Week 5

1
Week 5

• Hardware Layers
• The case of BBNs

2
Learning Objectives

• Understand BBN
• Basics
• Architectures
• Technologies
• Implications for analysis and design of networks
• Application exercises

3
BBN basics

• High speed networks that
• Link an organizations LANs and
• Provide connections to other BBNs, MANs, WANs and
  the Internet
• Campus network v/s enterprise network
• A campus network connects BBNs in several
  buildings
• An enterprise network connects ALL networks in an
  organization

4
Backbone architecture layers

• Block 1 The access layer connects nodes to a LAN
• Block 2 The distribution layer is the BBN that
  inter connects LANs
• Block 3 The core layer is the BBN that
  interconnects different BBNs (found in large
  organizations only)

5
BBN types

• Hierarchical Backbones
• Flat Backbones
• Collapsed Backbones
• Virtual LANs

6
Hierarchical BBNs

• LANs are connected by routers
• Within the LANs traffic is based on data link
  addresses
• Between LANs, message are sent to the router,
  which forwards the message based on its network
  layer address

7
Flat BBNs

• LANs are connected by layer-2 switches (or
  bridges)
• Packets are forwarded based on their data link
  layer addresses, making the entire flat backbone
  a single subnet
• Flat BBN were used when routers were very
  expensive

8
Collapsed BBNs

• LANs are connected by ONE high speed layer 2 or 3
  switch
• If a layer 2 switch is used ?BBN operates like a
  flat BBN
• If a layer 3 switch is used ? BBN operates like a
  hierarchical BBN
• Main advantages
• Point-to-point circuit (improved performance)
• Fewer devices in the network (easier to manage)
• Minor disadvantages
• Use more cable (cable runs for longer distances)
• If the central switch fails, the network goes
  down
• Location of different LAN and BBN connecting
  devices
• All in same room Rack-mounted or Chassis-based
  collapsed BBN (Fig 5.5)
• Different location (Fig 5.4)

9
Collapsed BBN architecture
10
Virtual LANs

• New flexible LAN/BBN architecture that assigns
  computers to LAN segments by software NOT by
  hardware
• Divides LANs in logical rather than physical
  segments
• Members of a VLAN can receive broadcast messages
• Basic design Single-switch v/s multiswitch-VLANs

11
Single switch VLANs

• ONE switch physically connect all nodes and
  assigns nodes to VLANs
• Layer 1, 2, 3 and 4 VLANs Node membership can be
  port-, MAC address-, IP address-,
  application-based ?See specs

12
Multiswitch VLANs

• Several switches are used in the BBN
• Each switch knows membership of nodes connected
  to other switches ? Tables
• Frames include a tag field carrying VLAN
  information field
• Multiswitch VLANs can prioritize traffic
  (IEEE802.1p)
• Two problems cost and management

13
Other BBN technologies

• Fiber Distributed Data Interface
• Operates at 100 Mbps over a fiber optic cable
• Star physical topology (hub) and Ring logical
  topoloy (token-passing system)
• OK in the 80s and 90s, now losing market share
  to GbE and ATM
• Asynchronous Transfer Mode (Fig 5.14)
• Operates at 155 Mbps, 622Mbps or higher
• Uses a mesh topology and fixed with full-duplex
  circuits
• Originally designed for WANs ? Use for LANs
  requires translations
• ATM edge switch (or ATM gateways) converts TCP/IP
  and Ethernet frames into ATM cells and then
  converts them back once they have reached their
  destination network
• ATM switches forward packets
• LANE (layer 2 translations) or MultiProtocol Over
  ATM (layer 3 translations)
• Complex, expected to lose market share to GbE

14
Best practice in BBN design

• Organizations are moving to collapsed BBNs or
  VLANs
• Ethernet dominates
• LANs 10/100 Mbps already very popular
• BBNs GbE use is growing (ATM remains more
  popular in WANs)
• Effective data rates
• Ethernet see assumptions and calculations in
  Chapter 4
• ATM Take into account some particularities
• Data Link efficiency 87
• MAC protocol efficiency 100 (ATM switches
  full duplex transmissions)
• Conversion between protocols decreases effective
  data rate by about 40
• ?Effective data rate on 155 Mbps ATM connection
• 155 Mbps 87 100 2 60 160 Mbps
• ?Effective data rate on 622 Mbps ATM connection
• 622 Mbps 87 100 2 60 650 Mbps
• ? Low compared to effective data rate on full
  duplex 1GbE (1.8 Gbps)

15
BBN recommendations

• Architecture collapsed backbone or VLAN
• Technology Gigabit Ethernet.
• Design combines use of layer-2 and layer-3
  Ethernet switches
• Access layer 10/100 layer-2 switches over cat 5e
  TP cables
• Distribution layer Layer-3 switches over
  1000Base T (cat 6 or 7 TP) or F
• Core layer 10GbE Layer-3 switches over fiber
• Network reliability Redundant switches and
  cabling

16
The best practice network design
17
Application exercise

• Key differences and similarities among
• Bridges
• Layer 2 switches
• Layer 3 switches
• Routers
• Gateways
• Use pairwise comparisons

18
Thank you