Integrated networking Columbia University ELE6905, Spring 2004

1. Integrated networking Columbia University ELE6905, Spring 2004   Thursdays 10:00-12:30, Mudd Building rm. 545 Class #8 March 11, 2004 Instructor Stephen Weinstein (Dept. of Elect. Eng.), sbw@cttcgroup.com Office hours: Thursdays 1:30-3, or by appointment. Lecture notes and references posting: http://www.cvn.columbia.edu/courses/Spring2004/ELENE6905.html

2. Today, class #6 Wired Access Networks xDSL, cable data, PON

3. But first, a bit more discussion of token/leaky bucket traffic smoothing - Token bucket imposes an average rate constraint, leaky bucket a peak rate constraint. Both offer some control of the duration of a high-speed burst from the source. - Can be used to police a DiffServ Service Level Specification (part of an SLA) between two network domains, specifying how traffic crossing the boundary of the two domains is to be treated. In particular, how each other’s traffic is conditioned (limited and smoothed) at the boundary, and how packets can be labeled or relabeled for different treatments.

4. Token bucket (limits average rate) Periodic token deposit, Rav tokens/sec (independent of packet arrivals) Bucket capacity C tokens One token withdrawn to serve a packet whenever a packet is present Server queue Shaped output traffic Arriving traffic rate r packets/sec Leaky bucket (limits peak rate) One token deposited each time a packet arrives Bucket capacity C tokens Tokens "leak" out at periodic rate Rp Server queue Shaped output traffic Arriving traffic rate r packets/sec

5. Burst length analysis of token bucket Bucket size C. Tokens deposited in bucket at constant rate Rav. Token removed from bucket each time a packet is served. Packets arrive at a rate r packets/sec. Assume token bucket initially full (C) after a period of little activity. High-speed burst of packets arrives at rate r > Rav and is immediately serviced, passing through at rate r, until the bucket empties (after which service is at Rav rate). Tb = maximum burst length time until the bucket empties. C + RavTb = no. of tokens already in bucket or added over Tb. rTb = ni, of tokens withdrawn over Tb. 0 = C + RavTb - rTb, or Tb = C/(r-Rav)

6. Cable data Digital access networks The communications facilities used between local/personal networks and metropolitan/core networks. Access networks PON Cellular mobile T-carrier services xDSL (and ISDN) Wireless MAN IEEE 802.16 UWB (Ultra Wideband) LEOS, direct satellite Powerline communications

7. Where is access networking heading?

8. The generic goal: An IP-oriented optical/electrical and optical/optical convergence architecture Optical metropolitan and core networks Ethernet frames? IP services overlay optical fiber Optical node Access network (optical, wireless, coax, twisted pair- it doesn't matter much) Subscriber

9. End-to-end Ethernet: A new communications paradigm, or just a fad? Ethernet bridge Access network Ethernet switch Ethernet switch Optical metropolitan and core networks Ethernet bridge OXC Optical framer Ethernet switch Ethernet frames Access network Ethernet bridge (IEEE802.1D) Ethernet switch IP stack LAN IP on Ethernet Ethernet card

10. Why are there many more cable data than ADSL subscribers in the U.S.? -Cable systems 15 years ago began major upgrades to HFC (hybrid fiber-coax) to reduce maintenance costs and improve transmission performance, before digital services came along. They were better prepared for digital services. Headend Runs of up to 20 amplifiers contributed to noise, distortion, frequent failures

11. -Cable systems have monopolies, but local telephone companies must lease facilities to competitors, discouraging major capital investment in access by telcos. -Cable operators began with a broadband services perspective, while telcos were associated with (and thought like) telephone companies. -ISDN was too little, too late.

12. Is any access system free from congestion problems? Basically no. All access systems have capacity bottlenecks because no carrier wishes to overinvest in excess capacity. Most capacity bottlenecks can be relieved with additional investment in facilities.

13. xDSL (Digital Subscriber Line) - Uses the telephone subscriber twisted pair, bypassing the voice switches with their 4KHz channel filters. - Supports (in some versions) normal analog telephone in addition to data services. - Comes in various symmetric and asymmetric versions (next page). - Performance, especially maximum dependable data rate, is dependent on distance from Central Office (or fiber node) and on crosstalk between twisted pairs in the same bundle.

