The Internet To Support Multimedia Traffic

Published Date: 02 Nov 2017

Abstractï¿½ QoS requirements for multimedia traffic have been covered by various normalisation groups, like 3GPP ITU, ETSI. Differentiated services is one method for applying Quality of Service policies, is the most advanced technique for managing traffic. DiffServ is protocol for specifying and controlling network traffic by simple classification schema. In this paper I bring closer issues related to the forms of QoS main traffic types, classification and marking of the packets, DiffServ architecture.

Keywordsï¿½ DiffServ, Quality of Service, traffic types, classification, marking

? Introduction

Different applications have different traffic characteristic often requiring guaranteed or regulated service. Quality of Service tolls has been designed and developed to provide special application (like voice and video) with guaranteed service in the deficiency of best bandwidth condition.

Presently we have three fundamental methodologies for apply

Quality of Service:

? Best-Effort,

? Integrated Services (IntServ);

? Differentiated Services (DiffServ).

A Best-Effort network does not support QoS, just use of the ï¿½best set of pathsï¿½ to destinations, and traffic is routed on a ï¿½first come, first serveï¿½ basis. There is no difference between different kinds of the traffic. Best-Effort is a default action of hardware, is easy to implement and very scalable.

Integrated Services, has been developed in order to provide quality of service - QoS (Quality of Services) - from beginning to end for the individual streams, the sequence of packets having one specific source and one destination. It is described in RFC 1633.

IntServ is based on two key principles:

? each network element needs quality of service control mechanisms,

? the application must be able to transmit to the network their quality of service requirements.

DiffServ implementing scalable service differentiation in the Internet, is based on a simple model where traffic entering a network is classified and possibly conditioned at the boundaries of the network, and assigned to different behavior aggregates, identified by a single DS codepoint.ï¿½Within the core of the network, packets are forwarded according to the per-hop behavior associated with the DS codepoint.

TABLE

Cisco IOS DiffServ Features and Benefits

Source: www.cisco.com/en/US/products/ps6610/products_d`ata_sheet09186a00800a3e30.html

Features Benefits

Full IETF compliance Standards based QoS that can be applied End-to-End

Packet classifications via DSCP Scalability: Fewer states are stored at the core of the network

Standard and user defined PHBs End-to-End construction of well-defined services for applications

Modular QoS CLI Granular traffic control and bendable management

AF,EF, and arbitrary classes Flexible classification and service offerings

? Main Traffic Types and QoS requirements

Many applications have special requirements of the network i.e. VoIP requires low latency and jitter however it has comparatively minimal bandwidth requirements. Video requires low jitter and high bandwidth even so it has relatively minimal latency requirements. Interactive video is the most rigorous in that it requires high bandwidth, low latency, and jitter.

? Viideo

The requirements for videoconferencing can be applied as either a one-to-one capability or a multipoint conference.

? = 150 ms of one-way latency from mouth to ear (per the ITU G.114 standard).

? = 30 ms jitter.

? = 1 percent packet loss.

? Minimum bandwidth guarantee is videoconferencing session + 20 percent. For example, a 384-kbps videoconferencing session requires 460 kbps guaranteed priority bandwidth.

The requirements for streaming video, such as IP multicast, executive broadcasts, and real-time training activities, are as follows:

? Four to 5 seconds of latency allowable (depending on the video application's buffering capabilities). No significant jitter requirements

? Two percent packet loss permissible. Bandwidth required depends on the encoding and the rate of the video stream.

? Video content distribution such as video on demand being replicated to distributed content engines.

? Delay- and jitter-insensitive.

? Large file transfers (traffic patterns similar to FTP sessions).

? Restrict to distribution to less-busy times of day.

? Provision as "less-than-best-effort" data.

? Voice

Voice calls require the following:

? = 150 ms of one-way latency from mouth to ear (per the ITU G.114 standard)

? = 30 ms jitter

? 17 to 106 kbps of guaranteed priority bandwidth per call (depending on the sampling rate, codec, and Layer 2 overhead )

? 150 bps (plus Layer 2 overhead) per phone of guaranteed bandwidth for voice control traffic

Your paper must be in two column format with a space of 4.22mm (0.17") between columns.

? Data

There are a few key points to remember about classifying data traffic:

? Profile applications to get a elementary perceptive of their network needs.

? Perform capacity planning to ensure an adequate bandwidth baseline.

? Use no more than four separate data traffic classes .

? Decrease the number of applications assigned to the transactional and bulk data classes (three or fewer are recommended).

? Use proactive provisioning polices before activated policing policies.

? DiffServ architecture

DiffServ architecture is build around concept of a domain, has two minor elements:

? Traffic conditioning ( policing, colouring, and shaping are done only at the edge of the network)

? Per-hop behaviours ( queuing, scheduling, and dropping are done at every hop in the network).

Fig.1 DiffServ architecture

Source: www.cisco.com/en/US/technologies

A traffic conditioner classifies the incoming packets into aggregates then meters them to determine agreement and marks them appropriately by writing/re-writing the DSCP. Finally internet packed are come through Shaper/Dropper for buffer to achieve a target flow rate or drop the packet in case of crowding.

