prof. younghee lee 1 computer networks u chap. 6 qos and multicast 전산학과 교수 이영희

1Prof. Younghee Lee

Computer Networks Chap. 6 QoS and Multicast

전산학과

교수 이영희

2Prof. Younghee Lee

DistributedSimulation

DistanceLearning

VideoConferencing

Games

Why Is It Not Happening?

Network QoS model is too primitive.

– Large gap between network and application QOS

– Too low level; hard to use Applications have insufficien

t information about the network to make informed decisions.

– Am I using a modem or a gigabit Ethernet?

– Where can I get more bandwidth

Service providers have little control over how their traffic is handled.

– No customization

User User

Too ComplexNo

InformationNo Control

3Prof. Younghee Lee

Internet Traffic: Inelastic Traffic Traffic which does not easily adapt to changes in delay and throughput across the Internet: real time traffic Requirements

– Throughput: A minimum throughput value– Delay: delay sensitive: ex) stock trading– Jitter: delay variation: teleconference require a reasonable upper bound on jitter– Packet loss: the amount of packet loss sustainable

New requirements – some means to give preferential treatment to applications with more demanding requirements.

» Application need to be able to state their requirements, either ahead of time or on the fly: stating ahead of time is preferable(negotiating) » elastic traffic must still be supported in times of congestion, inelastic traffic will continue to supply a high load, and elastic traffic will be crowded off the Internet

4Prof. Younghee Lee

Admission Control Admission control deciding when the addition of new people would

result in reduction of utility– Basically avoids overload

Problem: It requires the concurrence of all the nodes situated along the path– need global information

» not practical: diverse requirement of MM application. Broadcasting information in real time:

hard Large latency at gigabit speed: obsolete, inconsistent

Node Admission Control(NAC): the process of deciding whether a node can admit a new connection

Issues in admission control– the parameter specified by the user may not be correct. Conservative? -> low

utilization– admit new traffic taking into consideration the statistical smoothing effects?– Traffic existing in the network can be calculated from the user specified

characteristics or be based on actual measurement?» Admission control based on measurement: achieve high utilization

observation interval: window -> window size? ;issue decision made based on the past behavior + measured data

5Prof. Younghee Lee

How Things Fit Together

Admission Control

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Forwarding Table Per Flow QoS Table

6Prof. Younghee Lee

ISA Service level a number of general categories of service are provided

– Guaranteed: hard real-time (“real-time” applications)» For intolerant and rigid applications» Fixed guarantee, network meets commitment as long as clients send at match traffic agreement

– Control load: soft real-time (“tolerant and adaptive” applications)» network to client: similar performance as an unloaded best-effort network» client to network: the session does not send more than it specifies» Two components

If conditions do not change, commit to current service If conditions change, take steps to deliver consistent performance (help apps minimize playback delay) Implicit assumption – network does not change much over time

» video: adaptive by dropping a frame or delaying the output stream slightly» voice: adaptive by adjusting silent periods.

– Best effort: (“elastic” applications)

7Prof. Younghee Lee

Packet Scheduling

Network meet promises by scheduling– Queuing at router– Token bucket filter to characterize traffic

Possible Uses1. Shaping

Delay packets from entering point

2. Policing May drop packets that arrive without token or Marking: Let all pkts pass through with marking

8Prof. Younghee Lee

Token bucket Token bucket traffic scheme

– A token replenishment rate R: specifies the continually sustainable data rate– A bucket size B: specifies the amount by which the data rate can exceed R for short period of

time– During any time period T, the amount of data sent cannot exceed RT + B– Bucket: represent a counter that indicates the allowable number of octets

» Bucket fills with octet tokens at the rate of R

9Prof. Younghee Lee

ISA Services Token bucket traffic scheme

– two counters: token counter, counter to implement the timer– major advantage: simplicity – P :peak rate, A :average rate, R :token rate– A peak rate limiting spacer is implicit: R– P > R > A: – Maximum burst size: b’

» b(t)= B + (R-P) x t : assuming token is full at the beginning» 0 = B + (R-P) x t -> t = B/(P-R) -> b’ = Pt = B/(1- R / P)

10Prof. Younghee Lee

Scheduling: Queuing discipline Drawbacks to the FIFO queuing discipline

– No special treatment to packets from flow of higher priority such as delay sensitive traffic flow – larger average delay per packet than if the shorter packets were transmitted before the longer packet. Flows of larger packets get better service – A greedy TCP connection can crowd out altruistic connections. Ex) RTO backoff in congestion

Fair Queuing– A router maintains multiple queues at each output port– round robin, skip over empty queues. Load-balancing, protect greedy..


