Tài liệu IP over ATM doc

10 IP over ATM Overview This module focuses on IP QoS mechanisms that can be used on ATM interfaces. It includes the following topics: n Introduction to IP over ATM n Per-VC WRED n VC Bundling n Per-VC CB-WFQ n RSVP to SVC Mapping Objectives Upon completion of this module, you will be able to perform the following tasks: n List the requirements of IP QoS in combination with ATM QoS n Describe the hardware and software requirements for advanced IP QoS mechanisms on ATM interfaces n Describe per-VC queuing n Describe and configure per-VC WRED n Describe and configure VC bundling n Describe and configure per-VC CB-WFQ n Describe RSVP to SVC mapping n Monitor and troubleshoot IP QoS on ATM interfaces 10-2 IP QoS IP over ATM Copyright  2001, Cisco Systems, Inc. Introduction to IP over ATM Objectives Upon completion of this lesson, you will be able to perform the following tasks: n Describe the QoS-related problems when using ATM networks n Describe the hardware and software requirements for advanced IP QoS mechanisms on ATM interfaces n Describe per-VC queuing Copyright  2001, Cisco Systems, Inc. IP QoS IP over ATM 10-3 © 2001, Cisco Systems, Inc. IP QoS IP over ATM-5 IP vs. ATM Technology comparison IP vs. ATM Technology comparison IP • Connectionless • Per-packet QoS (IP precedence) • Small number of service classes • IP precedence or DSCP does not encode service parameters ATM • Connection oriented • Per-connection (virtual circuit) QoS • Large number of QoS traffic classes (CBR, VBR, UBR, ABR) • Rich traffic parameters (PCR, MCR, SCR ) specified for each VC The Internet Protocol (IP) is a routed protocol that is used to transmit data in packets. It uses the best-effort delivery for individual packets without any flow control. Transmission Control Protocol (TCP) is used with IP to provide a connection-oriented service. Asynchronous Transfer Mode (ATM), on the other hand, provides connections between endpoints in the ATM network. The connections are called virtual circuits (VCs). IP’s default best effort service can be supplemented by differentiated quality of service based on IP precedence or DSCP marking. A QoS solution using IP precedence is limited to 8 classes, 2 of which are reserved and 1 should be used for the default best-effort class. A QoS solution using DSCP scales up to 64 classes. ATM provides a wider range of services: n Constant Bit Rate (CBR) is useful for delay-sensitive applications such as voice. This service provides bandwidth and delay guarantees. n Variable Bit Rate—Real Time (VBR-RT) is useful for burstier delay-sensitive applications. This service provides bandwidth and delay guarantees. n Variable Bit Rate—Non Real Time (VBR-NRT) is useful for bursty traffic. This service provides bandwidth guarantees. n Available Bit Rate (ABR) is useful for best-effort traffic that is allowed more bandwidth, when available or configured. This service provides bandwidth guarantees and access to extra bandwidth. n Unspecified Bit Rate is useful for the real best effort where there are no guarantees. 10-4 IP QoS IP over ATM Copyright  2001, Cisco Systems, Inc. IP’s IP precedence or DSCP are only used to mark packets. They do not include any service parameters. Service parameters depend on the QoS mechanism being deployed. ATM’s services also include various per-connection service parameters, such as: n Sustained Cell Rate (SCR) for CBR, VBR and ABR services n Minimum Cell Rate (MIR) for ABR n Peak Cell Rate (PCR) for VBR, ABR and UBR services n Maximum Burst Size (MBS) Both IP and ATM can implement Quality of Service (QoS). The decision on which technology to use for quality of service should be based on a number of factors, such as: n Availability of ATM n Interaction between ATM and IP n Scalability options of the technology n Performance limitations This module introduces the possibilities of combining IP QoS with ATM. Copyright  2001, Cisco Systems, Inc. IP QoS IP over ATM 10-5 © 2001, Cisco Systems, Inc. IP QoS IP over ATM-6 Integrating IP and ATM Integrating IP and ATM • Overlay model (ATM