LAN History Introduction,, IEEE 80, LLC Local Area Networks (LANs) Principles, Standards IEEE 80, Logical Link Control (LLC) Local Area Network (LAN), invented late 0`s initially designed for a common transmission medium shared media high speed Mbit/s, 0 Mbit/s, Mbit/s, 00 Mbit/s nowadays up to 0 Gbit/s limited distance up to some km hence local because of high speed no network elements with store and forward and no routing originally no packet switching on layer!!! note: Ethernet bridging / Ethernet switching invented as L packet switching technology in the late 80 s therefore simple topologies bus, ring, star LAN Principles, v. Agenda Introduction IEEE 80 Logical Link Control LAN History Local Area Network (LAN) all network stations share the same media all stations have equal rights no Master - Slave a station can directly communicate with all other stations of the same LAN basis for client - server computing basis for distributed computing high speed extension of internal computer bus LAN Principles, v. LAN Principles, v. Page 0 - Page 0 -
LAN Characteristics multipoint line access control necessary Media Access Control (MAC) addressing necessary MAC-Address unstructured addresses note: there were initially no routing requirements because store and forward (packet switching) done by CPUs was too slow! broadcast behaviour message sent out by one station reaches all other stations on same LAN layer and layer of the OSI model are sufficient to fulfil communication aspects on LAN MAC Addresses every station is identified by unique MAC-address used as source MACaddress in frames so called Burn-In Address (BIA) in case address is administered universally by IEEE MAC address Byte (8 bit) I/G (Individual/Group) bit 0 individual address group address U/L (Universal/Local) bit 0 universal administered local administered LAN Principles, v. LAN Principles, v. LAN Communication IEEE-MAC-Address Format computer A computer B computer C computer D I/G U/L b,...,b........., b, b0 destination address (8 bit) X U/L b,...,b........., b, b0 source address (8 bit) LAN = broadcast medium! I/G Individual / Group (only for DA): I/G = 0 individual address, I/G = group broadcast (broadcast for a group is called multicast) address with all bits set to... broadcast-address hex FFFF FFFF FFFF (note: U/L is set to ) U/L Universal / Local: U/L = 0 global address, administered by IEEE U/L = local administered address bit (x) not used for source address LAN Principles, v. LAN Principles, v. 8 Page 0 - Page 0 -
IEEE Administered Addresses (U/L = 0) 0 byte 0 byte byte byte byte byte vendor code (Organizational Unique Identifier OUI) serial number IEEE assigns each vendor of network components an unique vendor code (OUI, byte 0,, ) vendors use byte, and for numbering their network components (serial number) called Burned In Address (BIA) LAN Principles, v. 9 Receipt of frames () higher layers (-) will see a received frame only if destination MAC-address is equal to the station MACaddress if destination MAC-address of the frame is the all broadcast address if a multicast address was configured in the station and the destination MAC-address is equal to the configured to avoid interruption of all stations by broadcast frames frames are destined to station specific MAC-addresses during normal operation broadcast should be used in initialization phases of a network only LAN Principles, v. Receipt of frames () every frame is received by the Network Interface Card (NIC) of the station because of the inherent broadcast behaviour of a LAN the NIC decides if a frame should be forwarded to the higher layers (-) of a station depending on its BIA and the destination address of the frame usually NIC interrupts the CPU of the station if frame is to be forwarded otherwise frame is silently discarded by the NIC Direct Communication computer A computer B computer C computer D MAC A MAC B MAC C MAC D LAN Principles, v. 0 computer B (SA) -> computer C (DA) LAN Principles, v. Page 0 - Page 0 -
