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COMP514 – Advanced Communications

COMP514 – Advanced Communications. Lecture 1: Introduction, ATM Matthew Luckie mluckie@cs.waikato.ac.nz. Introduction to Course. This is a course on modern Carrier Networks i.e., how a telco might organise its IP network from the customer to the core.

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COMP514 – Advanced Communications

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  1. COMP514 – Advanced Communications Lecture 1: Introduction, ATM Matthew Luckie mluckie@cs.waikato.ac.nz

  2. Introduction to Course • This is a course on modern Carrier Networks • i.e., how a telco might organise its IP network from the customer to the core. • ATM, SDH, DSL, DSLAM, BRAS, Wifi, PPP, DHCP, QoS, RADIUS, RED, GRE, L2TP, Ethernet, VLAN, BFD, VoIP, Multiplay, MPLS, LDP, RSVP, BGP

  3. Introduction to Course • Lectures • Tues 2-3 G.1.15 • Thurs 2-3 G.1.15 • Required Textbook • Broadband Network Architectures: Designing and Deploying Triple-Play Services • Chris Hellberg, Dylan Greene, Truman Boyes • Prentice Hall, 2007

  4. Introduction to Course • Lecturers • Donald Neal • Erin Gamble • Matthew Luckie • mluckie@cs.waikato.ac.nz • G.1.28

  5. Introduction to Course • Assessment • Two assignments • 15% each, 30% of final grade • Assignment 1: RADIUS. Due Fri, 7 Sept, 5pm • Assignment 2: MPLS. Due Fri, 12 Oct, 5pm • Mid-semester test • 20% • In class, Thurs 16 Aug, 2pm. • Final test • 50% • Date to be advised

  6. Introduction to Course • Volunteer for Class Rep?

  7. Modern carrier networks: motivation • In the beginning, a Telco provided an analog phone service • Cable networks provided television service over different set of cables • Then, Telco's started providing digital networking over different set of equipment

  8. Modern carrier networks: motivation • It would be nice if a different transmission network wasn’t required for each service • However, not all traffic is equal • Cable TV, Voice: real-time • Data: more tolerant of delay

  9. Modern carrier networks • Multiple ways to solve this problem • Have multiple networks • Asynchronous Transfer Mode (ATM) • MPLS • This lecture looks at the ATM solution • Cell networking

  10. Cell networking: motivation Small Packet Caught Behind Big Packet Source: Craig Partridge, Gigabit Networking, Figure 3.2

  11. Cell networking: motivation Serialisation with Cells Source: Craig Partridge, Gigabit Networking, Figure 3.3

  12. Cell networking packet cells reassembled packet Cells and Packets Source: Craig Partridge, Gigabit Networking, Figure 3.1

  13. ATM Networks • Organised in a hierarchy • Connection-oriented • Extremely low error-rate medium • Support low-cost attachments • Developed in early 1990s

  14. header data ATM Cell Format • 53 bytes: 5 byte header, 48 byte data • 48 bytes is a poor compromise • Compromise between 64-byte payload and 32-byte payload • Too large for voice, too small for data • Partially-filled cells == unproductive work

  15. ATM Hierarchy • ATM networks are designed to be interconnected • Customer/Provider: • User-Network Interface (UNI) • Protects telco’s ATM network from misbehaving customer equipment • Provider/Provider • Network-Network Interface (NNI) • Providers trust each other to be well behaved

  16. ATM Header: NNI 8 7 6 5 4 3 2 1 Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

  17. ATM Header: NNI 8 7 6 5 4 3 2 1 • VPI + VCI uniquelyidentify an ATMconnection • Two level routinghierarchy • A backbone ATMswitch routes on VPI Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

  18. ATM Header: NNI 8 7 6 5 4 3 2 1 • 3 bits of payload type • Distinguishes betweenoperations traffic anduser traffic • If the first bit is not set,the packet is user-traffic Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

  19. ATM Header: NNI 8 7 6 5 4 3 2 1 • CLP: Cell Loss Priority • Single bit • If ATM switch iscongested and has todrop packets, it shouldfirst drop packets withthis bit set Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

  20. ATM Header: NNI 8 7 6 5 4 3 2 1 • CRC: 1 byte CRCcomputed over the5 byte header Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

  21. ATM Adaptation Layer (AAL) • The ATM committee decided there was a need to define the way a packet was divided into cells • AAL 1: constant bit rate applications • AAL 2: variable bit rate applications • AAL 3: connection-oriented data applications • AAL 4: connection-less data applications

  22. AAL 3/4 Header (16 bits) Trailer (16 bits) Seq No T Data (44 bytes) Length CRC MID Type (T) values:10: Beginning of Message 00: Continuation of Message 01: End of Message 11: Single Segment Message AAL 3/4 SAR Format Source: Craig Partridge, Gigabit Networking, Figure 4.7

  23. AAL 5 • Developed by computing industry • Goal was for a more efficient AAL for data communications

  24. AAL 5 1-bit end of datagram field in ATM header header Data (48 bytes) 8-byte trailer Data + Pad (40 bytes) UU Length CRC-32 CPI AAL 5 SAR and Convergence Formats Source: Craig Partridge, Gigabit Networking, Figure 4.9

  25. Conclusion • Main contribution of cell networking is to prevent the medium being blocked by a large packet • Not as important as it once was • 1500 byte packet at 10Mbps = 1.2ms • 1500 byte packet at 10Gbps = 1.2us • QoS based on VPI/VCI still interesting

  26. Homework • Read chapter 4 of ‘Gigabit Networking’ by Craig Partridge

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