forum) – ATM VC’s are manually established between pairs of devices – IP packets are sent across these VC’s – ATM switches are not IP aware • Peer model (MPLS) – ATM switches are IP aware on control (but not data) plane – ATM VC’s are established on-demand based on IP routing tables There are two main approaches to integration of IP with/over ATM: n The traditional way (overlay model) is to use individual permanent virtual circuits (PVC) to establish point-to-point adjacencies between IP routers. IP routing protocols are used to provide reachability across a network of ATM connections. ATM has no knowledge of IP and cannot use IP information to optimize its links. n The newer approach (MPLS) is to make ATM switches IP aware. ATM switches run an IP routing protocol to establish virtual circuits. This module focuses on the QoS available with traditional permanent and switched virtual circuits (PVCs and SVCs). The IP QoS- IP over MPLS module discusses QoS possibilities when using the peer model. 10-6 IP QoS IP over ATM Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over ATM-7 IP QoS and ATM IP QoS and ATM • Routers can be interconnected over an ATM backbone using different ATM services: – UBR – congestion management is virtually impossible because routers are allowed to transmit packets at line speed – VBR – congestion management is easier, but it requires conservative setting of transmit rates – CBR – similar to VBR from IP perspective – ABR – pushes congestion back to the source, requires dynamic adjustment to available bandwidth Achieving good quality of service for IP classes greatly depends on the type of ATM network and services used. n Using UBR, prevents routers from detecting congestion in the network. It is therefore difficult to manage congestion based on IP precedence or DSCP. The reason for this is because all packet drops happen on the congested link somewhere in the ATM network. n VBR makes it easier to push congestion back to the source where it can be managed by routers. n CBR is typically used for non-bursty delay sensitive traffic. It is therefore more important to prevent congestion by correctly provisioning the class that is using CBR. n ABR is a good solution where bandwidth can be utilized to the maximum without having many drops in the ATM network. Copyright  2001, Cisco Systems, Inc. IP QoS IP over ATM 10-7 © 2001, Cisco Systems, Inc. IP QoS IP over ATM-8 UBR Virtual Circuits UBR Virtual Circuits • Solution: – Set CLP on the router based on IP information to minimize the effect of cell drops No congestion Router allowed to send at full speed Congestion Random CLP marking Unintelligent drops based on CLP A solution using UBR can be improved in terms of IP QoS, by marking less important packets with the CLP bit for congestion control. In case of congestion, the ATM switches will drop the less important packets to give more bandwidth for the higher-priority packets. The ATM FORUM also calls the UBR service category a “best effort” service, which requires neither tightly constrained delay nor delay variation. In fact, UBR provides no specific quality of service or guarantee throughput whatsoever. This traffic is therefore “at risk” since the network provides no performance guarantees for UBR traffic. The Internet and Local Area Networks are examples of this type of “best effort” delivery performance. Examples of this are LAN emulation (LANE), IP over ATM, and non-mission-critical traffic. This solution is fairly limited, since it allows for only two classes on the IP layer where congestion should be managed. 