Cisco Router 800 Series Software Configuration Guide
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1-19 Cisco 800 Series Software Configuration Guide 78-5372-06 Chapter 1 Concepts VoIP The gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup and request admission to a call from the gatekeeper. The gatekeeper is an H.323 entity on the LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper may provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways. Voice Dial Peers Dial peers enable outgoing calls from a particular telephony device. All of the voice technologies use dial peers to define the characteristics associated with a call leg. A call leg is a discrete segment of a call connection that lies between two points in the connection. It is important to remember that these terms are defined from the rou te r perspective. An inbound call leg means that an incoming call comes to the router. An outbound call leg means that an outgoing call is placed from the router. Dial peers are used for both inbound and outbound call legs. For inbound call legs, a dial peer might be associated with the calling number or the voice-port number. Outbound call legs always have a dial peer associated with them. The destination pattern is used to identify the outbound dial peer. The call is associated with the outbound dial peer at setup time. There are two kinds of dial peers that need to be configured for each voice implementation: POTS—(also known as “plain old telephone service” or “basic telephone service”) dial peer associates a physical voice port with a local telephone device. The key commands in your configuration are the port and destination-pattern commands. The destination-pattern command defines the telephone number associated with the POTS dial peer. The port command associates the POTS dial peer with a specific logical dial interface, normally the voice port connecting your router to the local POTS network. Vo I P—dial peer associates a telephone number with an IP address. The key commands in your configuration are the destination-pattern and session target commands.The destination-pattern command defines the telephone number associated with the VoIP dial peer. The session target command specifies a destination IP address for the VoIP dial peer. In addition, you can use VoIP dial peers to define characteristics such as IP precedence, additional QoS parameters, and codec.
Chapter 1 Concepts QoS 1-20 Cisco 800 Series Software Configuration Guide 78-5372-06 QoS This section describes quality of service (QoS) parameters, including the following: IP Precedence PPP Fragmentation and Interleaving CBWFQ RSVP Low Latency Queuing QoS refers to the capability of a network to provide better service to selected network traffic over various technologies, including ATM, Ethernet and IEEE 802.1 networks, and IP-routed networks that may use any or all of these underlying technologies. Primary goals of QoS include dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. QoS technologies provide the elemental building blocks for future business applications in campus, WAN, and service provider networks. QoS must be configured throughout your network, not just on your router running VoIP, to improve voice network performance. Not all QoS techniques are appropriate for all network routers. Edge routers and backbone routers in your network do not necessarily perform the same operations; the QoS tasks they perform might differ as well. To configure your IP network for real-time voice traffic, you need to consider the functions of both edge and backbone routers in your network. QoS software enables complex networks to control and predictably service a variety of networked applications and traffic types. Almost any network can take advantage of QoS for optimum efficiency, whether it is a small corporate network, an Internet service provider, or an enterprise network. IP Precedence You can partition traffic in up to six classes of service using IP Precedence (two others are reserved for internal network use). The queuing technologies throughout the network can then use this signal to expedite handling.
1-21 Cisco 800 Series Software Configuration Guide 78-5372-06 Chapter 1 Concepts QoS Features such as policy-based routing and committed access rate (CAR) can be used to set precedence based on extended access-list classification. This allows considerable flexibility for precedence assignment, including assignment by application or user, or by destination and source subnet, and so on. Typically this functionality is deployed as close to the edge of the network (or administrative domain) as possible, so that each subsequent network element can provide service based on the determined policy. IP Precedence can also be set in the host or network client with the signaling used optionally. IP Precedence enables service classes to be established using existing network queuing mechanisms (such as CBWFQ), with no changes to existing applications or complicated network requirements. PPP Fragmentation and Interleaving With multiclass multilink PPP interleaving, large packets can be multilink-encapsulated and fragmented into smaller packets to satisfy the delay requirements of real-time voice traffic; small real-time packets, which are not multilink encapsulated, are transmitted between fragments of the large packets. The interleaving feature also provides a special transmit queue for the smaller, delay-sensitive packets, enabling them to be transmitted earlier than other flows. Interleaving provides the delay bounds for delay-sensitive voice packets on a slow link that is used for other best-effort traffic. In general, multilink PPP with interleaving is used in conjunction with CBWFQ and RSVP or IP precedence to ensure voice packet delivery. Use multilink PPP with interleaving and CBWFQ to define how data is managed; use Resource Reservation Protocol (RSVP) or IP Precedence to give priority to voice packets. CBWFQ In general, class-based weighted fair queuing (CBWFQ) is used in conjunction with multilink PPP and interleaving and RSVP or IP precedence to ensure voice packet delivery. CBWFQ is used with multilink PPP to define how data is managed; RSVP or IP Precedence is used to give priority to voice packets.
