Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Lecture 1 Advanced Networking CSE 8344 Southern Methodist University Fall 2003 Mark E. Allen Welcome! • My contact info: – – – – Mark E. Allen [email protected] 972 747 1490 phone / messages Email is a great way to reach me. • Website – engr.smu.edu/cse/8344 – Will contain syllabus, notes, important dates, etc. Outline for Lecture 1 • • • • Preliminaries Discuss syllabus Course goals and outline for course Get into the content Intro (cont) • Lecture format – Power point slides – Some written examples – Please ask questions! (unless it’s a tape) • NOTE: – Next two lectures will be pre-taped • Aug 29 10 AM (lecture 2) • September 5 10 AM (lecture 3) – Tapes will play at regular time also. DISCUSS SYLABUS HERE Motivation • Purpose of networking: Sharing information between people. – Data is “information” – Voice is “information” – Evolution of networks • • • • • • Teletype (Morse code) was low bit rate. Voice (analog) Video (analog television) FAX Dial-up Modems and DDS circuits High-speed Internet Network evolution • Voice networks – Analog voice – Digital trunks introduced. – Digital switching – Out of band • SS7, AIN, etc. – Wireless voice – Voice over IP • Data networks – Mainframes connected with SNA – Ethernet, Token ring, Novell IPX – Ethernet wins out – Internet – WWW – TCP/IP wins out – GigE and Wireless Ethernet catching on Growth of traffic and internet traffic Traffic Growth: 1998 to 2002 3000 2500 2000 1500 1000 500 0 1998 1998=100 Source: RHK 1999 2000 Voice Other data 2001 Internet 2002 Data and multimedia now dominate traffic on the network • Eventually the network of the future will carry all types of service. • IP looks to be the “convergence layer” of the future. • Voice, video and data communications will eventually occur over a common network. Motivation (cont) • What are we really trying to get? – 1) Convergence: Voice, data, video, etc. all on the same user terminal – 2) Low cost: If we can afford it, we’ll use it. – 3) Mobility: We don’t want to be chained to a desk. (wireless, and the internet all give us freedom to access information wherever we are.) – 4) High bandwidth: Lots of speed will enable new and useful apps. Games, virtual reality, on demand movies, video conferencing, etc) – 5) Consumers want direct access into the data networks (B to B, e-commerce, databases, etc.) The requirements drive the technology • QoS – Bandwidth, Delay, Jitter, etc. • • • • Mobility Cost Power consumption These things are all related. – More bandwidth usually consumes more power – Mobility requires low power. – Etc. .. etc. Functions of network elements • Signaling / Addressing – Allows the users to control how information flows through the network (IP, dialed digits, etc.) • Switching – Devices necessary for steering information and signaling messages around the network • Multiplexing – Allows several information “flows” to share the same medium – We will discuss this in detail Public vs. Enterprise Networks • Millions of disparate customers • Distributed control • Usage based billing • 911 and public safety concerns • Lots of security concerns • Legacy infrastructure • FCC Issues • Large geography • 1 “customer” • Centralized decision making • No billing issues • Limited public safety concerns • Limited legacy concerns • Fewer FCC / regulatory issues. • Smaller geography The layered protocol approach Applications “layer 4” “layer 3” “layer 2” “layer 1” Transport layer Network layer Datalink layer Physical layer Ex: TCP, UDP ... defines how data is transported Ex: IP, IPX … defines the logical structure of the network Ex: ATM, Ethernet, Token ring… defines how the media is accessed Ex: 10base2, 10baseT, SONET… defines the voltages and physical connectors Limitations of OSI model • The layered model – Provided clear demarcation points for protocol developers. • Physical layer people needn’t be concerned with software. – Was intended to be the roadmap for the “OSI” protocol (never materialized) • But… – Often