Wide Area Networks (WANs) Chapter 7 (Modified April 2003)
Copyright 2003 Prentice-Hall Pankos Business Data Networks and
Telecommunications, 4 th edition
Slide 2
2 Figure 7.1: Wide Area Networks (WANs) Chapters 4 and 5: LANs
Customer premises operation, high speeds Chapter 6: Telephony LAN
building wiring PSTN carrier service Chapter 7: WANs WAN technology
often is based on telephone technology and services
Slide 3
3 Figure 7.1: Wide Area Networks (WANs) WAN Purposes Link sites
(usually) within the same corporation Provide remote access to
individuals who are off- site Internet access 1. Link Sites 2.
Remote Access 3. Internet Access
Slide 4
4 Figure 7.1: Wide Area Networks (WANs) WAN Technologies
Ordinary telephone line and telephone modem. Point-to-Point Leased
lines Public switched data network (PSDN) Send your data over the
Internet securely, using Virtual Private Network (VPN) technology
PSDN VPN
Slide 5
5 Figure 7.1: Wide Area Networks (WANs) High Speeds and Low
Speeds High cost per bit transmitted compared to LANs Lower speeds
(mostly commonly 56 kbps to a few megabits per second) LANs Cheap,
WANs Expensive (per bit transmitted) LANs Fast, WANs Slow
Slide 6
6 Figure 7.1: Wide Area Networks (WANs) WAN Technologies
Ordinary telephone line and telephone modem. (low-speed access
only) Point-to-Point Network of leased lines Public switched data
network (PSDN) Send your data over the Internet securely, using
Virtual Private Network (VPN) technology
Slide 7
7 Figure 7.2: Telephone Modem Communication PSTN Client A
Server A Telephone 33.6 kbps Modem Binary Data Analog Modulated
Signal Modem Need Modem at Each End Up to 33.6 kbps
Slide 8
8 Figure 7.2: Telephone Modem Communication PSTN Client B
Server B Telephone Digital Access Line 56 kbps Modem For 56 kbps
Download Speed Server Must Have a Digital Connection, Not a
Modem
Slide 9
9 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 Asymmetric speed is good for WWW service. Other party
must have a digital connection to the PSTN
Slide 10
10 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
Slide 11
11 Figure 7.3: Telephone Modem Modulation Standards and Speeds
Compression V.92 modems usually use V.44 compression, which
downloads webpages twice as fast as the old standard for
compression, V.42 bis Data: 112.5 kbps Signal: 33.6 kbps
Slide 12
12 Figure 7.1: Wide Area Networks (WANs) WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Point-to-Point Network of leased lines Public switched data network
(PSDN) Send your data over the Internet securely, using Virtual
Private Network (VPN) technology
Slide 13
13 Figure 7.5: Trunk Line-Based Leased Line Computer Telephone
Switch Telephone Switch Telephone Switch Server Access Line T1
Trunk Line (1.544 Mbps) T1 Leased Line (1.544 Mbps) End-to-End
Circuit with Trunk Line Speed Trunk Line Extend trunk line speeds
to end-to-end service
Slide 14
14 Figure 7.4: Leased Line Networks Leased Line (Private Line
or Dedicated Line) Point-to-point connection Always on Usually very
fast (56 kbps or more) Usually digital instead of analog Lower cost
per bit transmitted than dial-up service But speeds are higher, so
higher total cost Must be provisioned (set up). Can take weeks or
months
Slide 15
15 Figure 7.4: Leased Line Networks Trunk Line-Based Leased
Lines Require expensive optical fiber or (for 56 kbps, 64 kbps, T1
and E1 lines,) expensive data-grade copper UTP For data-grade UTP,
need two pairsone for transmission in each direction. Called
four-wire circuits. Data-Grade Copper UTP
17 Figure 7.4: Leased Line Networks Digital Subscriber Lines
(DSLs) Broadband speeds over single pair of voice-grade copper UTP
for transmission in both directions Does not always work: distance
limitations, etc. Where it does work, much cheaper than trunk line-
based leased lines Existing Voice-Grade UTP Single Pair
Slide 18
18 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL
Modem Splitter Telephone Subscriber Premises Telephone Company End
Office Switch 1. Existing Single Pair of Voice-Grade UTP Wires PC
2. 3.
