COMP312

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COMP312

  1. 1. OSI Protocol Model 7. Application Local Area Networks 6. Presentation COMP312 5. Session Richard Nelson richardn@cs.waikato.ac.nz 4. Transport http://www.cs.waikato.ac.nz 3. Network Department of Computer Science University of Waikato 2. Link LANs are L2 networks 1. Physical COMP312 - Local Area Networks – p. 1/58 COMP312 - Local Area Networks – p. 2/58 Lecture Outline Protocols and Standards • Protocols and Standards. • LAN Protocols. • Hubs, Bridges and Switches • LAN Standards. • Modern Ethernet. • Ethernet Frame Format. COMP312 - Local Area Networks – p. 3/58 COMP312 - Local Area Networks – p. 4/58
  2. 2. LAN Protocols LAN Framing Data Network Header Network Data LLC Header LLC Data 1. Physical MAC Header MAC Data COMP312 - Local Area Networks – p. 5/58 COMP312 - Local Area Networks – p. 6/58 IEEE 802.2 LAN Standards • Most MAC Layers provide and unreliable Datagram service • IEEE 802.2 provides a link layer service based on HDLC • Most LAN Standards are set by the IEEE • There are three classes of service • Most LANs started outside the IEEE in industry or academia but ◦ Unacknowledged connectionless-mode service only. later got taken to the IEEE ◦ Connection-mode service plus service • The IEEE 802 committee is responsible for LANs. ◦ Acknowledged connectionless service • 802.2 Also provides ◦ Addressing. ◦ Service Access Points • 802.2 Uses Sliding Window flow control and Go-Back-N ARQ error control Return to Section ToC COMP312 - Local Area Networks – p. 7/58 COMP312 - Local Area Networks – p. 8/58
  3. 3. IEEE 802 Standards IEEE 802 Standards IEEE Number Name 802.1 Bridging and Management 802.2 Logical Link Control 802.2 Logical Link Control 802.3 CSMA/CD - Ethernet Data 802.4 Token Bus - ARCNet Link 802.1 Bridging Layer 802.5 Token Ring 802.6 MANs - DQDB 802.3 802.4 802.5 802.6 802.11 802.12 802.15 802.16 CSMA/CD Token Bus Token Ring DQDB W−LAN DPA W−PAN WB−MAN 802.10 Security 802.11 Wireless LANs Physical 802.3 802.4 802.5 802.6 802.11 802.12 802.15 802.16 Layer 802.12 Demand Priority Access PHY PHY PHY PHY PHY PHY PHY PHY 802.15 PANs (Bluetooth) Return to Section ToC 802.16 Broadband Wireless MANs 802.17 Resilient Packet Ring 802.20 Mobile Broadband Access COMP312 - Local Area Networks – p. 9/58 COMP312 - Local Area Networks – p. 10/58 Ethernet Frame Format Ethernet (802.2) Addresses There are four different Ethernet frame formats • Addresses are six bytes long, Normally written as hyphenated hex e.g. AB-CD-EF-12-34-56. 1. Ethernet Version II. This is from the original Ethernet specification • The first three bytes are an IEEE assigned Organizationally released by Xerox, Intel and DEC. Unique Identifier (OUI) 2. Novell Proprietary ("802.3 Raw"). This format was used by Novell • The second three bytes are assigned by the manufacturer. Netware and was based on an early version of the 802.3 specification. • Properly assigned addresses are globally unique. 3. 802.3. The 802.3 standard specifies a header that includes the • Some hardware allows manually assigned addresses. 802.2 LLC fields. • Destination address of all ones is the broadcast address. 4. 802.3 SNAP. This provides an extended header that allows • Some addresses are reserved for multicast applications (normally backwards compatibility with the original Version II header. specific addresses are assigned for specific protocols). COMP312 - Local Area Networks – p. 11/58 COMP312 - Local Area Networks – p. 12/58
