Transcript Basic Concepts - Mahmoud Youssef

Wide Area Networks (WANs)
Chapter 7
Copyright 2003 Prentice-Hall
Panko’s Business Data Networks and Telecommunications, 4th edition
Figure 7.1: Wide Area Networks (WANs)

The Telephone Network


WAN technology often is based on telephone
technology
WAN Purposes

Link sites within the same corporation

Provide remote access to individuals who are offsite

Internet access
2
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data network (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
3
Figure 7.1: Wide Area Networks (WANs)

Low Speeds

High cost per bit transmitted compared to WANs

Lower speeds (mostly commonly 56 kbps to a few
megabits per second)
4
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data network (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
5
Figure 7.2: Telephone Modem Communication
Need Modem at Each End Up to 33.6 kbps
Digital Signal
Client A
Modulated
Signal
33.6 Telephone
kbps
Modem
PSTN (Digital)
Telephone
Modem
Server A
6
Figure 7.2: Telephone Modem Communication
PSTN (Digital)
Digital Access Line
Client B
56 kbps
Modem
Telephone
Server
B
For 56 kbps Download Speed
Server Must Have a Digital Connection, Not a Modem
7
Figure 7.3: Telephone Modem
Modulation Standards and Speeds


V.34

Send and receive at up to 33.6 kbps

Fall back in speed if line conditions are not optimal
V.90

Receive at up to 56 kbps

Send at up to 33.6 kbps

Other party must have a digital connection to the
PSTN
8
Figure 7.3: Telephone Modem
Modulation Standards and Speeds

V.92

Receive at up to 56 kbps

Send at up to 33.6 kbps or higher if the line permits

Other party must have a digital connection to the
PSTN

Modem on hold: can receive an incoming call for a
short time without losing the connection

Cuts call setup time in half
9
Figure 7.3: Telephone Modem
Modulation Standards and Speeds

V.92

Usually uses V.44 compression, which downloads
webpages twice as fast as the old standard for
compression, V.42 bis
10
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data network (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
11
Figure 7.5: Trunk-Line Based Leased Line
T1 Trunk Line (1.544 Mbps)
Access
Line
Computer
Telephone
Switch
Trunk
Line
Telephone
Switch
Telephone
Switch
Server
T1 Leased Line (1.544 Mbps)
End-to-End Circuit with Trunk Line Speed
Extend trunk line speeds to end-to-end service
12
Figure 7.4: Leased Line Networks

Leased Line (Private Line or Dedicated Line)

Point-to-point connection

Always on

Lower cost per minute than dial-up service

Must be provisioned (set up)
13
Figure 7.4: Leased Line Networks

Trunk Line-Based Leased Lines

Based on trunk lines discussed in the previous
chapter

Extend standard trunk line speeds to end-to-end
circuits between two customer premises

Require expensive data-grade copper or optical
fiber
Data-Grade UTP
14
Figure 7.4: Leased Line Networks

Trunk Line-Based Leased Lines

Fractional T1 lines offer low-speed choices
between 56 kbps and T1, typically:

128 bps

256 kbps

384 kbps

512 kbps

768 kbps
15
Figure 7.4: Leased Line Networks

Digital Subscriber Lines (DSLs)

Broadband speeds over single pair of voice-grade
copper

Does not always work: distance limitations, etc.

Where it does work, much cheaper than trunk linebased leased lines
Existing Voice-Grade UTP
16
Figure 7.6: ASDL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
PC
ADSL
Modem
Splitter
1.
Existing Pair of
Voice-Grade
UTP Wires
DSLAM
PSTN
Telephone
17
Figure 7.6: ASDL with Splitter
Subscriber
Premises
PC
ADSL
Modem
Splitter
1.
Data
256 kbps to
1.5 Mbps
Telephone Company
End Office Switch
Data
WAN
2.
64 kbps to
256 kbps
DSLAM
PSTN
Telephone
18
Figure 7.6: ASDL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
PC
ADSL
Modem
DSLAM
Splitter
Telephone
1.
Ordinary Telephone
Service
PSTN
19
Figure 7.4: Leased Line Networks

Digital Subscriber Lines (DSLs)

Asymmetric DSL (ADSL)
 Asymmetric speed

Downstream (to customer): 256 kbps to over
1.5 Mbps

Upstream (from customer): 64 kbps or higher

Simultaneous telephone and data service

DSL access multiplexer (DSLAM) at end
telephone office

Speed not guaranteed
20
Figure 7.4: Leased Line Networks

Digital Subscriber Lines (DSLs)

HDSL

Symmetric speed (768 kbps) over one voicegrade twisted pair

HDSL2: 1.544 symmetric speed over one voicegrade twisted pair

Needed in business. (ADSL primarily for home
and small business access.)

