Chapter 13 LAN Technology LAN Architecture BUSTREE LANs

Chapter 13. LAN Technology • LAN Architecture • BUS/TREE LANs • RING LANs • STAR LANs • Wireless LANs • Bridge 1

OSI v. s. IEEE 802 2

IEEE 802 Physical Layer • Encoding/decoding of signals • Preamble generation/removal (for sync. ) • Bit transmission/reception • Specification of – transmission medium – topology 3

IEEE 802 MAC and LLC • MAC Layer – On transmission, assemble data into a frame with address and error-detection fields – On reception, disassemble frame, perform address recognition and error detection – Govern access to the LAN transmission medium • LLC Layer – Provide an interface to higher layers and perform flow and error control 4

IEEE 802 Family 5

LAN Protocols 6

LAN Topologies 7

Transmission on a bus LAN 8

Transmission on a ring LAN 9

Transmission on a ring LAN (cont) 10

Medium Access Control • Synchronous – the same approach used in circuit switching • Asynchronous – round robin, reservation, contention 11

MAC Frame Format and LLC 12

Logical Link Control • LLC Services – Based on HDLC, and provides three services – Unacknowledged connectionless service • requires minimum logic – Connection-mode service • flow control and reliability mechanisms are provided – Acknowledged connectionless service • maintain some sort of table for each active connection 13

LLC Protocol • LLC protocol is modeled after HDLC • Type 1 operation – using the unnumbered information PDU to support connectionless service • Type 2 operation – makes use of the asynchronous, balanced mode of HDLC to support connection-mode LLC service • Type 3 operation – using two new unnumbered PDUs to support an acknowledged connectionless service 14

BUS/TREE LANs • Characteristics – multi-point configuration – need for a medium access control technique – signal balancing • divide the medium into smaller segments within which pairwise balancing is possible • using amplifiers or repeaters between segments • Types – Baseband coaxial cable – Broadband coaxial cable – Optical Fiber Bus 15

Coaxial Cable Bus/Tree LANs 16

Baseband Coaxial Cable 17

Baseband Coaxial Cable (cont) 18

Broadband Coaxial Cable 19

Optical Fiber Bus 20

Optical Fiber Bus (cont) 21

RING LANs • Ring repeater states Listen state To station 1 bit delay From station Transmit state To station From station Bypass state 22

RING LANs • Potential problem – A break in any link or the failure of a repeater disables the entire network – Installation of a new repeater to support new devices requires the identification of two nearby, topologically adjacent repeaters – Timing jitter must be dealt with • Limitation on the number of repeaters in a ring • Star-Ring Architecture 23

Bus v. s. Ring • Benefit of ring – it uses point-to-point links – Signal is regenerated at each node, tx errors are minimized and greater distances can be covered than with baseband bus – Ring can accommodate optical fiber links, which provide very high data rates and excellent electromagnetic interference (EMI) characteristics – The electronics and maintenance of point-topoint lines are simpler than for multi-point lines 24

STAR LANs 25

STAR LANs (cont) . . . N inputs . . . N outputs Intermediate hub . . . N inputs . . . N outputs Header hub 26

Hubs and Switches 27

Hubs and Switches (cont) 28

Hubs and Switches (cont) 29

Wireless LANs • Applications – LAN Extension – Cross-Building Interconnect – Nomadic Access – Ad Hoc Networking • Technology – Infrared (IR) LANs – Spread Spectrum LANs – Narrowband Microwave 30

Wireless LANs (cont) CM: Control Module UM: User Module 31

Wireless LANs (cont) 32

Wireless LANs (cont) 33

Wireless LANs (cont) • Ad Hoc LAN 34

Bridges • Bridge Operation • Routing with Bridges – Fixed Routing – Spanning Tree Routing – Source Routing • ATM LAN Emulation 35

Bridge Operation • Reason for using bridges – Reliability • the network can be partitioned into self-contained units – Performance • A number of smaller LANs will often given improved performance – Security • To keep different types of traffic that have different security needs on physically separate media – Geography 36

Bridge Operation (cont) 37

Design Aspects of Bridge • The bridge makes no modification to the content or format of the frames it receives, nor does it encapsulate them with an additional header • The bridge should contain enough buffer space to meet peak demands • The bridge must contain addressing and routing intelligence • A bridge may connect more than two LANs 38

Bridge Protocol Architecture • IEEE 802. 1 D specification for MAC bridges Station USER LLC t 1 Bridge t 8 LLC MAC t 2 t 7 MAC PHY t 3 MAC t 6 PHY LAN t 4 PHY t 1, t 8 t 2, t 7 t 3, t 4, t 5, t 6 PHY t 5 LAN User data LLC-H User data MAC-H LLC-H User data MAC-T 39

