Teletraffic engineering in broadband networks

Teletraffic engineering

Telecommunications traffic engineering, teletraffic engineering, or traffic engineering is the application of traffic engineering theory to telecommunications...

is a well-understood discipline in the traditional telephone network

Telephone network

A telephone network is a telecommunications network used for telephone calls between two or more parties.There are a number of different types of telephone network:...

, where traffic patterns are established, growth rates can be predicted, and vast amounts of detailed historical data are available for analysis. However, for modern broadband networks

Broadband Networks

The ideal telecommunication network has the following characteristics: broadband, multi-media, multi-point, multi-rate and economical implementation for a diversity of services [1][2]. The Broadband Integrated Services Digital Network provides these characteristics in today's networks...

, the teletraffic engineering methodologies used for voice networks no longer suffice [1]. Various aspects relating to teletraffic engineering in broadband networks are discussed in this article.

Firstly, the nature of broadband traffic is different from that of traditional voice networks. Many of the methodologies developed for traditional networks were based on the nature of voice calls, and are therefore not applicable to broadband networks. The nature of broadband traffic (broadband traffic characteristics) is discussed in the following sub-section.

The inherent nature of broadband networks is also different from that of traditional voice networks. Broadband networks have:

high speeds,
small cell sizes (in ATM networks), and
limited information in the header.

These factors make teletraffic engineering in broadband networks more difficult than in traditional voice networks. A few more factors that further complicate teletraffic engineering in broadband networks [2] are:

A wide range of applications with diverse Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

(QoS) requirements must be catered for.
Much of the traffic (e.g., voice, video) is not amenable to flow control
Flow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...

.
The feedback within the network is “slow”.
There are a large variety of traffic patterns (see long-tail traffic
Long-tail traffic
This article covers a range of tools from different disciplines that may be used in the important science of determining the probability of rare events....

).

Broadband traffic characteristics

In the traditional voice network, the study of traffic characteristics has matured over many years following the seminal work of Erlang

Agner Krarup Erlang

Agner Krarup Erlang was a Danish mathematician, statistician and engineer, who invented the fields of traffic engineering and queueing theory....

in 1909. However, the teletraffic theory that has evolved relied heavily on the facts that

Only one type of connection is offered, a circuit-switched connection, and
the order of magnitude of the call holding time is relatively stable and well-known, namely the few minutes of a telephone conversation.

The diversity of broadband service connections (see broadband networks

Broadband Networks

) and the variety of holding times make the application of teletraffic theory in voice networks to broadband networks very difficult [3]. Figure 1 and Figure 2 show some applications and the variation in holding time and burstiness

Burst transmission

In telecommunication, the term burst transmission or data burst has the following meanings:# Any relatively high-bandwidth transmission over a short period of time...

that may be expected for each one.
To manage the traffic implications of all these types of connections, we must return to the basic principles of traffic statistics. This has been extensively studied in recent years, and there is a large volume of published work on the subject. A Poisson process with one parameter does accurately model telephony traffic. However, to account for the changes with broadband traffic, alternatives to the Erlang

Erlang

Erlang may refer to:* Agner Krarup Erlang , a mathematician and engineer after whom several concepts are named** Erlang , a unit to measure traffic in telecommunications or other domains...

formula have been considered [4]. Two methods of modelling the traffic are considered, namely the Bernoulli-Poisson-Pascal approximation and the Maximum Entropy method. These methods use two parameters for describing the traffic – one for the mean demand and another to characterize the variability of the traffic. (See also Long-tail traffic

Long-tail traffic

This article covers a range of tools from different disciplines that may be used in the important science of determining the probability of rare events....

Mechanisms used for teletraffic engineering in broadband networks

There are two primary mechanisms that are used for teletraffic engineering in broadband networks, namely:

Traffic Control and Management, and
Congestion Control

These two mechanisms are described in the following two sub-sections.

Traffic control and Management

Traffic control and management is defined as [2] the set of actions performed by the network to:

avoid congestion
ensure that users get their required Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

(QoS) guarantees.

The basic control problem is related to the efficient allocation of network resources so as to:

satisfy different QoS requirements; and
provide fair access to the network resources for all users

Traffic control and management provides the means by which:

a user is ensured that the offered cell flows meet the rate specified in the traffic contract
Traffic contract
If a service wishes to use a broadband network to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic...

; and
the network is ensured that the traffic contract
Traffic contract
If a service wishes to use a broadband network to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic...

rates are enforced such that the Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

guarantees are provided for all users.

Congestion Control

Congestion control is defined as [2] the set of actions performed by the network to prevent or reduce congestion. Congestion control is the most important part of the traffic management issue.

A network that controls congestion must:

be responsive to the different utility functions of the users
be able to manage the resources so that there is no loss of utility as the load increases

See Congestion Control for the full article.

A simple example

The process of how a broadband network provides different levels of service to different types of traffic while avoiding congestion will be described briefly by means of a simple example. Links are provided for the reader interested in a more detailed description of the various concepts involved.

The concept of traffic control in broadband networks (particularly in ATM

Asynchronous Transfer Mode

Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

networks) is very simple: an application that requires the network to transport traffic from one location to another with a specific Quality of Service

Quality of service

The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

(QoS) follows the following procedure [5]:

The application declares the traffic’s characteristics and the Quality of Service required by the traffic in a traffic contract
Traffic contract
If a service wishes to use a broadband network to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic...

(in order to make a connection request).
The network judges whether it has enough resources available to accept the connection, and then either accepts or rejects the connection request. This is known as admission control.
If there are insufficient resources available in the network at the time, the connection request is rejected.
If there are sufficient resources available in the network at the time, the connection request is accepted and the network assigns the resources necessary to the connection.
During communication, the network monitors the conformity between the declared traffic characteristics (in the traffic contract) and the characteristics of the actual traffic entering the network. This is known as traffic policing
Traffic policing
Traffic policing is the process of monitoring network traffic for compliance with a traffic contract and taking steps to enforce that contract. Traffic sources which are aware of a traffic contract may apply traffic shaping to ensure their output stays within the contract and is thus not discarded...

.
The network has the capability to discard the non-conformant traffic in the network (using Priority Control).
The overall rate at which all the traffic is admitted into the network is governed by the network’s traffic shaping
Traffic shaping
Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...

policy.

The ATM Traffic Management Framework

The ITU-T has defined a collection of ATM control mechanisms that operate across a spectrum of timing intervals [6]. These control mechanisms are summarised in table 1.

Table 1: Summary of control mechanisms defined in ATM [2]
Response Time	Traffic Control Functions	Congestion Control Functions
Long term	Network Resource Management
Connection Duration	Connection Admission Control (CAC)
Round-trip propagation time	Fast Resource Management	Explicit forward congestion indication (EFCI),ABR Flow Control Flow control In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
Cell insertion time	UPC and NPC, Priority Control, Traffic Shaping Traffic shaping Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...	Selective Cell Discard, Frame discard