Processor sharing Drawbacks of fair queuing scheme

– Short packet are penalized » one packet per cycle

Processor sharing– transmit one bit from each queue on each round

» not practical to implement » : value of R(t) when packet i in queue alpha ends transmission

BRFQ– solve the problem in FQ: “short packet are penalized”

» BRFQ: uses packet length as well as flow identification– designed to emulate PS– rule: whenever a packet finishes transmission, the next packet sent is the one with the

smallest value of .– Good approximation to the performance of PS. Figure 11.10

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Bit-round Fair Queuing(BRFQ)


Generalized Processor Sharing Motivation

– BRFQ can’t provide different amount of the capacity to different flows.– Differential allocation capacity;

» To support QoS transport GPS

– provides a means of responding to different service requests– each flow is assigned a weight that is the number of bits transmitted from the queue during each round.

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Weighted Fair Queuing(WFQ) WFQ

– provide different amount of the capacity to different flows.– designed to emulate GPS– rule: whenever a packet finishes transmission, the next packet sent is the one with the smallest value of .

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Summary

Isolation– Isolates well-behaved from misbehaving sources

Sharing– Mixing of different sources in a way beneficial to all

Mechanisms:– WFQ

» Great isolation but no sharing» fairness

– FIFO» Great sharing but no isolation» Efficiency


Resource Reservation (RSVP)

RSVP Characteristics(1)– Unicast and multicast: make reservation for both– simplex:– receiver-initiated reservation

» ATM, FR: the source requests a given set of resources reasonable in a unicast environment but inadequate for multicasting; diff

erent resource requirements(subflow) QoS requirements of different receivers may differ depend on the output

device, processing power, and link speed of the receiver.

» A sender provides the routers with the traffic characteristics. The receivers specify the desired QoS.

– maintaining soft state in the internet» hard-state approach: a connection-oriented scheme:, fixed route

» soft-state approach: RSVP reservation state


Resource Reservation (RSVP) The call setup process and per-element call behavior


Differentiated Services

Standardizing “Services” or Packet Forwarding “Behavior”? – To deploy a new service, you have to upgrade the world– A router can’t actually do many different things to a packet

=> standardizing forwarding behavior(“send this packet first” or “drop this packet last”)

=> Behaviors + Rules = Services => flexibilityflexibility

=> No per flow state, resource reservation => scalabilityscalability

=> Better-than-best-effort service to applicationsBetter-than-best-effort service to applications, without the need for host RSVP signaling(Few hosts in today’s Internet are able to generate RSVP signaling. Users may only want to specify a more qualitative notion of the service they require)

* Think in terms of IP Forwarding/Routing architectural separation


Differentiated Services Edge functions: packet classification and traffic conditioning

– packet marking, forwarding immediately/delayed/dropped– passes: VIP pass...

Core function: forwarding according to per-hop behavior– packet marking: the class of traffic(the behavior aggregate) – obviates the need to keep router state for individual source-

destination pairs


Differentiated Services Traffic Classification and conditioning

– DS field: IPv4 Type of Service field, IPv6 Traffic Class field– DSCP: per-hop behavior; class of traffic– simple packet classification and marking

– packet classification and traffic conditioning at the edge router


Differentiated Services Edge Router

– Traffic Conditioning Agreement(TCA): describes the rules and traffic profiles required for conditioning

– Classification: Identifying the flow the packet belongs to– Metering: Measuring the temporal properties of a flow– Shaping: Delaying and/or dropping packets so that a flow confirms to

it’s profile.– Marking: Setting the code point in the packets that have been shaped

– Edge router need to understand RSVP » interoperability with IntServ domains must be ensured» RSVP can be used as a signaling mechanism for provisioning and configuration.

– Service Level Agreement(SLA): an agreement between a customer and the DS domain. TCA is a subset of SLA

» other details: Routing constraint, encryption requirements etc.» Edge routers are responsible for interfacing with the customers by executing SLAs» Bandwidth Broker helps the Edge routers in the admission control of the SLAs.


