1. Digital Access Services T-1 and SONET2

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

3. Leased Line Service Rates
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 * = 193 bits/frame
8000 frames/sec * 193 bits/frame = Mbps
8000 Framing bits sent per second

6. Channelized? Channelized T-1 Circuit Unchannelized T-1
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 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
Bit robbing - the signaling that can be sent includes:
Supervision: on, off-hook
Address: call destination
Audible tone signals: dial tone, busy, ringing.
Source: KnowledgeLink, Inc.

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

10. T-1 Framing Bits D4 T-1 lines (1972): D5 (ESF) T-1 lines (1983):
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
When T1 use was expanded to include transmission of digital data as well as coded voice samples, bit robbing presented a problem. Data does care about the value of every digit. (Think of your social security number or your bank account number.) The TI designers had two choices: limit the usable data per channel to 7 bits rather than 8, or come up with another way to send signaling information.
Limiting the usable data to 7 bits reduces the available bandwidth of the T1 system to 7 bits x 8000 samples per second, or 56 Kbps per channel, rather than 64 Kbps as actually intended. Although this rate is still acceptable for digital voice, it limits data transmission and is not a good permanent solution. The designers came up with the Superframe concept as a first step toward reclaiming the 8th bit.
Superframes are sets of 12 normal TI frames. This is illustrated above. Within the superframe, frames 6 and 12 are designated as the A and B signaling frames. Within these frames, and only within these frames, bits are robbed from the least significant digits of each 8-bit word for signaling and supervision. What has been accomplished is that the remaining 10 frames contain "clear channels," or have a full 64 Kbps available for data.
12th frame
Figure 15.8

12. T1 Extended Super Frame (ESF) (ABCD Signal)
24 frames
= 1 ESF
Unfortunately, end users still could not transmit data at 64 frames. For voice transmission, because the sample was represented accurately by full 8-bit frames, and for the frames where the bit was still robbed, the inaccuracy became even less significant. For the full 64 Kbps to be available for data transmission, a new type of out-of-band signaling, called Signaling System (SS7), needed to be implemented. SS7 is a special type of packet network, totally separate from the network used to transmit user data. telephone equipment to communicate signaling, call setup, related information.
For more information on SS7, see the GWEC module TT-SS7.
The way the signaling frames of a superframe are recognized is by changing the function of the framing bit. The framing bit of the even-numbered frames is used to create a six-digit sequence that marks the 6th and 12th frames. Specifically, after six even frames, the framing bit pattern of the even frames is This pattern repeats each set of six even frames.
It is important to note that it is channel bits and not framing bits that carry signaling and supervisory information. The framing bits are only used to mark the position of these frames so the equipment can find the appropriate channels containing the signaling and supervisory information.
Synchronization is still required, however, and this is accomplished in the odd frames. The sequence of the framing bit values in the odd frames is still an alternating pattern of 1/0, such that after six odd frames, the framing bits will have formed the pattern
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) 48

14. AMI and B8ZS Signal 1 0 0 0 0 0 0 0 0 0 1 Sender T1 sent T1 recv
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 = Mbps.
A clear-channel T-1 carries 24 x 64 Kbps = 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 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. Leased Line Service (T1) (example: to Internet)
Customer
router
CSU/DSU
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

23. Example: Leased Line Internet Service (T1)
ISP
(Cogent)
$350
Carrier
(AT&T)
$200
Internet
Chicago
Installation
N/A
Service Order
Full T1 Monthly Charge
$350
Circuit (local loop) Monthly Charge
$200

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)
Installation
$700
Service Order
$325
Circuit (monthly) – one per location
$575
Per Mile (monthly)
$1.85
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 OC STS SDH Line Rate (Mbps) Payload Rate (Mbps) OC-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
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): M bps

31. Virtual Tributaries VT Type Cols Rate (bps) Carries # in STS-1 VT1.5 3
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

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 Metro SONET Ring Access Ring Access Ring Access Ring
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
DS1s, DS3s, Ethernet, ...
SONET Terminal
Protect
SONET Terminal
DS1s, DS3s, Ethernet, ...
Faults detected and managed using span switching within 50 msec automatically!

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

36. SONET Networks (BLSR) Ring Topology BLSR (2-fiber)
SONET ADM
SONET ADM
SONET ADM
SONET ADM
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
Enhanced protection due to both span switching and ring switching
4-fiber per node interface (vs 2)
used extensively in “backbone” network S