Proposed Differentiated Services on the Internet By Dr. Junaid A. Zubairi Department of Math and Computer Science SUNY at Fredonia

Overview of Presentation §The Evolution of Internet §The Types of Traffic on the Internet §Performance Issues in Packet Switching §The World Wide Web §Changing Traffic on the Internet §The Birth and Death(?) of ATM!! §IETF’s DiffServ Model §MPLS

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 and ftp

The Evolution of Internet §Internet was primarily used for , usenet, file transfer and remote usage of machines §With , users were able to keep in touch §With usenet, users were able to discuss topics of interest in focussed newsgroups §With file transfer, users could download and upload articles, programs and images  With telnet, a user could login to his or her UNIX account from anywhere

Types of Traffic on the Internet § , 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 took §With 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

Adapted for academic use from OPNET Modeler Tutorial

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 easy §Due 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 l ATM is too complex (From packets to cells to SONET frames, using AAL’s, emulating LAN) l ATM is expensive l Ethernet has evolved into much faster 100Mbps and 1000Mbps services l 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

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

IETF’s DiffServ Model

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