Outline. A variety of datalinks. The Origins X.25. Origins of the WAN type datalink. X.25 Network Model. Outline of HDLC (1)

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1 Outline A variety of datalinks Suguru Yamaguchi Nara Institute of Science and Technology Graduate School of Information Science A variety of datalinks WANX.25 LANMedia Access Control (MAC) Evolution of MAC ALOHA CSMA/CD, CSMA/CA Evolution of datalink I / 4 1 I / 4 2 The OriginsX.25 Origins of the WAN type datalink WAN: Wide Area Network Technology built at a time when LAN (Local Area Network) and WAN were connected through different technologies communication networks by telephone engineers Nowadays, almost extinct e.g., ISDN Approved as an international standard -T standard Layer 1 Layer 3 of the OSI reference model Network layer I / 4 3 I / 4 4 X.25 Network Model Outline of HDLC (1) DTE DCE PSN DTE: Data Terminal Equipment DCE: Data Circuit terminating Equipment PSE: Packet Switch Exchange PSN: Packet Switch Network PSE DCE DCE DTE DTE Datalink layer in X.25 Development based on SDLC (Synchronous Data Link HDLC High-speed Data Link Control protocol SDLC was internationally standardized by ITU-T/ISO ISO Standard 3309 LAPB Link Access Procedure B Datalink layer in CCITT X.25 HDLC subset I / 4 5 I / 4 6

2 Overview of HDLC (2) Still widely used nowadays even if it is an old protocol Employed in public data communication networks such as ISDN Existing online network e.g., online banking system X.21 is basically used as physical layer protocol Characteristics bit-oriented Permeability of data transfer based on bit-stuffing connection-oriented Requires datalink configuration/disconnection process Telephone networks HDLC frame (1) Address: identifies a communication station (terminal) Control: information for communication control Data: information to be transmitted Checksum: CRC-CCITT >= address Control Data Checksum I / 4 7 I / 4 8 HDLC frame (2) Frame types Information Frame Supervision Frame Unnumbered Frame HDLC frame (3) poll/final bit Poll bit is set to indicate a response is required Used when sending commands Final bit is set to indicate the last frame of the message Used when sending responses Information Frame Actual data transmission N(S) defines the frame sequence number - N(S): Sent frame sequence N(R): Received frame sequence P/F: Poll/Final bit S: Supervision bit M: Management bit I / 4 9 I / 4 10 HDLC frame (4) HDLC frame (4) Supervision Frame Control during datalink communication S bit type is as follows RR correctly received a frame with a sequence number smaller than N(R) requests the next frame RNR correctly received a frame with a sequence number smaller than N(R) notifies temporary impossibility to receive additional frames (e.g, due to buffer overflow, etc.) resumes communication by sending RR REJ did not correctly receive a frame with a sequence number bigger than N(R) retransmits frames from sequence number N(R) using Go-back-N SREJ correctly received a frame with a sequence number smaller than N(R) only the frame with sequence number N(R) is retransmitted by Selective- Repeat Unnumbered frame Used for datalink configuration/termination Many various modes A SNRM(B),P B UA(B),F (data transmission) DISC(B),P UA(B),F I / 4 11 I / 4 12

3 PPP (Point-to-Point Protocol) Not much different to HDLC Basic idea Technical term Frame format Address is fixed to IETF standard PPP over SONET/SDH 2-point connection in large-scale or long-distance >= address Control Proto Data Checksum HDLC & PPP technical components Frame synchronization bit stuffing Error detection / collection CRC-CCITT Frame retransmission ARQ: Go-back-N, selective-repeat Addressing 8bits Link management unnumbered frame I / 4 13 I / 4 14 LAN LAN with Medium Access Control Shared medium, multiple-access Shares a single physical transmission medium between several hosts How to use this shared medium? Medium Access Control MAC medium access I / 4 15 I / 4 16 Types of Medium Access Control Controlled Type Statistical multiplexing TDMA (Time Division Multiple Access) Circuit mode Token Passing Contention Type ALOHA, CSMA, CSMA/CD... TDMA (1) Time Division Multiple Access dividing the medium into different time slots A single frame is composed of N slots Terminal uses a specific slot Example Multiplexing digital private line Shares 1.5Mbps line to multiple devices Divides the medium in time slots (TDMA) Sells each 64Kbps-slot private line I / 4 17 I / 4 18

