Basic Concepts - Mahmoud Youssef
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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