Differentiated Services Per-Hop behavior

– a description of the externally observable forwarding behavior of a DS node applied to a particular DS behavior aggregate

» PHB defines differences in performance» does not mandate any particular mechanism for achieving these behavior» differences in performance must be observable, and measurable

– Expedited Forwarding: can be used to construct services with quantitative guarantees

» EF PHB specifies that the departure rate of an aggregate class of traffic from a router must equal or exceed a configured rate

» minimum guaranteed link bandwidth

– Assured Forwarding» four classes: each class is guaranteed to be provided with some minimum amount of

bandwidth and buffering» within each class, packets are further partitioned into one of three “drop preference”» Could be used as a building block to provide different levels of service to the end

systems: Olympic-like service; qualitative services like better than best effort



Core Router– DS Codepoint(DSCP): Edge routers classify and stamp the packets w

ith appropriate DSCP– DSCP is translated into a PHB

» can be many codepoint to one PHB

» may vary from one DS domain to another

– PHB: » Basic building block for service construction.

» Resources are allocated to PHB


Differentiated Services Bandwidth Broker

– Responsible for resource management in a DS-domain.– Repository for domain wide policies.– Serves as an authenticating agent for users.– Maintains the global state of the DS domain.– Make sure that the number of simultaneous uses of the PHBs fit within th

e resource allocation. Also helps the edge routers in admission control– controls provisioning and configuration of all nodes.– Actual implementation can be

» Centralized: easy to implement; but known problems in terms of performance, scalability, fault tolerance

» Distributed: hard to implement and get it right

– Can be thought as the brain or the control center for a DS domain.


Differentiated Services Service Creation

– DS architecture, lets you create a wide variety of services.

Service– The overall treatment of a customer’s traffic within a DS domain or from

end-to-end– can be

» Quantitative: virtual leased line» Qualitative: Olympic service(Gold, Silver, Bronze)» Neither: BW allocated to class A is always double that of class B

Scope of service: The topological extent of the service– From a given ingress point

» to a given egress point, to a given set of egress point, to any egress point.(Open-ended Scope)

– From a egress point» from a given ingress point, from a given set of ingress point, from any ingress point(open-

ended point)


Differentiated Services Research Issues

– BB: Centralized Vs. Distributed.» Efficient collection and maintenance of global state of the domain» coordination and consistency in case of distributed implementation» suitable algorithms for completely automated resource management and admissio

n control.(measurement based?)

– SLA and TCA» details that go into SLA/TCA and their format» protocols for automatic SLA negotiation» accommodating dynamically changing SLAs» SLA conflict resolution

– Implementation of PHBs(E.g.: EF)» choice of scheduler» buffer management strategies(how much to allocate?)

– multicast: dynamic multicast groups make provisioning difficult– security: Denial of service attacks are easy



RED with In or Out (RIO)– Has two classes, “In” and “Out” (of profile)

» “Out” class has lower Minthresh, packets are dropped from this class first Based on queue length of all packets

– As avg queue length increases, “in” packets are also dropped

» Based on queue length of only “in” packets


Approaches for QoS in the Internet IPv4 TOS: not widely implemented in the current systems

– service request is associated with individual packet rather than sequence of packets. So may not be meaningful always.

– Service offerings have been tied to the implementation Diffserv: Layer 3 only Label switching: MPLS: specifies ways that layer 3 traffic can be mapped to

CO layer 2 transports like ATM and FR– QoS state is set up on a Hop-by-Hop basis– also helps in speeding up of forwarding process– overhead of setting up and maintaining the labeled paths

Intserv/RSVP Cost: Compatibility:

• MPLS can be an intra-domain implementation technology


Multicast

Packets sent by a sender are received by more than one receiver.– Network replicates the packet

– Limits the communication overhead on the sender, making it possible to send to a large number of receivers

– Potentially reduces bandwidth consumption in the network Union” of point-to-point paths.

– combine message over shared links Many issues/challenges.

– How (receiver) multicast group membership managed?

– How do we route packets?

– How do routers forward multicast packets?

“Optimizations possible but difficult if the receivers are not known.– model used in internet

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Requirements for Multicasting A convention for identifying a multicast address

– IPv4: class D addresses. 32-bit; 1110 + 28-bit group identifier– IPv6: 128-bit; 8-bit prefix(all 1s)+4-bit flags+4-bit scope+112-bit group id

» flags: permanently assigned or not» scope field: ranging from a single subnetwork to global

A router must translate between an IP multicast address and a subnetwork multicast address Individual host informs routers of its inclusion in and exclusion from the group for dynamic multicast address generation . Routers must exchange two sorts of information: => routing protocol

– Subnetworks include members of a given multicast group.– Information to calculate the shortest path

A routing algorithm to calculate shortest paths Each router must determine multicast routing paths on the basis of both source and destination addresses Anonymity Dynamic join/leave


Multicast Routing Source-Based Tree

– Shortest path tree for each sender: DVMRP, MOSPF, PIM-DM– Shortest path trees – low delay, better load distribution– More state at routers (per-source state)

– Efficient for in dense-area multicast Group-shared tree

– center-based approach: center node( rendezvous point or core)* How to select the center?