Fig.2 Traffic conditioning block

Source: http://140.116.82.38/members/html/ms03/dclin/technique_paper/Qos/Differentiated%20Service%20Router.pdf

Classifier ï¿½ select a internet packet based on packet header.

Meter ï¿½ check compliance to traffic parameters.

Marker ï¿½ writes/ re-writes DSCP.

Shaper ï¿½ Delays some internet packets.

Dropper - Dropping some internet packet.

? Differentiated services code point

Differentiated Services Code Point (DSCP) is a field in an IP packet that enables different levels of service to be assigned to network traffic. Each packet is marked with DSCP code and befitting to the corresponding level of service.

DSCP is the aggregation of IP Precedence and ToS fields.

ï¿½

Fig.2 The Original IPv4 ToS Byte

Source: www.cisco.com/en/US/technologies/tk543/tk766/technologies_white_paper09186a00800a3e2f.html

ï¿½

IP Precedence has used the first three bits of the ToS field to give 8 possible precedence values:

111 - Network Control

110 - Internetwork Control

101 - CRITIC/ECP

100 - Flash Override

011 - Flash

101 - Immediate

001 - Priority

000 - Routine

Bits (3-6): The type of Service Defined

0000 -All Normal

1000 -Minimise Delay

0100 -Maximise Throughput

0010 ï¿½ Maximise Reliability

0001 ï¿½ Minimise Monetary Cost

Fig.3 DiffServ Code-point Field

Source: www.cisco.com/en/US/technologies/tk543/tk766/technologies_white_paper09186a00800a3e2f.html

Priority of a packer is identify by the first 6 bits of the Type of Service. IP Precedence is matched with the Class Selector and is correspond by the first 3 bits. Next 3 bits set Drop Precedence.

IP Precedence has six class from 0-5 where 0 means default (Best - Effort forwarding). Better level of service is provided by the higher classes value.

Inside each IP Precedence traffic is assigned a Drop Probability(from low to high)

Classes names for the IP Precedence from 1 to 4 starts with letters 'AF ' which means ASSURED FORWARDING. Following digit applied identify IP Precedence and Drop Probability for example:

AF42- class 4, drop probability medium

Packet with IP Precedence 0 (default) and 5 (Expedited Forwarding) do not have any level of the Drop Probability.

TABLE

DSCP values

Source: www.http://www.rhyshaden.com/qos.htm

? Classification

DiffServ QoS has only few steps. Traffic must be identified and classified into groups then is marked (within Layer2 or Layer 3 header) on trust boundaries, after this must be made POLICIES to describe the per-hop behaviour.

Classification can be based on:

? ACLs (Access control list),

? L2 ( Class of Service ï¿½ Ethernet header),

? L3 ( Type of Service ï¿½ IP Precedence, DSCP),

? MAC address,

? NBAR,

? Variety of UDP port numbers,

? Incoming interface,

? MPLS EXP ( MPLS header ).

? Layer 2 and Layer 3 marking

We use both of Layer 2 and Layer 3 to marking the internet packets. Layer 2 markings are made by switches and Layer 3 by WAN. Most present QoS solutions are distribute at Layer 3.

Layer 2 devices using the three bits CoS field in 802.1Q tagged frames to transfer high status information.

Layer 3 devices use three bits of IP Precedence field from the ToS of the IP header or can use DiffServ field from (ToS octet)

Fig.4 L2 and L3 marking

Source: http://www.perihel.at/2/rno/02-QoS-Marking.pdftml

? NBAR

NBAR is awesome feature created by CISCO. NBAR, routers can look at Layers 4 through 7 and can identifies applications. When application is recognised NBAR can take certain steps to ensure that the application has correct priority.

NBAR with iOS 12,3 is able to identify more applications due to the availability of the Packet Description Language Module (PDLM) feature.

The IOS uses PDLMs to know which application is what when it looks through the traffic flow. Cisco regularly releases new PDLMs for new applications, and you can find the list on the PDLM Web page (valid CCO login required).

Configuring NBAR

? Configuration start from 'cef' command.

Router(config)# ip cef

Router(config)#class-map match-any bad-traffic

Router(config-cmap)# match protocol http

Router(config)#class-map match-all nbar

Router(config-cmap)#match pro ?

? Creating policy.

Router(config)# policy-map mark-bad-traffic

Router(config-pmap)# class bad-traffic

Router(config-pmap)# set ip dscp 1

? Applying policy to the interface.

Router(config)# interface serial 0/0

Router(config-if)#service-policy input mark-bad-traffic

? Create ACL.

Router(config)# access-list 190 deny ip any any dscp 1

Router(config)# access-list 190 permit ip any any

Source:http://www.techrepublic.com/blog/networking/what-can-ciscos-network-based-application-recognition-nbar-do-for-you/399

? Queuing

Queuing is used to store internet packet until they can by processed. We have a lot of queuing methods:

? First-In First-Out (FIFO do not need any configuration, has very simple processing routine and treat all the internet packets the same. No delay guarantee for real ï¿½ time applications like VoIP).

Fig.4 First-In First-Out queuing