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Integrated Services (RFC 1633)
 Architecture for providing QoS guarantees to individual
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application sessions
Call setup: a session requiring QoS guarantees must reserve
sufficient resources at each router on its path before
transmitting data
A session must:
 declare its QoS requirement using R-spec
 characterize traffic it will send into network using T-spec
A signaling protocol is needed to carry R-spec and T-spec to
routers
Router must determine whether or not it can admit the call
Router must maintain per-flow state (allocated resources,
QoS requests)
RSVP
 RSVP: a signaling protocol for applications to reserve
resources (link bandwidth and buffer space)
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Make reservations for both unicast and multicast transmissions
Receiver-oriented
Can reserve resources for heterogeneous receivers
 Sender sends a PATH message to the receiver specifying R-
spec and T-spec
 Receiver responds with a RESV message to request
resources for the flow
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An intermediate router can reject or accept the request of the
RESV message
A router may merge the reservation messages arriving from
downstream
Intserv Service Models
Guaranteed service:
 Provide firm bounds on end-toend datagram queuing delays.
 Provide bandwidth guarantee
 Token-bucket-policed source +
WFQ
arriving
traffic
Controlled load service:
 Provide a quality of service
closely approximating the QoS
that the same flow would
receive from an unloaded
network element.
 A very high percentage of
transmitted packets will be
successfully delivered to the
token rate, r
destination.
 A very high percentage of
transmitted packets will
bucket size, b
experience a queuing delay
per-flow
close to 0.
rate, R
WFQ
Dmax= b/R
Differentiated Services (RFC 2475)
Concerns with Intserv:
 Scalability: router need to process resource reservations
and maintaining state for each flow.
 Flexible Service Models: not allow relative service
distinctions.
Diffserv approach:
 Goal: provide the ability to handle different classes of
traffic in different ways
 Scalable: simple functions in network core, relatively
complex functions at network edge
 Flexible: don’t define specific service classes, provide
functional components to build service classes
Diffserv Architecture
Edge router:
-Packets are marked
-The mark of a packet
identifies the class of traffic
to which the packet belongs
Core router:
-Packet forwarded to the next hop
according to the per-hop behavior
(PHB) associated with that
packet’s class
-PHB determines buffering
and scheduling at the routers
- Routers needn’t maintain states
for individual flows
Classification and Marking at Edge-Router
 Classification: packets classified based on packet header
fields (source/destination IP address, source/destination
port, protocol ID)
 Marking: packet marked based on per-flow profile
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Traffic profile: pre-negotiated rate A, bucket size B
Meter used to compare the incoming packet flow with the
traffic profile
In-profile packet receive priority marking, out-of-profile
packets might be marked differently, shaped (i.e. delayed), or
dropped
Packet Marking
 Packet is marked in the DS field of the IP packet header
(Type of Service (TOS) field in IPv4, and Traffic Class field
in IPv6)
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6 bits used for Differentiated Service Code Point (DSCP) and
determine PHB that the packet will receive
2 bits are currently unused
 All packets with the same DSCP are referred to as a
behavior aggregate
Forwarding (PHB)
 PHB is “a description of externally observable
forwarding behavior of a Diffserv node applied to
a particular Diffserv behavior aggregate”.
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A PHB can result in different classes of traffic receiving
different performance.
A PHB does not specify what mechanisms to use to
achieve required behaviors
Differences in performance must be observable and
hence measurable
 Examples:
 Class A gets x% of outgoing link bandwidth over time
intervals of a specified length
 Class A packets leave before class B packets
Service Level Agreements
 A customer must have a Service Level Agreement
(SLA) with its ISP.
 A SLA specifies the service classes supported
(traffic profile, performance metrics, actions for
non-conformant packets) and the amount of
traffic allowed in each class.
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Static SLA: pre-provisioned
Dynamic SLA: signaled on demand
 Boundary routers mark, drop, shape packets based
on SLA
 When a packet enters one domain from another
domain, its DS field may be re-marked, as
determined by the SLA between the two domains.
Example Diffserv Services
 Premium Service: low delay and low jitter service
 Assured Service: better reliability than Best
Effort Service
 Olympic Service: three tiers of services: Gold,
Silver and Bronze, with decreasing quality.