– Steiner Tree problem: finding a minimum cost tree: not popular * information needed: all links in the network, must rerun whenever link costs change, performance is but one of many concerns – Higher delay (bounded by factor of 2), traffic concentration– Choice of core affects efficiency– Per-group state at routers– Efficient for sparse-area multicast

Major concern might be: extra state in routers


Group Management

Management strategy depends on usage.– how quickly does membership change?– restrictions on membership– size of the group

Internet: focus on large groups that can change rapidly and with little control over membership.– distributed algorithm (scalability, again)– receiver-initiated management (scalability, again)

» Receiver initiated reliable multicast protocols(end-to-end); NACK implosion

– sender does not have list of receivers (scalability, again)


Group Management Internet Group Management Protocol (IGMP).

– Routers jointly keep track of membership– Relies on multicast (e.g. Ethernet) in leaf networks– Protocol defines how receivers contact routers to join a group– Operates locally between a host and an attached router– IGMPv2 Message types

» Membership query» Membership report» Leave group

– Feedback suppression» After receiving a membership_query message and before sending a

membership_report message, a host waits a random amount of time between 0 and the maximum response time value defined in IGMP message.

» Some other attached host reports -> suppress(discard) its own pending report(waiting)

– Soft state– Joining a multicast group: receiver driven


Routing Approaches Create a spanning tree to all routers and prune the tree for each specific

multicast group– Begin by flooding traffic to entire network– pruning critical to reduce traffic. (Grafting)– scaling is a concern

– Examples: DVMRP, PIM-DM– Unwanted state where there are no receivers

Link-state multicast protocols– Routers advertise groups for which they have receivers to entire network– Compute trees on demand– Example: MOSPF– Unwanted state where there are no senders

Core-based multicast routing– create tree for each multicast address with root in the center of the network– multicast messages are sent to the root, which forwards them down the tree– scales better, but potentially less efficient and less robust– CBT, PIM-SM


Routing Protocol

Routing protocols– IGMP: a protocol that enable hosts to join and leave multicast group– DVMRP: Distance Vector Multicast Routing Protocol. – MOSPF: extension to the OSPF for multicast routing within an AS.– PIM: Protocol Independent Multicast– BGMP: for interdomain multicast routing.


Routing: Group shared tree Single routing tree for the entire multicast session Steiner Tree problem: finding a minimum cost tree: not popular

* information is needed about all links in the network

* needs to be re-run whenever link costs change Center-based approach: center node(rendezvous point or core)

* process used to select the center- chosen so that the resulting tree is within a constant factor of optimum

* CBT, sparse-mode PIM, BGMP

A single, shared tree

two source-based tree

A minimum cost multicast tree

Constructing a center-based tree(E:center)


Core-Based Trees(CBT) CBT multicast routing protocol

– group-shared tree with single core» Unidirectional tree/ bi-directional tree, Core placement/selection, Multiple core, Dynamic core…

– Core forwards over multicast tree– Operation

» sends a JOIN_REQUEST message towards the tree core» The core(or the first router that receives the message) respond with JOIN_ACK» maintained by having a downstream router send keepalive messages(ECHO_REQUEST)» immediate upstream router responds with ECHO_REPLY message» FLUSH_TREE: if no ECHO_REPLY received


Routing: Source-based tree

Shortest path tree: DVMRP, Dijkstra’s algorithm– requires that each router know the state of each link in the network– compute the least cost path tree from the each source to all destina

tion– Good delay property, Per source and group overhead


Routing: Source-based tree RPF(reverse path forwarding)

– When a router receives a multicast packet with a given source address, it transmits the packet on all of its outgoing links(except the one on which it was received) only if the packet arrived on the link that is on its own shortest path back to the sender.

– Otherwise the router simply drops the incoming packet without forwarding it on any of its outgoing links. => avoid flooding loop

» Need to know unicast shortest path to the sender. Not the shortest path from the source to itself(assumption:symmetric). Asymmetric case?