Slide 19
19 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL
Modem Splitter Telephone Subscriber Premises Telephone Company End
Office Switch PC 1. Data 256 kbps to 1.5 Mbps 2. 64 kbps to 256
kbps
Slide 20
20 Figure 7.6: ASDL with Splitter Data WAN PSTN DSLAM ADSL
Modem Splitter Telephone Subscriber Premises Telephone Company End
Office Switch PC 1. Ordinary Telephone Service
Slide 21
21 Figure 7.4: Leased Line Networks 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 Designed as consumer service, so speed is not
guaranteed
Slide 22
22 Figure 7.4: Leased Line Networks HDSL High-rate DSL
Symmetric speed (768 kbps both ways) over one voice-grade twisted
pair Needed in business. (ADSL primarily for home and small
business access.) Speed guaranteed HDSL2 1.544 symmetric speed over
one voice-grade twisted pair
Slide 23
23 Figure 7.4: Leased Line Networks 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 Mbps
Speed guaranteed
Slide 24
24 Figure 7.7: Cable Modem Services PC Subscriber Premises 5.
Cable Modem 4. Coaxial Cable to Premises 2. Optical Fiber to
Neighborhood 3. Neighborhood Splitter ISP 1. Cable Television Head
End 6. Requires NIC or USB port
Slide 25
25 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
Slide 26
26 Figure 7.8: GEO Satellite System 2. Point-to-Point Uplink 3.
Broadcast Downlink 4. Footprint 5. Earth Station A Earth Station B
1. Geosynchronous Satellite Satellite appears stationary in sky
(35,785 km or 22,236 mi) Far, so earth station needs dish
antenna
Slide 27
27 Figure 7.9: LEO and MEO Satellite Systems 3. Small
Omnidirectional Transceiver 1. Currently Responsible LEO or MEO 2.
Next Responsible LEO or MEO A few thousands of km or miles (Low
Earth Orbit) or tens of thousands of km (miles) (Medium Earth
Orbit) Closer than GEO, so omnidirectional transceivers can be used
User is served by a succession of satellites
Slide 28
28 Figure 7.1: Wide Area Networks (WANs) WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Point-to-Point network of leased lines Public switched data
networks (PSDN) Send your data over the Internet securely, using
Virtual Private Network (VPN) technology PSDN
Slide 29
29 Figure 7.10: Leased Line versus Public Switched Data
Networks T3 Lease Line Site C Site A Site B OC3 Leased Line T1
Leased Line T1 Leased Line Site E Site D 56 kbps Leased Line 56
kbps Leased Line 56 kbps Leased Line Multisite Leased Line Mesh
Network
Slide 30
30 Figure 7.10: Leased Line versus Public Switched Data
Networks Public Switched Data Network (PSDN) POP Site A Site B
Point of Presence One leased line per site Site D Site C Site E
Public Switched Data Network (PSDN)