4 TDMA (2) TDMA (3) frame (N=8) Slot reservation and release Easy: Statistical multiplexing Assigned by administrator beforehand Dynamic assignment is complex Special function is necessary in terminals Time synchronization Slot is determined on a time basis Time synchronization between terminals and switching nodes is necessary terminal B terminal A I / 4 19 I / 4 20 DigressionFrom TDMA to ATM TDMA is a widely used medium access technology It is simple as it is multiplexing technology Can guarantee its performance TDMA is still used in many products Based on STM (Synchronous transfer mode) Synchronous networks were widely used until now TDMA has hardships to accommodate LAN traffic Unable to estimate bandwidth used by terminal beforehand Arrival of ATM Accepts LAN traffic Aims at performance using multiplexing like TDMA Asynchronous Transfer Mode Pure ALOHA (1) Contention type History Developed in the ALOHA System at the University of Hawaii Two wireless lines Terminal -> host uplink Host -> terminal Downlink Develops shared medium access for two wireless lines Methodology Each terminal runs independently Transmission as soon as a terminal has data to send In the case an ACK is not returned within the RTT (Round Trip Time), it is treated as a packet collision Back off process Generation of a random number in [0,K] : r Retransmission after r seconds I / 4 21 I / 4 22 Pure ALOHA (2) Each terminal autonomously accesses the medium Systematic order leads to a complexification of the system Frequent collisions cause performance degradation Increase of the number of access terminals Increase of the traffic load Back-off time K Affects communication performance slotted ALOHA Enhanced version of pure ALOHA Transmission time is divided into time slots Transmission from terminals is made to follow time slots Chaotic line access collision becomes slot contention Reduces occurrence of contention Improves performance Issue Time slot is difficult to implementtime synchronization Remains a theoretical model I / 4 23 I / 4 24

5 CSMA Carrier Sense Multiple Access Senses the medium to confirm whether it is used before transmission If the medium is not being used, data is transmitted ASAP Collision unfortunately occurs due to transmission delay If another terminal transmits a packet within RTT/2, collision occurs Time for the transmission spreads along the medium CSMA In case a carrier is detected 1-persistent CSMA p-persistent CSMA p non-persistent CSMA Run retransmission algorithm when a collision occurs In case a collision occurs Wait some time (randomly determined), sense the medium again I / 4 25 I / 4 26 CSMA/CD CSMA with Collision Detection Monitors frames during communication and detects collisions Stops transmission immediately upon detecting a collision Avoids occupying the disused line after collision occurred Retransmission Algorithm In Ethernet, the binary backoff algorithm is employed Once a collision happens, the backoff timer is set to twice its previous value Ethernet: unslotted 1-persistent CSMA/CD Token Passing Employed in (Token Bus), (Token Ring) FDDI is also a type of Token Passing (more complex) Method a token is passed around between nodes in a certain order a node with the token can communicate token holding timer Characteristics unlike contention type datalink, degradation is not enforced during high load periods for this reason, token bus and token ring are preferred I / 4 27 I / 4 28 Historical transition Slotted ALOHA Pure ALOHA CSMA Token Ring CSMA/CD (Ethernet) FDDI Summary Many methods have been proposed so far Methods still in operation nowadays are Unslotted 1-persistent CSMA/CD (Ethernet) Token Ring Considering performance CSMA/CD collapses Token Ring does not TDMA ATM I / 4 29 I / 4 30

6 Ethernet Ethernet (IEEE802.3 family) LAN technology based on CSMA/CD Standardized as IEEE Mbps, base-band transmission 1500octet MTU Designed and developed as bus type LAN Coaxial cable and Transceiver 10Base5, 10Base2 Emergence of 10BaseT technology using UTP cables Cabling in star topology Emerging hub and switch I / 4 31 I / 4 32 Fast Ethernet 100Mbps Ethernet Medium is UTP/CAT5 as well as optical fiber Direct switchover from 10 Mbps Ethernet environment Bidirectional 100BaseT Wider bandwith due to bidirectional data transmission Auto-sense / Auto-negotiation Connection type is automatically determined 10BaseT/100BaseT, Unidirectional / Bidirectional Interoperability Gigabit Ethernet (IEEE802.3z) 1Gbps Bidirectional data channel technology Half-channel is 1Gbps Full duplex Transmission medium is optical fiber 1000Base-SX (Short-wavelength), 1000Base-LX (Longwavelength) Most of the current products today obey IEEE802.3z standard Interoperability deployment is progressing steadily NICs altogether with switches are widespread I / 4 33 I / 4 34 Gigabit Ethernet (IEEE802.3ab) New Gigabit Ethernet standard 1000Base-T UTP 1Gbps Ethernet Maximum 100m Ethernet Family Strengths Rapid spread of Fast Ethernet Simple switchover from 10BaseT Many cheap products Substitute 10BaseT networks for Fast Ethernet Does not require special network management Plug-and-play Significant difference with ATM I / 4 35 I / 4 36

