proposed differentiated services on the internet by dr. junaid a. zubairi department of math and...
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TRANSCRIPT
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
Performance Issues in Packet Switching
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
Performance Issues in Packet Switching
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
Performance Issues in Packet Switching
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
Performance Issues in Packet Switching
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
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
The Birth and Death(?) of ATM!!
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)
The Birth and Death(?) of ATM!!
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.
The Birth and Death(?) of ATM!!
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
The Birth and Death(?) of ATM!!
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
The Birth and Death(?) of 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!!
IETF’s DiffServ Model
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.
IETF’s DiffServ Model
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
IETF’s DiffServ Model
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
IETF’s DiffServ Model
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
IETF’s DiffServ Model
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.
http://www.ietf.org/rfc/rfc2597.txt
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