Slide 31
31 Figure 7.10: Leased Line versus Public Switched Data
Networks Leased Line Network Many leased lines Individual leased
line spans long distances Company must plan, buy switching
equipment, and operate the network Public Switched Data Network
Only need one leased line from each site to a POP Few and
short-distance leased lines PSDN carrier provides planning,
switching, and operation of the network
Slide 32
32 Figure 7.11: Popular PSDN Services Service Typical Speeds
Circuit- or Packet- Switched Reliable or Unreliable Virtual
Circuits? Relative Price X.25 9,600 kbps to about 40 Mbps
PacketReliableYesModerate Frame Relay 56 kbps to about 40 Mbps
PacketUnreliableYesLow X.25 (Obsolete): Slow because of reliability
Frame Relay Dominates PSDNs Today Unreliable for Lower Carrier Cost
Speed Range is in Main Range of Corporate Demand
Slide 33
33 Figure 7.11: Popular PSDN Services Ethernet 10 Gbps and 40
Gbps PacketUnreliableNo Probably Low ATM 1 Mbps to about 156 Mbps
PacketUnreliableYesHigh Service Typical Speeds Circuit- or Packet-
Switched Reliable or Unreliable Virtual Circuits? Relative Price
ATM is Faster than Frame Relay Should Grow in Demand as Corporate
Demand Outgrows FR However, Ethernet MANs are Appearing Should
Offer Lower Prices for Comparable Speeds
Slide 34
34 Frame Relay and ATM FR and ATM are Not Competitors Most PSDN
carriers offer both so they can server any speed range Many
interconnect their FR and ATM services, so that individual sites
can use whatever service is best for them
Slide 35
35 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
Slide 36
36 Figure 7.11: Popular PSDN Services Service Typical Speeds
Circuit- or Packet- Switched Reliable or Unreliable Virtual
Circuits? Relative Price ISDN Two 64 kbps B channels One 16 kbps D
channel CircuitUnreliableNoModerate ISDN is Not Popular Expensive
for its Slow Speed Has Niche in Backup Connections Because Dial-Up,
So Only Pay for When Needed
Slide 37
37 Figure 7.12: Integrated Services Digital Network (ISDN)
Personal Computer Desktop Telephone 3. 64 kbps B Channel Analog
Voice Signal On Telephone Wires 2. 64 kbps B Channel Digital Signal
On Serial Cable (1010) 1. 3 Multiplexed Channels on One Pair of
Telephone Wires (2B+D) ISDN Wall Jack (RJ-45) 4. 16 kbps D channel
is for Supervisory signaling 2B+D
Slide 38
38 Quiz In ISDN, 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?
Slide 39
39 Figure 7.12: Integrated Services Digital Network (ISDN)
Personal Computer Desktop Telephone ISDN Modem 64 kbps B Channel
Digital Signal On Serial Cable (1010) Internal DSU Converts Serial
Port Signal to Digital B Channel Signal at 64 kbps (1010)
All-digital Service (1101001..) ISDN Wall Jack (RJ-45) Bonding Use
Both B Channels for Data Send and Receive at 128 kbps
Slide 40
40 Figure 7.14: Pricing Elements in Frame Relay Service Frame
Relay Pricing Frame relay access device at site CSU/DSU at physical
layer (converts between internal, PSDN digital formats) Frame Relay
at the Data Link 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
Slide 41
41 Figure 7.13: Access Devices CSU/DSU Channel service unit
(CSU) protects the access line from unapproved voltage levels, etc.
coming from the firm Data service unit (DSU) converts between
internal digital format and digital format of access link to Frame
Relay network. May have different baud rate, number of states,
voltage levels, etc. DSU
Slide 42
42 Figure 7.13: Access Devices Site A Site B PC Server T1
CSU/DSU at Physical Layer Frame Relay at Data Link Layer T3 CSU/DSU
at Physical Layer ATM etc. at Data Link Layer T1 Line T3 Line
Access Device (Frame Relay Access Device) Access Device
(Router)
Slide 43
43 Figure 7.14: Pricing Elements in Frame Relay Service Switch
POP Customer Premises B Customer Premises C 1. Access Device
Customer Premises A
Slide 44
44 Figure 7.14: Pricing Elements in Frame Relay Service Switch
POP Customer Premises B Customer Premises C Customer Premises A 2.
T1 Leased Access Line to POP
Slide 45
45 Figure 7.14: Pricing Elements in Frame Relay Service Switch
POP Customer Premises B Customer Premises C Customer Premises A CIR
= 56 kbps ABR = 1 Mbps 3. Port Speed Charge
Slide 46
46 Figure 7.14: Pricing Elements in Frame Relay Service Switch
PVC 2 PVCs 1&2 POP PVC 2PVC 1 Customer Premises B Customer
Premises C Customer Premises A PVC 1 4. PVC Charges
Slide 47
47 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
Slide 48
48 Figure 7.15: Frame Relay Pricing Details To Determine Needs
for Each Site Step 1: Determine PVC Needs Determine needed speed
from this site to each other site You will need a virtual circuit
to serve the needed speed to each other site Sum all the virtual
circuit speeds New Not in Book Site Being Analyzed 30 kbps needed
56 kbps PVC 800 kbps needed, 1 Mbps PVC Sum 1,056 kbps
Slide 49
49 Figure 7.15: Frame Relay Pricing Details Step 2: Determine
Port Speed You need a port speed equal to or greater than the sum
of the PVCs You can get by with 70% 70% of 1,056 kbps is 739 kbps
Next-higher port speed may be 1 Mbps Dont overdo port speed because
port speed is most expensive component New Not in Book
Slide 50
50 Figure 7.15: Frame Relay Pricing Details Step 3: Determine
Leased Line Speed Remember that port speed is more expensive than
leased line speeds In general, dont waste port speed by using a
leased line much under its capacity If port speed is 1 Mbps, leased
line should be T1 with 1.544 Mbps capacity New Not in Book
Slide 51
51 Figure 7.15: Frame Relay Pricing Details Example The
Situation Headquarters and two branch offices. Branches communicate
with HQ at 200 kbps Branches communicate with each other at 40 kbps
HQ B1 B2 New Not in Book
Slide 52
52 Figure 7.15: Frame Relay Pricing Details Example For HQ How
many connections will HQ need? What are their speeds? What will be
their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps) If
port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port
speed will be needed? What leased line will be needed if speeds are
56 kbps, 256 kbps, 512 kbps, or T1? HQ New Not in Book
Slide 53
53 Figure 7.15: Frame Relay Pricing Details Example For Each
Branch How many links will the branch need? What are their speeds?
