Some other QoS tools

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2.5. Some other QoS tools

If you are actually using Cisco routers to manage your networks you should know that Cisco has many more tools to offer in its bag than just PQ, CQ, WFQ and CAR. This company has advanced farthest into the QoS technology offering some very useful tools for implementing QoS services. Next is a brief recount of some other QoS tools from this great company.

ACL - Standard & Extended Access-Lists: ACL can be used for implementing firewalls and sophisticated packet filtering schemes.

PBR - Policy-Based Routing: PBR allows you to classify traffic based on extended access list criteria; sets IP Precedence bits and routes specific traffic to engineered paths, which may be required to allow a specific QoS service through the network. With PBR routing is done by policies allowing more intelligent routing decisions based on packet header information farther than destination addresses.

BGPPP - Border Gateway Protocol Policy Propagation: BGPPP is a scalable means of utilizing attributes, such as community values, to propagate destination-based packet classification policies throughout a large network via BGP routing updates.

WRED - Weighted Random Earlier Detection: RED is an algorithm designed by Van Jacobson and Sally Floyd to improve TCP response behavior in presence of congestion. Basically it tries to inform as earlier as possible to TCP sender about incipient congestion by using a random packet dropping mechanism. WRED is Cisco's implementation of the RED class of congestion avoidance algorithm.

GTS - Generic Traffic Shaping: GTS shapes traffic by reducing outbound traffic flow to avoid congestion by constraining it to a particular bit rate using the token bucket mechanism. It works with a variety of Layer 2 technologies, including FR, ATM, SMDS and Ethernet.

FRTS - Frame Relay Traffic Shaping: Frame Relay implementation of GTS. Using FRTS you can eliminate bottleneck in FR networks that have high-speed connections at the central site and low-speed connections at branch sites. This way, you can configure rate enforcement to either the CIR or some other defined value such as the excess information rate, on a per-virtual-circuit VC basis. Using BECN & FECN tagged packets received from the network, FRTS can also dynamically throttle traffic.

CBWFQ - Class-Based Weighted Fair Queue: CBWFQ is one of Cisco's newest congestion-management tools for providing greater flexibility. When you want to provide a minimum amount of bandwidth, use CBWFQ. This is in contrary to GTS or CAR that provide a maximum amount of bandwidth.

FBWRED - Flow-Based Weighted Random Earlier Detection: It is a generalization of the WRED algorithm. By allowing multiple independent configurated virtual queues (VQ) on the same physical queue it is possible to classify flows previously to be assigned to different VQs. By configuring correctly the VQs, problems related to the interaction between responsive flows (as TCP is) and unresponsive flows (as UDP is) can be resolved. This way responsive and fragile TCP flows are protected for starvation from unresponsive and/or aggressive flows, like UDP, MM, and heavy RTP flows.

NBAR - Network Based Application Recognition: We talked a little about it somewhere above in this document. The traffic identification phase of the QoS studies is really horrible for saying the less. Having your domain properly identified you could stay hours, days, weeks and even more trying to building up a traffic identification scheme of it. NBAR is a tool to help us to have this cup of castor-oil faster. NBAR is actually an identification tool that is really the hard part of the process. Having identified the traffic, marking the packet later is relatively easy. NBAR takes the identification portion of classification to another level. Looking deeper into the packet, identification can be performed farther away than just classifying them by source and destination addresses and ports or even protocol type.

QPM & QDM: QPM (Quality of Service Policy Manager) and QDM (Quality of Service Device Manager) are very advanced Cisco's tools for ease of deployment of QoS services.

IPM - Internetwork Performance Monitor: another very advanced Cisco's tool for verification of service levels on already QoS implemented networks.

VLAN Tagging: A very ingenious layer-2 QoS scheme that allows to classify ethernet segment by tagging them. Forwarding behavior will be dependant of class of tag carrying for each segment travelling by the network.

LFI - Link Fragmentation and Interleaving: some really incredible tool from Cisco folks. It's explained more or less as this: interactive traffic (always fragile traffic like Telnet, Voice over IP, SSH, interactive WWW as chating and lived questionaries) is susceptible to increase latency and jitter (have a look to http://opalsoft.net/qos/QoS.htm for a brief explanation of these terms) when the network processes large packets (for example, LAN-to-LAN FTP big packets transversing a low bandwidth WAN link), especially when their packets (from interactive flows) are queued on these slower links. LFI reduces delay and jitter by breaking up large datagrams and interleaving low-delay traffic packets with the resulting smaller packets. For combining large file FTP transfer traffic (where latency and jitter really don't matter) with low-bandwidth fragile traffic like Telnet, VoIP, SSH, etc. (where latency and jitter really matter) LFI is the right solution. Combined again with RTPC (see below) is a must. Really a hit from Cisco people.

RTPC - Realtime Transport Protocol Header Compression: RTP is a protocol used for carrying multimedia application traffic, including audio and video, over an IP network. RTP packets have a 40-byte header and typically a 20 to 150 payload. RTP protocol travels over UDP. Given the size of the IP/UDP/RTP header combination, it is inefficient to transmit those small payloads using an uncompressed header. RTPC is a technology that helps RTP run more efficiently, especially over lower-speed links, by compressing the RTP/UDP/IP header from 40 bytes to 2 to 5 bytes. This is especially beneficial for smaller packets (such as IP voice traffic) on slower links, where RTP header compression can reduce overhead and transmission delay significantly.

RSVP - Resource Reservation Protocol: RSVP is a signalling protocol used for implementing Integrated Service architecture. It is a protocol for dynamically setting end-to-end QoS across heterogeneous network. RSVP, which run directly over IP, allows an application to dynamically reserve network bandwidth. Integrated Service is a very difficult to implement architecture that can be considered the state-of-the-art of the providing QoS services paradigm.

RMON: It is an advanced test tool used to develop a good understanding of traffic characteristic. As I understand it goes even farther than NBAR providing a very complete information about the network behavior. Also, information obtained from it helps to validate any QoS deployment. It is used in conjunction with NBAR, IPM, QPM and QDM as a bag of tools that makes Cisco the most advanced company in offering QoS tools around the world.

QoS on Ethernet: The Catalyst line of multilayer switches have the capability to provide QoS services at Layer-2. At this layer, the frame uses class of service (CoS) in 802.1p and Interlink Switch Link (ISL). CoS uses 3 bits, just like IP-precedence, and maps well from Layer-2 to Layer-3, and viceversa. The switches have the capability to differentiate frames based on CoS settings.

MPLS - Multi Protocol Label Switching: It is a flexible technology that enables new services in IP networks and makes routing more effective. The protocol was standarized by IETF based on a Cisco invented technology known as "Tag Switching". It combines two different approaches, datagram and virtual circuit, as a compact technology. MPLS is based on short fixed length labels, which are assigned to each packet at the ingress node of the MPLS cloud (something related to the concept of domain). These labels are used to make forwarding decisions at each node. The principle is some similar to DSCP on Differentiated Service architecture, but difference (a big one, by the way), is that forwarding decisions are based on tag labels instead of destination address as standard routing does. DS architecture provides differentiated treatment to each packet based on its DSCP but forwarding is based on standard destination address routing tables. On the contrary, MPLS uses a stack of tag labels assigned to the packet at the ingress node to make routing decisions, being the process a lot faster.

SNA ToS: SNA ToS, in conjunction with data-link switching plus (DLSW+), allows mapping of traditional IBM SNA class of service (CoS) into IP differentiated service.

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