This Lecture. BUS Computer Facilities Network Management X.25. X.25 Packet Switch. Wide Area Network (WAN) Technologies. X.

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1 This ecture BUS350 - Computer Facilities Network Management Wide rea Network (WN) Technologies. X.5 Frame Relay TM Faculty of Information Technology Monash University Faculty of Information Technology Faculty of Information Technology X.5 X.5 Packet Switch User data and X.5 protocol control information: User data Packet switching Wide rea Network (WN) developed by the ITU-T. Issued in 976 and revised in 980, 98, 988, and 99. Describes the procedures for establishing, maintaining, and terminating connections. Virtual circuit (VC) approach to packet switching. VC setup and clearing messages in the same channel as data. Three layer protocol (Third layer for multiplexing). Flow control and error control between each node in the network. 3 Faculty of Information Technology Packet level: ink level: level: PB header ayer 3 header level - X. - similar to RS3C. ink access level - P-B - a subset of HDC PB trailer Provides reliable transfer of data across the physical layer. Packet level - provides Virtual Circuit (VC) Enables a user to set up a logical connection. X.5 packet PB frame Faculty of Information Technology

2 Packet Switch Operation X.5 imitations dd packet dd packet Store Store Network ayer Network ayer Route Route Route Route Route Route dd frame dd frame Terminal Store Store Error control Error control Remove frame Remove frame dd frame dd frame Error control Remove packet ink ayer ink ayer 5 Terminal Faculty of Information Host Technology (a) Packet switching (a) Packet switching Store Store Frame Relay Operation Error control ayer ayer Remove packet Remove frame Remove frame Host X.5 results in considerable overhead: Includes extensive error checking and flow control. Call control packets are carried on the same channel and same VC as data packets. Multiplexing of VC takes place at layer 3. t each intermediate node, state tables must be maintained for each VC for call management. Overhead reduces channel capacity that can be otherwise used for transmitting data. Overhead justified when significant probability of error exits in transmission links. Today s digital transmission is more reliable. 6 Faculty of Information Technology Frame Relay dd frame dd frame Route Route Route Route Route Route Remove frame Remove frame ink ayer ink ayer ayer ayer N Host N Host (b) Frame relay (b) Frame relay Figure. Packet Switching and Frame Relay Operation Figure. Packet Switching and Frame Relay Operation 7 Faculty of Information Technology Higher data rates at lower cost. Support for bursty data. ess overhead due to improved transmission media. 8 Faculty of Information Technology

3 Frame Relay Frame Relay: Virtual Circuits X.5 simplified. No hop by hop flow and error control between nodes. End-to-end flow and error control (if used) done using higher layers. Two layers (multiplexing in the second layer). X.5 Switching versus Frame Relay: Switching = Relaying + ck + Flow control + Error recovery + oss recovery Relay = Unreliable multiplexing service. llows for higher speeds than X.5 (.5 Mbps.376 Mbps). Varying delay not suitable for real-time voice or video. 9 Faculty of Information Technology Frame Relay transmission is based on virtual circuit (VC) connections. Permanent Virtual Circuits (PVC): Network provider No call set up Switched Virtual Circuits (SVC): Setup on request Release on completion. 0 Faculty of Information Technology Data ink Control Identifier (DCI) Virtual Channel Identifier (VCI) Example Used to identify the virtual circuits (form of VCI). llows multiple logical connections over one circuit. Only local significance (unique for a particular interface). Faculty of Information Technology Faculty of Information Technology

4 Virtual Channel Identifier (VCI) Example TM Design Goals VOICE VOICE TM Network DT VIDEO VOICE DT DT VIDEO VIDEO 3 Faculty of Information Technology The ultimate integrated services network. Move cells with low delay and low delay variation at high speeds. Devices at ends translate between cells and original traffic. Faculty of Information Technology Packet and Cell Networks TM Cell Size Modern data communications is based on packet switching and packet networks. Packet: self-contained network entity combining data and overhead bits. Overheads contain identification, addressing, routing, flow control, error control, etc. Vary in size: trade-off between header size (network complexity) and data size. arge packets create significant delay for smaller packets (last week). Cell: small data unit of fixed size used as the basic unit of data exchange. arge packets segmented into cells: reduce delay and approximate continuous streams. Known size and format makes switching and multiplexing more efficient (hardware). X Z Y X X C Z B Y X C B MUX C B MUX Fixed size: 5 octet header and 8 octet information field. Small cells reduce queueing delay for high priority cells. Small cells can be switched more efficiently (hardware). Cell size comes from a compromise between Europe (required low delay to prevent echo) and US (desired efficiency). % Overhead Overhead Payload (bytes) Delay Delay (ms) Multiplexing using different packet sizes Multiplexing using cells 5 Faculty of Information Technology Compromise reached (ITU-TS SG-8 June 89) Percent overhead and delay for 6 kbps voice. 6 Faculty of Information Technology

