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Digital Access Services T-1 and SONET

Digital Access Services T-1 and SONET. Topics. T-Carrier Hierarchy SONET Hierarchy Other fiber Leased Line Details Pricing and Billing Router configuration PPP configuration. Leased Line Service Rates. T1 Channelized T1: 24 × DS0 (64k bps) unchannelized T1: 1.544MP bps

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Digital Access Services T-1 and SONET

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  1. Digital Access Services T-1 and SONET

  2. Topics • T-Carrier Hierarchy • SONET Hierarchy • Other fiber • Leased Line Details • Pricing and Billing • Router configuration • PPP configuration

  3. Leased Line Service Rates • T1 • Channelized T1: 24 × DS0 (64k bps) • unchannelized T1: 1.544MP bps • Fractional T1 (n × 64 kbps) • physical facility: same as T1 (4-wire copper) • STS-1/DS3 (45M bps) • physical facility: DS3X coax (in-building) • physical facility: fiber (out-building) • Fractional DS3 (n x T1) • SONET OC-3 (155M bps) – fiber facility • SONET OC-12 (622M bps) - OC-?? • Dark Fiber

  4. T-Carrier Systems

  5. T-1 Frame Format Each DS0 called a time slot 8000 frames/sec * 8 bits/slot = 64 Kbps 24 * 8 + 1 = 193 bits/frame 8000 frames/sec * 193 bits/frame = 1.544 Mbps 8000 Framing bits sent per second

  6. Channelized? • Channelized T-1 Circuit • T-1 is utilized as 24 DS0 channels of 64 Kbps each. • Each DS0 can be allocated to carry any single service, such as CO trunk, DID trunk, WATS, FX, 56K data, switched 56K, etc. • Unchannelized T-1 • T-1 is utilized as a single 1.536 Mbps data circuit.

  7. Leased Line – Fractional T1 CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 used 09 10 11 12 13 14 15 16 unused 17 18 19 20 21 22 23 24 Physical facility: T-1 (4-wire) Data rate: 64 kbps × 8 = 512 kbps (for this example) The customer pays a monthly charge of physical facility (data rate independent) + data services (data rate dependent)

  8. Signaling • The basic purpose of signaling is to determine the status and control of each 64 Kbps channel. There are two basic types: • In-band • Out-of-band • T1 systems originally provided for signaling using: • In-Band Robbed-Bit Signaling Source: KnowledgeLink, Inc.

  9. 1 0 1 0 1 0 1 1 Bit Robbing Bit robbing “steals” the least significant bit for signaling transport Least Significant Bit Value is determined by Signaling, NOT Channel Sample 1 0 1 0 1 0 1 1 Source: KnowledgeLink, Inc.

  10. T-1 Framing Bits • D4 T-1 lines (1972): • Allow receiver to find the start-of-frame (frame synchronization). • Group sets of 12 frames into superframes • Indicate that frames 6 and 12 contain signaling bits (to specify if channel is in use or not) • D5 (ESF) T-1 lines (1983): • Provide error checking (CRC) (ESF T1) • Provide Facilities Data Link channel to transmit network management messages (ESF T1)

  11. T-1 Super Frame (SF)(AB Signal) 6th frame 12 frames = 1 SF 12th frame Figure 15.8

  12. T1 Extended Super Frame (ESF)(ABCD Signal) 24 frames = 1 ESF Figure 15.9 S: Synchronization (001011) C: error detection F: Facility Data Link control

  13. DS1 Line Coding - placing 1’s and 0’s • AMI (Alternate Mark Inversion) • AMI sends zero volts for a "0" (space) and alternately sends +V and -V volts for a "1" (mark). Doesn’t guarantee 0’s density so it is susceptible to clock drift since clock is imbedded in data. • General Requirements: 12.5% 1’s and no more than 15 consecutive 0’s • B8ZS (Binary 8 Zero Substitution) • Replaces 8 consecutive 0s with 000VB0VB (bi-polar violation)

  14. AMI and B8ZS Signal 1 0 0 0 0 0 0 0 0 0 1 Sender T1 sent T1 recv Receiver Figure 15.6

  15. Data over T-1 • A T-1 carries 24 DS0 channels • Each DS0 may carry a maximum of 56 Kbps or 64 Kbps of data • A restricted T-1 carries 24 x 56 Kbps = 1.344 Mbps. • A clear-channel T-1 carries 24 x 64 Kbps = 1.536 Mbps. • How do you make sure that you get a clear-channel T1? ASK about it!!

  16. Summary - T1 Configuration • Line Coding • AMI (Alternate Mark Inversion) Coding is the older standard and only allows restricted T1 data service (i.e. 56 Kbps per DS0) • B8ZS (Binary 8-Zero Substitution) Coding allows clear-channel service. • Signaling • Robbed Bit Signaling is the older method and only allows restricted service. • No signaling (i.e. leased line) or Common Channel Signaling (CCS) or Signaling System 7 (SS7) allows clear-channel service. • Framing • D4 or SuperFrame (SF) Framing is the older standard and does not allow error detection or automatic failover services from carrier. • Extended SuperFrame (ESF) Framing allows carrier to automatically detect errors and to perform failover to good circuit when errors occur.