  4. 4. Ethernet Version II Novell Proprietary Dst Src Etype Data FCS Dst Src Length Data FCS • Dst: Destination Address - 6 bytes. • Dst: Destination Address - 6 bytes. • Src: Source Address - 6 bytes. • Src: Source Address - 6 bytes. • Ethertype: Specifies the protocol being carried within the data section. Used for • Length: The length of the entire frame not including the preamble or CRC - 2 bytes. multiplexing protocols. Ethertypes are all greater than 1536 and are assigned by • Data: Variable length payload. Netware Packets always start with 0xFFFF. Must be Xerox- 2 bytes. padded if less than the minimum length - 46-1500 bytes. • Data: Variable length payload. Must be padded if less than the minimum length - • FCS - Frame Check Sequence used for CRC - 4 bytes. 46-1500 bytes. • FCS - Frame Check Sequence used for CRC - 4 bytes. COMP312 - Local Area Networks – p. 13/58 COMP312 - Local Area Networks – p. 14/58 802.3 802.3 SNAP 802.2 LLC Header 802.2 LLC Header Dst Src Length DSAPSSAP Ctrl Data FCS Dst Src Length DSAPSSAP Ctrl SNAP Data FCS • DSAP: Destination Service Access Point. References the process associated with • SNAP: SubNetwork Access Protocol - 5 bytes. The first three bytes carry the the protocol of data section of the packet at the receiving station - 1 byte. Organisation Unique Identifier and are usually the same as the first three bytes of • SSAP: Source Service Access Point. References the process associated with the the source address. The last two bytes carry a protocol identifier that is usually an protocol of data section of the packet at the sending station - 1 byte. Ethertype. • Ctrl: Specifies the type of packet as used by the LLC protocol. May be Informational, Control or Data. 04 - IBM SNA 06 - IP 80 - 3Com AA - SNAP Common DSAP/SSAP values include: BC - Banyan E0 - Novell F4 - Lan Manager COMP312 - Local Area Networks – p. 15/58 COMP312 - Local Area Networks – p. 16/58
  5. 5. Protocols and Standards - Summary Hubs, Bridges and Switches • The IEEE has separated Link Layer functions from Media Access • This makes all IEEE standard LANs compatible in terms of the • Hubs. services they offer. • Bridges. • The Ethernet Frame format has evolved as the standard has • Switches. progressed. Return to Section ToC Return to ToC COMP312 - Local Area Networks – p. 17/58 COMP312 - Local Area Networks – p. 18/58 Hubs Broadcast Bus • A hub is a collapsed broadcast bus. • stations connected to hubs must run CSMA/CD. • Hubs are normally used with UTP wiring and provide digital regeneration of the signal. • Stations connected to hubs see all packets and select those with addresses that are of interest. A B C D COMP312 - Local Area Networks – p. 19/58 COMP312 - Local Area Networks – p. 20/58
  6. 6. Hub Bridges • Bridges are intelligent repeaters. They forward packets without changing them. • Bridges are Layer 2 devices so they are transparent to end stations. • Identical L2 protocols are required on both sides of a bridge (may be LLC identical). • They divide up collision domains so CSMA/CD runs either side of a bridge, but not across it. A B C D • Bridges can buffer packets to ensure they are not lost without the original transmitter knowing. COMP312 - Local Area Networks – p. 21/58 COMP312 - Local Area Networks – p. 22/58 Bridge Advantages Bridge • LAN coverage by increasing the distance that packets can cover. • Performance by reducing collision domain size and so lowering the rate of collisions. • Throughput and security by not forwarding packets that do not need to be forwarded. • Bridges may be used to connect incompatible media (e.g. coax to UTP) or even networks that are use incompatible MACs, but compatible LLC layers (e.g. WLANs are normally bridged to Ethernet networks). • Bridges may be used to connect remote networks using a wide area link. • Collision Detection does not work on fibre optic links so they have to be point to point links and bridged to the rest of the network. A B C D COMP312 - Local Area Networks – p. 23/58 COMP312 - Local Area Networks – p. 24/58