Broadcast computer A computer B computer C computer D MAC A MAC B MAC C MAC D Agenda Introduction IEEE 80 Logical Link Control computer B (SA) -> Broadcast (DA) LAN Principles, v. LAN Principles, v. Multicast computer A computer B computer C computer D MAC A+Group MAC B MAC C+Group MAC D IEEE 80 LAN Standardization is done by IEEE (Institute of Electrical and Electronics Engineers) workgroup 80 (February 980) OSI Data Link Layer (Layer ) was originally designed for point-to-point line but LAN = multipoint line, shared media therefore OSI Layer must be split into two sublayers Logical Link Control Media Access Control computer B (SA) -> Group (DA) LAN Principles, v. LAN Principles, v. Page 0 - Page 0-8
IEEE 80 versus OSI Tasks of LAN Layers 80. Management 80. CSMA/CD 80. Logical Link Control (LLC) Medium Access Control (MAC) 80. Token Bus 80. Token Ring PHY (MAU, AUI, PLS) 80. MAN DQDB Data Link Layer (OSI Layer ) Physical Layer (OSI Layer ) layer MAC (Media Access Control) takes care for medium access algorithms, framing, addressing and error detection avoid collisions grant fairness handle priority frames LLC (Logical Link Control) provides original services of data link layer connection-oriented services connection-less service SAPs (Service Access Points) for the higher layers LAN Principles, v. LAN Principles, v. 9 Tasks of LAN Layers The IEEE Working Groups layer physical layer (PHY) specifies actual transmission technique provides electrical/optical and mechanical interface encoding bit synchronisation consists of MAU (Medium Attachment Unit) AUI (Attachment Unit Interface) PLS (Physical Layer Signalling) LAN Principles, v. 8 80. Higher Layer LAN Protocols 80. Logical Link Control 80. Ethernet 80. Token Bus 80. Token Ring 80. Metropolitan Area Network (DQDB, MAN) 80. Broadband TAG 80.8 Fiber Optic TAG 80.9 Isochronous LAN (VGAnyLAN) 80.0 Security 80. Wireless LAN (WLAN) 80. Demand Priority 80. Not Used 80. Cable Modem 80. Wireless Personal Area Network (Bluetooth) 80. Broadband Wireless Access 80. Resilient Packet Ring LAN Principles, v. 0 Page 0-9 Page 0-0
IEEE 80.x Standards IEEE 80. LLC (Logical Link Control) IEEE 80. CSMA/CD, Ethernet IEEE 80. Token-Bus IEEE 80. Token-Ring IEEE 80. DQDB (Distributed Queued Dual Bus) for MAN (Metropolitan Area Network) LAN Principles, v. IEEE 80. Standards IEEE 80. specifies a common framework for all 80.x LANs addressing rules, relations to the OSI model subnet addressing, Bridging Ethernetv to 80. LANs Management (80.B) Bridging (80.D) including STP (Spanning Tree Protocol) Single STP in case of VLANs System Load Protocol (80.E) Virtual (V) LANs (80.Q) Tagging STP Rapid Configuration (80.w) Multiple STP (80.w) Multiple STP instances in case of VLANs EAP Authentication (80.x) Extensible Authentication Protocol LAN Principles, v. IEEE 80.x Standards IEEE 80.0 Interoperable LAN/MAN Security IEEE 80. Wireless LAN IEEE 80. Demand Priority Access Method, VGAnyLan IEEE 80. Wireless Personal Area Networks, Bluetooth IEEE 80. Fixed Broadband Wireless Access IEEE 80. Resilient Packet Ring LAN Principles, v. Agenda Introduction IEEE 80 Logical Link Control LAN Principles, v. Page 0 - Page 0 -
LAN Framing with LLC every data block is encapsulated in a L LAN frame L LAN frame consists of MAC header followed by LLC in case of IEEE 80 LAN MAC trailer MAC header and trailer are LAN type specific L L L-L MAC header LLC header DATA MAC trailer L DSAP and SSAP a IEEE 80 LAN can be used by different protocol families sharing the same communication media e.g. TCP/IP parallel to Novell IPX, IBM SNA, NetBeui, Appletalk DSAP and SSAP identify the higher level protocol family, which is the destination and the source of the given frame protocol type or protocol stack identifier Media Access Control, MAC Addresses Checksum, Frame Status LAN Principles, v. LAN Principles, v. LLC Header LLC header is appended to higher layer data DSAP (Destination Service Access Point), 8 bit SSAP (Source Service Access Point), 8 bit Control Field, 8 or bit Protocol Stack Distinction computer B computer C TCP/IP Novell TCP/IP Novell Application Application Application Application TCP SPX TCP SPX IP IPX IP IPX SSAP = 0 SSAP = E0 DSAP = 0 DSAP = E0 LLC L-L MAC header DSAP SSAP Control DATA MAC trailer MAC B SA B DA C SSAP E0 DSAP E0 MAC C SA B DA C SSAP 0 DSAP 0 LAN Principles, v. LAN Principles, v. 8 Page 0 - Page 0 -
