Application Scenarios

In previous work, it showed some suitable applications for anycasting [11]. If there are several hosts that provide the same service in the network, anycast can be used to help clients to find the nearest service. Most of recent implementations of Internet focus on the routing protocols in the network layer. When anycast is realized in the network layer, the anycast functions can be added to existing applications without editing the source codes.

Another type is the application layer anycast, where the application implements the anycast mechanism. In this case, we should edit or make new source codes for the applications. This subsection reviews what kinds of applications are suitable to anycast communications. One important example is server location [12], through which the sender host can choose one of many functionally identical hosts.

As a result, load distribution among anycast hosts can be achieved if we utilize some appropriate anycast routing method, where anycast requests are evenly distributed to hosts.

Figure 2.1 shows the client communicated with same anycast address of the group.

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Figure 2.1 Anycast communication (Router).

While this kind of service can be obtained through application–layer anycast, the node can communicate automatically with an appropriate (e.g., nearest) server through network–layer anycasting. Moreover, the additional anycast examples listed below clearly demonstrate this scenario.

Anycast in P2P IPTV System

The gate to overlay network is an example of an anycast application. A P2P (Peer-to-Peer) service server constructs a logical network topology among nodes participating in the service. However, the peer needs to know the address to connect the logical network prior to the service. Each peer only specifies the anycast address in order to participate in the logical network and one of the participating peers becomes the gate of the logical network for the new node, which should be determined by the anycast routing protocol. All nodes have the same service in this logical network.

So, even when the connected peer leaves the logical network, it is possible to continue participating via another peer, which is automatically changed by the anycast routing protocol. Figure 2.2 shows the Gate to Overlay Network in the Internet.

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Figure 2.2 A Gate to Overlay Network.

DNS /WWW Redundancy

IP anycast can also support host auto-configuration by assigning an anycast address to the DNS service; after moving to a new network, a host can continue to contact the DNS anycast address instead of being re-configured with the new local DNS server. In this case, a host that is moved to a new network need not be reconfigured with the local DNS address.

The host can use the global anycast address to access the local DNS server anywhere.

There’s the overall redundancy that each name server instance achieves by distributing DNS service for the same IP address across multiple data centers. A global distribution of DNS name servers significantly reduces the latency for users to reach / obtain a DNS response when connecting to a site because of the distributed nature of the network.

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Figure 2.3 Anycast DNS.

Figure 2.3 shows an example of Anycast DNS. A single DNS client workstation, configured with the anycast DNS IP address of 10.10.10.10, is shown performing DNS resolution against its "closest" of three DNS name servers deployed using the same anycast IP address.

SIP Proxy Server Discovery

The session initiation protocol (SIP) is increasingly becoming the de-facto standard for VoIP deployments in fixed and wireless networks. Proxy server is an optional SIP component that handles requests or forward requests to other servers. Every such SIP proxy server SHOULD configure this anycast address on the IP interface that it uses to communicate with SIP clients. In a network there can be multiple SIP proxy servers that are configured to act as outbound proxy servers and all of these servers SHOULD configure this anycast address on the appropriate IP interface. Figure 2.4 shows the SIP Proxy Server.

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Figure 2.4 SIP Response Through a Proxy Server.

FTP Server Discovery

IP anycast can provide automatic service discovery in the Internet. By assigning the same anycast address to replicated FTP servers, users can download from the closest server without manually choosing from a list of mirrors. Users can get access through the best shortcut to any server that provides the same service. The user can use the anycast address to directly download the file from the nearest replica.

Mobile IPv6 Home Agent Discovery

The Home Agent (HA) [13] concept from having a single entity on the home link towards several geographically distributed Home Agents. The home agent list is sent to a mobile node when the mobile node requests the latest list of home agents. Every home agent has a special anycast address, called a home agent anycast address. A problem that has to be solved within this context is locating the closest HA to the Mobile Node (MN) or Mobile Router (MR), for which the Anycast based Dynamic Home Agent Address Discovery mechanism. The semantics of Anycast are suitable for this task as data is routed

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to the “nearest” destination, with distance being defined by the routing metrics.

Figure 2.5 Replying to a Dynamic Home Agent Address Discovery Reply message.

Figure 2.5 show the Replying to a Dynamic Home Agent Address Discovery Reply message. A Dynamic Home Agent Address Discovery request message is delivered to one of the home agents in a home network thanks to the anycast address mechanism. The home agent that receives the message will reply to the mobile node with a Dynamic Home Agent Address Discovery reply message containing all of the home agent addresses which the home agent currently knows. The address list is ordered by the preference value of each home agent. If a mobile node does not receive a reply message, the node will resend a request message.