cos 338 day 11. 2 day 11 agenda questions? capstone proposal overdue 3 accepted, 2 in mediation, 1...
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COS 338
Day 11
2
DAY 11 Agenda
Questions? Capstone Proposal Overdue
3 accepted, 2 in mediation, 1 MIA
Assignment 3 Due 1 B, 2 C’s, 1 F and 2 MIA
Assignment 4 Posted Due Oct 20
Lab 4 is on Oct 20 OpNet lab 3 – Evaluating WAN Performance
Lab 5 is on oct 24 (after exam) OpNet Lab 4 – Large WAN
Exam 2 is on Oct 24 Chap 4-7, open book, open notes, 60 min, 25 M/C questions
Today is Lecture on WAN’s
Wide Area Networks (WANs)
Chapter 7
Copyright 2005 Prentice-HallPanko’s Business Data Networks and Telecommunications, 5th edition
4
Wide Area Networks (WANs)
Chapters 4 and 5: LANs LANs for customer premises operation, high
speeds (Ethernet and WLANs)
Chapter 6: Telephony PSTN carrier service
Chapter 7: WANs WAN technology often is based on telephone
technology and services
5
Figure 7-1: Wide Area Networks (WANs)
WAN Purposes
1. Link sites (usually) within the same corporation
2. Remote access for individuals who are off-site
3. Internet access for individuals or firms
6
Figure 7-1: Wide Area Networks (WANs), Continued
Technologies for Individual Internet Access and remote access to Corporate Networks Telephone modems DSL lines Cable modems Wireless Internet access
Site-to-Site Transmission within a Firm Private line networks Public switched data networks (PSDNs) Virtual Private Networks (VPNs)
Propagation over the Internet with added security Low cost per bit transmitted
7
Figure 7-1: Wide Area Networks (WANs), Continued
High Costs and Therefore Low Speeds High cost per bit transmitted compared to LANs
Lower speeds (most commonly 56 kbps to a few megabits per second)
Typical WAN speeds:56 kbps to a few megabits per second.
Individual Internet Access:Telephone Modems
9
Telephone Modem Communication
Computers are digital sources
Telephone transmission lines are analog
A modem converts between the two
Client ATelephone56 kbps
Modem
DigitalComputer
Signal
AnalogSignal
10
Figure 7-2: Amplitude Modulation
LowAmplitude
(0)
HighAmplitude
(1)
AmplitudeModulation
(1011)
Amplitude (low)
Amplitude (high)
11
Figure 7-3: Telephone Modem Communication
PSTN
Client ATelephone
Digital Access Line
56 kbpsModem
For 56 kbps Download SpeedISP Must Have a Digital Connection, Not a Modem
ISP
Digital Subscriber Lines (DSLs)
DSLs provide data over the existing 1-pair voice-grade access line that already goes to residences and small businesses
13
Digital Subscriber Lines (DSLs)
DSLs provide digital data transmission over the single-pair voice-grade local loop that already runs to residential customer premises.
These lines are already installed, so no cost to run new access lines (as there is with private lines).
Single-pair voice-grade UTP was not meant to carry data. Sometimes it works. Other times, it does not. Depends primarily on whether distance to the nearest end office is too far.
14
Figure 7-4: Digital Subscriber Lines (DSLs)
Asymmetric DSL (ADSL) Asymmetrical throughput
Downstream speed of 512 kbps to 1.5 MbpsUpstream speeds of 90 kbps to 384 kbpsGood for Web access with large downloadsSufficiently fast for e-mail
Aimed at residential customersThroughput is NOT guaranteedDSLAM (discussed later) often oversubscribed,
slowing access
15
Figure 7-4: Digital Subscriber Lines (DSLs), Continued
Symmetric DSL Services Speed is symmetric
Same upstream and downstream
Aimed at business customersThroughput IS guaranteed
Several Types of Symmetric DSLHDSL (768 kbps): Half of a T1 private line (later)HDSL2 (1.544 kbps): Full T1 private line speedSHDSL: Flexible (384 kbps to 2.3 Mbps)
16
Figure 7-5: Asymmetric Digital Subscriber Line (ADSL)
DataWAN
PSTN
6. DSLAM
ADSLModem
2. Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
1.Existing 1-PairVoice-Grade
UTP
PC
5.Ordinary Telephone
Service
3.Downstream Data
512 kbps to1.5 Mbps
4.Upstream
90 kbps to 384 kbps
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Fiber to the Home (FTTH)
Single-pair voice-grade copper running to residences is limited in the speed it can provide for data transmission
Fiber to the home (FTTH) will bring optical fiber to each home
Higher speeds for data transmission, video, etc.
