2. 2
Who Uses the Internet?
Mobile
Small
Office
Remote Office
Corporate Enterprise
Backbone ISP POP
SOHO
Traveller
Video
PBX
LANS
Video
Phone
Fax
LAN
PC
Internet
PC
Phone
PC
Phone
Fax
PC
LANS
3. 3
User/Access Sites
Home Office
(Single User)
Applications
• Internet Access
• On-Line Services Access
• Telecommuting
• Shopping
Access Lines
• Circuit Switched
Traffic
• Data
• Voice
• Fax
Phone
Fax
PC
Phone
4. 4
Applications
• Internet Access
• Telecommuting
• Electronic Commerce
• Storefront
Access Lines
• Circuit Switched
Traffic
• Data
• Voice
• Fax
User/Access Sites
Small Office
(Multiple Users)
PC
Phone
PC
PC
LAN
LAN
5. 5
User/Access Sites
Remote Office
(Multiple Users)
Applications
• Internet Access
• Intranet/Extranet Access
• Corporate Access
• Telecommuting
• VideoConferencing
Access Lines
• Circuit Switched
• Leased
Traffic
• Data
• Voice
• Fax
• Video
Video
Phone
Fax
LAN
PC
6. 6
User/Access Sites
Corporate Enterprise
Video
PBX
Applications
• Internet Access
• Corporate Communication
• Intranet/Extranet Access
• Telecommuting
• VideoConferencing
• Electronic Commerce
• Virtual Private Network
Access Lines
• Circuit Switched
• Leased
Traffic
• Data
• Voice
•Fax
•Video
Video
PBX
LAN
LAN
PC
7. 7
User/Access Sites
Corporate Backbone Network
Application
• Internet Access
• Intranet/Extranet Access
• Network Management
• Virtual Private Network
Access Lines
• Leased
Traffic
• Data
• Voice
• Fax
• Video
Internet
8. 8
User/Access Sites
ISP POPApplications
• Internet Access
• Network Management
• Web Site
• Security
• Virtual Private Network
• Wholesaling
Access Lines
• Circuit Switched
• Leased
Traffic
• Data
• Voice
• Fax
• Video
InternetInternet
9. 9
What Is Internet Access?
• The use of service provider offerings to establish a
connection between a user’s location and the Internet
• This may be either analog or digital
• The traffic may be data, voice or fax
• Access may be through an Internet service provider’s
point of presence or a corporate gateway
Internet
Service
Provider
Telecommuter
LAN
Remote Office
Customer Site
LAN
Carrier
ServicesInternet
11. 11
Where Are We Going?
Public Switched Public Internet
Telephone Network Protocol Network
Designed a Century Ago Designed for Modern High-speed
for Analog Voice Digital Communications
Circuit-oriented Packet/celłframe-oriented
Point-to-Point Only Point-to-Point
Any-to-Any
Any-to-Many
“Constant Bit Rate” Only Constant, Variable and Available
Bit Rates
64 Kbps Channels Only Virtually Unlimited Bandwidth
Complex Layer-1 Signaling Simple Layer-2,3 Switching/Routing
Difficult and Expensive to Scale Scales Easily and Affordably
Limited “Add-on” Management Management Features Built-in
15. 15
Network Trunks (T1)
• Key point: The network is a fabric of 64 Kbps threads
(DS0s), originally designed to carry digital voice
On a DS1 trunk, 24 64 Kbps channels are time
division multiplexed into one 1536 Kbps circuit
One
DS1
Circuit
24
channels
1 2 3 4 5 6 7 823 22 23 24 1 2 32124
One DS1 frame (1536 Kbps)
16. 16
Leased Line Traffic
(Point to Point Circuit)
One or more channels from origin to
destination dedicated full-time to the user
User
Access Line
(Local Loop)
Access
Equipment
Central
Site
Access Line
(Local Loop)
Access
Equipment
Central
Office
Central
Office
17. 17
Circuit Switched Traffic
(Time Division Multiplexed Bandwidth)
a.k.a. Public Switched Telephone Network (PSTN)
One or more channels from origin to
destination dedicated to the user
for the length of the call
PSTN
User
Access Line
(Local Loop)
Access
Equipment
Central
Site
Access Line
(Local Loop)
Access
Equipment
Central
Office
Central
Office
18. 18
Central Office
Circuit
Switch
Access Lines Network Trunks
Service
Provider
Networks
MDF = Main Distribution Frame
2 Wire
4 Wire
6 Wire
Point-to-Point
Circuit
Circuit-Switched
Trunk
MDF
Users
19. 19
Circuit Switched Access
• One 3.4 kHz channel
• Up to 33.6 Kbps data using symmetric modem
• Up to 56 Kbps data using asymmetric modem
• In-band signaling (DTMF)
Analog
2 wire
Access
Equipment
PSTN
Central
Office
20. 20
Circuit Switched Access
• Two 64 Kbps data channels
• One 16 Kbps out-of-band signaling channel
• ISDN “U” (2 wire) or “S/T” (4 wire) interface
ISDN BRI
U or S/T interface
Access
Equipment
B2
D
B1
OneOne
CircuitCircuit
BRIBRI
PSTN
Central
Office
D DD
BRI frame
B1B2 B2 B1 B2B1
21. 21
Circuit Switched Access
• 24 56 Kbps data
channels, 56 Kbps
• In-band signaling
T1 Access Line
4 wire
Access
Equipment
One T1 frame (1536 Kbps)
1 2 3 4 5 6 7 823 22 23 24 1 2 32124
One
T1
Circuit
24 channels
PSTN
Central
Office
22. 22
Central SiteRemote User
Bandwidth Allocation Control Protocol
(BACP)
• Adds control channel and intelligent dialing
• Both ends communicate during session
• Allows the dynamic allocation of bandwidth
• Open specification allows interoperability
among multiple vendors’ equipment
End-to-end communications
channel to control all circuits
used by MP
Multiple analog lines, switched
56 circuits, ISDN B-channels, etc...
