1. Chapter 7 Backbone Network

2. Announcements and Outline
Grades for Assessment 2 and Assessment 2 Review Posted
Exercise 6 due tonight before midnight
Design Quiz will be moved from Tuesday to Thursday
Tuesday – finish Chapter 8 (Wide Area Network) & start on designing networks
Outline
Backbone Network Components
Switches, Routers, Gateways
Backbone Network Architectures
Backbone Best Practices
Improving backbone performance
Copyright 2010
John Wiley & Sons, Inc 2

3. Backbone Networks High speed networks linking an organization’s LANs
Making information transfer possible between departments
Use high speed circuits to connect LANs
Provide connections to other backbones, MANs, and WANs
Sometimes referred to as
An enterprise network
A campus network

4. Backbone Network Components
Network cable
Functions in the same way as in LANs
Optical fiber - more commonly chosen because it provides higher data rates
Hardware devices
Computers or special purpose devices used for interconnecting networks
Switches
Routers
Gateways

5. Backbone Network Devices

6. Switches

7. Switches

8. Routers

9. Routers Operations Compared to Switches Operates at the network layer
Examines the destination address of the network layer
Strips off the data link layer packet
Chooses the “best” route for a packet (via routing tables)
Forwards only those messages that need to go to other networks
Compared to Switches
Performs more processing
Processes only messages specifically addressed to it
Recognizes that message is specifically addressed to it before message is passed to network layer for processing
Builds new data link layer packet for transmitted packets

10. Backbone Network Architectures
Identifies the way backbone interconnects LANs
Manages way packets from one network move through the backbone to other networks
Three layers:

11. Backbone Network Design Layers

12. Fundamental Backbone Architectures
Switched Backbones: most common type of backbone, used in distribution layer, used in new buildings, sometimes in core layer, can be rack or chassis based.
Routed Backbones: move packets along backbone on basis of network layer address, typically using bus, Ethernet 100Base-T, sometimes called subnetted backbone
Virtual LANs: networks in which computers are assigned into LAN segments by software rather than by hardware; can be single switch or multiswitch VLANs. Very popular technology.

13. Switched Backbone
Inse

14. Switched Backbones Replaces the many routers of other designs
Advantages:

15. Rack-Mounted Switched Backbones

16. Rack-Based Switched Backbones
Places all network switch equipment physically in one “rack” room
Easy maintenance and upgrade
Requires more cable, but usually small part of overall cost
Main Distribution Facility (MDF) or Central Distribution Facility (CDF)
Another name for the rack room
Place where many cables come together
Patch cables used to connect devices on the rack
Easier to move computers among LANs

17. Main Distribution Facility (MDF)

18. Rack Room 18

19. Chassis-Based Switched Backbones
Use a “chassis” switch instead of a rack
Enables administrators to plug modules into switch
Modules can vary in nature, router or 4-port 100Base T switch
Example of a chassis switch with 710 Mbps capacity
5 10Base-T hubs, 2 10Base-T switches (8 ports each)
1 100Base-T switch (4 ports), 100Base-T router
 ( 5 x 10) + (2 x 10 x 8) + (4 x 100) = 710 Mbps
Advantage is flexibility
Enables users to plug modules directly into the switch
Simple to add new modules

20. Routed Backbone

21. Routed Backbones
Move packets using network layer addresses Commonly used at the core layer LANs can use different data link layer protocols Main advantage Main disadvantages

22. Virtual LANs (VLANs) A new type of LAN-BN architecture
Made possible by high-speed intelligent switches
Computers assigned to LAN segments by software
Often faster and provide more flexible network management
Much easier to assign computers to different segments
More complex and so far usually used for larger networks
Basic VLAN designs:
Single switch VLANs
Multi-switch VLANs

23. VLAN-based Backbone

24. Multi-switch VLAN-Based Backbone

25. How VLANs Work
Each computer is assigned into a VLAN that has a VLAN ID
Each VLAN ID is matched to a traditional IP subnet
Each computer gets an IP address from that switch
Similar to how DHCP operates
Computers are assigned into the VLAN based on physical port they are plugged into

26. Multiswitch VLAN Operations
Same as single switch VLAN, except uses several switches, perhaps in core between buildings
Inter-switch protocols
Must be able to identify the VLAN to which the packet belongs
Use IEEE 802.1q (an emerging standard)
When a packet needs to go from one switch to another
16-byte VLAN tag inserted into the packet by the sending switch
When the IEEE 802.1q packet reaches its destination switch
Its header (VLAN tag) stripped off and Ethernet packet inside is sent to its destination computer

27. VLAN Operating Characteristics
Advantages of VLANs
Faster performance: Allow precise management of traffic flow and ability to allocate resources to different type of applications
Traffic prioritization (via 802.1q VLAN tag)
Include in the tag: a priority code based on 802.1q
Can have QoS capability at MAC level
Similar to RSVP and QoS capabilities at network and transport layers
Drawbacks
Cost
Management complexity
Some “bleeding edge” technology issues to consider

28. Recommendations for Backbone Design
Best architecture
Best technology:
Ideal design:

29. Chapter 8 Wide Area Networks

30. 8.1 Introduction
Wide area networks (WANs) Typically built by using leased circuits from common carriers such as AT&T

31. 8.1 Introduction (Cont.) Regulation of services Common Carriers
Federal Communications Commission (FCC) in the US
Canadian Radio Television and Telecomm Commission (CRTC) in Canada
Public Utilities Commission (PUC) in each state
Common Carriers
Local Exchange Carriers (LECs) like Verizon
Interexchange Carriers (IXCs) like Sprint

