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

2. OSI v.s. IEEE 802

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

4. 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

5. IEEE 802 Family

6. LAN Protocols

7. LAN Topologies

8. Transmission on a bus LAN

9. Transmission on a ring LAN

10. Transmission on a ring LAN (cont)

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

12. MAC Frame Format and LLC

13. 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

14. 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

15. 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

16. Coaxial Cable Bus/Tree LANs

17. Baseband Coaxial Cable

18. Baseband Coaxial Cable (cont)

19. Broadband Coaxial Cable

20. Optical Fiber Bus

21. Optical Fiber Bus (cont)

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

23. 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

24. 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

25. STAR LANs

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

27. Hubs and Switches

28. Hubs and Switches (cont)

29. Hubs and Switches (cont)

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

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

32. Wireless LANs (cont)

33. Wireless LANs (cont)

34. Wireless LANs (cont)
Ad Hoc LAN

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

36. 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

37. Bridge Operation (cont)

38. 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

39. 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

40. 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

41. 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

42. 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

43. Fixed Routing

44. Fixed Routing (cont)

45. Fixed Routing (cont)

46. 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.

47. 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

48. Frame Forwarding
Address learning

49. Address Learning
Frame forwarding
300 sec

50. 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

51. 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

52. 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

53. 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

54. 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

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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

61. 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

62. 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

63. 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

64. ATM LAN Emulation (cont)

65. 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?

66. LAN Emulation Protocol Architecture

67. LAN Emulation Clients and Servers

68. LAN Emulation Client Connection

69. 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

70. 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

71. 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

72. 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

73. 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

74. 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

75. 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