creates duplication of efforts (error correction, restoration, management, etc.) $$$$ • More on this later Defining dB • dB is a convenient way of describing loss and gain • dB can be added where multiplication is normally required XdB = 10 log (X) Note: 3dB = 10 log (2) 6dB = 10 log (4) 9dB = 10 log (8) Ex) 3dB 6dB G=2 G=4 Gtotal= (2)(4) = 8 = 9dB Defining dBm • dBm describes power – YdBm= 10 log(Ymw) • Ex, 15 mwatts = 11.8 dBm 30 mwatts = 14.8 dBm (note: 2X the power is 3dBm more) Types of transmission mediums • Open copper pair – Low attenuation (few hundredths of dB per km at Voice frequencies) – Takes up lots of space (not used much anymore) • Paired wire – – – – Many pairs in a bundle (up to a few thousand) Can be buried or put on telephone poles Higher attenuation than Open wire Figure 1 shows the attenuation of copper pairs vs. frequency and wire gauge – Example: T1 (~1 MHz signal) experiences 30 dB of attenuation over 1 mile on 22 gauge wire – Common in buildings and LAN installs. 100BaseT runs on twisted pair Types of transmission mediums (cont) • Coaxial cable – Good for higher bandwidth signals (several hundred MHz) for several km – Takes up much more space – Digital 50ohm used to carry DS3 signals – Analog 75ohm used to carry TV • Fiber optic cable – Extremely wide bandwidth (several THz) – Low attenuation 0.25dB per km Loops to the home • Transmission from phone to CO occurs on a single pair of wires – A “hybrid” on either side of the two wire circuits (one in the phone, on at the subscriber side of the switch) – Implemented using specialized transformers – Imperfections in the hybrid can cause echos (see figure 2) • Loading coils – Were installed extensively on long loops (3-15 mile) – Reduces attenuation at VF (~3500 Hz) but sharp cutoff at higher frequencies – Big problem for DSL installations Pair-gain systems • Used to pack several subscribers onto a single loop – Acts time division multiplexor – Commonly called “subscriber loop carriers” – Present a problem when installing DSL • Some pair gain systems use Concentration – Acts as a statistical multiplexer – The terminal that needs the line grabs from the available pool. Some probability exists that the request is blocked. Multiplexing scheme • FDM – Frequency Division Multiplexing – Several analog VF signals are mixed using different local oscillators – A5 Channel bank multiplexor was used to mux 12 voice calls into a group – See figure 3 for groups, supergroups, etc. • This scheme worked well with analog Voice channels and microwave transmission systems. Transmission impairments (cont) • Distortion – Envelope delay refers to the delay seen by a particular frequency – Loops impose non-uniform envelope delay – Voice is not severely impacted but it’s a problem for modems • Echos – – – – Occur when there is reflection at the opposite end of the line Normally causes by hybrid imbalance (2W to 4 Wire) Attenuation in the circuit helps the problem Not noticed in short circuits less than 1500 miles (10 msec of delay per 1000 mile circuit) which experience 30 msec of delay (round trip) – Old echo suppressors used active impedence device in reverse path – New echo “cans” are DSP based and use a variant of adaptive filters. Impairments (cont) • Via Net Loss (VNL) is built-in loss proportional to the length of the circuit. – Combats ringing and echo • Zero transmission level point (TLP) – 0TLP : Reference point in a circuit into the first switch – Measurements taken along the path are referenced back to 0TLP – (see examples) Digital Signals • Two Symbols: Binary Signaling Symbol is a.k.a. Bit • M Symbols: M-Ary Signaling M is usually a power of 2 Log2M bits/symbol • Baud rates same? Symbol shapes similar? If yes.. Bandwidth required is similar M-Ary signaling allows increased bit rate Symbols get closer together if Power fixed Receiver detection errors more likely in presence of noise • Bandwidth, Bit Rate, SNR, and BER related Example: Binary Signal • Serial Bit Stream (a.k.a. Random Binary Square Wave) – One of two