  7. 7. Loops Spanning Tree • Loops may be formed with multiple bridges on a LAN segments • A spanning tree is a subset of the bridge topology that: ◦ Deliberately for redundancy. ◦ Covers the entire network (spanning), ◦ Accidentally through misconfiguration. ◦ Includes no loops (tree). • This can cause significant problems • Spanning Tree works by: ◦ Multiple copies of packets ◦ Bridges exchange topology information using specific bridge ◦ Bridges learning the wrong location of stations and not topology packets and a multicast address, forwarding packets ◦ A root bridge is elected, ◦ Cascading multiplication of packets ◦ Bridges then caculate their path cost to the root bridge, ◦ A designated bridge is elected to each lan segment, ◦ Redundant bridge interfaces are set to not forward packets. • Changes in link costs or link availability result in re-calculation of the spanning tree. COMP312 - Local Area Networks – p. 25/58 COMP312 - Local Area Networks – p. 26/58 Spanning Tree Switches • Switches are multiport bridges. ◦ Each port is regarded as a separate LAN segment. ◦ They perform MAC learning ◦ They participate in spanning tree calculations • Forwarding speed is not limited by the segment speed. • Different ports may run at different speeds • Ports that have only one device attached may send and receive simultaneously, i.e. full duplex. • The main disadvantage of switches over hubs is traditionally cost but this is now much less significant than it used to be. COMP312 - Local Area Networks – p. 27/58 COMP312 - Local Area Networks – p. 28/58
  8. 8. Switch Switch Buffering A B C D • Switches and bridges can buffer packets that cannot be immediately sent to a segment. ◦ The receiving segment is busy or experiencing collisions. ◦ The sending segment runs at a higher speed than the receiving segment. ◦ Multiple segments are sending packets to the same receiving segment. A B C D COMP312 - Local Area Networks – p. 29/58 COMP312 - Local Area Networks – p. 30/58 Switch Buffering -2 Autonegotiation • It is possible that the buffering requirements may exceed the • Switches may be connected to devices of varying speeds. memory of the switch. • UTP Ethernet uses the same connector for 10Mbps, 100Mbps, • The switch can respond in various ways 1000Mbps ◦ Do Nothing; assume higher layer flow/error control will • 10Mbps UTP Ethernet sends a half pulse every 16ms to verify the respond. link status, called Normal Link Pulse - NLP. Reception of this ◦ Backpressure; Cause collisions on the sending segments to pulse causes the link status LED to light on a NIC and above a slow down the sender. switch port . ◦ Flow control; uses special Pause 802.3x Mac Control Frame to tell senders to stop sending for a short period of time. NLP 16ms COMP312 - Local Area Networks – p. 31/58 COMP312 - Local Area Networks – p. 32/58
  9. 9. Autonegotiation - 2 Autonegotiation - 3 • 100Mbps and 1000Mbps send multiple clock and data pulses at 2ms burst the same time intervals, called Fast Link Pulse - FLP. of 33 pulses • The clock signals are used to determine the speed capability of the communicating entities. FLP • The data pulses contain information describing the device 16ms capabilities (e.g. full duplex). • The link speed defaults to the lowest capability level of the two stations. • Autoconfiguration is useful to decrease the chance of user mis-configuration. data data data data data i 2 3 4 16 clock clock clock clock clock 1 2 3 4 16 Return to Section ToC COMP312 - Local Area Networks – p. 33/58 COMP312 - Local Area Networks – p. 34/58 Hubs Bridges and Switches - Summary Modern Ethernet • Hubs are compressed busses used to allow star wiring (UTP). • Bridges break up collision domains and extend LANs. • Speeds. • Bridges use spanning tree routing to break up loops. • VLANS. • Switches are multiport bridges. • Other Features. Return to Section ToC Return to ToC COMP312 - Local Area Networks – p. 35/58 COMP312 - Local Area Networks – p. 36/58
