver In case of non-permanent conversations Needs to dynamic bind a slot to a conservation How to do this? If a conversation does not use its circuit the capacity is lost! Alan Mislove amislove at ccs.neu.edu Northeastern University 3

11 Circuit Switching Three phases 1. circuit establishment 2. data transfer 3. circuit termination If circuit not available: busy Examples Telephone networks ISDN (Integrated Services Digital Networks) Alan Mislove amislove at ccs.neu.edu Northeastern University 4

12 Timing in Circuit Switching Host 1 Host 2 Switch 1 Switch 2 Transmission delay propagation delay between Host 1 and Switch1 propagation delay between Host 1 and Host 2 Information time Alan Mislove amislove at ccs.neu.edu Northeastern University 5

13 Timing in Circuit Switching Host 1 Host 2 Switch 1 Switch 2 Circuit Establishment Transmission delay propagation delay between Host 1 and Switch1 propagation delay between Host 1 and Host 2 Transmission Circuit Termination Information time Alan Mislove amislove at ccs.neu.edu Northeastern University 5

14 Packet Switching: Multiplexing/ Demultiplexing Alan Mislove amislove at ccs.neu.edu Northeastern University 6

15 Packet Switching: Multiplexing/ Demultiplexing Alan Mislove amislove at ccs.neu.edu Northeastern University 6

16 Packet Switching: Multiplexing/ Demultiplexing Data from any conversation can be transmitted at any given time Alan Mislove amislove at ccs.neu.edu Northeastern University 6

17 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 Alan Mislove amislove at ccs.neu.edu Northeastern University 6

18 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 demultiplex? Alan Mislove amislove at ccs.neu.edu Northeastern University 6

19 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 demultiplex? Use meta-data (header) to describe data Alan Mislove amislove at ccs.neu.edu Northeastern University 6

20 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) At each node the entire packet is received, stored briefly, and then forwarded to the next node based on the header information (Store-and-Forward Networks) Allows statistical multiplexing Alan Mislove amislove at ccs.neu.edu Northeastern University 7

21 Packet Switch incoming links Node Memory outgoing links Alan Mislove amislove at ccs.neu.edu Northeastern University 8

22 Datagram Packet Switching Host C Host A Host D Node 1 Node 2 Node 3 Node 5 Host B Node 4 Node 6 Node 7 Host E Alan Mislove amislove at ccs.neu.edu Northeastern University 9

23 Datagram Packet Switching Host C Host A Host D Node 1 Node 2 Node 3 Node 5 Host B Node 4 Node 6 Node 7 Host E Each packet is independently switched Alan Mislove amislove at ccs.neu.edu Northeastern University 9

24 Datagram Packet Switching Host C Host A Host D Node 1 Node 2 Node 3 Node 5 Host B Node 4 Node 6 Node 7 Host E Each packet is independently switched Each packet header contains destination address Alan Mislove amislove at ccs.neu.edu Northeastern University 9

25 Timing of Datagram Packet Switching Host 1 Host 2 Switch 1 Switch 2 transmission time of Packet 1 at Host 1 Packet 1 Packet 2 Packet 3 propagation delay between Host 1 and Switch 2 Packet 1 Packet 2 Packet 3 processing delay of Packet 1 at Switch 2 Packet 1 Packet 2 Packet 3 Alan Mislove amislove at ccs.neu.edu Northeastern University 10

26 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 preestablished path (=virtual circuit) Packet header only contains local virtual circuit identifier (VCI) Demultiplexing and switching based on VCI Guarantees in-sequence delivery of packets Example: ATM networks Alan Mislove amislove at ccs.neu.edu Northeastern University 11

27 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 Alan Mislove amislove at ccs.neu.edu Northeastern University 12

28 Timing of Virtual-Circuit Packet Switching Host 1 Node Node Host VC establishment propagation delay between Host 1 and Node 1 Packet 1 Data transfer Packet 2 Packet 3 Packet 1 Packet 2 Packet 3 Packet 1 Packet 2 Packet 3 VC termination Alan Mislove amislove at ccs.neu.edu Northeastern University 13

29 Virtual Circuit Switching Host C Host A Host D Node 1 Node 2 Node 3 Node 5 Host B Node 4 Node 6 Node 7 Host E Alan Mislove amislove at ccs.neu.edu Northeastern University 14

30 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 Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network Alan Mislove amislove at ccs.neu.edu Northeastern University 15

31 Packet-Switching vs. Circuit- Switching Alan Mislove amislove at ccs.neu.edu Northeastern University 16

32 Packet-Switching vs. Circuit- Switching Most important advantage of packet-switching over circuit switching: ability to exploit statistical multiplexing More efficient bandwidth usage However, packet-switching needs to buffer and deal with congestion More complex switches Harder to provide good network services (e.g., delay and bandwidth guarantees) Alan Mislove amislove at ccs.neu.edu Northeastern University 16