Being held back by high installation costs, which require provable strong demand
http://www.broadweave.com/home.htm
Cable Modem Service
19
Figure 7-6: Cable Modem Service
PCSubscriberPremises
6. CableModem
4. CoaxialCable to
Neighborhood
2. OpticalFiber to
Neighborhood
3.Neighborhood
Splitter
ISP
1. CableTelevisionHead End
7. PC needs NIC or USB portHybrid Fiber Cable (HFC)
5. CoaxialDrop Cable
20
Figure 7-6: Cable Modem Service, Continued
Cable Modem Delivered by cable television operator
Cable modems follow the Data-Over-Cable Interface Specification (DOCIS) standard
Up to 10 Mbps downstream128 kbps to 512 kbps upstreamHeavy users get throttled back by operator
Speed is shared in a neighborhoodOnly users sending and receiving simultaneously In practice, medium ADSL speed or higher
21
Figure 7-7: Wireless Access Systems
Wireless Access to the Internet Fixed Versus Mobile
FixedFor homes and offices (fixed locations)Use dish antennasHigher speeds
MobilePeople traveling within a city or fartherNeed omnidirectional antennasLower speeds
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http://www.pwless.net/corporate/default.htm
23
Figure 7-7: Wireless Access Systems, Continued
Satellite Versus Terrestrial Wireless Satellite
Expensive because of transmission distanceExpensive because satellites are expensive
to launch and maintainCan cover large areas
TerrestrialEarth-based radio stationsService within a city
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Figure 7-7: Wireless Access Systems, Continued
3G Cellular Service Telephone modem and DSL/cable modem speeds
802.16 WiMAX One of several terrestrial wireless access standards
under development
Fixed version being standardized first20 Mbps up to 50 km (30 miles)
Mobile version under development (802.16e)3 Mbps to 16 Mbps for mobile users
Site-to-Site Networking:Private Line Networks
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Figure 7-8: Private Line Networks for Voice and Data
Connect sites via private lines
Perspective User firm must do all the planning and installation
User firm must operate and maintain the network
Labor-intensive site-to-site networking
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Figure 7-8: Private Line Networks for Voice
T3 PrivateLine
Site C
Site A Site B
OC3 Private Line
T1 PrivateLine
T1 PrivateLine
Site ESite D
56 kbpsPrivate
Line
56 kbpsPrivate
Line
56 kbpsPrivate
Line
PBX Private Line Voice NetworksHave a PBX at Each Site
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Figure 7-8: Private Line Networks for Data
T3 PrivateLine
Site C
Site A Site B
OC3 Private Line
T1 PrivateLine
T1 PrivateLine
Site ESite D
56 kbpsPrivate
Line
56 kbpsPrivate
Line
56 kbpsPrivate
Line
Router Private Line Data NetworksHave a Router at Each Site
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Figure 7-9: Full Mesh Topology
Site C
Site A Site B
Site ESite D
Very ReliableVery Expensive
In a Full Mesh Topology,Each Site Connects
Directly to Each Other Site
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Figure 7-9: Pure Hub-and-Spoke Topology
Site C
Site A Site B
Site ESite D
In a Pure Hub-and-SpokeTopology, There is OnlyOne Line for Each Site