Routing: Source-based tree RPF(reverse path forwarding)

– RPB: Reverse Path Broadcasting– TRPB: Truncated Reverse Path Broadcasting: router truncate its transmission to the local network if none of the hosts attached to the n

etwork belong to the multicast group. Leaf router only– RPM: Reverse Path Multicasting: with IGMP

» pruning: A multicast router that receives multicast packets and has no attached hosts joined to that group will send a prune message to its upstream router.

If there were 1000 routers downstream from D; (initial Mbone) Grafting message to its upstream router to cancel its earlier prune message


Internet Group Management Protocol (IGMP) IGMP: used by hosts and routers to exchange multicast group membership information over a LAN Message format: Figure 15.4

– version, type, checksum, group address(0 in a request message, valid group address in a report message) IGMP Operation

– to join a group: host sends an IGMP report message.» Group address field: destination address field of IP header» All member hosts will receive the message, and learn of the new member.

– to maintain a valid current list: multicast router periodically issues a IGMP query message, sent in an IP datagram with an all-hosts multicast address. Must respond with a report message to remain a member.

– Multicast router needs to know that there is at least one group member still active. Not need to know the identity of every host in group.» Any host hears: if some host reports -> cancels report. if no report within the timeout -> sends report.

– Group Membership with IPv6» IGMP:IPv4» ICMPv6: includes all of the functionality of ICMPv4 and IGMP.

* ICMP: Internet Control Message Protocol


Distance Vector Multicast Routing Protocol (DVMRP)

DVMRP:– source-based trees with reverse path forwarding, pruning, and grafting. Use distance vector algorithm to compute shortest

path back to source» Not from source to the members

– Data stream reaches all LANs (possibly multiple times). If a router is attached to a set of LANs that do not want to receive a particular multicast group, the router can send a "prune" message back up the distribution tree to stop subsequent packets from traveling where there are no members.

– Since new hosts may want to join the multicast group at any time, DVMRP must periodically re-flood. This creates a scaling problem, especially if pruning not effective or not implemented.


Distance Vector Multicast Routing Protocol (DVMRP)

DVMRP implements its own unicast routing protocol (similar to RIP) to determine which interface leads back to the source of the data stream. The path that the multicast traffic follows may not be the same as the path that the unicast traffic follows. (asymmetric case?)

DVMRP has been used to build the MBONE by building tunnels between DVMRP-capable machines. DVMRP: de-facto Interdomain multicast protocol DVMRP is state of the art today.?


Multicast Extensions to Open Shortest Path First (MOSPF)

MOSPF: enhancement to OSPF for the routing of IP multicast datagram within an AS. MOSPF works only in internetworks that are using OSPF.

– MOSPF is best suited for environments that have relatively few source/group pairs active at any given time. It will work less well in environments that have many active sources or environments that have unstable links.

Operation:– Each router floods information about local group membership to all other routers in its area.(Each router attached to a LAN uses IGMP to maintain a correct picture of

local group membership).» Using Dijkstra’s algorithm, each router constructs the shortest-path spanning tree from a source network to all network containing members of a multicast group.; done only on demand.

(When it receives a multicast datagram)– For any hop that is across a broadcast network such as LAN, an IP multicast datagram is transmitted inside a MAC-level multicast frame.

Equal-cost Multipath Ambiguity: tiebreaker rule



Interarea multicasting– OSPF: backbone, area, border router– Each router within a area only knows about the multicast groups that have members in its area.– Interarea multicast forwarder:

» subset of an area’s border routers» forward group membership information and multicast datagrams between areas

receives the multicast link status reports, knows all of the multicast group in the area backbone routers exchange the information on multicast group also wild-card multicast receiver. Receive all multicast datagrams generated in an area



Inter-AS multicasting– MOSPF has no responsibility for multicasting beyond its AS.– Responsible for providing multicast group information to outside entities and for accepting multicast

datagrams for groups contained within its AS.» Boundary router: inter-AS multicast forwarders.(+ MOSPF + OSPF)» It receive all multicast datagrams from within the AS; wild-card multicast receiver» reverse-path routing: to get the knowledge of the source of a datagram.

Assumes that source X (outside the AS) will enter the MOSPF AS use to send a unicast datagram to X


Protocol Independent Multicast (PIM) PIM

– to provide a more general solution to multicast routing.– Independent of any existing unicast routing protocol– designed to extract needed routing information from any unicast routing protocol and may work across multiple ASs with a number of different unicast routing protocol– supports two different types of multipoint traffic distribution patterns.

