UNIT-III NETWORK SYNCHRONIZATIN CONTROL AND MANAGEMENT

1. UNIT-III NETWORK SYNCHRONIZATIN CONTROL AND MANAGEMENT

2. Timing RecoveryReview of Timing Recovery Problem • Synchronization is the process of aligning the time scales between two or more periodic processes that are occurring at spatially separated points. This is one of the most critical receiver functions in synchronous communication systems. • The receiver synchronization problem is to obtain accurate timing information indicating the optimal sampling instants of the received data signal.

3. In early systems, the timing information was transmitted on a separate channel or by means of a discrete spectral line at an integer multiple of the clock frequency imposed on the data signal itself. • Clearly such systems had many disadvantages, including inefficient utilization of bandwidth. • In digital communication systems that are efficient in power requirements and bandwidth occupancy, the timing information must be derived from the data signal itself and based on some meaningful optimization criterion which determines the steady-state location of the timing instants.

4. Mixer Symbol Detector Analog Matched Filter Carrier Recovery Clock Recovery Block Diagram of an Analog Receiver

5. Recall that we need samples of matched filter at ,also in a digital receiver the only time scale available is defined by unites of Ts and therefore the transmitter time scale defined by units T must be expressed in terms of units of Ts, So:

6. (a) Transmitter Time Scale(nT) (b) Receiver Time Scale(kTs)

7. The timing parameters are uniquely defined given so in practice there is a block labeled timing estimator which estimates , on the other hand in completely digital timing recovery ,the shifted samples must be obtained from asynchronous samples solely by an algorithm operating on these samples (rather than shifting a physical clock ) , Hence digital timing recovery includes 2 basic functions: 1-Estimation of 2-Interpolation& Decimation

8. The ultimate goal of a receiver is to detect the symbol sequence a in a received signal disturbed by noise with minimal probability of detection error. It is known that this is accomplished when the detector maximizes the a posteriori probability for all sequences a. • As far as detection is concerned they must be considered as unwanted parameters which are removed by averaging.

9. PHASE LOCKED LOOPWhat is it? • PLL = Phase Lock Loop • A circuit which synchronizes an adjustable oscillator with another oscillator by the comparison of phase between the two signals. • An electronic circuit that synchronizes itself to an external reference signal.

10. What is it for? • To generate High Frequency Clock in Microprocessor. • In Mobile Communication to generate Carrier Frequency. • Can you think of any other Application? Actually there are many.

11. What does Industry say? • ST Microelectronics has vacancies for “PLL Designers”. • Texas Instruments (TI) want to recruit “PLL designers”. • A lot more Opportunities…….. • Why it is so challenging?

12. Basic Block Diagram

13. 1.Voltage Controlled Oscillator (VCO) • What it does? • Requirements: • High Frequency Operation • Good Programmability Range • Less sensitive to environment • Basic Model: Fout =K * Vin • Different Oscillators in literature. How to Select? • A simple Example: Ring Oscillator • Common Challenges: • Programmability Range ( Giga-Hertz Order) • Maximum Noise limit

14. 2. Divider • What it Does? • Requirements: • Should work on High Frequency( Giga Hertz Order) • Should be less power Consuming • Challenges: • Power Consumption (Power is proprotional to frequency) • Switching Speed.

15. 3. Phase-Frequency Detector (PFD) • What it does? • Requirement: • High Sensitivity • Moderate Frequency Operation • Challenges: • Linearity of PFD • Gain of PFD

16. 4. Loop Filter • Functionality • Low pass filter • Filters out noise of PLL loop

17. Control Model of PLL

18. Some definitions: • Order of PLL – Highest degree of polynomial of characteristics equation (1+ G(s)H(s)) • Type of PLL – No of poles of loop Transfer function (G(s)H(s)) locate at origin

19. Food for Thought • What will be the resolution in terms of frequency of PLL? How will you increase it? • What changes you need to do to achieve above goal? • What will be specifications of PLL? • What is the performance metric of VCO? • For Microprocessor? • For Transmitter/Receiver IC?

20. Multimedia Transmission Challenges and Solutions • Jitter • buffering, time-stamps • Packet loss • loss-tolerant apps • Interleaving • retransmission (ARQ) or Packet-Level Forward Error Correction (FEC) • Single-rate Multicast • Destination Set Splitting • Layering

21. ? t’s up? Hi The re, Wha Jitter • The Internet makes no guarantees about time of delivery of a packet • Consider an IP telephony session: Hi There, What’s up? Speaker Listener Time

22. Jitter (cont’d) • A packet pair’s jitter is the difference between the transmission time gap and the receive time gap • Desired time-gap: Si+1 - SiReceived time-gap: Ri+1 - Ri • Jitter between packets i and i+1: (Ri+1 - Ri) - (Si+1 - Si) Pkt i+1 Pkt i Sender: Pkt i Receiver: Pkt i+1 Si+1 Si Time jitter Ri Ri+1

23. Buffering: A Remedy to Jitter • Delay playout of received packet i until time Si + C (C is some constant) • How to choose value for C? • Bigger jitter  need bigger C • Small C: more likely that Ri > Si + C missed deadline • Big C: • requires more packets to be buffered • increased delay prior to playout • Application timing reqmts might limit C: • Interactive apps (IP telephony) can’t impose large playout delays (e.g., the international call effect) • non-interactive: more tolerant of delays, but still not infinite...