What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps,
1 Mbps) If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps,
what port speed will be needed? What leased line will be needed if
speeds are 56 kbps, 256 kbps, 512 kbps, or T1? B1 New Not in
Book
Slide 54
54 Figure 7.1: Wide Area Networks (WANs) WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Point-to-Point Network of leased lines Public switched data
networks (PSDN) Send your data over the Internet securely, using
Virtual Private Network (VPN) technology VPN
Slide 55
55 Figure 7.17: Virtual Private Network VPN Server Corporate
Site A VPN Server Corporate Site B 2. Remote Customer PC (or site)
3. Remote Corporate PC Tunnel Internet Extranet Remote Access for
Intranet 1. Site-to-Site
Slide 56
56 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 Only good for
internal corporate communication But Internet reaches almost all
sites in all firms Low transmission cost per bit transmitted
Slide 57
57 Figure 7.16: Virtual Private Network (VPN) Issues VPN
Problems Latency and Sound Quality Internet can be congested
Creates latency, reduces sound quality Use a single ISP as for VoIP
(see Chapter 6) Security PPTP for remote access is popular IPsec
for site-to-site transmission is popular
Slide 58
58 Figure 7.18: ISP-Based PPTP Remote Access VPN RADIUS Server
PPTP RAS Internet ISP PPTP Access Concentrator Local Access Remote
Corporate PC Corporate Site A Remote Access VPNs: ISP Mode User
dials into a remote access server (RAS) RAS often checks with
RADIUS server for user identification information. Allows or
rejects connection Secure Tunnel Unsecure TCP Control Channel
Slide 59
59 Figure 7.18: ISP-Based PPTP Remote Access VPN RADIUS Server
PPTP RAS Internet Remote Corporate PC Corporate Site A Remote
Access VPNs: Direct Mode End-to-End VPN protection to client PC
Setup required on remote corporate PC Secure Tunnel Unsecure TCP
Control Channel New
Slide 60
60 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 Some security
limitations No security between user site and ISP No
message-by-message authentication of user Uses unprotected TCP
control channel New
Slide 61
61 Figure 7.19: IPsec in Tunnel Mode Tunnel Only Between Sites
Hosts Need No Extra Software Secure Tunnel Mode IPsec Server IPsec
Server Local Network Local Network No Security In Site Network No
Security In Site Network
Slide 62
62 Figure 7.19: IPsec in Transfer Mode End-to-End
(Host-to-Host) Tunnel Hosts Need IPsec Software Secure Tunnel
Transfer Mode IPsec Server IPsec Server Local Network Local Network
Security In Site Network Security In Site Network Module F
Slide 63
63 Figure 7.16: Virtual Private Network (VPN) Issues IP
Security (IPsec) 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 Module F
Slide 64
64 Figure 7.16: Virtual Private Network (VPN) Issues IP
Security (IPsec) At internet layer, so protects information at
higher layers Transparent: upper layer processes do not have to be
modified Internet Layer with IPsec Protection TCPUDP
HTTPSMTPFTPSNMP Protected
Slide 65
65 Figure 7.16: Virtual Private Network (VPN) Issues IP
Security (IPsec) Security associations: Agreement on how security
options will be implemented May be different in the two directions
Security Association (SA1) for Transmissions From A to B Security
Association (SA2) for Transmissions From B to A Party B Party
A
Slide 66
66 Figure 7.16: Virtual Private Network (VPN) Issues IP
Security (IPsec) Security associations: Governed by corporate
policies List of Allowable Security Associations List of Allowable
Security Associations Party B Party A IPsec Policy Server
Slide 67
67 PPTP and IPsec VPNs PPTP Simpler, software is on almost all
client PCs Limited to remote access VPNs Only moderate security
IPsec For both remote access and site-to-site VPNs Better security
More difficult to implement As increasing numbers of clients and
servers implement it, should become dominant
Slide 68
68 Recap Reasons for WANs Remote access Site-to-site
transmission Internet access
Slide 69
69 Recap WAN Technologies Telephone modems and the PSTN (slow;
only for remote access) Leased line meshes (offer whatever speed is
needed; popular but use has peaked) DSLs and cable modems (leased
line speeds over a single pair of inexpensive voice-grade UTP
already going to the home) Public Switched Data Networks (offers
any needed speeds; inexpensive, widely used, and growing) Virtual
Private Networks (inexpensive but very new so just getting
started)