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Chap. 1 Backbone Network Design

Chap. 1 Backbone Network Design BTECH2431 | Network Design & Management Prepared by Noris Bt. Ismail. Components of Backbone networks Bridges, Routers, Gateways Backbone network architectures Backbone technologies Best practice backbone design Improving backbone performance. Outline.

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Chap. 1 Backbone Network Design

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  1. Chap. 1 Backbone Network Design BTECH2431| Network Design & ManagementPrepared by Noris Bt. Ismail

  2. Components of Backbone networks Bridges, Routers, Gateways Backbone network architectures Backbone technologies Best practice backbone design Improving backbone performance Outline

  3. 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-wide network Backbone Networks

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

  5. Five categories of connecting devices

  6. Device Operates at Packets Physical Layer Data Link Layer Network Layer Bridge Data Link Layer Filtered using data link layer addresses Same or Different Same Same Router Network Layer Routed using network layer addresses Same or Different Same or Different Same Gateway Network Layer Routed using network layer addresses Same or Different Same or Different Same or Different Backbone Network Devices

  7. Bridges • Data link layer devices • Connect LANs with the same Data Link and same Network layers Allows different types of cabling Operate in a similar way to layer 2 switches (learning bridges)

  8. Operate in a similar way to layer 2 switches: Learn which computers are on each side of the bridge By reading the source addresses on incoming frames and recording this information in forwarding tables Data link layer devices Connecting similar type of networks But they can connect different types of cable Not popular anymore Losing market share to layer 2 switches as the latter become cheaper and more powerful Learning Bridges

  9. A bridge connecting two LANs

  10. A learning bridge and the process of learning

  11. Loop Problem • Sys. Admin. like to have redundant bridges (>1 bridge) to make the system more reliable. • Redundancy can create loops in the systems which is undesirable. • Result – There are two copies of the frame in LAN 1 and LAN 2. • Solving the problem - IEEE specification requires that bridges use the spanning tree algo. to create loopless topology.

  12. Loop problem in a learning bridge

  13. Forwarding and blocking ports after using spanning tree algorithm

  14. Routers connecting independent LANs and WANs

  15. Routers • Operate at the network layer • Connect LANS with different data link layer, but the same network layer protocol Allows different types of cabling Perform more processing than bridges or layer 2 switches

  16. Operations Strip off the header and trailer of the incoming L2 frame Examine the destination address of the network layer Build a new frame around the packet Choose the “best” route for a packet (via routing tables) Send it out onto another network segment Compared to Bridges Perform more processing Process L3 messages (no changes made) Form new L2 messages for outgoing packets Processes only messages specifically addressed to it Routers (Cont.)

  17. Gateways Also operate at network layer (like routers) Connect LANS with different data link layer and different network layer protocols Some operate at the application layer as well

  18. Multiprotocol routers Can handle several different protocols (no translation) In and out protocols must be the same Brouters Combine bridge and router functions Examine L2 addresses of all messages Can also process directly addressed (L2) messages Layer-3 switches Similar to L2 switches, but switch messages based on L3 addresses Can support many more simultaneous ports than routers Other BB Network Devices

  19. 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 Backbone Network Architectures

  20. Access Layer (not part of BB) Closest to the users; Backbone Design Layers Distribution Layer Connects the LANs together (often in one building Core Layer (for large campus/enterprise networks) Connects different BNs together (building to building) Backbone Architecture Layers

  21. Backbone Architecture Layers

  22. Bridged Backbone bus topology Entire network is just one subnet

  23. 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 Bridged Backbones

  24. Routed Backbone Example of a routed BB at the Distribution layer Usually a bus topology Each LAN is a separate subnet

  25. 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 Routed Backbones

  26. Collapsed Backbone Most common type BB mainly used in distribution layer A connection to the switch is a separate point-to-point circuit Star topology

  27. 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. Collapsed Backbones

  28. Rack-Based Collapsed Backbones

  29. Places all network equipment (hubs and switch) in one room (rack room) Easy maintenance and upgrade Requires more cable (but cables are cheap) Main Distribution Facility (MDF) or Central Distribution Facility 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 Useful when a busy hub requires offloading Rack-Based Collapsed Backbones

  30. Main Distribution Facility (MDF) Switches Room

  31. Use a “chassis” switch instead of a rack A collection of modules Number of hubs with different speeds L2 switches 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) + 100 = 710 Mbps Flexible Enables users to plug modules directly into the switch Simple to add new modules Chassis-Based Collapsed Backbones