Bridge over a Point-to-Point Link Station USER LLC Bridge t 1 MAC t 2 PHY t 3 LAN t 4 MAC PHY Link PHY Bridge t 5 t 1, t 9 t 2, t 8 t 3, t 4, t 6, t 7 t 5 Link PHY MAC PHY t 9 LLC t 6 LAN t 8 MAC t 7 PHY User data LLC-H User data MAC-H LLC-H User data MAC-T Link-H MAC-H LLC-H User data MAC-T Link-T 40

Bridge over a X. 25 Network Station Bridge USER LLC t 1 MAC t 2 PHY t 3 Station Bridge X. 25 -3 USER t 12 LLC X. 25 -3 MAC X. 25 -2 t 5 t 11 MAC t 8 X. 25 -2 MAC t 4 PHY X. 25 -1 t 6 X. 25 t 7 X. 25 -1 PHY t 9 t 10 PHY LAN t 1, t 12 User data t 2, 11 LLC-H User data MAC-H LLC-H User data MAC-T t 5, t 8 X. 25 H MAC-H LLC-H User data MAC-T t 6, t 7 Link-H X. 25 H MAC-H LLC-H User data MAC-T Link-T t 3, t 4, t 9, t 10 41

Routing with Bridges • Fixed Routing • IEEE 802. 1 – Based on spanning tree algorithm • IEEE 802. 5 – Source routing – Suggests that • 16 -bit MAC address 7 -bit LAN number and 8 -bit station number • 48 -bit MAC address 14 -bit LAN number and 32 -bit station number 42

Fixed Routing 43

Fixed Routing (cont) 44

Fixed Routing (cont) 45

Fixed Routing (cont) • Widely used in commercially available products • Advantage of simplicity and minimal processing requirements • Limited in a complex internet, in which bridges may be dynamically added and in which failures must be allowed for. 46

Spanning Tree Routing • Basic idea – Bridges automatically develop a routing table and update that table in response to changing topology • Consists of three mechanisms – Frame forwarding • Filtering database – Address learning • Timer for each entry in the database – Loop resolution 47

Frame Forwarding Address learning 48

Address Learning Frame forwarding 300 sec 49

Spanning Tree Algorithm • Address learning mechanism is effective if the topology of the internet is a tree • Terminology – Root bridge: Lowest value of bridge identifier – Path cost: Associated with each port – Root port: Port to the root bridge – Root path cost: Cost of the path to root bridge – Designated bridge/port • The only bridge allowed to forward frames to and from the LAN 50

Spanning Tree Algorithm (cont) • Determine the root bridge – All bridges consider themselves to be the root bridge, Each bridge will broadcast a BPDU on each of its LAN the asserts this fact – Only the bridge with the lowest-valued identifier will maintain its belief – Over time, as BPDU propagate, the identity of the lowest-valued bridge identifier will be known to all bridges 51

Spanning Tree Algorithm (cont) • Determine the root port on all other bridges – The root bridge will regularly broadcast the fact that it is the root bridge on all of the LANs; It allows the bridges on those LANs to determine their root port and the fact that they are directly connected to the root bridge – Each of these bridges turn broadcasts a BPDU on the other LANs to which it attached, indicating that it is one hop away from the root bridge • Determine the designated port on each LAN – On any LAN, the bridge claiming to be the one that is closest to the root bridge becomes the designated bridge 52

Spanning Tree Algorithm (e. g. ) LAN 2 C = 10 C=5 Bridge 3 Bridge 4 C = 10 C=5 C = 10 Bridge 1 LAN 5 C = 10 C=5 Bridge 5 C=5 LAN 3 C = 10 Bridge 2 C=5 LAN 1 LAN 4 53

Spanning Tree Algorithm (e. g. ) Bridge 1 Root Path Cost = 0 C = 10 D LAN 1 R C=5 Bridge 5 RPC = 5 Bridge 4 RPC = 5 R C = 10 Bridge 2 Root Path Cost = 10 LAN 3 D LAN 2 C=5 D C = 10 C=5 D LAN 4 R C = 10 Bridge 3 RPC = 10 C=5 D LAN 5 C = 10 R = root port D = designated port 54

Source Routing • Basic idea – The sending station determines the route that the frame will follow and includes the routing information with the frame – Bridges read the routing information to determine if they should forward the frame • When a bridge receives a frame, it will forward that frame if the bridge is on the designated route; all other frames are discarded • Bridges need not maintain routing tables • Bridges only have to know its own unique identifier and the identifier of each LAN to which it is attached 55

Source Routing (e. g. ) LAN 3 B 1 LAN 2 Z LAN 1 B 4 X B 2 LAN 4 Station X Station Z Route 1: LAN 1, bridge B 1, LAN 3, bridge B 3, LAN 2 Route 2: LAN 1, bridge B 2, LAN 4, bridge B 4, LAN 2 56

Source Routing Directives • NULL – No routing is desired, the frame can only be delivered to stations on the same LAN as the source station • Nonbroadcast – The frame includes a route, consisting of a sequence of LAN numbers and bridge numbers, that defines a unique route • All-routes broadcast – Each bridge will forward each frame once to each of its ports in a direction away from the source node, and multiple copies of the frame may appear on a LAN • Single-route broadcast – The frame is forwarded by all bridges that are on a spanning tree. The destination station receives a single copy of the frame 57