  17. The E-1 Interface Similar to T-1, used outside North America The E-1 interface provides a 2,048 kbit/s access rate. It can support up to 32 channels (64 Kbps DS0). “Framed E1” supports 30 voice channels Unchannelized E1 gives you the full 2.048 Mbps.

  18. E1 Frame TS0 is dedicated for synchronization, alarms, control messages, and future extensions. TS16 is usually used for signaling. It is known as Clear Channel Signaling, an example of out of band signaling. TS0 and TS16 can carry data as well (unchannelized E1) TS1-TS15 and TS17-TS31 are used for carrying user data.

  19. CSU/DSU Leased Line Service (T1)(example: to Internet) Customer router V.35 Enterprise Network T1 4-wire Local Carrier (AT&T) Internet ISP

  20. CSU/DSU CSU/DSU

  21. “WIC Module” CSU card in router RJ48C Cisco 2600 Router

  22. Equipment Cost (example) 10/100BaseTX T1 LAN WAN Cisco 2811 Router $1,779.99 WIC T1 CSU/DSU $689.99 http://www.cdw.com/shop

  23. Example: Leased Line Internet Service (T1) ISP (Cogent) $350 Carrier (AT&T) $200 Internet Chicago www.cogentco.com

  24. Leased Line Pt-Pt Service (T1) $575 $575 $1.85 ×300 Carrier (AT&T) Carrier (AT&T) St. Louis Chicago Leased Line Service Charge (1Y pan) Monthly charge = $575*2 + $1.85 ×300 (miles) × (1-25%) = $1,278 .

  25. Synchronous Optical Network (SONET) ADM = Add-Drop Multiplexer SONET Ring pass frame add frame to the ring drop frame out of the ring

  26. SONET Overview • Synchronous Optical NETwork standards developed by Bellcore. • Advantages: • transmission standards for optical networks allows “mid-span meet” between different equipment (vendor interoperability!) • Synchronous multiplexing allows add-drop multiplexing of any low speed signal into any high speed signal (to fully appreciate this advantage, consider the activities a multiplexer must perform to add-drop a T1 to/from a T3 signal). • Operations and Maintenance capabilities greatly improved over previous systems • Deployment began in the late 80’s and significantly increased each year. • International equivalent to SONET is known as the Synchronous Digital Hierarchy (SDH) standards developed by the ITU.

  27. SONET Interfaces SDH: Synchronous Digital Hierarchy by ITU-T SONET: Synchronous Optical Network by ANSI OC: Optical Carrier STS: Synchronous Transport Signal STM: Synchronous Transmission Mode

  28. 3-Layer SONET Transport

  29. STS-1 Frame Format

  30. STS-1 Frame 8,000 frames/second Each frame: 90 col × 9 rows = 810 bytes Payload: 86 col × 9 rows = 774 bytes Each byte of payload can be allocated as a separate 64 Kbps customer channel STS-1 frame can support up to 774 standard DS0 channels (digital voice or 64 Kbps data). Transmission Rate (raw): 51.84M bps Transmission Rate (payload): 49.54M bps

  31. Virtual Tributaries SPE (payload) = 7 VT Groups + packing bytes One VT Group = 12 columns Each VT Group is split into multiple VTs of the same type Either 4 x VT1.5 or 3 x VT2 or 2 x VT3 or 1 x VT6

  32. SONET Networks SONET Transmission Equipment: • SONET Repeater • SONET Terminal/Multiplexer • SONET ADM (Add Drop Multiplexers) • SONET DCS (Digital Cross-Connect Systems) SONET Network Topologies: • Point-to-Point (w/ Automatic Protection Switching) • Ring Configuration • Unidirectional Line Switch Rings (ULSR) • a.k.a Unidirectional Path Switch Ring (UPSR) • 2-fiber Bidirectional Line Switch Rings (BLSR) • 4-fiber Bidirectional Line Switch Rings (BLSR)

  33. SONET Access Long Haul (DWDM) Network Core Router Metro SONET Ring Voice Switch Access Ring Access Ring T1 Access Ring T1 ADM: Add/Drop Multiplexer PBX

  34. SONET (APS) Point-to-Point (with Automatic Protection Switching (APS)) Working Protect DS1s, DS3s, Ethernet, ... DS1s, DS3s, Ethernet, ... SONET Terminal SONET Terminal Faults detected and managed using span switching within 50 msec automatically!

  35. SONET (ULSR) FIGURE 20-7 2-fiber ULSR (Unidirectional Line Switched Ring) uses one ring in normal operation. If both fibers are cut, the rings are wrapped around.

  36. SONET ADM SONET ADM SONET ADM SONET ADM SONET ADM S S SONET Networks (BLSR) Ring Topology BLSR (2-fiber) Ring Topology BLSR (4-fiber) SONET ADM SONET ADM SONET ADM • Traffic broadcast to rotating and counter-routing paths • dropped traffic selected based on path level performance by the selector, • used extensive in access network • Enhanced protection due to both span switching and ring switching • 4-fiber per node interface (vs 2) • used extensively in “backbone” network

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