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

OSI v.s. IEEE 802

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

IEEE 802 MAC and LLC MAC Layer LLC 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

IEEE 802 Family

LAN Protocols

LAN Topologies

Transmission on a bus LAN

Transmission on a ring LAN

Transmission on a ring LAN (cont)

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

MAC Frame Format and LLC

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

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

BUS/TREE LANs Characteristics Types 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

Coaxial Cable Bus/Tree LANs

Baseband Coaxial Cable

Baseband Coaxial Cable (cont)

Broadband Coaxial Cable

Optical Fiber Bus

Optical Fiber Bus (cont)

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

RING LANs Potential problem Star-Ring Architecture 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

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-to-point lines are simpler than for multi-point lines

STAR LANs

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

Hubs and Switches

Hubs and Switches (cont)

Hubs and Switches (cont)

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

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

Wireless LANs (cont)

Wireless LANs (cont)

Wireless LANs (cont) Ad Hoc LAN

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

Bridge Operation Reason for using bridges Reliability Performance 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

Bridge Operation (cont)

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

Bridge Protocol Architecture IEEE 802.1D specification for MAC bridges Station Station USER USER LLC t1 Bridge t8 LLC MAC t2 t7 MAC MAC t3 t4 t5 t6 PHY LAN LAN PHY PHY PHY t1, t8 User data t2, t7 LLC-H User data t3, t4, t5, t6 MAC-H LLC-H User data MAC-T

Bridge over a Point-to-Point Link Station Station USER USER Bridge Bridge LLC t1 t9 LLC MAC Link Link MAC MAC t2 t8 MAC t3 t4 t5 t6 t7 PHY LAN PHY PHY PHY PHY LAN PHY t1, t9 User data t2, t8 LLC-H User data t3, t4, t6, t7 MAC-H LLC-H User data MAC-T t5 Link-H MAC-H LLC-H User data MAC-T Link-T

Bridge over a X.25 Network Station Station Bridge Bridge X.25 PHY PHY MAC X.25-2 X.25-3 X.25-1 PHY Bridge MAC X.25-2 X.25-3 USER USER LLC t1 t12 LLC MAC t2 t5 t8 t11 MAC t3 t4 t6 X.25 t7 t9 t10 PHY LAN LAN PHY t1, t12 User data t2, 11 LLC-H User data t3, t4, t9, t10 MAC-H LLC-H User data MAC-T t5, t8 X.25H MAC-H LLC-H User data MAC-T t6, t7 Link-H X.25H MAC-H LLC-H User data MAC-T Link-T

Routing with Bridges Fixed Routing IEEE 802.1 IEEE 802.5 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

Fixed Routing

Fixed Routing (cont)

Fixed Routing (cont)

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.

Spanning Tree Routing Basic idea Consists of three mechanisms 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

Frame Forwarding Address learning

Address Learning Frame forwarding 300 sec

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

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

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

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

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

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

Source Routing (e.g.) Station X  Station Z LAN 3 B3 B1 LAN 2 LAN 1 Z B4 X B2 LAN 4 Station X  Station Z Route 1: LAN 1, bridge B1, LAN 3, bridge B3, LAN 2 Route 2: LAN 1, bridge B2, LAN 4, bridge B4, LAN 2

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

Single-Route Broadcast (e.g.) DA = Z SA = X RC = Single-route broadcast LAN 1 LAN 3 LAN 2 X B1 B3 Z LAN 4 B2 B4

All-Routes Broadcast (e.g.) DA = X SA = Z RC = All-routes broadcast LAN 1 LAN 3 LAN 2 X B1 B3 Z LAN 4 B2 B4

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

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

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

ATM LAN Emulation Objective Defines the following: 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

ATM LAN Emulation (cont)

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?

LAN Emulation Protocol Architecture

LAN Emulation Clients and Servers

LAN Emulation Client Connection

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

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

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

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

Example of Emulated LANs LECS LES BUS ELAN B LES BUS B.1 ATM Network ELAN C LEC C.4 B.2 LEC LEC S.A.2 C.3 B.3 S.A.1 LEC LEC C.2 LEC C.1 A.1 A.2 A.3 LEC LEC User LES BUS LEC LEC A.4 C.2.1 User User A.1.1 ELAN A A.3.1

E.g. A.1.1 Sends a packet to A.3.1 A.1.1 (Source) A.1 (LEC) LES BUS (Switch) S.A.2 (Switch) A.3 (LEC) A.3.1 (Dest.) IP ARP RQ IP ARP RQ IP ARP RQ IP ARP RQ IP ARP REPLY IP ARP REPLY IP ARP REPLY LE_ARP RQ Packet LE_ARP RP SETUP SETUP SETUP Packet Packet CONNECT Packet CONNECT CONNECT Connection Established READY_INDICATE READY_INDICATE Flush READY_INDICATE Flush Flush Response Flush Response

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 QoS features of the ATM to be hidden Thus, LANE cannot be used for LAN-based, delay- sensitive applications that may require some QoS guarantee The emulated LAN is functionally a single LAN segment Traffic that has to cross emulated LAN boundaries must go through a router