1. From circuit to packet switching
PSDN and VPN
From circuit to packet switching 1 1

2. Packet-Switched Services
Offered by Carriers
X.25
Old, slow, and not sufficiently cheaper than frame relay
Frame Relay
Speeds in main range of user demand
Dominated the market in the 1990s
ATM
High speeds and costs, requiring equipment changes
Carrier Internet and MPLS services
Dominant services today 2

3. X.25 Packet-Switched Data Networks
Oldest packet switched network service (1970s)
Low speed (maximum around 64 kbps)
Mature: easy to implement
Uses PVCs
Reliable service, so latency in transmission
Mostly replaced by Frame Relay 3

4. Frame Relay Packet-Switched Data Networks
Software upgrade to X.25 switches
Uses PVCs
Unreliable, so much faster on same switches
Good speed range: 56 kbps - 40 Mbps: Meets most corporate needs (most under 2 Mbps)
Grew rapidly in the 90s, to equal leased line WANs in terms of market share (about 40%)
See more here. 4

5. Pricing of Packet Switching
Speed of the Access Line from Site to Network
Determines maximum transmission rate to the network
Often called the Port Speed
Often the most important price determinant
Must be fast enough for needs
See Frame Relay vs. DSL -- a price issue 5

6. ATM (Asynchronous Transfer Mode)
Offers very high speeds: 622 Mbps, 2.5 Gbps to 40 Gbps. Speeds are beyond most corporate needs today and high costs.
Connection-oriented (PVCs), unreliable
Quality of Service (QOS) guarantees critical traffic
Minimize latency (delays)
Inherent reliability (low loss rate)
Seen as the next generation before Ethernet surge
But Frame Relay kept increasing in speed in low Mbps range where market demand was highest 6

7. Pricing/Performance of Packet Switched Services
Pricing of Frame Relay and ATM
Customer Premises Equipment
Access Line to Point of Presence
Port Speed
Per PVC Price
Distance and Traffic Volume
The demise of Frame Relay and ATM
Transition from Frame Relay and ATM to Carrier Ethernet stimulated by Verizon, AT&T, etc.
The move to Ethernet and IP based services a win-win situation. 7

8. Customer Premises Equipment
Access Device
Has link to internal system (often a LAN)
Has CSU/DSU to put internal traffic into format for Packet switching transmission
In Frame Relay, called Frame Relay Access Device (FRADS)
Access Device
Access Line
to Network
LAN 8

9. Router Switching Circuitry
Modular Routers
CSU/DSUs are removable expansion boards
Modular Router
Router Switching Circuitry
Port 1
CSU/DSU
(T1)
Port 2
CSU/DSU
(56 kbps)
Port 3
CSU/DSU
(T3)
Port 4
CSU/DSU
(56 kbps)
T1 Line
56 kbps Line
T3 Line
56 kbps Line 9

10. Elements of a Packet Switched Network
Customer
Premises A
You need a leased access line to the network’s POP.
Sometimes the packet switched network vendor pays the cost of the access line for you and bundles it into your service charges.
Leased
Access Line
to POP
LEC
Switching
Office
Leased
Access Line
to POP
POP
at LEC
Office 10 10

11. Elements of a Packet Switched Network
Data
Network
Trunk
Line
Network
Switching
Office
POP
Customer
Premises B
Leased
Access Line 11 11

12. Calculations Situation Questions You have four sites
You want any one to be able to reach any other
Questions
How many PVCs do you need?
How many access lines do you need? 12

13. Calculations PVCs Access Lines
If you have N sites, there are N(N-1)/2 possible connections
In this case, you would have 4(3)/2 or 6 possible connections
Some vendors count this as 6 PVCs, others as 12 PVCs
Access Lines
You would need four access lines (one for each site)
Each will multiplex 3 PVCs
Must be fast enough for the needs of communication with the three other sites 13

14. Leased Lines vs. Packet-Switched Data Networks
Point-to-point, inexpensive for thick routes
Inflexible: must be established ahead of time
Packet Switched Networks
Also must be established ahead of time for PVCs
Competitor for leased line networks
Priced aggressively
Carrier does all the management
Killing the leased line business 14