Less Expensive, butNo Redundancy for Reliability
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Figure 7-9: Pure Hub-and-Spoke Topology, Continued
T3 PrivateLine
Site C
Site A Site B
OC3 Private Line
T1 PrivateLine
T1 PrivateLine
Site ESite D
56 kbpsPrivate
Line
56 kbpsPrivate
Line
Most Firms Mix the Two TopologiesTo Balance Cost and Reliability
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Figure 7-10: Private Line Speeds
Trunk Line Speed
North American Digital Hierarchy
56 kbps (DS0 Signaling)56 kbps
(sometimes 64 kbps)
T1 (DS1 Signaling) 1.544 Mbps
Fractional T1128 kbps, 256 kbps,384 kbps, 512 kbps,
and 768 kbps
Bonded T1s (multiple T1sacting like a single line)
Varies(usually up to 6 Mbps)
T3 (DS3 Signaling) 44.7 Mbps
Medium
2-pair DG* UTP
2-pair DG* UTP
2-pair DG* UTP
2-pair DG* UTP
Optical Fiber
*DG = Data Grade
33
Figure 7-10: Private Line Speeds, Continued
Trunk Line Speed
Japanese Multiplexing Hierarchy
64 kbps 64 kbps
J1 1.544 Mbps (same as U.S. T1)
J3 32.1 Mbps
CEPT Multiplexing Hierarchy (Europe)
64 kbps 64 kbps
E1 2.048 Mbps
E3 34.4 Mbps
34
Figure 7-10: Private Line Speeds, Continued
Trunk Line Speed
SONET/SDH*
OC3/STM1 156 Mbps
OC12/STM4 622 Mbps
OC48/STM16 2.5 Gbps
OC192/STM64 10 Gbps
OC768/STM256 40 Gbps
Notes: SONET and SDH speeds are multiples of 51.84 Mbps. (Figures listed are rounded off for readability)
OCx is the SONET designation.STMx is the SDH designation.
35
Figure 7-10: Private Line Speeds, Continued
Perspective
Most the range of greatest demand for site-to-site transmission is 56 kbps to a few megabits per second
So the largest market for private lines consists of T1 and fractional T1 lines or the equivalent in various countries
Site-to-Site Networking:Public Switched Data Networks
37
Figure 7-11: Private Line versus Public Switched Data Networks
Public Switched DataNetwork (PSDN)
POPPOP
POPPOP
Site A Site B
Point of PresenceOne privateline per site
Site D Site C Site E
Public Switched Data Network (PSDN)
38
Figure 7-11: Private Line versus Public Switched Data Networks, Continued
Private Line Network Company must plan, buy switching equipment, and
operate the network. Requires much labor.
Public Switched Data Network PSDN carrier provides planning, switching, and
operation of the network. This greatly reduces corporate management labor.
PSDN drawn as a cloud to indicate that users do not need to understand it because the PSDN handles all of the details.
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Figure 7-12: Virtual Circuit
PSDN Switches Are Arranged in Meshes Loops so multiple alternative paths between stations Switches must consider alternative paths This is complex, making switching expensive
40
Figure 7-12: Virtual Circuit, Continued
PSDNs Create Virtual Circuits Virtual circuit is a single path (data link) between two
stations Set up before transmission begins Only a single possible path, so switching is fast and
inexpensive
Virtual Circuit
Virtual Circuit
41
Figure 7-12: Virtual Circuit, Continued
PSDNs Create Virtual Circuits Switching table has virtual circuit instead of data link
layer addresses Frame header has a virtual circuit number,
NOT a destination address Virtual CircuitA . . .B . . .C . . .D . . .
