<p> Physical Layer: Network Overviews</p><p>Text: Data and Computer Communications, William Stallings Chapter 8</p><p>Objectives: The student shall be able to:  Define ADSL, SDSL, T1, cable modem, DWDM. Describe the media used by these technologies, where and why they are used.  Describe the type of multiplexing used for ADSL and T1.</p><p>Class Time: The class shall be conducted as follows: Wireless Presentation 2 hours T1 / Cable ¼ hour DSL ½ hour SONET ¼ hour Exercise 1 hour Total: 4 hours Wired Networks</p><p>T1 Multiplexing T1: 1.544 Mbps total rate  Used between PBXs, Phone company to connect 24 digital phones or data channels.  Used to interface LAN with Internet.  Channel Rate: 8 bits x 8000 times per second = 64 kbps.  Requires 2 twisted pairs and repeaters every 3k-6k feet.  Using analog 24 pairs would be required.</p><p>Circuit Bit Rate (Mbps) # Voice Data Channels T1 = DS1 1.54 24 DS1C 3.15 48 DS2 6.31 96 T3 = DS3 44.74 672 DS4E 139.26 1,920 DS4 274.18 4,032</p><p>Originally set up for speech: T1 using Digital Signaling 1 (DS1): 8000 times per second generates 1 frame = 1.544 Mbps 1 bit 8 bits 8 bits 8 bits ... 8 bits Framing1010 Channel 1 Channel 2 Channel 3 Channel 24 Currently used for data: 1.544 Mbps without separating into channels. Cable Modems Traditional cable operates in range 50 MHz - 550 MHz in 6 Mhz channels Splitter separates TV from modem data. Downstream data: 550-750 MHz band uses 64QAM to achieve 27 Mbps per 6 MHz channel Upstream: 5-50 MHz band uses QPSK to achieve 500 kbps-10 Mbps per 6 MHz channel 10BaseT modem interface constrains data to 10 Mbps. DOCSIS: Standard based upon IP packets. Asymmetric Digital Subscriber Line (ADSL) ADSL: Can use analog phone and place data calls simultaneously.  Asymmetric: varied rate uplink and downlink.  Implements phone and PC Internet on existing Cat 3 UTP phone line  Implements always-on data above 4000 Hz  Splitter separates voice from ADSL data.  Intended for home use, monthly charge</p><p>Competition:  ISDN: 64 or 128 kbps  Analog modems: 14.4, 28.8, 33.6 or 56 kbps.  Cable modems: to 10 Mbps</p><p>Uses Frequency Division Multiplexing:  POTS (Plain Old Telephone Service): 0-4 KHz Voice frequencies separated by splitter & forwarded to a voice switch. 4 KHz to 25 KHz: Buffer (not used) to avoid crosstalk  Data carried from 25 KHz to 1.1 MHz Data frequencies separated off & forwarded to an Internet service. 25-200 KHz: Upstream (to network) 250-1000 KHz: Downstream (to home) With echo cancellation, both can send and receive on data frequencies  Upstream (to network): 640 kbps to 9 kft; 256 kbps to 12 kft; 64 kbps to 18 kft.  Downstream (to home): 8.5 Mbps to 9 kft; 6.3 Mbps to 12 kft; 1.5 Mbps to 18 kft  Modifications required in cable network to provide expanded frequencies.</p><p>Technology:  DMT: Discrete Multitone: selects multiple 256 4 kHz ‘subchannels’  Transmits up to 60 kbps on each subchannel  Uses QAM & forward error correction - i.e. error correcting codes.  Standard accepted by ANSI and ETSI.</p><p>Home equipment:  Network Interface Card (NIC) and ADSL modem runs 10BaseT  Splitter divides speech from data (at home & end office) End office equipment  DSLAM: Digital signal processor multiplexes 250 QAM modems</p><p>G.lite or splitterless ADSL:  1.544 Mbps downstream; 512 kbps upstream  Self-installed: reduced cost, reduced speed</p><p>Some alternate DSL services: SDSL: Symmetric Digital Subscriber Line:  Upstream = downstream bandwidth  Separate from phone  Intended for business or multi-tenant use  Single copper pair  1.544 to 2.048 Mbps</p><p>HDSL: High bit-rate Digital Subscriber Line  Symmetric T1-type interface: 1.544 -2.048 Mbps  1.5 Mbps bidirectional to12 kft or 3.7 km Line Coding: 2B1Q = 4 PAM Requires 2 twisted pairs of copper, no repeaters, no line conditioning. Uses echo-canceled bidirectional transmission carrying half the load on each pair.</p><p>VDSL: Very high speed Digital Subscriber Line  Downstream: 13 Mbps - 4 kft; 26 Mbps - 2 kft; 52 Mbps - 1 kft ????  Upstream: 1.5 – 2.3 Mbps  Uses fiber optics to 3000 ft of customer and one twisted pair for final run to 1.4 km.  Line Coding: DMT & QAM</p><p>Problems:  Copper subject to crosstalk, attenuation SONET</p><p>Synchronous Optical Network (SONET)  Standard defined for Fiber Optics use  Potential for mixed media - voice, video, data</p><p>Current Use: High data rate (bypass) applications  Customers: upgrade for companies with multiple T-3s.  BISDN, HDTV</p><p>SONET Designation Data Rate (MBPS) Payload Rate (MBPS) STS-1/OC-1 51.84 50.11 STS-3/OC-3 155.52 150.34 STS-9/OC-9 466.56 451.01 STS-12/OC-12 622.08 601.34 STS-18/OC-18 933.12 902.02 STS-24/OC-24 1,244.16 1,202.69 STS-36/0C-36 1,866.24 1,804.03 STS-48/OC-48 2,488.32 2,405.38</p><p>Synchronous Digital Hierarchy (SDH): Worldwide standard  to 155 Mbps: copper or fiber  above 155 Mbps: fiber only</p><p>Tributary: A component stream input to SONET multiplexer</p><p>Structure of SONET OC-1: 51.84 Mbps:  Based on TDM  One frame every 125 microseconds  Each frame consists of 9 rows of:  Overhead: 3 octets  Synchronous Payload Envelope = data carried: 87 octets.</p><p>STS-N  Byte interleaved STS-1  One frame every 125 microseconds (including interleaving)</p><p>Equipment:  Path Terminating Equipment: Origination & Termination SONET  Add/Drop Multiplexer (ADM): Inserts extracts tributary streams  Regenerator: Repeater  Digital Cross Connect Switch (DCS)</p><p>Section: Between transmitters / receivers (between Regenerators)  Uses: framing & error monitoring (performance monitoring, OAM&P, parity, orderwire) Line: Between Add/Drop Multiplexers or Splitters and end terminal equipment  Uses: synchronization, multiplexing, protection-switching  Byte stuffing: Adjust to speed of input stream data. If input data is:  too slow: stuff non-data character;  too fast: store byte in Line Overhead H3 byte. Path: End-to-end connection between SONET multiplexers  Includes: path status, path trace (framing), performance monitoring (parity)</p><p>Network Architectures: 1. Point-to-Point 2. Point-to-Multipoint: uses Add Drop Multiplexer 3. Hub: uses Digital Cross Connect 4. Dual ring: 2 Fibers for network survivability</p><p>Virtual Tributaries:  Channels can range in bandwidth from 64 kbps to T-1 size.  Virtual Tributaries are allocated a set of columns in payload.</p><p>Wavelength Division Multiplexing (WDM): Optical signals at different optical wavelengths (colors) Example: 16 wavelengths at OC-48 = 16 x 2.5 Gbps = 40 Gbps</p>