5 TM Protocol Reference Model TM Plane-ayer Three separate planes - User plane: Provides for user information transfer. Control plane: Call and connection control. Management plane: Plane management: Whole system functions. ayer management: Resources and parameters in protocol entities. TM Control Plane Higher ayer TM daptation ayer () TM ayer ayer Management Plane User Plane TM Protocol rchitecture 7 Faculty of Information Technology TM TM ayer Management Plane Management TM ayer ayer ayer Name Higher ayers Sublayer (CS) SR Sublayer TM ayer Transmission (TC) ayer Medium (PM) Functions Performed Higher ayer Functions Common Part (CP) Service Specific (SS) Segmentation and Reassembly Generic Flow Control Cell Header Generation/Extraction Cell VCI/VPI Translation Cell Multiplexing/Demultiplexing Cell Rate Decoupling Cell Delineation Transmission Frame daptation Transmission Frame generation/recovery Bit Timing Medium 8 Faculty of Information Technology ayer Management TM ogical Connections TM ogical Connections Connection between two end points is accomplished through: Transmission paths (TP): physical connections between switches and end points. Virtual paths (VP): provides a set of connections between two switches. Virtual channel (VC): basic unit of switching where all cells in a message follow the same VC and are delivered in the order they are sent (connection oriented). virtual path is a bunch of virtual channels with the same end points that are switched transparently across the TM network. Virtual channel connections (VCC). nalogous to a virtual circuit in X.5; basic unit of switching. Between two end users with variable-rate, full-duplex, fixed-size and ordered flow of cells. Used for: user-user data, user-network exchange (control signalling) and network-network exchange (network management and routing). Include Quality of Service (QoS): parameters including cell loss ratio and cell delay variation. Virtual path connection (VPC): Bundle of VCC with same end points (reduce control cost). 9 Faculty of Information Technology 0 Faculty of Information Technology

6 . TM ogical Connections Example of VPs and VCs UNI End points NNI Switch NNI Switch NNI Switch 3 Switch UNI End points VCs VP VP VP VP 3 VCs UNI VCs UNI: user to network interface NNI: network to network interface Virtual Channels End points Virtual Path Transmission Path Faculty of Information Technology Eight points communicating using four virtual channels. First two VCs share the same path from switch to switch 3: combine into a VP. Remaining two VCs share a virtual path from switch to switch. Switch only needs to worry about switching based on virtual paths. Faculty of Information Technology dvantages of Virtual Paths Figure. TM Connection Relationships Call Establishment Using Virtual Paths Simplified network architecture. Individual logical connection (virtual channel) and a group of logical connections (virtual paths). Increased network performance and reliability. Network deals with fewer aggregated entities. Reduced processing and short connection setup time. Much of the work with virtual path set up. Reserving capacity on a virtual path for new virtual channels. Minimal processing for a new virtual channel to an existing virtual path. Enhanced network services. User may define closed user groups or closed network of virtual channel bundles. 3 Faculty of Information Technology Request for VCC Originates VPC Exists? No Establish a New VPC Yes Make Connection Faculty of Information Technology Yes Can Quality of Service be Satisfied? No Block VCC or Request More Capacity Yes Request Granted? No Reject VCC Request

