UNIT-III NETWORK SYNCHRONIZATIN CONTROL AND MANAGEMENT

UNIT-III NETWORK SYNCHRONIZATIN CONTROL AND MANAGEMENT

Timing Recovery Review 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.

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.

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

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:

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

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

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.

PHASE LOCKED LOOP What 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.

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.

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?

Basic Block Diagram

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

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

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

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

Control Model of PLL

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

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?

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

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

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

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...

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

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

Internet Phone with Fixed Playout Delay

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

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

Packet Loss / Recovery Problem: Internet might lose / excessively delay packets making them unusable for the session arrival time: Pkt i Pkt i+1 Pkt i+3 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

Timing Alignment in Wireless
BS - A BS - B Df = frequency offset between BSs DT = time offset between BSs Mobile in motion; speed = X m/s 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 Df compromises 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

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)

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 ... 25 November 2014

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 C (target: 1 ms accuracy) «The smart grid is a planned nationwide network that uses information technology to deliver electricity efficiently, reliably, and securely» Source: NIST

Asynchronous multiplexing Time-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 Bandwidth is limited because each switching must occur at a rate fast enough for each line to have a continuous conversation.

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)

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

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

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

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

Grating Multiplexer Lens focuses all signals to the same point
Grating reflects all signals into one signal Even though all the incident angles are different, the reflection is the same because the wavelengths are different in such a way to be related through d(sinθi + sinθo) = mλ.

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

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 Multiplexer is designed such that each wavelength and incident angle are related such that all the signals are reflected into one signal

Net work Synchronization in 2G/GSM
Current 2G/GSM Networks Future 2G/GSM Networks BTS BSC Ref. clock MS IP BSC PSN IP BTS Circuit Emulation E1 FE GE BTS BSC Ref. clock MS SDH E1 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. 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another.

Synchronization in 3G/TD-SCDMA
Future 3G/TD-SCDMA Networks Current trail 3G/TD-SCDMA Networks RNC NodeB PSN FE GE Ref. clock RNC NodeB SDH ATM 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 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another.

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. 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another. AGW eNB PSN Ref. clock

Synchronization in different parts
Requirements schematic diagram Base station Base station controller UE Radio Interface SYNC Ref. Clock Network SYNC Node SYNC Synchronization requirements in different positions Layer Sub Items Frequency Accuracy Phase Accuracy Network Sync E1 50ppm - STM-N 4.6ppm PTN Not so strict Node Sync Controller-Base station 50ppb(If base station pick up time from base station controller) 3us(if base station pick up time from base station controller) Inter-Base station 50ppb(If base station pick up time from other base station) 3us(If base station pick up time from other base station) Radio interface GSM 50ppb WCDMA TD-SCDMA 3us TDD LTE TBD FDD LTE

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

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

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

Three Principles for Network 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

Network-wide Views: Design network to provide timely, accurate info Topology, traffic, resource limitations Give logic the inputs it needs Reachability matrix Traffic engineering rules Management Logic Read state info

Direct Control: Allow logic to directly set forwarding state FIB entries, packet filters, queuing parameters Logic computes desired network state, let it implement it Reachability matrix Traffic engineering rules Write state Management Logic Read state info

Overview of the 4D Architecture
Network-level objectives Decision Dissemination Direct control Network-wide views Discovery Data Decision Plane: All management logic implemented on centralized servers making all decisions Decision Elements use views to compute data plane state that meets objectives, then directly writes this state to routers

Network-level objectives Decision Dissemination Direct control Network-wide views Discovery Data Dissemination Plane: Provides a robust communication channel to each router – and robustness is the only goal! May run over same links as user data, but logically separate and independently controlled

Network-level objectives Decision Dissemination Direct control Network-wide views Discovery Data Discovery Plane: Each router discovers its own resources and its local environment E.g., the identity of its immediate neighbors

Network-level objectives Decision Dissemination Direct control Network-wide views Discovery Data Data Plane: Spatially distributed routers/switches Can deploy with today’s technology Looking at ways to unify forwarding paradigms across technologies

The Feasibility of the 4D Architecture
We designed and built a prototype of the 4D Architecture 4D Architecture permits many designs – prototype is a single, simple design point Decision plane Contains logic to simultaneously compute routes and enforce reachability matrix Multiple Decision Elements per network, using simple election protocol to pick master Dissemination plane Uses source routes to direct control messages Extremely simple, but can route around failed data links

Evaluation of the 4D Prototype
Evaluated using Emulab ( Linux PCs used as routers (650 – 800MHz) Tested on 9 enterprise network topologies ( routers each) Example network with 49 switches and 5 DEs

4D Separates Distributed Computing Issues from Networking Issues
Distributed computing issues ! protocols and network architecture Overhead Resiliency Scalability Networking issues ! management logic Traffic engineering and service provisioning Egress point selection Reachability control (VPNs) Precomputation of backup paths

Fundamental Problem: Conflating Distributed Systems Issues with Networking Issues
Routing Process D left D D Routing Process D Routing Process D D left D left Distributed Systems Concern: resiliency to link failures Solution: multiple paths through routing process graph

Reachability Example Packet filter: Drop nyc-FO -> * Permit *
chi Data Center Front Office Packet filter: Drop chi-FO -> * Permit * R5 nyc R3 R4 chi-DC chi-FO nyc-DC nyc-FO

UNIT-III NETWORK SYNCHRONIZATIN CONTROL AND MANAGEMENT

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