24. Real-Time (Phone) Over IP’s Best-Effort • Internet phone applications generate packets during talk spurts • Bit rate is 8 KBs, and every 20 msec, the sender forms a packet of 160 Bytes + a header to be discussed below • The coded voice information is encapsulated into a UDP packet and sent out • some packets may be lost; up to 20 % loss is tolerable; • using TCP eliminates loss but at a considerable cost: variance in delay; • FEC (Forward Error Correction) is sometimes used to fix errors and make up losses

25. Real-Time (Phone) Over IP’s Best-Effort • End-to-end delays above 400 msec cannot be tolerated; packets that are that delayed are ignored at the receiver • Delay jitter is handled by using timestamps, sequence numbers, and delaying playout at receivers either a fixed or a variable amount • With fixed playout delay, the delay should be as small as possible without missing too many packets; delay cannot exceed 400 msec

26. Internet Phone with Fixed Playout Delay

27. Adaptive Playout • For some applications, the playout delay need not be fixed • e.g., [Ramjee 1994] / p. 430 in Kurose-Ross • Speech has talk-spurts w/ large periods of silence • Can make small variations in length of silence periods w/o user noticing • Can re-adjust playout delay in between spurts to current network conditions

28. Adaptive Playout Delay • Objective is to use a value for p-r that tracks the network delay performance as it varies during a phone call • The playout delay is computed for each talk spurt based on observed average delay and observed deviation from this average delay • Estimated average delay and deviation of average delay are computed in a manner similar to estimates of RTT and deviation in TCP • The beginning of a talk spurt is identified from examining the timestamps in successive and/or sequence numbers of chunks

29. Packet Loss / Recovery • Problem: Internet might lose / excessively delay packets making them unusable for the session Pkt i+1 Pkt i+3 Pkt i arrival time: app deadline: i i+1 i+2 i+3 usage status: …, i used, i+1 late, i+2 lost, i+3 used, ... • Solution step 1: Design app to tolerate some loss • Solution step 2: Design techniques to recover some lost packets within application’s time limits

30. Timing Alignment in Wireless Df = frequency offset between BSs DT = time offset between BSs • When hand-over occurs, the mobile must reacquire carrier frequency • Mobile in motion (X m/s) introduces a Doppler shift (X/c) • Loop bandwidth wide enough to handle (Df+ X/c +LO) (LO = local oscillator offset) • Loop bandwidth should be small from a noise rejection viewpoint • Large Dfcompromises the reliability of hand-over; 50 ppb typical requirement • TDD networks require time/phase alignment between A & B • To control interference between uplink and downlink • Requirement in the microsecond range • LTE-Advanced require DT to be small (microsec) for providing the more bandwidth intensive features BS - B BS - A Mobile in motion; speed = X m/s

31. Current Timing Issues • Networks are being migrated to packet switching as opposed to circuit-switched (i.e. based on TDM) • Significant impact of variable delay (packet delay variation) • Timing requirements remain • Going “IP” does not mean that real-time services or mobile networks no longer need synchronization! • Transition Phase: • Hybrid Networks (IP/TDM islands) • Circuit Emulation • Timing over Packet Networks (packet-based methods) • PTP, NTP, adaptive clock recovery • Monitoring and Testing • Metrics for packet-based timing methods (quantifying PDV)

32. Emerging Needs • Increased need of time/phase sync in Mobile networks • Time sync over various technologies (microwave, OTN, MPLS, etc.) • Financial Sector • IoT, Network of Sensors • Power Networks • ...

