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Backbone Network Architectures
• Identifies the way backbone interconnects LANs
• Defines how it manages packets moving through BB
• Fundamental architectures– Bridged Backbones
– Routed Backbones
– Collapsed Backbones
• Rack-based
• Chassis-based
– Virtual LANs
• Single-switch VLAN
• Multiswitch VLAN
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Bridged Backbone
bus topologyEntire network is just one subnet
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Bridged Backbones
• Move packets between networks based on their data link layer addresses
• Cheaper (since bridges are cheaper than routers) and easier to install (configure)– Just one subnet to worry
– Change in one part may effect the whole network
• Performs well for small networks – For large networks broadcast messages (e.g., address
request, printer shutting down) can lower performance
• Formerly common in the distribution layer– Declining due to performance problems
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Routed Backbone
Usually a bus topology
Example of a routed BB at the Distribution layer
Each LAN is a separate subnet
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Routed Backbones
• Move packets using network layer addresses
• Commonly used at the core layer– Connecting LANs in different buildings in the campus
– Can be used at the distribution layer as well
• LANs can use different data link layer protocols
• Main advantage: LAN segmentation– Each message stays in one LAN; unless addressed
outside the LAN
– Easier to manage
• Main disadvantages– Tend to impose time delays compared to bridging
– Require more management than bridges & switches
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Star topology
Collapsed Backbone
A connection to the switch is a separate point-to-point circuit
Most common type BB mainly used in distribution layer
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Collapsed Backbones
• Replaces the many routers or bridges of the previous designs– Backbone has more cables, but fewer devices
– No backbone cable used; switch is the backbone.
• Advantages:– Improved performance (200-600% higher)
• Simultaneous access; :switched” operations
– A simpler more easily managed network – less devices
• Two minor disadvantages– Use more and longer cables
– Reliability:
• If the central switch fails, the network goes down.
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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
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Single Switch VLAN Collapsed Backbone
Switchacting as a large physical switch
Computers assigned to different LANs by software
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VLAN Operating Characteristics
• Advantages of VLANs– Faster performance
• Precise management of traffic flow
• 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 802.1p
• Can have QoS capability at MAC level– Similar to RSVP and QoS capabilities at network and
transport layers
• Drawbacks– Cost
– Management complexity
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Basic Internet Architecture
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Internet’s Access Points• Network Access Points (NAPs)
– Connect National ISPs together
– Sometimes large regional and local ISPs also have access directly to NAPs
• Indiana University, for example, which provides services to about 40,000 individuals, connects directly to the Chicago NAP
– About a dozen NAPs in the U.S.– Run by common carriers such as Sprint and AT&T
• Metropolitan Area Exchanges (MAEs)– Connect Regional ISPs together– About 50 such MAEs in the U.S. today
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Packet Exchange Charges
• Peering
– ISPs at the same level usually do not charge each other for exchanging messages
• Higher level ISPs charge lower level ones
– National ISPs charge regional ISPs which in turn charge local ISPs
• Local ISPs charge individuals and corporate users for access
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Connecting to an ISP
• Done by through ISP’s Point of Presence (POP)– A place ISP provides service to its customers
• Individual users – Typically through a dial-up line using the PPP protocol
• Handled by the ISP’s modem pool– Userid and password checked by Remote Access
Server (RAS)
• Once logged in, the user can send packets over the phone line
• Corporate users – Typically access the POP using a T-1, T-3 or ATM OC-3
connections provided by a common carrier
• Cost = ISP charges + circuit charges
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ISP Point-of Presence
Modem Pool
Individual Dial-up Customers
Corporate T1 Customer
T1 CSU/DSU
Corporate T3 Customer
T3 CSU/DSU
Corporate OC-3 Customer
ATM Switch
Layer-2 Switch
ISP POP
ISP POP
ISP POP
NAP/MAE
RemoteAccess Server
ATM Switch
Inside an ISP POP
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Internet Governance
• No one operates the Internet
• Closest thing: Internet Society (ISOC)– Open membership professional society
– Over 175 organizational and 8000 individual members in over 100 countries
– Mission: “Open development, evolution and use of the Internet for the benefit of the people in the world.”
– ISOC work areas
• Public policy:– Involves in debates in copyright, censorship, privacy
• Education– Training and education programs
• Standards
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ISOC Standard Bodies
• Internet Engineering Task Force (IETF)– Concerned with evolution of Internet architecture and
smooth operation of Internet
– Work through groups (organized by topics)
– Request For Comments (RFC): basis of Internet standards
• Internet Engineering Steering Group (IESG)– Responsible for management of the standard process
– Establishes and administers rules in creating standards
• Internet Architecture Board (IAB)– Provides strategic architectural oversight, guidance
• Internet Research Task Force (IRTF)– Focus on long-term specific issues
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Internet 2
• Many new projects designing new technologies to evolve Internet
• Primary North American projects– Next Generation Internet (NGI) funded by NSF
• Developed very high performance Backbone Network Service (vBNS)
– Run by WorldCom
– University Corporation for Advanced Internet Development (UCAID) with 34 universities
• Developed Abilene network (also called Internet 2)
– Advanced Research and Development Network Operations Center (ARDNOC) funded by Canadian government
• Developed CA*Net
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Internet2 Backbone Networks
Donna Cox,Robert Patterson, NCSA
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Features of Future Internet
• Access via Gigapops, similar to NAPs– Operate at very high speeds (622 Mbps to 2.4 Gbps)
using SONET, ATM and IPv6 protocols
• IPv6 not IPv4
• New protocol development focuses on issues like – Quality of Service
– Multicasting
• New applications include– Tele-immersion
– Videoconferencing
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Tele-immersion
• Shared virtual reality
• University of Illinois at Chicago
Images courtesy Univ. of Illinois-
Chicago