1. Rami Neiman & Yaron Perry
Intserv vs. Diffserv
Rami Neiman
&
Yaron Perry

2. QoS=Quality of Service
Different web applications have different needs for QoS
QoS criterias are:
Delay
Delay variation (jitter)
Bandwidth
Packet loss rate

3. An example VoIP conversation requires: Very low jitter
One way delay in order of 150 ms
Guaranteed bandwidth in the range
8Kbps – 64Kbps
FTP application on the other hand doesn’t
suffer from jitter,but requires low packet loss

4. How do we provide QoS?
The IP protocol utilizes the “Best Effort” approach which states:
”I'll do my best under the given curcomstances,but I make no promises.”

5. Is it enough?? The “Best effort” policy was fine once,
but nowdays with introduction to new types
of traffic such as streaming video,VoIP etc.
it’s just not enough.
We need a model that will give us QoS

6. The Solution
To facilitate true end-to-end QoS on an IP-network, the Internet Engineering Task Force (IETF) has defined two models:
Integrated Services (IntServ)
and
Differentiated Services (DiffServ)

7. IntServ
IntServ provides individualized QoS guarantees to individual sessions.
Provides services on a per flow basis where a flow is a packet stream with common source address, destination address and port number.

8. IntServ
Relies on Resource Reservation Protocol (RSVP) to signal and reserve desired QoS for each flow.
IntServ routers must maintain per flow state
information.

9. IntServ:How it works? End hosts signal their QoS needs to the network
Much like in classic telephony,a route for the
flow is being set up.
Every device along the path reserves the resources
needed by the session (flow).
A flow is uniquely identified by:source IP and port,
destination IP and port and it’s transport protocol.

10. IntServ:What it does? From the end-host perspective,IntServ
provides a virtual channel
with given QoS
characteristics.
IntServ can provide
assured bandwidth and
strict delay times.

11. IntServ:Problem solved?
It looks like IntServ model can satisfy every QoS
requirement an application may have.
So it does.
Then, why this presentation has another 18 slides?
Because as you know all the good things come
with a price….

12. IntServ:Disadvantages
Every device along the path of a packet need to be fully aware of RSVP and capable of signaling the required QoS.
Reservations in each device along the path are “soft,” which means they need to be refreshed periodically
- adding to the traffic on the network
- increasing the chance that the reservation may
time out if refresh packets are lost.

13. IntServ:Disadvantages
Maintaining soft-states in each router.
- increased memory requirements to support a large
number of reservations.
- adds to the complexity of each node along the
path.
QoS reservations are made for the “Worst case scenario”,which happens very seldom.
- not a “Web friendly” solution.
- a lot of web resources are being wasted.

14. A different approach How do we overcome the IntServ disadvantages?
A different approach to QoS providing is needed.
What if we aggregate flows (sessions) into classes
and QoS will be given for the class, rather than for
the individual flows?
After all, flows of the same type have nearly the
same QoS requirements.

15. A different approach We can aggregate traffic into classes and provide
each class the type of QoS it needs the most.

16. Traffic aggregation: How it’s done?
The first attempt was the IPv4 ToS (Type Of Service) byte in the IP-header:
- first 3 bits classify the packet into 8 possible classes of traffic.
- latter 4 bits specify the drop priority in case there is a congestion.

17. IPv4 ToS byte: a solution?
No, it failed completely.
- only 8 possible classes of traffic (two of which are
being reserved for control and Internetwork control) are
allowed. It’s not enough.
- drop priority specifications are situation limited.
- the bit mapping is not implemented consistently by
network vendors today.
A different solution is needed.

18. DiffServ: How it works? Packet marking: DiffServ model uses 6 bit
from IP ToS byte to classify packets into groups.
Up to 64 classes (in theory) is available now.This new
field is called Differentiated Services Codepoint (DSCP).

19. DiffServ: How it works? Per-Hop Behavior (PHB): packets,that have
the same DSCP are called “Behavior Aggregate”
or BA. PHB refers to the packet scheduling,
queuing, policing,or shaping behavior of a node on
any given packet belonging to a BA.
In simple words: PHB defines the QoS given to a
group of flows with the same DSCP field value.
The value of DSCP field dictates the PHB of a packet.

20. DiffServ: PHB To date four standard PHBs are available:
Default PHB: (DSCP value of “000000”) provides
the traditional “Best Effort” service.
Class-Selector PHB: (DSCP value of “xxx000”)
provides backward compatibility with IP ToS
model, where “xxx” are the class selector bits.

21. DiffServ: PHB
Expedited Forwarding PHB: (DSCP value of “101110”) provides low-loss, low-latency, low-jitter, and assured bandwidth service.
Assured Forwarding PHB: (DSCP value of “xxxyy0”) provides assurance of delivery (according to “xxx” pattern) as long as the traffic does not exceed some subscribed rate. But when it does the “yy” pattern specifies the drop precedence of a packet.

22. DiffServ: Summary
DiffServ is a simple, scalable and coarse-grained mechanism for classifying, managing network traffic and providing QoS guarantees on modern IP networks.
DiffServ is much more scalable than IP ToS model.
DiffServ wastes less network resources than IntServ does.
DiffServ doesn’t require such node complexity and resources as IntServ.
However DiffServ doesn’t provide such fine-grained per-flow QoS as IntServ does.

23. DiffServ vs. IntServ
Just to visualize the differences between the two models here’s an example from your everyday life to help you understand.
Picture this…
Just like an IP packet you have multiple
transportation options to get from point A to
point B.

24. DiffServ vs. IntServ
The most comfortable way is to travel in your private car:
- you can listen to whatever
music you like.
- adjust the air conditioning.
- take with you whoever you
whish or you can travel alone.
That would be traveling with
IntServ – best QoS you can get.

25. DiffServ vs. IntServ However… When everybody is
using their private car,
traffic jam is the only
possible outcome.
It is also the most expensive way to get around.

26. DiffServ vs. IntServ The second option is to travel by minibus.
This way it’s cheaper and helps to reduce the traffic and avoid traffic jams.
In addition we can put people
with the same type of interest
in the same minibus and
provide them with type of
comfort they need.

27. DiffServ vs. IntServ
For instance students can travel together, and we'll
install a Wi-Fi hotspot in their
minibus to provide Internet access.
Solders can have a large trunk for their bags
And children can watch cartoons as they ride.
It’s a fair trade between comfort and price and it’s called DiffServ

28. DiffServ vs. IntServ
While the pure IP “Best effort” type of traveling is more like…
Most traffic friendly however 

29. DiffServ vs. IntServ To summarize here’s some coarse comparison
between the QoS and Network utilization provided by IntServ,
DiffServ and “Best Effort” models.