proposed differentiated services on the internet by dr. junaid a. zubairi department of math and...

Proposed Differentiated Services on the Internet

By

Dr. Junaid A. ZubairiDepartment of Math and Computer Science

SUNY at Fredonia

Overview of Presentation

The Evolution of InternetThe Types of Traffic on the InternetPerformance Issues in Packet SwitchingThe World Wide WebChanging Traffic on the InternetThe Birth and Death(?) of ATM!! IETF’s DiffServ ModelMPLS

The Evolution of Internet

DARPA (Defense Advanced Projects Research Agency) started the ARPAnet in 1969 between four nodes

The Internet was primarily used for connecting academic campuses together until the mid 80’s

Academicians used the Internet for sharing ideas and research results via email and ftp

The Evolution of Internet

Internet was primarily used for email, usenet, file transfer and remote usage of machines

With email, users were able to keep in touchWith usenet, users were able to discuss

topics of interest in focussed newsgroupsWith file transfer, users could download and

upload articles, programs and imagesWith telnet, a user could login to his or her

UNIX account from anywhere

Types of Traffic on the Internet

Email, usenet, ftp and telnet were applications that generated almost similar type of traffic stream on the Internet

This traffic required “reliability”. The protocols were expected to deliver all

the data no matter how long it tookWith high error rate, the elapsed time

simply increased but the transmissions were completed

Performance Issues in Packet Switching

For transmission on the Internet, the TCP/IP suite of protocols breaks the data into datagrams or packets and routes each packet through an independently selected path

Packets may arrive at the destination out of sequence but due to buffering and re-ordering, the actual data can be recovered easily


Path selection criterion is usually shortest path first

If the shortest path is congested or unreliable, the router can choose another path

All routers decide independently and it is a distributed environment

Traditional TCP/IP based traffic is bursty and it can increase or decrease abruptly


Given this scenario, a router may find itself overwhelmed with a lot more packets than it can handle

Routers have limited buffering space in which a queue of packets is managed (Refer to Figure on next slide )

Usually routers would use simple FIFO scheme to select the next packet to be transmitted

Adapted for academic use from OPNET Modeler Tutorial


If the queue is full, the newly arrived packets must be dropped (or discarded)

Thus increase in traffic may increase time-outs, retransmissions and decrease in efficiency

To sum it up, the traditional TCP/IP network based on packet switching is a “best effort” network


The packet switching network makes its best effort to deliver the data however it makes no guarantees or promises to the user about the network performance

What is meant by network performance?Network performance is “Throughput”Throughput could be defined as the aggregate

rate of transmission offered by the network to the user

The World Wide Web

The introduction of hypertext marking language (HTML) in early 1990 has revolutionized the Internet

HTML and its associated protocol HTTP have transformed the Internet into a user-oriented information repository

HTML has also made it very easy to “publish” information online even for users with very little computer expertise

The World Wide Web

The open ended HTTP has resulted in supporting the linking of various types of data into the web published documents

HTTP makes it possible for web sites to offer binary files, images, and multimedia documents to the users with the click of a button

HTTP has also resulted in making the Internet very popular. Internet continues to expand in number of websites and the number of users

The World Wide Web

Web deployment is flexible and easyDue to the web technologies, the Internet has

been put to use in almost all areas of human knowledge

For example, water distribution monitoring, real-time traffic maps of big cities, free long distance calling, distance learning with lecture videos, buying and selling shares, online shopping etc., the list appears endless

The Changing Traffic on the Internet

Due to the web enabled applications on the Internet, there has been a tremendous change in the types of traffic

Now we have to deal with a significant amount of traffic that is time-sensitive

For example, consider the case of an audio based application that needs to transmit the data across the Internet

Adapted for Academic Use from "Computer Networks: A Systems Approach" Peterson and Davie Morgan Kaufmann 2000

The Changing Traffic on the Internet

The Birth and Death(?) of ATM!!

In this scenario, ATM offered a great promise to the users

ATM (Asynchronous Transfer Mode) is a cell-switching technology that was targeted to become the B-ISDN (Broad ISDN) network of the future

ATM was developed with the right targets and it offered the much awaited performance assurance


ATM is a connection-oriented technology that offers various categories of services (performance promises) to the users

Service categories include• CBR (Constant Bit Rate such as telephony)

• RT-VBR (real-time video such as videoconference)

• NRT-VBR (Non real-time video e.g. stored video)

• ABR (Available BR such as web browsing)

• UBR (Unspecified BR such as ftp)


If a user requests a certain service, ATM uses CAC (Connection Admission Control) to determine if granting this request would not jeopardize existing contracts

User and network agree on certain QoS parameters such as PCR (Peak Cell Rate), SCR (Sustained Cell Rate) and CDV (Cell Delay Variation) etc.