possible pulses is transmitted every T seconds. Here the symbol is either a positive or negative going pulse. – When two symbols are used, a symbol is known as a ‘bit’. volts +1 If T = .000001 seconds, then this signal moves 1 Mbps. 0 time -1 T Example:M-Ary Signal • One of M possible symbols is transmitted every T seconds. EX) 4-Ary signaling. Note each symbol can represent 2 bits. volts +1.34 If T = .000001 seconds, then this 1 MBaud signal moves 2 Mbps. +.45 time -.45 -1.34 T M-Ary Signaling • Bandwidth required – Function of symbols/second & symbol shape – The more rapidly changing is the symbol, the more bandwidth it requires. – An M-Ary signal with the same symbol rate and similar symbol shape as a Binary signal has essentially the same bandwidth. • The previous two slides show... – Equal Power & Equal Bandwidth Signals – M-Ary signal transfers more bits/second BUT detection errors more likely at the receiver Wired Physical Links • Untwisted Pair Cabling – Highly susceptible to EM interference – Bad choice for telecom systems • Example: Speaker Wires, Power Lines • Twisted Pair Cabling – Fairly resistant to EM interference – Bandwidth typically in 1-2 digit MHz • Examples: LAN wiring, Home telephone cables Twisted Pair Cables Wired Physical Links • Coaxial Cable – Resistant to EM interference – Bandwidth typically in 2-3 digit MHz • Example: Cable TV • Fiber Optic Cable – Immune to EM interference – Bandwidth in GHz to THz Physical Layer Ailments... • Attenuation Signal power weakens with distance • Distortion Pulse shapes change with distance – Copper cabling High frequencies attenuate faster Pulses smear – Fiber cabling Frequencies propagate at different speeds Dispersion Generating a Square Wave... 5 Hz + 15 Hz + 25 Hz + 35 Hz 1.5 0 -1.5 0 1.0 cos2*pi*5t - (1/3)cos2*pi*15t + (1/5)cos2*pi*25t - (1/7)cos2*pi*35t) Effects of Dispersion... 5 Hz + 15 Hz + 25 Hz + 35 Hz 1.5 0 -1.5 0 1.0 cos2*pi*5t + (1/3)cos2*pi*15t + (1/5)cos2*pi*25t + (1/7)cos2*pi*35t) In this example the 15 and 35 Hz signals have suffered a phase shift (which can be caused as a result of different propagation speeds) with respect to the 5 and 25 Hz signals. The pulse shape changes significantly. Receiver Detection • SNR tends to worsen with distance • Digital Receiver Symbol Detectors – Examine received symbol intervals (T sec.) – Decide which of M symbols was transmitted – Single Sample Detectors Sample each symbol once Make decision based on sample value – Matched Filter Detectors (Optimal) Sample each symbol effectively an infinite number of times Make decision based on an average SNR = (Average Signal Power) Average Noise Power 4.5 z2 x k k 0 4.5 0 0 20 40 60 k Binary Signal 10 Bits showing 80 100 99 SNR = 100 4.5 z2 x 0 k k 4.5 0 0 20 40 60 k Sequence = 0011010111 80 100 99 SNR = 10 4.5 z2 x 0 k k 4.5 0 0 20 40 60 80 k Signal a sequence +1 and -1 volt pulses 100 99 SNR = 1 4.5 z2 x 0 k k 4.5 0 0 20 40 60 k 80 100 99 SNR = .1 8.5 z2 x 0 k k 8.5 0 0 20 40 60 k 80 100 99 Single Sample Detector: SNR = 1 Threshold is placed midway between nominal Logic 1 and 0 values. 4.5 0 4.5 0 0 20 40 60 k 80 100 99 Detected sequence = 0011010111 at the receiver, but there were some near misses. Matched Filter Detector: SNR = 1 Orange Bars are average voltage over that symbol interval. 4.5 0 4.5 0 0 20 40 60 80 k Averages are less likely to be wrong. 100 99 Channel Capacity (C) • C = W*Log2(1 + SNR) bps – W = channel bandwidth (Hz) – SNR = channel signal-to-noise ratio • Maximum bit rate that can be reliably shoved down a connection • EX) Analog Modem (30 dB SNR) C = 3500 *Log2(1 + 1000) = 34,885 bps • EX) 6 MHz TV RF Channel (42 dB SNR) C = 6,000,000 *Log2(1 + 15,849) = 83.71 Mbps Why not just keep amplifying to counter-act attenuation? • Amplifiers add noise as they boost the power. – For analog signals, this degrades the signal to noise ratio (SNR) – With digital signals, the SNR (Eb/No) is degraded until the system takes errors • Low noise and multistage amplifiers are used to combat this problem. Amplifiers in