7 Comparison of Ethernet Technology 6 octet (48 bit) First three octets defined by IEEE, identify the vendor The following three octets are assigned by the vendor IEEE MAC address Assigned by IEEE Assigned by vendor 00 a0 cc 7c *IEEE half duplex/full duplex note: IEEE 802.3z I / 4 37 I / Gbps Ethernet IEEE802.3ae Standardized by IEEE in June 2002 Divided into WAN use and LAN use WAN PHY Using SONET frame Considering interoperability with SONET/SDH 300m, wavelength: 850nm 10km, wavelength: 1310nm 40km, wavelength: 1550nm LAN PHY Using Ethernet Frame 300m, wavelength: 850nm 10km, wavelength: 1310nm 40km, wavelength: 1550nm 10km, wavelength: 1310nm Introduced in the market in GBASE-LR serial (1310nm) 10GBASE-EX4(1550nm WWDM Transmission distance: 10Km 50Km 40Gbps/100Gbps Ethernet IEEE802.3ba In discussion at IEEE (July 2009) Goal: To support fast networks over 10Gbps Only supports full-duplex communication Preserves the current standard framesize Supports a transmission quality characterized by a BER (Bit Error Rate) better or equal to at the interface with upper layers Supports OTNOptical Transport Network) Provides physical layer specifications which support 40Gbps operation over: SMF >10km OM3 MMF >100m Copper cable assembly >7m Backplane >1m Provides physical layer specifications which support 100Gbps operation over: SMF >40km or >10km OM3 MMF >100m Copper cable assembly >7m I / I / 4 40 Furthermore 802.3an: 10GBASE-T Finished standardization in June 2006 Compliant with Ethernet cable category 6, 6A, and aq: 10BASE-LRM New 10 Gbps Ethernet standard for multi-mode fiber Further advances 40Gbps ethernet 100Gbps ethernet Advancing standardization process Requirements for datalink I / 4 41 I / 4 42

8 Development of datalink technologies Wide bandwidth Large scale Virtualization Coverage expansion Wide bandwidth Large scale Virtualization Coverage expansion Switched media Bridges VLAN Broadband wireless, residential access, etc. I / 4 43 I / 4 44 Wide bandwidth switched media High-bandwidth and commodity LAN Spread of Processor Interconnect Technology medium Shifting to switched media Confusing switched media and shared media carries out significant problems Failure of demonstration is caused by this access Non-blocking crossbar switch Shared media Wireless LAN Voice (MPEG2) (MotionJPEG) Switched media Ethernet Voice (MPEG2) (MotionJPEG) (D1) (HD D1) I / 4 45 I / 4 46 Large scale Bridges Compatibility between physical limitations and LAN convenience Coverage, capacity Wiring in floorcoax 100m Bridge basics: Transparent bridge Host is not aware of the bridge Transparent bridge No modification of MAC frame Promiscuous: capture all flowing packets Administrator builds the bridge forwarding table Transparent bridge 1 2 Wiring between buildingsoptical fiber 5km Fwd to 1 Fwd to 2 A, B, C, D E, F, G, H I / 4 47 I / 4 48

9 Learning bridge When a frame destined to an unknown MAC is received Forward to other ports (flooding) When a frame destined to a known MAC is received Forward to appropriate port Broadcast transmission Received by all active hosts in a same medium Loops in learning bridges Based on the previous algorithm, what would happen if A sends a frame to G? Construct a table with learning I / 4 49 I / 4 50 Spanning tree bridges Spanning tree 1D 3D 7D 2D 8D 4R 10R 6A 5D R: root port D: designated port 9D A: alternative port More various technologies VLAN Network virtualization Nowadays, VLAN is frequently used Single medium, multiple-network installation WDM MPLS I / 4 51 I / 4 52