DSAP and SSAP structure Values for DSAP / SSAP 0 8 DDDDDD U I/G SSSSSS U C/R DSAP I / G = 0... Individual DSAP I / G =... Group DSAP SSAP C/ R = 0... Command C/ R =... Response U = 0... user defined U =... IEEE defined examples (cont.): Hex E0... Novell (U=0) Hex Fy... reserved for IBM (U=0) Hex F0... NetBIOS (U=0) Hex F... IBM LAN manager individual (U=0) Hex F... IBM LAN manager group (U=0, I/G =) Hex F8... remote program load (U=0) Hex 0... SNA path control individual (U=0) Hex 0... SNA path control group (U=0, I/G =) range Hex 8y to 9C (with U=0) is reserved for free usage except y = xxx (binary notation); U= LAN Principles, v. 9 LAN Principles, v. Values for DSAP / SSAP 8 values possible for I/G = 0 are reserved for IEEE protocols (U =) for vendor specific protocols and for free usage (U = 0) examples: Hex 00... Null SAP station with running LLC software always responds to a frame destined to the Null SAP -> LLC Ping can be implemented Hex 0... LLC sub-layer group management (U=, I/G=) Hex 0... DoD IP (U=) Hex... 80.d Spanning Tree Protocol (U=) Hex AA... TCP/IP SNAP (U=) Hex FE... ISO Network Layer (U=) LLC Control Field LLC Control field and protocol procedures are very similar to HDLC remember: HDLC procedures allow connection-less and connection-oriented services on a layer link connection-less mode of LLC is used by IP, IPX, AppleTalk, etc connection-oriented mode of LLC is used by SNA over LLC Type NetBIOS over LLC Type (NetBeui) e.g. Microsoft Network (old style already obsoleted) LAN Principles, v. 0 LAN Principles, v. Page 0 - Page 0 -
LLC Control Field four service methods defined for LANs Class : connectionless unacknowledged service (datagram) type - frames: UI,XID,TEST Class : connection oriented service plus Class type - frames: I,RR,RNR,REJ, SABME,UA,DM Class : Class plus connectionless acknowledged service type -frames plus additional type - frames: AC0, AC Class : Class plus connectionless acknowledged service type - frames plus additional type - frames: AC0, AC LAN Principles, v. Frame Types and Classes Type Type Type Cmd UI XID TEST I RR RNR REJ SABME DISC AC0 AC Control 00p000 p 00p 0 n(s) p n(r) 0000000 p n(r) 000000 p n(r) 000000 p n(r) p0 00p00 0p0 0p Resp XID TEST I RR RNR REJ UA DM FRMR AC0 AC Control f 00f 0 n(s) f n(r) 0000000 f n(r) 000000 f n(r) 000000 f n(r) 00f0 f00 0f00 0f0 0f Class LAN Principles, v. LLC Control Field 0... 8 9 0... 0 N(S) 0 S S x P/F P/F N(R) N(R) I - format (Information) S - format (Supervisory) 0 M M P/F M M M U - format (Unnumbered) N(S), N(R)... send- and receive - sequence numbers S S, MMM... selection bits for several functions P / F... poll / final bit ( P in commands, F in responses; distinction of commands and responses through a dedicated SSAP bit -> C/R bit) LLC Procedures and Service Types Datagram Service UI (Unnumbered Information) -> Datagram Info XID (Exchange Identification) -> LLC Ping TEST -> Ping plus test data Connection Oriented Service SABME (Set Asynchronous Balanced Mode Ext.) connection establishment UA (Unnumbered Acknowledgement) connection establishment acknowledgement DM (Disconnected Mode) negative acknowledgement for connection establishment or connection abort DISC (Disconnect) connection tear down LAN Principles, v. LAN Principles, v. Page 0 - Page 0-8
LLC Procedures and Service Types I (Information) data frame RR (Receiver Ready) ACK plus station ready RNR (Rec. Not Ready) ACK plus station not ready REJ (Reject) NACK with GoBackN FRMR (Frame Reject) for signalling error situations Acknowledged Datagram-Service ACx command with data immediately acknowledged by ACx response, next ACy command only after arrival of ACx Idle RQ protocol (stop and wait) LAN Principles, v. LAN Framing with Ethernetv every data block is encapsulated in an Ethernetv LAN frame most common framing used today only connectionless service possible on layer LAN frame consists of Ethernet MAC header Protocol stack identified by protocol type field in MAC header Ethernet MAC trailer L-L Ethernet MAC header DATA MAC trailer MAC Addresses, protocol type Checksum LAN Principles, v. 8 Page 0-9