  10. 10. Speeds Modern Ethernet Timeline Ethernet has rapidly increased in speeds • 1973 - Original experimental Ethernet at Xerox PARC - 3Mbps • 1980 - DEC, Intel, Xerox (DIX) Ethernet - 10Mbps • 1982 - Ethernet II (DIX v2.0) - 10 Mbps • 1985 - IEEE 802.3 CSMA/CD - 10Mbps • 1995 - IEEE 802.3u Fast Ethernet - 100Mbps • 1998 - IEEE 802.3z - Gigabit Ethernet • 2002 - IEEE 802.3ae - 10 Gigabit Ethernet COMP312 - Local Area Networks – p. 37/58 COMP312 - Local Area Networks – p. 38/58 Thick Ethernet (10base5) Thick Ethernet (10base5) COMP312 - Local Area Networks – p. 39/58 COMP312 - Local Area Networks – p. 40/58
  11. 11. Thin Ethernet (10base2) UTP Ethernet COMP312 - Local Area Networks – p. 41/58 COMP312 - Local Area Networks – p. 42/58 Fibre Optic Ethernet Ethernet Physical Layers Medium Signaling Topology Max Segment Nodes 10Base5 10mm 50 ohm Coax Manchester Bus 500m 100 10Base2 5mm 50 ohm Coax Mancheter Bus 185m 30 10BaseT UTP Manchester Star 100m 2 10BaseF Fiber Manchester Star 500m 2 100BaseTX (UTP) UTP 4B5B MLT−3 Star 100m 2 100BaseFX Fiber 4B5B NRZI Star 100m 2 1000BaseT UTP PAM5x5 Star 100m 2 1000BaseSX 50micron Fiber 8B10B Star 550m 2 1000BaseSX 62.5micron Fiber 8B10B Star 275m 2 1000BaseLX 50/72.5micron Fiber 8B10B Star 550m 2 1000BaseLX 9micron Fiber 8B10B Star 5000m 2 1000BaseLH ~9micron Fiber 8B10B Star 50~100km 2 COMP312 - Local Area Networks – p. 43/58 COMP312 - Local Area Networks – p. 44/58
  12. 12. MLT3 Line Coding Block Coding • Used with NRZI or MLT3 coding MLT−3 • Ensures that there are always several 1s in a block. • Ensure transitions for synchronisation. • 4B5B 4bits coded as five. 1 0 0 1 1 1 1 0 0 0 0 1 0 1 1 1 0 1 1 0 1 1 1 0 • 8B10B 8 bits coded as 10 -gives better DC balance. • Three level code - transition on 1, not on 0. • Lower bandwidth than NRZI - less crosstalk COMP312 - Local Area Networks – p. 45/58 COMP312 - Local Area Networks – p. 46/58 4B5B Block Coding 10 Gigabit Ethernet Physical Layers 4B5B Ten Gigabit Ethernet has many different physical layer options. Most 0000 11110 11111 idle are optical, but differences arise due to: 0001 01001 11000 delimiter • The length of the link may be from 2 m to 40 km or more. 0010 10100 10001 delimiter 0011 10101 01101 delimiter • The type of fibre and its characteristics: multimode/ singlemode, 0100 01010 00111 delimiter dispersion shifted etc. 0101 01011 00100 transmit error • The wavelength of the laser used. 0110 01110 other invalid • Whether a 10Gb/s LAN interface is required or a 9.9532Gb/s SDH 0111 01111 compatible WAN interface. 1000 10010 1001 10011 Copper interface was added to the 10GB specification in Feb 2004. It 1010 10110 requires special shielded cable and connectors and has a maximum 1011 10111 distance of 15m. 1100 11010 Return to Section ToC 1101 11011 1110 11100 1111 11101 COMP312 - Local Area Networks – p. 47/58 COMP312 - Local Area Networks – p. 48/58
  13. 13. Virtual LANs VLAN Concept • The logical and physical structure of an organisation are not always the same. • Dividing a network according to the logical organisation may have security and performance advantages through traffic localisation. • Virtual LANs (VLANs) allow a single physical network to be subdivided arbitrarily into multiple virtual networks. • Packets are tagged according to which VLAN they belong to. • Switches maintain separate forwarding tables for separate VLANs and will not forward packets from one VLAN to another COMP312 - Local Area Networks – p. 49/58 COMP312 - Local Area Networks – p. 50/58 Virtual LAN Tags VLAN Tagging • There is no support for VLANs in any standard Ethernet header VLAN Header type. routing dest src proto = Tag Control type information data CRC • A new extension header IEEE 802.1Q has been defined that adds 0x8100 (optional) VLAN information. 