7 . Identifiers and Switches Representation of VP and VC Switching Hierarchy Virtual connections need identification to route data between end points. VC switch/cross connect Two levels: virtual path identifier (VPI) and virtual channel identifier (VCI). endpoint of VPC VCI VCI VCI 3 VCI Virtual Channels VCI= VCI=3 VCI=5 VCI=70 VCI=7 VCI=5 Virtual Path VPI= VPI=8 This virtual connection is uniquely defined using the pair Transmission Path (, ) VPI VCI VPI= VPI=8 VCI= VCI=3 VCI=5 VCI=70 VCI=7 VCI=5 VCI VCI VCI VCI VPI VPI VPI VPI 3 VPI VPI VCI VPI 3 VCI 3 VCI VPI 5 VCI VP switch/cross connect 37 VIDEO 37 VIDEO 5 DT 78 VOICE 3 76 VIDEO 88 VOICE Figure. TM Connection Relationships 6 5 DT VIDEO VPI/VCI 0/37 0/5 0/37 0/78 5 Faculty of Information Technology VIDEO DT VIDEO VOICE Port Input Connection Table Port Output VPI/VCI 0/76 0/ 0/ 0/88 (a) Representation of VC and VP switching VCI VCI 3 VPI VPI 5 VCI VCI VCI 3 VCI 5 VPI VPI 6 VCI VCI VCI 5 VCI VPI 3 VPI 7 VCI VCI VP switch/cross connect (b) Representation of VP switching 6 Faculty of Information Technology TM Cell TM Cell Format Two parts: Header: 5 octets Information field: 8 octets Total of 53 octets/cell. Different cell structure for UNI (User-Network Interface) and NNI (Network- Network Interface) Generic flow control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Payload Type Header Error Control Information field (8 octets) CP 5 octet header 53 octet cell Virtual Path identifier Virtual Channel Identifier Payload Type Header Error Control Information field (8 octets) CP 7 Faculty of Information Technology (a) User network interface (b) Network network interface 8 Faculty of Information Technology

8 TM Cell Header TM Cell Header Generic Flow Control (GFC) Only at the user-to-network interface (UNI) - controls flow only at this point to alleviate short term overload. Every connection either subject to flow control or not. Flow control is from the subscriber to network and is controlled by the network side. Virtual Path Identifier (VPI) In conjunction with VCI, identifies the next destination of a cell as it passes through a series of TM switches. Virtual Channel Identifier (VCI) In conjunction with VPI, identifies the next destination of a cell as it passes through a series of TM switches. 9 Faculty of Information Technology Payload Type (PT) Three bit field: Bit : Indicate user data (0) or network management cell (). Bit : Cell experienced no congestion (0) or congestion/excessive delay (). Bit 3: Signalling bit. Used in 5 to indicate end of CS PDU (see later). Cell oss Priority (CP) Indicates whether the cell should be discarded in case of extreme congestion at a switch. Header Error Control (HEC) n 8-bit CRC on the first octets of the header. Used for error control and synchronization. 30 Faculty of Information Technology TM Service Categories Real-Time Services Real-time: Service classes CBR VBR BR UBR rt VBR Constant bit rate (CBR). nrt VBR Real-time variable bit rate (rt-vbr). Non-real-time: Non-real-time variable bit rate (nrt-vbr) vailable bit rate (BR) Unspecified bit rate (UBR) 3 Faculty of Information Technology mount of delay and variation of delay (jitter). CBR: Fixed data rate continuously available. Tight upper bound on delay. Uncompressed and CBR compressed audio and video: Video conferencing, interactive audio, /V distribution and retrieval. rt-vbr: Time sensitive application: tightly constrained delay and delay variation. rt-vbr applications transmit at a rate that varies with time. e.g. Compressed video: Produces varying sized image frames at a constant frame rate (original uncompressed rate). So compressed data rate varies. Can statistically multiplex connections. 3 Faculty of Information Technology

9 Non-Real-Time Services Non-Real-Time Services Bursty traffic without constraints on delay and its variation. nrt-vbr: May be able to characterise expected traffic flow. Improve QoS in loss and delay. End system specifies: Peak cell rate, sustainable or average rate and measure of how bursty traffic is. e.g. irline reservations, banking transactions. 00% Percentage of line capacity vailable Bit Rate and Unspecified Bit Rate Variable Bit Rate Constant Bit Rate 0 Time 33 Faculty of Information Technology UBR: May be additional capacity over and above that used by CBR and VBR traffic Not all resources dedicated. Bursty nature of VBR. For application that can tolerate some cell loss or variable delays. e.g. TCP based traffic. Cells forwarded on FIFO basis. Best efforts service: no commitment or feedback on congestion. BR: pplication specifies peak cell rate (PCR) and minimum cell rate (MCR). Resources allocated to give at least MCR. Spare capacity shared among all RB sources. e.g. N interconnection. 3 Faculty of Information Technology TM daptation ayer Supported pplication Types Support for information transfer protocol not based on TM. For example: PCM (voice): ssemble bits into cells. Re-assemble into constant flow. IP: Map IP packets onto TM cells. Fragment IP packets. Use IP over TM to retain all IP infrastructure. daptation ayer Services: Handle transmission errors. Segmentation and re-assembly. Handle lost and miss-inserted cell conditions. Flow control and timing control. 35 Faculty of Information Technology pplications include: Circuit emulation: synchronous TDM (T) over TM. VBR voice and video: real-time transmission of compressed data. General data service: non-real-time messaging and transaction services. IP over TM: transmission of IP packets in TM cells. Multiprotocol encapsulation over TM (MPO): Other than IP (e.g. IPX, ppletalk, DECNET). N emulation (NE): N-to-N traffic with emulation of N broadcast capability. 36 Faculty of Information Technology