10-8 IP QoS IP over ATM Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over ATM-9 VBR Virtual Circuits VBR Virtual Circuits • Solution: – Set CLP on the router based on IP information – Use available IP QoS mechanisms to manage congestion at the source Router is sending at configured rate Congestion is possible Unintelligent random drops Congestion! A solution using VBR is better at providing feedback to routers sending cells into the ATM network. Congestion will occur on a router’s virtual circuit, where it can be managed by using the QoS mechanisms available in the Cisco IOS software. CLP marking can be used for less-important packets or for those packets above the Sustained Cell Rate (SCR) to improve the chances for higher-priority packets when congestion occurs in the ATM network. The rt-VBR service category supports time-sensitive applications, which also requires constrained delay and delay variation requirements, but which transmit at a time varying rate constrained to a PCR, SCR, and MBS define a traffic contract in terms of the worst-case source traffic pattern for which the network guarantees a specified QOS. Examples of such bursty, delay-variation-sensitive sources are voice and variable-bit-rate video. The nrt-VBR service category supports applications that have no constraints on delay and delay variations, but which still have variable-rate, bursty traffic characteristics. This class of application expects a low Cell Loss Ratio (CLR). The traffic contract is the same as that for rt-VBR. Applications include packet data transfers, terminal sessions, and file transfers. Networks may statistically multiplex these VBR sources effectively. Copyright  2001, Cisco Systems, Inc. IP QoS IP over ATM 10-9 © 2001, Cisco Systems, Inc. IP QoS IP over ATM-10 CBR and ABR Virtual Circuits CBR and ABR Virtual Circuits • Solution: – Use available IP QoS mechanism to handle congestion at the source Router is sending at configured rate. Congestion! CBR virtual circuits, are used for delay-sensitive traffic. This traffic should not experience congestion due to keeping the quality of data being transmitted. If congestion occurs, it can be managed by the IP layer using the IP QoS mechanisms on the router’s ATM interface. The CBR service category supports real-time applications requiring a fixed amount of capacity defined by the PCR. CBR supports tightly constrained variations in delay. Example applications are voice, constant-bit-rate video, and Circuit Emulation Services (CES). Normally, networks must allocate the peak rate to these types of source. The ABR service category works in cooperation with sources that can change their transmission rate in response to rate-based network feedback used in the context of closed-loop flow control. The aim of ABR service is to dynamically provide access to capacity currently not in use by other service categories to users who can adjust their transmission rate in response to feedback. In exchange for this cooperation by the user, the network provides a service with very low loss. Applications specify a maximum transmit-rate (PCR_ and the minimum required rate, called the Minimum Cell Rate (MCR). ABR service does not provide bounded delay variation; hence real-time applications are for ABR are LAN interconnection, high-performance file transfers, database archival, non-time- sensitive traffic, and web browsing. 10-10 IP QoS IP over ATM Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over ATM-11 Congestion Management in ATM Networks Congestion Management in ATM Networks • Congestion management on routers should be performed on a per-VC basis • Design options: – Make sure there is no congestion in the ATM network (ABR, CBR, VBR) and use IP QoS mechanisms at the source (CB-WFQ, WRED) – Mark less important packets with the CLP bit in case there is congestion in the ATM network (CB- Policing, CB-Marking) – Use multiple parallel (per-CoS) virtual circuits with ATM QoS (VC Bundling) This module discusses three different approaches to designing QoS in IP networks on ATM: 1. Using IP QoS mechanisms to ensure there is no congestion in the AMT network 2. Using ATM QoS mechanisms with IP precedence used for classification (VC Bundling) 3. Combining both IP and ATM QoS mechanisms [...]