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Telecommunications Concepts

Chapter 3.1 Packet Switched Local Area Networks. Telecommunications Concepts. Contents. Original Local Area Networks Ethernet Token Ring, Token bus, Cambridge ring, Liu ring, … The IEEE 802 standards IEEE 802.3, IEEE 802.4, IEEE 802.5, ... IEEE 802.2 : Logical Link Control

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Telecommunications Concepts

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  1. Chapter 3.1 Packet Switched Local Area Networks TelecommunicationsConcepts

  2. Contents • Original Local Area Networks • Ethernet • Token Ring, Token bus, Cambridge ring, Liu ring, … • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Tracks • Interconnection of data communication systems.

  3. Contents • OriginalLocal Area Networks • Ethernet • Token Ring, Token bus, Cambridge ring, Liu ring, … • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Tracks • Interconnection of data communication systems.

  4. Shared Media Networks Need for Medium Access Control Protocols Commonly used in Local Area Networks The network itself has practically no storage capacity

  5. Transport Layer Interoperability Connectivity The 7 OSI layers 7 : Application Applications Layer 6 : Presentation 5 : Session 4 : Transport Internet Sublayer 3 : Network 2 : Data Link Networks Layer 1 : Physical

  6. The 3 lower OSI layersFor Shared Medium Networks Internet 3 Network Data Link Control 2 Medium Access Control 1 Physical

  7. Contents • Original Local Area Networks • Ethernet • Token Ring, Token bus, Cambridge ring, Liu ring, … • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  8. Developed in the seventies at Xerox Parc Invented by Lamport Commercially supported by Digital and Intel Still has a dominant market position Originally based on coaxial bus Passive broadcast medium Length limited by electrical properties of cable Thick coaxial : 500 m Thin coaxial : 185 m Repeaters ( = electronic amplifiers ) allow to extend cable length replace coaxial bus by twisted pairs star Medium access control inspired by Aloha Ethernet

  9. Aloha(N.Abramson, F.Kuo, 1970) Communication between terminals and mainframe via geostationary satellite h = 36 000 Km Propagation delay = 240 mS REPEAT Transmit data block B; Receive same block Br; ok := B = Br; IF NOT ok THEN Wait Random Delay END UNTIL ok

  10. t : Transmission time for one data block. G : Total proposed traffic ( # of blocks in time t ) S : Throughput ( # of successful blocks in time t ) 0 <= S <= 1 p : Probability that a block will avoid collision S = G . p ALOHA Performance

  11. ALOHA Collision Window Station A Station B 2t Blocks transmitted according to Poisson Distribution p = e - 2G S = G . e - 2G

  12. S ( G ) ALOHA Throughput 0.2 0.184 0.1 G 0 0 0.5 1 1.5

  13. Carrier Sense Listen before sending Multiple Access Everybody noticing silence can start sending Collision Detect Stop sending when noticing that others sending Collision fragments characterized by insufficient length and therefore discarded by MAC entity. CSMA/CD operation Graceful degradation due to average repetition delay proportional to number of retransmissions

  14. Carrier Sense Listen before talking (carrier sense) A B Send data Listen and wait A B No carrier sensed, transmission starts A B

  15. Collision Enforcement Collision A B Collided signals propagate B detects collision and transmits jam A B Collided signals reach A Station A should detect the collision BEFORE it has send its last databit A B

  16. Minimum packet size No carrier sensed, transmission starts A B Collided signals reach A Station A should detect the collision BEFORE it has send its last databit A B Min. packet time > max. round trip delay

  17. Efficiency of channel

  18. Ethernet Data Frame Preamble (7 bytes) Start Frame (1 byte) Destination Address (6 bytes) Min : 64 bytes Max : 1518 bytes Source Address (6 bytes) Length payload (2 bytes) Payload (evt. + Padding) Frame Check Sequence (4 bytes)

  19. Thick Ethernet Thick cable Total Length <= 500 m

  20. Ethernets with repeaters Repeaters Distance <= 3000 m Half Repeaters Optical Link

  21. Thin Ethernets Thin cable Total Length <= 185 m

  22. Thin Ethernets Thin cable Distance <= 3000 m Segment Length <= 185 m Repeaters

  23. Repeaters for thin Ethernet

  24. Ethernet over twisted pairs One or two pairs per direction

  25. Twisted pair Ethernet(10 Mb/s) Twisted pairs Distance <= 3000 m Segment Length <= 100 m Repeaters (= hubs) Class 3 utp

  26. B B B B B B B B Cascade of Ethernet hubs A HUB = Set of repeaters > all frames broadcasted

  27. Twisted pairs Distance <= 400m Segment Length <= 100 m 2 twisted pairs (class 5) Repeaters 4 twisted pairs (class 3) High-performance Ethernet(100 Mb/s)

  28. Ethernet in office buildings

  29. Contents • Original Local Area Networks • Ethernet • Token Ring, Token bus, Cambridge ring, Liu ring, … • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  30. Contents • Original Local Area Networks • Ethernet • Token Ring • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  31. 802.3 ~ Ethernet 802.4 ~ Token Bus 802.5 ~ Token Ring 802.6 Metropolitan 802.7 Broadband 802.? ??? IEEE 802 Standardsin the OSI model 3 IEEE 802.1 Management, interconnection , Upper layers interface IEEE 802.2 Logical Link Control LLC 2 MAC 1 Physical

