Transcript PPT

Outlines
Received
due 13 March 2000
24 %
Homework
Review for Midterm (1 March 2000)
 Research Paper
 Readings
[9] “MPLS: Special Delivery”
[10] “Diversifying Internet Delivery”

Frame Relay
ANSI Standard covering OSI Layer 2
 Accessed by Routers or FRAD’s
 Derived from X.25 Protocol
Dumps almost all error checking
Requires fiber on the long haul
 Uses Permanent Virtual Circuits (PVC’s)
VC differs from Datagram
Long Term Connection
Requires Carrier intervention to
change

Frame Relay
Committed Information Rate (CIR)
Is a Quality of Service Guarantee
‘Guaranteed’ minimum Bandwidth
Should be set > average traffic during
appropriate peak period
 Port Connection Speed
a.k.a. Port Speed or Burst Speed
Bandwidth you can burst to provided
network capacity exists.

Ex) 1.54 Mbps Leased Lines
Detroit
OKC
IXC Leased
Line Network
NYC
IXC & Local Carriers
dedicate 1.54 Mbps to our use via
Circuit Switching & TDM.
Router
Carrier Leased Line Network
Cross-Connect
Leased Line ‘Cloud’
Trunks use TDM & Circuit Switching
Ex) Frame Relay
Detroit
IXC Frame
Relay Network
OKC
Router
NYC
Local Carriers
dedicate 1.54 Mbps to our use. IXC provides random
Packet Switched StatMux connectivity via PVC’s.
Frame Relay Backbone
FR Switch
Frame Relay ‘Cloud’
Trunks use StatMux & Packet Switching
Ex) Internet
Detroit
ISP Network
OKC
Router
NYC
Local Carriers
dedicate 1.54 Mbps to our use. ISP provides random
Packet Switched StatMux connectivity via datagrams.
Internet Service Provider Backbone
Router
ISP ‘Cloud’
Trunks use StatMux & Packet Switching
WAN Design (Link Reduction)
Start with Traffic Matrix
 Examine Full Mesh
 Consider eliminating lightly used links
 Compare costs at each iteration

Circuit Switched connections waste
bandwidth for bursty traffic.
traffic
NYC
to OKC
1.54 Mbps Line Speed
146 Kbps Average
time
Idle Time >> Active Time
Frame Relay
End-to-End Delay
Frame Relay > equivalent sized Leased
Line Network
 Cost Tendency
Frame Relay < equivalent sized Leased
Line Network

Frame Relay (Inside the Cloud)

Examined a specific case
Frame Relay
Switch
100 Mbps
Trunk
?? 1.54 Mbps Connections
P(Access Line is Active) = 10%
How many access lines can this switch support?
Availability
Bounds on Packet Switch Carrying Capacity
100 Mbps Trunk, 1.54 Mbps Inputs
with 154 Kbps average loads
Lower
90%
559
99%
494
99.9% 452
99.99% 421
Where switch
probably operates
Upper
649
649
649
649
Where switch
could operate
Given 100 Mbps of Bandwidth...

64

421 - 649
1.54 Mbps Circuit Switched
TDM Customers
1.54 Mbps Packet Switched
StatMux Customers with
154 Kbps average load &
99.99% availability
More Bursty Data Traffic can be moved
with the Packet Switched StatMux network.
Network Cost...
Can be spread over 64 Leased Line customers
 Can be spread over 421 Frame Relay
customers
 Frame Relay & the Internet
Are Packet Switched StatMux network
Largely hauling bursty data traffic
Effectively haul bursty data traffic
Inexpensive (compared to a Leased Line)

Switched Network Carrying Capacities
Packet Switch
StatMux
Circuit Switch
TDM
0% Data
100% TST
Offered Load
100% Data
0% TST
Voice Over Frame Relay
Many of same problems as Voice over IP
Designed for data
One Priority
 Quality is worse than Telephone System
 Quality is better than Internet Voice
CIR guarantees Bandwidth
FRAD can prioritize voice
 Video over FR products now available

Priorities are a double edged sword...

There is only so much pie to go around
Frame Relay
Switch
Hi Priority Voice PVC’s
Lo Priority Data PVC’s
100 Mbps
Trunk
If voice gets preference, data will suffer!
QoS
DE bit used by FR switches to police
network
 Traffic > CIR enters switch in a 1 second
interval? Marked DE
 If you are behaving...
...and other users exceed their CIR’s...
...and FR switch becomes congested...
...then other users’ traffic gets dumped 1st...
...your traffic is protected.
 Helps shelter you from behavior of others

Internet Performance
Probability of
dropped packets
Average Delay for
delivered packets
0%
Trunk Offered Load
100%
Frame Relay Performance
Probability of
dropped packets*
Average Delay for
delivered packets
0%
Trunk Offered Load
100%
*Dashed: If we are transmitting at > CIR
Solid: Provided we are transmitting at < CIR
Worldwide Frame Relay Revenues
Source:
Data Communications