Switching systems lecture6

Editor's Notes

• #5: ATM (Asynchronous Transfer Mode) is a high speed packet switching technology. It supports any kind of service. ATM is a flexible high bandwidth, low delay network technology that is:Capable of handling voice, video and data on a single network; and Generally used in the backbone
• #6: VPI:Virtual Path Identifier VCI:Virtual Channel Identifier ATM is a circuit switched procedure The connection through ATM network is called as “virtual”, since it does not exist physically, but it is present only in the form of routing tables in the switching center.
• #9: Here statistical multiplexing means, TS are not fixed. Information is sent over several TS may these are adjacent or may be different.
• #14: Why two fields? think VPI as a bundle of virtual channels. (256 VPI on one link) the individual virtual channels have unique VCIs. The VCI values may be reused in each virtual path
• #15: GFC ( Generic Flow Control): Supports the configuration of the subscriber equipment. It is intended for the control of a possible bus system at the user interface. VPI ( Virtual Path Identifier): VPI contains the second part of the addressing instructions and is of higher priority than the VCI. This allows the rapid direction of the cells through the network. ATM cross-connects the cell stream in various directions based on VPI. The VPI and VCI are assigned by the switching centers when the call is being established. VCI ( Virtual Channel Identifier): This field contains part of the addressing instructions. All cells belonging to the same virtual channel have the same VCI. VCI indicates a path section between switching centers or between switching center and subscriber. PTI ( Payload Type Identifier): A distinction is made between network and user information. CLP ( Cell Loss Priority): The contents of this field determines whether a cell can be preferentially deleted or not during congestion. CLP=0 Lower priority CLP=1 Higher priority HEC ( Header Error Control): The HEC is used to synchronize the receiver to the start of the cell. CRC code is also sent over it (x8+x2+x+1) There are cells for transmitting the signaling information and OAM cells.
• #16: There are two types of ATM connections Virtual path connections –identified by virtual path identifiers (VPI) Virtual channel connections –identified by a combination of virtual path and circuit identifiers (VPI and VCI) 􀂄Virtual channels (VC) are the basic unit that carry a stream of ATM cells from one user to another are identified by a virtual channel identifier can be concatenated can be configured statically or dynamicallyStatically as PVCs (permanent virtual circuits) that are set up at network configuration time Dynamically as SVCs (switched virtual circuits) that are dynamically configured on-demand can be bundled together into virtual path connections 􀂄Virtual paths (VP) contain one or more virtual channels are identified by a virtual path identifier are routed through a network as a single entity can be used internally for bundling virtual circuits between switches
• #20: PVC: Permanent Virtual Channel, A PVC in the usual meaning is a VC that is not signaled by the end points. Both of the endpoint (user) VC values are manually provisioned. The link-by-link route through the network is also manually provisioned. If any equipment fails, the PVC is down, unless the underlying physical network (SONET, for example) can re-route below ATM. SVC: A SVC is established by UNI signaling methods. So an SVC is a request oriented connection initiated by the user. If some equipment in the path fails, the SVC is broken and would have to be reconnected.