14. Digital Subscriber Line Types(24-26AWG twisted pair) (POTS: Plain Old (analog) Telephone Service) NameRates down/upPOTSDistance  ISDN (Basic Rate) 144kbps/144kbps no 18Kft ADSL (Asymmetric 1.5-8 Mbps/128-640Kbps yes 6.5-24Kft Digital Subscriber Line) G.lite (ITU-T G.992.2) 0.78-4Mbps/<512Kbps yes <24Kf "splitterless" SHDSL (or just HDSL) 0.768Mbps each way no <18Kft (Symmetric High Speed DSL) G.shdsl (ITU-T G.91.2) 0.144-2.32Mbps each way no 12-20Kft "Multi-rate and extended reach" [http://www.cisco.com/warp/public/cc/so/neso/dsso/global/shdsl_wp.htm] VDSL 26-55Mbps/2Mbps no ~1Kft (Very High Speed Digital Subscriber Line) ADSL standard: T1.413-1998, "Network to Customer Installation Interfaces - Asymmetric Digital Subscriber Line (ADSL) Metallic Interface: November, 1998" available for $350 at www.atis.org/atis/docstore/doc_display.asp?ID=159

15. ADSL can operate much faster than a telephone modem because the data signal bypasses the voiceband filters of telephone switches a) Dialup Modem voice carrier system PSTN ISP 3KHz voiceband filter PSTN switch Line concentrator (the bottleneck)

16. b) ADSL Digital Subscriber Line Access Multiplexer ADSL subscriber termination Line concentrator (voice bottleneck) voice carrier system PSTN Voiceband filters Data bottleneck trunk(s) ... Router DSLAM Data network(s) ADSL modem with data passband filter Typically an ATM switch ISP Commercial ref. for a DSLAM: http://www.adtran.com/static/docs/DOC000965.pdf

17. "G.lite" (G.992.2) Subscriber ADSL modem plugs into computer, just like a voiceband modem. So-called "Splitterless" system. Lower rate, smaller BW (512KHz upper edge). ADSL subscriber termination To DSLAM Convenient installation, but unreliable inside wiring usually degrades performance Commercial example: www.hellosoft.com/products/hdsl/hdsl.htm

18. ADSL modulation formats - Primary standard: DMT (discrete multitone) Generate with Discrete Fourier Transform, as described previously. Different data rates and amounts of transmitted power can be allocated to different subbands, in accordance with transmission rate requirement and quality of channel at different frequencies. sinc(f) spectrum (magnitude shown here) has nulls at carrier frequencies of adjacent subbands, eliminating interband interference (in a system with no channel distortion). Upstream ~20KHz 138KHz 1.1MHz 4KHz (POTS) May use QAM signal constellations of different sizes in different subbands.

19. DMT/OFDM performance costs to maintain orthogonality of subbands - Overhead from cyclic extension (extending blocks beyond multipath dispersion) - Virtual (unused) subbands on the edges of the total band to avoid interference with other bands. 1.1MHz 138KHz

20. Filtered MultiTone (FMT) A variation on DMT applied in VDSL. Mitigates DMT/OFDM performance costs. "With FMT, orthogonality between subchannels is ensured by using non-overlapping spectral characteristics instead of overlapping sinc(f) type spectra. Since the linear transmission medium does not destroy orthogonality achieved in this manner, cyclic prefixing is not needed". Bandpass versions of a standard low-pass filter Line signal Parallel data IDFT Parallel/serial Ref: I. Berenguer & I. Wassell, "FMT Modulation: Receiver filter bank definition for the derivation of an efficient implementation" www-lce.eng.cam.ac.uk/~ib226/papers/fmt_modulation.pdf

21. - Secondary standard: CAP (Carrierless Amplitude-Phase Modulation) Essentially the same as QAM (quadrature amplitude modulation), generated by direct inband digital techniques. Passband signal samples Information stream Store of inband digitally modulated signal sequences Line signal D/A By proper design, can generate signals for an infinite variety of information streams from a finite set of stored inband digital segments

22. ADSL modem KHz 26 138 Data from computer ADSL modu- lator/filter Pulse shaper Subscriber line Ethernet Hybrid coupler Demodulation/ equalization/ detection Receiving filter Coder/ decoder MHz .138 1.1 Telephone filter RJ-11 jack KHz 0.3 3.3 Splitter

23. ADSL protocol stack ISP (Internet Service Provider) Exchange office Subscriber DSLAM Data network terminal Computer (or appliance) ADSL terminal TCP/UDP Protocol services such as DHCP IP Ethernet TCP/UDP IP IP PPP IP ATM (optional) ATM (optional) ATM (optional) ATM (optional) PPP ADSL Ethernet ADSL SONET SONET

24. The future of xDSL? -Existing full-length subscriber line ADSL doesn’t work (at any attractive rate) on a significant percentage (30%?) of subscriber lines. VHDSL will develop as fiber nodes come closer to subscribers. -Requires capital investment in metropolitan data networking to alleviate congestion as subscriber population grows. Telcos want exclusive right to offer xDSL on their subscriber lines; enthusiastic deployment and performance advances depends on that. [They object to unbundling rules.]