Port1234
Site-to-Site Networking:Frame Relay (FR)
The most popular PSDN
43
Frame Relay (FR)
The most popular PSDN Today Speed range is 56 kbps to up to 40 Mbps
Matches main speed range of corporate WAN demand (56 kbps to a few megabits per second)
FR Switching is Designed to Minimize Cost Switching is unreliable to reduce the cost per frame
Switching uses virtual circuits to reduce cost
Cost minimization is important in WAN communication
44
Figure 7-13: Frame Relay Network
SwitchPOP
Customer Premises B
Customer Premises C
1.Access DeviceCustomer
Premises A
45
Figure 7-13: Frame Relay Network, Continued
Site A
Site B
PC
Server
T1 CSU/DSU atPhysical Layer
Frame Relay atData Link Layer
T3 CSU/DSU atPhysical Layer
ATM etc. atData Link Layer
T1 Line
T3 Line
Access Device(Frame Relay
Access Device)
Access Device(Router)
46
Figure 7-13: Frame Relay Network, Continued
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 Or Private Line (teleco).
May have different baud rate, number of states, voltage levels, etc.
DSU
47
Figure 7-13: Frame Relay Network, Continued
SwitchPOP
Customer Premises B
Customer Premises C
Customer Premises A
2.T1 Private Access
Line to POP
48
Figure 7-13: Frame Relay Network, Continued
SwitchPOP
Customer Premises B
Customer Premises C
Customer Premises A
3.Port
SpeedCharge at
POPSwitch
49
Figure 7-13: Frame Relay Network, Continued
Switch
PVC 2
PVCs 1&2
POP
PVC 2 PVC 1
Customer Premises B
Customer Premises C
Customer Premises A
PVC 1
PVC 1
4.PVC
Charges
50
Figure 7-13: Frame Relay Network, Continued
Permanent Virtual Circuits (PVCs) Set up once, kept in place for months or years
Between a firm’s sites (which rarely change)
The most common form of virtual circuit today
Switched Virtual Circuits (SVCs) Set up at beginning of a communication session
Taken down at the end of the session
More expensive than PVCs, less common
51
Figure 7-13: Frame Relay Network, Continued
Frame Relay Pricing Recap Frame relay access device at site (or router) Private line from site to POP Port on the POP
Pay by port speedUsually the largest price component
Permanent virtual circuits (PVCs) among communicating sites
Usually the second-largest component of prices
Other charges
52
Figure 7-14: Frame Relay Frame
Variable Length Frames Start flag (01111110) to signal start of frame Address field has variable length (2-4 octets) Information field to carry data (variable) CRC (Cyclical Redundancy Check) field to detect
errors (2 octets) If find errors, switch discards the frame
Stop flag (01111110) to signal end of frame
01111110 01111110Address Information CRC
53
Figure 7-14: Frame Relay Frame, Continued
Address Field of Frame Relay Frame Variable Length: 2-4 octets
Usually 2 octets (as shown below)
Data link control indicator (DLCI, pronounced dull’-see) is the virtual circuit number (10 bits long in 2-octet form)
0 7
DLCI (6 bits) C/R 0
DLCI (4 bits) FECN BECN DE 1
Bits
54
Frame Relay Design
Determine Needs for Each Site Site A to Site B needs 30 kbps Site A to Site C needs 800 kbps Site B to Site C needs 100 kbps
Design FR Requirements One Site at a Time
Site A
Site B
800 kbps needed
30 kbps needed
Site C
100 kbps needed
55
Frame Relay Design, Continued
Step 1: Determine the Site’s PVC Needs Determine needed speed from this site to each
other
You will need a PVC at least as high (vendors only offer some PVC speeds)
Sum all the virtual circuit speeds
Site BeingAnalyzed
30 kbps needed;Select 56 kbps PVC
800 kbps needed; Select 1 Mbps PVC
Sum of PVCs1,056 kbps
56
Frame Relay Design, Continued
Step 2: Determine the Port Speed Required
For each private line connection to an FR switch, pay according to port speed