  32. 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 Virtual LANs (VLANs)

  33. Traditional LAN vs Virtual LAN

  34. Sample of VLAN Configuration

  35. Single Switch VLAN Collapsed Backbone acting as a large physical switch Computers assigned to different LANs by software Switch

  36. Port-based VLANs (Layer 1 VLANs) Use physical layer port numbers on the front of the VLAN switch to assign computers to VLAN segments Use a special software to tell the switch about the computer - port number mapping MAC-based VLANs (Layer 2 VLANs) Use MAC addresses to form VLANs Use a special software to tell the switch about the computer - MAC address mapping Simpler to manage Even if a computer is moved and connected to another port, its MAC address determines which LAN it is on Types of Single Switch VLANs

  37. IP-based VLANs (Layer 3 VLANs, protocol based VLANs) Use IP addresses of the computers to form VLANs Similar to MAC based approach (use of IP instead of MAC address) Application-based VLANs (Layer 4 VLANs, policy-based VLANs) Use a combination of the type of application (Indicated by the port number in TCP packet) and The IP address to form VLANs Complex process to make assignments Allow precise allocation of network capacity Types of Single Switch VLANs

  38. Multi-switch VLAN-Collapsed Backbone Switch Switch Switch Switch

  39. 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 802.3 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 Multi-switch VLAN Operations

  40. 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 VLAN Operating Characteristics

  41. Gigabit Ethernet Fiber Distributed Data Interface (FDDI) Asynchronous Transfer Mode (ATM) Backbone Technologies

  42. A set of standards designed in 80’s for MANs (ANSI X3T9.5) Also used as BB and LAN technologies Limited future Gigabit Ethernet’s strong presence A ring network operating at 100 Mbps over fiber cables Assumes a mix of 1,000 stations and 200 Km path With repeaters at every 2 Km Uses 2 counter rotating rings: primary and secondary Data on the primary; secondary used as backup FDDI

  43. FDDI Topology DAS - Dual attachment Station – on both rings SAS – Single attachment Station – on single ring. Two types of FDDI computers secondary ring flows in opposite direction

  44. Managing a Broken Ring in FDDI If a ring is broken, the ring can still operate in a limited fashion A B DAS DAS H C SAS SAS F will then reroute the traffic back to E on the primary ring, from where it will flow back on the primary ring to G (F  E  D  C  B  A  H  G) SAS D G DAS DAS DAS F E Line Break

  45. Break in the ring between F and G • Both are DAS – G can reroute traffic from H on the primary ring to A on the secondary ring. • The data will travel along the secondary ring from A to B to E to F. • F will then reroute the traffic back to E on the primary ring, from where it will flow back on the primary ring to G (F  E  D  C  B  A  H  G)

  46. Uses a controlled access token passing scheme Sending computer Wait for the token, when receive it Attach the packet to the token and transmit them Receiving computer See if there is a packet attached to the token If there is  process the packet If it needs to transmit a packet  follow the steps above If no packet to send  simply transmit the token to the next computer Very reliable and provide adequate response time until it almost reaches saturation at 100 Mbps FDDI Media Access Control

  47. Originally designed for use in WAN Often used now in BNs Standardized; simple to connect BNs and WANs Also called cell relay Includes Layer 3, Layer 2 and Layer 1 technologies in the specifications Compatible with TCP/IP and Ethernet as if ATM was Layer 2 technology A connection oriented technology ATM switches Provide point-to-point full duplex circuits at 155 Mbps (622 Mbps for switch-to-switch) ATM (Asynchronous Transfer Mode)

  48. Packet format: Uses fixed-length packets (cells) of 53 bytes: 5-byte header, 48 byte data Designed to make switching faster (in hardware) Error Checking Error checking done for header only (not on data) If error detected, cell is discarded Addressing Uses a virtual channel(VC) between sender and receiver All cells use VC Identifier as addresses QoS (prioritized transmissions) Each VC assigned a specific class of service with a priority ATM vs. Ethernet

  49. Identified by a two-part number Path number Circuit number within that path A physical port on a switch may have many paths A path may have many circuits A switch may have thousands of VCs A VC table is used to map the connections which can be established either: Permanently: Permanent Virtual Circuit (PVC) Temporarily: Switched Virtual Circuit (SVC) Deleted when the connection is not needed Virtual Channels in ATM

  50. Addressing and Forwarding in ATM When a cell arrives, switch checks the cell’s VC identifier at the table and determines where to send it . ATM Switch A 1 2 3 4 ATM Switch B 1 2 3 4

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