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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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topics
Topics
  • T-Carrier Hierarchy
  • SONET Hierarchy
  • Other fiber
  • Leased Line Details
    • Pricing and Billing
    • Router configuration
    • PPP configuration
leased line service rates
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
t 1 frame format
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

channelized
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.
leased line fractional t1
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)

signaling
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.

bit robbing

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.

t 1 framing bits
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)
t 1 super frame sf ab signal
T-1 Super Frame (SF)(AB Signal)

6th frame

12 frames

= 1 SF

12th frame

Figure 15.8

t1 extended super frame esf abcd signal
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

ds1 line coding placing 1 s and 0 s
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)
ami and b8zs signal
AMI and B8ZS Signal

1 0 0 0 0 0 0 0 0 0 1

Sender

T1 sent

T1 recv

Receiver

Figure 15.6

data over t 1
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!!
summary t1 configuration
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.
the e 1 interface
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.

e1 frame
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.

leased line service t1 example to internet

CSU/DSU

Leased Line Service (T1)(example: to Internet)

Customer

router

V.35

Enterprise Network

T1

4-wire

Local

Carrier

(AT&T)

Internet

ISP

csu dsu
CSU/DSU

CSU/DSU

slide21

“WIC

Module”

CSU card

in router

RJ48C

Cisco

2600

Router

equipment cost example
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

example leased line internet service t1
Example: Leased Line Internet Service (T1)

ISP

(Cogent)

$350

Carrier

(AT&T)

$200

Internet

Chicago

www.cogentco.com

leased line pt pt service t1
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

.

synchronous optical network sonet
Synchronous Optical Network (SONET)

ADM = Add-Drop Multiplexer

SONET Ring

pass frame

add frame

to the ring

drop frame

out of the ring

sonet overview
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.
sonet interfaces
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

sts 1 frame
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

virtual tributaries
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

sonet networks
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)
sonet access
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

sonet aps
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!

sonet ulsr
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.

sonet networks blsr

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