Single-Route Broadcast (e. g. ) DA = Z X SA = X LAN 1 B 2 RC = Single-route broadcast LAN 3 LAN 4 B 3 LAN 2 Z B 4 58

All-Routes Broadcast (e. g. ) DA = X LAN 1 SA = Z B 1 RC = All-routes broadcast LAN 3 B 3 LAN 2 Z X LAN 4 B 2 B 4 59

Source Routing Addressing Mode Individual Group All-Station No routing Nonbroadcast Received by station if it is on one of the LANs on is on the same LAN the route Received by all group members on the same LAN Received by all group members on all LANs visited on this route Received by all stations on the same LAN Received by all stations on all LANs visited on this route 60

Source Routing Addressing (cont) Addressing Mode Individual Group All-Station All-routes Single-route Received by station if it is on any LAN Received by all group members on all LANs Received by all stations on all LANs 61

Route Discovery and Selection • Two alternatives S all-routes D nonbroadcast S Route 1 Route 2 Route 3 … single-route Route 1 Route 2 Route 3 … D all-routes 62

ATM LAN Emulation • Objective – to enable existing shared-media LAN nodes to interoperate across an ATM network and to interoperate with devices that connect directly to ATM switches. • Defines the following: – The way in which end systems on two separate LANs of the same type can exchange MAC frames across the ATM network – The way in which an end system on a LAN can interoperate with an end system emulating the same LAN type and attached directly to an ATM switch 63

ATM LAN Emulation (cont) 64

ATM LAN Emulation (cont) • Issues that must be addressed: – Translations between ATM-based addresses (ATM switch, ATM-to-LAN converter) and MAC addresses? – Connection-oriented protocol of ATM v. s. Connectionless LAN MAC protocol? – How is the multicasting and broadcast capability carried over into the ATM environment? 65

LAN Emulation Protocol Architecture 66

LAN Emulation Clients and Servers 67

LAN Emulation Client Connection 68

LAN Emulation Scenario • Initialization – The client establishes a virtual channel connection to LECS • Configuration – The LECS assigns the client to a particular emulated LAN service by giving the client the LES’s ATM address • LECS returns information to the client about the emulated LAN, including MAC protocol, max. frame size, the name of the emulated LAN 69

LAN Emulation Scenario (cont) • Joining – The client sets up a control connection to the LES • The client provides its ATM address, MAC address, LAN type, max. frame size, client identifier, and a proxy indication • Registration and BUS initialization – If the client is a proxy for a number of end systems on a legacy LAN • it sends a list of all MAC addresses on the legacy LAN that are to be part of this emulated LAN to the LES 70

LAN Emulation Scenario (cont) – The client sends a request to the LES for the ATM address of the BUS • Data transfer – Once a client is registered, it is able to send and receive MAC frames – In the case of a proxy client, it functions as a bridge – 1. Unicast MAC frame, ATM address known • Set up virtual data connection via ATM address 71

LAN Emulation Scenario (cont) – 2. Unicast MAC frame, address unknown • Send it to BUS • BUS either transmits the frame to the intended MAC destination or else broadcast the frame to all MAC destinations on the emulated LAN • The client attempts to learn the ATM address for this MAC for future reference by sending request to LES – 3. Multicast or broadcast MAC frame • The sending client transmits the frame to the BUS over the virtual data connection it has to the BUS • The BUS then replicates that frame and sends it over virtual data connections to all of the clients on the emulated LAN 72

Example of Emulated LANs ELAN B B. 1 LECS LES BUS ATM Network LEC ELAN C C. 4 LEC B. 2 LEC S. A. 2 B. 3 C. 3 LEC S. A. 1 LEC C. 2 LEC C. 1 A. 1 LEC LES BUS A. 2 A. 3 LEC LEC A. 4 User A. 1. 1 ELAN A User C. 2. 1 User A. 3. 1 73

E. g. A. 1. 1 Sends a packet to A. 3. 1 A. 1. 1 (Source) A. 1 (LEC) IP ARP RQ LES S. A. 1 (Switch) BUS IP ARP RQ A. 3 (LEC) A. 3. 1 (Dest. ) IP ARP RQ IP ARP REPLY Packet S. A. 2 (Switch) IP ARP REPLY LE_ARP RQ LE_ARP RP SETUP Packet CONNECT Packet Connection Established READY_INDICATE Flush Response Flush Response 74

Summary of ATM LANE • Enables legacy systems to use an ATM network in a transparent manner – It hides the ATM network from legacy systems – Also causes the Qo. S features of the ATM to be hidden – Thus, LANE cannot be used for LAN-based, delaysensitive applications that may require some Qo. S guarantee • The emulated LAN is functionally a single LAN segment – Traffic that has to cross emulated LAN boundaries must go through a router 75