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Update Info about single routes through internet List of routes being withdrawn Includes path info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:crw@transcendental.com sip:voicemail@iptel.org?subject=callme sip:17005553171@asterisk.sip.ilabs.interop.net

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