MP Datastream
23. 23
Circuit Switched Access with
External WAN Interfaces
Access Server
LAN
Analog
Modem
Users
Digital
ISDN BRI
Users
Dial-Up
Services
Multiple
Digital Access
Lines
Multiple
Analog Access
Lines
TA
or
DSU
Modem
Digital
Calls
Multiple
Serial Ports
Analog
Calls
Protocol
Processing
24. 24
Circuit Switched Access with
Integrated WAN Interfaces
Analog
Modem
Users
Digital
ISDN BRI
Users
Dial-Up
Services
100% Digital Access
(ISDN PRI, T1 or E1)
Integrated
TAs and
DSUs
Integrated
Digital
Modems
Protocol Processing
Access Server
Analog
Calls
Digital
Calls
LAN
25. 25
Today’s Circuit Switched/Leased
Point-to-Point Connections to the
Internet Protocol (IP) Based Internet
The
Internet
Leased or
Circuit
Switched
Circuit
Switched
Circuit Switched
Circuit
Switched
ISP
ISP
ISP
ISP
Corporate
Location
Remote
Office
Leased
Mobile
Travelers
Customer/
Supplier
Telecommuter
26. 26
IP Based Internet Uses
Packet Switched Traffic
(Statistically Multiplexed Bandwidth)
A packet protocol over fixed bandwidth circuits
that can be shared by multiple users
data data data
data data
data
data data data
DigitalDigital
CircuitCircuit
examined by switch
F
L
A
G
address data
frame
check
sequence
F
L
A
G
examined by switch
27. 27
Packet Network Virtual Circuits
Frame Relay or ATM
Virtual Circuit
• Provides connectivity between locations
Switched Virtual Circuit
• Dynamically established when needed
• Released when not needed
Permanent Virtual Circuit
• Statically defined at configuration
• Always configured (active or idle)
28. 28
Packet Switched Access
Digital Subscriber Line (xDSL)
• DSL Technologies
– IDSL
– HDSL
– SDSL
– ADSL-CAP, ADSL-DMT
• High bandwidth over existing “local
loop” twisted pair of wire
Access
Equipment
Access Line
(Local Loop) Central
Office
User Packet
Network
29. 29
xDSL Access Options
Central Office
SOHOCopper Loops
Any ISDN
CPE
SOHO
SOHO
Ethernet
Ethernet
Ethernet
IDSL
Up to 128 Kbps
SDSL
Up to 768 Kbps
ADSŁData w/POTS
Up to 7 Mbps
POTS
SplitterPSTN
Packet
Network
CO
Circuit
Switch
DSL
Access
Module
MDF
30. 30
Packet Switched Access
ISDN Digital Subscriber Line (IDSL)
• IDSL – Technological innovation from Ascend
• 128 Kbps symmetric data rate
• Single pair local loop to 18,000 ft.
• Compatible with any ISDN BRI TA, bridge or router
• 2B1Q line code for transparent operation
data
dataAccess
Equipment
Packet Network
IDSL
2 Wire data
dataCentral
Office
31. 31
Packet Switched Access
ISDN Digital Subscriber Line (IDSL)
Voice and Data
Telephone Company
Central Office
2-Wire
Local Loop
CO Circuit
Switch
Customer Premises
T1 or
T1/PRI
Packet
Network
(IP, ATM,
Frame Relay)
PSTN