... Systems, Inc IP QoS IP over ATM 10-13 Per-VC WRED • Single ATM VC is established over an ATM cloud between a pair of routers – ABR, VBR, UBR or CBR – Using UBR will not result in proper operation, as there is no ATM shaping in UBR • All IP traffic toward a next-hop router is forwarded across a single ATM VC • Congestion is managed entirely on the IP layer using WRED on each individual ATM VC, resulting... based on the IP precedence or DSCP value 10-14 IP QoS IP over ATM Copyright © 2001, Cisco Systems, Inc Per-VC WRED : Intelligent IP Packet Discard Traffic Shaping Threshold Exceeded VIP2-50 PA-A3-XX VC1 VC2 VC3 Per-VC WRED: Intelligent Discard © 2001, Cisco Systems, Inc Per-VC Queues No discard on PA IP QoS IP over ATM- 18 Per-VC queuing requires an Enhanced ATM Port Adapter that support up to 4096 cell... 2001, Cisco Systems, Inc IP QoS IP over ATM- 26 The figure shows the configuration of WRED profiles used for fast VCs Note 10-24 IP QoS IP over ATM This configuration simply uses scaled thresholds to support up to 100 packets in the queue Copyright © 2001, Cisco Systems, Inc Router Configuration • Step #3 - Apply WRED profile on various PVCs interface ATM1 1/0/0 interface ATM1 1/0/0 ip address 17.1.0.1 255.255.255.0... not supported 10-28 IP QoS IP over ATM Copyright © 2001, Cisco Systems, Inc VC Bundling Case Study ATM VC ATM VC type Control VC (routing updates) VBR Voice CBR VPN traffic VBR Premium Internet traffic VBR Best-effort Internet traffic ABR IP prec 6-7 5 4 2-3 0-1 Control (routing) Voice VPN traffic Premium Internet Best-effort Internet © 2001, Cisco Systems, Inc IP QoS IP over ATM- 33 The figure illustrates... identified by IP precedence • Each VC uses an ATM service based on the requirements of the class • Routers automatically map packets in VCs based on their IP precedence value • Multiple parallel VCs are needed for each IP adjacency © 2001, Cisco Systems, Inc IP QoS IP over ATM- 32 VC Bundling is a solution where the task of providing differentiated quality of service is offloaded to the ATM switches... 2001, Cisco Systems, Inc IP QoS IP over ATM 10-15 Configuring Per-VC WRED Configuring • The following configuration steps are needed to enable per-VC WRED: – Create a Random-Detect-Group template with a WRED profile – Apply the WRED template to an ATM interface or to individual ATM VCs – Verify and monitor the operation of per-VC WRED © 2001, Cisco Systems, Inc IP QoS IP over ATM- 19 Applying WRED to... IP precedence values: n IP precedence 6 and 7 traffic is forwarded through the Control VC n IP precedence 5 traffic is forwarded through the Voice VC n IP precedence 4 traffic is forwarded through the VPN VC n IP precedence 2 and 3 traffic is forwarded through the Premium VC n IP precedence 0 and 1 traffic is forwarded through the Best-effort VC Copyright © 2001, Cisco Systems, Inc IP QoS IP over ATM. .. point-to-point link on the IP layer 10-30 IP QoS IP over ATM Copyright © 2001, Cisco Systems, Inc VC Provisioning • VCs are dimensioned based on expected load for the precedence(s) level transported on that VC • More isolation between classes • At the expense of – less statistical multiplexing, – more complex provisioning/engineering © 2001, Cisco Systems, Inc IP QoS IP over ATM- 35 VC Bundling provides... is used on the ATM PVC © 2001, Cisco Systems, Inc IP QoS IP over ATM- 21 The last step in the configuration of per-VC WRED is to attach a random-detectgroup to a virtual circuit The random-detect command is used in the VC configuration mode to enable WRED If no random-detect-group is specified WRED will use the default WRED profiles Copyright © 2001, Cisco Systems, Inc IP QoS IP over ATM 10-19 Monitoring... enable per-VC WRED? 10-26 IP QoS IP over ATM Copyright © 2001, Cisco Systems, Inc VC Bundling Objectives Upon completion of this lesson, you will be able to perform the following tasks: n Describe VC bundling n Configure VC bundling n Monitor and troubleshoot VC bundling Copyright © 2001, Cisco Systems, Inc IP QoS IP over ATM 10-27 VC Bundling • VC Bundling is a solution where ATM QoS mechanisms are . Inc. IP QoS IP over ATM 10-3 © 2001, Cisco Systems, Inc. IP QoS IP over ATM- 5 IP vs. ATM Technology comparison IP vs. ATM Technology comparison IP • Connectionless •. combining IP QoS with ATM. Copyright  2001, Cisco Systems, Inc. IP QoS IP over ATM 10-5 © 2001, Cisco Systems, Inc. IP QoS IP over ATM- 6 Integrating IP and