10 Protocols Protocols sublayer (CS): Support for specific applications using. user attaches at SP (address of application). Service dependent layer. Segmentation and re-assembly sublayer (SR): Packages and unpacks info received from CS into cells. Four protocol types: CS Sublayer SR Segmentation and Reassembly CS Sublayer SR Segmentation and Reassembly 37 Faculty of Information Technology 3 SR / TM CS Sublayer Segmentation and Reassembly 5 CS Sublayer SR Segmentation and Reassembly User Sublayer (CS) Segmentation and Reassembly (SR) Sublayer TM ayer ayer SR PDU SR PDU User Data SR PDU CS PDU SR PDU TM cell TM cell TM cell TM cell 38 Faculty of Information Technology Protocol Types - Constant Bit Rate Source Type : CBR source. SR packs and unpacks bits into cells. Block accompanied by a sequence number (SN): track errored PDUs. Type : VBR analog applications (e.g. video and audio). Type 3/: Connectionless or connection oriented. Message mode or streaming mode. Type 5: Streamlined transport for connection oriented higher layer protocols. Many fields in the Type 3/ SR and CPCS PDU are not needed. 39 Faculty of Information Technology CS SR CSI bit... SC 3 bits Constant bit rate data from upper layer 7 bytes 7 bytes... 7 bytes... Header byte CRC 3 bits P bit Payload 7 bytes CSI: sublayer identifier SC: Sequence count CRC: Cyclic redundancy check P: Parity 0 Faculty of Information Technology

11 - Variable Bit Rate Source 3/ - Connection/Connectionless Packet Data CS SR CSI bit... SC 3 bits Variable bit rate data from upper layer 5 bytes 5 bytes... 5 bytes... Header byte IT bits CSI: sublayer identifier SC: Sequence count IT: Information type Payload 5 bytes I 6 bits Trailer bytes CRC 0 bits I: ength Indicator CRC: Cyclic redundancy check Faculty of Information Technology 3 / T: Type BT: Begin tag B: Buffer allocation CS SR Header T BT B bytes Header bytes... ST CSI SC MID bits bit 3 bits 0 bits ST: Segment type CSI: sublayer identifier SC: Sequence MID: Multiplexing ID User data <= bytes Payload bytes Trailer bytes : lignment ET: End tag : ength bytes... bytes I 6 bits PD ET CRC 0 bits I: ength Indicator CRC: Cyclic redundancy check Faculty of Information Technology 0 3 Trailer 5 - Simple and Efficient daption ayer (SE) Example 5 Transmission User data <= bytes Higher layer PDU 5 CS SR 8 bytes... Payload 8 bytes PD UU T 0 7 UU: User to user ID T: Type : ength 8 bytes... 8 bytes CRC 3 Faculty of Information Technology Trailer SDU 0 SR PDU payload SDU 0 CPCS PDU payload SR PDU payload SDU 0 CPCS = common part convergence sublayer SR = segmentation and reassembly PDU = protocol data unit CPCS T = CPCS trailer TM H = TM header SDU = Service Data Unit type bit SR PDU payload CPCS T SR PDU payload TM H TM cell payload CPCS PDU SR PDU SR PDU SR PDU SR PDU TM cell Faculty of Information Technology SDU pad

12 Further Reading Stallings, W. ISDN and Broadband ISDN with Frame Relay and TM, Prentice Hall, 999. Stallings, W. Data and Computer Communications, Prentice Hall. Chapter. Forouzan, B. Data Communications and Networking, McGraw-Hill, 00. Chapter 9. 5 Faculty of Information Technology