In order to meet the QoS contract obligations, ATM network enforces traffic shaping and policing

Shaping involves techniques such as “Leaky Bucket Algorithm” to regulate bursty traffic

Policing means marking CLP (Cell Loss Priority) on the offending cells that violate the maximum rates agreed

Adapted for academic use from "Computer Networks" Tanenbaum Prentice Hall 1996

Leaky Bucket Algorithm


However, the evolution of shared Ethernet into switched Ethernet at 10Mbps and development of Fast Ethernet at 100Mbps stalled the ATM’s march to the desktop

ATM was pushed back to the backbones of campus networks

Gigabit Ethernet in the backbone appears to be the last nail in the coffin for ATM


ATM failed because of several factors ATM is too complex (From packets to cells to

SONET frames, using AAL’s, emulating LAN) ATM is expensive Ethernet has evolved into much faster 100Mbps

and 1000Mbps services All popular and established network

applications are packet based

IETF’s Models

It was felt that instead of focussing on coping with congestion, Internet should be run in a way that there is no congestion

Applications should be able to reserve network resources at a given QoS

IETF has been working on developing new models and protocols for the Internet and private networks

IETF’s Models

IntServ and RSVP provide quantitative guarantees to each flow. RSVP requires all intermediate routers to keep track of each and every flow through “soft state”.

RSVP flows involve signaling and soft state overhead and RSVP does not scale well to the Internet. It may be successfully deployed in a campus network

IETF’s DiffServ Model

IETF is developing a model to provide differing levels of service to different applications without the overhead of signaling and state maintenance

The DiffServ model uses the TOS field in IPv4 header to affix labels on packets belonging to different service levels

DiffServ has the potential to offer QoS on the

Internet, at last!!


Consider a gas station, you can buy regular, super or premium gas from the same pump

DiffServ offers various service levels to the customer from the same network with SLA

DiffServ adopts techniques used in ATM for traffic management, in a simplified way

DiffServ treats the network and the customer in the way the ATM does.i.e. Customer gets a link at the specified level of service to the network.


DiffServ levels of service are implemented in a DiffServ domain

The customer connects to the “edge router” at the edge of the DiffServ domain

The edge router performs traffic classification (using DS codepoint marked by customer in TOS to separate the packets)

It then measures submitted traffic for conformance to the agreed profile


The edge router then changes the DS code byte of offending packets

It may also do traffic shaping by delaying the packets as necessary and dropping the offending packets

Refer to the diagram in the next slide to see the edge router function

Adapted for Academic Use from "Data and Computer Communications" W. Stallings Prentice Hall 2000


IETF has defined two DS services that are visible as PHB (per-hop-behavior) of an intermediate router for the marked packet

EF (Expedited Forwarding) EF is the premium service offered. It can appear

as a virtual leased line for the customer. It offers low loss/latency and assured bandwidth

http://www.ietf.org/rfc/rfc2598.txt



AF (Assured Forwarding) The AF PHB group provides delivery of IP

packets in four independently forwarded AF classes. Within each AF class, an IP packet can be assigned one of three different levels of drop precedence. A DS node does not reorder IP packets of the same microflow if they belong to the same AF class.



MPLS

MPLS (Multi Protocol Label Switching) is the most promising protocol for the Internet

An MPLS domain has an ingress node that nails down paths through the maze of core routers for every requesting flow until the exit door (egress node)

Thus every router does not have to decide about the path of each packet

MPLS

Intermediate routers use a “shim header” or a layer 2.5 header to decide about the next hop of a packet

This shim header is inserted between the frame header and packet header

It is used by the router to consult a table that tells what path is good for this packet

This shim header is the “Label” and the whole thing is called “Label Switching”

MPLS

Instead of routing, now the routers do label switching

Since the path is pre-determined, routers can speed up the processing of packets

Also, the management can decide LSP’s (label switched paths) based on load distribution and other administrative goals

Thus the connectionless network changes into a connection oriented network

Summary

Thus we can see that the Internet is changing in a major way

MPLS and Diffserv are being combined to provide EF paths to certain flows such as IP telephony, AF paths to multimedia streaming and DF paths to ftp, email etc

In future, Internet may be able to provide the QoS that is only enjoyed by telephone and Radio/TV broadcasting

proposed differentiated services on the internet by dr. junaid a. zubairi department of math and...

Documents

evolution of internet

internet performance

packet switching

internet email

network performance

ftp slide

fredonia slide

transmitted slide