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Network Protocols
UNIT III- INTERNETWORK PROTOCOLS
Routing ProtocolsRouting Information
About topology and delays in the internet
Routing Algorithm Used to make routing decisions based on
information
Autonomous Systems (AS)Group of routersExchange informationCommon routing protocolSet of routers and networks managed by
signle organizationA connected network
There is at least one route between any pair of nodes
Interior Router Protocol (IRP)Passes routing information between routers
within ASMay be more than one AS in internetRouting algorithms and tables may differ
between different ASRouters need some info about networks
outside their ASUsed exterior router protocol (ERP) IRP needs detailed modelERP supports summary information on
reachability
Application of IRP and ERP
Border Gateway Protocol (BGP)For use with TCP/IP internetsPreferred EGP of the InternetMessages sent over TCP connections
Open Update Keep alive Notification
Procedures Neighbor acquisition Neighbor reachability Network reachability
BGP Messages
BGP ProcedureOpen TCP connectionSend Open message
Includes proposed hold time
Receiver selects minimum of its hold time and that sent Max time between Keep alive and/or update
messages
Message TypesKeep Alive
To tell other routers that this router is still here
Update Info about single routes through internet List of routes being withdrawn Includes path info
Origin (IGP or EGP)AS_Path (list of AS traversed)Next_hop (IP address of boarder router)Multi_Exit_Disc (Info about routers internal to AS)Local_pref (Inform other routers within AS)Atomic_Aggregate, Aggregator (Uses address tree
structure to reduce amount of info needed)
Uses of AS_Path and Next_HopAS_Path
Enables routing policyAvoid a particular ASSecurityPerformanceQualityNumber of AS crossed
Next_Hop Only a few routers implement BGP
Responsible for informing outside routers of routes to other networks in AS
Notification MessageMessage header error
Authentication and syntax
Open message error Syntax and option not recognized Unacceptable hold time
Update message error Syntax and validity errors
Hold time expired Connection is closed
Finite state machine errorCease
Used to close a connection when there is no error
BGP Routing Information ExchangeWithin AS, router builds topology picture
using IGPRouter issues Update message to other
routers outside AS using BGPThese routers exchange info with other
routers in other ASRouters must then decide best routes
Open Shortest Path First (1)OSPF IGP of InternetReplaced Routing Information Protocol (RIP)Uses Link State Routing Algorithm
Each router keeps list of state of local links to network
Transmits update state info Little traffic as messages are small and not sent often RFC 2328
Route computed on least cost based on user cost metric
Open Shortest Path First (2)Topology stored as directed graphVertices or nodes
Router Network
TransitStub
Edges Graph edge
Connect two routerConnect router to network
Sample AS
Directed Graph of AS
OperationDijkstra’s algorithm (Appendix 10A) used
to find least cost path to all other networks
Next hop used in routing packets
Integrates Services ArchitectureChanges in traffic demands require variety
of quality of service Internet phone, multimedia, multicastNew functionality required in routersNew means of requesting QoSISARFC 1633
Internet TrafficElastic
Can cope with wide changes in delay and/or throughput
FTP sensitive to throughputE-Mail insensitive to delayNetwork Management sensitive to delay in times of
heavy congestionWeb sensitive to delay
Inelastic Does not easily adapt to variations e.g. real time traffic
Requirements for Inelastic TrafficThroughputDelay Jitter
Delay variation
Packet loss
Require preferential treatment for certain types of traffic
Require elastic traffic to be supported as well
ISA ApproachCongestion controlled by
Routing algorithms Packet discard
Associate each packet with a flow Unidirectional Can be multicast
Admission ControlRouting AlgorithmQueuing disciplineDiscard policy
ISA Components
Token Bucket Traffic SpecificationToken replenishment rate R
Continually sustainable data rate
Bucket size B Amount that data rate can exceed R for short
period During time period T amount of data sent can
not exceed RT + B
Token Bucket Scheme
ISA ServicesGuaranteed
Assured data rate Upper bound on queuing delay No queuing loss Real time playback
Controlled load Approximates behavior to best efforts on
unloaded network No specific upper bound on queuing delay Very high delivery success
Best Effort
Queuing DisciplineTraditionally FIFO
No special treatment for high priority flow packets Large packet can hold up smaller packets Greedy connection can crowd out less greedy