Speed guaranteed
21
Figure 7.4: Leased Line Networks

Digital Subscriber Lines (DSLs)

SHDSL

Super High rate DSL

Single voice-grade twisted pair; longer distances
than ASDL, HSDL

Symmetric speed

Variable speed ranging from 384 kbps to 2.3
Mbps

Speed guaranteed
22
Figure 7.7: Cable Modem Services
6. To Other Subscribers
Sharing Neighborhood Capacity
Subscriber
Premises
PC
ISP
4. Coaxial
Cable to
Premises
5. Cable
Modem
6. Requires NIC or USB port
2. Optical
Fiber to
Neighborhood
3.
Neighborhood
Splitter
1. Cable
Television
Head End
23
Figure 7.4: Leased Line Networks

Cable Modem

Delivered by cable television operator

High asymmetric speed


Up to 10 Mbps downstream

64 kbps to 256 kbps upstream
Speed is shared by people currently downloading in
a neighborhood

In practice, medium ADSL speed or higher
24
Figure 7.8: GEO Satellite System
2. Point-to-Point
Uplink
1.
Geosynchronous
Satellite
3.
Broadcast
Downlink
5. Earth Station A
4.
Footprint
Earth Station B
Appears stationary in sky (36,000 km or 22,300 mi)
Far, so earth station needs dish antenna
25
Figure 7.9: LEO and MEO Satellite Systems
1. Currently Responsible LEO or MEO
2. Next Responsible
LEO or MEO
3. Small
Omnidirectional
Transceiver
A few thousands (LEO) or tens of thousands of km (miles) (MEO)
Closer, so omnidirectional transceivers can be used
26
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data networks (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
27
Figure 7.10: Leased Line versus Public
Switched Data Networks
Site A
Multisite Leased Line Mesh Network
Site B
OC3 Leased Line
T3 Lease
Line
56 kbps
Leased
Line
T1 Leased
Line
Site C
T1 Leased
Line
56 kbps
Leased
Line
56 kbps
Leased
Line
Site D
Site E
28
Figure 7.10: Leased Line versus Public
Switched Data Networks
Public Switched Data Network (PSDN)
Site A
Site B
POP
Point of Presence
POP
Public Switched Data
Network (PSDN)
POP
POP
One leased
line per site
Site D
Site C
Site E
29
Figure 7.10: Leased Line versus Public
Switched Data Networks


Leased Line Network

Many leased lines

Individual leased line spans long distances

Company must buy switching, plan, and manage
Public Switched Data Network

Only need one leased line from each site to a POP

Few and short-distance leased lines

PSDN carrier provides switching, planning, and
management of the network
30
Figure 7.11: Popular PSDN Services
Typical
Service
Speeds
ISDN
X.25
Frame
Relay
Circuit- or
PacketSwitched
Two 64 kbps
B channels
Circuit
One 16 kbps
D channel
9,600 kbps
to about
Packet
40 Mbps
56 kbps
to about
Packet
40 Mbps
Reliable or Virtual
Relative
Unreliable Circuits? Price
Unreliable
No
Moderate
Reliable
Yes
Moderate
Unreliable
Yes
Low
31
Figure 7.11: Popular PSDN Services
Service
ATM
Ethernet
Typical
Speeds
Circuit- or
PacketSwitched
1 Mbps
to about Packet
156 Mbps
10 Gbps
and
Packet
40 Gbps
Reliable or Virtual
Relative
Unreliable Circuits? Price
Unreliable
Yes
High
Unreliable
No
Probably
Low
32
Figure 7.11: Popular PSDN Services

Most PSDNs are packet-switched, unreliable,
and use virtual circuits

All of these are designed to reduce carrier
transmission costs so that lower competitive prices
can be set

Packet switching multiplexes trunk line
transmissions, reducing trunk line costs

Unreliability and virtual circuits simply
switching, reducing switching costs
33
Figure 7.12: Integrated Services Digital
Network (ISDN)
Personal
Computer
2.
64 kbps B Channel
Digital Signal
On Serial Cable
(1010)
3.
64 kbps B Channel
Analog Voice Signal
On Telephone Wires
2B+D
Desktop Telephone
1.
ISDN
3 Multiplexed
Wall
Channels on
Jack
One Pair of
Telephone Wires (RJ-45)
(2B+D)
4.
16 kbps D channel
is for
Supervisory
signaling
34
Quiz

