Content Introduction Layer 2: Frames Error Handling Media Access Control General approaches and terms Network Topologies Media Access Principles (Random) Aloha Principles CSMA, CSMA/CD, CSMA / CA Media Access Principles ( Deterministic) Master-Slave Approaches (Polling) Time based solutions Token based solutions (Token Ring) FDDI 50 Polling(1) Master-Slave principles: Master works as coordinator. He organises the communication: determines, who is allowed to transmit Typical solution: Master polls different slave (e.g. Bluetooth) 51
Polling (2): Multi-Slot packets Bluetooth Packets can cover multiple Slots (1,3,5 Slots) 52 Polling (3), LIN 53 LIN Cluster: one master, serveral slaves Frame: Header (from master) + Response (from slave)
Polling (4), LIN Frame Break + Byte-Fields (4-11) Byte-Field recessive 54 dominant Content Introduction Layer 2: Frames Error Handling Media Access Control General approaches and terms Network Topologies Media Access Principles (Random) Aloha Principles CSMA, CSMA/CD, CSMA / CA Media Access Principles ( Deterministic) Master-Slave Approaches (Polling) Time based solutions Token based solutions (Token Ring) FDDI 55
Time Slots (1) The node knows, when a message has to be transmitted. Needs an internal clock Needs time-syncronisation between nodes 56 Time Slots (2), Principle Ref. Msg Basic Cycle Time Windows for Messages Ref. Msg Time Master generates Reference Message Timewindows are relative to Reference-Message (Sync) Fault Tolerance-> potential Time Master TTCAN Level 1: Ref Msg only has some control Info TTCAN Level 2: Ref. Msg has global time Information Global Time 57
Time Slots (3), Principle(2) Ref. Msg MsgA Arbitrating Window Basic Cycle Free MsgB MsgB Ref. Msg Exclusive Time Window Cyclic messages (predefined) No automatic repeat allowed Arbitrating Window Different messages try to access (CSMA) Node specific knowledge is a minimum MsgA 1 2 3 4 5 6 1 Global Time 58 Time Slots (4) One TDMA Frame Preamble Information Message Trail Bits Slot 1 Slot 2 Slot 3... Slot N Trail Bits Sync. bits Information Data Guard Bits Master transmits Syncronisation Frame Each node has a timeslot to transmit its message Sync-Frame is cyclically repeated over time 59
TDMA (4) 60 Total number of bits per frame T f : frame duration R : channel bit rate Number of Overhead bits per frame b = N b + N b + N b + N b OH r r t p = T R Nr: Number of reference bursts per frame Nt: Number of traffic Bursts per frame br: number of overhead bits per reference burst bp: number of overhead bits per preamble bg: number of equivalent bits in each guard-time interval b = Efficiency 1 OH η f 100% b T t g r g b T f Time Slots (5), Flexray 61
Time Slots (6), Flexray 62 Time Slots (7), Flexray 63
Content Introduction Layer 2: Frames Error Handling Media Access Control General approaches and terms Network Topologies Media Access Principles (Random) Aloha Principles CSMA, CSMA/CD, CSMA / CA Media Access Principles ( Deterministic) Master-Slave Approaches (Polling) Time based solutions Token based solutions (Token Ring) FDDI 64 Ring topology 65
Data passing When a station has information to transmit, it seizes the token and sends data frame to the next station. When frame reaches the destination station, the data is copied for processing. Frame continues to circle the ring until it returns to the sending station. Sending station removes the frame from the ring, verifies receipt, and releases the token. 66 Variants IBM developed the first Token Ring network in the 1970s. It is still IBM's primary LAN technology, and is second only to Ethernet (IEEE 802.3) in terms of LAN implementation. 67
Token-Ring frame format 68 Start delimiter and End delimiter Start delimiter. Alert for the arrival of a token. Includes an identification symbol. Violates encoding system to differentiate from other frame fields. End Delimiter Completes the token or data/command frame. Contains damage indicator. Last of logical sequence. 69
Access control P P P T M R R R P: Priority bits T: Token bit M: Monitor bit R: Reservation bits B'000' Normal User Priority B'001' Normal User Priority B'010' Normal User Priority B'011' Normal User priority B'100' Bridge/Router B'101' Reserved IBM B'110' Reserved IBM B'111' Station Management 70 Priority management Using the priority field and the reservation field. Stations with a higher priority can reserve the token for the next network pass. Stations that raise a token's priority level must reinstate the previous priority after their transmission has been completed. 71
Management mechanisms Active Monitor One station acts as centralized source of timing information for other stations. Removes continuously circulating frames by set monitor bit to 1. Start a token, when token have been lost. Beaconing Detects and repairs network faults. Initiates auto-reconfiguration. 77 Physical topology Physical topology : Star. Logical topology : Ring. IBM Token Ring network stations are connected to MSAU (Multi-Station Access Unit). Many MSAU can be wired together to form one large ring. 78
Content Introduction Layer 2: Frames Error Handling Media Access Control General approaches and terms Network Topologies Media Access Principles (Random) Aloha Principles CSMA, CSMA/CD, CSMA / CA Media Access Principles ( Deterministic) Master-Slave Approaches (Polling) Time based solutions Token based solutions (Token Ring) FDDI 79 Characteristics Fiber Distributed Data Interface. FDDI is popular as a campus backbone technology. 100 Mbps Token passing Dual-ring Fiber Optic Cable Total fiber length of 200Km Station distances up to 2Km 80
FDDI dual-ring (PR and SR) 81 FDDI Media Fiber Optic Single-mode, Laser (< 40Km) Multi-mode, LED (< 2Km) Multi-mode low cost, LED (< 500m) Twisted Pair Copper UTP, STP (< 100m) - CDDI 82
FDDI Connections Class A: connect directly with PR SR. DAC: Dual Attachment Concentrator DAS: Dual Attachment Station Class B: connect via FDDI concentrator. SAS: Single Attachment Station 84 Station Management (SMT) Defines the FDDI station configuration, enables stations to work together within the ring : Ring configuration Initialization Station insertion and removal Fault isolation and recovery Scheduling Collection of statistics 87
Types of traffic Synchronous traffic can consume a portion of the 100 Mbps total bandwidth of an FDDI network, while asynchronous traffic can consume the rest. Synchronous Mode: Allocated parts of the bandwidth to one or more workstations. Predictable response time. Asynchronous Mode: Priority scheme. 88 FDDI frame format 89
Preamble, Start and End delimiter Preamble. Prepares for the upcoming frame Start delimiter. Alert for the arrival of a token. Differentiate from other frame fields. End Delimiter Completes the frame. Contains damage indicator. 90 Operation mechanisms Connection Establishment Station connect to neighbors to form the ring. Negotiate the length of the link. Ring Initialization Station claim the right to generate a token. Steady-state Operation Token passing Ring Maintenance Detects and repairs token or network faults. 96