connection
Fair queuing Queue maintained at each output port Packet placed in queue for its flow Round robin servicing Skip empty queues Can have weighted fair queuing
FIFO and Fair Queue
Resource Reservation: RSVPUnicast applications can reserve resources
in routers to meet QoS If router can not meet request, application
informedMulticast is more demandingMay be reduced
Some members of group may not require delivery from particular source over given time
e.g. selection of one from a number of “channels”
Some group members may only be able to handle a portion of the transmission
Soft StateSet of state info in router that expires
unless refreshedApplications must periodically renew
requests during transmissionResource ReSerVation Protocol (RSVP)RFC 2205
RSVP GoalsAbility for receivers to make reservationsDeal gracefully with changes in multicast
group membershipSpecify resource requirements such that
aggregate resources reflect requirementsEnable receivers to select one sourceDeal gracefully with changes in routesControl protocol overheadIndependent of routing protocol
RSVP CharacteristicsUnicast and MulticastSimplexReceiver initiated reservationMaintain soft state in the internetProvide different reservation stylesTransparent operation through non-RSVP
routersSupport for IPv4 and IPv6
Data Flow ConceptsSession
Data flow identified by its destination
Flow descriptor Reservation request issued by destination Made up of flowspec and filterspec Flowspec gives required QoS Filterspec defines set of packets for which
reservation is required
Treatment of Packets
RSVP Operation
RSVP Message TypesResv
Originate at multicast receivers Propagate upstream through distribution tree Create soft states within routers Reach sending host enabling it to set up traffic
control for first hop
Path Provide upstream routing information
Operation From Host PerspectiveReceiver joins multicast group (IGMP)Potential sender issues Path messageReceiver gets message identifying senderReceiver has reverse path info and may
start sending Resv messagesResv messages propagate through
internet and is delivered to senderSender starts transmitting data packetsReceiver starts receiving data packets
Differentiated Services Provide simple, easy to implement, low overhead
tool to support range of network services differentiated on basis of performance
IP Packets labeled for differing QoS using existing IPv4 Type of Service or IPv6 Traffic calss
Service level agreement established between provider and customer prior to use of DS
Built in aggregation Good scaling to larger networks and loads
Implemented by queuing and forwarding based on DS octet No state info on packet flows stored
DS ServicesDefined within DS domain
Contiguous portion of internet over which consistent set of DS policies are administered
Typically under control of one organization Defined by service level agreements (SLA)
SLA ParametersDetailed service performance
Expected throughput Drop probability Latency
Constraints on ingress and egress pointsTraffic profiles
e.g. token bucket parameters
Disposition of traffic in excess of profile
Example ServicesLevel A - low latencyLevel B - low lossLevel C - 90% of traffic < 50ms latencyLevel D - 95% in profile traffic deliveredLevel E - allotted twice bandwidth of level
F trafficTraffic with drop precedence X higher
probability of delivery than that of Y
DS Octet - Code PoolsLeftmost 6 bits used3 pools of code pointsxxxxx0
assignment as standards
xxxx11 experimental or local use
xxxx01 experimental or local but may be allocated for
standards in future
DS Octet - Precedence FiedlRouting selectionNetwork serviceQueuing discipline
DS Domains
DS Configuration and OperationWithin domain, interpretation of DS code
points is uniformRouters in domain are boundary nodes or
interior nodesTraffic conditioning functions
Classifier Meter Marker Shaper Dropper
DS Traffic Conditioner
What Protocols Are Needed for IP Telephony?Signaling protocol to establish presence,
locate users, set up, modify and tear down sessions
Media Transport Protocols for transmission of packetized audio/video
Supporting Protocols for Gateway Location, QoS, interdomain AAA, address translation, IP, etc.
SIP is the Session Initiation Protocol SIP is an application layer signaling protocol
create, modify and terminate sessions two or more participants
Uses URL style addresses and syntax Flexible transport: can use UDP, TCP, TLS, or SCTP Uses SDP for describing media sessions: Audio,
Video, realtime Text, IM, speech services, etc. Applications include (but not limited to): Voice,
video, gaming, instant messaging, presence, call control, etc.
