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

Bridged Backbone

bus topologyEntire network is just one subnet

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

Routed Backbone

Usually a bus topology

Example of a routed BB at the Distribution layer

Each LAN is a separate subnet

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

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

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.

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

Single Switch VLAN Collapsed Backbone

Switchacting as a large physical switch

Computers assigned to different LANs by software

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

Basic Internet Architecture

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

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

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

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

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

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

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

Internet2 Backbone Networks

Donna Cox,Robert Patterson, NCSA

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

Tele-immersion

• Shared virtual reality

• University of Illinois at Chicago

Images courtesy Univ. of Illinois-

Chicago