25. -Unbundling rules (carriers required to "unbundle" their facilities and lease the pieces to service competitors at reasonable rates) Telcos may be holding back on broadband access (especially VHDSL) until their monopoly is comparable with cable's. Telco ADSL Central Office Telco-built subscriber lines Co-located competitor ADSL?

26. Cable Data System DOCSIS: Data-Over-Cable Service Interface Specifications: Radio Frequency Interface Specification SP-RFIv1.1-I06-001215, Cable Laboratories, December 15, 2000

27. Main DOCSIS Technical Specifications ModulationBandwidth (MHz)Data Rate(Mbps) Down 64 or 256 QAM 6 27 or 36 Up QPSK or 16-QAM 0.2-3.2 0.32-10 In both directions: MPEG-2 framing, Reed-Solomon forward error correction coding, DES encryption. Upstream Medium Access Control: Packet-based, contention and reservation slots, QoS capabilities. Management: SNMP, with MIB definitions. Residential network interface: 10BT Ethernet (USB and IEEE 1394 planned). Business network interfaces: 10/100BaseT, ATM, FDDI

28. Spectrum utilization (within the cable) Upstream (0.2-3.2MHz channels in usable parts of this noisy spectrum) Downstream ................................ MHz 6MHz channelization 5 42 50 860 Each downstream channel can be used for: -One analog TV signal, or -Six-seven 4Mbps MPEG-2 digital TV signals, or -One 19Mbps HDTV signal plus two digital TV signals, or -Data (e.g. Internet downloads) at 30Mbps. 64-QAM or 256-QAM used downstream for high spectral efficiency.

29. Telco return access concentrator (TRAC) To PSTN Switch or network adaptor Cable Headend Analog satellite programming Digital satellite programming Local server facility Backbone network Analog headend term Cable Modem Termination System (CMTS) Network termination ... ... ... ... R T Remote server facility R T T T T T T T Splitter Operations Support Combiner (mux) Analog signal modulators (6MHz channels) Security & Access Controller O/E E/O Single-mode optical fibers OC3-OC12 MPEG, control functions QAM receiver 125-500 subscri- bers Fiber node (O/E, E/O) Set-top box Digital or Analog TV Coaxial cable distribution network Ethernet Contention in shared coaxial cable tree Cable modem: QAM receiver, QPSK transmitter

30. Contention for (upstream) bandwidth in the DOCSIS MAC (medium access control) Resources are allocated as "minislots" of upstream transmission time. Requests Client sources Mediator Alloc. Medium

31. Mapping MAC frame into minislots In the upstream direction, transmission time is slotted into minislots for TDMA (time division multiple access). The time duration of a packet transmission is a power of two multiple of 6.25s minislot increments. If grant isn’t sufficient, MAC frame is fragmented and part is sent later. fragmentation Example MAC frame 6.25μs 6.25μs Grant: 4 x 6.25μs 6.25μs Minislots Used by others Later grant for remainder of request

32. Minislot allocation for upstream traffic (Cable Modem Termination System) Medium Access Protocol management message CMTS Requests Information elements assign slots to different modems Slots not yet mapped Cable modem transmit opportunity Slots previously mapped Request contention area Maintenance Request contention resolved through backoff algorithm.

33. The future of cable data and the comparison with xDSL? -Cable operators (at least in U.S.) are advanced in broadband digital services (entertainment as well as Internet access) and with further innovations may continue in lead. -Congestion on shared coaxial cable tree can be resolved by splitting the fiber node (making two nodes, each of which takes half the lower distribution tree). (This requires capital investment!) Fiber node (O/E, E/O) Fiber node (O/E, E/O) Fiber node (O/E, E/O) 400 subscribers 200 subs 200 subs (more)

34. -Modern cable plants can offer high-speed data service to almost all of their customers, unlike ADSL that can only be offered to about 70%. -Telcos still ahead in quality of plant engineering and maintenance. -Telcos may catch up and pass cable operators when and if the investment cable operators made in fiber nodes is matched by telco investment in fiber nodes (to implement VHDSL). -Both systems have capacity bottlenecks, but cable's may be more expensive to resolve. -xDSL and cable data likely converge to a common "fiber to the neighborhood" architecture with a variety of "last mile" transmission media.

35. PON (Passive Optical Network) A passive splitter in the field reduces cost and makes fiber to the home/business more practical. May replace T-carrier access systems and services.