How many bits per second are multiplexed
over the single wire pair connected to the wall
jack and to the single pair running from the
customer premises to the carrier end office?
35
Figure 7.12: Integrated Services Digital
Network (ISDN)
Personal
Computer
Internal DSU
Converts Serial Port
64 kbps B Channel Signal to Digital
Digital Signal
B Channel
On Serial Cable
Signal at 64
(1010)
kbps
(1010)
“ISDN Modem”
ISDN
Wall
Jack
(RJ-45)
All-digital
Service
(1101001..)
The Data Channel
Desktop Telephone
Uses 232 Serial Cable
36
Figure 7.12: Integrated Services Digital
Network (ISDN)
Personal
Computer
The Voice Channel
Uses Home Telephone Cord
ISDN
Wall
Jack
(RJ-45)
“ISDN Modem”
64 kbps B Channel
Analog Voice Signal
On Telephone Wires
Desktop Telephone
All-digital
Internal Codec
Service
Converts
(1101001..)
Analog Voice
Signal to Digital
B Channel
Signal at 64 kbps
(000010000))
37
Figure 7.12: Integrated Services Digital
Network (ISDN)
Personal
Computer
Internal DSU
Converts Serial Port
64 kbps B Channel Signal to Digital
Digital Signal
B Channel
On Serial Cable
Signal at 64
(1010)
kbps
(1010)
“ISDN Modem”
ISDN
Wall
Jack
(RJ-45)
All-digital
Service
(1101001..)
Bonding
Desktop Telephone
Use Both B Channels for Data
Send and Receive at 128 kbps
38
Figure 7.14: Pricing Elements in Frame Relay
Service

Frame Relay Pricing

Frame relay access device at site
 CSU/DSU at physical layer

Leased line from site to POP

Port on the POP
 Pay by port speed
 Usually the largest price component

Permanent virtual circuits (PVCs) among
communicating sites

Other charges
39
Figure 7.13: Access Devices
Site A
Access Device
(Frame Relay
Access Device)
T1 CSU/DSU at
Physical Layer
T1 Line
Frame Relay at
Data Link Layer
PC
Site B
Server
Access Device
(Router)
T3 CSU/DSU at
Physical Layer
T3 Line
ATM etc. at
Data Link Layer
40
Figure 7.14: Pricing Elements in Frame Relay
Service
Customer
Premises A
1.
Access Device
Switch
POP
Customer
Premises B
Customer
Premises C
41
Figure 7.14: Pricing Elements in Frame Relay
Service
Customer
Premises A
2.
T1 Leased Access
Line to POP
Switch
POP
Customer
Premises B
Customer
Premises C
42
Figure 7.14: Pricing Elements in Frame Relay
Service
Customer
Premises A
CIR = 56 kbps
ABR = 1 Mbps
3.
Port
Speed
Charge
Switch
POP
Customer
Premises B
Customer
Premises C
43
Figure 7.14: Pricing Elements in Frame Relay
Service
Customer
Premises A
4.
PVC
Charges
PVCs 1&2
Switch
POP
PVC 2
PVC 1
PVC 1
PVC 2
Customer
Premises B
PVC 1
Customer
Premises C
44
Figure 7.14: Pricing Elements in Frame Relay
Service
5.
Sometimes
Traffic
Charges and
Other Charges
Customer
Premises A
6. Management
Switch
POP
Customer
Premises B
Customer
Premises C
45
Figure 7.15: Frame Relay Pricing Details


Other Charges

Flat rate versus traffic volume charges

Installation charges

Managed service charges

Service level agreement (SLA) charges
Geographical Scope

Frame Relay systems with broader geographical
scope cost more
46
Figure 7.15: Frame Relay Pricing Details

To Determine Needs

For Each Site
New
Not in Book

Determine needed speed to each other site

You will need a virtual circuit of this speed

Sum all the virtual circuit speeds

You will need a leased line this fast
 Actually, you usually can get by with a least line
70% this fast because not all virtual circuits will
always be in use
47
Figure 7.15: Frame Relay Pricing Details

To Determine Needs

For Each Site
New
Not in Book

You need a port speed equal to or greater than the
sum of the PVCs
 Again, you can get by with 70%

Remember that port speed is more expensive than
leased line speeds
 In general, don’t waste port speed by using a
leased line much under its capacity
48
Figure 7.15: Frame Relay Pricing Details

New
Not in Book
Example

The Situation
 Headquarters and two branch offices.
 Branches communicate with HQ at 256 kbps
 Branches communicate with each other at 56
kbps
B1
HQ
B2
49
Figure 7.15: Frame Relay Pricing Details

Example

New
Not in Book
For HQ
HQ

How many PVCs will HQ need?