PIM strategy– many multicast members, many subnetworks within a configuration have the members of a given multicast group => frequent exchange of group membership information is justifi

ed => data-driven– widely scattered members => flooding of multicast group information is inefficient => receiver-driven => a center based approach– dense-mode protocol: for multicast routing within AS; potential alternative to MOSPF . uses flood-and-prune Reverse Path Forwarding and looks a lot like DVMRP. However, dens

e-mode PIM is that PIM works with whatever unicast protocol is being used – sparse-mode protocol: for inter-AS multicasting routing??


Protocol Independent Multicast (PIM) Sparse-Mode PIM

center-based approach1. For a multicast group, a router is designated as a rendezvous point (RP)2. A group destination router sends a Join message to the RP. Requesting router uses a unicast shortest-path route to send message. The reverse of path become part of

the distribution tree from RP to destinations.3. A group source router sends packets to RP using unicast shortest-path route.– From RP to the multicast receivers, shared tree is used minimizing the number of packets replicated.– PIM allows a destination router to replace the group-shared tree with a shortest-path tree to any source.(source-specific tree); Once it receives a packet from the source,

it send a Join message back to the source router => sends Prune message to RP – The selection of an RP is dynamic.– RP placement is not a critical issue.


Protocol Independent Multicast (PIM)


Inter-domain Multicast Routing(BGMP) The case that different AS’s choose to run different multicast routing protocols

– IETF idmr working group – DVMRP: defacto interdomain multicast routing protocol

» not well suited to the sparse set of routers participating in today’s Internet Mbone

– group-shared tree approach toward routing» problem: a center could conceivably be chosen in a domain that does not contain any hosts in the multicast group : third party dependency(No pr

oblems in the intradomain case) “unfairly” burden the domain which has no interest in the multicast group performance dependencies on domains outside of those participating in the group


Overlay Multicast: ALM Potential benefit over IP multicast

– Quick deployment– All multicast state in end systems– Computation at forwarding points simplifies support for higher level functionality

Concerns– closely matched to real network topology to be efficient?– Performance

» Increase in delay

– Bandwidth waste (packet duplication)


Mobile IP

Communicate with mobile hosts using their home IP address.– should be transparent to applications and higher level protocols– minimize changes to host and router software

Each area has a home agent and foreign agent that managing packet forwarding.– binding = (IP address, foreign agent address) – binding includes time stamp

Try to short circuit the home location by going directly to the foreign agent.– cache bindings in the appropriate places– protocol to update/invalidate caches– security considerations


Mobile IP in IPv4 Registration process

– mobile host registers with home and foreign agent

– cache bindings: address, care-of-address

Tunneling is used to forward packets between agents.

Supporting mobility– invalidating old caches explicitly or

in a lazy fashion Many variants and optimizations

possible.– Mobile host can be its own foreign

agent, e.g. can get local addresses– Source can redirect packet directly

to foreign agent

Source

HomeAgent

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ForeignAgent 2


Mobile IP Goals

IP address encodes the host’s network.– Simplifies routing in the common case: look only at network

identifier, but not not at the host id– Makes special cases hard, e.g. what happens when the host

moves?

Communicate with mobile hosts using their “home” IP address.– should be transparent to applications and higher level protocols

Minimize changes to host and router software– No changes to communicating host

Security should not get worse.


Mobile IP (IPv4)

Home network has a home agent that is responsible for intercepting packets and forwarding them to the mobile host.– E.g. router– Forwarding is done using tunneling

Remote network has a foreign agent that manages communication with mobile host.– Point of contact for the mobile host

Binding ties IP address of mobile host to a “care of” address.– binding = (IP address, foreign agent address) – binding includes time stamp


Mobile IP Operation Agents advertise their presence.

– Using ICMP or mobile IP control messages

– Mobile host can solicit agent information– Mobile host can determine where it is

Registration process: mobile host registers with home and foreign agent.– Set up binding

Tunneling– forward packets to foreign agent– foreign agent forwards packets to

mobile host Supporting mobility

– invalidating old caches in a lazy fashion

Source

HomeAgent

ForeignAgent 1

ForeignAgent 2


Optimizations

Mobile host can be its own the foreign agent.– mobile host acquires local IP address

– performs tasks of the mobile agent Short circuit the home location by going directly to

the foreign agent.– Routers in the network store cache bindings and

intercept and tunnel packets before they the mobile host’s home network

– Need a protocol to update/invalidate caches

– Raises many security questions and is not in the standard

prof. younghee lee 1 computer networks u chap. 6 qos and multicast 전산학과 교수 이영희

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