Simple extensible protocol Methods—Define transaction Headers—Describe transaction Body—SDP and other MIME content
VoIP in the EnterpriseServices available to all company’s users, on-site, offsite and multi-site – toll bypass.
•No telephone line required for home-workers and remote offices.
•Single infrastructure for data and voice.
•Effectiveness tools.
•Service operation can be outsourced in a Centrex-like manner (MCI Advantage). Like with web/email, single server may host multiple domains
SIP Makes VoIP Easyand Interoperable IETF development, learning from HTTP
experience, leads to (eventually) excellent interoperability
Becoming an IP-Telephony operator takes complexity comparable to setting up E-mail server: – Configure DNS – Download and configure a SIP proxy server – Configure supporting services: web provisioning,
database back-end typically. – Configure PSTN gateway for use with your proxy
server.
SIP Architecture is Easy to Understand
Directory:DNS
ENUM
Call Setup:SIPSDP
Call Transport:RTP
AAA:Radius
Diameter
IP Network
PSTN GatewayPSTN
IP Softphone
SIP Addresses are Global SIP gives you a globally reachable address.
Callees bind to this address using SIP REGISTER method. Callers use this address to establish real-time
communication with callees.
URLs used as address data format; examples: sip:[email protected] sip:[email protected]?subject=callme sip:[email protected]
RTP: A Transport Protocol for Real-Time ApplicationsProvides end-to-end delivery services for
data with real-time characteristics, such as interactive audio and video.
Those services include payload type identification, sequence numbering, timestamping and delivery monitoring.
Applications typically run RTP on top of UDP
Audio and Video Conference Audio and video media are are transmitted as separate
RTP session and RTCP packets are transmitted for each medium using two different UDP port pairs and/or multicast addresses.
There is no direct coupling at the RTP level between the audio and video sessions, except that a user participating in both sessions should use the same distinguished (canonical) name in the RTCP packets for both so that the sessions can be associated.
Despite the separation, synchronized playback of a source's audio and video can be achieved using timing information carried in the RTP packets for both sessions.
MIXERReceives streams of RTP data packets
from one or more sources, possibly changes the data format, combines the streams in some manner and then forwards the combined stream.
All data packets forwarded by a mixer will be marked with the mixer's own SSRC identifier. In order to preserve the identity of the original sources contributing to the mixed packet
TranslatorForwards RTP packets with their SSRC
identifier intactMay change the encoding of the data and
thus the RTP data payload type
RTP Header
Sequence numberPayload type
Timestamp
SSRC identifier
RTCPIs based on the periodic transmission of
control packets to all participants in the session and perform the following functions: provide feedback on the quality of the data
distribution and allows one who is observing problems to evaluate whether those problems are local or global.
RTCP carries an identifier for an RTP source called the canonical name or CNAME. Receivers use CNAME to associate multiple data streams from a given participant in a set of related RTP sessions, for example to synchronize audio and video.
RTCP Packet Format
SR: Sender report, for transmission and reception statistics from participants that are active senders.
RR: Receiver report, for reception statistics from participants that are not active senders.
SDES: Source description items, including CNAME.
BYE: Indicates end of participation.APP: Application specific functions.
RTCP Transmission Interval RTP is designed to allow an application to scale
automatically over session sizes ranging from a few participants to thousands.
In an audio conference the data traffic is inherently self- limiting because only one or two people will speak at a time, so with multicast distribution the data rate on any given link remains relatively constant independent of the number of participants.
However, the control traffic is not self-limiting. If the reception reports from each participant were sent at a constant rate, the control traffic would grow linearly with the number of participants.
To maintain scalability, the average interval between packets from a session participant should scale with the group size.
The control traffic should be limited to a small and known fraction of the session bandwidth: small so that the primary function of the transport
protocol to carry data is not impaired; known so that each participant can independently
calculate its share.
It is suggested that the fraction of the session bandwidth allocated to RTCP be fixed at 5%
Receiver Report RTCP Packet
Type Length
SSRC of packet sender
SSRC of first source
Fraction lost Cumulative number of packet lost
Interarrival jitter
Last SR
Delay since last SR
RC
Rep
ort b
lock
1
Report block 2