36. Telco serving office Metropolitan/ core networks CO terminal ATM or (newer) Ethernet based transmissions Passive splitter Up to 64 broadcast drops ONU

37. PON interfaces DS-1 DS-3 OC-3 CO terminal OC-12 IP router ATM switch DS-1 PBX DS-3 POTS ONU Enet Layers 2/3 switching & routing Data provisioning in 64kbps increments up to 1 Gbps Dedicated wavelength Tutorial ref: www.iec.org/online/tutorials/epon/topic04.html?Next.x=37&Next.y=14

38. EPON (Ethernet PON) Objectives: - Point-to-multipoint, low-cost architecture using single-mode fiber. - Access network distances (at least 10km) - Standard Ethernet frames, no contention - Standard 1 Gigabit Ethernet rate - Minimum 1:16 split - Replacement for earlier ATM PON Ref (brief tutorial): www.ieee802.org/3/efm/public/jul01/tutorial/pesavento_1_0701.pdf

39. 1 1 1 3 3 3 1 1 1 2 2 2 EPON (Ethernet PON) Users Optical network unit Downstream: 1 1 1 1 3 1 2 ONU1 Headend (e.g. CO terminal) 2 OLT ONU2 2 splitter 3 ONU3 Optical line terminal 3 All packets broadcast to all ONUs, where Ethernet frames for particular users are separated on the basis of the MAC (medium access control) addresses.

40. Ethernet packet Header Type, or length of data field (2 bytes) Checksum (2 bytes) Data field (up to 1500 bytes for 10Mbps) Source address (2 or 6 bytes) Pad (0-46 bytes) Preamble (7 bytes) Destination address (2 or 6 bytes) Start of frame delimiter (1 byte) 6 bytes (each hexadecimal pair is one byte) Example of MAC address: 00-50-DA-CE-E2-76

41. EPON Users Upstream: 1 1 1 ONU1 1 1 2 OLT 1 1 2 3 3 3 2 ONU2 2 splitter 3 3 3 3 ONU3 3 Optical line terminal 3 3 Synchronized system does upstream time slicing, so there are no collisions and no need for packet fragmentation. "MAC uses existing PAUSE control frame or other control messages."

42. EPON optical aspects OLT 1:N optical splitter ONU1 λ1 Medium access logic T WDM ONU2 R λ2 ONU3 T Medium access logic Data WDM R Full duplex operation using separate wavelengths. (example: 1550nm/1310nm) Headend permits only one subscriber at a time to transmit. End users see only traffic from headend, not from each other.

43. Review for the midterm exam

44. n Analog to digital conversion Sampling theorem: For x(t) bandlimited to (-W, W) Hz, x(t) = x(n/2W)sin[2W(t-n/2W)]/[2W(t-n/2W)] Interpolation function (what is its frequency spectrum?) 3T 4T time (sec) 5T T 2T T= 1/2W Reconstruction formula above realized in a low-pass filter limited to what frequencies? What are advantages of digitized media? Does a digitized media stream necessarily use less bandwidth than the original analog media signal?

45. Wireless LAN (IEEE 802.11) Cable data Switched Ethernet Infrastructure network types Metropolitan area networks (MANs) Core (or long haul) networks Local area networks (LANs) Access networks PON Optical Core Network (DWDM) Cellular mobile T-carrier services SONET ring, RPR Resilient Packet Ring Subscriber line 1-10Gbps Ethernet Satellite transport, broadcasting IEEE 802.16 UWB LEOS, direct satellite IR Wireless local loop ("wireless MAN") Bluetooth Personal Area Networks

46. Protocol layers offering services to higher layers and peer-to-peer interaction across networks Information unit transfer Application Application request transport Transport data package transfer Transport Transport request packet forwarding Packet transfer Network Network request link access & physical commun. Physical network Link, Phys Link, Phys

47. Virtual Circuits, e.g. in ATM CBR CBR VBR VBR Pools of capacity for different services ABR ABR guaranteed peak capacity guaranteed average capacity whatever is left over CBR: Continuous bit rate VBR: Variable bit rate ABR: Available bit rate UBR: unrestricted bit rate, best effort service

48. Virtual Private Network Encrypted end-end packet Public Internet (or any data network) Enterprise network segment (or individual remote host) Firewall router Enterprise network segment Encapsulating "tunnel" packet addressed to firewall Destin. host

49. VoIP (general concepts of Internet-PSTN interworking) Peer-to-peer IP communication IP tel. IP telephone (H.323 compliant) Addr. Dir. Mike buf codec RTP Spkr buf Signaling (e.g. SIP) Media gateway controller Telephony Application Port zz UDP/IP/ Phys Internet IP address xxx.xx.xxx.xx H.248 Echo canceler Internet/PSTN Gateway PSTN PSTN telephone Tel number (212) 854-xxxx

50. Spectrum policy (e.g. renting spectrum in bandwidth and time) and applications of software-defined radio - Multiple air interfaces. - Agility to move between available time/bandwidth slots rather than stick to fixed assignments. Frequency Time