series SNRin SNRout G1 F1 G2 F2 Feff ( F2 1) F1 G1 • A pre-amp with a low noise figure reduces the overall noise figure while providing high gain – For example, using this equation, the effective noise figure of a preamp with a gain of 20dB and noise figure of 3 dB followed by an amplifier of gain 30dB and noise figure 9 dB would be 2+(8-1)/100 = 2.07 or 3.16 dB. The total gain would be 50 dB. (make sure to use non-dB numbers in the equations) Overview of telephony • Telecommunication networks were originally designed for voice – Analog signals of 4 kHz bandwidth – Sampled at 8 kHz with 8 bits of quantizing levels for 64kbps circuit • Digital TDM multiplexing has been the technique of choice since the late 70’s. Multiplexing Formats • Why multiplex?? – Combine several lower bandwidth signals onto a single faster channel – Saves running thousands of individual wires – Allows single carrier for several signals • Frequency division multiplexing – Multiple frequencies “stacked” – This was done in the analog days. – Each voice channel was mixed up to higher center frequency. – Doesn’t lend itself to digital technology – Requires very (spectrally) flat channels FDM Hierarchy With digital T-Carriers, this is now obsolete From: Digital Telephony Bellamy, chapter 1 FDM (cont) From: Digital Telephony Bellamy, chapter 1 Time division multiplexing • With TDM, every low speed signal gets a fixed amount of bandwidth in the high speed signal Low speed High speed Current North American TDM multiplexing scheme T1 1.544 Mbps 24 DS0 64kbps 44.736 Mbps Channel Bank 28 2.5 Gbps M13 48 10 Gbps OC48 4 OC192 What is a T1? • • • • Four-wire circuit: one pair for transmit, one for receive. Full-duplex: information goes both ways all the time. Digital: transports binary data or voice TDM: Capable of transporting 24 digitized voice channels. • Pulse code format: Individual voice channels are normally digitized using PCM. • Framed synchronous transmission: samples from each voice channel (8 bits) are taken and sent sequentially. A frame bit is added resulting in 193 bit frames. Analog to PCM conversion Understanding SONET/SDH, Kartalopoulos Analog to DSO with CODEC Understanding SONET/SDH, Kartalopoulos DS0 to DS1 MUX (channel bank) Understanding SONET/SDH, Kartalopoulos European muxing standard Understanding SONET/SDH, Kartalopoulos T1(cont) • Note: each voice channel is sampled at 8000 hz, so a T1 must send 193 bits in 125 usec, or 1.544 Mbps. • Line coding for T1 is bipolar, AMI. Every other 1 is represented by a positive pulse. 0’s are represented by no pulse. – This gives the signal zero average value. – The required bandwidth is 770 kHz. • T1 uses byte synchronous transmission – Receiving end needs to distinguish which channels are which and which 8 bits make up the bytes. – Framing bits make this work Evolution of T1 muxes • T1 to DS0 mux commonly called “channel banks” • D1 channel bank format – Robbed bit signaling – LSB of each byte was used to carry signaling for voice channels (no significant degradation) – If data was carried, 56k was max amount • D2 – D3 channel banks were small improvements • D4 channel bank was common and introduced the “superframe” format. T1 Superframe • Superframe concept: 12 frames together became a “superframe” framing bits occur in a special pattern. – Allows only 6th and 12th frames to give up signaling bits. – The 24 signaling bits in the 6th frame are called the A bits, 24 in the 12th frame are called the B bits. – B8ZS was introduced to solve the “ones density rule” when carrying data: In every 24 bits, there must be at least 3 pulses and no more than 15 consecutive zeros. • Recall that 8 zeros are substituted with a pattern then a BPV is generated. D5 Extended superframe (ESF) • There was a desire to improve the D4 SF format: – More performance monitoring capabilities • Customer equipment didn’t pass through Bipolar Violation information – 8kbps F bits are redefined to create a 2kbps framing sequence, 4kbps data link channel, and 2kbps CRC channel. • Data