Usually the most expensive element in FR costs
Vendors usually offer only a few options for port speeds
Frame RelaySwitch
Port
Private Line
57
Frame Relay Design, Continued
Step 2: Determine Port Speed Port speed must be equal to or greater than 70% of
the sum of the PVCs
This is called oversubscription70% reflects the fact that not all PVCs will be at
maximum speed all of the time
70% of 1,056 kbps is 739 kbps
Next-higher port speed may be 1 Mbps
Pick the minimum port speed that is as high or higher than your need
58
Frame Relay Design, Continued
Step 3: Determine Private Line Speed Remember that port speed is more expensive than
private line speeds
In general, don’t waste port speed by using a private line much under its capacity
If port speed is 1 Mbps, the private line should be T1 with 1.544 Mbps capacity
Private Line ForMultiple PVCs
59
Frame Relay Design, Continued
Some Frame Relay Vendors Use Multi-Tier Pricing
Committed Information Rate (CIR) Pretty much guaranteed
Excess Burst Speeds Faster bursts up to excess burst speeds are
available if there is capacity
If there is congestion, frames beyond CIR are eligible to be discarded
60
Frame Relay Design, Continued
Example Firm needs four PVCs from a site
Each will have a CIR of 128 kbpsEach will have an excess burst speed of 256
kbps
Will pick a port speed of 4 x 128 kbps = 512 kbps or higher (based on CIR)
Note that oversubscription is not used when bursting is used. Port speed is the sum of the PVC CIRs
61
Frame Relay Design, Continued
Example The Situation
Headquarters and two branch offices.Branches communicate with HQ at 200 kbpsBranches communicate with each other at 40
kbps
HQ
B1
B2
62
Frame Relay Design, Continued
Example For HQ
How many connections will HQ need?
What are their speeds?
What will be their PVC speeds (if options are 0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps)?
HQ
63
Frame Relay Design, Continued
Example For HQ
If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed?
What private line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
HQ
64
Frame Relay Design, Continued
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, or 1 Mbps)?
B1
65
Frame Relay Design, Continued
Example For Each Branch
If port speeds are 56 kbps, 256 kbps, 384 kbps, or 512 kbps, what port speed will be needed?
What private line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
B1
Site-to-Site Networking:Asynchronous Transfer Mode (ATM)
67
Asynchronous Transfer Mode (ATM)
ATM is a faster PSDN than Frame Relay Frame Relay: 56 kbps up to about 40 Mbps
ATM: 1 Mbps up to about 156 Mbps
Not Competitors. Most PSDN Vendors Offer Both to Customers FR for low-speed customer needs
ATM for higher speeds (at higher prices)
As corporate demand grows, ATM may increase its market share
68
ATM Cell
Fixed Length (53 octets) Frame Allows Simpler and Therefore Faster Processing at Switches
For instance, switch does not have to do calculations to figure out how much buffer space it will need for a cell, as is the case with Frame Relay’s variable-size frame.
53 Octets5 octets of header48 octets of payload (data)
Fixed length frames are called cells
69
ATM Cell, Continued
Short Cell Length Limits Latency at Each Switch Switches may have to wait until the entire frame
arrives before processing it and sending it back out.
With shorter frames, there is less latency at each switch along the path
Important in continent-wide WANs that require cells to pass through many switches
Especially important for voice, which is highly latency-intolerant (ATM was created for digitized voice)
70
ATM QoS
Quality of Service
ATM provides strong QoS guarantees for voice traffic (latency, jitter, etc.)