6 6 2 2 2 2−30 4 octets • Normally this runs only between switches although newer priority CFI reserved VLAN ID interface cards may add VLAN support. 3 1 4 8 bits • Packets may be assigned to a VLAN in three different ways: CFI indicated if routing data is present ◦ A switch port may be assigned to a VLAN. Return to Section ToC ◦ MAC addresses may be assigned to specific VLANs. ◦ Layer 3 protocols or IP addresses may be assigned to specific VLANs. COMP312 - Local Area Networks – p. 51/58 COMP312 - Local Area Networks – p. 52/58
  14. 14. Other Features Link Aggregation • Link aggregation is combining multiple switched links to appear as • Link Aggregation a single high speed link. • Packet Priority • Can be used to provide redundancy on a network connection. • Management • Proprietry solutions offered for several years, then standardised asIEEE 802.3ad in 1999. • Used for switch to switch links and also server-switch links. • Tends to become redundant as higher speed Ethernet becomes available at reasonable prices. COMP312 - Local Area Networks – p. 53/58 COMP312 - Local Area Networks – p. 54/58 Packet Priority Management • Standardised by the IEEE as 802.1p. • Many of the features of switches need some management control • Uses three priority bits of VLAN header. to set up (e.g. VLANs). • Indicates a relative priority. • Switches can count traffic and provide usage statistics. • Higher priority packets are transmitted first. • Large networks may have hundreds of switches. • Lower priority packets are dropped first. • Most large equipment vendors provide some form switch management. • At low loads there may be no packets in a switch buffer so it has • There are some standards e.g. SNMP. no effect. • Priorities may be assigned by switches the same way VLAN • Support for proprietry management systems is sometimes added, membership is. e.g. Cisco. • Priorities may be assigned by stations if they support 802.1Q • Often a simple telnet interface and a web based interface is headers. provided. • The standard has no admission control so it provides relative service classification, but not strict service quality levels. COMP312 - Local Area Networks – p. 55/58 COMP312 - Local Area Networks – p. 56/58
  15. 15. Layer 3 Switches Modern Ethernet - Summary • Although bridges and switches break up collision domains, they • Ethernet is now a switched network technology: for most links only do not break up broadcast domains. the frame format is the same as the original 802.3 specifications. • Traditional LAN protocols (e.g. Netware, Netbios) often use • Ethernet speeds have grown 1000x since the original broadcast extensively. specifications. • Every broadcast packet must be forwarded to every node on the • Ethernet links are limited in distance only by the choice of LAN so the load grows as the square of the number of packets. transmission technology and can span hundreds of kilometers. • Dividing Layer 2 broadcast domains requires Layer 3 devices; • Ethernet switches have sophisticated features to manage packet routers in IP terminology. flows, priorities and security. • Traditional routers use general purpose CPUs running UNIX and Return to Section ToC Return to ToC are much slower than hardware based Ethernet switches. • The solution is to implement some Layer 3 (IP) functions in switch circuits. • Such devices are called Layer 3 switches. COMP312 - Local Area Networks – p. 57/58 COMP312 - Local Area Networks – p. 58/58

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