Slide 1: Interconnection of Content Delivery Networks Brad Cain Chief Scientist Cereva Networks © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 2: Content Delivery Networks 101  CDNs are solving: - Poor and inconsistent site performance - Flash crowd protection - Availability  CDN business model: - Customer is content provider - Value: quality of service  CDNs are: - A distributed overlay network of servers (surrogates) which serve content on behalf of an origin server - Redirect requests via DNS global load balancing systems © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 3: Architectural Components  Distribution System - A collection of surrogates which act on behalf of the origin server to delivery content - A set of signaling protocols and signal delivery mechanism for the control of content  Request Routing - Direct user requests to the “closest” and “least-loaded” cache (or surrogate in CDN terminology)  Accounting / Billing - The logging and billing of CDN surrogate events - The processing, collection, and accounting of these events - Usually have customer portal as well © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 4: CDN Example =origin server A. B. 5. 6. 4. 1. =surrogate RR Client 3. 2. LDNS If surrogate has content then It serves it Else It is retrieved from origin (steps A & B) with policy 1. In-line retrieval OR 2. Re-direct and retrieve later © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 5: Request Routing  CDNs use the Domain Name System (DNS) to direct user requests to a surrogate - Handled by load balancing DNS servers in CDN - Each CDN has one or more domains for this purpose  Content provider modifies web content - CNAMEs or direct reference to CDN in URLs  Request routing systems use various methods to determine best surrogate - No exact science - Visibility is local DNS IP address © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 6: Distribution System  Distribution System is the set of surrogates (or caches) which serve actual content - Simplified web server (i.e. no CGI, etc) - Surrogates are exist in various parts of Internet  Key differentiator between CDNs  If object does not exist at surrogate, it is retrieved from origin server on demand (in-line or later) - Configured with <origin server, host header> pairs  Surrogates must have method of obtaining a “content signal” to control content - Purge, etc © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 7: CDN Interconnection  There are multiple CDN service providers offering commercial service  Next step is to interconnect these overlay networks  Analogy: Layer-3 CDN Switching Elements Information Units Interconnect Inter-domain Protocol Routers Routes Carry traffic BGP DNS Request Routers Surrogates / Content Serve content (coming soon) © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 8: CDN Interconnection (2)  Technical - Network expansion and better performance  Business - Content providers want access to as many surrogates as possible - ISPs and Enterprises want to make use of existing caches  And why not make money with them?  ISPs/Enterprises have eyeballs and true network edge - ISPs and Enterprises deploying their own CDNs - New business models © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 9: Requirements  CDN interconnection seems to be at odds with CDN value proposition - Need to ensure quality of service between providers - Not easy!  Becomes more difficult with arbitrary topologies - May be easier with CDNs than layer-3 because CDNs are overlay  Equals dense interconnection  CDN interconnection must also take into account paranoia regarding content assets - Who do I trust to distribute my content? © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 10: The Model (first cut)  Each piece of content has an authoritative CDN - Identified by DNS name in URL  The authoritative CDN may direct request to: - Its own network of surrogates - Another network (I.e. another DNS server)  Must direct request to network that: - Is authorized to distribute content - Actually has the content  Taking “black-box” approach right now - No visibility into neighbor networks - Each network makes decision regarding the best surrogate © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 11: More than Routing…  Shouldn’t direct a request to a CDN that does not have the content - If content is to be “pushed” (e.g. streaming media)  Configuration information: - What content should be distributed and how? - What content types are supported? - When is content ready to be distributed?  Accounting information: - Needs to be sent to authoritative CDN for content provider - Required for multi-tier settlement © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 12: The Big Picture Content Provider Content Interconnection CDN A CPG ISP CDN ISP Internet © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 13: Inter-domain DNS Request Routing Example CDN1 CDN2 =surrogate RR 2. LDNS 7. 1. Client 3. 6. 4. 5. 1. 2. 3. 4. 5. 6. 7. Client Request to LDNS LDNS to Auth CDN RRS RR makes decision Returns CNAME to CDN2 Lookup to CDN2 CDN2 returns surrogate Answer to client © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 14: Inter-domain DNS Request Routing  Provider A has site cdn.blah.com to distribute - Origin is: www.blah.com - Assume A is authoritative CDN  If provider B wants to distribute, it must supply a CNAME for redirect of www.blah.com  Provider A request-routing system will redirect requests to B according to its policy - Provider B will receive request (through CNAME) and pick an appropriate surrogate in its network  Key points: - Must agree to distribute - Must supply information back to upstream © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 15: Inter-provider CDN Routing  Two ways to route to content - DNS - Layer-7 router/switch  Simplify in short term - DNS with mesh connectivity (e.g. not arbitrary topologies) - Probably don’t want to DNS route more than two anyway - Remember we are dealing with overlay networks! - As we learn more, integrate layer-7 router/switches © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 16: Dynamic Exchange  Desire to add dynamic exchange of information between CDNs  Concept of Content Peering Gateways (CPG) - Each CDN has at least one  Each CPG exchanges information about request routing AND distribution - “Coverage” area for CDN surrogates - Content specific information  What content am I serving?  Is content ready?  Lots of information needs to be exchanged - Currently working on requirements and scenarios © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 17: Problems to Solve  How to decide which CDN to route to?  How to exchange enough information to be effective but not overload CPGs?  How to ensure loop freedom?  How to aggregate information in exchange?  How to signal meta-data updates to content in scalable manner?  How to signal neighbors for distribution when content push is used?  Remember this is all very new… © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 18: CDI Testbed  CDNs are peering in test-bed coordinated - Content Alliance initiated  Several providers and vendors participating (e.g. Cisco, AT&T, Speedera)  Peering is through DNS request-routing - CNAME hand-off  Lots of manual configuration - “Static routing” with simple policies (e.g. round-robin) - Per domain CNAME mappings  Several test sites being distributed  www.cditestbed.net © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 19: Standards  IETF Content Distribution Internetworking (CDI) group  BOF at each of last two IETF meetings to discuss problems to solve - Lots of interest!  Mailing list - List: cdn@ops.ietf.org - Subscribe: cdn-request@ops.ietf.org  Should be official working group by next IETF - Focus on solving short term interconnection - Inter-CDN protocol work © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 20: Internet drafts  An introduction to the problem area and proposed vocabulary: - draft-day-cdnp-model-05.txt  Some scenarios of use: - draft-day-cdnp-scenarios-03.txt  A description of a proposed architecture for interoperation: - draft-green-cdnp-gen-arch-03.txt  Known mechanisms for request-routing - draft-cain-cdnp-known-request-routing-01.txt  Request-routing requirements for CDI - draft-cain-request-routing-req-01.txt  Distribution requirements for CDI - draft-amini-cdi-distribution-reqs-00.txt  Authentication/Authorization/Accounting requirements for CDI - draft-gilletti-cdnp-aaa-reqs-00.txt © 2000-2001 Cereva Networks Inc. All rights reserved.
Slide 21: Summary  Many problems left to sort out for inter-CDN communication  Test-bed is running with static routes  Dynamic information exchange for both request routing and distribution is next  Need more experience particularly in figuring out what information needs to be exchanged  CDI interconnection will be evolution - IETF approach to protocol deployment - Start simple, test and grow © 2000-2001 Cereva Networks Inc. All rights reserved.