• #24: SSCS:Service Special Convergence Sublayer CPCS:Common Part Convergence Sublayer CS:Convergence Sublayer SAR:Segmentation And Reassembly AAL:ATM Adaptation Layer PHY: Physical Layer TC:Transmission Convergence Sublayer PMD:Physical Medium Dependent Sublayer
• #25: Physical Layer The physical layer is responsible for placing and removing cells from the physical transport medium. 􀂄Standards for physical interfaces to various media exist and are discussed later. 􀂄SONET/SDH based transmission media are the most common for transmission of ATM. 􀂄The physical layer performs two types of functions: -Functions associated with the structure or format of the info to be transmitted and other specific functions (e.g. multiplexing). These functions are independent of the transmission medium. -Functions associated with the transmission of signals over a particular medium (e.g. line coding for a particular medium). These functions are dependent on the transmission medium
• #26: ATM Layer -provides services to higher layers (e.g. multiplexing ATM connections on to a single connection) and facilitates the forwarding of ATM cells through the network by the setting of parameters in the ATM cell header (e.g. prioritization, traffic management). -delivers ATM cells to the physical layer for transport -A number of parameters are set at the ATM layer that determine quality of service and traffic management Quality of Service (QoS) refers to a collection of performance parameters whose values have to do with the speed and accuracy/reliability characteristics of the ATM connection. Negotiable parameters (determined by customer) ppCDV –peak to peak cell transfer delay variation Max CTD –maximum cell transfer delay CLR –cell loss ratio Non-negotiable parameters(determined by service provider) CER –cell error ratio CMR –cell mis-insertion rate SECBR –severely errored cell block ratio Traffic parametersdefine characteristics of the traffic to be offered over the ATM connection. PCR –peak cell rate SCR –sustainable cell rate MBS –maximum burst rate MCR –minimum cell rate ICR –initial cell rate
• #27: ATM adaptation Layer -The AAL maps higher-level data (e.g. legacy technologies) onto ATM cells making the data suitable for transport through the ATM network and isolates higher layers from the ATM layer. These functions are performed on the user side.
• #28: ATM adaptation Layer -The AAL maps higher-level data (e.g. legacy technologies) onto ATM cells making the data suitable for transport through the ATM network and isolates higher layers from the ATM layer. These functions are performed on the user side. -The concept of Service Classes is used to define traffic corresponding to specific combinations of: timing relations between source and destination (required/not required) constant vs. variable bit rate connection mode (connection oriented vs. connectionless oriented) -Defined service classes are: Class A –synchronous, connection oriented, constant bit rate (e.g. DS, DS3 circuit emulation) Class B –synchronous, connection oriented variable bit rate (e.g. packet video) Class C –asynchronous, connection oriented, variable bit rate (e.g. frame relay) Class D –asynchronous, connectionless, variable bit rate (e.g. SMDS) -AAL protocols are defined to handle one of more of the above service classes and create properly formatted ATM cells. There is no stipulation that rigidly binds an AAL protocol to a service class. AAL type 1–meets the needs of class A services Provides for the acceptance of user info at a fixed rate and delivery of this info at the destination at the same fixed rate and indication of loss or errored information AAL type 2–meets the needs of class B services Designed to carry low bit rate, variable-length, delay-sensitive packets AAL type 3/4-meets the needs of class C and D services Designed to carry variable bit rates with no timing relationship AAL type 5–meets the needs of class C services Simplified and more efficient than 3/4 -simple and efficient data protocol
• #29: -The concept of Service Classes is used to define traffic corresponding to specific combinations of: timing relations between source and destination (required/not required) constant vs. variable bit rate connection mode (connection oriented vs. connectionless oriented) -Defined service classes are: Class A –synchronous, connection oriented, constant bit rate (e.g. DS, DS3 circuit emulation) Class B –synchronous, connection oriented variable bit rate (e.g. packet video) Class C –asynchronous, connection oriented, variable bit rate (e.g. frame relay) Class D –asynchronous, connectionless, variable bit rate (e.g. SMDS) -AAL protocols are defined to handle one of more of the above service classes and create properly formatted ATM cells. There is no stipulation that rigidly binds an AAL protocol to a service class. AAL type 1–meets the needs of class A services Provides for the acceptance of user info at a fixed rate and delivery of this info at the destination at the same fixed rate and indication of loss or errored information AAL type 2–meets the needs of class B services Designed to carry low bit rate, variable-length, delay-sensitive packets AAL type 3/4-meets the needs of class C and D services Designed to carry variable bit rates with no timing relationship AAL type 5–meets the needs of class C services Simplified and more efficient than 3/4 -simple and efficient data protocol
• #31: IP Over ATM
• #32: This page reference page :AAL5 Process. Reference：RFC1483 SNAP: Sub-network Access Protocol LLC: Low Layer Compatability