What are their speeds?

If POP speeds are 56 kbps, 256 kbps, 512 kbps,
what port speed will HQ need?

What leased lines will HQ need if speeds are 56
kbps, 256 kbps, 512 kbps, or T1?
50
Figure 7.15: Frame Relay Pricing Details

Example

New
Not in Book
For Each Branch
B1

How many PVCs will the branch need?

What are their speeds?

If POP speeds are 56 kbps, 256 kbps, 512 kbps,
what port speed will the branch need?

What leased lines will the branch need if speeds
are 56 kbps, 256 kbps, 512 kbps, or T1?
51
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data networks (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
52
Figure 7.1: Wide Area Networks (WANs)

WAN Technologies

Ordinary telephone line and modem. (low-speed
access only)

Network of leased lines

Public switched data network (PSDN)

Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
53
Figure 7.17: Virtual Private Network
Site-to-Site
for Internet
Tunnel
Internet
VPN Server
VPN Server
Corporate
Site B
Corporate
Site A
Extranet
Remote
Customer PC
(or site)
Remote
Access for
Intranet
Remote
Corporate PC
54
Figure 7.16: Virtual Private Network
(VPN) Issues


Virtual Private Network (VPN)

Transmission over the Internet with added security

Some analysts include transmission over a PSDN
with added security
Why VPNs

PSDNs are not interconnected

Internet reaches almost all sites

Low transmission cost per bit transmitted
55
Figure 7.16: Virtual Private Network
(VPN) Issues

VPN Problems

Latency
 Reduces by having all communication go
through a single ISP

Security
 PPTP for remote access is popular
 IPsec for site-to-site transmission is popular
56
Figure 7.18: ISP-Based PPTP Remote
Access VPN

Remote Access VPNs


User dials into a remote access server (RAS)
RAS often checks with RADIUS server for user
identification information
Local
Access
Internet
RADIUS
Server
PPTP
RAS
Corporate
Site A
ISP
PPTP
Access
Concentrator
Remote
Corporate
PC
57
Figure 7.16: Virtual Private Network
(VPN) Issues

Point-to-Point Tunneling Protocol

Available in Windows since Windows 95
 No need for added software on clients

Provided by many ISPs
 PPTP access concentrator at ISP access point

Secure tunnel between access concentrator and RAS
at corporate site

Some security limitations
 No security between user site and ISP
 No message-by-message authentication of user
58
Figure 7.16: Virtual Private Network
(VPN) Issues

Site-to-Site VPNs and Extranets

Site-to-site networks link sites within a single
company
 Often part of an intranet—use of TCP/IP
transmission and applications internally
 TCP/IP transmission is low in cost
 TCP/IP applications are good, standardized, and
inexpensive

Extranet: communication with customers and
suppliers with security over the Internet
59
Figure 7.19: IPsec in Tunnel Mode
Local
Network
IPsec
Server
Tunnel
Mode
IPsec
Local
Server
Network
Secure
Tunnel
No Security
In Site Network
Tunnel Only
Between Sites
Hosts Need No
Extra Software
No Security
In Site Network
60
Figure 7.19: IPsec in Tunnel Mode
Module F
Local
Network
IPsec
Server
Transfer
Mode
IPsec
Local
Server
Network
Secure
Tunnel
Security
In Site Network
End-to-End (Host-to-Host)
Tunnel
Hosts Need IPsec Software
Security
In Site Network
61
Figure 7.16: Virtual Private Network
(VPN) Issues

IP Security (IPsec)
Module F

At internet layer, so protects information at higher
layers

Tunnel mode: sets up a secure tunnel between
IPsec servers at two sites
 No security within sites
 No need to install IPsec software on stations

Transfer mode: set up secure connection between
two end hosts
 Protected even on internal networks
 Must install IPsec software on stations
62
Figure 7.16: Virtual Private Network
(VPN) Issues

IP Security (IPsec)

Security associations:

Agreement on how security options will be
implemented

Established before bulk of secure
communication begins

May be different in the two directions

Governed by corporate policies
63
Figure 7.20: Policy-Based Security
Associations in IPsec
Security Association (SA1) for Transmissions
From A to B
Party A
Security Association (SA2) for Transmissions
From B to A
Party B
List of
Allowable
Security
Associations
List of
Allowable
Security
Associations
IPsec Policy Server
64