Lan Wan Architecture

TCP/IP Protocol Suite*COMP 416Internet Protocols and SoftwareInstructor: Zhijun Wang

Note: Projects are available online The first quiz will be given in next lecture (Oct. 15) It covers the first 4 lectures Todays contentsUnderlying TechnologyVirtual LAN

TCP/IP Protocol Suite

TCP/IP Protocol Suite*Chapter 3Objectives Underlying Technology Understand the Ethernet Understand the types of point-to-point WANs Understand the types of switched WANs Differentiate between repeaters, bridges, routers, and hubs


TCP/IP Protocol Suite*3.1 Local Area NetworksA local area network (LAN) is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographic area such as a single department, a single building, or a campus. A large organization may need several connected LANs. The most popular LANs are Ethernet and wireless LANs.


TCP/IP Protocol Suite* Figure 1 Carrier sense multiple access with collision detection ( CSMA/CD)LAN is a communication medium shared by multiple users.


TCP/IP Protocol Suite*Figure 2 Ethernet layersResponse for Flow and error controlResponsible for the operation of the CSMA/CD access methodEthernet layer is above physical layer including logical link control andMedia access control sub-layers


TCP/IP Protocol Suite*Figure 3 Ethernet frameUsed for synchronizationIdentify the frame start


TCP/IP Protocol Suite*3.2 Point-to-Point WANsA second type of network we encounter in the Internet is the point-to-point wide area network. A point-to-point WAN connects two remote devices using a line available from a public network such as a telephone network.


TCP/IP Protocol Suite*Figure 4 56K modemPCM: Pulse code modulation


TCP/IP Protocol Suite*ADSL (Asynchronous digital subscriber line) is an asymmetric communication technology designed for residential users; it is not suitable for businesses.Note:


TCP/IP Protocol Suite*Figure 5 Bandwidth division in ADSLTelephone call


TCP/IP Protocol Suite*Figure 6 ADSL and DSLAMDigital subscriber line access multiplexer


TCP/IP Protocol Suite*Figure 7 Cable bandwidth


TCP/IP Protocol Suite*Figure 8 Cable modem configurationsCable modem transmission system


TCP/IP Protocol Suite*Table 1 Synchronous Optical Network (SONET) rates5 Gbps10 GbpsSTS: synchronous transport signal


TCP/IP Protocol Suite*3.3 Switched WANsThe backbone networks in the Internet are usually switched WANs. A switched WAN is a wide area network that covers a large area (a state or a country) and provides access at several points to the users. Inside the network, there is a mesh of point-to-point networks that connects switches. The switches, multiple port connectors, allow the connection of several inputs and outputs.

X.25Frame relay Asynchronous Transfer Mode (ATM)


TCP/IP Protocol Suite*A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-size block of information.Note:


TCP/IP Protocol Suite*Figure 9 Architecture of an ATM networkUNI: User-to-network interfaceNNI: Network-to-network interfaceATM: asynchronous transfer mode


TCP/IP Protocol Suite*Figure 10 Virtual circuitsVCI: Virtual circuit identifierVPI: Virtual path identifier


TCP/IP Protocol Suite*Note that a virtual connection is defined by a pair of numbers: the VPI and the VCI.Note:


TCP/IP Protocol Suite*Figure 11 An ATM cellATM cell is a 53-byte packet


TCP/IP Protocol Suite*3.4 Connecting DevicesLANs or WANs do not normally operate in isolation. They are connected to one another or to the Internet. To connect LANs or WANs, we use connecting devices. Connecting devices can operate in different layers of the Internet model. We discuss three kinds of connecting devices: repeaters (or hubs), bridges (or two-layer switches), and routers (or three-layer switches). Repeaters and hubs operate in the first layer of the Internet model. Bridges and two-layer switches operate in the first two layers. Routers and three-layer switches operate in the first three layers


TCP/IP Protocol Suite*Figure 13 Connecting devicesRouter is a three-layer device (physical, data link and network layers)Bridge is a two-layer device (physical and data link layers)Repeater is a physical layer device


TCP/IP Protocol Suite*Figure 14 RepeaterA repeater connects segments of a LAN.A repeater forwards every bit; it has no filtering capability.


TCP/IP Protocol Suite*Figure 15 Function of a repeaterA repeater is a regenerator, not an amplifier.


TCP/IP Protocol Suite*Figure 16 BridgeA bridge has a table used in filtering decisions.


TCP/IP Protocol Suite*Figure 17 Learning bridgeA bridge does not change the physical (MAC) addresses in a frame.


TCP/IP Protocol Suite*Figure 18 Routing exampleA router is a three-layer physical, data link, and network) device.A router changes the physical addresses in a packet.


TCP/IP Protocol Suite*A repeater or a bridge connects segments of a LAN.A router connects independent LANs or WANs to create an internetwork (internet).Note:


TCP/IP Protocol Suite*Gateways The term Gateway is used with different meanings in different contextsGateway is a generic term for routers (Level 3)Gateway is also used for a device that interconnects different Layer 3 networks and which performs translation of protocols (Multi-protocol router)


Token-ring

Cloud

PBX

Desktop System

Computer

Ethernet

Gateway

IP Network

X.25 Network

SNA Network

Gateway

Gateway

Host

Host

TCP/IP Protocol Suite*

Many times it is necessary to connect a local area network to another local area network or to a wide area network.Local area network to local area network connections are often performed with a bridge-like device.Local area network to wide area network connections are usually performed with a router.A third device, the switch, can be used to interconnect segments of a local area network.Interconnection



To separate / connect one corporate division with another.To connect two LANs with different protocols.To connect a LAN to the Internet.To break a LAN into segments to relieve traffic congestion.To provide a security wall between two different types of users.Why Interconnect?