link channel used to control end equipment • 24 rather than 12 frames are now used, framing bits occur in frames 6, 12, 18 and 24. These bits now become the A,B,C,D bits for each channel. Uses for T1 • T1 was primarily used for voice trunks between voice switches. – Now many customers use to connect PBX – May buy T1 to the internet • Connect a Router to ISP’s router • Channel Service Unit (CSU) is often used Central Customer premise office T1 CSU Router Internet Other common TDM rates • E1: European version of the DS1, contains 32 voice channels • DS3: multiplexed version of 28 DS1’s – DS3 uses “bit-interleaving” rather than byteinterleaving in DS1 format. – DS3 is 44.736 Mbps – B3ZS is used to maintain 1’s density. – Multiplexing is done in two stages: • 4 DS1 signals are muxed using pulse stuffing synchronization to form a DS2 • 7 DS2 are muxed using a fixed pulse stuffing synchronization to form a DS3 signal. DS3 muxing (cont) • In DS1 to DS2 muxing, stuffing is used to get rate to 1.545796 Mbps (with overhead). – Each DS1 can be running at a different speed ranging from 1.540 to 1.545 Mbps – Bit interleaving and bit stuffing allow all the DS1s to maintain their independent rates. – 48 bits are collected to make a block, 6 blocks to make a subframe, 4 subframes to make DS2 frame. (subframes are not individual DS1s)” • See figures 1 and 2 in TTC “Fundamentals of DS3” DS3 muxing (cont) • For DS2 to DS3 muxing, 84 bits make a block, 8 blocks make a subframe, 7 subframes make a frame. – Bit stuffing may again be used incase DS2s are not at the same rates. • Note that C-bits are used in both stages 1>2 and 2>3 to control bit stuffing. – If all DS2s are in sync, this is not necessary for second stage – C-bit format uses C bits in DS2>DS3 stage for other purposes. Drawbacks to DS3 based transport • Difficult to drop individual voice or DS1 channels – Bit muxing and bit stuffing makes channels locations unknown • Not fast enough for some applications – No standard Proprietary muxing schemes were developed to transport 12 or 24 DS3 on a fiber link. – Interconnects between carriers at rates higher than 45 Mbps were complex • Required them to purchase same type of fiber muxes. • Runs on Coax vs. unshielded twisted pair (UTP) or fiber. Sonet is defined to address these problems • Standardized rates beyond 10Gbps on fiber • “Synchronous” for improved add/drop capability • Standards for both Electrical and Optical interfaces. • Backward compatible with T1, DS3, E1, E3, and other “async” standards. Traditional multiplexing hierarchy DS0 64 kbps T1 1.544 Mbps 24 44.736 Mbps Channel Bank 28 2.5 Gbps M13 48 10 Gbps OC48 4 OC192 Traditional hierarchy Signal Bit Rate Channels DS0 64 kbps 1 DS0 DS1 1.544 Mbps 24 DS0s DS2 6.312 Mbps 96 DS0s DS3 44.736 Mbps 28 DS1s SONET • SONET byte oriented frame format – Path, line, and section – Multiplexing format • Virtual Containers • Synchronous payload envelope (SPE) • Pointers – Timing issues – This is what makes SONET synchronous -- the payload can float in the SONET frame. • Overhead – Line, Section, and Path • Performance monitoring SONET Hierarchy Signal Bit rate Capacity STS-1, OC-1 51.840 Mbps 28 DS1s, 1 DS3 STS-3, OC-3 155.520 Mbps 84 DS1s, 3 DS3s STS-12, OC-12 622.080 Mbps 336 DS1s, 12 DS3s STS-48, OC-48 2488.320 Mbps 1344 DS1s, 48 DS3s STS-192, OC-192 9953.280 Mbps 5376 DS1s, 192 DS3s SONET Network LINE SECTION Terminal (LTE) REG ADM or DCS (LTE) REG REG Terminal (LTE) Router (PTE) Router (PTE) PATH SONET Networking 810 bytes x 8000 frame/sec x 8 bits = 51,840,000 bps OH PAYLOAD 9 rows OH PAYLOAD OH STS-1 Synchronous Payload Envelope 90 columns (87 columns of payload) 3 columns of transport overhead: Section overhead Line overhead Path overhead PAYLOAD BIP-8/BI: Parity Checking 9 Rows STS-1 Frame Section Trace/Growth A1 A2 JO/Z0 J1 B1 E1 F1 B3 D1 D2 D3 C2 H1 H2 H3 G1 B2 K1 K2 F2 D4 D5 D6 H4 D7 D8 D9 Z3 D10 D11 D12 Z4 E2 Z5 S/Z1 M0/M1 87 Columns of Payload STS-1 Synchronous Payload Envelope (STS-1 SPE) BIP-8/B2: Error Monitoring Z2 90 Columns