33. Power – the need for Sync • “The Power Grid” is one of the world’s largest infrastructures High synchronization requirements due to distributed nature of the grid and the critical balance between power generation and consumption • Power can’t be stored easily so Grids Generate according to Demand • Need good Comms and Sync to correlate Demand and Generation • Has evolved from seconds to milliseconds and will evolve to microseconds → Greater Efficiencies • Also enables the Greater Diversity of the Smart Grid • Power Profile – IEEE C37.238-2011 (target: 1 ms accuracy) Source: NIST

34. Asynchronous multiplexingTime-Division Multiplexing • Transmitting digitized data over one medium • Wires or optical fibers • Pulses representing bits from different time slots • Two Types: • Synchronous TDM • Asynchronous TDM

35. Synchronous TDM • Accepts input in a round-robin fashion • Transmits data in a never ending pattern • Popular – Line & Sources as much bandwidth Examples: • T-1 and ISDN telephone lines • SONET (Synchronous Optical NETwork)

36. Asynchronous TDM • Accepts the incoming data streams and creates a frame containing only the data to be transmitted • Good for low bandwidth lines • Transmits only data from active workstations • Examples: • used for LANs

37. Optical Time Division Multiplexing (OTDM) • OTDM is accomplished by creating phase delays each signal together but with differing phase delays

38. Frequency-Division Multiplexing (FDM) • All signals are sent simultaneously, each assigned its own frequency • Using filters all signals can be retrieved

39. Wavelength-Division Multiplexing (WDM) • WDM is the combining of light by using different wavelengths

40. Grating Multiplexer • Lens focuses all signals to the same point • Grating reflects all signals into one signal

41. Grating Multiplexer • Reflection off of grating is dependent on incident angle, order, and wavelength d(sinθi + sinθo) = mλ

42. Grating Multiplexer • Multiplexer is designed such that each λ and θi are related • Results in one signal that can then be coupled into a fiber optic cable

43. BSC BTS Ref. clock Circuit Emulation MS MS MS E1 E1 E1 E1 Ref. clock FE GE BTS SDH PSN BSC IP BSC IP BTS Net work Synchronization in 2G/GSM • Current 2G/GSM Networks • Future 2G/GSM Networks • Sync Requirements in current 2G/GSM Networks • SDH transport network need frequency sync: +/- 50ppm • Base stations need frequency sync: +/- 0.05ppm • Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH • Sync Requirements in future 2G/GSM Networks • Packet switching network do not need strict synchronization • Base stations need frequency sync: +/- 0.05ppm • For base stations, Reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) or packet-based synchronization (e.g. 1588). • Note: Previous SDH transport network maybe still exist for traditional base stations, sync requirement is the same as before.

44. Ref. clock GE NodeB PSN ATM NodeB SDH RNC RNC FE ATM NodeB NodeB Synchronization in 3G/TD-SCDMA • Future 3G/TD-SCDMA Networks • Current trail 3G/TD-SCDMA Networks • Sync Requirement in future 3G/TD-SCDMA Networks • Packet switching network do not need strict synchronization • Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us • For base stations, reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) for frequency sync or packet-based synchronization (e.g. 1588) for time/phase sync. • Sync Requirement in current 3G/TD-SCDMA Networks • SDH transport network need frequency sync: +/- 50ppm • For transport network, Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH • Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us • For base stations, reference clock is distributed via GPS

45. eNB eNB eNB Ref. clock PSN AGW eNB eNB eNB eNB Synchronization in 4G/TDD-LTE/FDD-LTE • Possible synchronization requirements in LTE • Synchronization requirements in ALL-IP network • Synchronization requirements in distributing Base Station (mesh topology among base stations) • Synchronization requirements in distributing BBU & RRU • Synchronization requirements in radio interfaces • Note: synchronization requirement in LTE is under discussion.

46. Base station Base station controller Ref. Clock UE UE RadioInterfaceSYNC Node SYNC Network SYNC Base station Synchronization in different parts • Requirements schematic diagram • Synchronization requirements in different positions

47. The Role of Network Control and Management • Many different network environments • Access, backbone networks • Data-center networks, enterprise/campus • Sizes: 10-10,000 routers/switches • Many different technologies • Longest-prefix routing (IP), fixed-width routing (Ethernet), label switching (MPLS, ATM), circuit switching (optical, TDM) • Many different policies • Routing, reachability, transit, traffic engineering, robustness The control plane software binds these elements together and defines the network

48. We Can Change the Control Plane! • Pre-existing industry trend towards separating router hardware from software • IETF: FORCES, GSMP, GMPLS • SoftRouter [Lakshman, HotNets’04] • Incremental deployment path exists • Individual networks can upgrade their control planes and gain benefits • Small enterprise networks have most to gain • No changes to end-systems required

49. A Clean-slate Design • What are the fundamental causes of network problems? • How to secure the network and protect the infrastructure? • How to provide flexibility in defining management logic? • What functionality needs to be distributed – what can be centralized? • How to reduce/simplify the software in networks? • What would a “RISC” router look like? • How to leverage technology trends? • CPU and link-speed growing faster than # of switches

50. Three Principles forNetwork Control & Management Network-level Objectives: • Express goals explicitly • Security policies, QoS, egress point selection • Do not bury goals in box-specific configuration Reachability matrix Traffic engineering rules Management Logic