Chapter 1 Concepts QoS 1-22 Cisco 800 Series Software Configuration Guide 78-5372-06 There are two levels of queuing: ATM queues and Cisco IOS queues. CBWFQ is applied to Cisco IOS queues. A first-in-first-out (FIFO) Cisco IOS queue is automatically created when a PVC is created. If you use CBWFQ to create classes and attach them to a PVC, a queue is created for each class. CBWFQ ensures that queues have sufficient bandwidth and that traffic gets predictable service. Low-volume traffic streams are preferred; high-volume traffic streams share the remaining capacity, obtaining equal or proportional bandwidth. RSVP RSVP enables routers to reserve enough bandwidth on an interface to ensure reliability and quality performance. RSVP allows end systems to request a particular QoS from the network. Real-time voice traffic requires network consistency. Without consistent QoS, real-time traffic can experience jitter, insufficient bandwidth, delay variations, or information loss. RSVP works in conjunction with current queueing mechanisms. It is up to the interface queuing mechanism (such as CBWFQ) to implement the reservation. RSVP works well on PPP, HDLC, and similar serial-line interfaces. It does not work well on multi-access LANs. RSVP can be equated to a dynamic access list for packet flows. You should configure RSVP to ensure QoS if the following conditions characterize your network: Small-scale voice network implementation Links slower than 2 Mbps Links with high utilization Need for the best possible voice quality Low Latency Queuing Low latency queuing (LLQ) provides a low-latency strict priority transmit queue for real-time traffic. Strict priority queuing allows delay-sensitive data to be dequeued and sent first (before packets in other queues are dequeued), giving delay-sensitive data preferential treatment over other traffic.
1-23 Cisco 800 Series Software Configuration Guide 78-5372-06 Chapter 1 Concepts QoS Committed Access Rate Committed access rate (CAR) can be used to limit bandwidth or transmission rates based on traffic sources and destinations and to specify policies for handling traffic that breaches the specified bandwidth allocations. CAR provides configurable actions, such as transmit, drop, set precedence, or set QoS group, when traffic conforms to or exceeds the rate limit. The CAR feature performs the following functions: Limits the input or output transmission rate on an interface or subinterface, based on a flexible set of criteria. Classifies packets by setting the IP Precedence or QoS group, which is a class identifier that is internal to the router. To enable CAR, enter the rate-limit command while in ATM interface configuration mode. Rate Limitation The rate limitation feature of CAR provides the network operator with the means to define Layer 3 aggregate or granular access, or egress bandwidth rate limits, and to specify traffic handling policies when the traffic either conforms to or exceeds the specified rate limits. Aggregate access or egress matches all packets on an interface or subinterface. Granular access or egress matches a particular type of traffic based on precedence. You can designate CAR rate limitation policies based on physical port, packet classification, IP address, MAC address, application flow, and other criteria specifiable by access lists or extended access lists. CAR rate limits may be implemented either on input or output interfaces or subinterfaces including Frame Relay and ATM subinterfaces. An example of the use of the rate-limiting capability of CAR is application-based rates limiting HTTP World Wide Web traffic to 50 percent of link bandwidth, which ensures capacity for non-Web traffic including mission-critical applications. Marking of IP Precedence Extended access list classification can be used to set precedence that might be needed for features like class-based traffic shaping and CAR. This allows considerable flexibility for precedence assignment, including assignment by
Chapter 1 Concepts QoS 1-24 Cisco 800 Series Software Configuration Guide 78-5372-06 application or user, or by destination and source subnet, and so on. Typically this functionality is deployed as close to the edge of the network (or administrative domain) as possible, so that each subsequent network element can provide service based on the determined policy. IP Precedence can also be set in the host or network client with the signaling used optionally. IP precedence enables service classes to be established using existing network queuing mechanisms (such as CBWFQ), with no changes to existing applications or complicated network requirements. Weighted Fair Queuing Weighted fair queuing (WFQ) enables slow-speed links, such as serial links, to provide fair treatment for all types of traffic. WFQ classifies the traffic into different flows (also known as conversations) based on Layer 3 and Layer 4 information, such