1. Chapter 8: Backbone Networks
MIS 430 – Chapter 8
Backbone Networks
Chapter 8: Backbone Networks

2. Chapter 8: Backbone Networks
Overview
Backbone networks connect LANs and also link BNs to WANs
BNs connect networks
Can be called a campus network or an enterprise network
Technology is different – typically ATM or fiber
Much higher speed circuits than most LANs
Chapter 8: Backbone Networks

3. I. Backbone Network Components
BN Components
Network cable
Hardware Devices
Bridges: connect two or more network segments that use the same data link and network protocol
Routers: connect 2 or more network segments with same or different data link protocols but same network protocols
Gateways: connect 2 or more network segments with same or different data link and network protocols
Chapter 8: Backbone Networks

4. Chapter 8: Backbone Networks
Bridges
Understand only data link protocols and addresses
May connect same or different types of cable
As switches were introduced, bridges have become obsolete
Chapter 8: Backbone Networks

5. Chapter 8: Backbone Networks
Routers
May connect same or different cable types
Routers are “TCP/IP gateways” of ch. 6
Router processes only those messages directed toward it
Router learns best routes by building routing table
Chapter 8: Backbone Networks

6. Chapter 8: Backbone Networks
Gateways
Ex: connect TCP/IP to IBM SNA protocol
Think “dissimilar” networks 
Gateway must transform message to make it look like it came from other network
See Figure 8-4 p. 260:
TCP/IP LAN (ASCII)
Token ring LAN
IBM Mainframe (EBCDIC)
Gateway avoids having to install SNA HW/SW on each client that wants to talk to mainframe
Chapter 8: Backbone Networks

7. A Caveat from Dr. Dennis…
Industry jargon may differ from the definitions in chapter 8
One vendor’s bridge may do router functions
Multiprotocol routers (TCP/IP and IPX/SPX) are gateways
Brouters combine functions of bridges and routers
Layer-3 switches provide both switch and router functions (but are much faster than routers) … we use Cisco layer-3 switches instead of routers now.
Chapter 8: Backbone Networks

8. II. Backbone Network Architectures
Basic Types
Routed backbone (use NL addresses)
Bridged backbone (use DLL addresses)
Collapsed backbone (switches using DLL addresses)
Virtual LANs (switches moving packets through virtual but not physical LANs)
Can be mixed and matched
Chapter 8: Backbone Networks

9. Backbone Architecture Layers
Access layer (e.g., 10BaseT) – actually part of LAN, but affects BN speeds
Distribution layer – part that connects the LANs together
Core layer – part that connects BNs together
Chapter 8: Backbone Networks

10. Chapter 8: Backbone Networks
Routed Backbone
Former ISU technology – see fig 8-6 p 265
Advantages
It clearly segments each part of network, each with own subnet address
LANs separated, can have different protocols
Users can access own server or others easily
Disadvantages
Routers introduce time delay
This requires lots of management
Chapter 8: Backbone Networks

11. Chapter 8: Backbone Networks
Bridged Backbone
Similar design, see fig 8-7 p. 267 but all on same subnet
Disadvantages (really not used on new networks)
Major performance problems
All LANs must have same DLL protocol
A change in one LAN can affect other LANs
Advantages
Simpler, easier to install, less expensive
Chapter 8: Backbone Networks

12. Collapsed Backbone - ISU
Most common for new nets, fig 8-8 p. 268
Advantages
Improved performance due to core switch allowing simultaneous access from LANs
Fewer networking devices: lower cost and network mgt is simpler, done in one place
Disadvantages
Use more cable, run longer distances (fiber)
If core switch fails, so does entire BN!
Chapter 8: Backbone Networks

13. Rack-Based Collapsed Backbones
Most organizations use 19” rack mount devices: see fig 9,10 p (HP gear)
All devices located in same room
MDF (main distribution facility) or CDF (central distribution facility)
Cables enter from back, are routed in front
Can move clients from one router to another to load balance
Chapter 8: Backbone Networks

14. Chassis-Based Collapsed Backbone
Can use a chassis switch instead of a rack
Plug in modules to represent a network device
16 port 10BaseT hub
Router
4-port 100BaseT hub, etc.
Key: flexibility and cost is less than rack mount
Chapter 8: Backbone Networks

15. Mgt Focus 8-2 Central Parking
See fig 8-11, p. 273: collapsed backbone
Chapter 8: Backbone Networks

16. Chapter 8: Backbone Networks
Virtual LAN (VLAN)
Separate the physical subnets from the logical subdivisions (we do this at ISU)
Computers are assigned to subnets by software rather than hardware
Advantages
Faster, more flexible
Easier to manage flow of traffic than previous
Disadvantage: more complex, for large networks
Chapter 8: Backbone Networks

17. Chapter 8: Backbone Networks
More on VLANs
Single Switch VLAN
See fig 8-12, p. 274
Everything is inside one switch
Looks like computers are linked through hubs
Multiswitch VLAN
Fig P 276
Multiple switches are involved
Chapter 8: Backbone Networks

18. FDDI-Fiber Distributed Data Interface
Originally for MANs, now in backbones
Ring topology, 100 Mbps, up to 200 km
Primary ring
Secondary ring (backup)
CDDI is just like FDDI but uses copper Cat 5 cable
Chapter 8: Backbone Networks

19. ATM - Async Transfer Mode
Originally for WANs, now also in BNs
Topology: point to point full 155 Mbps (310 Mbps in half duplex) or 622 Mbps
Originally designed for fiber, now on Cat 5e
ATM differs from switched Ethernet
Fixed length packets (53 bytes) – fast switching
No error correction of user data
Different addressing: virtual channel, not fixed
ATM prioritizes transmissions based on basis of QoS – 5 classes of service in ATM (voice is highest priority)
Chapter 8: Backbone Networks

20. III. Improving Backbone Performance
Similar to LANs: find the bottleneck
Eliminating the bottleneck generally means moving it elsewhere, so this is iterative
Speed up computers on the network
Speed u pother device on the network
Upgrade circuits between computers
Change the demand placed on the network
Chapter 8: Backbone Networks

21. Improve Computers/Devices
Buy faster devices (routers and switches)
Change to a more appropriate routing protocol (static usually or dynamic)
Buy devices and SW from one vendor (C!)
Reduce translation between different protocols
Increase the device’s memory (because devices are store and forward)
Chapter 8: Backbone Networks

22. Increase Circuit Capacity
Go from 100BaseT to Gigabit Ethernet
Buy additional circuits alongside existing
Replace shared circuit backbone with switched circuit backbone
Replace Ethernet with switched Ethernet
Usually OK to have 10 Mbps to desktops but a faster circuit to the server (e.g. 807)
Chapter 8: Backbone Networks

23. Chapter 8: Backbone Networks
Reduce Network Demand
Restrict high bandwidth applications (video conferencing or multimedia)
Reduce broadcast messages
looking for data link layer addresses
Some NOS ask for status of computers on net
Filter broadcast messages outside of LAN
Time shift the demand  flextime?
Chapter 8: Backbone Networks

24. IV. Best Backbone Practice
New technologies (ATM, gigabit Ethernet)
New architectures (collapsed backbones, VLANs)
Today’s best
Ethernet-based collapsed backbone with Switched Ethernet in LAN
Gigabit Ethernet will probably replace ATM, FDDI at BN
Chapter 8: Backbone Networks

25. ISU Machine Room Photos
You will see
Monitoring stations
Rack-mount servers
Stand-alone servers
Blade server
Chapter 8: Backbone Networks