However, ATM usually offers few or no QoS guarantees for data traffic—get what is left over after capacity reserved for voice QoS
71
ATM QoS, Continued
Manageability Strong management tools (designed for the PSTN
transport core)
So it is very expensive for small and medium firms
Site-to-Site Networking:Metropolitan Area Ethernet
Ethernet is moving into metropolitan area networks
73
Metropolitan Area Ethernet
Ethernet is moving beyond the LAN Moving into the metropolitan area network (within a
single urban area)
New 802.3 standards (10 Gbps and 40 Gbps) being developed primarily for long distances of 10 km or more
E-Line service: to connect LANs at two sites
E-LAN service: to connect LANs at multiple sites
74
Metropolitan Area Ethernet, Continued
Cheaper than ATM for high speeds
Familiar technology so easy to manage
Still lacks standards for carrier-class service
New but growing rapidly compared to Frame Relay and ATM
Site-to-Site Networking:Virtual Private Networks (VPNs)
VPNs: Transmission over the Internet with added security
76
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? Lower transmission cost per bit transmitted than
PSDNs
Adequate security
77
Figure 7-16: Virtual Private Network (VPN)
VPN Server
Corporate Site A
VPN Server
CorporateSite B
3. Host-to-HostVPN
RemoteCorporate PC
Tunnel
Internet
2.Remote
Access VPN
1.Site-to-Site
VPN
78
VPN Technologies
SSL/TLS Limited to remote access VPNs SSL (Secure Sockets Layer) was its original name
IETF changed it to Transport Layer Security Created to protect HTTP traffic in e-commerce Built into every browser and webserver, so easy to
implement Good if all traffic over the VPN will be HTTP
Beginning to handle other applications (not in book)
Moderate security
79
VPN Technologies, Continued
Point-to-Point Tunneling Protocol (PPTP) For remote access VPNs Operates at the data link layer
Transparently provides security to all messages at higher layers
Software exists on all client PCs, but individual PCs must be configured to work with PPTP, and this is somewhat expensive
Good for remote access when not all traffic is HTTP
SSL/TLS has pushed PPTP almost entirely aside in the marketplace (New: Since book was written)
80
VPN Technologies, Continued
IPsec For all types of VPN (remote access, site-to-site,
host-to-host) Operates at the Internet layer
Transparently protects traffic at all higher layers Very strong security Requires digital certificates for all computers
Creating an infrastructure for certificates is expensive
Installation and setup on individual client PCs is expensive
81
IPsec in Tunnel Mode
Security Only Between SitesHosts Need No Extra Software
Only IPsec Gateways need Digital CertificatesEasier to Set Up than Transport Mode
SecureTunnel
TunnelMode IPsec IPsec
GatewayIPsec
GatewayLocal
NetworkLocal
Network
No SecurityIn Site Network
No SecurityIn Site Network
82
IPsec in Transport Mode
End-to-End (Host-to-Host)Tunnel
Each Host Needs IPsec SoftwareAnd Digital Certificate
SecureTunnel
TransportMode IPsec
IPsecGateway
IPsecGateway
LocalNetwork
LocalNetwork
SecurityIn Site Network
SecurityIn Site Network
Topics Covered
84
Topics Covered
Technologies for Individual Internet Access Telephone modems DSL lines Cable modems Wireless Internet access
Site-to-Site Transmission within a Firm Private line networks Public switched data networks (PSDNs) Virtual Private Networks
Propagation over the Internet with added security
85
Market Data
Individual Internet Access About two-thirds telephone modem access
About one-third broadband (DSL and cable modem)
Half broadband in large cities
Site-to-Site Networking Frame Relay: about 45% of the market
Private lines: about 45% of the market
VPNs: very small but growing rapidly
86
Key Points
WANs speeds are slow because long-distance transmission is costly Most WAN links are 56 kbps to a few megabits per
second
DSLs use the existing 1-pair UTP wiring that runs to residences and small businesses Limited transmission capability, but no cost to run
new wiring
87
Key Points
The most widely used private lines are Fractional T1 and T1
Because in the range of greatest corporate demand for WAN links
PSDNs have one private line running from each site to the PSDN cloud
Virtual circuits reduce cost No need to compute the best alternative path for
each frame separately
88
Key Points
Frame Relay Pricing
Multiple PVCs (one to each other site) are multiplexed over a site’s single private line and single POP port.
Port speed charges are the biggest price factor in Frame Relay pricing
PVC charges are the second biggest price factor
89
Key Points
Virtual private networks (VPNs) Communication over the Internet with added
security Why? Cheaper than other WAN alternatives
Moderate security for remote access VPNs SSL: simplest but limited to HTTP PPTP: protects all traffic above the data link layer
IPsec has the strongest VPN security But costly to set up because of digital certificates