15. Virtual Private Network1.
Site-to-Site
VPN Server
Tunnel
Internet
VPN Server
Corporate
Site B
Corporate
Site A
3. Remote
Corporate PC
2. Remote
Customer PC
(or site)
Remote
Access for
Intranet
Extranet 15

16. VPN advantage Virtual Private Network (VPN) Why VPNs?
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 16

17. VPN issues VPN Problems Latency and Sound Quality
Internet can be congested
Creates latency, reduces sound quality
Use a single ISP as for VoIP (voice over IP)
Security
PPTP for remote access is popular
IPsec for site-to-site transmission is popular 17

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. Allows or rejects connection
Unsecure TCP
Control Channel
Local
Access
RADIUS
Server
PPTP
RAS
Secure Tunnel
Internet
ISP
PPTP
Access
Concentrator
Corporate
Site A 18

19. VPN and PPTP 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 19

20. Hosts Need No Extra Software
IPsec in Tunnel Mode
Tunnel
Mode
IPsec
Server
IPsec
Server
Local
Network
Local
Network
Secure
Tunnel
Tunnel Only
Between Sites
Hosts Need No Extra Software
No Security
In Site Network
No Security
In Site Network 20

21. IPsec in Transfer Mode 21 Transfer Mode IPsec Server IPsec Server
Local
Network
Local
Network
Secure
Tunnel
Security
In Site Network
Security
In Site Network
End-to-End (Host-to-Host)
Tunnel
Hosts Need IPsec Software 21

22. IPsec alternatives 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, but default in current OSs (Windows, Linux, UNIX). 22

23. Security at the internet layer
IP Security (IPsec)
At internet layer, so protects information at higher layers
Transparent: upper layer processes do not have to be modified
HTTP
SMTP
FTP
SNMP
TCP
UDP
Protected
Internet Layer with IPsec Protection 23

24. Common IPsec configuration
IP Security (IPsec)
Security associations:
Governed by corporate policies
Party A
Party B
List of
Allowable
Security
Associations
List of
Allowable
Security
Associations 24
IPsec Policy Server

25. SSL/TLS for Browser–Webserver Communication25

26. Metropolitan Area Ethernet
Metropolitan Area Network (MAN)
A carrier network limited to a large urban area and its suburbs
Metropolitan area Ethernet (metro Ethernet) is available for this niche
Metro Ethernet is relatively new, but is growing very rapidly
802.3ad standard
Ethernet in the first mile
Standard for transmitting Ethernet signals over PSTN access lines
1-pair voice-grade UTP, 2-pair data-grade UTP, optical fiber 26

27. Metropolitan Area Ethernet
Attractions of Metropolitan Area Ethernet
Low prices per bit transmitted
High speeds
Familiar technology for networking staff
Rapid provisioning
Rapid capacity increases for special events
Carrier Class Service
Basic metro Ethernet standards are insufficient for large wide area networks
Quality of service and management tools must be developed
The goal: To provide carrier class services that are sufficient for customers 27

28. Carrier Ethernet and MPLS services28

29. Carrier Ethernet and MPLS services
The two most popular WAN options today are: MPLS and Carrier Ethernet.
Carrier Ethernet services include virtual private LAN service (VPLS), Gigabit and metro Ethernet.
E-LINE service -- site-to-site service, competes directly with leased lines.
E-LAN -- extends the LAN to the wide area, as if the PSDN service was only trunk lines between switches.
MPLS (Multiprotocol Label Switching) services typically refer to Layer 3 MPLS VPN services
a MPLS network determines the best path for packets between two hosts -- the label switched path.
Routers will send all packets along this path that receive a label path number. 29

30. Overview of MPLS services
A MPLS primer at 30

31. More in the MPLS service
The label switched path 31

32. Carrier Ethernet and MPLS services
A historic view of Carrier Ethernet in Wikipedia
An example of carrier services: AT&T
Keeping up with news about Carrier Ethernet:
Carrier Ethernet vs MPLS services.
Software-Defined Networks (SDN)
Overview in Wikipedia.
Pros and cons of SDN. 32