  32. Contents • Original Local Area Networks • Ethernet • Token Ring • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  33. Contents • Original Local Area Networks • Ethernet • Token Ring • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  34. Purpose : To fit LAN’s into the general OSI framework Correct transmission errors Services offered : Data link multiplexing by means of LLC addresses Data link error correction and flow control Class 1 : Connectionless, unacknowledged service Class 2 : Connection oriented reliable link control Sliding window protocol Window size = 128 frames. Class 3 : Connectionless, acknowledged. IEEE 802.2Logical Link Control

  35. Flag : Unique bit pattern (01111110) Address (2*16 bit) : allows to multiplex a single MAC address for different data links. Control (16 bit) : Controls the sliding windows Payload (variable length) : Data from layer 3 CRC (16 bit) : Redundant bits obtained by dividing the address, control and payload fields by a predefined polynomial. Flag Address Control CRC Flag Payload LLC Frame Format

  36. The bit pattern 01111110 should never occur in the address, control, payload and CRC fields. After 5 consecutive 1’s a 0 is inserted by the TX A 0 preceded by 5 1’s is removed by the RX. LLC bit stuffing Message to be transmitted : 0100110111110101101111111110111111000110000 Message effectively transmitted : 0100110111110010110111110111101111101000110000

  37. LLC Frame Types • Unnumbered • used to set up connections • used to transfer data in connectionless mode • Supervisory • used for managing the sliding window • in connection oriented mode • Information • used to transfer data in connection oriented mode

  38. Contents • Original Local Area Networks • Ethernet • Token Ring • The IEEE 802 standards • IEEE 802.3, IEEE 802.4, IEEE 802.5, ... • IEEE 802.2 : Logical Link Control • IEEE 802.1 : Learning bridges • High Performance LAN’s and MAN's • High performance Ethernet • Metropolitan Networks • Wireless LAN's • Side Track • Interconnection of data communication systems.

  39. Layer 7 : Application level Gateways Layer 3 : ROUTERS Independent networks (lan or wan) interconnected by means of an internet protocol. Layer 2 : BRIDGES Independent MAC protocols on interconnected lan’s. Distance restrictions apply to each lan individually Half bridges can be interconnected by any lan or wan. Traffic between lan’s can be filtered according to MAC level addresses. Layer 1 : REPEATERS No influence on MAC protocol Same traffic in all interconnected lan’s Interconnection of LAN’s

  40. Repeaters Internet Layer 3b Layer 3b Network Layer 3a Layer 3a Data Link Layer 2b Layer 2b Medium Access Control Layer 2a Layer 2a Repeater Layer 1 Layer 1 Layer 1 Layer 1

  41. Practical Ethernets Repeaters Distance <= 3000 m Half Repeaters Optical Link

  42. Layer 7 : Application level Gateways Layer 3 : ROUTERS Independent networks (lan or wan) interconnected by means of an internet protocol. Layer 2 : BRIDGES Independent MAC protocols on interconnected lan’s. Distance restrictions apply to each lan individually Half bridges can be interconnected by any lan or wan. Traffic between lan’s can be filtered according to MAC level addresses. Layer 1 : REPEATERS No influence on MAC protocol Same traffic in all interconnected lan’s Interconnection of LAN’s

  43. Application Level Gateways Application gateway Layer 7 Layer 7 Layer 7 Layer 7 Layer 6 Layer 6 Layer 6 Layer 6 Layer 5 Layer 5 Layer 5 Layer 5 Layer 4 Layer 4 Layer 4 Layer 4 Layer 3 Layer 3 Layer 3 Layer 3 Layer 2 Layer 2 Layer 2 Layer 2 Layer 1 Layer 1 Layer 1 Layer 1

  44. X400 users SMTP users mail gateway Gateway exampleX400 - SMTP mail gateway

  45. An application gateway between the Internet and an intranet is a fairly secure firewall. Firewalls Firewall Internet Intranet

  46. Layer 7 : Application level Gateways Layer 3 : ROUTERS Independent networks (lan or wan) interconnected by means of an internet protocol. Layer 2 : BRIDGES Independent MAC protocols on interconnected lan’s. Distance restrictions apply to each lan individually Half bridges can be interconnected by any lan or wan. Traffic between lan’s can be filtered according to MAC level addresses. Layer 1 : REPEATERS No influence on MAC protocol Same traffic in all interconnected lan’s Interconnection of LAN’s

  47. Routers Router Layer 3b Layer 3b Layer 3b Layer 3b Layer 3a Layer 3a Layer 3a Layer 3a Layer 2b Layer 2b Layer 2b Layer 2b Layer 2a Layer 2a Layer 2a Layer 2a Layer 1 Layer 1 Layer 1 Layer 1

  48. Layer 7 : Application level Gateways Layer 3 : ROUTERS Independent networks (lan or wan) interconnected by means of an internet protocol. Layer 2 : BRIDGES Independent MAC protocols on interconnected lan’s. Distance restrictions apply to each lan individually Half bridges can be interconnected by any lan or wan. Traffic between lan’s can be filtered according to MAC level addresses. Layer 1 : REPEATERS No influence on MAC protocol Same traffic in all interconnected lan’s Interconnection of LAN’s

  49. Bridges Internet Layer 3b Layer 3b Network Layer 3a Layer 3a Data Link Layer 2b Layer 2b BRIDGE Layer 2a Layer 2a Layer 2a Layer 2a Layer 1 Layer 1 Layer 1 Layer 1

  50. Bridges Bridge

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