as IP addresses and TCP ports. WFQ performs this classification without requiring you to define access lists. This means that low-bandwidth traffic effectively has priority over high-bandwidth traffic because high-bandwidth traffic shares the transmission media in proportion to its assigned weight. WFQ is now available on IP Base and IP Firewall Cisco IOS images. Weighted Random Early Detection Random early detection (RED) is a congestion-avoidance mechanism that takes advantage of TCP’s congestion control mechanism. By randomly dropping packets prior to periods of high congestion, RED tells the packet source to decrease its transmission rate. Assuming that the packet source is using TCP, it will decrease its transmission rate until all the packets reach their destination, indicating that the congestion is cleared. Weighted RED (WRED), the Cisco implementation of RED, generally drops packets selectively, based on IP precedence. Packets with a higher IP precedence are less likely to be dropped than packets with a lower precedence. Thus, higher priority traffic is delivered with a higher probability than lower priority traffic. It can selectively discard lower priority traffic when the interface begins to get congested and provide differentiated performance characteristics for different classes of service. WRED is also RSVP-aware.
1-25 Cisco 800 Series Software Configuration Guide 78-5372-06 Chapter 1 Concepts Access Lists ATM Traffic Policing The traffic policing feature performs the following functions: Limits the input or output transmission rate of a class of traffic, based on user-defined criteria Marks packets by setting the IP Precedence value, the QoS group, or the differentiated service code point (DSCP) value Access Lists With basic standard and static extended access lists, you can approximate session filtering by using the established keyword with the permit command. The established keyword filters TCP packets based on whether the ACK or RST bits are set. (Set ACK or RST bits indicate that the packet is not the first in the session and the packet therefore belongs to an established session.) This filter criterion would be part of an access list applied permanently to an interface.
Chapter 1 Concepts Access Lists 1-26 Cisco 800 Series Software Configuration Guide 78-5372-06
CHAPTER 2-1 Cisco 800 Series Software Configuratio Guide 78-5372-06 2 Configuring Basic Networks This chapter describes three networks that network administrators in small independent offices or that telecommuters can set up. You can familiarize yourself with the three networks, determining which one is best suited for your situation. Following are the three basic network types: Private IP network to Internet Public IP network to Internet Remote office network to corporate office network using IP The following sections contain information about preparing for the configurations and the steps to configure each of the three basic networks. Before Configuring Basic Networks Before configuring the three basic networks, you must do the following: Step 1If using ISDN, order an ISDN line from your telephone service provider. For complete information on ordering your ISDN line, see Appendix D, “Provisioning an ISDN Line.”
Chapter 2 Configuring Basic Networks Before Configuring Basic Networks 2-2 Cisco 800 Series Software Configuratio Guide 78-5372-06 Step 2While ordering your ISDN line, gather the following information from your telephone service provider: ISDN switch type. Service profile identifiers (SPIDs). Only telephone service providers in North America assign SPIDs. SPIDs identify the ISDN B channels. The SPID format is generally an ISDN telephone number with additional numbers at the end; for example, 40855522220101. Depending on the switch that supports your ISDN line, your ISDN line could be assigned zero, one, or two SPIDs. ISDN local directory numbers (LDNs), which are the local ISDN telephone numbers of your router. Examples are 4085552222 or 5553333. NoteThe format of the LDN varies from region to region, depending on the telephone service provider. In some regions, you need to add the area code to the telephone number. Find out from your local telephone service provider whether or not you need to specify an area code for the LDN. Step 3If setting up an Internet connection, gather the following information from your Internet service provider (ISP): Point-to-Point Protocol (PPP) client name that the ISP assigns as your login name. PPP authentication type: Challenge Handshake Authentication Protocol (CHAP) or Password Authentication Protocol (PAP). PPP password to access your ISP account. IP address information: the IP address and subnet mask of the ISP ISDN interface. Also, if configuring a public IP network, you must gather the registered IP addresses and subnet masks to be used on your router LAN and WAN interfaces. ISP telephone number.