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

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-Carrier Systems

Service Circuit Bit Rate # Voice Channels

DS0 64 Kbps 1

DS1 T1 1.544 Mbps 24

DS2 T2 6.312 Mbps 96

DS3 T3 44.736 Mbps 672

DS4 T4 274.176 Mbps 2016

T-1 Frame Format

1 b it 8 b its 8 b its8 b its8 b its

F DS0 #1 DS0 #24DS0 #3DS0 #2 . . .

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 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

CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8

09 10 11 12 13 14 15 16

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)

used

unused

The basic purpose of signaling is to determine the status and control of each 64 Kbps channel. There are two basic types:In-bandOut-of-band

T1 systems originally provided for signaling using:

In-Band Robbed-Bit Signaling

Signaling

Source: KnowledgeLink, Inc.

1 0 1 0 1 0 1 1

1 0 1 0 1 0 1 1

Bit robbing “steals” the least significant bit forsignaling transport

Least Significant Bit

Value is determined bySignaling, NOT Channel Sample

Bit Robbing

Source: KnowledgeLink, Inc.

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)

Figure 15.8

12 frames= 1 SF

6th frame

12th frame

T1 Extended Super Frame (ESF)

(ABCD Signal)

Figure 15.9

24 frames= 1 ESF

S: Synchronization (001011) C: error detection F: Facility Data Link control

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

Figure 15.6

1 0 0 0 0 0 0 0 0 0 1Sender

T1 sent

T1 recv

Receiver

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

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 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 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

T1Enterprise Network

Customerrouter

V.35

LocalCarrier(AT&T)

ISPInternet

4-wire

CSU/DSU

CSU/DSUCSU/DSU

“WICModule”CSU cardin router

Cisco2600Router

RJ48C

Equipment Cost (example)

http://www.cdw.com/shop

Cisco 2811 Router$1,779.99

WIC T1 CSU/DSU$689.99

LAN WAN

10/100BaseTX T1

Example: Leased Line Internet Service (T1)

Installation N/A

Service Order N/A

Full T1 Monthly Charge $350

Circuit (local loop) Monthly Charge $200

Chicago

Carrier(AT&T)

ISP(Cogent)Internet

$200$350

www.cogentco.com

Leased Line Pt-Pt Service (T1)

Installation $700

Service Order $325

Circuit (monthly) – one per location $575

Per Mile (monthly) $1.85

St. Louis Chicago

Leased Line Service Charge (1Y pan)

Monthly charge = $575*2 + $1.85 ×300 (miles) × (1-25%) = $1,278.

Carrier(AT&T)

Carrier(AT&T)

$575 $575$1.85 ×300

Synchronous Optical Network (SONET)

SONET Ring

ADMADM

ADMADM

ADMADM

ADMADM

add frameto the ring

drop frameout of the ring

pass frame

ADM = Add-Drop Multiplexer

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

SDH: Synchronous Digital Hierarchy by ITU-TSONET: Synchronous Optical Network by ANSIOC: Optical CarrierSTS: Synchronous Transport Signal STM: Synchronous Transmission Mode

OC STS SDH Line Rate

(Mbps)

Payload Rate

(Mbps)OC-1 STS-1 51.84 49.54

OC-3 STS-3 STM-1 155.52 150.34

OC-12 STS-12 STM-4 622.08 601.34

OC-48 STS-48 STM-16 2,488.32 2,405.38

OC-192 STS-192

STM-64 9,953.28 9,621.50

OC-768 STS-768

STM-256 39,813.12 38,486.02

3-Layer SONET Transport

STS-1 Frame Format

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 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

VT Type

Cols Rate (bps) Carries # in STS-1

VT1.5 3 1.728M T1/DS1 28

VT2 4 2.304M E1 21

VT3 6 3.456M DS1-C 14

VT6 12 6.912M DS2 7

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

Long Haul(DWDM)Network

Metro SONET Ring

Access Ring

Access Ring

Access Ring

ADMADMADMADM

ADMADM

ADMADM

ADMADM

ADMADMADMADM

ADM: Add/Drop Multiplexer

Voice Switch

PBX

Core Router

T1

T1

SONET (APS)

Point-to-Point (with Automatic Protection Switching (APS))

SONET Terminal

SONET Terminal

DS1s, DS3s, Ethernet, ...

DS1s, DS3s, Ethernet, ...

Working Protect

Faults detected and managed using span switching within 50 msec automatically!

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)Ring Topology BLSR (2-fiber) Ring Topology BLSR (4-fiber)

SONET ADM

SONET ADM

SONET ADM

SONET ADM

S

Traffic broadcast to rotating and counter-routing paths

dropped traffic selected based on path level performance by the selector,

used extensive in access network

S

SONET ADM

SONET ADM

SONET ADM

SONET ADM

Enhanced protection due to both span switching and ring switching

4-fiber per node interface (vs 2) used extensively in “backbone” network