An Example of Internetworking



A transparent bridge does not need programming but observes all traffic and builds routing tables from this observation.This observation is called backward learning.Each bridge has two connections (ports) and there is a routing table associated with each port.A bridge observes each frame that arrives at a port, extracts the source address from the frame, and places that address in the ports routing table.A transparent bridge is found with CSMA/CD LANs.Transparent Bridges-I



A transparent bridge can also convert one frame format to another, but this does not happen too often anymore since most networks are CSMA/CD.Note that some people / manufacturers call a bridge such as this a gateway or sometimes a router.The bridge removes the headers and trailers from one frame format and inserts (encapsulates) the headers and trailers for the second frame format.Transparent Bridges-II



A remote bridge is capable of passing a data frame from one local area network to another when the two LANs are separated by a long distance and there is a wide area network connecting the two LANs.A remote bridge takes the frame before it leaves the first LAN and encapsulates the WAN headers and trailers.When the packet arrives at the destination remote bridge, that bridge removes the WAN headers and trailers leaving the original frame.Remote Bridges



An Example of Remote Bridges



What happens if you have many LANs interconnected with multiple bridges?Data that leaves one workstation could travel to a bridge, across the next network, into the next bridge, and back onto the first network.A packet may continue to cycle like this forever!Loop in Connected LANs


TCP/IP Protocol Suite*Consider the two LANs that are connected by two bridges.Assume host n is transmitting a frame F with unknown destination.What is happening?Bridges A and B flood the frame to LAN 2.Bridge B sees F on LAN 2 (with unknown destination), and copies the frame back to LAN 1Bridge A does the same. The copying continuesWheres the problem? Whats the solution ?Danger of LoopsF



How do we stop this from happening?Disconnect one of the bridges? Maybe we want bridge redundancy in case one bridge fails.How about applying the spanning tree algorithm.How is the algorithm applied?Spanning Tree Algorithm


TCP/IP Protocol Suite*Spanning Tree Protocol (IEEE 802.1d)The Spanning Tree Protocol (SPT) is a solution to prevent loops when forwarding frames between LANs

The SPT is standardized as the IEEE 802.1d protocol

The SPT organizes bridges and LANs as spanning tree in a dynamic environmentFrames are forwarded only along the branches of the spanning tree Note: Trees dont have loops


TCP/IP Protocol Suite*Spanning Tree Protocol (IEEE 802.1d)Bridges that run the SPT are called transparent bridges

Bridges exchange messages to configure the bridge ( Configuration Bridge Data Unit or BPDUs) to build the tree.



Virtual LANsA virtual LAN, or VLAN, is a logical subgroup within a local area network that is created via switches and software rather than by manually moving wiring from one network device to anotherEven though the employees and their actual computer workstations may be scattered throughout the building, LAN switches and VLAN software can be used to create a network within a network. Virtual LAN (VLAN)



A relatively new standard, IEEE 802.1Q, was designed to allow multiple devices to intercommunicate and work together to create a virtual LAN Instead of sending a technician to a wiring closet to move a workstation cable from one switch to another, an 802.1Q-compliant switch can be remotely configured by a network administrator VLAN



Review of LAN



What is a VLAN



VLAN



Why do we need VLAN



VLAN Tagging



IEEE 802.1Q:Features-I



IEEE 802.1Q:Features-II



IEEE 802.1Q:Features-III



IEEE 802.1Q:Features-IV



VLAN Tag


TCP/IP Protocol Suite*Tagging rule


TCP/IP Protocol Suite*Tagged Frame Format


TCP/IP Protocol Suite*Communications in VLANs


TCP/IP Protocol Suite*Metro Ethernet All information of Metro Ethernet can be found on The Metro Ethernet Forum (MEF): http://en.wikipedia.org/wiki/Metro_Ethernet_Forum A Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan access network to connect subscribers and businesses to a Wide Area Network, such as the Internet. Large businesses can also use Metro Ethernet to connect branch offices to their Intranets.

Advantages of Metro Ethernet: Cost-effective equipmentEasy network managementFast speed


TCP/IP Protocol Suite*Excises:Match the following to one or more layers of OSI model (a) interface to transmission media (b) provides access for the end user (c) route selection (d) communicates directly with users application medium (e) define frames (f) ensure reliable transmission of data2. (a) What are the differences between a repeater and a bridge? (b) What are the differences between a bridge and a router?


TCP/IP Protocol Suite*AnswersMatch the following to one or more layers of OSI model (a) interface to transmission media ( Physical layer) (b) provides access for the end user (Application layer) (c) route selection (Networking layer) (d) communicates directly with users application medium (Application layer) (e) define frames (Data link layer) (f) ensure reliable transmission of data (Data link and transport layers)


TCP/IP Protocol Suite*Answers-Cont.2. (a) What are the differences between a repeater and a bridge? (b) What are the differences between a bridge and a router?

Ans: (a) A repeater only operates in physical layer, but a bridge operates in both physical and data link layers; A repeater has no filter function, a bridge has filter function. (b) A bridge connects segments of a LAN, and a router connects LANs and WANs; A bridge operates in physical and data link layer and a router operates in physical, data link and networking layers; A bridge cannot change the physical address in a packet A router does


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Lan Wan Architecture

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