32. 8.2 MANs/WANs Services Circuit-Switched Networks
Dedicated-Circuit Networks
Packet-Switched Networks
Virtual Private Networks

33. 8.21 Circuit Switched Networks – Architecture

34. 8.21 Circuit Switched Networks
Oldest and simplest WAN approach
Uses the Public Switched Telephone Network (PSTN), or the telephone networks
Provided by common carriers
Basic types in use today:
POTS (Plain Old Telephone Service)
Via use of modems to dial-up and connect to ISPs
ISDN (Integrated Services Digital Network )
Basic Rate Interface (BRI) – 128 Kbps
Primary Rate Interface (PRI) – 1.5 Mbps

35. 8.21 Circuit Switched Services
Simple, flexible, and inexpensive
When not used intensively
Main problems
Varying quality
Each connection goes through the regular telephone network on a different circuit,
Low Data transmission rates
Up to 56 Kbps for POTS, and up to 1.5 Mbps for ISDN
An alternative
Use a private dedicated circuit
Leased from a common carrier for the user’s exclusive use 24 hrs/day, 7 days/week

36. 8.22 Dedicated Circuit Services – Basic Architecture

37. 8.22 Dedicated Circuits

38. 8.22 Ring Architecture
Reliability
Performance

39. 8.22 Star Architecture
Easy to manage
Reliability
Performance

40. 8.22 Mesh Architectures

41. 8.22 Dedicated Services - T-Carrier
Most commonly used dedicated digital circuits in North America
Units of the T-hierarchy
T-1
T-2
T-3
T-4

42. 8.22 T-Carrier Digital Hierarchy
T-Carrier Designation
DS Designation
Data Rate
DS-0
64 Kbps
T-1
DS-1
1.544 Mbps
T-2
DS-2
6.312 Mbps
T-3
DS-3
Mbps
T-4
DS-4
Mbps

43. 8.22 Dedicated Services - Synchronous Optical Network (SONET)
ANSI standard for optical fiber transmission in Gbps range
Similar to ITU-T-based, synchronous digital hierarchy (SDH)
SDH and SONET can be easily interconnected
SONET hierarchy
Begins with OC-1 (optical carrier level 1) at
51.84 Mbps
Each succeeding SONET hierarchy rate is defined
as a multiple of OC-1

44. 8.22 SONET Digital Hierarchy
SONET Designation
SDH Designation
Data Rate
OC-1
STM-0
51.84 Mbps
OC-3
STM-1
Mbps
OC-9
STM-3
Mbps
OC-12
STM-4
Mbps
OC-18
STM-6
Mbps
OC-24
STM-8
1.244 Gbps
OC-36
STM-12
1.866 Gbps
OC-48
STM-16
2.488 Gbps
OC-192
STM-64
9.952 Gbps
OC-1 52 Mbps $ ,000/mo
OC Mbps $30,000 + /mo
OC Mbps $50,000 +/mo

45. 8.23 Packet Switched Services – Basic Architecture

46. 8.23 Packet Switched Services
Recap: In both circuit switched and dedicated services…
Packet switched services

47. 8.23 Packet Switching
Interleave packets from separate messages for transmission
Most data communications consists of short burst of data
Packet switching takes advantage of this burstiness
Interleaving bursts from many users to maximize the use of the shared network

48. 8.23 Packet Switched - Service Protocols
X.25
Oldest packet switched service (widely used in Europe)
Not in widespread use in North America
Low data rates (64 Kbps) (available now at Mbps)
Asynchronous Transfer Mode (ATM)
Newer than X.25; also standardized
Data Rates
Same rates as SONET: 51.8, 466.5, Mpbs
New versions: T1 ATM (1.5 Mbps), T3 ATM (45 Mbps)
Provides extensive QoS information
Enables setting of precise priorities among different types of transmissions (i.e. voice, video & )

49. 8.23 Packet Switched - Service Protocols
Frame Relay
Faster than X.25 but slower than ATM
NO QoS support (under development)
Common CIR speeds:
56, 128, 256, 384 Kbps, 1.5, 2, and 45 Mbps
Ethernet Services
Most organizations use Ethernet and IP in the LAN and BN.
Currently offer CIR speeds from 1 Mbps to 1 Gbps at 1/4 the cost of more traditional services
No need to translate LAN protocol (Ethernet/IP) to the protocol used in MAN/WAN services
X.25, ATM, & Frame Relay use different protocols requiring translation from/to LAN protocols

50. 8.24 Virtual Private Networks
Provides equivalent of a private packet switched network over public Internet Provides low cost and flexibility Disadvantages of VPNs:

51. 8.24 VPN – Basic Architecture

52. 8.24 Layer 3 VPN Using IPSec

53. 8.24 VPN Types
Intranet VPN Extranet VPN Access VPN

54. 8.3 WAN Design Practices
Difficult to recommend best practices Factors used Design Practices

55. 8.3 MAN/WAN Services Summary

56. 8.3 Recommendations Best Practices MAN/WAN

57. 8.4 Improving Performance
MAN/WAN: Handled in the same way as improving LAN performance
By checking the devices in the network,
By upgrading the circuits between computers
By changing the demand placed on the network
Device:
Upgrade the devices (routers) and computers that connect backbones to the WAN
Examine the routing protocol (static or dynamic)
Dynamic routing
Increases performance in networks with many possible routes from one computer to another
Better suited for “bursty” traffic
Imposes an overhead cost (additional traffic)
Reduces overall network capacity
Should not exceed 20%

58. 8.4 Improving Circuit Capacity

59. 8.4 Reducing Network Demand