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Elements of Network Connectivity • • • • • • • • • Serial and Parallel communication Modems Modem Pools ISDN DSL Routing Cable systems Leased Lines Other interconnection systems Serial vs. Parallel • Serial – – – – needs one wire plus return per direction bits are sequenced by time slicing needs synchronization needs handshaking codes or lines • Parallel – all bits sent at one time – needs 1 wire per bit – needs handshaking lines Serial Frame (Async) 0 1 2 3 4 5 6 7 Stop Start Time Word=01011100 Hex=5C Ascii= \ Serial Frame (Synchronous) Bit 7 0 1 2 3 4 5 6 7 0 Time No start or stop bits, timing synchronized with special ascii characters (SYN) c07dem13 and c07dem14 Bits Parallel 0 0 0 1 1 1 0 1 0 Pulse 1 2 3 4 5 6 7 Strobe Time Serial Communications • Serial Data Stream (asynchronous) – – – – – – – 8 bits data start/stop bits Parity bit baud rate limits Errors c07dem10 Serial Communications • • • • • RS-232 standard Modems PC Serial Ports Speeds Synchronous/Asynchronous – Advantages/Disadvantages • PPP (Point to Point Protocol) RS232 Standard +3 to 25 25 ping connector Volts 9 pin connector Ground 0 volts Transmit Receive Clear to Send Request to Send -3 to 25 Carrier Detect Volts Data Set Ready Data Terminal Ready Ring Detect Modem Operation • • • • Modulator/Demodulator (Digital to Analog) Use a standard (Hayes) command set. Dialup Sequence Training/Speed Negotiation – Error detect and compression/decompression – Latest and greatest (??) is V.90 (56KB) • • • • Carrier Detect Requirements for 56K xDSL (Digital Subscriber Line) ISDN (digital telephone lines) PPP Primer • • • • • Point to Point protocol Physical Layer protocol Authentication (PAP/CHAP) Addressing (dynamically assigned) Client Configuration Modem Pools • • • • • • • Requirements ISDN BRI lines (single connection) ISDN PRI (23 BRI) lines (equal a T1) Tariffs (QWest) Multiplexing BRI’s to save $$ Central Office Switch Line selection/hunting PPP Installation Modems Modem Controller $52.50 per line Ethernet 56K (ISDN) Modem Installation Controller Central Office $33.50 per line T1’s or ISDN PRI Ethernet ISDN • Handles Voice, Data, Video • Each BRI (Basic Rate Interface) has 2 64 Kbps lines, either can be used for data or voice, combined gives 128 Kbps data. • BRIs and PRIs (Primary Rate Interface) – BRI 64 Kbps, 128 Kbps – PRI 1544 Kbps (23 BRIs) • Dial up standard – Each line has a phone number DSL • Asymmetric Digital Subscriber Line • Asymmetric (High speed downlink, slow uplink) • Uses existing telephone cabling to the DSL modem router • Modem/router typically provides ethernet connection to your LAN • Uses existing telephone devices for voice (single twisted pair) • Simultaneous data and voice • Distance limitation from central office (12000 feet) DSL • Digital Subscriber Link – ADSL Asymmetric DSL – xDSL • 18000 foot radius of Central Office • Speeds to 1,544 KB downstream – 640 kbps upstream • Simultaneous voice/data • Uses existing telephone twisted pair More DSL • HDSL High Speed DSL – 2 Mbps at 3 miles of cable • VDSL Very High Speed DSL – 52 MBS downstream, 1.5-2.3 MBS upstream – 3000 foot limit • SDSL Symmetric DSL – 1.544 MBps up and down, 11000 foot limit Even More DSL • Pricing: $45/month and up • http://www.qwest.com/residential/products/ dsl/index.html • Requires: – Telephone line (POTS) – DSL Modem – External Modem requires Ethernet to the PC Routing • Routers operate at the Network layer • They use tables to keep track of the best path from source to destination • They segment the network based on Network layer traffic • They filter broadcast traffic to a single port on the router • Routers listen on the ports and determine the best path using OSPF (open shortest path first), RIP (Routing Information Protocol), or NSLP (NetWare Link Services Protocol) for IPX Routing Continued • Some protocols don’t route: – Netbeui – Local Area Transport (DEC) • Routers can be either: – Static, addresses to other routers are fixed – Dynamic, addresses to other routers are discovered automatically. • Routers can use multiple links to another site to take advantage of available bandwidth on each link. Gateways • Gateways are like routers but switch between protocols • Example: – Token-Ring to ethernet – IBM HDLC/SNA to Internet TCP/IP • Because of the switching algorithms needed they are usually slow. Radio and Satellite • Bandwidth versus available frequencies • High Power and Broad Bandwidth requires FCC licensed equipment • Interference (electrical, atmospheric, animal) • Timing problems ( 1 foot = 1 ns.) – 23500 miles to satellite ( .25 sec round trip) Cable TV modems • Use existing cable installation • Uses broadband network technology via fiber optics and coaxial cable • Asymmetric (8 MB down/1 MB up) • Costs about $40.00/month RAS • Remote Access Service – NT interconnection system – Can use several different media including dialup – Can filter specific protocols, it can audit connections and use Callback security. – Works up to about 128 kbps. Telco Leased Line Networks • ISDN • DSL • T1, DS1, T3, DS3 – T1 is 1.544 Mpbs – Interfaces, CSU/DSU, Framing – CSU/DSU Channel Service Unit/Data Service Unit • OC1, OC3, OC12 – Optical Circuits, OC1 is 51.84 Mbps, OC3 is 155.52 Mbps Leased Lines • DS-1/T1 1.544 Mbps or 24 voice channels • DS3/T3 44.736 Mbps (28 T1s), 672 voice • Packet Switched – Uses best route – Uses small packets • Virtual Circuit Packet Switching – Bandwidth Allocated on demand – SVC (Switched Virtual Circuit) – PVC (Permanent Virtual Circuit) Frame Relay • Fast, variable length, packet switching network. • Uses PVCs for point to point communication • Provides customers with variable rate bandwidth, customers share bandwidth with other customers. ATM (Asynchronous Transfer Mode) • Used for high speed data communications primarily by common carriers (Telco). • Uses cell relay rather than variable length frames • ATM is expensive and fairly complicated to set up and troubleshoot. FDDI • Fiber Distributed Data Interface • Dual Ring (Token ring topology) – Redundant (Fault Tolerant) • Handles long distances (because of fiber) – 200 kilometers (124 miles) – immune to electromagnetic noise/interference • 100 Mbps • Protocol includes built in troubleshooting • Interfaces are fairly expensive SONET (Synchronous Optical Network) • Fiber Optic Gigabit communications protocol. • Standard for long distance high speed transport of data and voice • Basic transmission unit is STS-1 at 51.84 Mbps up to STS-192 or 9,953.28 Mbps