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Frame Relay, ATM and VPN. 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 Attractive prices Dominates the market today ATM High speeds and costs.

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PowerPoint Slideshow about 'Frame Relay' - RexAlvis


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Presentation Transcript
packet switched services
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
    • Attractive prices
    • Dominates the market today
  • ATM
    • High speeds and costs
x 25 packet switched data networks
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
frame relay packet switched data networks
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)
  • Priced aggressively to kill leased lines (succeeding)
  • Best-selling packet switched network service

See more here.

atm asynchronous transfer mode
ATM (Asynchronous Transfer Mode)
  • Offers very high speeds
    • 622 Mbps, 2.5 Gbps to 40 Gbps
  • Connection-oriented (PVCs), unreliable
  • Quality of Service (QOS) guarantees critical traffic
    • Minimize latency (delays)
    • Inherent reliability (low loss rate)
  • Technical details beyond this course

Building more bandwidth than needed

slide6
ATM
  • Speeds are beyond most corporate needs today
  • High costs
  • Seen as the next generation
    • But Frame Relay keeps increasing in speed in low Mbps range where market demand is highest
  • Used by providers
    • e.g. AT&T, to support both ATM and Frame Relay for customers

See AT&T ATM pricing

pricing packet switched services
Pricing Packet Switched Services
  • Customer Premises Equipment
  • Access Line to Point of Presence
  • Port Speed
  • Per PVC Price
  • Distance and Traffic Volume
customer premises equipment
Customer Premises Equipment
  • Access Device
    • Has link to internal system (often a LAN)
    • Has CSU/DSU to put internal traffic into format for Frame Relay transmission
    • In Frame Relay, called Frame Relay Access Device (FRADS)

Access Device

Access Line

to Network

LAN

modular routers
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

elements of a packet switched network
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

elements of a packet switched network11
Elements of a Packet Switched Network

Switched

Data

Network

Trunk

Line

Network

Switching

Office

POP

Customer

Premises B

Leased

Access Line

pricing of frame relay
Pricing of Frame Relay
  • Speed of the Access Line from Site to Network
    • Determines maximum transmission rate to the network
    • Often called the Port Speed (not in the book)
    • Often the most important price determinant
    • Must be fast enough for needs

See Frame Relay over DSL -- a price issue

pricing of frame relay13
Pricing of Frame Relay
  • In Some Frame Relay networks, two speeds
    • Committed Information Rate (pretty much guaranteed)
    • Available Bit Rate (like flying standby) for bursts. Not guaranteed.
    • Price depends both on CIR and ABR
    • Access line speed must be fast enough for ABR
pricing of frame relay14
Pricing of Frame Relay
  • Additional price per PVC
    • Usually small compared to the access line charge
    • One access line can multiplex all PVCs to/from site
    • PVCs share access line speed

Site

PVC1

PVC2

calculations
Calculations
  • Situation
    • 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?
calculations16
Calculations
  • PVCs
    • 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
pricing of frame relay17
Pricing of Frame Relay
  • May Depend on Distance
    • But often a flat monthly rate throughout the carrier’s service area
  • May Depend on Traffic
    • But often a flat monthly rate based only on the speed of the access line
leased lines vs packet switched data networks
Leased Lines vs. Packet-Switched Data Networks
  • Leased Lines
    • 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
circuit switched vs packet switched services
Circuit-Switched vs. Packet-Switched Services
  • Circuit Switched Networks (ISDN, Switched 56)
    • Any-to-any connectivity by dialing number
    • Highest speed is ISDN: 64 kbps to 128 kbps
  • Packet Switched Networks (X.25, Frame Relay, ATM)
    • PVCs make them primarily competitors to leased lines
    • Megabit to gigabit speeds
    • SVCs may provide any-to-any flexibility in the future
    • IP services, MPLS, ATM trends

Note: more MPLS details

virtual private network

VPN Server

3. Remote

Corporate PC

2. Remote

Customer PC

(or site)

Virtual Private Network

1.

Site-to-Site

Tunnel

Internet

VPN Server

Corporate

Site B

Corporate

Site A

Remote

Access for

Intranet

Extranet

vpn advantage
VPN advantage
  • 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
vpn issues
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
    • New IP services (see MCI offerings)
isp based pptp remote access vpn

RADIUS

Server

PPTP

RAS

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

Secure Tunnel

ISP

PPTP

Access

Concentrator

Internet

Corporate

Site A

vpn and pptp
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
ipsec alternatives
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
ipsec in tunnel mode
IPsec in Tunnel Mode

Tunnel

Mode

IPsec

Server

IPsec

Server

Local

Network

Local

Network

Secure

Tunnel

Tunnel Only

Between Sites

Hosts Need NoExtra Software

No Security

In Site Network

No Security

In Site Network

ipsec in transfer mode
IPsec in Transfer Mode

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

security at the internet layer
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

common ipsec configuration
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

IPsec Policy Server

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